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Broadband Wireless

Technologies, Standards and Service

Riaz EsmailzadehCarnegie Mellon [email protected]

27 July 2007 © Riaz Esmailzadeh 2

Overview

Broadband Wireless Technologies

Transmission Rates Technology DifferencesThroughput Calculations

Standards 3G to 4G

CDMA – BasedOFDMA – Based Enhancing Technologies

Services

Revenue FlowValue ChainExpected Growth





3G to 4G Standards


Services



Edholm’s Law

Ex-CTO of Nortel, projected several years ago that with the presentrate of growth in both fixed and wireless transmission rates, in a few years the transmission rates will be comparable.It would make more sense to roll-out a wireless network that a fixed network…

Source: IEEE Spectrum July 2004


Downlink Transmission Rate: 5 Giga-bit/sec

Japanese operator DoCoMo announced field test results in FebruarySystem parameters:

Multiplexing method: Variable Spreading Factor – Orthogonal Frequency Division Multiple Access (VSF-OFDMA) Bandwidth: 100 MHzModulation: (256 QAM)12 x 12 MIMO antennasSingle cell


There Are Challenges…

Propagation lossFrom Hata-Okumura model

Path loss increases as a power of 2.6 or (f1/f2)2.6

For f1=2 GHz and f2=5 GHz, the signal loss is almost 10 times higher at 5 GHz than 2 GHz

Required transmit power is a factor of transmission rateA 100 Kbps transmission requires 100 times more power than a 1 kbps

For a 4G vs. 3G system comparison:10 times signal loss10 times higher required transmission power due to higher bit rates100 times more required peak transmission power

Available bandwidthA chunk of 100 MHz neededGo to the 5 GHz band?

Extra path loss of 10 dB compared with the 2 GHz band

However, we have come a long way. 10-3

0 4 8 12 16 20 24

Eb/N0

BER

Fading channel

Static channel

10-2

10-1


Key Requirements for 4G

High data rate, low latency, packet-optimized radio access100 Mbps peak DL rate in 20 MHz allocation50 Mbps peak UL rate in 20 MHz allocation

Spectrum flexibilityScalable bandwidths [1.25, 2.5, 5, 10, 15, 20MHz]Support for paired and unpaired spectrum assignments

Support for high speed mobility (up to 350 km/h)

Flat backbone architecture (all IP)


Which Technologies

Two paths have emerged:Evolution of CDMA – based system (3GPP)Evolution of OFDMA – based systems (IEEE)

What is the difference?Philosophical really!

How is the wireless channel equalised(And how multi-user interference is dealt with).

How to operate in very wide-band channels


Pos

itio

n (c

m)

Frequency (MHz)

-20

-10

0

10

Ch

an

nel g

ain

(d

B)

20102000 20050

50

40

30

20

10

Fading in Two Domains

Wireless communications system performance is degraded due to signal fading in two domains: frequency and time.Wireless transmission technologies are designed to compensate for these conditions Or Equalize the channel

*Source: Adachi, et al.


Shannon Theorem

In mobile communications, which re-use frequency resources, the amount of interference from other users must be taken into account

Shannon Theorem on capacity can be approximated to include the effect of interference, I

Throughput here is calculated as a function of SINR, or SIR

The efficiency of each technologycan be evaluatedbased on this theorem

0

1

2

3

4

5

6

7

8

9

-10 -5 0 5 10 15 20 25S/(N+I) (dB)

No

rmalise

dC

ap

aci

ty (

bp

s/H

z)

Shannonlimit

⎟⎠⎞

⎜⎝⎛

++≈

IN

SBC 1log2


How to Equalise

For Time and Frequency domains fading:CDMA systems equalise through

Diversity combining (rake, multiple antennas)Power control

OFDM systems equalise throughNarrow-band sub-carrier with flat fadingPower control

The other equalisation problemMulti-user interference


Sources of Interference

In the uplink:All active mobile in the system transmit signals that are interference to the desired user signal

In the downlinkAll signals from other active base stations, and signals intended for other users within the same cell area are interference


WCDMA (and HSDA)

The two systems differ in the way they treat interferenceCDMA systems use frequency re-use factor of oneThe sources of interference come from both within and without the cell

How these interference are minimised contributes to the increase of WCDMA average throughput

The system may be equalised through joint detection techniques (interference mitigations, both inter- and intra-cell)

32

1


WiMAX

OFDMA-based systems use a TDMA system per sub-carrier, and transmits to one user at a timeHowever, inter-cell interference remains

Therefore they need to have a frequency re-use factor of more than one as the interference from neighbouring cell can be destructive

Adaptive array antenna systems, as well as adaptive frequency re-sue factors are used to reduce interference and increase the throughput efficiency

1


Peak throughputAn example for a WCDMA system is calculated below. It should be noted that peak throughput figures of up to 14 Mbps have been reported. These require higher coding rates and better information efficiency than listed in this example.

