May 2004
doc.: IEEE 802.11-04/553r0
MIMO Mode Table for 802.11n
DCN 802.11-04/553r0
May 2004
Ravi Mahadevappa, [email protected]
Stephan ten Brink, [email protected]
Realtek Semiconductors, Irvine, CA
Submission
Slide 1
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
Overview
•
•
•
•
•
•
•
•
•
Why Different MIMO Modes
Preliminaries, MIMO Modes
Maximum ratio combining (MRC)
„Circular Alamouti“ (CIRCAL) versus orthogonal
space/time block codes (OSTBC)
MIMO mode table
„Circular SMX“ (CIRCSMX)
Example, discussion 4x4
Conclusions
Appendix, results 1x1 to 4x4
Submission
Slide 2
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
Why Different MIMO Modes
• We should allow both
– Small/low cost terminals (moderate speed)
with e.g. 2 TX-ant. (for use in handhelds, digital cameras etc.)
– And high speed terminals
with e.g. up to 4 TX-ant. (for use in laptop computers etc.)
• Thus, there will be equipment with a variety of number of TX/RX
antennas out there operating under the 802.11n-“umbrella”
• Solution: Switch between MIMO modes depending on available
number of TX and RX antennas of the equipment involved
– Spatial multiplex (SMX):
• High data rates, short range; optimal detection tends to be complex
– Space time block codes (STBC), e.g. Alamouti 2x1
• Long range, lower data rates; optimal detection is simple
• Should be transparent, 11a to 11n modes
• From today’s perspective: Max. NT=4 TX antennas, NR=4 RX
antennas reasonable (full RF chain TX, RX antennas)
Submission
Slide 3
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
Preliminaries, MIMO Modes
• General scenario: NTxNR
– Obvious: For 1xNR use MRC at receiver
– For NT>NR, in particular, for NTx1: Use simple TX
diversity schemes based on space/time block
codes
• No general construction known
• 2x1: Alamouti (perfect; full diversity, “rate 1”)
• Should 3x1, 4x1, full diversity, “rate 3/4”-codes be used?
• For NT>NR, NR>1
– use STBC and MRC at receiver
– Or, use SMX with subset of TX antennas
• For NT<=NR: use SMX for high rate
Submission
Slide 4
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
1x1 up to 1x4 MRC
70
1x4 MRC
60
1x2 MRC
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• Performance
measure: required
SNR for 10% PER
• Packet length:
1000 bits
• exponential decay,
Trms = 60ns
• For simulation:
Perfect
1x1
Code Rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8
64QAM
Rate (Mbps)
50
40
16QAM
30
20
QPSK
10
1x3 MRC
0
-10
-5
0
5
10
15
20
25
30
SNR for 10% PER (dB)
More receive antennas improve SNR (range)
Submission
Slide 5
– Channel estimation
– Packet detection,
synchronization
– foff estimation
– No clipping
DAC/finite precision
ADC
– No front-end
filtering
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
MIMO Mode Table (I)
TX ant.
RX ant.
NT=1
NR=1
1x1 11a
2
1x2 11a
MRC
3
1x3 11a
MRC
4
1x4 11a
MRC
2
3
4
Table specifies the allowed MIMO modes depending on NT, NR
NT=1, simple MRC for any NR
Submission
Slide 6
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
TX Diversity with “Circular Alamouti”
• NTx1 Space/Time Block Codes (STBC)
– Orthogonal STBC (OSTBC) allow simple ML detection
– For NTx1, no general construction of OSTBC known with full spatial
diversity and full rate
– Moreover, it can be proved that no full rate OSTBC exists with NT>2
– 2x1, Alamouti: only known OSTBC with full diversity and “rate 1”
– 3x1, 4x1, full diversity, spatial “rate 3/4” codes known
• We can easily build orthogonal NTx1 STBC based on the 2x1
Alamouti code with spatial “rate 1”; however, no full diversity
– “circular Alamouti” 2(NT)x1 CIRCAL:
• For each channel symbol, only use 2 TX antennas out of the NT
available ones
• Cycle through all NT!/(2! (NT-2)!) combinations (2 out of NT)
• Example: NT=3, cycle period is 2.3=6 combinations; NT=4, cycle period
is 2.6=12 combinations
• Experiment: Compare performance of 3x1, 4x1 full diversity rate
3/4 OSTBC with 2(3)x1, 2(4)x1 rate 1 CIRCAL for MIMO-OFDM
Submission
Slide 7
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
2x1 Orthogonal Design (“Alamouti”)
• Provides TX diversity
• NT=2 TX antennas, NR=1 RX antennas
• 2 channel uses, 2 symbols transmitted; thus, spatial rate 1
 s1
S *
  s2
s2 
s1* 
• To read as
– At time 1, transmit s1 from antenna 1, s2 from antenna 2
– At time 2, transmit -s2* from antenna 1, s1* from antenna 2
– Repeat pattern with new symbols s1, s2
Submission
Slide 8
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
3x1 Orthogonal Design
• Provides TX diversity
• NT=3 TX antennas, NR=1 RX antennas
• 4 channel uses, 3 symbols transmitted; thus, spatial rate 3/4
 s1
s2
 *
*

