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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 LabsDecember 6, 2000
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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 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 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 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.
1
10
100
1000
1 10 100 1000
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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SpectrumSpectrum
• 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 Content
• Successful wireless services are preceded by growth of wired demandPOTS Mobile TelephonyDial-up Internet WAP, Cellular DataDSL, 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 Characterization
0
2000
4000
6000
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12000
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16000
18000
2800 2820 2840 2860 2880 2900 2920 2940 2960 2980 3000
Pack
et D
ata
Rate
(byt
es p
er se
cond
)
Time during Session (seconds)
Web browsing session (TCP) Video Download (UDP)
Internet Telephony Audio – from Client Internet Telephony Audio – to Client
0
250500750
10001250
15001750200022502500
500 520 540 560 580 600 620 640 660 680 700
Pac
ket D
ata
Rat
e (b
ytes
per
sec
ond)
Time during Session (seconds)
0
250500750
10001250
15001750200022502500
500 520 540 560 580 600 620 640 660 680 700
Pac
ket D
ata
Rat
e (b
ytes
per
sec
ond)
Time during Session (seconds)
0
1000
2000
3000
4000
5000
6000
7000
8000
500 520 540 560 580 600 620 640 660 680 700
Pac
ket D
ata
Rat
e (b
ytes
per
sec
ond)
Time during Session (seconds)
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Typical 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 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 Areas
AdaptiveAntennas for
Broadband
Broadband Air Interface
Research
BroadbandImplementations
4G System Design
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Potential 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 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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ClosingClosing
• 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