1. Inprocomm PHY Proposal for IEEE 802.11n: MASSDIC-OFDM
Aug 2004
Inprocomm PHY Proposal for IEEE n: MASSDIC-OFDM
Kim Wu, Chao-Yu Chen, Tsung-Yu Wu,
Racy Cheng, Chi-chao Chao, Mao-Ching Chiu
Inprocomm, Inc.
Please refer to for technical specifications and for description of the LDPCC parity check matrices.
Kim Wu et al., MASSDIC-OFDM

2. Assumptions in the proposal Main features of the proposal
Aug 2004
Content
Assumptions in the proposal
Main features of the proposal
Proposed Multiple-Antenna Signal Space DIversity Coded OFDM (MASSDIC-OFDM) PHY System architecture
Modulation, precoding, FEC, proposed receiver structure
PLCP Frame format
Preamble
FEC Coding
Compatibility to a
Simulation Results
Summary
Kim Wu et al., MASSDIC-OFDM

3. Assumptions in the proposal
Aug 2004
Assumptions in the proposal
The proposal is targeted at the physical layer
A MAC efficiency of 60% is assumed
To reach the 100 Mbps MAC Goodput, a minimum of 167 Mbps is required.
The proposal shall have another portion of MAC enhancement proposal. It can be amended later.
Kim Wu et al., MASSDIC-OFDM

4. Main features of the proposal 1/3
Aug 2004
Main features of the proposal 1/3
This proposal inherits the good features of a OFDM standard
Spectrally efficient, robust against narrowband interference
Low complexity in channel equalization
No ISI and intercarrier interference (ICI) if channel max delay is less than the guard interval
Good performance by bit-interleaved convolutional coded modulation
This proposal uses MIMO (2x2 Mandatory) architecture to double the capacity. 4x4 and 3x3 configurations are optional
This proposal uses variable guard intervals to optimize the data rate against different channel delay spread
The operation bandwidth is 20 MHz.
Kim Wu et al., MASSDIC-OFDM

5. Main features of the proposal 2/3
Aug 2004
Main features of the proposal 2/3
This proposal uses 256-QAM to boost bandwidth efficiency
The number of subcarriers in an OFDM symbol is increased from 64 to 128 to gain guard interval efficiency.
This proposal explores the signal and space diversity without sacrificing BW via linear constellation precoding technique (LCP) (optional)
With low rate (e.g. 3/4) FEC, OFDM is shown to be inferior to single-carrier transmission due to loss of multipath diversity
This problem is resolved by artificially making ICI among independent subcarriers
The LCP is a kind of signal-space diversity coding
Only PHY data rates more than 53 Mbps are newly defined
For HT devices transmitting legacy data rates, space-time block coding (STBC) schemes are used to enhance system performance.
Kim Wu et al., MASSDIC-OFDM

6. Main features of the proposal 3/3
Aug 2004
Main features of the proposal 3/3
No more overhead is needed for the PHY header relative to legacy frame format
New preamble structures are designed to minimize the overhead without sacrificing performance.
Only one OFDM symbol time interval is used for channel estimation
Long training symbols transmit higher power than other fields.
The maximum data length is extended from 4096 bytes to bytes.
This proposal uses modern powerful error control code: extended irregular repeat-accumulated (eIRA) low density parity check (LDPC) code to improve performance
Coding rates of 1/2, 2/3, 3/4 are separately designed with codeword length 2667 to optimize performance.
A new scheme to shorten codewords with hybrid code rate combination is proposed.
Kim Wu et al., MASSDIC-OFDM

7. Aug 2004
Proposed PHY: Multiple-Antenna Signal Space DIversity Coded OFDM (MASSDIC-OFDM)
Kim Wu et al., MASSDIC-OFDM

8. MASSDIC-OFDM Tx Architecture for 2x2 configuration
Aug 2004
MASSDIC-OFDM Tx Architecture for 2x2 configuration
Linear constellation Precoding Q
QAM mapping
Scrambler
FEC p RF
Nc-IFFT
L-CP
Subcarrier grouping
Spatial Processing
Nc-IFFT
L-CP RF
Nt=2 ( 3, 4 optional), # of Tx antennas
Nc=128, the number of subcarriers per antenna
p: bit level interleaver (optional)
Q : a 4x4 unitary matrix
L-CP: 1200 or 800 ms cyclic prefix
Spatial processing: spatial multiplexing or space time block coding
FEC: eIRA LDPC code (2676, 2007), (2676, 1784), (2676,1338)
Kim Wu et al., MASSDIC-OFDM