s
s
1
 2
S   s3*
s3*
2
 *2
s3*
 s3
 2  2
Submission


s3

2
 s1  s1*  s2  s2* 
2

*
*
s 2  s2  s1  s1 
2

Slide 9
s3
2
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
4x1 Orthogonal Design
• Provides TX diversity
• NT=4 TX antennas, NR=1 RX antennas
• 4 channel uses, 3 symbols transmitted; thus, rate 3/4
 s1
 *
  s2
S   s3*
 *2
 s3
 2
Submission
s2
s3
s1*
s3
s3*
 s1  s1*  s 2  s 2*

2
2
2
s3*
2
2
s 2  s 2*  s1  s1*
2
Slide 10


 2 
 s 2  s 2*  s1  s1* 
2

*
*
 s1  s1  s 2  s 2 
2

s3
2
s3
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
Example: 2(3)x1 CIRCAL
•
•
•
•
Based on 2x1 Alamouti (full diversity, spatial rate 1)
Cycling for averaging good/bad MIMO subchannels
NT=3 TX antennas, 2 used at a time, NR=1 RX antennas
6 channel uses, 6 symbols transmitted; thus, „rate 1“
 s1
 s *
 2
 s3
S *
  s4
 0

 0
Submission
s2
s1*
0
0
s5
 s6*
0
0 
s4 
*
s3 
s6 
*
s5 
Slide 11
(or any other way
of cycling through
2 TX antennas used
at a time)
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
Example: 2(4)x1 CIRCAL
•
•
•
•
Based on 2x1 Alamouti (full diversity, spatial rate 1)
Cycling for averaging good/bad MIMO subchannels
NT=4 TX antennas, 2 used at a time, NR=1 RX antennas
12 channel uses, 12 symbols transmitted; thus, „rate 1“
 s1
  s*
 2
 0

 0
 s5
 *
 s
S 6
0

 0
 0

 0

 s11
*
 s12
Submission
s2
0
s1*
0
0
s3
0
 s4*
0
s6
0
s5*
s7
0
 s8*
0
s9
s10
*
 s10
s9*
0
0
0
0
Slide 12
0
0 
s4 

