PhilipsResearch

11-02-708r0-WNG 1 / 23IEEE 802.11 session Hawaii November

2002

Alexei Gorokhov, Paul Mattheijssen, Manel Collados,Bertrand Vandewiele, Gunnar Wetzker

Philips Research

PHY options for high throughput wireless LANs

Right time and place for MIMO?

Performance enhancement via antenna selection

Experimental set-up and channel measurements

MIMO architectures for high data rates

Experimental results

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Requirements

Higher data rates (> 100Mbps) Increased throughput Extended range

Better coverage

Higher network capacity

Possible solutions

Increase bandwidth per link

Higher order modulation

More powerful CODEC

TX / RX diversity

MIMO

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Requirements

Higher data rates (> 100Mbps)Higher data rates (> 100Mbps) Increased throughputIncreased throughput Extended rangeExtended range

Better coverageBetter coverage

Higher network capacity

Possible solutions

Increase bandwidth per linkIncrease bandwidth per link

Higher order modulation

More powerful CODEC

TX / RX diversity

MIMO

Currently 12 channels 2 x rate 6 channels

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Requirements

Higher data rates (> 100Mbps)Higher data rates (> 100Mbps) Increased throughput Extended range

Better coverage

Higher network capacityHigher network capacity

Possible solutions

Increase bandwidth per link

Higher order modulationHigher order modulation

More powerful CODEC

TX / RX diversity

MIMO

Over 64-QAM: severe requirements to analogue & mixed signal circuits

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Requirements

Higher data rates (> 100MbpsHigher data rates (> 100Mbps) Increased throughputIncreased throughput Extended rangeExtended range

Better coverageBetter coverage

Higher network capacityHigher network capacity

Possible solutions

Increase bandwidth per link

Higher order modulation

More powerful CODECMore powerful CODEC

TX / RX diversity

MIMO

Higher complexity: power & area

Iterative demodulation with “anti-Gray” maps Turbo coded CODEC

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Possible solutions

Increase bandwidth per link

Higher order modulation

More powerful CODEC

TX / RX diversityTX / RX diversity

MIMO

Requirements

Higher data rates (> 100MbpsHigher data rates (> 100Mbps) Increased throughputIncreased throughput Extended rangeExtended range

Better coverageBetter coverage

Higher network capacityHigher network capacity

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Requirements

Higher data rates (> 100Mbps)Higher data rates (> 100Mbps) Increased throughputIncreased throughput Extended rangeExtended range

Better coverageBetter coverage

Higher network capacityHigher network capacity

Possible solutions

Increase bandwidth per link

Higher order modulation

More powerful CODEC

TX / RX diversity

MIMOMIMO

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TX

RX

Theoretical throughput scales linearlyw.r.t. the # of antennas:

Increased range / coverage in NLOS environments

Cheap RF-CMOS technology:

fractional cost per RF front-end (5.x GHz)

Keep DSP complexity limited

Motivation

Constraint

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TX

RX Need for extra degrees of freedom at RX to ensure enough diversity ( ) High incremental cost of adding RF front-end versus the cost of antenna

Use antennas and front-ends at RX, select adaptively a subset of antennas,

select out of antennas

optimal selection is rather complex simple sub-optimal selection possible

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Receiver Transmitter

4 TX chains 4 RX chains f ~ 5.8GHz BW 20MHz

14 bit ADC 35 dB AGC

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DAC/ADC

LNA

mixer

AGC+LPF

Monopoles

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1 2 3 4 5 6 7 8 9 10 11 12

“soft” walls, much glass few heavy metallic constructions lots of furniture few concrete walls / blocks

Total TX power 14dBm

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0.0

0.5

1.0

1.5

2.0

2.5

3 6 9 12 15 18 21 24 27 30 33 36

Range (m)

RM

S d

ela

y s

pre

ad

[x

sym

bo

l ra

te]

80% quantil

50% quantil

10% quantil 1% quantil

RMS delay spread versus range

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Range (m)

SN

R p

er

RX

an

ten

na

[d

B]

80% quantil

50% quantil

10% quantil 1% quantil

Signal-to-noise ratio per RX antenna versus range

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FEC encoder

interleaver

mapper IFFT

cyclic extension

pulse shaping

FEC encoder

interleaver

mapper IFFT

cyclic extension

pulse shaping

FEC encoder

FFT

sampling

pulse shaping

FEC encoder

FFT

sampling

pulse shaping

MUX

DEMUX

streamcycling

MMSE filter

MRC

+

+

interleaver

mapper FEC encoder

-

-

latency of ~ one TX/RX cycle

deinterleavedemap

TX signal path

RX signal path

deinterleavedemap

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space frequency

interleaver

mapper IFFT

cyclic extension

pulse shaping

FEC decoder

FFT

sampling

pulse shaping

FFT

sampling

pulse shaping

FEC encoder

mapper IFFT

cyclic extension

pulse shaping

space frequency

de-interleaver

2 x 2MMSE

filter

TX signal path

RX signal path

demapper

demapper

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0

50

100

150

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3 6 9 12 15 18 21 24 27 30 33 36