9. Linear constellation precoding matrix Q - 4x4 case (optional)
Aug 2004
Linear constellation precoding matrix Q - 4x4 case (optional)
Kim Wu et al., MASSDIC-OFDM

10. Subcarrier Grouping in LCP for 2x2 and 3x3
Aug 2004
Subcarrier Grouping in LCP for 2x2 and 3x3
Group 1
Group 50 …
Antenna 1
Antenna 2 d0
d49
d50
d99
d100
d124
d125
d174
NT=2
d175
d199
Group 1
Group 75 …
Antenna 1
Antenna 2 d0
d74
d75
d99
d100
d150
d149
d199
d200
d224
d225
Antenna 3
NT=3
d299
Kim Wu et al., MASSDIC-OFDM

11. Subcarrier Grouping in LCP for 4x4
Aug 2004
Subcarrier Grouping in LCP for 4x4 …
Group 2
Group 100
Antenna 2
Antenna 4
d149
d150
d199
d300
d324
d325
d374
d375
d399
NT=4
Group 1
Group 99
Antenna 1
Antenna 3
d49
d50
d99
d200
d224
d225
d274
d275
d299 d0
d100
Kim Wu et al., MASSDIC-OFDM

12. Performance improvement with LCP (ML-soft output sphere decoding)
Aug 2004
Performance improvement with LCP (ML-soft output sphere decoding)
Kim Wu et al., MASSDIC-OFDM

13. Aug 2004
System Parameters
Kim Wu et al., MASSDIC-OFDM

14. System Parameters Nt=2 (Other data rates are the same as those in 802
System Parameters Nt=2 (Other data rates are the same as those in a)
Aug 2004
MAC Goodput Mbps
--- 32 42 47 63 75 89
100
Info.Data Rate Mbps *X 53 70 79
105
125
148
167
QAM Constellation 16 64
256
FFT Size
128
Coding Rate R
1/2 (CC)
1/2
2/3
3/4
Pilot Tones
Data Tones
Info. Length ms
6.4
Cyclic Prefix ms
1200
800
Null Tones 12
Symbol Length ms
7.6
7.2
Channel Bit Rate Mbps
158
222
* Rate X is dedicated for the header. The K=7, CC encoded data is 16-QAM modulated and inserted into the pilot tones of the first OFDM symbol of the first 2 antennas.
Kim Wu et al., MASSDIC-OFDM

15. System Parameters Nt=3 (Optional)
Aug 2004
System Parameters Nt=3 (Optional)
MAC Goodput Mbps 48 63 71 95
113
133
150
Info.Data Rate Mbps 80
105
118
158
188
222
250
QAM Constellation 16 64
256
FFT Size
128
Coding Rate R
1/2
2/3
3/4
Pilot Tones
Data Tones
100
Info. Length ms
6.4
Cyclic Prefix ms
1200
800
Null Tones 12
Symbol Length ms
7.6
7.2
Channel Bit Rate Mbps
159
237
333
Kim Wu et al., MASSDIC-OFDM

16. System Parameters Nt=4 (Optional)
Aug 2004
System Parameters Nt=4 (Optional)
MAC Goodput 64 84 95
126
150
178
200
Info.Data Rate Mbps
106
140
158
211
250
296
333
QAM Constellation 16
256
FFT Size
128
Coding Rate R
1/2
2/3
3/4
Pilot Tones
Data Tones
100
Info. Length ms
6.4
Cyclic Prefix ms
1200
800
Null Tones 12
Symbol Length ms
7.6
7.2
Channel Bit Rate Mbps
159
316
444
Kim Wu et al., MASSDIC-OFDM