s3* 
0

0
s8 

s7* 
0

0

s12 
*

s11
(or any other way
of cycling through
2 TX antennas used
at a time)
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
2(NT)xNR CIRCAL
•
•
•
•
•
Based on 2x1 Alamouti (full diversity, spatial rate 1)
Rotation for averaging good/bad MIMO subchannels
NT TX antennas, nT=2 used at a time, NR RX antennas
Use MRC (maximum ratio combining) for NR receive antennas
Cycling through all PCIRCAL = NT!/(nT! (NT-nT)!) combinations on a
per OFDM symbol basis
– since two OFDM symbols per Alamouti code are used, the cycle
period in OFDM symbols is 2. PCIRCAL
• For better averaging in OFDM systems, TX antenna cycling can
be applied over both, time index and subcarrier index
Submission
Slide 13
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
3x1: 2(3)x1 CIRCAL versus OSTBC
70
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• 3x1 STBC: „full
diversity“, but (spatial)
rate 3/4, rate loss
• 2(3)x1 CIRCAL
outperforms 3x1
STBC
3x1
60
Rate (Mbps)
50
40
2(3)x1 CIRCAL
STBC “full diversity”
Rate 3/4
30
– suffers no rate loss
– cycling/rotating
compensates some of
the diversity losses
20
10
0
-5
0
5
10
SNR for 10 % PER (dB)
15
20
25
2(3)x1 CIRCAL better than 3x1 OSTBC
Submission
Slide 14
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
4x1: 2(4)x1 CIRCAL versus OSTBC
70
• 4x1 STBC: „full
diversity“, but (spatial)
rate 3/4, rate loss
• 2(4)x1 CIRCAL
outperforms 4x1
STBC
4x1
60
2(4)x1 CIRCAL
Rate (Mbps)
50
– suffers no rate loss
– cycling/rotating
compensates some of
the diversity losses
40
STBC “full diversity”
Rate 3/4
30
• 2(NT)x1 CIRCAL
better than known
OSTBC
• 2(NT)xNR CIRCAL by
using MRC at the RX
20
10
0
-5
0
5
10
SNR for 10% PER (dB)
15
20
25
2(4)x1 CIRCAL better than 4x1 OSTBC
Submission
Slide 15
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
2x1, 2(3)x1, 2(4)x1 CIRCAL
70
64QAM
60
Code Rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8
2(4)x1 CIRCAL
2(3)x1 CIRCAL
2x1 AL
Rate (Mbps)
50
40
16QAM
30
20
QPSK
10
0
0
5
10
15
SNR for 10% PER (dB)
20
25
• 2(3)x1 CIRCAL
improves over 2x1
AL by about 0.5dB
• 2(4)x1 CIRCAL
improves over 2x1
AL by about 1dB
• Only 2 antennas
used at a time, but
rotated through all
combinations
• The antenna cycling
captures more of the
available diversity in
the system
• More transmit
antennas improve
diversity, even if only
used in rotation with
Alamouti code
Gains of 2(NT)x1 CIRCAL over 2x1 AL saturate for NT=4 and more
Submission
Slide 16
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
MIMO Mode Table (II)
TX ant.
NT=1
2
3
4
NR=1
1x1 11a
2x1
AL
3x1
2(3)x1 CIRCAL
4x1
2(4)x1 CIRCAL
2
1x2 11a
MRC
2x2
Low rate, 1: 2x2 ALMRC
3x2
1: 2(3)x2 CIRCAL/MRC
4x2
1: 2(4)x2 CIRCAL/MRC
3
1x3 11a
MRC
2x3
1: 2x3 ALMRC
3x3
1: 2(3)x3 CIRCAL/MRC
4x3
1: 2(4)x3 CIRCAL/MRC
4
1x4 11a
MRC
2x4
1: 2x4 ALMRC
3x4
1: 2(3)x4 CIRCAL/MRC
4x4
1: 2(4)x4 CIRCAL/MRC
RX ant.
Table specifies the allowed MIMO modes depending on NT, NR
NT>=NR, low rate: Use Circular AL (CIRCAL) and MRC
Submission
Slide 17
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
Circular SMX
• When NT>NR, we use same idea as with CIRCAL:
– collect diversity by cycling through TX antennas
• nT(NT) CIRCSMX:
– Use nT TX antennas per channel use for SMX, out of NT>nT
available antennas at transmitter