1Spreading factor (chip per symbol)

4Data bits per symbol (16 QAM)

95%Information bits / transmitted bits

10.944 MbpsPeak throughput

3/4Channel coding rate

3.84 McpsChip rate

Peak Throughput

Peak throughput is calculated similarly for all technologiesIt is primarily a function of system bandwidth, and frequency re-use factor


WiMAX peak throughputAn example for a 5 MHZ WiMAX system is calculated below.

12 MbpsChannel coding rate 3/4

16 Mbps64-QAM modulation: 6 bits/symbol

8680Symbol rate per sub-carrier (1 / 115.2 μsec)

115.2 μsecOFDM symbol duration

9.766 kHzSub-carrier frequency spacing

384Number of sub-carriers

2.67 MspsInformation symbol ratio (80%)

12 MbpsPeak throughput

3.3 MspsTotal symbol rate (8680x384)

5 MHz McpsSystem bandwidth

WiMAX Peak Throughput

WiMAX peak throughput is similarly calculated. It is also directly related to the system bandwidth


SIR = 12 dB

SIR = 9 dB

SIR = 6 dB

SIR = 0 dB

SIR = 3 dB

Average Throughput

Average throughput is calculated from SIR distribution and Shannon theoremVarious standards differ here on how they can minimize interference


t1t3

t4

t2

Multi-hop Networking

With path loss and the required received power significantly higher, transmission range is significantly reduced. To increase coverage, a user device may be used to relay signals to a user outside the coverage area


Fixed and wireless transmission rates are becoming more and more comparable

The question of which technology to choose is answered by which way multi-user interference is handled

An operator should be most interested in average throughput rates for the system, rather than a marketing-oriented peak throughput figure

To summarize …


3G to 4G Standards



3G to 4G Standards


Services



Technologies: WCDMA-HSPA

WCDMA HSPA standard is in various stages of standardization within ITU, 3GPP and ARIB

3GPP has already made 5 formal releases of the CDMA standardMost of these standards have been ratified by the ITU

June 2006Release 7

2001Release 4

Dec 2002Release 5

Dec 2004Release 6

1999Release 99

2007/2008Long Term Evolution

3GPP (Expected) Release Date


A Combination of…

It is a combination of FDD, CDMA and TDMAThe Duplex mode is Time DivisionUser simultaneously connect to the system in Code division multiple access fashionUser traffic is also handled in a Frequency Division mannerThe TDD mode is a complimentary component for the new standard

FDD CDMA

TDMA

WCDMA-HSPA

Such as: GSMWCDMA

Such as: FOMAcdmaOne

Such as: GSMPDC


FDD and TDD

In FDD two different frequency bands are used for downlink and uplink transmissionsIn TDD Uplink and downlink transmissionsare carried out in thesame frequency band,but at different times

While CDMA systemshave been mainly FDD, a joint TDD/FDD is being developed

While initially WiMAXsystems went the FDDway, they are now focusing on TDD

Uplink frequency band

Downlink frequency band

(FDD)

Base station

Common uplink and downlink frequency band

(TDD)

Base stationEnd-user device

End-user device


Technologies: WiMAX

WiMAX specifications are being developed under IEEE 802.16e group, with several other working group contributing to the final standard: Release dates have varied: the following was presented by Intel last October: Definite Final Release 1 is expected this year...

