Bab II Contents

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BAB II

CONTENTSA.Cognitive Radio

Cognitive radio (CR) is a newly emerging technology, which has been

recently proposed to implement some kind of intelligence to allow a radio

terminal to automatically sense, recognize, and make wise use of any

available radio frequency spectrum at a given time. The use of the available

frequency spectrum is purely on an opportunity driven basis. In other words,

it can utilize any idle spectrum sector for the exchange of information and

stop using it the instant the primary user of the spectrum sector needs to use

it. Thus, cognitive radio is also sometimes called smart radio, frequency agile

radio, police radio, or adaptive software radio,1 and so on. For the same

reason, the cognitive radio techniques can, in many cases, exempt licensed

use of the spectrum that is otherwise not in use or is lightly used; this is done

without infringing upon the rights of licensed users or causing harmful

interference to licensed operations.


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The only difference with SDR (Software Defined Radio) is that a

cognitive radio needs to scan a wide range of frequency spectra before

deciding which band to use, instead of a predefined one, as an SDR terminal

does. One of the most important characteristic features of an SDR terminal is

that its signal is processed almost completely in the digital domain, needing

very little analogue circuit. This brings a tremendous benefit to make the

terminal very flexible (for a multimode terminal) and ultrasmall size with the

help of state-of-the-art microelectronics technology.

a. Main focution of Cognetive Radio Spectrum Sensing: detecting the unused spectrum and sharing it without

harmful interference with other users, it is an important requirement of the

Cognitive Radio network to sense spectrum holes, detecting primary

users is the most efficient way to detect spectrum holes. Spectrum

sensing techniques can be classified into three categories:


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o Transmitter detection: cognitive radios must have the capability todetermine if a signal from a primary transmitter is locally present in

a certain spectrum, there are several approaches proposed:

matched filter detection energy detection cyclostationary feature detection

o Cooperative detection: refers to spectrum sensing methods whereinformation from multiple Cognitive radio users are incorporated

for primary user detection.

o Interference based detection.

Spectrum Management: Capturing the best available spectrum tomeet user communication requirements. Cognitive radios should

decide on the best spectrum band to meet the Quality of service

requirements over all available spectrum bands, therefore spectrum

management functions are required for Cognitive radios, these

management functions can be classified as:

o spectrum analysiso spectrum decision

Spectrum Mobility: is defined as the process when a cognitive radio userexchanges its frequency of operation. Cognitive radio networks target to

use the spectrum in a dynamic manner by allowing the radio terminals to

operate in the best available frequency band, maintaining seamless

communication requirements during the transition to better spectrum

Spectrum Sharing: providing the fair spectrum scheduling method, one ofthe major challenges in open spectrum usage is the spectrum sharing. It

can be regarded to be similar to generic media access control MAC

problems in existing systems


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B.Access schemeAs the wireless standards evolved, the access techniques used

also exhibited increase in efficiency, capacity and scalability. The first

generation wireless standards used plain TDMA and FDMA. In the

wireless channels, TDMA proved to be less efficient in handling the

high data rate channels as it requires large guard periods to alleviate

the multipath impact. Similarly, FDMA consumed more bandwidth for

guard to avoid inter carrier interference. So in second generation

systems, one set of standard used the combination of FDMA and

TDMA and the other set introduced an access scheme called CDMA.

Usage of CDMA increased the system capacity, but as a drawback

placed a soft limit on it rather than the hard limit (i.e. a CDMA network

will not reject new clients when it approaches its limits, resulting in a

denial of service to all clients when the network overloads). Data rate is

also increased as this access scheme (providing the network is not

reaching its capacity) is efficient enough to handle the multipath

channel. This enabled the third generation systems, such as IS-2000,

UMTS, HSXPA, 1xEV-DO, TD-CDMA and TD-SCDMA, to use CDMA

as the access scheme. However, the issue with CDMA is that it suffers

from poor spectral flexibility and computationally intensive time-domain

equalization (high number of multiplications per second) for wideband

channels.

