Doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 1 HNS Proposal for 802.11n Physical Layer Mustafa Eroz, Feng-Wen

Sept 2004

Mustafa Eroz, Hughes Network Systems

Slide 1

doc.: IEEE 802.11-04/0abcr0

Submission

HNS Proposal for 802.11n Physical Layer

Mustafa Eroz, Feng-Wen Sun, & Lin-Nan Lee [email protected]@[email protected]

Hughes Network Systems11717 Exploration Lane Germantown, MD 20876

Sept 2004


Slide 2


Submission

Proposal Topics • PHY and Air Interface Description • Supported Rate Set (mandatory/optional)• Proposed Scheme• Preamble Design Approach• Spectral Mask with non-linear model• Short Block Length LDPC Performance

Curves

Sept 2004


Slide 3


Submission

PHY and Air Interface • The air interface is built upon IEEE 802.11a (1999) PHY

specifications and associated overhead– OFDM Modulation with PSK and QAM – (20/64) MHz subcarrier spacing, 52 Sub-carrier set

• 48 data carriers and 4 pilots (center location not used)

– Preamble modified for MIMO• Compatible with 802.11a air-interface

– 1, 2, 3 and 4 TX antenna for high throughput modes– One TX Antenna mode for legacy STA support – PHY-MAC maximum efficiency of 60% assumed

• In AP-STA test, 100Mbps at MSDU 167 Mbps at PHY

Sept 2004


Slide 4


Submission

802.11n Rate Set Supported No. of TX Antennas

Modulation Type Transmit bits per channel use

Code Rate Info. Bytes per channel. use

PHY Info Rate (Mbps)

MAC Info Rate (Mbps) @60% of PHY Rate

4 BPSK 192 1/2 12 24 14.4

2/3 18 36 21.6

QPSK 384 1/2 24 48 28.8

8-PSK 576 1/2 36 72 43.2

16-QAM 768 1/2 48 96 57.6

32-QAM 960 1/2 60 120 72

64-QAM 1152 1/2 72 144 86.4

2/3 96 192 115.2

3 QPSK 288 1/2 18 36 21.6

2/3 24 48 28.8

16-QAM 576 1/2 36 72 43.2

2/3 48 96 57.6

64-QAM 864 1/2 56 112 67.2

2/3 72 144 86.4

2 BPSK 96 1/2 6 12 7.2

QPSK 192 1/2 12 24 14.4

8-PSK 288 1/2 18 36 21.6

16-QAM 384 1/2 24 48 28.8

32-QAM 480 1/2 30 60 36

64-QAM 576 1/2 36 72 43.2

2/3 48 96 57.6

Sept 2004


Slide 5


Submission

Proposed PHY Layer Block Diagram (Tx)

IFFT

IFFT

Prefix Digital-RF-PA

OFDMSymbol

Generator(frequency domain)

PreambleAttachment

&1:n OFDM

SymbolDemux

InsertPilots

PSK/QAMModulator

LDPCEncoder

MIMO LDPCBlock Formatter

Information bits

Prefix Digital-RF-PA

MIMOPreambles

PA = Rapp’s model, p=3

Inx = [x1 x2… xn]T

x1

xn

Sept 2004


Slide 6


Submission

Proposed PHY Layer Block Diagram (Rx)

FFT Remove P/fix

FFT Remove P/fix RF-Digital

RF-Digital

Prefix Timing/Channel Estimation/Symbol Timing/ Frequency/Phase Acquisition/Tracking

OFDMDemod

MAP Detector

LDPCDECODER

y1

ym

y = [y1… ym]T

ReconstructPSDU

Information bits

out

Channel Estimates

Sept 2004


Slide 7


Submission

Key Elements of the Physical Layer Proposal

• A family of high-performance FEC codes optimized for the application– Capable of decoding at information rate close to 200

Mbps with modest implementation complexity– Exceptional performance in fading channel at near 10-2

packet error rate– Flexibility to support short as well as long packets

without compromise in throughput at MAC layer

• An 802.11a/b/g compatible preamble design supports up to 4 Tx antennas

Sept 2004


Slide 8


Submission

Considerations for FEC Code Selection

• With their inherent parallel architecture, Low-Density Parity Check (LDPC) decoders are more suitable for high-speed operation than turbo decoders

• LDPC codes with block length equal to integer number of OFDM channel uses maximize efficiency by eliminating unnecessary padding or shortening of a code block

• At one (1) percent or higher block error rates, the performance gap between short and long block codes diminishes

• Longer codes are extremely inefficient for the transmission of short bursts or the last block of a long burst due to need of padding or shortening

• Short burst traffic cannot be ignored, as applications such as VoIP and video games are important

• Decoders for short LDPC codes are much simpler to implement than long LDPC codes

Sept 2004


Slide 9


Submission

Our FEC Choice

• A base LDPC code of block length 192 bits (4 x number of data carriers in an OFDM symbol)

• A simple means to extend block length with minimal performance compromises to any length in increment of 192 bits.