17. Proposed Receiver Structure for 2x2 case
Aug 2004
Proposed Receiver Structure for 2x2 case RF
DU1
MIMO Equalization (MMSE, DEF, ML-S)
LCP-decoding (ML-S) RF
DU2
Information
bits
De-Scrambler
FEC-decoder
QAM Demapping
De-int.
Demodulation Unit ( DU )
Channel
Estimation,
Equalization
Sym.
Detection CP
Remove
FFT
Synch.
Kim Wu et al., MASSDIC-OFDM

18. Aug 2004
PLCP Frame format
Kim Wu et al., MASSDIC-OFDM

19. The FCS only checks for payload.
Aug 2004
The FCS only checks for payload.
First OFDM symbol
PLCP preamble
PHY
Header
Repeated PHY Header
Pad
bits
Payload: bytes
FCS
CRC-16
Data field
K=7, R=1/2 CC encoded and inserted into the pilot tones of the first OFDM Symbol of the fist two antennas.
Rate
6 bits
Reserved
2 bits
LCP
1 bit
Interleaver
1 bit
Length
16 bits
Service
16 bits
HCS
16 bits
Tail
6 bits
Kim Wu et al., MASSDIC-OFDM

20. Repeated Header Using pad bits to convey a repeated header information
Aug 2004
Repeated Header
Using pad bits to convey a repeated header information
If the number of pad bits NPAD > , then a 16-QAM modulated repeated header is sequentially inserted into the following 32 data subcarriers
{d53, d59, d65, d71, d78, d84, d90, d96, d3, d9, d15, d21, d28, d34, d40, d46} of the 2nd antenna,
and {d53, d59, d65, d71, d78, d84, d90, d96, d3, d9, d15, d21, d28, d34, d40, d46} of the 1st antenna.
Then the number of pad bits is recalculated
Kim Wu et al., MASSDIC-OFDM

21. Operation for lower transmission rates
Aug 2004
Operation for lower transmission rates
For n Tx-Rx in 2x2 case operating in the lower transmission rate mode (6~54Mbps), the mapped information is encoded as complex 2x2 Alamouti space-time code in the 2 Tx antennas
For n Tx-Rx in 4x4 case, the mapped information is encoded as complex space-time code in the 4 Tx antennas
For n Tx-Rx in 3x3 case, the third Tx antenna is turned off while the others are the same as the case in 2x2
Kim Wu et al., MASSDIC-OFDM

22. PLCP Preamble N mode preamble structure LN mode preamble structure
Aug 2004
PLCP Preamble
N mode preamble structure
An access mode that is intended for a scenario that all devices are n.
LN mode preamble structure
An access mode that is intended for a scenario that some of the devices are legacy and others are n.
Kim Wu et al., MASSDIC-OFDM

23. N mode Preamble structure 2X2 case
Aug 2004
N mode Preamble structure 2X2 case
5.6 ms
2.4 ms X X X X X X -X -X -X -X Y Y Y Y Y Y -Y -Y -Y -Y
TX 1 S1 CP L1
Data 1
TX 2 S2 CP L2
Data 2
1.6 ms
6.4 ms
Si’s: Short Training Symbols, X is the same as a, Y is orthogonal to X.
Li’s: Long Training Symbols
CP: Cyclic Prefix
Kim Wu et al., MASSDIC-OFDM

24. Aug 2004
Kim Wu et al., MASSDIC-OFDM

25. Take the first 16 samples of s1 and s2, namely u1 and u2.
Aug 2004
Generate time domain signals s1 and s2 from frequency domain signals S1 and S2 respectively via 128-IFFT.
Take the first 16 samples of s1 and s2, namely u1 and u2.
Get unity v1 and v2 via Gram-Schmidt procedure from u1 and u2.
Set and
Kim Wu et al., MASSDIC-OFDM
and

26. N mode Preamble structure 3X3 case
Aug 2004
N mode Preamble structure 3X3 case
5.6 ms
2.4 ms X X X X X X -X -X -X -X Y Y Y Y Y Y -Y -Y -Y -Y Z Z Z Z Z Z -Z -Z -Z -Z
TX 1 S1 CP L1
Data 1
TX 2 S2 CP L2
Data 2
TX 3 S3 CP L3
Data 3
1.6 ms
6.4 ms
X ,Y, Z orthogonal.
Kim Wu et al., MASSDIC-OFDM

