K101 Telecommunications Fundamentals - Formatted

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K101

Telecoms Fundamentals

Training Guide



The information in this document is subject to change without notice anddescribes only the product defined in the introduction of thisdocumentation. This document is intended for the use of AIRCOMInternational's customers only for the purposes of the agreement under

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Copyright © AIRCOM International 2010. All rights reserved.



Contents

1 Introduction to Telecoms...................................................................................................9

1.1 The Basics of Radio Communication............................................................9

1.2 Propagation Models....................................................................................20

1.3 Drive Testing...............................................................................................38

1.4 The Fixed Line Network..............................................................................42

1.5 Multiplexing Systems Background...............................................................45

1.6 GSM Air-Interface....................................................................................... 52

1.7 Questions....................................................................................................59

2 Understanding GSM........................................................................................................61

2.1 GSM (Global System for Mobile Communications) Evolution......................62

2.2 Global System for Mobile Communications (GSM).....................................63

2.3 Base Transceiver Station (BTS)..................................................................64

2.4 Base Station Subsystem (BSS)...................................................................65

2.5 Base Station Controller (BSC).....................................................................67

2.6 International Mobile Equipment Identity (IMEI)............................................68

2.7 Subscriber Identification Module (SIM)........................................................69

2.8 International Mobile Subscriber Identity (IMSI)............................................70

2.9 Network and Switching Sub-System (NSS).................................................71

2.10 Mobile Switching Centre (MSC)................................................................72

2.11 Gateway MSC (GMSC).............................................................................74

2.12 Visitor Location Register (VLR).................................................................75

2.13 Blacklist of Stolen Devices........................................................................76

2.14 Central Equipment Identity Register (CEIR)..............................................76

2.15 Equipment Information Register (EIR).......................................................77

2.16 Home Location Register (HLR).................................................................78

2.17 Data Bearer Services................................................................................84

2.18 Authentication Centre (AUC).....................................................................87

2.19 Location Area............................................................................................91

2.20 Basic Mobile Terminated (Network Originated) Call Procedure.................94

2.21 Questions..................................................................................................96

3 Fundamentals of Frequency Planning............................................................................99

3.1 What is a Frequency Band?......................................................................100

K101 Telecommunications Fundamentals Page 7Contents



3.2 Capacity and Quality.................................................................................108

3.3 Interference...............................................................................................109

3.4 Principles of Cellular Frequency Reuse.....................................................114

3.5 Basics of Radio Networks Operation.........................................................1223.6 Questions..................................................................................................123

4 Fundamentals of GPRS................................................................................................125

4.1 GPRS Class Types...................................................................................130

4.2 GPRS Support Nodes (GSN)....................................................................131

4.3 Packet Switching.......................................................................................133

4.4 Circuit Switching........................................................................................134

4.5 A GPRS Roaming Exchange (GRX).........................................................137

4.6 Home Location Register (HLR).................................................................138

4.7 Circuit-Switched........................................................................................140

4.8 Packet-Switched.......................................................................................142

4.9 Coding schemes....................................................................................... 143

4.10 Questions................................................................................................147

5 Comparison of Different Mobile Technologies..............................................................149

5.1 Introduction............................................................................................... 150

5.2 Key Performance Indicators (KPI).............................................................171

5.3 3G Networks............................................................................................. 182

5.4 Long Term Evolution (LTE).......................................................................200

6 Glossary of Terms.........................................................................................................205

Page 8 K101 Telecommunications FundamentalsContents



1 Introduction toTelecoms

1.1 The Basics of Radio Communication

Radio communication is the transmission of signals by modulation of electromagnetic waves with frequencies below those of visible light.Electromagnetic radiation travels by means of oscillating electromagneticfields that pass through the air and the vacuum of space. Information iscarried by systematically changing (modulating) some property of theradiated waves, such as amplitude, frequency, phase, or pulse width. Whenradio waves pass an electrical conductor, the oscillating fields induce analternating current in the conductor. This can be detected and transformedinto sound or other signals that carry information.

1.1.1 Frequency & Wavelength

C H A P T E R 1

K101 Telecommunications Fundamentals Page 9Introduction to Telecoms



A Wave is one oscillation of a radio signal, from mid-point to mid-point.

The depth of the wave from crest to trough is known as the Amplitude.

The Frequency of a wave is described as the number of occurrences of the

wave per unit time.Wavelength is the physical distance between successive crests of a wave,esp. points in a sound wave or electromagnetic wave

The Period is the duration of one cycle of a wave in seconds.

The frequency of a repeating event is calculated by counting the number of times that event occurs within a specific time interval, then dividing thecount by the length of the time interval.

For example, if 100 events occur within 10 seconds, the frequency is:100/10, or 10 Hertz

1.1.2 The Radio Spectrum

Usable radio frequencies range from 3 kHz to 300 GHz. The lower thefrequency, the longer the wavelength. Different frequency ranges areappropriate for different uses.

Low Frequencies

•

Require longer aerials• Require more power




• Signals tend to bounce off of the ionosphere and hence cover largerdistances, regardless of the curvature of the earth

High Frequencies

• Require smaller aerials

• Require less power

• Signals do not bounce around the ionosphere, and are limited to “line-of-sight” communications




1.1.3 Radio Spectrum Utilisation

The following chart shows how sections of the spectrum are used forvarious purposes:

Band Name ITU Band Frequency &Wavelength in air

Example Uses

Sub-Hertz 0 <3 Hz

> 100,000 km

Natural and man-made electromagnetic waves

Extemely Low Frequency 1 3-30 Hz

100,000 km - 10,000 km

Communication with submarines

Super Low Frequency 2 30-300 Hz

10,000 km - 1000 km

Communication with submarines, Main power (50/60Hz)

Ultra Low Frequency 3 300-3000 Hz

1000 km - 100 km

Communication with mines

Very Low Frequency 4 3-30 kHz

100 km - 10 km

Submarine communication, wireless heart ratemonitors

Low Frequency 5 30-300 kHz

10 km - 1 km

AM Longwave broadcasting, amateur radio

Medium Frequency 6 300-3000 kHz

1 km - 100 m

Am (medium wave) broadcasts, amateur radio

High Frequency 7 3-30 MHz

100m - 10 m

Shortwave broadcasts, citizen's band radio, amateurradio

Very High Frequency 8 30-300 MHz

10 m - 1 m

FM, television broadcasts and line-of-sight ground toaircraft and aircraft to aircraft communications

Ultra High Frequency 9 300-3000 MHz

1 m - 100 mm

Television broadcasts, microwave ovens, mobilephones

Super High Frequency 3-30 GHz

100 mm - 10 mm

Microwave, satellites

Extremely High Frequency 30-300 GHz

10 mm - 1 mm

Page 12 K101 Telecommunications FundamentalsIntroduction to Telecoms



1.1.4 Ultra High Frequency

Ultra High Frequency (UHF) is a designated range of electromagnetic waveswith frequencies between 300 MHz and 3 GHz (3,000 MHz). It is reservedfor television broadcasts, microwave ovens and mobile phones.

Main Advantages

• UHF antennas tend to be stubby, short and less conspicuous.

• Less power is needed to send a signal

These factors make UHF ideal for small, hand-held mobile phones.

Main Disadvantage• UHF offers a limited broadcast range and reception.

Consequently, mobile networks require abundant antennas andinfrastructure. This is costly.




1.1.5 Microwaves

Microwaves are electromagnetic waves with wavelengths ranging in lengthfrom one meter to one millimetre. The broad definition of microwavecovers the range of frequencies between 300 MHz (0.3 GHz) and 300 GHz.

This includes three bands:

• UHF - Ultra High Frequency

• SHF - Super High Frequency

• EHF - Extremely High Frequency.

However, various sources quote different boundaries. For example, RFengineers often put the lower boundary at 1 GHz (30 cm), and the upper,

around 100 GHz (3mm). The term "microwave" always includes the entireSHF band (3 to 30 GHz, or 10 to 1 cm).




Microwaves are typically short enough to employ tubular metal waveguidesof reasonable diameter.

Uses

Uses include IEEE 802.11a wireless LANs; satellite uplinks and downlinks;and terrestrial high-speed data links, which are sometimes referred to as"backhauls", or the "core network".

Super High Frequency (SHF) refers to radio frequencies (RF) in the range 3 GHzto 30 GHz.

Extremely High Frequency is the highest radio frequency band. EHF runs therange of frequencies from 30 to 300 GHz.




1.1.6 Microwave Planning

The siting of microwave links requires judicious planning to ensure that thesignal transmitted reaches the intended receiver.

Radio Line-of-sight

When you deploy an RF link between two distant sites at UHF andmicrowave frequencies, you need to make sure you have "line of sight"between the two antennas. But at these frequencies "line of sight" does notsimply mean that from one site you can "see" the other. When yourdistance exceeds, about 5 miles (8 Km), you need to take into account thefollowing factors:

• The curvature of the earth.

• Fresnel Zone clearance.

• Atmospheric refraction




Fresnel Zone

Radio waves travel in a straight line, unless something refracts or reflectsthem, but the waves are not “pencil thin.” The farther they get from theradiating source, the more they spread out, like ripples on a pond.

The area into which the signal spreads is called the Fresnel Zone. If there isan obstacle in the Fresnel zone, part of the radio signal will be diffracted orbent away from the straight-line path. The practical effect is that on apoint-to-point radio link, this refraction will reduce the amount of RF energyreaching the receive antenna.

Whether your link is point-to-point or point-to-multipoint, you must ensuretwo things:

• It must have a clear line of sight

• At least 60 percent of the first Fresnel zone clear of obstructions.

These factors become more important as the distance increases. If theFresnel zone is blocked, you will get a lower signal level on the distant endthan expected — even if you can literally see the other antenna in thedistance.

It is still possible to get a link, even if your Fresnel zone is partially blocked,provided your system is designed to have a strong signal at the other endof the link. An RF path analysis should be done if you are not sure whetheryou have a clear Fresnel zone and unobstructed line-of-site. There aremany software packages available which can create a path profile fromterrain data and a set of latitude/longitude coordinates, but these programscan only take terrain obstruction into account when ascertaining whether

or not a link will work. A clear path on paper is no guarantee that your linkwill work, since it does not take into account trees or buildings. Even a“clear” link might have 80-foot trees in the way that could block the signal.

You could be wasting your time and money by ignoring Fresnel zone andline of site issues when attempting to set up a link. The resultant link islikely to be unreliable, if not completely ineffective.

Even assuming that you do have clear line-of-site and 60 percent of thefirst Fresnel zone clear (or nearly clear), there are still many unansweredquestions. How do you know if you will have a good link or not? How muchgain do your antennas need to have? How much coax cable loss is toomuch? If your link is at 2.4 GHz, should external amplifiers be used? Givenyour fixed base station antenna with a pre-set gain, how far can you reachwith the different types of client antennas? Which clients will needamplification? These are just a few of the more advanced considerations.




1.1.7 Frequency Bands

Bandwidths in any one country are allocated to various operators by therelevant government department. For example, in the United Kingdomthere are two main bandwidths for GSM. These are GSM900 and GSM1800.Certain bandwidths in the vicinity of these frequencies are reserved foruplink (mobile to cell) and downlink (cell to mobile) communication.Operators will typically buy licences in both frequency ranges.

In GSM900, uplink communication is designated the range 890-915 MHz,and downlink is designated 935-960 MHz. This means that the bandwidthavailable for uplink and downlink on GSM900 is 25MHz each for the entirecountry. This bandwidth must be shared among various mobile operatorsaccording to their licences. In order to minimise interference between

frequencies, there must be a difference of 200 KHz between them, knownas the frequency interval. Since the bandwidth for both uplink and downlinkGSM900 is 45 MHz, there can only ever be 125 frequencies countrywide foreach direction:

Number of frequencies = Bandwidth available / Frequency Interval.

Downlink traffic is typically allocated a higher frequency range than uplinkbecause higher frequencies offer less coverage but greater capacity. This isuseful due to download-intensive nature of mobile communications.

Similarly, mobile operators typically use their GSM1800 bandwidthallocations in built up areas, where capacity is more important thancoverage. They tend to use GSM900 frequencies for less busy areas wherecoverage is more important.




1.2Propagation Models

Coverage in a cell is dependent upon the area covered by the signal. Thedistance travelled by the signal is dependent upon radio propagationcharacteristics in the given area. Radio propagation varies from region toregion and should be studied carefully before predictions for both coverageand capacity are made.