Sept 2004


Slide 10


Submission

LDPC Details

• Code rates of 1/2 and 2/3 are sufficient to cover a broad range of throughput due to various choice of modulation schemes such as QPSK, 8-PSK, 16-QAM, 32-QAM and 64-QAM.

• Base LDPC codes have a coded block length of 192 bits with the following parity check matrix format which ensures simple encoding

][ )()()()( knxknxkknxnkn BAH

1

1

1

1

1

1

1

1

1

1

1

B 00

where

Sept 2004


Slide 11


Submission

LDPC Details• The A sub-matrix has a constant column weight of 3.

• The small column weight ensures simpler decoding while performance is not sacrificed on the fading channel.

• Larger block sizes are supported by simply concatenating base LDPC codes and adding one extra base block of parity check on select LDPC bits.

x x x x x x x x x x x x x





:::

:::

:::

:::

LDPC Block 1

LDPC Block 2

LDPC Block 3

LDPC Block m

Parity Check Block

Pa

rity

che

ck o

n k

bits

k < or = m

Sept 2004


Slide 12


Submission

• We base our approach on the 802.11a OFDM Specifications – There are 53 frequency bins in 802.11a OFDM

• Indexed -26, -25, …-1, 0, 1 … 25 and 26. • The zero index (frequency location) is not used.

– -21, -7, 7 and 21 are used as Pilots during data transmission • Modulated by127 bit long PN code (x7 + x4 + 1) on the ‘1st’ Antenna• Use the same frequency set on each of the TX Antennas• Use different phase of the 127 bit PN (quasi-orthogonal) on each of the other Antennas

– 48 remaining bins are used for data transmission• Each TX antenna uses the same 48 sub-carrier set but with different data stream

• The transmission commences with an 802.11a specified preamble called the PLCP preamble

– 8 usec ‘short’ preamble with only 12 sub-carriers active– 8 usec ‘long’ preamble all sub-carriers active per a specified 52 bit sequence – Short preamble empty bins are used by secondary antennas 4 TX supported– 52 bits of the Long preamble are transmitted sequentially over the TX antenna set

Preamble/ Pilot Approach to HNS PHY Proposal

Sept 2004


Slide 13


Submission

(-26) (26) Δf 0.3125 MHz

1 1 -1 -1 1 1 . . . . . . . . .

Proposed: Long Preamble Sequence Spread Sequentially over the Four TX Antennas

Proposed: Short Training Preamble (First 8 usec) over one ‘First’ and Three ‘Other’ Antennas

1+ j 1+ j -1- j -1- j 1+ j 1+ j 1+ j 1+ j -1- j -1- j -1- j 1+ j

Prea

mbl

e D

urat

ion

= 8

use

cPr

eam

ble

dur

atio

n =

8 u

sec

1.0

1+ j 1+ j -1- j -1- j 1+ j 1+ j 1+ j 1+ j -1- j -1- j -1- j 1+ j

Prea

mbl

e D

urat

ion

= 8

use

c

IEEE 802.11a Standard Short Training Preamble (i.e. first 8 usec) from one TX Antenna - 26 + 26

First Antena (s0) Other Antennas (s1, s2 and s3)

Δf

Δf

. . . . . . -1 1 1 1 1 L-26,26 per section 17.3.3 Std 802.11a -1999

Preamble Approach for Multiple TX Antennas

Sept 2004


Slide 14


Submission

Simulation Conditions • 2,3 and 4 TX antenna cases simulated• AWGN with recommended channel matrices

simulated• NLOS Model for B, D and E used in simulation• Florescent light effects included for Model D&E• Antenna Spacing of half-wavelength used

Sept 2004


Slide 15


Submission

-30 -20 -10 0 10 20 30

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

Frequency in MHz

Rel

ativ

e P

ower

Spe

ctru

m D

ensi

ty in

dB

-30 -20 -10 0 10 20 30

-50

-45

-40

-35

-30

-25

-20

-15

-10

-5

0

Frequency in MHzR

elat

ive

Po

we

r Sp

ectru

m D

ens

ity in

dB

OFDM Signal 16-QAM after Non-linear Amplifier IBO = 3 dBOFDM Signal 16-QAM after Non-linear Amplifier IBO = 8 dB

Transmit Spectrum of the OFDM Signal Through PA Model

• Fully compliant with spectral mask • Essentially the same spectral density for 64-QAM