*Source: Intel Presentation at Wireless Broadband Technical Seminar, Tokyo, Japan, 31 October 2005


Uses OFDMA …

WiMAX is a combination of TDD OFDMA and TDMAThe Duplex is Time DivisionUser simultaneously connect to the system in an Orthogonal Frequency Division Multiple Access fashionUser traffic is also handled in a Time Division manner

TDD OFDMA

TDMA

WiMAX

Such as: DECTPHS

Similar to: 802.11aDAB/DVB

Such as: GSMPDC


WCDMA LTE: OFDMA with Spreading

Long term evolution of CDMA standards envisages usage of OFDMAA combination of CDMA and OFDM as in the DoCoMo proposal

The OFDM part will use a scalable variable number of sub-carriersFixed sub-carrier spacing (15kHz)Spectral compatibility for deployment in existing bands

20MHz

5MHz

10MHz

15 kHz


Frequency (sub-carriers)

Time(sub-frames)

code

Physical Layer: Resource Segmentation

Time, frequency and (possibly) code domain resource partitioningTime domain

Accommodates bursty traffic profiles (packet data)Enables channel dependent scheduling (multi-user diversity)

Frequency domainFurther granularity, and channel dependent schedulingLocalised resources or distributed resources


System Parameters

Although both 3GPP WCDMA LTE and WIMAX evolution envisage a range of bandwidths, it is expected that mostly a 5 or 10 MHz bandwidth will be usedBoth systems use similar coding and modulation schemesThe only difference between the two systems is the choice of access technology

This leads to different frequency re-use factor requirements

QPSK ~ 16 QAM

QPSK ~ 64 QAM

Uplink

Downlink QPSK ~ 64 QAM

1.25 ~ 20 MHz

OFDMA

QPSK ~ 64 QAM

Modulation

CDMA-OFDMAAccess Technology

Turbo and LDPC Codes Coding

1.25 ~ 20 MHzBandwidth

WiMAXWCDMA-HSPA


Key Parameters

The following table shows the general guidelines for the LTEThese are expected within 2009-2010 release

Paired & Unpaired

1.25, 2.5, 5, 10, 15, 20

< 5 ms

192-256 kbps

1 – 2 Mbps

0.48 – 0.72 b/s/Hz

1.2 – 1.6 b/s/Hz

2.5b/s/Hz

5b/s/Hz

Net Requirement Set By Operators

Duplex Modes

Cell Edge Rate - Downlink

Cell Edge Rate - Uplink

Parameter

Channel bandwidths (MHz)

Delay one way (active state, single user, unloaded)

Spectral efficiency- Uplink

Spectral efficiency- Downlink

Uplink Peak User Throughput

Downlink Peak User Throughput


Frequency Re-Use

Usually the spectrum is re-used in many different base stationsIf two base stations are sufficiently separated, they can re-use the same spectrum to communicate with their mobiles

WiMAX systems propose a partialfrequency re-use, where areas in the centre of a cell can havere-use factor of 1, and cell-edgea re-use factor of 3.

f1+f2+f3

f1

f2f3

f1+f2+f3

f1+f2+f3


IMT Extension band:Europe, Japan, KoreaTDD or FDDMMDS band:USA, CanadaTDD or FDD

2.5 ~ 2.69 GHz

IMT 2000: FDDEurope, Japan, Korea, China

2.11 ~ 2.17 GHz

IMT 2000: TDDEurope, Japan, Korea, China

2.01 ~ 2.025 GHz

IMT-2000 TDDChinaMobile InternetKorea

2.3 ~ 2.4 GHz

2 G

Hz

Ban

d

1.92 ~ 1.98 GHz

Presently usedfor 1G, 2G450 MHz800 MHz bandsTDD or FDDVarious Worldwide

Sub 1 GHz

IMT-2000 FDD1.72~1.78JapanCanada?

1.7 GHz

< 2

GH

z B

an

d

Possible BroadbandWireless5.470 – 5.725 : Asia, Americas, Europe

5.7 ~ 5.8 GHz

Broadband Wireless3.3- 3.4 GHz: China, India3.4-3.6 GHz: Worldwide3.6-3.8 GHz: USA, CanadaTDD or FDD

3.3 ~ 3.8 GHz

3 &

5 G

Hz

Ban

d

IMT-2000 TDDEurope, ChinaKorea

1.9 ~ 1.92 GHz

IMT 2000: FDDEurope, Japan, Korea, China

Allocated Spectrum

Several frequency bands can be considered for future releases of 3G standards.