Range (m)

Maxim

um

ra

te [M

bp

s]

1 x 1 RX 11 x 1 RX 42 x 2 RX 22 x 2 RX 43 x 3 RX 33 x 3 RX 44 x 4 RX 4

Outage capacities versus rangeoutage rate 1%

optimal RX antenna selection

S-F modulation / layered RXMIMO channel

0

50

100

150

200

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3 6 9 12 15 18 21 24 27 30 33 36

Range (m)

Maxim

um

ra

te [M

bp

s]

1 x 1 RX 11 x 1 RX 42 x 2 RX 22 x 2 RX 43 x 3 RX 33 x 3 RX 44 x 4 RX 4

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0

50

100

150

200

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3 6 9 12 15 18 21 24 27 30 33 36

Range (m)

Maxim

um

ra

te [M

bp

s]

1 x 1 RX 11 x 1 RX 42 x 2 RX 22 x 2 RX 43 x 3 RX 33 x 3 RX 44 x 4 RX 4

Outage capacities versus rangeoutage rate 1%

optimal RX antenna selection

S-F interleaving / MMSE MIMO channel

0

50

100

150

200

250

300

3 6 9 12 15 18 21 24 27 30 33 36

Range (m)

Maxim

um

ra

te [M

bp

s]

1 x 1 RX 11 x 1 RX 42 x 2 RX 22 x 2 RX 43 x 3 RX 33 x 3 RX 44 x 4 RX 4

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Outage capacities versus rangeoutage rate 1%

optimal RX antenna selection

S-F interleaving / MMSE S-F modulation / layered RX

0

50

100

150

200

250

300

3 6 9 12 15 18 21 24 27 30 33 36

Range (m)

Maxim

um

ra

te [M

bp

s]

1 x 1 RX 11 x 1 RX 42 x 2 RX 22 x 2 RX 43 x 3 RX 33 x 3 RX 44 x 4 RX 4

0

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100

150

200

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3 6 9 12 15 18 21 24 27 30 33 36

Range (m)

Maxim

um

ra

te [M

bp

s]

1 x 1 RX 11 x 1 RX 42 x 2 RX 22 x 2 RX 43 x 3 RX 33 x 3 RX 44 x 4 RX 4

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MIMO capacities

MIMO capacity scales almost linearly w.r.t. the number of TX/RX antennas space-frequency modulation with layered RX : ~90% of theoretical limit space-frequency interleaving with MMSE: ~60% of theoretical limit …………… with adaptive RX selection: ~80% of theoretical limit

Feasibility aspects

channel processing beyond 2 x 2 system is hardly feasible (baseband) layered reception yields higher complexity & processing latency,

seems prohibitive beyond 2 x 2 systems sub-optimal RX antenna selection looks attractivesub-optimal RX antenna selection looks attractive

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0

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3 6 9 12 15 18 21 24 27 30 33 36

Range (m)

Maxim

um

ra

te [M

bp

s]

2 x 2 RX 2

2 x 2 RX 4 (opt)

2 x 2 RX 4 (sub)

2 x 4 RX 4 (MRC)

1 x 1 RX 1

Outage capacities versus rangeoutage rate 1%

S-F modulation with MMSE receiver & sub-optimal RX selection looks attractive

0

20

40

60

80

100

120

140

160

180

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3 6 9 12 15 18 21 24 27 30 33 36

Range (m)

Maxim

um

ra

te [M

bp

s]

2 x 2 RX 2

2 x 2 RX 4 (opt)

2 x 2 RX 4 (sub)

2 x 4 RX 4 (MRC)

1 x 1 RX 1

S-F modulation / layered RX S-F interleaving / MMSE

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Candidate FEC structures

Standard convolutional code rate (1/2) 64-state (NASA) code [133,171]8 puncture to achieve mandatory / supplementary rate modes soft-input Viterbi decoding at RX easy to implement, IEEE 802.11 acceptance expected to be sensitive to SINR discrepancy

Turbo- CODEC similar to that of UMTS rate (1/3) PCCC with 8-state components [13,15]8 puncture to achieve desired rates iterative SISO decoding (Max-Log-MAP) reduced SINR margin, less sensitive to SINR discrepancy rather high complexity

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0.1%

1.0%

10.0%

100.0%

3 6 9 12 15 18 21 24

Range (m)

Ou

tag

e r

ate

[%

]

108 Mbps 96 Mbps 72 Mbps 64 Mbps 36 Mbps 32 Mbps 24 Mbps

108Mbps 64QAM, rate 3/4 96Mbps 64QAM, rate 2/372Mbps 16QAM, rate 3/464Mbps 16QAM, rate 2/336Mbps 16QAM, rate 3/432Mbps QPSK, rate 2/324Mbps QPSK, rate 1/2

Signalling

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Observations

Maximum data rate scales linearly w.r.t. to the number of antennas

Receive antenna selection improves substantially maximum data rates (limited number of TX/RX chains)

2 x 2 space division multiplexing with selection 2 of 4 RX antennas 200%-300% of single-antenna rates