Sept 2004


Slide 16


Submission

Simulation Methodology• Coding and BB TX module

– Information bits encoded into 192 bit LDPC code blocks– LDPC code blocks extended to longer code blocks as described

previously – generate PSK/QAM modulation symbols

• OFDM and Channel Model – Arranges into transmission vector for 2, 3 or 4 TX antennas – Converts modulation symbol stream into OFDM symbols with

cyclic prefix, 4 usec/OFDM Symbol– Runs through channel model– Detects OFDM signals on each of the Rx antenna – Delivers demodulated samples from each Rx antenna to MAP

detector

Sept 2004


Slide 17


Submission

Performance for Channel Model B

1.0E-03

1.0E-02

1.0E-01

1.0E+00

2.0 6.0 10.0 14.0 18.0 22.0 26.0 30.0Es/No (dB)

Pa

cke

t E

rro

r R

ate

64QAM, R=2/3

4x4, 8PSK R=1/2

QPSKR=1/2

3x3, 16QAM R=2/3

16QAMR=1/2

3x3, QPSK R=2/3

4x4

2x2

4x4

2x2

4x4

2x2

3x3

Sept 2004


Slide 18


Submission

Performance for Channel Model D

1.0E-03

1.0E-02

1.0E-01

1.0E+00

2.0 6.0 10.0 14.0 18.0 22.0 26.0 Es/No (dB)

Pac

ket

Err

or

Rat

e

64QAMR=2/3

4x4, 8PSK R=1/2

QPSKR=1/2

3x3, 16QAM R=2/3

16QAMR=1/2

3x3, QPSK R=2/3

2x2

2x22x2

4x44x4

4x4

3x3

Sept 2004


Slide 19


Submission

Performance for Channel Model E

1.0E-03

1.0E-02

1.0E-01

1.0E+00

2.0 6.0 10.0 14.0 18.0 22.0 26.0 Es/No (dB)

Pac

ket

Err

or

Rat

e

4x4, 64QAM R=2/3

4x4, 8PSK R=1/2

QPSKR=1/2

3x3, 16QAM R=2/3

16QAMR=1/2

3x3, QPSK R=2/3

4x4

4x44x4

2x2

2x2

2x2

3x3

Sept 2004


Slide 20


Submission

1.0E-03

1.0E-02

1.0E-01

1.0E+00

2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 Es/No (dB)

Pac

ket

Err

or

Rat

e

AWGN, 1x1, 2x2, 3x3, 4x4

8PSK,R=1/2QPSK,R=1/2 16QAM,R=2/3

16QAM,R=1/2

QPSK,R=2/3

64QAM,R=2/3

AWGN Channel Performance

Sept 2004


Slide 21


Submission

Channel Model B

1.0E-03

1.0E-02

1.0E-01

1.0E+00

6.0 7.0 8.0 9.0 10.0 11.0 12.0Es/No (dB)

Pac

ket

Err

or

Rat

e

4x4, QPSK R=1/2

OneLDPC Block

Append a parity blockfor every 10 LDPC block

Sept 2004


Slide 22


Submission

Channel Model D

1.0E-04

1.0E-03

1.0E-02

1.0E-01

1.0E+00

4.0 5.0 6.0 7.0 8.0 9.0 10.0 Es/No (dB)

Pac

ket

Err

or

Rat

e

4x4, QPSK R=1/2

OneLDPCblock

Append a parity blockfor every 10 LDPC block

Sept 2004


Slide 23


Submission

Channel Model E

1.0E-03

1.0E-02

1.0E-01

1.0E+00

4.0 5.0 6.0 7.0 8.0 9.0 10.0 Es/No (dB)

Pac

ket

Err

or

Rat

e

4x4, QPSK R=1/2

OneLDPCblock Append a parity block

for every 10 LDPC block

Sept 2004


Slide 24


Submission

Required Es/No vs PHY Data Speed

5

10

15

20

25

30

0 50 100 150 200

Info Speed (Mpbs)

Es/

No

(dB

)4x4 B 4x4 D 4x4 E 3x3 B 3x3 D

3x3 E 2x2 B 2x2 D 2x2 E

Sept 2004


Slide 25


Submission

Conclusion• All the design requirements of 802.11n met with the

PHY partial proposal– FEC and MIMO alone achieve the goal– Compatible with current MAC, expect to be compatible

with any MAC proposal.– In the interest of best overall proposal, PHY needs to be

evaluated separately and then combined with the best MAC.

• Capable of supporting both 1x and 2x 20MHz approaches.

• Extremely simple to implement• Highly efficient due to its flexible construction

technique

Documents

Doc.: IEEE 802.11-04/0abcr0 Submission Sept 2004 Mustafa Eroz, Hughes Network SystemsSlide 1 HNS Proposal for 802.11n Physical Layer Mustafa Eroz, Feng-Wen