Radio planners aspire to a network design that covers 100% of the area,however, this is usually impossible. Instead, efforts are concentrated ondesigning a network that covers all the regions that may generate traffic,

with ‘holes’ appearing only in no-traffic zones. To do this, the whole land area is divided into three major classes – urban,suburban and rural – based on human-made structures and naturalterrains. The cells (sites) that are constructed in these areas can beclassified as outdoor or indoor cells. Outdoor cells can be further classifiedas macro-cellular, micro-cellular or pico-cellular.




There are five factors affecting coverage which should be taken intoaccount when planning a network:

• Path Loss

• Frequency

• BTS Transmitter Height

• MS Height

• Clutter

Propagation models are complex mathematical algorithms which take intoaccount these factors in designing networks. Information regarding theseand other factors (such as transmitter type and topography) are fed into apropagation model, which then estimates the likely coverage. Propagationmodels are normally computer-based, owing to the complexity of thecalculations. Aircom's ASSET module is an example of such software which

is capable of interpreting many different models.




1.2.1 Path Loss

Radio signals, particularly high frequency waves, gradually lose strength asdistance increases. This loss of signal strength is called Path Loss.

Path loss is the dominant factor in characterization of propagation for thelink, so radio propagation models typically focus on realisation of path loss.Prediction of the area coverage for a transmitter and modelling of distribution signals are auxiliary tasks.

Since each individual telecommunication link will encounter differentterrain, path, obstructions, atmospheric conditions and other phenomena,it is problematic to formulate the exact loss for all telecommunicationsystems in a single mathematical equation. As a result, different models

exist for different types of radio links under different conditions. Themodels rely on computing the median path loss for a link under a certainprobability that the considered conditions will occur.

Wave propagation models are necessary to determine the propagationcharacteristics for the installation of mobile radio systems. The path losspredictions are required for the coverage planning, the determination of multipath effects as well as for interference and cell calculations, which arethe basis for the high-level network planning process.




The environments where these systems are intended to be installed rangefrom large rural areas (macrocells) down to indoor environments(picocells). Hence wave propagation prediction methods are required tocover the whole range of macro-, micro- and pico-cells, including in-building scenarios and situations in special environments such as tunnels

or highway routes.




1.2.2 Frequency

Frequency plays an important part in propagation models, since differentfrequencies cover different distances.

The lower the frequency, the greater the coverage. Thus, lower frequencyantennas can be located further apart.

Each GSM frequency can carry up to 8 concurrent calls. Therefore, it makessense to use more, higher frequency antennas in built up areas and fewer,lower frequency antennas in rural areas.




1.2.3 BTS Transmitter Height

Base Transceiver Stations transmit more effectively the higher they aresituated. Therefore, coverage is enhanced by installing higher platforms.

1.2.4 MS Height

The height of the Mobile Station (mobile phone) being used also affects thequality of coverage. For example, someone standing on the roof of abuilding opposite a BTS will receive a better signal than someone at streetlevel.




1.2.5 Clutter

Buildings, trees, vehicles, people and other objects create a disturbance inradio waves. Such influences are known collectively as clutter.

When the signal strikes the surface of a building, it may be diffracted orabsorbed to some extent. This has the effect of reducing the signalstrength. The amount of absorption is dependent on factors such as:

• the type of building and its environment

• the amount of solid structure and glass on the outside surface

• the propagation characteristics near the building

• the orientation of the building with respect to the antenna orientation




These are important considerations in the coverage planning of a radionetwork. The same concept applies to other obstructions, fixed ormoveable.




1.2.5.1 Multi-Path Fading

Diffraction is a phenomenon that takes place when the radio wave strikes asurface and changes its direction of propagation owing to the inability of the surface to absorb it. The loss due to diffraction depends upon the kindof obstruction in the path. In practice, the mobile antenna is at a muchlower height than the base station antenna, and there may be highbuildings or hills in the area. Thus, the signal is highly likely to undergodiffraction before reaching the mobile antenna. This phenomenon is alsoknown as ‘shadowing’ because the mobile receiver is in the shadow of these structures.




1.2.5.2 Propagation of a Signal Over Water

Propagation over water is a big concern for radio planners. The reason isthat the radio signal might create interference with the frequencies of other cells. Moreover, as the water surface is a very good reflector of radiowaves, there is a possibility of the signal causing interference to theantenna radiation patterns of other cells.




1.2.5.3 BTS Positioning - Topographic Effects




1.2.5.4 BTS Positioning - Traffic Routes

Traffic routes provide a unique set of challenges. They require continuouscoverage, but not always over a widespread area. For example, countryroads often require little or no coverage away from the road, and city roadsoften have dead spots because of the buildings around them. In bothcases, a directional antenna can be used to cover the road. Such antennasproduce an elongated coverage area rather than the usual circular area.

The same kind of antennas cam provide coverage in dead spots created byvalleys.




1.2.5.5 Environmental Aspects

Different environmental aspects pose different challenges. Ruralenvironments have coverage as a priority over capacity, whilst capacityand interference issues dominate urban environments. Path loss predictionis notoriously difficult in dense urban environments.




Planning constraints and local resistance may limit antenna heights,particularly in suburban areas.

Roads are sometimes covered by antennas with a narrow beam, whilstintersections may have other special arrangements




1.2.6 If I Have a Signal, Can I Always Make a Call?

There are two communication elements in a call: the incoming signal (callrecipient) and the outgoing (caller). The incoming call is carried by thedownlink signal from the tower to the mobile phone, and the outgoing callis carried by the uplink signal from the mobile phone to the tower. Both of these links should be effective for a call to take place, otherwise one of theparticipants in the conversation may not hear the other.

Since the uplink and downlink are handled by different transmitters, it ispossible for one of these signals to be weaker or to fall short of the other.When this happens, the link is said to be "unbalanced". The mobile phonewill detect that there is a signal, but it may not be sufficiently strong inboth directions for both participants to hear each other.

Unbalanced links are usually ascertained during drive-tests, and theyoccur as a result of badly tuned network links. To overcome the problem,one of the transmitters should be tuned by increasing or decreasing thesignal strength so that uplink and downlink signals match.




1.2.7 Radio Propagation Models

A Radio Propagation Model, also known as the Radio Wave Propagation Model orthe Radio Frequency Propagation Model, is a mathematical formulation forthe characterization of radio wave propagation as a function of frequency,distance and other conditions.

Because each individual telecommunication link will encounter differentterrain, path, obstructions, atmospheric conditions and other phenomena,it is impossible to formulate the exact loss for all telecommunicationsystems in a single mathematical equation. As a result, different modelsexist for different types of radio links under different conditions

Different models have been developed to meet the needs of realizing thepropagation behaviour in different conditions. Types of models for radio

propagation include:

• Models for indoor applications

• Models for outdoor applications




Various models exist specifically for city conditions, each of which is builtinto Aircom's Asset (c) software:

• Young Model

• Okumura Model

• Hata Model for Urban Areas

• Hata Model for Suburban Areas

• Hata Model for Open Areas

• COST Hata model

1.2.7.1 Okumura-Hata Model




The Okumura model for Urban Areas is a radio propagation model that wasbuilt using the data collected in the city of Tokyo, Japan. The model is idealfor using in cities with many urban structures but not many tall blockingstructures. The model served as a base for the Hata Model. It assumes the

following parameters:Coverage

• Frequency = 150 MHz to 1920 MHz

• Mobile Station Antenna Height: between 1 m and 10 m

• Base station Antenna Height: between 30 m and 1000 m

• Link distance: between 1 km and 100 km




1.3Drive Testing

Drive testing is normally performed during the launch of a new service. Itinvolves driving around the designated area in a vehicle equipped withspecialised equipment to pick up and analyse radio signals in the vicinity.

Advantages of Drive Testing

1 Replicate Subscriber Conditions

The measurements taken should be identical to those experienced by astandard MS.

2 Comparative Operator Performance

In the increasingly competitive cellular market, visibility of competitors'strengths and weaknesses can be key to gaining and/or maintainingmarket share. Drive test measurements enable operators compare theperformance of their own network with those of its competitors in orderidentify and improve areas of comparative weakness.

3 Focusing on Particular Parameter Set and/or Geographical Regions

Drive testing can be a resource and time-intensive activity. By selectinga suitable route and/or parameter set, the drive test team can focus onspecific problem areas rather than having to carry out network-widetesting.




Limitations of Drive Testing

1 Replicating Subscriber Usage Profiles

Whist the test mobile can simulate a standard MS from a functionalviewpoint, it is less simple to accurately replicate subscribers usage

profiles in terms of frequency of received calls and types of servicesused.

2 Restricted Area Access

Restrictions on accessing certain areas may preclude accurate drive testmeasurements in a specific geographical area. In such cases,alternative methods can be used such as call tracing

3 Network-Wide Performance Measurements

Due to limited resources, it may not be possible to obtain a globalimpression of network performance within an acceptable time perioddue to having to continuously redeploy test teams (e.g. attempting togain a day-long or busy-hour performance indication). In order toovercome this limitation, the centralised monitoring based on BSC/MSCstatistics can be used in tandem with field tests.

4 Restricted to some areas

The field investigations can be done only if field test engineers canphysically access the area. But not all areas are easy to get access in it.If some of those are not important from operating point of view (ex:private garden), others are very important (ex: residential houses andoffices). Alternative investigation methods shall be used here – i.e. calltracing.

5 Based mostly on down-link analysis

The measurements are, by their nature on field tests, resumed ondownlink information received by test MS; except Layer3 messages sentby mobile, there is no information available during drive tests regardingup-link behaviour. Some correlation with system measurement reportscan enhance the depth of analysis.




Drive Testing is used to identify:

• Coverage gaps

• Abnormal interference levels

• Missing neighbour relationships (unidentified neighbouring cells)

• Messaging protocol performance (between phone and network)




Drive testing field tests are carried out using a Test Mobile MS as aninterface to the network. The test mobile is the same as a standard MSfrom RF performance point of view, however, it contains a number of

hardware modifications to enable network performance data to bemeasured and exported to a recording device (e.g. a laptop withappropriate software).

The drive testing system consists of:

• Test mobiles - either one or two for benchmarking against anothernetwork.

• GPS and differential receivers to provide location information

• Logging box to interface the measurement equipment to a laptopcomputer

• Computer running logging and analysis software

When the drive testing starts, two mobiles are used to generate calls with agap of few seconds (usually 15–20). The third mobile is usually used fortesting the coverage. It makes one continuous call, and if this call drops itwill attempt another call. The purpose of this testing to collect enoughsamples at a reasonable speed and in a reasonable time




1.4The Fixed Line Network

1.4.1 Analogue and Digital Transmission

First generation cellular technology relied on an analogue signal whichoccupied a chunk of bandwidth continuously. This was inefficient andresource-intensive. In second generation (and subsequent) technology, thesignal is digitised, meaning that the phone converts your voice into data. Incontrast to analogue signals, digital signals are discontinuous, changing fromone state to another in discrete steps. A popular form of digital modulationis binary, or two level digital modulation. This means that the voiceinformation is translated into a series of 1's and 0's, or "on's and off's".

Digital phones are able to compress this data so that it occupies lessbandwidth, allowing between 3 and 10 digital cell-phone calls to occupy thespace of a single analogue call.

Digital cell phones use the same radio technology as analogue phones, butthey use it in a different way. They utilize the signal between the phoneand the cellular network more efficiently. This is the reason why manycable companies are switching to digital - so they can fit more channelswithin a given bandwidth .Digital systems are eminently more efficient thananalogue.




1.5 Multiplexing Systems Background

One of the aims of communications systems has always been to transmitmany thousands of voice or data channels over a single transmission path.

To do this, these systems have to multiplex and de-multiplex individualchannels.

Earlier systems used Frequency Division Multiplexing (FDM), which involvedindividual channels being modulated with different carrier frequencies toshift the signals into a different frequency range. In this analogue systemeach channel is separated by frequency. FDM was arranged in a 4 levelmultiplexing hierarchy, with each level carrying more channels. Those earlyFDM systems have but vanished from telecommunication provider

companies. For many technical and cost reasons analogue transmissionsystems were unable to satisfy today’s demand for quality higherbandwidth/bit rates, particularly over great distances.