Recently, new access schemes like Orthogonal FDMA

(OFDMA), Single Carrier FDMA (SC-FDMA), Interleaved FDMA and

Multi-carrier CDMA (MC-CDMA) are gaining more importance for the

next generation systems. These are based on efficient FFT algorithm

and frequency domain equalization, resulting lower number of

multiplications per second. They also make it possible to control the


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bandwidth and form the spectrum in a flexible way. However, they

require advanced dynamic channel allocation and traffic adaptive

scheduling.

WiMax is using OFDMA in the downlink and in the uplink. For

the next generation UMTS, OFDMA is used for the downlink. By

contrast, IFDMA is being considered for the uplink since OFDMA

contributes more to the PAPR related issues and results in nonlinear

operation of amplifiers. IFDMA provides less power fluctuation and

thus avoids amplifier issues. Similarly, MC-CDMA is in the proposal for

the IEEE 802.20 standard. These access schemes offer the same

efficiencies as older technologies like CDMA. Apart from this,

scalability and higher data rates can be achieved.

The other important advantage of the above mentioned access

techniques is that they require less complexity for equalization at the

receiver. This is an added advantage especially in the MIMO

environments since the spatial multiplexing transmission of MIMO

systems inherently requires high complexity equalization at the

receiver.

In addition to improvements in these multiplexing systems,

improved modulation techniques are being used. Whereas earlier

standards largely used Phase-shift keying, more efficient systems such

as 64QAM are being proposed for use with the 3GPP Long Term

Evolution standards.

a)OFDMOrthogonal Frequency-Division Multiple Access (OFDMA) is a multi-

user version of the popular Orthogonal frequency-division multiplexing


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(OFDM) digital modulation scheme. Multiple access is achieved in OFDMA

by assigning subsets of subcarriers to individual users as shown in the

illustration below. This allows simultaneous low data rate transmission from

several users.

a. The advantages and disadvantagesThe advantages and disadvantages summarized below are

further discussed in the Characteristics and principles of operation

section.

1. Claimed advantages over CDMA OFDM can combat multipath interference with more robustness

and less complexity.

OFDMA can achieve a higher MIMO spectral efficiency due toproviding flatter frequency channels than a CDMA RAKE receiver

can.

No Cell size breathing as more users connect


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2. Claimed advantages over OFDM with time-domainstatistical multiplexing

Allows simultaneous low-data-rate transmission from severalusers.

Pulsed carrier can be avoided. Lower maximum transmission power for low data rate users. Shorter delay, and constant delay. Contention-based multiple access (collision avoidance) is

simplified.

Further improves OFDM robustness to fading and interference.

3. Claimed OFDMA Advantages Flexibility of deployment across various frequency bands with little

needed modification to the air interface.

Averaging interferences from neighboring cells, by using differentbasic carrier permutations between users in different cells.

Interferences within the cell are averaged by using allocation withcyclic permutations.

Enables orthogonality in the uplink by synchronizing users in timeand frequency.[1]

Enables Single Frequency Network coverage, where coverageproblem exists and gives excellent coverage.

Enables adaptive carrier allocation in multiplication of 23 carriers =nX23 carriers up to 1587 carriers (all data carriers).

Offers Frequency diversity by spreading the carriers all over theused spectrum.

Offers Time diversity by optional interleaving of carrier groups intime.

Using the cell capacity to the utmost by adaptively using thehighest modulation a user can use, this is allowed by the gain


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added when less carriers are allocated (up to 18dB gain for 23

carrier allocation instead of 1587 carriers), therefore gaining in

overall cell capacity.

4. Recognized disadvantages of OFDMA Higher sensitivity to frequency offsets and phase noise. Asynchronous data communication services such as web access

are characterized by short communication bursts at high data rate.

Few users in a base station cell are transferring data

simultaneously at low constant data rate.

The complex OFDM electronics, including the FFT algorithm andforward error correction, is constantly active independent of the

data rate, which is inefficient from power consumption point of

view, while OFDM combined with data packet scheduling may

allow that the FFT algorithm hibernates during certain time

intervals.

