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

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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