Digital transmission systems were adopted as the way forward for bothvoice and data transmission. In such systems, voice (or any) analoguesignals are converted to a digital format and then multiplexed. Theanalogue to digital conversion is Pulse Code Modulation (PCM) producing64kbs channels with the multiplexing process separating individualchannels by time, known as Time Division Multiplexing (TDM).




Whilst those earlier FDM systems have gone in modern networks, a variantof FDM is used in today’s DSL technology over the local copper accessnetwork with the digital signal converted into frequencies. A complexconversion of digital signals into phase separated frequency multiplexingprovides the extra bandwidth for broadband services over the relatively

short copper local loop.

TDM of Europe’s telecomm networks standard formed the base 2.048Mbit/s multiplexed signal frame structure with a signal designation identityof E1. For individual narrow-band circuits this usually meant thirty 64 kbit/s(E0) channels plus two additional channels for synchronisation andsignalling. This was and still is transmitted over two (transmit and receive)high-grade copper coaxial cable links.

The North American and Japanese system whilst similar is based on twenty-four 64 kbit/s channels DM forming the 1.544 Mbit/s signal designation of DS1.Subsequent digital hierarchical multiplexing systems increased this tomany hundreds of channels over copper with eventual conversion of electrical to laser light signals over optical fibre cable.

The first multiplexing PCM digital systems appeared in the 1960s, followedby further multiplexing systems in the 1970s of Plesiochronous DigitalHierarchy (PDH). Finally in the late1980’s early 1990’s with European‘Synchronous Digital Hierarchy’ (SDH) & American ‘Synchronous OpticalNETwork’ (SONET).

PCM - converts analogue speech into a digital coded format (bit rate 64kbs)then time division multiplexes speech channels along with synchronisationand signalling channels into a 32 channel frame with a bit rate of 2Mbs(European) and a 24 channel frame with a bit rate of 1.5Mbs (American &

Japanese).PDH – a basic hierarchical multiplexing system with lowest tributaries of 1.5or 2Mbs with subsequent hierarchical levels. The E-n signal designationterm identifies the European standard signal bit rates. The Americansystem uses the DS-n designation term.

• E1 - 2 Mbit/s. 32 x 64 kbit/s (E0) time slots synchronously multiplexed (byteinterleaved) into a data stream - 30 time slots for traffic, one forsignalling and one for framing (synchronisation).

• E2 - 8 Mbit/s. 4 x 2 Mbit/s data streams bit interleaved into a data stream

with the addition of framing and timing justification.• E3 - 34 Mbit/s. 4 x 8 Mbit/s data streams bit interleaved into a data stream

with the addition of framing and timing justification.

• E4 - 140 Mbit/s. 4 x 34 Mbit/s data streams bit interleaved into a datastream




1.5.1 Pulse Code Modulation (PCM)

Pulse Code Modulation is a method used to digitally represent sampledanalogue signals. A PCM stream is a digital representation of an analoguesignal, in which the magnitude of the analogue signal is sampled regularlyat uniform intervals, with each sample being quantized to the nearestvalue within a range of digital steps.

In digital telecommunications, where a single physical wire pair can beused to carry many simultaneous voice conversations by time-divisionmultiplexing, worldwide standards have been created and deployed.

Physically E1 is transmitted as 32 timeslots (30 user circuits).

The line data rate is 2.048 Mbit/s (full duplex, i.e. 2.048 Mbit/s downstream

and 2.048 Mbit/s upstream) which is split into 32 timeslots, each beingallocated 8 bits in turn. Thus each timeslot sends and receives an 8-bit PCMsample, usually encoded according to A-law algorithm, 8000 times persecond (8 x 8000 x 32 = 2,048,000). This is ideal for voice telephone callswhere the voice is sampled into an 8 bit number at that data rate andreconstructed at the other end. The timeslots are numbered from 0 to 31.

One timeslot (TS0) is reserved for framing purposes, and alternatelytransmits a fixed pattern. This allows the receiver to lock onto the start of each frame and match up each channel in turn. The standards allow for afull Cyclic Redundancy Check to be performed across all bits transmitted ineach frame, to detect if the circuit is losing bits (information), but this is not

always used.




One timeslot (TS16) is often reserved for signalling purposes, to control callsetup and teardown according to one of several standardtelecommunications protocols.




Complete the table by filling in the number of channels for each signal.




1.5.2 Public Switched Telephone Network (PSTN)

The public switched telephone network (PSTN) is the network of the world's publiccircuit-switched telephone networks. It consists of telephone lines, fibreoptic cables, microwave transmission links, cellular networks,communications satellites, and undersea telephone cables allinterconnected by switching centres. The network allows any telephone inthe world to communicate with any other. Originally a network of fixed-lineanalogue telephone systems, the PSTN is now almost entirely digital in itscore and includes mobile as well as fixed telephones.




1.6GSM Air-Interface

Architecture Overview The term "Air Interface" incorporates all of the equipment andcommunication at the mobile phone end of a call, as opposed to the corenetwork where calls are forwarded to the relevant party.




Traffic Channels

In GSM, under normal conditions, each frequency can carry 8 channels. This is referred to as TCH/F (Full) mode. However, under certaincircumstances (such as emergencies where the network is flooded withcalls), the system can automatically change to TCH/H (Half) mode. Thisallows for the simultaneous transmission of twice as many calls at half thecapacity.

Full Rate

GSM-FR or GSM 06.10 was the first digital speech coding standard used inthe GSM digital mobile phone system. The bit rate of the codec is 13 kbit/s.

Half-Rate

GSM-HR or GSM 06.20 is a speech coding system for GSM, developed in theearly 1990s.Since the codec, operating at 5.6 kbit/s, requires half thebandwidth of the Full Rate codec, network capacity for voice traffic isdoubled, at the expense of audio quality




GSM Voice and Channel Coding Sequence




1.6.1 Base Transceiver Station

A base transceiver station (BTS) or cell site is a piece of equipment that facilitateswireless communication between user equipment (UE) and a network. It isresponsible for all the radio related functions in the system, such as:

• Radio communication with the mobile units

• Handover of calls in progress between cells

• Management of all radio network resources and cell configuration data




Typically, a BTS will have several transceivers (TRXs) which allow it toserve several different frequencies and different sectors of the cell (in thecase of sectorised base stations). A BTS cabinet can have up to 16 TRX

(GSM).

To increase or widen the coverage area (and thus the number of servedclients), several sector antennas are installed on the same supportingstructure, e.g. tower or mast. Such a construction is often called asectorised antenna. Once the antenna unit is attached to a supportingstructure, it has to be positioned. Positioning means not only setting acorrect direction or azimuth, but also setting the correct downtilt.




1.6.2 Base Station Controller

1.6.3 Base Station Subsystem

The base station subsystem (BSS) is the section of a traditional cellulartelephone network which is responsible for handling traffic and signallingbetween a mobile phone and the network switching subsystem. The BSScarries out transcoding of speech channels, allocation of radio channels tomobile phones, paging, transmission and reception over the air interfaceand many other tasks related to the radio network.

The BSS comprises one Base Station Controller (BSC) and several BTS's.




1.6.4 The Transcoding Rate and Adaptation Unit. (TRAU)

The BSC can be located close to the base stations. It concentrates thetraffic towards the MSC, optimizing the utilization of the associated leasedlines. In addition, the BSC supports various BSC-BTS configurations (e.g.,star, multi-drop and loop) and star configurations towards the TRAU.

The TRAU is a stand-alone unit and can be located close to a MobileSwitching Centre (MSC), thus optimally utilizing 16kbit/s channel sub-multiplexing and saving line costs.




1.7Questions

If I have signal can I always make a call?

If you had one TRX. How many Time Slots are there?

What is the advantage of half rate?

As the frequency increases what happens to wavelength?

On GSM to increase capacity. What needs to be added?

Give 3 items which affect coverage?




What is meant by path loss?

What is a propagation model?

What is an E1 signal?




2 Understanding GSM

C H A P T E R 2

K101 Telecommunications Fundamentals Page 61Understanding GSM



2.1 GSM (Global System for MobileCommunications) Evolution

GSM formed the second generation of mobile technology. It was enhancedwith the introduction of General Packet Radio System (GPRS), and later,Enhanced Data for GSM Evolution (EDGE). These are commonly known asthe GSM family of technologies. Technology has moved on since then, butsizeable legacy GSM networks still exist in many countries, often side-by-side with newer technology.

Universal Mobile Telecommunications System (UMTS), also known asWCDMA or HSPA, signified the start of third generation (3G) technology.




2.2 Global System for Mobile Communications(GSM)

More than 3.8 billion people worldwide used the Global System for MobileCommunications (GSM) family of technologies as of May 2009. GSM is themost widely used wireless technology in the world, available in more than219 countries and territories worldwide, with a market share of more than89 percent

When GSM began, its main advantages were as follows:

• Clear voice quality

• International roaming

• Spectral flexibility

Spectral flexibility is provided in that network infrastructure and userdevices are available for the 450, 850, 900, 1800 and 1900 MHz bands.

This is the widest variety of any wireless technology. Some countries,notably the U.S.A, use different band ranges, but tri and quad-band phonesare capable of accessing all of them. Tri and quad-band GSM phones arecommon, reducing the chances that users will ever travel to an areawithout at least one GSM network to which they can connect.




2.3 Base Transceiver Station (BTS)

The BTS houses the radio transceivers that make up a cell. It handles the

radio link protocols with the MS. In a large urban area, a large number of BTS's may be deployed.

A BTS will typically have several transceivers (TRXs) which allow it to serveseveral different frequencies as well as different sectors of the cell. Smallcells, where limited coverage is required, are the exception.

A TRX transmits and receives according to the GSM standards, whichspecify eight TDMA timeslots per radio frequency. A TRX may lose some of this capacity as some information is required to be broadcast to handsetsin the area that the BTS serves. This information allows the handsets toidentify the network and gain access to it. This signalling makes use of achannel known as the broadcast control channel (BCCH).

Page 64 K101 Telecommunications FundamentalsUnderstanding GSM



2.4 Base Station Subsystem (BSS)

The function of the BSS is to connect the Network and Switching Sub-System (NSS) to the Mobile Station (MS).

The BSS is also connected to the Operations and Maintenance Centre(OMC) for:

• configuration management

• fault and performance reporting

Other elements of the network may be located in any convenient place, butthe position of the BTS is crucial to the provision of acceptable radiocoverage for subscribers. Cell site location, taking into account the effect of

the surroundings on radio propagation, is a critical issue in the design of aGSM network.




The BSS is composed of two parts:

• One or more Base Transceiver Stations (BTS)

• The Base Station Controller (BSC)




2.5 Base Station Controller (BSC).

The BSC provides the control functions and physical links between theMobile Switching Centre (MSC) and the Base Transceiver Station (BTS). Itprovides functions such as handover, cell configuration data and control of radio frequency (RF) power levels in Base Transceiver Stations. A numberof Base Station Controllers (BSCs) are served by a single Mobile SwitchingCentre (MSC).




2.6 International Mobile Equipment Identity (IMEI)

The IMEI (International Mobile Equipment Identity) is a unique 17 or 15 digit

code used to identify an individual mobile station to a GSM or UMTSnetwork. It is a useful in preventing stolen handsets from accessing anetwork and placing calls. Mobile phone owners who have their phonesstolen can contact their mobile network provider and ask them disable aphone. This will be done quickly and easily, using its IMEI number.

It is important to note that swapping a SIM card will not stop a phone frombeing banned. IMEI numbers are stored in the phones themselves, not onthe SIM cards. SIM card must be blocked separately.




2.7 Subscriber Identification Module (SIM)

A Subscriber Identification Module (SIM), which appears on a removable SIM card, securely stores the service-subscriber key (IMSI). The IMSI is used toidentify a subscriber on mobile telephony devices. The SIM card allowsusers to change phones by simply removing the SIM card from one mobilephone and inserting it into another mobile phone or broadband telephonydevice.




2.8 International Mobile Subscriber Identity (IMSI)

The IMSI (International Mobile Subscriber Identity) is a unique 15-digit codeused to identify an individual user on a GSM network.

IMSI analysis is the process of examining a subscriber's IMSI to identifywhich network it belongs to, and whether subscribers from that networkmay use a given network. If they are not local subscribers, a roamingagreement is required.