The OFDM diversity gain, and resistance to frequency-selectivefading, may partly be lost if very few sub-carriers are assigned to

each user, and if the same carrier is used in every OFDM symbol. Adaptive sub-carrier assignment based on fast feedback

information about the channel, or sub-carrier frequency hopping,

is therefore desirable.

Dealing with co-channel interference from nearby cells is morecomplex in OFDM than in CDMA. It would require dynamic

channel allocation with advanced coordination among adjacent

base stations.

The fast channel feedback information and adaptive sub-carrierassignment is more complex than CDMA fast power control.


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b. Characteristics and principles of operationBased on feedback information about the channel conditions,

adaptive user-to-subcarrier assignment can be achieved. If the

assignment is done sufficiently fast, this further improves the OFDM

robustness to fast fading and narrow-band cochannel interference, and

makes it possible to achieve even better system spectral efficiency.

Different number of sub-carriers can be assigned to different

users, in view to support differentiated Quality of Service (QoS), i.e. to

control the data rate and error probability individually for each user.

OFDMA resembles code division multiple access (CDMA)

spread spectrum, where users can achieve different data rates by

assigning a different code spreading factor or a different number of

spreading codes to each user.

OFDMA can be seen as an alternative to combining OFDM with

time division multiple access (TDMA) or time-domain statistical

multiplexing, i.e. packet mode communication. Low-data-rate users

can send continuously with low transmission power instead of using a

"pulsed" high-power carrier. Constant delay, and shorter delay, can be

achieved.

OFDMA can also be described as a combination of frequency

domain and time domain multiple access, where the resources are

partitioned in the time-frequency space, and slots are assigned alongthe OFDM symbol index as well as OFDM sub-carrier index.

OFDMA is considered as highly suitable for broadband wireless

networks, due to advantages including scalability and MIMO-


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friendliness, and ability to take advantage of channel frequency

selectivity.[1]

In spectrum sensing cognitive radio, OFDMA is a possible

approach to filling free radio frequency bands adaptively. Timo A.

Weiss and Friedrich K. Jondral of the University of Karlsruhe proposed

a spectrum Pooling system in which free bands sensed by nodes were

immediately filled by OFDMA subbands.

c. UsageOFDMA is used in:

the mobility mode of the IEEE 802.16 Wireless MAN standard,commonly referred to as WiMAX,

the IEEE 802.20 mobile Wireless MAN standard, commonlyreferred to as MBWA,

the downlink of the 3GPP Long Term Evolution (LTE) fourthgeneration mobile broadband standard. The radio interface was

formerly named High Speed OFDM Packet Access (HSOPA), nownamed Evolved UMTS Terrestrial Radio Access (E-UTRA).

the Qualcomm Flarion Technologies Mobile Flash-OFDM the now defunct Qualcomm/3GPP2 Ultra Mobile Broadband (UMB)

project, intended as a successor of CDMA2000, but replaced by

LTE.

OFDMA is also a candidate access method for the IEEE

802.22 Wireless Regional Area Networks (WRAN). The projectaims at designing the first cognitive radio based standard

operating in the VHF-low UHF spectrum (TV spectrum).


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The term "OFDMA" is claimed to be a registered

trademark by Runcom Technologies Ltd, with various other

claimants to the underlying technologies through patents.

b)FDD and TDD

TDD and FDD Mode of Operation

Basically most of the UMTS networks in operation are Frequency

Division Duplex (FDD) based. There is also another variant called the Time

Division Duplex or TDD. In reality there is more than one variant of TDD, so

the normal 5MHz bandwidth TDD is called Wideband TDD of WTDD. There

is also another name for WTDD to confuse people, called the High Chip Rate

TDD (HCR-TDD). There is another variant of TDD as would have guessed

known as the Narrowband TDD (NTDD). NTDD is also known as Low Chip

Rate TDD (LCR-TDD) and most popularly its known as TD-SCDMA or Time

Division Synchronous CDMA.

