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doc.: IEEE 802.11-04/792r1
Submission Slide 1 André Bourdoux (IMEC)
July 2004
Transmit processing:a viable scheme
for MIMO-OFDM in 802.11n
André Bourdoux
Bart Van Poucke
Liesbet Van der Perre
IMEC, Wireless Research
doc.: IEEE 802.11-04/792r1
Submission Slide 2 André Bourdoux (IMEC)
July 2004
Need for 4G High-Speed WLANs
5 m
1 Mbps 10 Mbps 100 Mbps 1 Gbps
Maximum Data rate100 kbps
50 m
500 m
Range
Higher data rates Larger range More users
1GWLAN
802.11
1-2 Mbps
3GWLAN
802.11a/g
6-54 Mbps
2GWLAN
802.11b
5.5-11 Mbps
4GWLAN
802.11n
> 100 Mbps
doc.: IEEE 802.11-04/792r1
Submission Slide 3 André Bourdoux (IMEC)
July 2004
MIMO-OFDM boosts performancesin frequency selective environments
MIMOoffers:
-10 -5 0 5 10 15 20 25 300
2
4
6
8
10
12
14
16
18
20MIMO Channnel Capacity (Nt = Nr)
SNR per receive antenna in dB
Cap
acity
in b
it/s/
Hz
Nt = Nr = 1Nt = Nr = 2Nt = Nr = 3Nt = Nr = 4Nt = Nr = 5Nt = Nr = 6
SISO
MIMOor
SISOCapacity
(bit/s/Hz)
SNR (dB)
MIMO 2x2
3x3
4x4
1x1
-10 -5 0 5 10 15 20 25 300
2
4
6
8
10
12
14
16
18
20MIMO Channnel Capacity (Nt = Nr)
SNR per receive antenna in dB
Cap
acity
in b
it/s/
Hz
Nt = Nr = 1Nt = Nr = 2Nt = Nr = 3Nt = Nr = 4Nt = Nr = 5Nt = Nr = 6
SISO
MIMOor
SISOCapacity
(bit/s/Hz)
SNR (dB)
MIMO 2x2
3x3
4x4
1x1
Higher capacitySDM, SDMA
H
Stream 1
Stream N
Stream 1
Stream N… … … …H
Stream 1
Stream N
Stream 1
Stream N… … … …Higher robustnessDiversity (MRC, STBC)
H Stream 1Stream 1
…
HStream 1 Stream 1
…
H Stream 1Stream 1
…H Stream 1Stream 1
…
HStream 1 Stream 1
… HStream 1 Stream 1
…
Frequency
Mag
nitu
de
doc.: IEEE 802.11-04/792r1
Submission Slide 4 André Bourdoux (IMEC)
July 2004
A smart MIMO system adapts to scene and actual user needs
SDMA multiplies cell capacitySDM brings higher throughput
in DL/UL
STBC brings robustness
MRC brings robustness
MIMO-TX !
MIMO-TX !
MIMO-TX !
doc.: IEEE 802.11-04/792r1
Submission Slide 5 André Bourdoux (IMEC)
July 2004
A wide variety of MIMO schemes are available
SDMA
s1 s2
s1 s2
RX-SDMA
SDM
s1 s2
s1 s2
RX-SDM
MRC
s1
s1
RX-MRC
STBC
s1
s1
STBC
STBC
Uplink
SDM
s1 s2
s1 s2
TX-SDM
SDMA
s1 s2
s1 s2
TX-SDMA
MRC
s1
s1
TX-MRC
STBC
s1
s1
STBC
STBC
STBC
s1
s1
STBC
stbc
Downlink H H H
“MIMO-TX”schemes,
focus of this presentation
doc.: IEEE 802.11-04/792r1
Submission Slide 6 André Bourdoux (IMEC)
July 2004
MIMO-TX requires “TX-CSI”
Simpler receiver (no MIMO processing needed, SISO equalizer needed)
Transmitter processing: low complexity (Zero-forcing, MMSE, MRC)
Channel H needed at TX ( “TX-CSI” )
Option 1: by feedback
Option 2: from channel estimation in reverse link, reciprocity needed only works for TDD set-ups
Reciprocity:
Propagation channel: OK if delay kept short
Front-ends: not OK, calibration needed to measure transfer function of the front-ends
hS1
H
MIMOTX MRC …
MIMO with TX pre-processing
S1
……
H
S1
H
MIMOTX
SDM(A)
… … MIMO with TX pre-processing
SN
S1
SN
doc.: IEEE 802.11-04/792r1
Submission Slide 7 André Bourdoux (IMEC)
July 2004
Example of Channel estimation and TX processing
UL1
APUT1
UL2
APUT2
Channel estimation,AGC couples
nhnh
nhnh
2,22,1
1,21,1ULUL
ULUL
H
ULUL
ULUL
2,22,22,12,1
1,21,21,11,1
hfchfc
hfchfc
H with FE. C.