The IMSI consists of three components:

• Mobile Country Code (MCC)

• Mobile Network Code (MNC)

• Mobile Subscriber Identity Number (MSIN)

The IMSI number is stored in the Subscriber Identity Module (SIM)




2.9 Network and Switching Sub-System (NSS)

The Network and Switching Sub-System (NSS) sits between the BSS andother telecommunications networks (e.g. PSTN).

The functions of the NSS are:

• to manage communications between subscribers connected to differentBSC's

• to locate and track mobiles in the GSM network for call-routing purposes

• to provide connectivity to other networks, in particular the PSTN (PublicSwitched Telephone Network)

In practice a separate MSC, called the Gateway MSC (GMSC), provides

connection to external networks such as the PSTN. The various parts of aGSM NSS are connected using Signalling System 7 (SS7).




2.10 Mobile Switching Centre (MSC)

An MSC operates as an ISDN digital exchange with some additionalfeatures to manage the mobility.

Call Control and Routing

The call control procedures and messages closely follow those defined forISDN switching equipment. The MSC is responsible for the establishmentand release of all connections and for providing call routing via thegateway MSC.

MSC Interfaces

The MSC interfaces to the PSTN, ISDN, PSPDN as well as the internal GSMinterfaces to the BSS.

Mobility Management Functions

The MSC is responsible for mobility management as the MS moves throughthe radio network or roams into other networks.

Radion Resource Management

The MSC is also involved in radio resource functions such as handovers

between different BSC's and paging.




Billing Information

The MSC will collect billing information and traffic statistics for the PLMN.

The MSC is the primary service delivery node for GSM/CDMA, responsiblefor routing voice calls and SMS as well as other services (such asconference calls, FAX and circuit switched data).

The MSC sets up and releases the end-to-end connection, handles mobilityand hand-over requirements during the call and takes care of charging andreal time pre-paid account monitoring




2.11 Gateway MSC (GMSC)

The gateway MSC (G-MSC) is the MSC that determines at which visited MSCthe subscriber who is being called is currently located. It also interfaceswith the PSTN. All mobile to mobile calls and PSTN to mobile calls arerouted through a G-MSC.




2.12 Visitor Location Register (VLR)

Each Mobile Switching Centre (MSC) has a Visitor Location Register (VLR). This is

a temporary database containing details of the subscribers who haveroamed into the jurisdiction of the MSC which it serves. Each base stationin the network is served by exactly one VLR, thus, a subscriber cannot bepresent in more than one VLR at a time.

The primary functions of the VLR are:

• To inform the HLR that a subscriber has arrived in the particular areacovered by the VLR.

• To track where the subscriber is within the VLR area (location area)when no call is on-going.

• To allow appropriate services which the subscriber may use, anddisallow those they may not.

• To allocate roaming numbers during the processing of incoming calls.

• To purge the subscriber record if a subscriber becomes inactive whilst inthe area of a VLR. The VLR deletes the subscriber's data after a fixedtime period of inactivity and informs the HLR (e.g., when the phone hasbeen switched off and left off or when the subscriber has moved to anarea with no coverage for a long time).

• To delete the subscriber record when a subscriber explicitly moves toanother VLR, as instructed by the HLR




2.13 Blacklist of Stolen Devices

When mobile equipment is stolen or lost the owner can contact their localoperator with a request that it should be blocked. If the local operatorpossesses an Equipment Identity Register (EIR), they will then put thedevice IMEI into it. This can be optionally communicated to the CentralEquipment Identity Register (CEIR) which blacklists the device in all otheroperator switches that use the CEIR.

2.14 Central Equipment Identity Register (CEIR)

If a mobile handset is lost or stolen, the owner of the device can contactthe CEIR (Central Equipment Identity Register) which will blacklist thedevice in all currently operating switches. This renders the handset useless,which acts as a deterrent to crime. The system is not infallible, as it ispossible to change an IMEI with special tools. There are also certain mobilenetworks that do not automatically blacklist handsets registered with theCEIR, so the phone may still work if the SIM card is replaced with one fromone of those networks, or if the phone is taken to another country. Currentstatistics state that approximately ten percent of IMEI’s in use today arenot unique or have been reprogrammed (hacked).




2.15 Equipment Information Register (EIR)

The GSM EIR database contains information about the identity of mobileequipment. This is used to prevent calls from stolen, unauthorized ordefective mobile stations.GSM network operators maintain three lists of international mobileequipment identities (IMEI) in their equipment identity register :

• black - barred GSM mobile phones

• grey - GSM mobile phones to be tracked

• white - valid GSM mobile phones




2.16 Home Location Register (HLR)

The Home Location Register (HLR) is a central database that contains details of each mobile phone subscriber that is authorized to use the GSM corenetwork. There can be several logical, and physical, HLRs per public landmobile network (PLMN). However, one international mobile subscriberidentity (IMSI)/MSISDN pair can be associated with only one logical HLR(which can span several physical nodes) at a time.

The HLRs store details of every SIM card issued by the mobile phoneoperator. Each SIM has a unique identifier called an IMSI which is theprimary key to each HLR record.




The next important items of data associated with the SIM are the MSISDNs,which are the telephone numbers used by mobile phones to make andreceive calls. The primary MSISDN is the number used for making and

receiving voice calls and SMS, but it is possible for a SIM to have othersecondary MSISDNs associated with it for fax and data calls. Each MSISDNalso forms a primary key to the HLR record. The MSISDN is only ever usedin human interaction with a handset. The network immediately translatesthis number into an IMSI, which it uses to track and route calls thereafter.




The HLR connects to your Gateway MSC (G-MSC) for handling incomingcalls and the VLR for handling requests to register mobile phones on thenetwork. It is also fully integrated with the SMSC, allowing it to handle

incoming SMS messages; and with the voicemail system, which deliversnotifications to mobile phones when messages are waiting.




The GSM standard also provides separate facilities for transmitting digitaldata. This allows a mobile phone to act like any other computer on theInternet, sending and receiving data via Internet Protocol.

The mobile may also be connected to a desktop computer, laptop, or

Personal digital assistant (PDA)

2.16.1 Circuit-Switched Data

Circuit switching is a telecommunications technology by which two networknodes establish a dedicated communications channel (circuit) connectingthem for the duration of the communication session before the nodes maycommunicate. The bit delay is constant during a connection, as opposed topacket switching, where packet queues may cause varying packet transferdelay. Each circuit cannot be used by other callers until the circuit isreleased and a new connection is set up

A circuit-switched data connection reserves a certain amount of bandwidthbetween two points for the life of a connection, just as a traditional phonecall allocates an audio channel of a certain quality between two phones forthe duration of the call.

Two circuit-switched data protocols are defined in the GSM standard:Circuit Switched Data (CSD) and High-Speed Circuit-Switched Data(HSCSD). Circuit Switched Data (CSD) is the original form of datatransmission developed for the time division multiple access (TDMA)-basedmobile phone systems like Global System for Mobile Communications(GSM). CSD uses a single radio time slot to deliver 9.6 data transmission tothe GSM Network and Switching Subsystem where it could be connected

through the equivalent of a normal modem to the Public Switched Telephone Network (PSTN) allowing direct calls to any dial-up service

A CSD call functions in a very similar way to a normal voice call in a GSMnetwork. A single dedicated radio time slot is allocated between the phoneand the base station. A dedicated "sub-time slot" (16 kbit/s) is allocatedfrom the base station to the transcoder, and finally another time slot (64kbit/s) is allocated from the transcoder to the Mobile Switching Centre(MSC).

High-Speed Circuit-Switched Data

(HSCSD) is a system based on CSD but designed to provide higher datarates by means of more efficient channel coding and/or multiple (up to 4)time slots




2.17 Data Bearer Services

A Data Bearer Service (BS) needs to be enabled on the SIM Card (by theNetwork Operator) to send/receive data over the GSM network. Thedifferent Data Bearer Services are distinguished through different rates of data transmission.

• BS26, (9600 baud, V110 and V32)

• BS25, (4800 baud, V32)

• BS24, (2400 baud, V110 and V22bis)

Currently in GSM, there are two facsimile services specified: teleservice TS61 "Alternate speech/facsimile G3" and TS62 "Automatic facsimile G3".




In an emergency, there are advantages to using the GSM emergencynumber (like 112) over other emergency numbers:

•

GSM phones and networks give special priority to emergency calls• A phone dialling an emergency service number which it does not

recognise may refuse to roam onto another network if there is no accessto the home network. Using the known emergency number forces thephone to attempt to connect with any available network.




Messages are sent to a Short Message Service Centre (SMSC) which provides a"store and forward" mechanism. The SMSC attempts to send messages tothe SMSC's recipients, but if a recipient is not reachable, it queues the

message for later retry.




2.18 Authentication Centre (AUC)

The Authentication Centre (AUC) functions to authenticate each SIM cardthat attempts to connect to the GSM core network. This typically happenswhen the phone is powered on. Once the authentication is successful, theHLR is allowed to manage the SIM and services described above. Anencryption key is also generated that is subsequently used to encrypt allwireless communications (voice, SMS, etc.) between the mobile phone andthe GSM core network.




The AUC does not engage directly in the authentication process, butinstead generates data known as triplets for the MSC to use during theprocedure. The security of the process depends upon a shared secret

between the AUC and the SIM called the Ki. The Ki is securely burned intothe SIM during manufacture and is also securely replicated onto the AUC.

This Ki is never transmitted between the AUC and SIM, but is combinedwith the IMSI to produce a challenge/response for identification purposesand an encryption key called Kc for use in over the air communications.

This makes it extremely difficult for hackers to decipher hacked digitalcalls, as they do not ever see the Ki or the Kc.




The Visitor Location Register is a temporary database of the subscribers whohave roamed into the jurisdiction of the MSC (Mobile Switching Centre)which it serves. Each base station in the network is served by exactly oneVLR, hence a subscriber cannot be present in more than one VLR at a time.

Procedures implemented The primary functions of the VLR are:

• To inform the HLR that a subscriber has arrived in the particular areacovered by the VLR.

• To track where the subscriber is within the VLR area (location area)when no call is on-going.

• To allow or disallow which services the subscriber may use.

• To allocate roaming numbers during the processing of incoming calls.

• To purge the subscriber record if a subscriber becomes inactive whilst in

the area of a VLR. The VLR deletes the subscriber's data after a fixedtime period of inactivity and informs the HLR (e.g., when the phone hasbeen switched off and left off or when the subscriber has moved to anarea with no coverage for a long time).

• To delete the subscriber record when a subscriber explicitly moves toanother, as instructed by the HLR




2.19 Location Area

A Location Area is a set of base stations that are grouped together in order tooptimise signalling. Typically, tens or even hundreds of base stations sharea single Base Station Controller (BSC) in GSM, or a Radio NetworkController (RNC) in UMTS. The BSC handles allocation of radio channels,receives measurements from the mobile phones, controls handovers frombase station to base station.

A unique number called a Location Area Code is assigned to each location area. The location area code is broadcast by each base station (known as a"Base Transceiver Station" BTS in GSM, or a "Node B" in UMTS) at regularintervals.

If the location areas are very large, there may be many mobiles operatingsimultaneously. This results in very high paging traffic, as every pagingrequest has to be broadcast to every base station in the location area.Bandwidth and power are wasted on the handset as a result, since it isrequired to listen for broadcast messages too much of the time. On theother hand, if there are too many small location areas, a similar problemmay occur since the mobile must contact the network very often forchanges of location. A balance has therefore to be struck.




MSRN - Mobile Station Roaming Number

The Mobile Station Roaming Number is an E.164 defined telephone numberused to route telephone calls in a mobile network from a GMSC (GatewayMobile Switching Centre) to the target MSC. It can also be defined as adirectory number temporarily assigned to a mobile for a mobile terminatedcall. A MSRN is assigned for every mobile terminated call, not only the callswhere the terminating MS lives on a MSC other than the originating MS.

The VLR generates this address on request from the MSC, and the addressis also stored in the HLR.

The MSRN contains:

• the current visitor country code (VCC)

• the visitor national destination code(VNDC)

• the identification of the current MSC

• the subscriber number




2.20 Basic Mobile Terminated (Network Originated)Call Procedure

1 The incoming call is passed from the fixed network to the gateway MSC(GMSC).

2 Based on the IMSI numbers of the called party, its HLR is determined.

3 The HLR checks for the existence of the called number and identifies theVLR to which it is currently affiliated. The HLR requests the mobilestation roaming number (MSRN) from the identified VLR.

