4G basics

1. 1
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

2. 2
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
Wireles
s
wireline
Technolog
y trends
New
network
New air
interfac
e
Wireles
s
Internet
4G will
not
exist
Higher
bit rates
White
space
Strict
generatio
n
*
source: CSTL 4G white paper
Wireles
s
wireline
New
network
New air
interfac
e
Technolog
y trends
Cost
reductio
n
Higher
bit rates
User
service
s
White
space
Service
provider
s
Wireles
s
Internet

3. 3
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

4. 4
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

5. 5
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 fixed
geographic area due to an increase in either the system
data rate or carrier frequency.
1
10
100
1000
1 10 100 1000
Data Rate or Carrier Frequency Increase Factor
Assumptions: Constant EIRP, constant Rx
antenna gain, no change in diffraction,
absorption or other propagation
characteristics. Path loss exponent = 4
Carrier Frequency
Data Rate

6. 6
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

7. 7
Broadband Wireless ContentBroadband Wireless Content
• Successful wireless services are preceded by growth of wired demand
POTS  Mobile Telephony
Dial-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

8. 8
User Session Traffic CharacterizationUser Session Traffic Characterization
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
2800 2820 2840 2860 2880 2900 2920 2940 2960 2980 3000
PacketDataRate(bytespersecond)
Time during Session (seconds)
Web browsing session (TCP) Video Download (UDP)
Internet Telephony Audio – from
Client
Internet Telephony Audio – to Client
0
250
500
750
1000
1250
1500
1750
2000
2250
2500
500 520 540 560 580 600 620 640 660 680 700
PacketDataRate(bytespersecond)
Time during Session (seconds)
0
250
500
750
1000
1250
1500
1750
2000
2250
2500
500 520 540 560 580 600 620 640 660 680 700
PacketDataRate(bytespersecond)
Time during Session (seconds)
0
1000
2000
3000
4000
5000
6000
7000
8000
500 520 540 560 580 600 620 640 660 680 700
PacketDataRate(bytespersecond)
Time during Session (seconds)

9. 9
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 – 8.08.0
Ratio 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 – 1.851.85
Ratio 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 + AudioVideo + Audio
DownloadDownload
( UDP & VXtreme™ )( UDP & VXtreme™ )
Peak-to-Average Bit Rate Ratio – 1.371.37
Ratio 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

10. 10
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

11. 11
4G System Research Areas4G System Research Areas
Adaptive
Antennas for
Broadband
Broadband
Air Interface
Research
Broadband
Implementations
4G System Design

12. 12
Potential Coverage and Capacity SolutionsPotential Coverage and Capacity Solutions
Primary Benefit
Improved Coverage Higher Capacity
Asymmetric Data
Rate
X
High Power BTS X
Lower Frequency X
Small Cells X X
Adaptive Antennas X X
Advanced Air
Interface and Link
Adaptation
X X

13. 13
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

14. 14
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