– Cycle through all PCIRCSMX=NT!/(nT! (NT-nT)!) combinations on a per OFDM
symbol basis
– The cycle period in OFDM symbols is PCIRCSMX
• For example, say we have NT=3 TX antennas, but only NR=2 RX
antennas
– Possible cycling for 2(3)x2 CIRCSMX:
•
•
•
•
Submission
at time 1, transmit from antennas 1, 2
at time 2, transmit from antennas 1, 3
at time 3, transmit from antennas 2, 3
repeat the pattern
Slide 18
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
2x2 SMX, 2(3)x2, 2(4)x2 CIRCSMX
140
• Code rates 1/4,
1/3, 1/2, 2/3, 3/4,
7/8
• Modulation
QPSK, 16QAM,
64QAM
• CIRCSMX
improves TX
diversity
• 2(4)x2 SMX gains
about 1dB over
2x2 SMX
2x2
120
2(4)x2 CIRCSMX
2(3)x2 CIRCSMX
100
Rate (Mbps)
64QAM
2x2 SMX
80
64QAM
60
2(4)x2 CIRCAL/MRC 16QAM
40
2(3)x2 CIRCAL/MRC
20
2x2 AL/MRC
QPSK
0
-5
0
5
10
15
20
25
30
• CIRCAL curves
given as
references
SNR for 10% PER (dB)
For NT>NR: NR(NT)xNR CIRCSMX better than NRxNR SMX
Submission
Slide 19
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
MIMO Mode Table (III)
TX ant.
NT=1
2
3
4
NR=1
1x1 11a
2x1
AL
3x1
2(3)x1 CIRCAL
4x1
2(4)x1 CIRCAL
2
1x2 11a
MRC
2x2
Low rate, 1: 2x2 ALMRC
High rate, 2: 2x2 SMX
3x2
1: 2(3)x2 CIRCAL/MRC
2: 2(3)x2 CIRCSMX
4x2
1: 2(4)x2 CIRCAL/MRC
2: 2(4)x2 CIRCSMX
1x3 11a
MRC
2x3
1: 2x3 ALMRC
2: 2x3 SMX
3x3
1: 2(3)x3 CIRCAL/MRC
2: 2(3)x3 CIRCSMX
3: 3x3 SMX
4x3
1: 2(4)x3 CIRCAL/MRC
2: 2(4)x3 CIRCSMX
3: 3(4)x3 CIRCSMX
2x4
1: 2x4 ALMRC
2: 2x4 SMX
3x4
1: 2(3)x4 CIRCAL/MRC
2: 2(3)x4 CIRCSMX
3: 3x4 SMX
4x4
1: 2(4)x4 CIRCAL/MRC
2: 2(4)x4 CIRCSMX
3: 3(4)x4 CIRCSMX
4: 4x4 SMX
RX ant.
3
4
1x4 11a
MRC
Any NT, NR, high rate: SMX, or Circular SMX (CIRCSMX)
Submission
Slide 20
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
Example, Discussion of 4x4
300
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• The rate/SNR
envelope includes
4x4
250
4x4 SMX
Rate (Mbps)
200
– 2(4)x4 CIRCAL for
lowest rates
– 2(4)x4 CIRCSMX
– 3(4)x4 CIRCSMX
– 4x4 SMX for
highest rate
3(4)x4 CIRCSMX
150
• To simplify:
100
– Omit 2(4)x4
CIRCSMX
– Use 4x4 SMX for
highest two rates
– Use 2(4)x4 CIRCAL
for lowest
2(4)x4 CIRCSMX
50
2(4)x4
CIRCAL/MRC
0
-10
-5
0
5
10
15
SNR for 10 % PER (dB)
20
25
30
35
For NT>NR: NR(NT)xNR CIRCSMX better than NRxNR SMX
Submission
Slide 21
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
MIMO Mode Table (IV), any NT, NR
1
2
3
...
NT
1
1x1 11a
2x1
AL
3x1
2(3)x1 CIRCAL
...
NTx1
2(NT)x1 CIRCAL
2
1x2 11a
MRC
2x2
Low rate, 1: 2x2 ALMRC
High rate, 2: 2x2 SMX
3x2
1: 2(3)x2 CIRCAL/MRC
2: 2(3)x2 CIRCSMX
...
NTx2
1: 2(NT)x2 CIRCAL/MRC
2: 2(NT)x2 CIRCSMX
3
1x3 11a
MRC
2x3
1: 2x3 ALMRC
2: 2x3 SMX
3x3
1: 2(3)x3 CIRCAL/MRC
2: 2(3)x3 CIRCSMX
3: 3x3 SMX
.
.
.
.
.
.
.
.
.
.
.
.
RX
TX
NR
1xNR 11a
MRC
Submission
2xNR
1: 2xNR ALMRC
2: 2xNR SMX
3xNR
1: 2(3)xNR CIRCAL/MRC
2: 2(3)xNR CIRCSMX
…
For NT>NR:
NR: NR(NT)xNR CIRCSMX
For NT<=NR:
NT: NTxNR SMX
Slide 22
...
NTx3
1: 2(NT)x3 CIRCAL/MRC
2: 2(NT)x3 CIRCSMX
3: 3(NT)x3 CIRCSMX
.
.
.
...
NTxNR
1: 2(NT)xNR CIRCAL/MRC
2: 2(NT)xNR CIRCSMX
3: 3(NT)xNR CIRCSMX
…
For NT>NR:
NR: NR(NT)xNR CIRCSMX
For NT<=NR:
NT: NTxNR SMX
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
Conclusions
• Use 2(NT)x1 CIRCAL rather than full diversity, spatial rate 3/4 STBC for
NT=3, 4
• Always use all receive antennas
• Not always use all transmit antennas
– Only when very high rates are desired