4 Upon receipt, the HLR transmits the MSRN back to the GMSC.

5 When the GMSC receives a valid MSRN, it switches the call through to

the appropriate MSC.6 The VLR is queried for the location range and reachability status of the

mobile subscriber.

7 If the MS is marked reachable, a radio call is enabled at the MSC.

8 This generates a paging request from the MSC to all BSS's in the MS’slast recorded Location Area.

9 The mobile subscriber telephone responds to the paging request fromits current cell, the link is extended to the MS and authenticationinformation is passed from the MS to the MSC .

10 All necessary security procedures are executed.




11 If security procedures are successful, the VLR indicates to the MSC thatthe call can be completed.

12 The MSC then extends the call from the GMSC to the MS.




2.21 Questions

Identify the various components in the GSM network.

What is the function of the TRX?

Give 3 functions of the HLR?

What is a location area?

What is an IMSI?




What is an IMEI?

What is a BSS?

What is NSS?

What is the bit speed for GSM circuit switched?




3 Fundamentals of Frequency Planning

C H A P T E R 3

K101 Telecommunications Fundamentals Page 99Fundamentals of Frequency Planning



3.1What is a Frequency Band?

Cell planning is one of the most important aspects of GSM networkimplementation, and must be done before the network is installed. Theprocess involves studying the geographic area where the system will beinstalled to determine:

• the coverage radius of each BTS

• the frequencies to be used for each BTS.

Cell phones use radio waves to transmit conversations. These radio wavescan be transmitted at different frequencies, just the same as regular radiostations are found at different frequencies

For example:

• FM radio stations are in the FM radio band, between 88-108 MHz.

• AM radio stations are in the AM radio band, between 0.55 and 1.6 MHz




ARFCN

The Absolute Radio Frequency Channel Number (ARFCN) is a uniquenumber allocated to each radio channel in GSM. It can be used to calculatethe exact frequency of the radio channel. The following ARFCN numbersare allocated to the most common GSM bands as follows:

Band ARFCNRange

GSM900 1 to 124

GSM1800 512 to 885

GSM1900 512 to 810

•

The ARFCN's used in GSM1900 overlap with the ARFCN's used in GSM1800.Hence, a multiband mobile phone will interpret ARFCN numbers 512 to 810as either GSM1800 or GSM1900 frequencies.

GSM1800 is the term used to denote GSM operating in the 1800 MHz band.However, the 1800 MHz band actually ranges from 1710 - 1785 MHz andfrom 1805 - 1880 MHz. Mobiles transmit in the lower band and basestations transmit in the upper band.

The total GSM900 band defined in the standard ranges from 876 - 915 MHzis paired with 921 - 960 MHz. Mobiles transmit in the lower band and basestations transmit in the upper band.




GSM1900 is the term used to denote GSM operating in the 1900 MHz band,but the 1900 MHz band ranges from 1850 - 1910 MHz and from 1930 -1990 MHz. Again, mobiles transmit in the lower band and base stationstransmit in the upper band.

GSM1900 is primarily used in the Americas. GSM1900 is developed for theAmerican market because the 1800 MHz band (GSM1800) was notavailable for mobile communications in that part of the world at the time of implementation.

Page 102 K101 Telecommunications FundamentalsFundamentals of Frequency Planning



Two frequency bands are used by GSM services in the US, and two differentfrequency bands are used by GSM services elsewhere in the world.

The ideal phone would work on all four bands. Such a phone is commonlycalled a quad-band phone, but these are still rare and expensive.

If choosing a tri-band phone as a second best choice,???

GSM cell phones use frequencies within four different frequency bands:

• 850 MHz (824.2 - 848.8 MHz Tx; 869.2 - 893.8 MHz Rx)

• 900 MHz (880-2 - 914.8 MHz Tx; 925.2 - 959.8 MHz Rx)

• 1800 MHz (1710.2 - 1784.8 MHz Tx; 1805.2 - 1879.8 MHz Rx)

• 1900 MHz (1850.2 - 1909.8 MHz Tx; 1930.2 - 1989.8 MHz Rx)

Although 850 and 900, and 1800 and 1900 are very close together, aphone that works in one frequency band unfortunately cannot also work inthe frequency band next to it. Similarly, when you have your FM radiotuned to a radio station at 98.1 MHz, you cannot hear what is happening onanother radio station at 98.3 MHz unless you re-tune your radio. Individualphones are shipped with the ability to access a specified band or bands.




3.1.1 Which frequencies are used in the US?

Originally, the US used only 1900 MHz for its GSM cell phone service.However, in recent years there has been a growing amount of GSM serviceon the 850 MHz band. This type of service will usually be seen in rural

areas, because the 850 MHz band has better range than the 1900 MHzband due to its lower frequency. It can sometimes also be found in cityareas, particularly in cases where the cell phone company has run out of frequencies in the 1900 MHz band, but still has unused frequenciesavailable in the 850 MHz band.

3.1.2 Which frequencies are used internationally?

GSM was originally developed in Europe, and only came to the US in recentyears. Initially, all countries with GSM service used the 900 MHz band, butservice providers have lately been increasingly been 1800 MHz coverage

due to congestion in the 900 MHz band.When the US started to use GSM, a few other countries with very closelinks to the US chose to copy the US and use the same frequencies that theUS used - first 1900 MHz, and also in a few cases, 850 MHz.

Almost without exception, all international countries that use the non-USinternational frequency bands have 900 MHz service, and many also havesome 1800 MHz service.

3.1.3 Different Definitions of 'Tri-band Phone'

Tri-band phones support three different frequency bands, but they may

differ in their choice of which three of the four bands they support.

The two common variations are :

• 900/1800/1900 - Excellent internationally and very good in the US

• 850/1800/1900 - Excellent in the US but not very good internationally




The following table shows some examples of bandwidths used in variouscountries.

Country 900 1800 1900 850

Afghanistan

Albania

Algeria

Angola

Anguilla

Antigua & Barbuda

Argentina

Armenia

Aruba Australia

Azerbaijan

Austria

Bahamas

Bahrain

Bangladesh

Barbados

Belarus

Cambodia

Cameroon

Canada

Cayman Islands

Chad

Chile

China

Colombia

Congo

Congo, Democratic Rep

Costa Rica

Côte d'Ivoire

Croatia

Cuba

Cyprus

Iran

Iraq

Ireland

Israel




Country 900 1800 1900 850

Italy

Jamaica

Japan No GSM service in Japan

Jordan

Kazakhstan

Kenya

Korea (South) – CDMA not GSM No GSM service in South Korea

Kosovo

Kuwait

Kyrgyzstan




The BTS contains transceivers (the equipment for transmitting andreceiving radio signals), antennas, and equipment for encrypting and

decrypting communications with the Base Station Controller (BSC). Typically, a site (for anything other than a picocell) will have severaltransceivers (TRXs). This allows it to serve several different frequenciesand several different sectors of the site. Such sites are said to besectorised

A transceiver transmits and receives according to the GSM standards,which specify eight TDMA timeslots per radio frequency. It may lose someof this capacity, as some information is required to be broadcast tohandsets in the area which the BTS serves. This information allows thehandsets to identify the network and gain access to it. This signallingmakes use of a channel known as the broadcast control channel (BCCH).




3.2Capacity and Quality

The major aim of the radio planner is to increase the coverage area of acell and decrease the amount of equipment needed in the network, therebyobtaining the maximum coverage at minimum cost. Maximum coveragemeans that the mobile is connected to a given cell at a maximum possibledistance. This is possible if there is a minimum signal to noise ratio at boththe BTS and MS. Another factor contributing to the path length betweenthe two antennas (BTS and MS) is the propagation loss due toenvironmental conditions.




3.3 Interference

The signal at the receiving antenna can be weakened by interference fromother signals. These signals may be from the same network or they may bedue to man-made objects. But the major cause of interference in a cellularnetwork is the radio resources in the network itself. There are a limitednumber of radio channels in use in a network, so many of them share acommon bandwidth. The problem is that different sites using the samefrequency may interfere with each other if placed too close together.Accurate frequency planning provides the solution.




Frequency planning makes it possible to decide where to allocate variousfrequencies so that the experience the minimum of interference.




The geographical area covered by a group of cellular radio antennas (acell) is a complex object, but we use a simple hexagon to represent it. Thisshape allows us to picture the cellular idea, because on a map it only

approximates the covered area.

When showing a cellular system we want to depict an area totally coveredby radio, without any gaps. In reality, any cellular system will have gaps incoverage, but the hexagonal shape lets us more neatly visualize, in theory,how the system is laid out and how the cells knit together. Notice how thecircles above would leave gaps in our layout.




Most cells have been split into sectors or individual areas to make themmore efficient and to let them to carry more calls. Antennas transmitinward to each cell. This is very important to remember. They cover a

portion or a sector of each cell, not the whole thing. Antennas from othercell sites cover the other portions. In other words, a cell should not bevisualised as a broadcast hexagon surrounding one site, or a collection of antennas on a site; but a theoretical hexagon created by several sites, likethis:

The solid blue lines here represent the theoretical edges of each BTS area,whereas the red dotted lines represent the theoretical edges of the actualcells.

Of course, not all cells are covered by three transceivers on three differentBTS's. Combinations of two and six transceivers are common. Nonetheless,

the hexagon remains the most common method of depicting cells.




Since frequencies can only be re-used within certain distances, it isimportant to plan this aspect carefully. It is also important to note that,besides the intended signal from within the cell, signals at the same

frequencies (co-channel signals) can arrive from undesired transmitterslocated far away in other cells. This concept can also lead to deteriorationin receiver performance

In summary, the following factors form the basis of cell coverage criteria.

• Several carrier frequencies must be used in order to avoid interference.

• Adjoining cells should utilise different frequencies.

• Cell sizes should be taken into account, as they vary from 100 m up to35 km depending on factors such as user density, geography andtransceiver power.

• Cells should ideally be hexagonal in shape. When cell coverage overlapsat the edges, a hexagonal pattern of coverage results. Planners strive tocreate this idealised, hexagonal shape in adjoining cells, but in reality itis difficult to achieve.

• Connections should be handed over to adjoining cells as the mobile usermoves from cell to cell.




3.4 Principles of Cellular Frequency Reuse

In order to avoid putting the same frequencies too close to each other,cells are arranged into clusters. All of the frequencies in a cluster will beunique. This way, as long as a similar pattern is maintained acrossadjoining clusters, frequencies are unlikely to overlap. Thus in practice,cluster patterns and their corresponding frequencies tend to be reused in aregular pattern over the entire service area.

The closest distance between the centres of two cells using the samefrequency (in different clusters) is determined by the choice of the clustersize N and the layout of the cell cluster. This distance is known as thefrequency reuse distance.




The configuration shown above represents a reuse plan where N = 3 (threedifferent frequencies repeated over an area). Each colour represents one of the recurring frequencies. Notice that no one colour touches the samecolour. There may still be considerable interference where cells remain inrelative close proximity such as this. The next picture shows the same

effect where seven different frequencies are used (N = 7). Interference iseven less likely in this scenario, and increasingly unlikely as the number of frequencies increases.




Frequency re-use is the process of using the same radio frequencies onradio transmitter sites within a geographic area, which are separated bysufficient distance to cause minimal interference with each other.Frequency reuse allows for a dramatic increase in the number of customersthat can be served (capacity) within a geographic area on a limited amount

of radio spectrum (limited number of radio channels).

The frequency plan may use ratios that are different depending on the ratioof transmitting sites to the number of antennas (sectors) on each site. Acommon frequency reuse plan for GSM is known as "4/12". This signifiesthe ability to re-use a radio frequency on every fourth site, where each sitehas three 120 degree sectors – a total of 12 total sectors.




Tighter reuse allows for higher capacity from the same range of frequencies, but increases the chance of interference between cells.

Therefore, a balance must be sought. This is where planning tools such as

AIRCOM's ASSET can help.




The following pages show examples of various cluster patterns:




3.5 Basics of Radio Networks Operation

Optimisation is the process of monitoring, verifying and improving theperformance of the radio network. The task usually begins somewhere nearthe last phase of radio network planning. A cellular network covers a largearea, providing capacity to many people, so there are numerousparameters that must be continuously monitored and corrected. Inaddition, the network is always growing as a result of increasing subscribernumbers and increases in traffic. If network efficiency and revenue are tocontinually increase, the optimisation process needs to be on-going.




3.6Questions

What affects the quality of your call?

