Evolving 4G to the Next Level
A. Paulraj
Stanford UniversityBeceem Communications Inc.
GCOE Workshop onAdv. Wireless Signal Processing and
Networking Technology
How dense are Wireless networks
Mobile Phone Subscribers(Billions)
1990 1995 2000 2005 2010 2015
0
1
2
3
4
Internet UsersBillions
1990 1995 2000 2005 2010 2015
0
0.5
1
1.5
2
Source: IDC, The Digital Economy Fact Book
Exciting Promise
Mobile internet represents a new computing cycle
– Mainframe to Mini to PC to PC Internet to Mobile internet
Mobile Internet is the way Billions will connect to the internet. Paralleling trends in voice telephony
4G Requirements (NGMN)
Throughput > 100 Mbps Peak BS Radio > 10 Mbps Peak / Terminal Spectral Eff. > 2.5 bps/Hz/cell Cell range > 1 Mile dense urban Low delay < 10 ms RT Delay All IP
4G Technologies: WIMAX 16e R2 (2008), 3G LTE R8 (2011)
WIMAX Equipment
Infrastructure
– Motorola, Samsung, Nortel-Alvirion, Alcatel-Lucent, NEC, Fijitsu…
Chips
– Beceem, Intel, Sequans, GCT, Samsung*
7
Sprint Network – Herndon, VA
• FTP Throughputs
•12.8 Mbps (DL Peak)
• 6.9 Mbps (DL Avg)
• 3.2 Mbps (UL Peak)
• 2.3 Mbps (UL Avg)
Infra: Mot, Samsung, NSNTerminals – ZTE / Mot (both use Beceem Chipsets)
8
Clearwire Network - Portland
C:\Documents and Settings\jchen.BECEEM\M
• Coverage Test(145 km2)
• UDP Throughputs• 17Mbps (DL Peak)• 9 Mbps (DL Avg)• 2Mbps (UL Avg)
Infra: MotorolaTerminals – Mot (Beceem Chipsets)
Performance Goals
Higher Speed, Improved Spectrum Efficiency,
Lower Delay, Better QoS, Better Coverage,…
1.0
0.5
200
3G 4G IMT Adv. ??
1
10
2
10
2.5
20
2003 2008 2013 2018
100
7.5
5
Peak Mbps/ Term
Spec. Effbps/Hz/cell
Rnd Trip Delay ms
BS Peak Data Rates
1995 2000 2005 2010 2015 20201 Kbps
10 Kbps
100 Kbps
1 Mbps
10 Mbps
100 Mbps
1 Gbps
10 Gbps
100 Gbps
1 Tbps
10 Tbps
IS95A
GPRS EDGE
WCDMA HSDPA WiMax1
WiMax2/3GLTE
802.11
802.11b
802.11g
802.11n
VHT
Bluetooth1 Bluetooth2
WiMedia
WiMedia 60GHz
60GHz 60GHz
DOCSIS1
V90
ADSL
DOCSIS2
ADSL2
VDSL
VDSL2 DOCSIS3
100 BaseT
1G BaseX F1G BaseT
10G Fiber 10G BaseT
100G
USB1
PCI2.2
ATA4 FW400
ATA5
USB2
ATA6
FW800
PCIe1a
SATA150SATA300
PCIe2
USB3
PCIe3
Year of Standardization
Pe
ak s
ing
le-u
ser
up
link
PH
Y d
ata
rate
Evolution of wireless and wired networks
Wireless WANWWAN fitWireless LANWLAN fitWireless PANWired WANWired LANLAN fitWired PAN
Wired LAN
Wireless LAN
Wireless WAN
Intel document, Sumeet Sandhu and Ed Casas, Intel CorporationSource: S Sandhu / Intel
PHY Level Tools
BandwidthModulation, Multiple access, MIMO, Opportunistic scheduling, Relay, Cooperation,Interference mitigation, H -ARQ,…
Bandwidth
Wider band
– At low SNR (cell edge), more bandwidth does not increase data rates
Getting more bandwidth
– Multi-band OFDMA
• Rx compression, RF leakage
– Cognitive access to spectrum
Modulation
OFDM – most favorable
– Improving PA efficiency
Adaptive
– Per tone vs per FEC Block
Hierarchical Data over data
– Used in Broadcast / Multicast
Hierarchical Pilot over data
– Useful in Unicast
Multiple Access
OFDMA, TDMA for DL, OFDMA, DFT Coded OFDM for UL
Scalable / Adaptive
– FFT size, CP, Symbol period
MIMO
Conventional p2p MIMO is a great success!
