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Fourth Generation Cellular Systems:Fourth Generation Cellular Systems: Spectrum RequirementsSpectrum Requirements

Joseph M. Nowack Member of the Technical Staff

Communication Systems and Technologies Labs

December 6, 2000

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What is 4G?What is 4G?What is 4G?What is 4G?

• The simple answer: 4G is the next major generation of mobile cellular systems, to be deployed around the year 2010

• The multiple choice answer: The “twelve views” of 4G*

Is that your final answer?

Service provider

s

Cost reductio

n

User service

s

Wireless

wireline

Technology trends

New network

New air interfac

e

Wireless

Internet

4G will not

exist

Higher bit rates

White space

Strict generatio

n

*source: CSTL 4G white paper

Wireless

wireline

New network

New air interfac

e

Technology trends

Cost reduction

Higher bit rates

User services

White space

Service provider

s

Wireless

Internet

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A View of 4GA View of 4GA View of 4GA View of 4G

• Domain of 4G extends beyond 1G, 2G, and 3G• > 2 Mbps in a wide-area mobile system (> 20 Mbps peak)

• Could coexist with 2G and 3G

• 4G is not necessarily defined by the bit rate, but by a significant advance in system capability beyond what can be achieved with 3G

Data Rate

Coverage Area,

Mobility

Macrocell,High Mobility

Microcell,Limited Mobility

Fixed Access

64kbps 2Mbps 200Mbps

P-MP (LMDS)Milli-wave LAN

2G2G

WLAN

4G4G3G3G

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Some Key ChallengesSome Key ChallengesSome Key ChallengesSome Key Challenges

• Coverage

– Transmit power limitations and higher frequencies limit the achievable cell size

• Capacity – Current air interfaces have limited peak data rate, capacity,

and packet data capability

• Spectrum– Location and availability are key issues– Lower carrier frequencies (< 5 GHz) are best for wide-area

coverage and mobility

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The Coverage Problem - Carrier Frequency and Data RateThe Coverage Problem - Carrier Frequency and Data RateThe Coverage Problem - Carrier Frequency and Data RateThe Coverage Problem - Carrier Frequency and Data Rate

Increase in the number of cells needed to cover a fixedgeographic area due to an increase in either the systemdata rate or carrier frequency.

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Data Rate or Carrier Frequency Increase Factor

Assumptions: Constant EIRP, constant Rxantenna gain, no change in diffraction,absorption or other propagationcharacteristics. Path loss exponent = 4

Carrier Frequency

Data Rate

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SpectrumSpectrumSpectrumSpectrum

• Carrier frequency has a larger impact on cell size than data rate• In order to enable wide-area coverage, 4G needs “mobile

friendly” spectrum (ideally less than 5 GHz)– Mobile devices have low transmit power, limited antenna gain, and

predominately non-line-of-sight propagation

• Fixed wireless systems are more easily able to take advantage of higher carrier frequencies– No movement -> low Doppler

– Higher transmit power

– Power consumption/heat dissipation less critical

– Line-of-sight more likely

– High-gain, high-elevation antenna

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Broadband Wireless ContentBroadband Wireless ContentBroadband Wireless ContentBroadband Wireless Content

• Successful wireless services are preceded by growth of wired demandPOTS Mobile TelephonyDial-up Internet WAP, Cellular Data

DSL, Cable Data 4G Broadband Wireless

• Content is rapidly expanding to serve the Cable/DSL connected consumer

– Many sites focused on video delivery of “Broadband” video (typically 300 kbps and faster)

• MovieFlix, VideoSeeker, QTV, Quokka Sports

• Combinations of existing content may be valuable to mobile information consumers

– Expressway Travel Information – real time web cameras, traffic status and advisories

– Entertainment Selections – movie trailers, ticket reservation, TV guide, video-on-demand

– Business Guide – Stock market information, real-time video briefings, breaking news

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User Session Traffic CharacterizationUser Session Traffic CharacterizationUser Session Traffic CharacterizationUser Session Traffic Characterization

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Time during Session (seconds)