– For medium rates, it is better to use less antennas, but higher
modulation/rate; to have at least one excess antenna at receiver
• CIRCSMX NR(NT)xNR always better (slightly) than SMX NRxNR
• For low-complexity, suboptimal MIMO detection, excess antennas pay off
– For example 3x3
• for medium rate, use 2(3)x3 CIRCSMX (high rate code/modulation) rather than 3x3
SMX (medium code rate/modulation)
• Only use 3x3 SMX when really high rates are desired
Submission
Slide 23
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
Appendix
• Rate versus SNR-charts for NTxNR = 1x1 to 4x4
Submission
Slide 24
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
Performance Criteria/Abbreviations
•
•
Receiver sensitivity for 10% PER
Abbreviations:
–
–
–
–
–
–
•
SEL: selection diversity at RX
MRC: maximum ratio combining at RX
AL/MRC: Alamouti Space/Time with MRC at RX [7,8]
SMX: spatial multiplexing (i.e. MIMO mode, [4,5,6])
nT(NT) CIRCAL: “circular Alamouti”, using nT=2 antennas per channel use, out of NT>nT
available antennas at transmitter, and cycling through all PCIRCAL = NT!/(nT! (NT-nT)!)
combinations on a per OFDM symbol basis; since two OFDM symbols per Alamouti
code are used, the cycle period in OFDM symbols is 2. PCIRCAL
nT(NT) CIRCSMX: “circular SMX”, using nT transmit antennas per channel use for SMX,
out of NT>nT available antennas at transmitter, and cycling through all PCIRCSMX=NT!/(nT!
(NT-nT)!) combinations on a per OFDM symbol basis; the cycle period in OFDM
symbols is PCIRCSMX
MIMO detection used in following plots
–
–
Submission
ZF and APP post processing
Note: ZF with APP post processing provides close to optimal performance for higher
order modulation (increasing number of excess antennas); for small constellations
(QPSK), i.e., low-rate communication, ZF/APP suffers significant performance loss;
that’s the main reason why AL-type of STBC are a good choice for low-rate
communication
Slide 25
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
Simulation Environment/Assumptions
•
802.11a PHY simulation environment, plus
–
–
–
Higher order QAM constellations
Higher/lower channel code rates
TX/RX diversity/MIMO OFDM
•
•
•
•
ZF detection and soft post processing (shown in plots)
APP and reduced APP detection
Perfect channel knowledge/synchronization
Idealized multipath MIMO channel
– Sub-channels independent; exponential decay, Trms = 60ns
– Quasi static (channel stays constant during one packet)
•
•
Packet length: 1000 bits
Perfect
–
–
–
–
–
Submission
Channel estimation
Packet detection, synchronization
foff estimation
No clipping DAC/finite precision ADC
No front-end filtering
Slide 26
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
1x1 up to 1x4 MRC
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• More receive
antennas improve
SNR (range)
70
1x4 MRC
60
1x2 MRC
1x1
Code Rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8
64QAM
Rate (Mbps)
50
40
16QAM
30
20
QPSK
10
1x3 MRC
0
-10
-5
0
5
10
15
20
25
30
SNR for 10% PER (dB)
Submission
Slide 27
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
2x1 Alamouti STBC
70
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
2x1 AL
60
Code Rates 1/4, 1/3, 1/2, 2/3, 3/4, 7/8
64QAM
Rate (Mbps)
50
40
16QAM
30
20
QPSK
10
0
0
5
10
15
20
25
SNR for 10% PER (dB)
Submission
Slide 28