MIMO – OFDM is a good marriage!
Codes that are optimal (diversity –multiplexing gain) as well as easily decodable remains open for innovation …
Fast Rx decoding is also open for innovation – sphere decoding, iterative decoding,..
MIMO – Number of Antennas
Today: BS 4, MS 2 Future: Increasing MS antennas have tradeoffs
– RF chain power – Per antenna power constraint reduces array gain– Answer depends on
• Low vs High SNR• Good vs Poor CSI-Tx• Full vs Low rank channels
– Antenna EM issues
MIMO Relay
Wired and wireless relay create composite MIMO channels
Space time coding for location and directionally inhomogeneous antenna arrays
Composite MIMO Channel
Wired
Wireless
MIMO Broadcast
Multi-cell broadcast from directional sector antenna arrays.
Delivering directionally homogenous service using space-time coding.
SFN Networks
Cellular Networks
2-4 antennas per sector
One omni antenna per cell
Multi-Hop Relaying
Provides 1.5-3X gains in throughput for cell-edge users
Also Multi-hop diversity
Opportunistic Scheduling
Choosing best user for a resource such as time slot, x frequency sub-channel x antenna ,… based on some metric – SNR or SIR, capacity
Prop Fair / Max-percentile
Joint vs independent scheduling
Opportunistic Scheduling
SISO channel
We can get log(K) scaling in capacity for interference limited scheduling vs log log(K) scaling for noise limited scheduling
Interference Management
Reuse – controlling interference that the user sees Tx interference avoidance, Rx interference
cancellation BS Cooperation & MS Cooperation Interference averaging
Interference in Broadband Networks
C/I histogram
Growing density of subscribers per unit area → smaller cell increasingly interference dominant
Reuse and Power Control
Single Reuse Class
Dual Reuse Class
Multiple Reuse Classes: Interference can be varied by controlling loading and power control,… xx
xxx
xx
xxx
xx
x
x
x
x
x
1x3x1 1x3x1.5 1x3x
Reuse and Power control
When there is a dominant interference, the strategy usually suggests no reuse (time sharing)
Full reuse may be optimal only for high SIR
Spatial Filtering - Avoid / Cancel
Interference avoidance (linear precoding) at Tx
MMSE or ML interference cancellation
at Rx . Cardinality and SIR
BS Cooperation - Independent Encoding
Base stations use independent encoding (interference channel)
Weak interference – treat it as noise
– Medium interference – rate splitting
– Strong interference – can be decoded and stripped out
Infra Cooperation - Joint Encoding Base stations cooperate in encoding (multi-user channel)
– Dirty Paper coding (with individual power constraint)
– Both support only one user (~ soft handoff)
– User is served only one of BTS at a given time (FBSS)
Interference Diversity and Repetition Coding
Make a codeword see many diverse interferers by use of different PN seeds for codeword permutation (PUSC in WIMAX) . Also symbol repetition
Reduces interference variability
WIMAX Technology
Ops / Sec : WIMAX is ~10 GOPS ( x10,000 GSM)
Team: 250 man years per chip generation
Area / Power: 2 Tx, 2 Rx, multi-band DCR radio, PMU, PHY, MAC
– 9x9 x1.5 mm, 400 mW + PA
Power and Throughput Management: Clock, voltage and power islanding, power constrained processing, …
Beyond 4G Challenges
Goals are indeed challenging, but there many approaches to getting there (and there is always hope for fundamentally new ideas !)
Any solution must meet constraints on battery life, infrastructure cost and coverage reliability.
Thank You
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