2,22,1
1,21,1
ff
ff
Spatial pre-filter 1
IσHHHF 2HH
DL 2
s2
APs1s1
s2
UT1
UT2
DL 1
Time
Spatialdimension
doc.: IEEE 802.11-04/792r1
Submission Slide 8 André Bourdoux (IMEC)
July 2004
Front-end non-reciprocity can be solved by calibration
Base StationReceiverFront-end
Frommodulator
Todemodulator
TerminalTransmitterFront-end
TerminalReceiverFront-end
Frommodulator
Todemodulator
Base StationTransmitterFront-end
HDTX,AP DTX,MT
DRX,AP DRX,MT
Propagation Channel
nDnHnDnH MTTXAPRXUL
,, Uplink:
nDnHnDnH APTXT
MTRXDL
,, Downlink:HDL (HUL)
T
The channel includes: the propagation channel ( H ) front-end circuits (filters, etc..) linear and non linear ( Dxx,yy )
doc.: IEEE 802.11-04/792r1
Submission Slide 9 André Bourdoux (IMEC)
July 2004
Non-perfect reciprocity MUI
• Downlink model (for Inversion) :
nxDDHDDHDy
HFH
DL
Power
PMTTXT
APRXAPTXT
MTRXDL
TULDLDL
1
,1
,,,
nxDFHy DLP
DLDLDL
MTTXAPRXUL
,, DHDH
APTXT
MTRXDL
,, DHDH
TMTTXAPRX
TULTULDL ,,
ˆ DHDHHF
Not diagonal anymore Multi-user interference
doc.: IEEE 802.11-04/792r1
Submission Slide 10 André Bourdoux (IMEC)
July 2004
The Base Station Transceiver aloneis responsible for the MUI
nxDDHDDHDy
HFH
DL
Power
PMTTXT
BSRXBSTXT
MTRXDL
TULDLDL
1
,1
,,,
• Only the base station creates MUI (DTX,BS & DRX,BS)
• The terminal effects (DTX,MT & DRX,MT) only create scalar complex multiplication, can be equalized
• H includes all common (reciprocal) terms, including antenna coupling
• Common LO is mandatory
• Valid for all pre-filtering technique, including MIMO-TX, beamforming, SVD
doc.: IEEE 802.11-04/792r1
Submission Slide 11 André Bourdoux (IMEC)
July 2004
OFDM-MIMO Demo Set-up
Access Point with 2 antennas
2 Terminals with 1 antenna each
doc.: IEEE 802.11-04/792r1
Submission Slide 12 André Bourdoux (IMEC)
July 2004
Our advise for 802.11n
MIMO-TX and MIMO-RX schemes are both interesting for 802.11n
MIMO-TX needs channel knowledge at TX side Estimation in reverse link has lower latency Delay between reverse link estimation and MIMO-TX transmission must
be minimized must be supported by MAC Protocol
MIMO-TX has been demonstrated Real-time (VHDL, 5GHz band) Wireless, 2x2 antennas MIMO-OFDM-SDM (108 Mbps) and MIMO-OFDM-MRC (8 dB SNR
improvement)