"Synchronous" implies that uplink signals are synchronized at the base


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station receiver, achieved by continuous timing adjustments. This reduces

the interference between users of the same timeslot using different codes by

improving the orthogonality between the codes, therefore increasing system

capacity, at the cost of some hardware complexity in achieving uplink

synchronization.

The normal bandwidth of FDD or TDD mode of operation is 5 MHz. This

gives a chip rate of 3.84 Mcps (Mega chips per second). The corresponding

figure for TD-SCDMA is 1.66 Mhz and 1.28 Mcps.

Assymetric operation in TDD mode

a. The advantage of TDD over FDD are: Does not require paired spectrum because FDD uses different

frequencies for UL and DL whereas TDD uses the same frequency

hence its more easy to deploy

Channel charachteristics is the same in both directions due tosame band

You can dynamically change the UL and the DL bandwidthallocation depending on the traffic.


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b. The dis-advantage of TDD over FDD are: Switching between transmission directions requires time, and the

switching transients must be controlled. To avoid corrupted

transmission, the uplink and downlink transmissions require a

common means of agreeing on transmission direction and allowed

time to transmit. Corruption of transmission is avoided by allocating

a guard period which allows uncorrupted propagation to counter

the propagation delay. Discontinuous transmission may also cause

audible interference to audio equipment that does not comply with

electromagnetic susceptibility requirements.

Base stations need to be synchronised with respect to the uplinkand downlink transmission times. If neighbouring base stations use

different uplink and downlink assignments and share the same

channel, then interference may occur between cells. This can

increase the complexity of the system and the cost.

Also it does not support soft/softer handovers

Timing Synchronisation between different terminals


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C.Advance antena system

The performance of radio communications depends on an antennasystem. Recently, multiple antenna technologies are emerging to achieve

the goal of 4G systems such as high rate, high reliability, and long range

communications. In the early 90s, to cater the growing data rate needs of

data communication, many transmission schemes were proposed. One

technology, spatial multiplexing, gained importance for its bandwidth

conservation and power efficiency. Spatial multiplexing involves deploying

multiple antennas at the transmitter and at the receiver. Independent

streams can then be transmitted simultaneously from all the antennas.

This increases the data rate into multiple folds with the number equal to

minimum of the number of transmit and receive antennas. This is called

MIMO (as a branch of intelligent antenna). Apart from this, the reliability in

transmitting high speed data in the fading channel can be improved by

using more antennas at the transmitter or at the receiver. This is called

transmit or receive diversity. Both transmit/receive diversity and transmit

spatial multiplexing are categorized into the space-time coding

techniques, which does not necessarily require the channel knowledge at

the transmit. The other category is closed-loop multiple antenna

technologies which use the channel knowledge at the transmitter.

a)MIMOIn radio, multiple-input and multiple-output, or MIMO (commonly

pronounced my-moh or me-moh), is the use of multiple antennas at both the


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spatial multiplexing. In 2005, Airgo Networks had developed a pre-

11n version based on their patents on MIMO. Following that in

2006, several companies (including at least Broadcom, Intel, and

Marvell) have fielded a MIMO-OFDM solution based on a pre-

standard for IEEE 802.11n WiFi standard. Also in 2006, several

companies (Beceem Communications, Samsung, Runcom

Technologies, etc.) have developed MIMO-OFDMA based solutions

for IEEE 802.16e WIMAX broadband mobile standard. All

upcoming 4G systems will also employ MIMO technology. Several

research groups have demonstrated over 1 Gbit/s prototypes.

b. Functions of MIMOMIMO can be sub-divided into three main categories,

precoding, spatial multiplexing or SM, and diversity coding.