27. N mode Preamble structure 4X4 case
Aug 2004
N mode Preamble structure 4X4 case
5.6 ms
2.4 ms X X X X X X -X -X -X -X Y Y Y Y Y Y -Y -Y -Y -Y Z Z Z Z Z Z -Z -Z -Z -Z W W W W W W -X -W -W -W
TX 1 S1 CP L1
Data 1 S2 CP L2
Data 2 S3 CP L3
Data 3
TX 2 S4 CP L4
Data 4
1.6 ms
6.4 ms
X ,Y, Z W orthogonal.
Kim Wu et al., MASSDIC-OFDM

28. More on the Long Training Symbols in the frequency domain
Aug 2004
More on the Long Training Symbols in the frequency domain
with
The long training symbols are designed such that the Mean squared error (MSE) is minimized when ML-estimation is used
The long training symbols Li’s have the following properties:
The Li’s are orthogonal
The Li’s are nearly circular-shift orthogonal
Low PAPR
Kim Wu et al., MASSDIC-OFDM

29. Tone Interleaving for LTSs ( 2x2 case)
Aug 2004
Tone Interleaving for LTSs ( 2x2 case)
Kim Wu et al., MASSDIC-OFDM

30. PLCP Preamble N mode preamble structure LN mode preamble structure
Aug 2004
PLCP Preamble
N mode preamble structure
An access mode that is intended for a scenario that all devices are n.
LN mode preamble structure
An access mode that is intended for a scenario that some of the devices are legacy and others are n.
Kim Wu et al., MASSDIC-OFDM

31. LN mode Preamble structure 2X2 case
Aug 2004
LN mode Preamble structure 2X2 case
L-STS: The legacy short training symbols LTSs are the same as those in N mode
Kim Wu et al., MASSDIC-OFDM

32. LN mode Preamble structure 3X3 case
Aug 2004
LN mode Preamble structure 3X3 case
LTS1 is times the LTS1 in N mode. LTS2 and LTS3 are 800ns and 1200ns cyclic shifts of LTS1 respectively.
Kim Wu et al., MASSDIC-OFDM

33. LN mode Preamble structure 4X4 case
Aug 2004
LN mode Preamble structure 4X4 case
LTSs are the same as those in N mode
Kim Wu et al., MASSDIC-OFDM

34. Use the same scrambler as 802.11a
Aug 2004
Data Scrambler
Use the same scrambler as a
Kim Wu et al., MASSDIC-OFDM

35. Bit-level Interleaver for 2x2 case
Aug 2004
Bit-level Interleaver for 2x2 case
Kim Wu et al., MASSDIC-OFDM

36. Details of the Interleaver
Aug 2004
Details of the Interleaver
Denote by k the index before permutation and j the index after permutation. ( : the number of coded bits per OFDM symbol)
First permutation:
Second permutation:
where .
is obtained by concatenating two OFDM symbols that have been bit-interleaved by the above interleaver.
Kim Wu et al., MASSDIC-OFDM

37. Aug 2004
FEC Coding
Using extended irregular repeat-accumulate (eIRA) code (a kind of LDPC code)
For R=3/4: (2676, 2007)
For R=2/3: (2676, 1784)
For R=1/2: (2676,1338)
For information length other than 2007 (1784 or 1338) use code shortening
Header is CC encoded with R=1/2 and K=7 (the same as a)
Kim Wu et al., MASSDIC-OFDM

38. Packet size accommodation with concatenation and shortening
Aug 2004
Packet size accommodation with concatenation and shortening
2007 (1784, 1338) bit data field
669 (892, 1338) bit parity
2676 bit codeword
For long packets, codewords are concatenated
669 (892, 1338)
bit parity
2676-N bit zero pad
N bit data field
For short blocks, codeword shortening is adapted.
The zero pad will not be transmitted.
Kim Wu et al., MASSDIC-OFDM