Which frequencies are used in the USA?

GSM cell phones use frequencies in four different bands. What are they?

What is meant by ARFCN?




What is meant by frequency reuse?

In a 4/12 frequency plan, what does "4" represent? What does "12" represent?




4 Fundamentals of GPRS

C H A P T E R 4

K101 Telecommunications Fundamentals Page 125Fundamentals of GPRS



Whilst GSM (2G) networks are excellent for voice calls, they are limitedwhen it comes to sending and receiving data.

GSM phones use a technology called CSD (Circuit Switched Data) to transferdata. CSD requires the phone to make a special connection to the networkbefore it can transfer data (like making a voice call) which can take up to30 seconds. Once connected, the data is sent or received and the user isbilled for the time spent online. Data transfer is relatively slow

GPRS (General Packet Radio Service) is a method of enhancing 2G phones toenable them to send and receive data more rapidly. With a GPRSconnection, the phone is "always on" and can transfer data immediately,and at higher speeds: typically 32 - 48 kbps. An additional benefit is that datacan be transferred at the same time as making a voice call. GPRS is nowavailable on most new phones.




General Packet Radio Service (GPRS) is an efficient use of limitedbandwidth and is particularly suited for sending and receiving small bursts

of data (such as e-mail and Web browsing) as well as large volumes of data. GPRS supports a wide range of bandwidths. It works on GPRS cellphones as well as laptops and portable devices that have GPRS modems.

Page 128 K101 Telecommunications FundamentalsFundamentals of GPRS



56 K Dial-Up GSM HSCSD(maximum speed)

GPRSALL 8 TS

(maximum speed)

GPRS(realistic speed)

56 9.6 57.6 171.2 43 to 56




4.1 GPRS Class Types

The class of a GPRS phone determines the speed at which data can betransferred. Technically the class refers to the number of timeslotsavailable for upload (sending data from the phone) or download (receivingdata from the network). Timeslots used for data are reserved in addition tothe slot that is reserved for voice calls. These timeslots are availablesimultaneously, so the greater the number of slots, the faster the datatransfer speed.

Since GPRS transmits data in packets, the timeslots do not remain in useall the time, but are shared amongst all users of the network. Thisincreases the overall data capacity of the network, and it also means thatcustomers are billed for the quantity of data transmitted, not the time

spent online. It may mean that during busy times, data transfer rates slowdown because the network will give priority to voice calls.




4.2 GPRS Support Nodes (GSN)

A GPRS Support Node (GSN) is a network node which supports the use of GPRS in the GSM core network. All GSNs should have a Gn interface andsupport the GPRS tunnelling protocol.

There are two key variants of the GSN:

• Gateway GPRS Support Node

• Serving GPRS Support Node




4.2.1 Gateway GPRS Support Node (GGSN)

The Gateway GPRS Support Node (GGSN) is a main component of the GPRSnetwork. The GGSN is responsible for the interaction between the GPRS

network and external packet switched networks, like the Internet.From the point of view of an external network, the GGSN is a router to asub-network, as the GGSN effectively hides the GPRS infrastructure fromthe external network. When the GGSN receives data addressed to aspecific user, it checks if the user is active. If it is, the GGSN forwards thedata to the SGSN serving the mobile user, but if the mobile user is inactive,the data is discarded. On the other hand, mobile-originated packets arerouted to the relevant network by the GGSN.

The GGSN is responsible for IP address assignment, and is the defaultrouter for the connected user equipment (UE). The GGSN also performsauthentication and charging functions.

Other functions include:

• Subscriber screening

• IP Pool management and address mapping

• QoS and PDP context enforcement

4.2.2 Serving GPRS Support Node (SGSN)

A Serving GPRS Support Node (SGSN) is responsible for the delivery of datapackets from and to the mobile stations within its geographical service

area. The location register of the SGSN stores location information (e.g.,current cell, current VLR) and user profiles (e.g., IMSI, address(es) used inthe packet data network) of all GPRS users registered with this SGSN.

SGSN Functions include:

• Packet routing and transfer

• Mobility management (attach/detach and location management)

• Logical link management

• Authentication and charging functions




4.3Packet Switching

Packet switching is a digital networking communications method thatgroups all transmitted data – regardless of content, type, or structure – intosuitably-sized blocks, called packets. Packet switching features delivery of variable-bit-rate data streams (sequences of packets) over a sharednetwork. When traversing network adapters, switches, routers and othernetwork nodes, packets are buffered and queued. This results in variabledelay and throughput, depending on the traffic load in the network.




4.4Circuit Switching

Circuit switching was (and is still) used in GSM (2G) networks. Whilst GSM(2G) networks are excellent for voice calls, they are limited when it comesto sending and receiving data. GSM phones use a technology called CSD(Circuit Switched Data) to transfer data. CSD requires the phone to make aspecial connection to the network before it can transfer data (like making avoice call) which can take up to 30 seconds. Once connected, the data issent. In contrast to packet switching, circuit switching sets up a limitednumber of dedicated connections of constant bit rate and constant delay.




4.6 Home Location Register (HLR)

The Home Location Register (HLR) is a central database that containsdetails of each mobile phone subscriber that is authorized to use theGSM/GPRS core network

Other details stored against an IMSI record in the HLR include:

• GSM services that the subscriber has requested or been given

• GPRS settings to allow the subscriber to access packet services

• Current location of subscriber (VLR and serving GPRS supportnode/SGSN




4.7Circuit-Switched

Circuit-switched is a type of network in which a physical path is obtainedfor and dedicated to a single connection between two end-points in thenetwork for the duration of the connection. Ordinary voice phone service iscircuit-switched. The telephone company reserves a specific physical pathto the number you are calling for the duration of your call. During thattime, no one else can use the physical lines involved.




An Internet Protocol address (IP address) is a numerical label assigned toeach device (e.g., computer, printer, phone) participating in a computernetwork that uses the Internet Protocol for communication. An IP address

serves two principal functions: host or network interface identification andlocation addressing.




4.8Packet-Switched

Packet-switched describes the type of network in which relatively smallunits of data called packets are routed through a network based on thedestination address contained within each packet. Breaking communicationdown into packets allows the same data path to be shared among manyusers in the network.

GPRS terminals can share the same timeslot.




4.9Coding schemes

The choice of coding scheme depends on quality of the radio link betweencell phone and base station. If the channel is very noisy, the network mayuse CS-1 to ensure higher reliability; in this case the data transfer rate isonly 9.05 kbit/s per GSM time slot used. If the channel is providing a goodcondition, the network could use CS-3 or CS-4 to obtain optimum speed,which would provide up to 21.4 kbit/s per GSM time slot.

Channel Coding Scheme CS-1 CS-2 CS-3 CS-4

Maximum data speed with 8 time-slots

72.4 kb/s 107.2 kb/s 124.8 kb/s 171.2 kb/s




GPRS Class Types

The class of a GPRS phone determines the speed at which data can betransferred. Technically, the class refers to the number of timeslotsavailable for upload (sending data from the phone) or download (receivingdata from the network). The timeslots used for data are reserved inaddition to the slot that is reserved for voice calls. These timeslots areavailable simultaneously, so the greater the number of slots, the faster thedata transfer speed. Because GPRS transmits data in packets, the timeslotsare not in use all the time, but are shared amongst all users of the network.

This increases the overall data capacity of the network, and it also meansthat you are billed for the quantity of data transmitted, not the time thatyou are online. It may mean that during busy times, data transfer rates

slow down, because the network will give priority to voice calls.




4.10 Questions

What is meant by C/I ratio?

Draw a diagram showing two BTS. Label the C/I ratio




If you had a C/I ratio of +21dB. What CS will you get?

If you had a C/I ratio of +21dB and were given 2 timeslots. What is the speed?




5 Comparison of DifferentMobile Technologies

C H A P T E R 5

K101 Telecommunications Fundamentals Page 149Comparison of Different Mobile Technologies



5.1 Introduction

There have been several generations of mobile communications over theyears, each bringing with it new technologies and increases in data speedsand capacities.

First Generation

First generation technology used analogue signals as opposed to digital,and reserved a full frequency slot for the duration of the call. Thistechnology was inefficient and expensive, and is no longer in use.

Second Generation (2G)Second-generation networks marked the transition to digital transmission,and utilised the same frequency for eight concurrent calls, thus makinglarge-scale mobile usage viable. These networks are generally slow, withdata speeds similar to or lower than a 14Kbps modem. Another 2Gdrawback is that the data connections are circuit-switched, meaning usersmust initiate every connection.

Second Generation Advancements (2.5G)

Both of these issues, however, are partially solved by 2.5G networks. These

use packet-switched networks with a data connection that remains onthroughout. Data also travels faster than on 2G networks, with speedssimilar to a 56Kbps modem.




Third Generation (3G)

Third generation wireless ups the performance even further, purportedlyachieving speeds as high as 384Kbps, making multimedia features such asstreaming video a possibility for the first time.

High-Speed Downlink Packet Access (HSDPA) is a third generationimproved protocol for mobile telephone data transmission. It is known as a3.5G technology. Essentially, the standard provides download speeds on amobile phone equivalent to an ADSL (Asymmetric Digital Subscriber Line)line in a home, removing any limitations placed on the use of your phoneby a slow connection. It is an evolution of Wideband Code Division MultipleAccess (W-CDMA), a 3G protocol. HSDPA improves the data transfer rateover W-CDMA by a factor of at least five. HSDPA can achieve theoreticaldata transmission speeds of 8-14.4 Mbps (megabits per second).

High-Speed Uplink Packet Acc http://en.wikipedia.org/wiki/3g \o 3gess(HSUPA) is a http://en.wikipedia.org/wiki/mobile_telephony \o mobile

telephony3G protochttp://en.wikipedia.org/wiki/communications_protocol \o communicationsprotocolol family wi http://en.wikipedia.org/wiki/high-speed_packet_access \o high-speed packet accessth up-link speeds up to5.76 Mbit/

3GPP Long http://en.wikipedia.org/wiki/mbit/s \o mbit/sTerm Evolution (LTE)is the latest standard in the mobile network technology. It has peakdownload rates of 326.4 Mbit/s for 4x4 antennae, and 172.8 Mbit/s for 2x2antennae (utilizing 20 MHz of spectrum). Though some refer to it as afourth generation technology, it is officially recorded as an advancement in3G technology by the 3GPP.


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5.1.1 Structure of a Packet Service Session

Page 152 K101 Telecommunications FundamentalsComparison of Different Mobile Technologies



5.1.3 Enhanced Data rate for Global Evolution (EDGE)

Enhanced Data rates for GSM Evolution (EDGE, or EGPRS) provides datatransfer rates significantly faster than GPRS or HSCSD. EDGE increases thespeed of each timeslot to 48 kbps and allows the use of up to 8 timeslots,giving a maximum data transfer rate of 384 kbps. In places where an EDGEnetwork is not available, GPRS will be automatically used instead. EDGEoffers the best that can be achieved with a 2.5G network, and willeventually be replaced by 3G.




With EDGE, the operators and service providers can offer more wirelessdata applications, opening up a host of possibilities including:

•

Wireless multimedia• Web-based e-mail

• Web Infotainment

• Video Conferencing.

EDGE out-performs GPRS convincingly, providing data speeds andthroughput capacity by around 2-4 times. Based on an 8 PSK modulation, itallows higher bit rate across the air Interface.




EDGE has higher data rates due to several technological improvements.For example: GPRS uses GMSK modulation in its air interface, whereasEDGE, in addition to GMSK, uses higher bit rate 8-PSK modulation.

Moreover, GPRS is a best- effort packet switched service where limitedQuality of Service (QoS) is guaranteed during communication. In contrast,EDGE introduces data transfer during mobility with a higher level of confidence.




GMSK is similar to standard minimum-shift keying (MSK); however thedigital data stream is first shaped with a Gaussian filter before beingapplied to a frequency modulator. This has the advantage of reducing

sideband power, which in turn reduces out-of-band interference betweensignal carriers in adjacent frequency channels.




5.1.5 8-PSK

8-PSK has higher data rates due to several technological improvements.For example: GPRS uses GMSK modulation for air interface whereas EDGEand GMSK, use higher bit rate 8-PSK modulation.

5.1.6 Phase-Shift Keying (PSK)

Phase modulation is a version of frequency modulation, where the phase of the carrier wave is modulated to encode bits of digital information in eachphase change.