Precoding is multi-layer beamforming in a narrowsense or all spatial processing at the transmitter in a

wide-sense. In (single-layer) beamforming, the samesignal is emitted from each of the transmit antennas

with appropriate phase (and sometimes gain)

weighting such that the signal power is maximized at

the receiver input. The benefits of beamforming are to

increase the signal gain from constructive combining

and to reduce the multipath fading effect. In the

absence of scattering, beamforming results in a well

defined directional pattern, but in typical cellular

conventional beams are not a good analogy. When

the receiver has multiple antennas, the transmit

beamforming cannot simultaneously maximize the


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signal level at all of the receive antennas, and

precoding is used. Note that precoding requires

knowledge of the channel state information (CSI) at

the transmitter.

Spatial multiplexing requires MIMO antennaconfiguration. In spatial multiplexing, a high rate

signal is split into multiple lower rate streams and

each stream is transmitted from a different transmit

antenna in the same frequency channel. If these

signals arrive at the receiver antenna array with

sufficiently different spatial signatures, the receiver

can separate these streams, creating parallel

channels free. Spatial multiplexing is a very powerful

technique for increasing channel capacity at higher

Signal to Noise Ratio (SNR). The maximum numberof spatial streams is limited by the lesser in the

number of antennas at the transmitter or receiver.

Spatial multiplexing can be used with or without

transmit channel knowledge.

Diversity Coding techniques are used when there isno channel knowledge at the transmitter. In diversity

methods a single stream (unlike multiple streams in

spatial multiplexing) is transmitted, but the signal is

coded using techniques called space-time coding.

The signal is emitted from each of the transmit

antennas using certain principles of full or near

orthogonal coding. Diversity exploits the independent

fading in the multiple antenna links to enhance signal

diversity. Because there is no channel knowledge,


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o Single-input and multiple-output (SIMO) is adegenerate case when the transmitter has a single

antenna.

o single-input single-output (SISO) is a radio systemwhere neither the transmitter nor receiver have

multiple antenna.

Principal single-user MIMO techniqueso Bell Laboratories Layered Space-Time (BLAST),

Gerard. J. Foschini (1996)

o Per Antenna Rate Control (PARC), Varanasi,Guess (1998), Chung, Huang, Lozano (2001)

o Selective Per Antenna Rate Control (SPARC),Ericsson (2004)

Some limitationso The physical antenna spacing are selected to be

large-multiple wavelengths at the base station. The

antenna separation at the receiver is heavily space

constrained in hand sets, though advanced

antenna design and algorithm techniques are under

discussion. Refer to: Advanced MIMO

d. Multi-user typesRecently, the research on multi-user MIMO technology has

been emerging. While full multi-user MIMO (or network MIMO) can

have higher potentials, from its practicality the research on (partial)

multi-user MIMO (or multi-user and multi-antenna MIMO)

technology is more active.

Multi-user MIMO (MU-MIMO)


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o In recent 3GPP and WiMAX standards, MU-MIMO is beingtreated as one of candidate technologies adoptable in the

specification by a lot of companies including Samsung, Intel,

Qualcomm, Ericsson, TI, Huawei, Philips, Alcatel-Lucent,

Freescale, et al. since MU-MIMO is more feasible to low

complexity mobiles with small number of reception antennas

than SU-MIMO with the high system throughput capability.

o PU2RC allows the network to allocate each antenna to thedifferent users instead of allocating only single user as in

single-user MIMO scheduling. The network can transmit user

data through a codebook-based spatial beam or a virtual

antenna. Efficient user scheduling, such as pairing spatially

distinguishable users with codebook based spatial beams, are

additionally discussed for the simplification of wireless

networks in terms of additional wireless resource requirements

and complex protocol modification. Recently, PU2RC has been

adopted to use in 3GPP LTE standard and furthermore,

PU2RC is included the system description documentation

(SDD) of IEEE 802.16m (WiMAX evolution to meet the ITU-R's

IMT-Advance requirements).

o Enhanced multiuser MIMO: 1) Employ advanced decodingtechniques, 2) Employ advanced precoding techniques

o SDMA represents either space-division multiple access orsuper-division multiple access where super emphasises that

orthogonal division such as frequency and time division is not

used but non-orthogonal approaches such as super-position

coding are used.

Cooperative MIMO (CO-MIMO)o Utilizes distributed antennas which belong to other users.