39. Details of the proposed FEC code
Aug 2004
Details of the proposed FEC code
In general, the parity check matrix H of an (n,k) eIRA code could be written as the following form :
, where is a random spare matrix,
is the inverse of a lower-triangular
matrix.
Kim Wu et al., MASSDIC-OFDM

40. Then, we put 1’s on randomly and avoid the length-4 cycle.
Aug 2004
We decide the column and row weight distribution of through Gaussian Approximation.
Then, we put 1’s on randomly and avoid the length-4 cycle.
Kim Wu et al., MASSDIC-OFDM

41. The generator matrix is in the format of
Aug 2004
The generator matrix is in the format of
Usually, it costs large complexity to calculate
. However, the which is a full upper-triangle matrix can be implemented by a differential encoder
Kim Wu et al., MASSDIC-OFDM

42. Aug 2004
FEC encoder structure
Kim Wu et al., MASSDIC-OFDM

43. Aug 2004
Packet Encoding
For a short block, it is not efficient if we encode it in the original code rate. Hence, we choose higher code rate to decrease the number of parity check bits.
If the information block size is smaller than , we change the original code rate to a higher one according to the following table.
The original code rate
The changed code rate
R=1/2
850
R=2/3
480
R=3/4
1000
The threshold
( )
Kim Wu et al., MASSDIC-OFDM

44. Aug 2004
Decoder Structure
For a LDPC code, it can be described as a Tanner graph with variable nodes , check nodes and edges.
Kim Wu et al., MASSDIC-OFDM

45. Each check node represents a parity check equation.
Aug 2004
Each check node represents a parity check equation.
Check node j is connected to a variable node i if and only if the element hji in the parity check matrix H is a 1
Through the Tanner graph, belief propagation algorithm is used to decode the eIRA code.
Kim Wu et al., MASSDIC-OFDM

46. Codec Complexity Analysis
Aug 2004
Codec Complexity Analysis
There are two kinds of operations in the decoding process: addition and check node operation (*).
The two operations have comparable complexity.
The degree of a node means the number of edges connected to the node.
We define and respectively as the number of variable and check nodes of degree ; and as the maximum degree of variable and check nodes. *:
Kim Wu et al., MASSDIC-OFDM

47. check node operations in one iteration.
Aug 2004
There are
additions and
check node operations in one iteration.
Kim Wu et al., MASSDIC-OFDM

48. The weight distributions of column and row are:
Aug 2004
The weight distributions of column and row are:
Code Rate
Nv(i)
Nc(i)
R = 1 / 2
i: 1 2 4 5 6 7 1
1337
656
682
657
681
R = 2 / 3 3 9 10
891
453
1331
454
438
R = 3 / 4 11 12
668
1562
445
225
444
Kim Wu et al., MASSDIC-OFDM

49. Aug 2004
In our eIRA code, the numbers of operations per iteration are as follows:
Code Rate
addition
chk_op
Total
R = 1 / 2
15478
39603
55081
R = 2 / 3
12007
63642
75649
R = 3 / 4
8246
75555
83801
Kim Wu et al., MASSDIC-OFDM

50. Ratio to eIRA per iteration
Aug 2004
The Viterbi decoding complexity for Convolutional code (802.11a) with code word length 2676
Code rate
Addition
Ratio to eIRA per iteration
R = 1 / 2
256896
4.6643
R = 2 / 3
342528
4.5276
R = 3 / 4
385344
4.5984
(*): Here, we ignore the calculation of branch metric and the memory trace-back process.
And, we assume that the complexity of comparing is equal to that of addition.
Kim Wu et al., MASSDIC-OFDM

51. Aug 2004
Compatibility to a
The proposed n is compatible to a by defining the same PHY and MAC as that of a in low data rate mode (6Mbps~54Mbps mode).
A n device can distinguish between a and n packets by detecting different format of packet preambles.
A Legacy device can recognize the packet from n devices in LN mode.
Upon detection of a packets, the n device turns to operate in the a mode.
Kim Wu et al., MASSDIC-OFDM

52. Aug 2004
Simulation Results
PER vs. SNR performance for fading channel model channel B, C, D, E and AWGN channel.
Kim Wu et al., MASSDIC-OFDM