Switching Technology

Switching technologies have now also merged:Data over wired network has long been packet switchedVoice communications over wire is now increasingly packet switched: VoIP

Similarly in wirelessData is now increasingly packet switchedVoice is also converging to packet switching: Wireless VoIP

Web

Email Circuit Switched

Voice

2G

Email

Video

Voice

Web

Streaming

Packet Switched

MMS

Packet Switched

Email

VideoCircuit

SwitchedVoice

Web

Streaming

MMS

3G Early Releases

3G Release 5 ~


IP End-to-End

Services of the future will be packet switchedThe backbone network will operate using IPOffered services will also use IPUsing an end-to-end IP network design will reduce

Design costIntegration costOperating costLayout and expansion cost

Base station

IP Network

Server

Other Networks


LTE Architecture

The backbone is based on a flat all-IP architecture

IMS ServiceNetwork

“Public” IP WAN

ISP network

Private network

PSTN

Signalling

User data

E-UTRAN

Operator Managed IP backbone

E-Node BE-Node B

E-Node B

E-Node BE-Node B

LTE GW


Base station

User equipment

Antennaelements

Antennaelements

> λ/2

Using MIMO

MIMO (multiple-input multiple-output) technology is the usage of multiple antennas at both the transmitter and receiver sidesThis in effect creates parallel channels. The channel capacity can therefore be increased several times. For example the DoCoMo systems uses 12 antennas at each side

Under ideal conditions, this increases throughput 12 timesFor this to work, antenna elements must be sufficiently apart


Information bits

Transmittedpacket

NACK

Buffer

Re-transmitpunctured bit

if NACK

Information bits

Paritybits

Puncturedparity bit

Hybrid ARQ (Incremental Redundancy)

When “S” term is high in Shannon Theorem, higher transmission rates may be supported. This Hybrid ARQ scheme facilitates its realisation


0

50

100

150

200

250

300

350

-10 -5 0 5 10 15 20 25

Th

rou

gh

pu

t

Eb/N0

Mode 1

Mode 2

Mode 3

Mode 4

Mode 5

Mode 6

Mode 7

Adaptive Coding and Modulation

When channel conditions are good then channel coding rates and modulation rates may be increased so more information is sent through the channel.

64-QAM

16-QAM

16-QAM

16-QAM

QPSK

QPSK

QPSK

Modulation

1/32

1/24

3/43

1/21

3/47

3/46

1/35

CodingRateMode


Time

Am

pli

tud

e l

evel

Po

wer

level

Average power

Peak powerTime

Time

Time

Time

()2

Peak-to-Average Power Ratio (PAPR)

Multi-carrier systems suffer from large PAPR problemThis is significant particularly in regards to power amplification as non-linearity can cause clipping


Power Amplifier Efficiency

Power amplifiers have a saturation level

With PAPR, the device need to operate at well below saturation level

This leadsLess efficient operation (more battery power required, more heat generated)

Cost/Battery usage can be prohibitive for handsets.

This is the reason OFDM/Multi-carrier is not used in Uplink

Input level

Outputlevel

30%6-9 dB

44%3 dB

60%0 dB

EfficiencyInput backoff


To summarize …

“3G” standards evolution (both 3GPP and IEEE – based) intend to provide

Higher transmission ratesFlexible bandwidth allocationFull IP backbone architecture

Advanced antenna MIMO, and error control coding technologies helps increase the transmission rate

However, concerns remain with the electronics design aspects, specially PAPR issues for OFDM systems


Services



3G to 4G Standards


Services



End-User device

The services that can be provided are very much a factor of the end-user device capability, core purpose, and mobility

Mobility

Mini PCLaptop PC PDA Mobile


User MobileOperator

Third parties

RevenueFlow

RevenueFlow

RevenueFlow

User MobileOperator

RevenueFlow

Revenue Flow

Service models, and revenue flows are also changing as many new players are entering the value chainWith the introduction of new services in 2G and 3G, the flow of revenue has become more complexIt is expected to be more complex with (4G) broadband wireless services


Non-PortalContent

Aggregationand Creators

Non-PortalApplication

Platform

PortalContent

Aggregation

ThirdParty

Billing

PortalAccess

End-userBilling

IPNetwork

Access

MobileNetwork

Access

3. Access Focused Approach

2. Portal Focused Approach

1. Mobile Specialised Services

Value Chain

A value chain, based on 3G services and applications has been developed by UMTS ForumThey classify services into three groups:

*Source: UMTS Forum


CustomizedInfotainment

MultimediaMessaging

Service(MMS)

LocationBased

Services

Rich/SimpleVoice

MobileInternetAccess

MobileIntranet/ExtranetAccess

Access FocusedApproach

PortalFocused

Approach

Mobile Specialized Services

Content Connectivity(Internet)

Mobility

Information and Content(Non-Voice)

Voice

Service Classification

Using this classification, service categories are defined by UMTS Forum

*Source: UMTS Forum


Required Transmission Rates

Required transmission rates vary for different servicesMoreover they are expected to be different for downlink and uplinkThese help the decision making process: what amount of total transmission rates are needed for a certain customer base.