MIMO Routing


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o Routing a cluster by a cluster in each hop, where thenumber of nodes in each cluster is larger or equal to one.

MIMO routing is different from conventional (SISO) routing

since conventional routing protocols route a node by a

node in each hope.

e. Applications of MIMOSpatial multiplexing techniques makes the receivers very

complex, and therefore it is typically combined with Orthogonal

frequency-division multiplexing (OFDM) or with Orthogonal

Frequency Division Multiple Access (OFDMA) modulation, where

the problems created by multi-path channel are handled efficiently.

The IEEE 802.16e standard incorporates MIMO-OFDMA. The IEEE

802.11n standard, scheduled to be finalized in late 2009,

recommends MIMO-OFDM.

MIMO is also planned to be used in Mobile radio telephone

standards such as recent 3GPP and 3GPP2 standards. In 3GPP,

High-Speed Packet Access plus (HSPA+) and Long Term Evolution

(LTE) standards take MIMO into account. Moreover, to fully support

cellular environments MIMO research consortia including IST-

MASCOT propose to develop advanced MIMO techniques, i.e.,

multi-user MIMO (MU-MIMO).


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where we have used that and

. The functions of svd() and waterfilling()

represent singular value decomposition and power allocation by

the water filling rule, respectively.

The achievable capacity of open loop MIMO systems is

Since the use of any unitary matrix information shaping ofat the transmitter can achieve the capacity of an open-loop

MIMO system, which is mostly times larger than that

of a SISO system.

D.All-IP Network

Unlike 3G, which is based on two parallel infrastructures consisting

of circuit switched and packet switched network nodes respectively, 4G

will be based on packet switching only. This will require low-latency data

transmission.By the time that 4G is deployed, the process of IPv4 address

exhaustion is expected to be in its final stages. Therefore, in the context of

4G,IPv6 support is essential in order to support a large number of

wireless-enabled devices. By increasing the number of IP addresses, IPv6

removes the need for Network Address Translation (NAT), a method of

sharing a limited number of addresses among a larger group of devices,


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although NAT will still be required to communicate with devices that are on

existing IPv4 networks.

As of June 2009, Verizon has posted specifications that require any

4G devices on its network to support IPv6.

a) IPv6Internet Protocol version 6 (IPv6) is the next-generation Internet

Protocol version designated as the successor to IPv4, the first

implementation used in the Internet that is still in dominant use currently. It

is an Internet Layer protocol for packet-switched internetworks. The main

driving force for the redesign of Internet Protocol is the foreseeable IPv4

address exhaustion. IPv6 was defined in December 1998 by the Internet

Engineering Task Force (IETF) with the publication of an Internet

standard specification, RFC 2460ork address translation (NAT), which

gained widespread deployment as an effort to alleviate IPv4 address

exhaustion.

IPv6 also implements new features that simplify aspects of address

assignment (stateless address autoconfiguration) and network

renumbering (prefix and router announcements) when changing Internet

connectivity providers. The IPv6 subnet size has been standardized by

fixing the size of the host identifier portion of an address to 64 bits to

facilitate an automatic mechanism for forming the host identifier from Link

Layer media addressing information (MAC address).

Network security is integrated into the design of the IPv6

architecture. Internet Protocol Security (IPsec) was originally developedfor IPv6, but found widespread optional deployment first in IPv4 (into

which it was back-engineered). The IPv6 specifications

mandate IPsec implementation as a fundamental interoperability

requirement.


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In December 2008, despite marking its 10th anniversary as a

Standards Track protocol, IPv6 was only in its infancy in terms of general

worldwide deployment. A 2008 study by Google Inc. indicated that

penetration was still less than one percent of Internet-enabled hosts in any

country. IPv6 has been implemented on all major operating systems in

use in commercial, business, and home consumer environments.