53. 2X2 MIMO AWGN Channel PER vs. SNR for Different Data Rates
Aug 2004
2X2 MIMO AWGN Channel PER vs. SNR for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

54. 2X2 MIMO Channel B PER vs. SNR for Different Data Rates
Aug 2004
2X2 MIMO Channel B PER vs. SNR for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

55. 2X2 MIMO Channel C PER vs. SNR for Different Data Rates
Aug 2004
2X2 MIMO Channel C PER vs. SNR for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

56. 2X2 MIMO Channel D PER vs. SNR for Different Data Rates
Aug 2004
2X2 MIMO Channel D PER vs. SNR for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

57. 2X2 MIMO Channel E PER vs. SNR for Different Data Rates
Aug 2004
2X2 MIMO Channel E PER vs. SNR for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

58. Complexity relative to 802.11a
Aug 2004
Complexity relative to a
802.11n 167Mbps
Ratio to a
802.11n 54Mbps
802.11a 54Mbps
#multipliers for Equalization
12.37
4 (MMSE receiver for Nt=2) 1
#multipliers for Equalization with LCP
(Sphere decoding for LCP)
791.68
4*4^3=256(the size of LP is 4x4; the complexity of SD is 4^3)
#addition for FEC(R=1/2)
6.65
2.15 ( average 10 iterations when per<0.1)
1(viterbi decoder)
#addition for
FEC(R=2/3)
6.83
2.21 (average 10 iterations when per<0.1)
FEC(R=3/4)
6.71
2.17 (average 10 iterations when per<0.1)
#multipliers for FFT
7.22
128log(128)/64log(64)
=2.33
Kim Wu et al., MASSDIC-OFDM

59. Summary A PHY proposal MASSDIC-OFDM is with several unique features
Aug 2004
Summary
A PHY proposal MASSDIC-OFDM is with several unique features
Efficient preamble structure
Efficient Convey of Header(s)
Optional Signal Space diversity coding (LCP)
Advanced eIRA LDPCC (linear encoding complexity)
Efficient block shortening
The complexity is estimated and compared to that of a 54Mbps
Please refer to /r0 for technical specifications and /r0 for details of the LDPCC parity check matrix.
Kim Wu et al., MASSDIC-OFDM

60. Aug 2004
Backup Slides
Kim Wu et al., MASSDIC-OFDM

61. 2X2 MIMO AWGN Channel PER vs. Eb/No for Different Data Rates
Aug 2004
2X2 MIMO AWGN Channel PER vs. Eb/No for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

62. 2X2 MIMO Channel B PER vs. Eb/No for Different Data Rates
Aug 2004
2X2 MIMO Channel B PER vs. Eb/No for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

63. 2X2 MIMO Channel C PER vs. Eb/No for Different Data Rates
Aug 2004
2X2 MIMO Channel C PER vs. Eb/No for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

64. 2X2 MIMO Channel D PER vs. Eb/No for Different Data Rates
Aug 2004
2X2 MIMO Channel D PER vs. Eb/No for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

65. 2X2 MIMO Channel E PER vs. Eb/No for Different Data Rates
Aug 2004
2X2 MIMO Channel E PER vs. Eb/No for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

66. 2X2 MIMO AWGN Channel : throughput vs. SNR for Different Data Rates
Aug 2004
2X2 MIMO AWGN Channel : throughput vs. SNR for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

67. 2X2 MIMO Channel B : Throughput vs. SNR for Different Data Rates
Aug 2004
2X2 MIMO Channel B : Throughput vs. SNR for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

68. 2X2 MIMO Channel C : throughput vs. SNR for Different Data Rates
Aug 2004
2X2 MIMO Channel C : throughput vs. SNR for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

69. 2X2 MIMO Channel D : throughput vs. SNR for Different Data Rates
Aug 2004
2X2 MIMO Channel D : throughput vs. SNR for Different Data Rates
Kim Wu et al., MASSDIC-OFDM

70. 2X2 MIMO Channel E : throughput vs. SNR for Different Data Rates
Aug 2004
2X2 MIMO Channel E : throughput vs. SNR for Different Data Rates
Kim Wu et al., MASSDIC-OFDM