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
2x2
140
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• Low rate: AL/MRC
• High rate: SMX
2x2
120
2x2 SMX
Rate (Mbps)
100
80
60
40
2x2 AL/MRC
20
0
-5
0
5
10
15
20
25
30
SNR for 10% PER (dB)
Submission
Slide 29
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
2x3
140
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• Low rate AL/MRC
• High rate SMX
2x3
120
2x3 SMX
Rate (Mbps)
100
80
60
40
2x3
AL/MRC
20
0
-10
-5
0
5
10
15
20
25
SNR for 10 % PER (dB)
Submission
Slide 30
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
2x4
140
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• Low rate AL/MRC
• High rate SMX
• Almost all rates can
be covered with
SMX only
2x4
120
2x4 SMX
Rate (Mbps)
100
80
60
40
2x4
AL/MRC
20
0
-10
-5
0
5
10
15
20
SNR for 10 % PER (dB)
Submission
Slide 31
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
3x1
70
3x1
60
Rate (Mbps)
50
40
2(3)x1 CIRCAL
STBC “full diversity”
Rate 3/4
30
20
10
0
-5
Submission
0
5
10
SNR for 10 % PER (dB)
15
Slide 32
20
25
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• 3x1 STBC: „full
diversity“, but
(spatial) rate 3/4,
rate loss
• 2(3)x1 CIRCAL
outperforms 3x1
STBC (suffers no
rate loss; no
significant loss due
to smaller diversity;
circulating/rotating
compensates some
of the diversity
losses, see next
slide)
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
3x2
140
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• 2(3)x2
CIRCAL/MRC better
for low data rates
• 2(3)x2 CIRCSMX
better for higher
data rates (no rate
loss); for low data
rates: loss due to
ZF/APP detection
for small
constellation size
3x2
120
2(3)x2 CIRCSMX
Rate (Mbps)
100
80
60
40
2(3)x2
CIRCAL/MRC
20
0
-5
Submission
0
5
10
15
SNR for 10 % PER (dB)
20
Slide 33
25
30
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
3x3
200
180
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• 3x3 SMX only for
high rate
• 2(3)x3 CIRCSMX
better for medium
rate (easier
detection since
excess antenna)
3x3
3x3 SMX
160
140
Rate (Mbps)
120
100
80
2(3)x3 CIRCSMX2
60
40
20
0
-10
Submission
2(3)x3
CIRCAL/MRC
-5
0
5
10
15
SNR for 10 % PER (dB)
20
Slide 34
25
30
35
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
3x4
200
180
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• 3x4: highest rate
• 2(3)x4: medium rate
• 2(3)x4
CIRCAL/MRC:
lowest rate
3x4
160
3x4 SMX
140
Rate (Mbps)
120
100
80
2(3)x4 CIRCSMX
60
40
20
0
-10
Submission
2(3)x4
CIRCAL/MRC
-5
0
5
10
SNR for 10 % PER (dB)
15
Slide 35
20
25
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
4x1
70
4x1
60
2(4)x1 CIRCAL
Rate (Mbps)
50
40
STBC “full diverity”
Rate 3/4
30
20
10
0
-5
Submission
0
5
10
SNR for 10% PER (dB)
15
Slide 36
20
25
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• 4x1 STBC: „full
diversity“, but
(spatial) rate 3/4,
rate loss (as with
3x1 STBC case)
• 2(4)x1 CIRCAL
outperforms 4x1
STBC (suffers no
rate loss; no
significant loss due
to smaller diversity;
circulating/rotating
compensates some
of the diversity
losses, see next
slide)
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
4x2
140
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• 2(4)x2
CIRCAL/MRC better
for low data rates
4x2
120
2(4)x2 CIRCSMX
Rate (Mbps)
100
80
60
40
2(4)x2
CIRCAL/MRC
20
0
-5
Submission