Phased Shift Keying phase modulation is accomplished through the use of adiscrete number of states. 8PSK refers to PSK with 8 states.




5.1.7 Quadrature Phase Shift Keying (QPSK)

QPSK refers to PSK with 4 states.• Half that number of states would be BPSK (Binary Phased Shift Keying)

• Twice the number of states would be 8PSK.

The "Quad" in QPSK refers to four phases in which a carrier is sent in QPSK:45, 135, 225, and 315 degrees.

QPSK Encoding

Because QPSK has 4 possible states, it is able to encode two bits persymbol.

Phase Data 45 degrees Binary 00 135 degrees Binary 01 225 degreesBinary 11 315 degrees Binary 10 QPSK is more tolerant of link degradationthan 8PSK, but does not provide as much data capacity.




5.1.8 Higher Order Modulation - HSDPA

High Speed Downlink Packet Access (HSDPA) uses both the modulationused in WCDMA-namely QPS and, under good radio conditions, anadvanced modulation scheme-16 QAM. The benefit of 16 QAM is that 4 bitsof data are transmitted in each radio symbol as opposed to 2 bits withQPSK. Data throughput is increased with 16 QAM, while QPSK is stillavailable under adverse conditions. HSPA Evolution will add 64 QAMmodulation to further increase throughput rates.

Quadrature Amplitude Modulation (QAM) is widely used in many digitaldata radio communications and their applications. A variety of forms of QAM are available. Some of the more common forms include:16 QAM, 32QAM, 64 QAM, 128 QAM, and 256 QAM. The figures used here refer to the

number of points on the constellation, or the number of distinct states thatcan exist.




5.1.9 QAM Bits Per Symbol

The advantage of using QAM is that it is a higher order form of modulationand is consequently able to carry more bits of information per symbol. By

selecting a higher order format of QAM, the data rate of a link can beincreased.

QAM Noise Margin

While higher order modulation rates are able to offer much faster datarates and higher levels of spectral efficiency, this comes at a price, as theyare considerably less resilient to noise and interference. Consequently,many radio communications systems now use dynamic adaptivemodulation techniques. These sense the channel conditions and adapt themodulation scheme to obtain the highest data rate for the given conditions.As signal to noise ratios decrease, errors will increase (along with re-sends

of the data), thereby slowing throughput. By reverting to a lower ordermodulation scheme the link can be made more reliable, with fewer dataerrors and re-sends.




5.1.10 HSDPA UE Categories

The 3rd Generation Partnership Project (3GPP) has divided HSDPA UE's ormobile terminals into twelve categories. These categories define thedifferent characteristics, including the different HSDPA data rates.

Categories 1-10 support 16QAM (16 Quadrature Amplitude Modulation) aswell as QPSK (Quadrature Phase Shift Keying).

Categories 11 and 12 only support QPSK.

Universal Mobile Telecommunication System (UMTS) networks, based onwideband code division multiple access (WCDMA), have been deployedworldwide as 3rd generation mobile communications systems. UMTSprovides a clear evolution path to high speed packet access (HSPA). HSPA

refers to the combination of high speed downlink packet access (HSDPA)and high speed uplink packet access (HSUPA).

HSDPA allows data rates of up to 14 Mbit/s in the downlink. HSUPA makesuplink data rates of 5.76 Mbit/s possible.




5.1.11 HSPA+ Release 7

HSPA+ Features in Release 7. Features include:• Higher Order Modulation Schemes

• QPSK - 16QAM, 64QAM

• An introduction to MIMO technology

• Packet connectivity (CPC)

• HSPA+ brings a higher data rate and lower latency. This is a necessarystep for mobile broadband development.




5.1.12 LTE UE

The idea is that Long Term Evolution (LTE) will enable much higher speedsto be achieved along with much lower packet latency.

The LTE UE categories, or UE classes, are needed to ensure that the basestation (BTS), or eNodeB, (eNB) can communicate correctly with the userequipment. By relaying the LTE UE category information to the basestation, the UE allows the base station to determine the performance of theUE and communicate with it accordingly.

Since the LTE category defines the overall performance and the capabilitiesof the UE, it is possible for the eNB to communicate using capabilities thatit knows the UE possesses. Accordingly, the eNB will not communicate

beyond the performance of the UE. There are five different LTE UE categories. As seen in the table above, thedifferent LTE UE categories have a wide range of supported parametersand performance. LTE category 1, for example does not support MIMO, butLTE UE category five supports 4x4 MIMO.

It is also worth noting that UE class 1 does not offer the performanceoffered by that of the highest performance HSPA category. It is alsonoteworthy that all LTE UE categories are capable of receivingtransmissions from up to four antenna ports.




5.1.13 Differences Between GPRS and EDGE




5.2 Key Performance Indicators (KPI)5.2.1 KPI - Service Availability

Before a user can actually connect to the destination on the internet,GPRS/EDGE services are activated after proper GPRS/EDGE ATTACH andPDP activation sequences. At this stage in KPI definition, it is inadvisable totalk of categorising networks on the time taken to perform these protocols.However, if a failure on attach or PDP activation occurs, then a user is

unable to access the internet cloud. Therefore it is recommended that onlyGPRS/EDGE ATTACH and PDP activation success be measured at this stage.




5.2.2 3G Services and QoS Classes

Different data-oriented services place different demands on a network. Therefore, it is necessary for providers to divide their services into differentcategories; both in terms of how the data is routed through the network,and how it is billed. These categories are known as Quality of Service (QoS)classes.

Data-intensive services (where capacity is important) may follows differentpaths through the network to those of low data services like voice calls(where delay is important, but not capacity).

Details of the services applicable to each subscriber are stored in the HomeLocation Register (HLR) of each network, so that the system can identifywhich subscribers may use which of the services.

In UMTS, four QoS classes have been defined:

Conversational class

This is the QoS class for delay-sensitive real time services such as speechtelephony.




Streaming Class

This is also regarded as a real-time QoS class and is also sensitive todelays. It carries traffic which appears "real time" to a human user, such asvideo or audio streaming, where files are downloaded to the receiver.

Interruptions in this type of transmission are not relevant for theapplication user, as long as there is still enough data left in the buffer of the receiving equipment for seamless provision of data.

Interactive Class

This is a non-real time QoS class, which means it can be used forapplications with limited delay sensitivity. In other words, where it does notmatter if the process stops momentarily. This class includes interactiveapplications such as web browsing. However, many applications on theinternet still have timing constraints, such as http, ftp, telnet, and smtp. Inthese cases, a response to a request is still expected within a specific

period of time. This class of service must take such factors into account.

Background Class

This is a non-real time QoS class for background applications which are notdelay sensitive. Examples of such applications are e-mail and filedownloads.




5.2.2.1 Voice over Internet Protocol (VoIP)

Voice over Internet Protocol (VoIP) applications are transported via theInternet, rather than through the Public Switched Telephone Network(PSTN). The steps involved in originating a VoIP telephone call are:

• signalling and media channel setup

• digitisation of the analogue voice signal

• encoding

• packetisation

• transmission as Internet Protocol (IP) packets over a packet-switched

network




5.2.3 Latency – GPRS/EDGE

Latency in a packet-switched network is measured either one-way (thetime from the source sending a packet to the destination receiving it), orround-trip (the one-way latency from source to destination plus the one-way latency from the destination back to the source). For end to endtesting, round trip is better suited.




5.2.4 Latency - Rel’99




5.2.5 Latency - LTE




5.2.6 LTE will improve latency as well as speed

Attention has been focused on the higher speeds that will be offered bynext generation LTE (Long-Term Evolution) mobile networks, but improvedlatency will be equally important to users. Real time applications sensitiveto delays, including VoIP (Voice over IP) video streaming, videoconferencing and gaming will perform much better with LTE.




5.2.7 Link Speed GPRS/EDGE

Link Speed is the speed at which User Equipment (UE) is connected to itsserving BTS. A good connection speed, however, does not guarantee agood connection to any web server. In fact, Link Speed providesinformation about the capability of the host cellular GPRS/EDGE network atthat time. For example: a good link speed may signify a good serviceprovider network, but it may also mean that your network happens to becarrying a low level of real-time traffic (voice and data) at the time, andcan afford to allocate the available resources to the data request.




In communication networks such as Ethernet or packet radio, networkthroughput is the average rate of successful message delivery over acommunication channel. This data may be delivered over a physical or

logical link, or it may pass through a certain network node. The throughputis usually measured in bits per second (bps), though sometimes in datapackets per second or data packets per time slot.




.

The system throughput, or aggregate throughput, is the sum of the datarates that are delivered to all terminals in a network.




5.33G Networks




Third generation networks represent an international standard for wide-area cellular networks that are rapidly replacing second generationnetworks. The main advantage of 3G networks is the use of a wider radiospectrum, which results in larger network capacity and faster datatransmission for advanced multimedia services.

Today’s mobile devices offer high-speed web access, emailing, messaging,video phone and multimedia services. People want to be able to watchstreaming movies on their cellular phones; download and play music; storedata; and share files with other cellular users. 3G networks offer faster,slicker ways to do this.

The Universal Mobile Telecommunication System (UMTS) is a 3G wirelesssystem that delivers high-bandwidth data and voice services to mobileusers. UMTS evolved from GSM. It has an air interface based on W-CDMAand an Internet Protocol core network based on general-packet radioservice (GPRS).

User Equipment (UE)

The UMTS standard does not restrict the functionality of the UserEquipment in any way. Terminals work as an air interface counterpart forthe NodeB, and have many different types of identities. Most of theseUMTS identity types are taken directly from GSM specifications.

• International Mobile Subscriber Identity (IMSI)

• Temporary Mobile Subscriber Identity (TMSI)

• Mobile station ISDN (MSISDN)

• International Mobile Station Equipment Identity (IMEI)




UMTS operates in the frequency band of 2100 MHz, which is much higherthan the 900 MHz and 1900 MHz typically used in GSM and TDMA systems.Also, the higher data rates for UMTS require better signal strength, Eb/No.

This means that the radio propagation will be different to GSM. As a result,the old base station coverage areas are not necessarily valid in UMTS.

Although reusing the old base station sites would be very cost-effective,they are not necessarily the most optimum locations for UMTS coverage.

Interference directly limits the capacity of CDMA cell sites. One of thebiggest interference problems in WCDMA networks is pilot pollution. Pilotpollution is often caused by high-elevation sites with RF coverage footprintsmuch larger than normal.

The solution is to reduce the size of the coverage footprint. This can beaccomplished by reducing the elevation of offending antennas, introducingdowntilt, or reducing the transmitted power.




5.3.1 Frequency-Division Duplexing

Frequency Division Duplexing (FDD) means that the transmitter andreceiver operate at different carrier frequencies.

FDD systems utilise channel plans that are comprised of frequencies withequal bandwidth. Since each channel has a fixed bandwidth, the channelcapacity of each frequency also is fixed and equal to that of all otherchannels in the frequency band. This makes FDD ideal for symmetricalcommunication applications in which the same or similar information flowsin both directions, such as voice communications

TDD operates by toggling transmission directions over a time interval. Thistoggling takes place very rapidly and is imperceptible to the user. Thus,

TDD can support voice and other symmetrical communication services aswell as asymmetric data services. TDD can also handle a dynamic mix of both traffic types. The relative capacity of the downstream and upstreamlinks can be altered in favour of one direction by allowing a greater timeslot allocation to downstream transmission intervals than upstream. Thisasymmetry is useful for communication processes characterized byunbalanced information flow. One obvious application for this technique isInternet access, where a user enters a short message upstream andreceives large information payloads downstream.




Frequency planning is not as important in UMTS as it is in GSM. At most,UMTS operators have two or three carriers, so there is not much to plan.However, the operators do have to make some decisions:

• Which carrier(s) is used for macro cells?

• Which carrier(s) is used for micro cells?

• Which carrier(s) is used for HSDPA?

• Are there any carriers reserved for indoor solutions?

The antennas for macrocells are mounted on ground-based masts, rooftopsand other existing structures, at a height that provides a clear view overthe surrounding buildings and terrain.

The typical range of a microcell is less than two kilometres wide. A picocellis 200 meters or less, and a femtocell is in the order of 10 metres.