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BAB 4Conclution

4G refers to the fourth generation of cellular wireless standards. It is asuccessor to 3G and 2G standards, with the aim to provide a wide range of

data rates up to ultra-broadband (gigabit-speed) Internet access to mobile as

well as stationary users. Although 4G is a broad term that has had several

different and more vague definitions, this article uses 4G to refer to IMTAdvanced (International Mobile Telecommunications Advanced), as definedby ITU-R.

A 4G cellular system must have target peak data rates of up to approximately

100 Mbit/s for high mobility such as mobile access and up to approximately 1

Gbit/s for low mobility such as nomadic/local wireless access, according to

the ITU requirements. Scalable bandwidths up to at least 40 MHz should be

provided. A 4G system is expected to provide a comprehensive and secure

all-IP based solution where facilities such as IP telephony, ultra-broadband

Internet access, gaming services and HDTV streamed multimedia may be

provided to users

The pre-4G technology 3GPP Long Term Evolution (LTE) is often branded

"4G", but the first LTE release does not fully comply with the IMT-Advanced

requirements. LTE has a theoretical net bitrate capacity of up to 100 Mbit/s in

the downlink and 50 Mbit/s in the uplink if a 20 MHz channel is used - and

more if Multiple-input multiple-output (MIMO), i.e. antenna arrays, are used.

Most major mobile carriers in the United States and several worldwide

carriers have announced plans to convert their networks to LTE beginning in

2009. The world's first publicly available LTE-service was opened in the two

Scandinavian capitals Stockholm and Oslo on the 14 December 2009, and

branded 4G. The physical radio interface was at an early stage named High


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Speed OFDM Packet Access(HSOPA), now named Evolved UMTS

Terrestrial Radio Access (E-UTRA).

LTE Advanced (Long-term-evolution Advanced) is a candidate for IMT-

Advanced standard, formally submitted by the 3GPP organization to ITU-T in

the fall 2009, and expected to be released in 2011. The target of 3GPP LTE

Advanced is to reach and surpass the ITU requirements. LTE Advanced

should be compatible with first release LTE equipment, and should share

frequency bands with first release LTE

The Mobile WiMAX (IEEE 802.16e-2005) mobile wireless broadband access

(MWBA) standard is sometimes branded 4G, and offers peak data rates of

128 Mbit/s downlink and 56 Mbit/s uplink over 20 MHz wide channels.

The IEEE 802.16m evolution of 802.16e is under development, with the

objective to fulfill the IMT-Advanced criteria of 1000 Mbit/s for stationary

reception and 100 Mbit/s for mobile reception

UMB (Ultra Mobile Broadband) was the brand name for a discontinued 4G

project within the 3GPP2 standardization group to improve

theCDMA2000 mobile phone standard for next generation applications and

requirements. In November 2008, Qualcomm, UMB's lead sponsor,

announced it was ending development of the technology, favouring LTE

instead.[5] The objective was to achieve data speeds over 275 Mbit/s

downstream and over 75 Mbit/s upstream.

In all these suggestions for 4G, the CDMA spread spectrum radio technology

used in 3G systems and IS-95 is abandoned and replaced byfrequency-

domain equalization schemes, for example multi-carrier transmission such

as OFDMA. This is combined with MIMO (i.e. multiple antennas(Multiple In

Multiple Out)), dynamic channel allocation and channel-dependent

scheduling.


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COMPONENTS OF 4GAccess scheme

As the wireless standards evolved, the access techniques used also

exhibited increase in efficiency, capacity and scalability. The first generation

wireless standards used plain TDMA and FDMA. In the wireless channels,

TDMA proved to be less efficient in handling the high data rate channels as it

requires large guard periods to alleviate the multipath impact. Similarly,

FDMA consumed more bandwidth for guard to avoid inter carrier interference.

So in second generation systems, one set of standard used the combination

of FDMA and TDMA and the other set introduced an access schemecalled CDMA. Usage of CDMA increased the system capacity, but as a

drawback placed a soft limit on it rather than the hard limit (i.e. a CDMA

network will not reject new clients when it approaches its limits, resulting in a

denial of service to all clients when the network overloads). Data rate is also

increased as this access scheme (providing the network is not reaching its

capacity) is efficient enough to handle the multipath channel. This enabled

the third generation systems, such as IS-2000, UMTS, HSXPA, 1xEV-

DO, TD-CDMA andTD-SCDMA, to use CDMA as the access scheme.

