1. HNS Proposal for 802.11n Physical Layer
doc.: IEEE /0abcr0
Sept 2004
HNS Proposal for n Physical Layer
Mustafa Eroz, Feng-Wen Sun, & Lin-Nan Lee
Hughes Network Systems
11717 Exploration Lane
Germantown, MD 20876
Mustafa Eroz, Hughes Network Systems
Mustafa Eroz, Hughes Network Systems

2. Proposal Topics PHY and Air Interface Description
Sept 2004
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
Mustafa Eroz, Hughes Network Systems

3. Sept 2004
PHY and Air Interface
The air interface is built upon IEEE a (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 a 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
Mustafa Eroz, Hughes Network Systems

4. 802.11n Rate Set Supported Sept 2004
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 of PHY Rate 4
BPSK
192
1/2 12 24
14.4
2/3 18 36
21.6
QPSK
384 48
28.8
8-PSK
576 72
43.2
16-QAM
768 96
57.6
32-QAM
960 60
120
64-QAM
1152
144
86.4
115.2 3
288
864 56
112
67.2 2 6
7.2
480 30
Mustafa Eroz, Hughes Network Systems

5. Proposed PHY Layer Block Diagram (Tx)
Sept 2004
Proposed PHY Layer Block Diagram (Tx)
Information bits In
x = [x1 x2… xn]T
PA = Rapp’s model, p=3
MIMO LDPC
Block Formatter
MIMO
Preambles
Preamble
Attachment
&
1:n OFDM
Symbol
Demux
IFFT
Prefix
Digital-RF-PA x1
LDPC
Encoder
Insert
Pilots
IFFT
Prefix
Digital-RF-PA
PSK/QAM
Modulator
OFDM
Symbol
Generator
(frequency domain) xn
Mustafa Eroz, Hughes Network Systems

6. Proposed PHY Layer Block Diagram (Rx)
Sept 2004
Proposed PHY Layer Block Diagram (Rx)
y = [y1… ym]T
OFDM
Demod
FFT
Remove P/fix
RF-Digital
MAP
Detector
LDPC
DECODER y1
Reconstruct
PSDU
FFT
Remove P/fix
RF-Digital ym
out
Prefix Timing/Channel Estimation/Symbol Timing
/ Frequency/Phase Acquisition/Tracking
Information bits
Channel Estimates
Mustafa Eroz, Hughes Network Systems

7. Key Elements of the Physical Layer Proposal
Sept 2004
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 a/b/g compatible preamble design supports up to 4 Tx antennas
Mustafa Eroz, Hughes Network Systems

8. Considerations for FEC Code Selection
Sept 2004
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
Mustafa Eroz, Hughes Network Systems

9. Sept 2004
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.
Mustafa Eroz, Hughes Network Systems

10. Sept 2004
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
where é 1 ù ê ú 1 1 ê ú B ê 1 1 ú = ê ú ê 1 1 ú ê ú 1 1 ê ú ë ê 1 1 ú û
Mustafa Eroz, Hughes Network Systems

11. LDPC Details The A sub-matrix has a constant column weight of 3.
Sept 2004
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
x x x x x x x x x x x x x
LDPC Block 2
x x x x x x x x x x x x x
LDPC Block 3
Parity check on k bits : : : :
k < or = m : : : : : : : :
x x x x x x x x x x x x x
LDPC Block m
x x x x x x x x x x x x x
Parity Check Block
Mustafa Eroz, Hughes Network Systems

12. Preamble/ Pilot Approach to HNS PHY Proposal
Sept 2004
Preamble/ Pilot Approach to HNS PHY Proposal
We base our approach on the a OFDM Specifications
There are 53 frequency bins in a 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 a 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
Mustafa Eroz, Hughes Network Systems

13. Preamble Approach for Multiple TX Antennas
Sept 2004
(-26)
(26) Δf
MHz
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
Preamble Duration = 8 usec
Preamble duration = 8 usec
1.0
IEEE a Standard Short Training Preamble (i.e. first 8 usec) from one TX Antenna
- 26
+ 26
First Antena (s0)
Other Antennas (s1, s2 and s3)
L-26,26 per section Std a -1999
Preamble Approach for Multiple TX Antennas
Mustafa Eroz, Hughes Network Systems

14. Simulation Conditions
Sept 2004
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
Mustafa Eroz, Hughes Network Systems

15. Transmit Spectrum of the OFDM Signal Through PA Model
Sept 2004
Transmit Spectrum of the OFDM Signal Through PA Model
OFDM Signal 16-QAM after Non-linear Amplifier IBO = 8 dB
OFDM Signal 16-QAM after Non-linear Amplifier IBO = 3 dB
Fully compliant with spectral mask
Essentially the same spectral density for 64-QAM
Mustafa Eroz, Hughes Network Systems

16. Simulation Methodology
Sept 2004
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
Mustafa Eroz, Hughes Network Systems

17. Performance for Channel Model B
Sept 2004
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
30.0
Es/No (dB)
Packet Error Rate
64QAM,
R=2/3
4x4, 8PSK
R=1/2
QPSK
3x3, 16QAM
16QAM
3x3, QPSK
4x4
2x2
3x3
Mustafa Eroz, Hughes Network Systems

18. Performance for Channel Model D
Sept 2004
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)
Packet Error Rate
64QAM
R=2/3
4x4, 8PSK
R=1/2
QPSK
3x3, 16QAM
16QAM
3x3, QPSK
2x2
4x4
3x3
Mustafa Eroz, Hughes Network Systems

19. Performance for Channel Model E
Sept 2004
Performance for Channel Model E
1.0E+00
3x3, QPSK
QPSK
R=2/3
R=1/2
4x4
16QAM
4x4
R=1/2
1.0E-01
4x4
Packet Error Rate
2x2
2x2
1.0E-02
4x4, 8PSK
R=1/2
3x3, 16QAM
4x4, 64QAM
R=2/3
R=2/3
3x3
1.0E-03
2x2
2.0
6.0
10.0
14.0
18.0
22.0
26.0
Es/No (dB)
Mustafa Eroz, Hughes Network Systems

20. AWGN Channel Performance
Sept 2004
AWGN Channel Performance
Mustafa Eroz, Hughes Network Systems

21. 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
Sept 2004
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
12.0
Es/No (dB)
Packet Error Rate
4x4, QPSK
R=1/2
One
LDPC
Block
Append a parity block
for every 10 LDPC block
Mustafa Eroz, Hughes Network Systems

22. Channel Model D 1.0E+00 1.0E-01 Packet Error Rate 1.0E-02 1.0E-03
Sept 2004
Channel Model D
1.0E+00
4x4, QPSK
R=1/2
One
LDPC
block
1.0E-01
Append a parity block
for every 10 LDPC block
Packet Error Rate
1.0E-02
1.0E-03
1.0E-04
4.0
5.0
6.0
7.0
8.0
9.0
10.0
Es/No (dB)
Mustafa Eroz, Hughes Network Systems

23. 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
Sept 2004
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)
Packet Error Rate
4x4, QPSK
R=1/2
One
LDPC
block
Append a parity block
for every 10 LDPC block
Mustafa Eroz, Hughes Network Systems

24. Required Es/No vs PHY Data Speed
Sept 2004
Required Es/No vs PHY Data Speed
Mustafa Eroz, Hughes Network Systems

25. Sept 2004
Conclusion
All the design requirements of n 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
Mustafa Eroz, Hughes Network Systems