5.3.2 Handover Control

For UMTS the following types of handover are specified:

• Handover 3G -3G (i.e. between UMTS and other 3G systems)

• FDD soft/softer handover

• FDD inter-frequency hard handover

• FDD/TDD handover (change of cell)

• TDD/FDD handover (change of cell)

• TDD/TDD handover

•

Handover 3G - 2G (e.g. handover to GSM)• Handover 2G - 3G (e.g. handover from GSM)




5.3.3 Hard Handover

In Hard Handover, all the old radio links in the UE are removed before thenew radio links are established. Hard handover can be seamless or non-seamless. Seamless hard handover means that the handover is notperceptible to the user. In practice, a handover that requires a change of the carrier frequency (inter-frequency handover) is always performed ashard handover.

5.3.4 Inter-RAT Hard Handover

If UE supports multiple RAT, it can hand over to a 2G service such as GSMwhen it reaches the end of the coverage area for UMTS services. Inter-RAThandover procedure can be initiated in variety of ways:

• RNS might send a Handover From UTRAN command explicitly telling theUE to move to a different RAT

• The UE might select a cell that belongs to a different RAT

• The Network may ask the UE to perform Cell Change Order from UTRAN.




5.3.5 Soft Handover

Soft handover means that the radio links are added and removed in such away that the UE always keeps at least two radio links to the UTRAN. Softhandover is performed by means of macro diversity, meaning that severalradio links are active at the same time. Soft handover can normally beused when cells operated on the same frequency are changed.




W-CDMA can support mobile/portable voice, images, data, and videocommunications at up to 2 Mbps (local area access) or 384 Kbps (wide areaaccess). The input signals are digitised and transmitted in coded, spread-spectrum mode over a broad range of frequencies. A 5 MHz-wide carrier isused.

Core Network

The Core Network is divided into circuit switched and packet switcheddomains. Some of the circuit switched elements include:

• The Mobile Services Switching Centre (MSC)

• The Visitor location register (VLR)

• The Gateway MSC

Packet switched elements include:

• The Serving GPRS Support Node (SGSN)

• The Gateway GPRS Support Node (GGSN)

Some network elements, like EIR, HLR, VLR and AUC, are shared by bothdomains.

The functions of RNC are:

• Radio Resource Control

• Admission Control

• Channel Allocation

• Power Control Settings

• Handover Control

• Macro Diversity

• Ciphering

• Segmentation / Reassembly

• Broadcast Signalling

•

Open Loop Power Control




5.3.6 Softer Handover

Softer handover is a special case of soft handover where the radio linksthat are added and removed belong to the same Node B. In other words, atthe site of co-located base stations from which several sector-cells areserved. In softer handover, macro diversity with maximum ratio combiningcan be performed in the Node B, whereas soft handover generally appliesmacro diversity with selection combining on the downlink.

5.3.7 Active Set

Active Set is defined as the set of Node-Bs to which UE is simultaneouslyconnected. These are the UTRA cells currently assigning a downlink DPCHto the UE.

5.3.8 Monitored Set.

Monitored Set Cells, are not included in the active set, but are included inthe CELL_INFO_LIST belong to the Monitored Set.




5.3.9 Cell Breathing

When a cell becomes heavily loaded, it shrinks. Subscriber traffic is thenredirected to a neighbouring cell that is more lightly loaded, in a processcalled load balancing. At times when there is less traffic, the cell willincrease to its original size. This phenomenon, known as Cell Breathing iscommon in 2G and 3G wireless systems including code-division multipleaccess (CDMA).




5.3.10 High Speed Download Packet Access

HSDPA allows mobile phone operators to offer their users much greaterbandwidth speeds and makes general improvements to the mobile webbrowsing experience. The term ‘mobile broadband’ or ’3.5G’ is often usedto denote HSDPA services and devices. HSDPA supports download speedsof up to 14.4Mbps. This compares very favourably to landline based ADSLconnections in the UK.

However, in reality, average HSDPA connections are much lower thanadvertised.




5.3.11 High Speed Uplink Packet Access

One of the downsides to HSDPA is that the maximum upload speed is ameagre 384Kbps. This can be frustrating when trying to send large emailattachments or posting video or podcasts. A new protocol, HSUPA wasintroduced in 2004 to improve upon this. It is capable of upload speeds of 5.76Mbps, resulting in real world speeds of up to 2Mbps. This is still a vastimprovement.




5.3.12 MIMO

Multiple-Input Multiple-Output (MIMO) refers to the use of multipleantennas at both the transmitter and receiver in order to improvecommunication performance. It is one of several forms of smart antennatechnology.

MIMO technology has attracted attention in wireless communicationsbecause it offers significant increases in data throughput and link rangewithout additional bandwidth or transmit power.

SU-MIMO (Single User MIMO)

• It is an example of downlink 2x2 single user MIMO with precoding

• Two data streams are mixed (precoded) to best match the channelconditions.

• The receiver reconstructs the original streams resulting in increasedsingle-user data rates and corresponding increase in cell capacity.

• 2x2 SU-MIMO is mandatory for the downlink.




5.3.14 HSPA+ Channel Quality Report

In HSDPA the channel quality report is a measure of the mobile channelwhich is sent regularly from the UE to the Node B. These measurementsare used to adapt modulation and coding for the corresponding UE and itcan be also used for the scheduling algorithms.

The CQI is calculated at the UE based on the signal-to-noise ratio of thereceived common pilot. Instead of expressing the CQI as a received signalquality, the CQI is expressed as a recommended transport-block size, alsotaking into account, the receiver performance.




5.4 Long Term Evolution (LTE)

5.4.1 Introduction

Although 3G technologies deliver significantly higher bit rates than 2Gtechnologies, there is still a great opportunity for wireless service providersto capitalize on the ever-increasing demand for wireless broadband andtake advantage of the technology innovation that improves the economicsof deploying mobile broadband networks.

With Long Term Evolution (LTE) there is a new radio platform technologythat will allow operators to achieve even higher peak throughputs thanHSPA+ in higher spectrum bandwidth.

LTE assumes a full Internet Protocol (IP) network architecture and isdesigned to support voice in the packet domain.

However, in the same way that 3G coexists with second generation (2G)systems in integrated networks, LTE systems will coexist with 3G and 2Gsystems. Multimode devices will function across LTE/3G or even LTE/3G/2G,depending on market circumstances.

LTE capabilities include:

• Downlink peak data rates up to 300 Mbps with 20 MHz bandwidth

• Uplink peak data rates up to 86 Mbps with 20 MHz bandwidth

• Operation in both TDD and FDD modes

•

Scalable bandwidth up to 20 MHz, covering 1.4, 3, 5, 10, 15, and 20 MHz• Reduced latency, up to 10 milliseconds (ms) round-trip times between

user equipment and the base station.

• Multiple Input Multiple Output (MIMO). When using MIMO, it is necessaryto use multiple antennas to enable the different paths to bedistinguished. Accordingly schemes using 2 x 2, 4 x 2, or 4 x 4 antennamatrices can be used. While it is relatively easy to add further antennasto a base station, the same is not true of mobile handsets, where thedimensions of the user equipment limit the number of antennas whichshould be place at least a half wavelength apart.




5.4.2 FDD and TDD LTE Frequency Bands

Frequency Division Duplex (FDD) spectrum requires pair bands, one for theuplink and one for the downlink. Time Division Duplex (TDD) requires asingle band as uplink and downlink are on the same frequency but timeseparated. As a result, there are different LTE band allocations for TDD andFDD. These are shown in the diagram above.

FDD LTE frequency band allocations

There is a large number of allocations of radio spectrum that has beenreserved for FDD LTE use. The FDD LTE frequency bands are paired toallow simultaneous transmission on two frequencies.

TDD LTE frequency band allocations

The TDD LTE allocations are unpaired because the uplink and downlinkshare the same frequency, being time multiplexed.




Scalable bandwidth up to 20 MHz, covering 1.4, 3, 5, 10, 15, and 20 MHz




5.4.3 LTE - Terminal Categories

Five different UE categories have been defined for LTE. These UEcategories are often referred to as UE classes. As seen in the table above,the low end UE does not support MIMO but the high end UE will support 4x4MIMO. It is also worth noting that UE class 1 would be inferior to that of thebest HSPA UE.




6 Glossary of TermsA

A3

Authentication algorithm

A5Ciphering algorithm

A8

Ciphering key computation

AGCH

Access Grant Channel

AMPS

Advanced Mobile Phone Service

AoC

Advice of Charge

ARQ

Automatic Repeat request mechanism

AuC

Authentication Centre.

B

BAIC

Barring of All Incoming Calls

BAOC

Barring Of All Outgoing Calls

K101 Telecommunications Fundamentals Page 205Glossary of Terms



BCCH

Broadcast Control Channel

BCH

Broadcast Channel

BER

Bit Error Rate

BOIC

Barring of Outgoing International Calls

BOICexHCBarring of Outgoing International Calls except those directed toward theHome PLMN Country

Bps

Bits per second

BSC

Base Station Controller. A piece of equipment that controls one or more

BTS's.

BSS

Base Station Subsystem.

BTS

Base Transceiver Station.

C

C/I

Carrier to Interference Ratio

CC

Call Control

CCCH

Common Control Channel

Page 206 K101 Telecommunications FundamentalsGlossary of Terms



CDMA

Code Division Multiple Access

CEPT

Conference of European Posts and Telecommunications

CFB

Call Forwarding on mobile subscriber Busy

CFNRc

Call Forwarding on mobile subscriber Not Reachable

CFNRyCall Forwarding on No Reply

CFU

Call Forwarding Unconditional

CGI

Cell Global Identity

CLIP

Calling Line Identification Presentation

CLIR

Calling Line Identification Restriction

CM

Communication Management

CoLP

Connected Line identification Presentation

CoLR

Connected Line identification Restriction

CUG

Closed User Group




CW

Call Waiting

D

DCCH

Dedicated Control Channel

DCS

Digital Cellular System

DTX

Discontinuous Transmission

E

EIR

Equipment Identity Register.

ETSI

European Telecommunications Standards Institute

F

FACCH

Fast Associated Control Channel

FCCH

Frequency Correction Channel

FDMA

Frequency Division Multiple Access

FEC

Forward Error Correction code

FER

Frame Erasure Rate

G

GIWU

GSM Interworking Unit




GMSC

Gateway Mobile services Switching Centre

GMSK

Gaussian Minimum Shift Keying

GP

Guard Period

GSM

Global System for Mobile communications

H

HLR

Home Location Register.

I

IMEI

International Mobile Equipment Identity

IMSI

International Mobile Subscriber Identity

ISDN

Integrated Services Digital Network

J

JDC

Japanese Digital Cellular

L

LA

Location Area

LAI

Location Area Identity

LOS

Line Of Sight




M

MM

Mobility Management

MoU

Memorandum of Understanding

MS

Mobile Station (mobile phone).

MSC

Mobile Switching Centre. In a cellular network, this is a switch or exchangethat interworks with location databases.

MSISDN

Mobile Station ISDN number

MSRN

Mobile Station Roaming Number

N

NADC

North American Digital Cellular

NMT

Nordic Mobile Telephone

NSS

Network and Switching Subsystem

O

OAM

Operation, Administration and Maintenance

OMC

Operations and Maintenance Centre.

OSS

Operation and Support Subsystem




P

PAD

Packet Assembler Disassembler

PCH

Paging Channel

PCS

Personal Communication Services

PDC

Personal Digital Cellular

PIN

Personal Identification Number

PLMN

Public Land Mobile Network

PSPDN

Packet Switched Public Data Network

PSTN

Public Switched Telephone Network. This is the traditional public telephonesystem, comprised of telephones, local and interexchange trunks, transportequipment and exchanges.

R

RACH

Random Access Channel

RF

Radio Frequency

RPELTP

Regular Pulse Excitation Long-Term Prediction

RR

Radio Resources management




S

S

Stealing flags

SACCH

Slow Associated Control Channel

SCH

Synchronisation Channel

SDCCH

Standalone Dedicated Control Channel

SIM

Subscriber Identity Module

SMS

Short Message Service

SMSCB

Short Message Services Cell Broadcast

SMSMT/PP

Short Message Services Mobile Terminating/Point to Point

SMSO/PP

Short Message Services Mobile Originating/Point to Point

SNR

Signal to Noise Ratio

SRES

Signed Result

SS

Supplementary Services

T




T

Tail bits

TACS

Total Access Communication System

TCH

Traffic Channel

TCH/F

Traffic Channel/Full rate

TCH/H

K101 Telecommunications Fundamentals - Formatted

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