However, the issue with CDMA is that it suffers from poor spectral flexibility

and computationally intensive time-domain equalization (high number of

multiplications per second) for wideband channels.

Recently, new access schemes like Orthogonal

FDMA (OFDMA), Single Carrier FDMA (SC-FDMA), Interleaved

FDMA and Multi-carrier CDMA(MC-CDMA) are gaining more importance for

the next generation systems. These are based on efficient FFT algorithm and

frequency domain equalization, resulting lower number of multiplications per

second. They also make it possible to control the bandwidth and form the


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spectrum in a flexible way. However, they require advanced dynamic channel

allocation and traffic adaptive scheduling.

WiMax is using OFDMA in the downlink and in the uplink. For the next

generation UMTS, OFDMA is used for the downlink. By contrast, IFDMA is

being considered for the uplink since OFDMA contributes more to

the PAPR related issues and results in nonlinear operation of amplifiers.

IFDMA provides less power fluctuation and thus avoids amplifier issues.

Similarly, MC-CDMA is in the proposal for the IEEE 802.20standard. These

access schemes offer the same efficiencies as older technologies like CDMA.

Apart from this, scalability and higher data rates can be achieved.

The other important advantage of the above mentioned access

techniques is that they require less complexity for equalization at the receiver.

This is an added advantage especially in the MIMO environments since

the spatial multiplexing transmission of MIMO systems inherently requires

high complexity equalization at the receiver.

In addition to improvements in these multiplexing systems,

improved modulation techniques are being used. Whereas earlier standards

largely used Phase-shift keying, more efficient systems such as 64QAM are

being proposed for use with the 3GPP Long Term Evolution standards.

IPv6 supportUnlike 3G, which is based on two parallel infrastructures consisting

of circuit switched and packet switched network nodes respectively, 4G will

be based on packet switching only. This will require low-latency data

transmission.

By the time that 4G is deployed, the process of IPv4 address

exhaustion is expected to be in its final stages. Therefore, in the context of

4G,IPv6 support is essential in order to support a large number of wireless-

enabled devices. By increasing the number of IP addresses, IPv6 removes


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the need for Network Address Translation (NAT), a method of sharing a

limited number of addresses among a larger group of devices, although NAT

will still be required to communicate with devices that are on

existing IPv4 networks.

As of June 2009, Verizon has posted specifications that require any

4G devices on its network to support IPv6. [11]

Advanced Antenna Systems

The performance of radio communications depends on an antenna

system, refer to smart or intelligent antenna. Recently, multiple antenna

technologies are emerging to achieve the goal of 4G systems such as high

rate, high reliability, and long range communications. In the early 90s, to cater

the growing data rate needs of data communication, many transmission

schemes were proposed. One technology, spatial multiplexing, gained

importance for its bandwidth conservation and power efficiency. Spatial

multiplexing involves deploying multiple antennas at the transmitter and at thereceiver. Independent streams can then be transmitted simultaneously from

all the antennas. This increases the data rate into multiple folds with the

number equal to minimum of the number of transmit and receive antennas.

This is called MIMO (as a branch ofintelligent antenna). Apart from this, the

reliability in transmitting high speed data in the fading channel can be

improved by using more antennas at the transmitter or at the receiver. This is

called transmitorreceive diversity. Both transmit/receive diversity and

transmit spatial multiplexing are categorized into the space-time coding

techniques, which does not necessarily require the channel knowledge at the

transmit. The other category is closed-loop multiple antenna technologies

which use the channel knowledge at the transmitter..


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Software-Defined Radio (SDR)SDR is one form of open wireless architecture (OWA). Since 4G is acollection of wireless standards, the final form of a 4G device will constitute

various standards. This can be efficiently realized using SDR technology,

which is categorized to the area of the radio convergence.

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