Web browsing session (TCP) Video Download (UDP)

Internet Telephony Audio – from Client Internet Telephony Audio – to Client

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Time during Session (seconds)

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Typical ObservationsTypical ObservationsTypical ObservationsTypical Observations• 200-second sections of sessions using three applications• Packet data traffic rates are provided in bytes per second

Browsing the World Wide WebBrowsing the World Wide Web( TCP & HTTP )( TCP & HTTP )

Peak-to-Average Bit Rate Ratio – 8.08.0Ratio of Download Byte Volume

To Upstream – 8.88.8

164721647200 average = 2059average = 2059• Bursty data traffic • Acquisition of various sources for a single site • Long pauses by user• TCP upstream packet traffic volume moderate

Interactive Internet Telephony( UDP & Internet Phone™ )

Peak-to-Average Bit Rate Ratio – 1.851.85Ratio of Download Byte Volume

To Upstream – 1.271.27

2474247400 average = 1362average = 1362• Packet data rates reflect telephone speech patterns • Remote participant responsible for more speech and packet traffic than client in this trace • Byte volumes generally comparable

Video + Audio DownloadVideo + Audio Download( UDP & VXtreme™ )( UDP & VXtreme™ )

Peak-to-Average Bit Rate Ratio – 1.371.37Ratio of Download Byte Volume

To Upstream – 394.8394.8

7166716628532853 average = 5232average = 5232• UDP data uses fewer upstream packets than TCP• Peak-to-Average data rate ratio low in this trace • Mainly due to embedded constant bit rate (CBR) audio stream of the downloaded sample • Variable bit rates (VBR) are more common for most video applications

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4G Concept System4G Concept System4G Concept System4G Concept System

• A demonstration of broadband mobile systems in Schaumburg, Illinois– A one-directional broadband downlink carrier on DVB-T (WA9XHI)

– A narrowband uplink via a cellular data connection (Sprint CDMA data)

• Proving ground for asymmetric mobile broadband• Develop application understanding to apply to broadband air interface designs• Platform to demonstrate custom applications• Increasing levels of integration

– Phase 1 – Vehicular mobility with a larger off-the-air receiver – May 2000

– Phase 2 – Personal mobility with an integrated laptop receiver – Progressing

Sprint PCS

Intranet/Internet Server

Proxy & Router

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4G System Research Areas4G System Research Areas4G System Research Areas4G System Research Areas

AdaptiveAntennas for

Broadband

Broadband Air Interface

Research

BroadbandImplementations

4G System Design

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Potential Coverage and Capacity SolutionsPotential Coverage and Capacity SolutionsPotential Coverage and Capacity SolutionsPotential Coverage and Capacity Solutions

Primary Benefit

Improved Coverage Higher Capacity

Asymmetric DataRate

X

High Power BTS X

Lower Frequency X

Small Cells X X

Adaptive Antennas X X

Advanced AirInterface and LinkAdaptation

X X

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4G Air Interface Characteristics4G Air Interface Characteristics4G Air Interface Characteristics4G Air Interface Characteristics

• Higher bit rates than 3G (20 Mbps < peak < 200 Mbps)• Higher spectral efficiency and lower cost per bit than 3G• Air interface and MAC optimized for IP traffic (IPv6, QoS)

– Adaptive modulation/coding with power control, hybrid ARQ

• Smaller cells, on average, than 3G– However, cell size will be made as large as possible via:

• Asymmetry - used to boost uplink range when necessary• Adaptive antennas (4 to 8 elements at base station, 2 elements at

terminal)

• Higher frequency band than 3G (below 5 GHz preferred)

• RF channel bandwidths of 20-100 MHz

• OFDM is promising (especially for downlink), but also investigating other methods

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ClosingClosingClosingClosing

• 4G still in a formative stage (commercial 2010)• Frequency bands less than 5 GHz preferred for wide-area,

mobile services• 4G system bandwidth between 20 and 100 MHz (paired or

unpaired)• ITU Working Group 8F beginning to consider the requirements

and spectrum needs• International 4G spectrum harmonization