UplinkDownlink

Simple Voice

Rich Voice

Location Based Services

Multimedia Messaging Service

Customised Infotainment

Mobile Intranet/Extranet Access

Mobile Internet Access

8 kbps ~ 16 kbps16 kbps ~ 64 kbps




8 kbps ~ 16 kbps

128 kbps ~ 256 kbps

32 kbps ~ 64 kbps

64 kbps ~ 128 kbps

500 kbps ~ 1 Mbps

500 kbps ~ 1 Mbps

*Source: UMTS Forum


Uplink and Downlink Asymmetry

The amount of traffic in the uplink and downlink are going to be differentTDD systems are more flexible in traffic allocation

Uplink frequency band

Downlink frequency band

(FDD)

Common uplink and downlink frequency band

(TDD)

One slot

One frame

0

500

1000

1500

2000

2500

1997 2002 2007Year

Kb

ps

DownlinkUplink

Maximum throughput for D/L and U/L per User


Simple and Rich Voice

This is the traditional voice service, and voice enriched by video and other functionsWhile the revenue from simple voice service is expected to decrease, revenue from rich voice service is expected to increaseTransmission rates are moderate

Source: Esmailzadeh based on UMTS Forum data 0

20

40

60

80

100

120

2005 2006 2007 2008 2009 20100

100

200

300

400

500

600

700

Rich Voice revenue ($B)Simple Voice revenue ($B)Simple voice subscribers (M)

Year

Reven

ue (

$B

)

Su

bsc

rib

ers

(M

)


Customized Infotainment

Information and entertainment services are going to be a major revenue growth for operatorsModerate transmission rates

0

10

20

30

40

50

60

70

80

90

100

2005 2006 2007 2008 2009 2010Year

Reven

ue (

$B

)

0

50

100

150

200

250

300

350

Su

bsc

rib

ers

(M

)

Customised Infotainment revenue ($B)Customised Infotainment Subscribers (M)

Source: Esmailzadeh based on UMTS Forum data


Mobile Intranet/Extranet

Wireless ADSL type of services, specially for the business segment is expected to grow. High transmission rates, perhaps counting for the lion share of inforamtion transferHowever, revenues are not expected to be correspondingly high

0

10

20

30

40

50

60

70

2005 2006 2007 2008 2009 2010Year

Reven

ue (

$B

)

0

50

100

150

200

250

300

Su

bsc

rib

ers

(M

)

Intranet/Extranet revenue ($B)Intranet/Extranet subscribers (M)



Multimedia Messaging Service

Short messaging services, enhanced by multimedia features is expected to growMMS services for business, including machine-to-machine services are expected to grow rapidly.Transmission rates are expected to be low

0

5

10

15

20

25

30

35

40

45

2005 2006 2007 2008 2009 20100

20

40

60

80

100

120

140MMS business segement revenue ($B)MMS consumer segment revenue ($B)MMS consumer segment subscribers (M)

Year

Reven

ue (

$B

)

Su

bsc

rib

ers

(M

)



Location Based Services

Location based services, including both consumer and business segments (asset tracking etc.) will show significant growthLow transmission rates

0

2

4

6

8

10

12

2005 2006 2007 2008 2009 2010Year

Reven

ue (

$B

)

101Business asset tracking

18018Consumer third party

194LBS transactions

11739LBS advertising

18722Consumer navigation

Unit (M) 2010

Unit (M) 2005



To summarize …

A good classification of the future services have been done by the UMTS forum

Based on this classification a value chain and market forecast has been made

It is expected that a mixture high and low data rates will exist, and generate revenues unrelated to their transmission rates

The future wireless technology needs to be flexible to provide these service mixture


Overall Summary

There appears to be convergence between CDMA and OFDMA campsPerhaps driven by the 3GPP camp to remove any differentiation WiMAX camp may have

Although provision of high transmission rates is being addressed, the two camps still are in the marketing mode:

Peak transmission rates are braggedService provision is not really addressedEssential problems are still ignored

The end-user major present-and-now need is wireless DSL–type services

Which neither technology with their present capacities can provideAnd which may be best provided by proprietary technologies

The challenge of transmission of higher rates at higher frequency bands and reduced transmission range also needs to be addressed.

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