0
5
10
15
SNR for 10% PER (dB)
20
Slide 37
25
30
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
4x3
200
180
3(4)x3 CIRCSMX
4x3
160
140
Rate (Mbps)
120
2(4)x3 CIRCSMX
100
80
60
40
20
0
-10
2(4)x3
CIRCAL/MRC
-5
0
5
10
15
20
SNR for 10% PER (dB)
Submission
Slide 38
25
30
35
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• 2(4)x3
CIRCAL/MRC better
for low data rates
(hardly)
• 2(4)x3 CIRCSMX
better for medium
data rates
• 3(4)x3 CIRCSMX
better for high data
rates
• Note for all SMX at
low data rates: loss
due to ZF/APP
detection for small
constellation size;
that is why 2(4)x3
CIRCSMX better
than 3(4)x3
CIRCSMX at
medium data rates
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
4x4
300
• Code rates 1/4, 1/3,
1/2, 2/3, 3/4, 7/8
• Modulation QPSK,
16QAM, 64QAM
• Similar situation as
for 3x3
• 4x4 SMX only for
highest rates
4x4
250
4x4 SMX
Rate (Mbps)
200
3(4)x4
CIRCSMX
150
100
2(4)x4 CIRCSMX
50
2(4)x4
CIRCAL/MRC
0
-10
Submission
-5
0
5
10
15
SNR for 10 % PER (dB)
20
Slide 39
25
30
35
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
Other Designs Considered
• Linear dispersion (LD) codes [9]
–
–
–
–
Very general set-up
Powerful codes designed using an optimization algorithm
Good performance for any NT, NR
However, generally requires ML/APP detection (e.g. Sphere
detection); complexity is an issue
• Delay diversity
– good for MIMO-OFDM since guard interval eliminates need
for multi-tap channel equalizer
– However, it has been shown that to obtain „full diversity“, the
delay needs to be bigger than the guard interval (and, in turn,
would require a multi-tap channel equalizer, counteracting the
benefits of OFDM transmission)
Submission
Slide 40
Ravi Mahadevappa, Stephan ten Brink, Realtek
May 2004
doc.: IEEE 802.11-04/553r0
Some References
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
IEEE Std 802.11a-1999, Part 11: Wireless LAN Medium Access Control (MAC) and
Physical Layer (PHY) Specifications, High-speed Physical Layer in the 5 GHz Band
S. Sandhu, M. Ho, “Transmit diversity for MIMO OFDM”, IEEE 802.11-03/847r0, Nov. 2003
H. Sampath, R. Narasimhan, “Advantages and drawbacks of circular delay diversity for
MIMO-OFDM”, IEEE 802.11-04/075r1
J. H. Winters, J. Salz, R. D. Gitlin, “The impact of antenna diversity on the capacity of
wireless communication systems”, IEEE Trans. Commun., vol. 42, no. 2/3/4, pp. 17401751, Feb./Mar./Apr. 1994
G. J. Foschini, “Layered space-time architecture for wireless communication in a fading
environment when using multi-element antennas”,Bell Labs. Tech. J., vol. 1, no. 2, pp. 4159, 1996
H. Sampath, S. Talwar, J. Tellado, V. Erceg, A. Paulraj, “A fourth-generation MIMO-OFDM
broadband wireless system: Design, performance, and field trial results”, IEEE Commun.
Mag., pp. 143-149, Sept. 2002
S. M. Alamouti, “A simple transmit diversity technique for wireless communications”, IEEE
J. on Select. Areas in Commun., vol. 16, pp. 1451-1458, Oct. 1998
V. Tarokh, H. Jafarkani, A. R. Calderbank, “Space-time block codes from orthogonal
designs”, IEEE Trans. Inform. Theory, vol. 45, pp. 1456-1467, July 1999
B. Hassibi, B. M. Hochwald, “High-rate codes that are linear in space and time,” IEEE
Transactions on Information Theory, July 2002.
Submission
Slide 41
Ravi Mahadevappa, Stephan ten Brink, Realtek