1. New preamble structure for AGC in a MIMO-OFDM system
January 2004
New preamble structure for AGC in a MIMO-OFDM system
Tsuguhide Aoki, Daisuke Takeda, Takahiro Kobayashi and Kazuaki Kawabata
Corporate R&D center, TOSHIBA corporation
Tsuguhide Aoki, TOSHIBA

2. January 2004
Main scope of TGn
“Achieve 100Mbps measured at MAC SAP” (PAR & FR)
⇒MIMO-OFDM is one of the possible candidates.
“Some of the modes shall be backwards compatible and interoperable with a and/or g” (PAR & FR)
Backward compatibility between legacy 11a and MIMO-OFDM is one of the main issues.
Preamble structure of 11a should be maintained
in a MIMO-OFDM system.
Alternatively, use protection mechanisms as defined in 11g (RTS-CTS, CTS self)
Tsuguhide Aoki, TOSHIBA

3. Example of preamble structure for MIMO system
January 2004
Example of preamble structure for MIMO system
Same as 11a
→Backward compatibility
Channel estimation for MIMO signals
TX1 SP GI LP
Sig
Sig 2 GI LP GI LP GI LP GI LP
DATA
TX2 GI LP GI LP GI
-LP GI
-LP
DATA
TX3
Indicate 11n preamble structure GI LP GI
-LP GI
-LP GI LP
DATA
TX4 GI LP GI
-LP GI LP GI
-LP
DATA
*Similar structure is presented in 03/714r0
AGC for Tx1 could be performed by using SP transmitted during the legacy period.
It is difficult to adjust the gain control for Tx2-Tx4 during MIMO signals because of the insufficient information for other antennas.
→This causes a severe saturation or quantification error in ADC.
Tsuguhide Aoki, TOSHIBA

4. New preamble structure with 2nd SPs for MIMO system
January 2004
New preamble structure with 2nd SPs for MIMO system
1st AGC
2nd AGC
TX1 SP GI LP
Sig
Sig2
2nd SP GI LP GI LP GI LP GI LP
DATA
TX2
2nd SP GI LP GI LP GI
-LP GI
-LP
DATA
TX3
2nd SP GI LP GI
-LP GI
-LP GI LP
DATA
TX4
2nd SP GI LP GI
-LP GI LP GI
-LP
DATA
2nd SP for MIMO-AGC
The 1st AGC for Tx 1 could be performed by using legacy SP.
The 2nd AGC for MIMO signals could be performed by using the 2nd SPs.
The 2nd SP with same sequence for Tx1-Tx4 causes a Null (beamforming) effect.
-->Different sequence should be used for the 2nd SP on each antenna.
Tsuguhide Aoki, TOSHIBA

5. Simulated transmit signals with 2nd SP
January 2004
Simulated transmit signals with 2nd SP
Total transmission power is always the same. SP LP
SIG1&2
2nd SP
MIMO LP
MIMO DATA
・・・
Tx 1* f
・・・
Tx 2 f
・・・
Tx 3 f
・・・
Tx 4 f
Base-band transmit signals (In-phase)
*Tx 1 transmits same sequence of legacy SP.
Tsuguhide Aoki, TOSHIBA

6. Simulated receive signals with 2nd SP
January 2004
Simulated receive signals with 2nd SP
Target gain for the selected antenna is used for all RF/IF chains.
Select an antenna with maximum power.
1st SP
2nd SP
Rx 1
Rx 2
Rx 3
Rx 4
1st AGC
2nd AGC
Base-band transmit signals (In-phase)
Tsuguhide Aoki, TOSHIBA

7. January 2004
Distribution of the received power for data part and 1st /2nd SP part in channel model C(NLOS)
#Tx=3, #Rx=3
Normalized received power for data
Normalized received power for data
Normalized received power of 2nd SP
(new preamble)
Saturation
Quantization error
Normalized received power of SP
(conventional preamble)
This figure shows the power of antenna with maximum power in SP(2nd SP)
Tsuguhide Aoki, TOSHIBA

8. Simulation parameters
January 2004
Simulation parameters
Architecture
IEEE802.11a-based MIMO-OFDM
Antenna element
ULA (half a wavelength)
Modulation and coding scheme
54Mbps(64QAM, R=3/4)
Channel model
TGn Channel model (03/940)
IF/RF impairment
Ignored
Synchronization (Timing sync. Frequency sync.)
Ideal
Channel estimation
MIMO detection algorithms
MMSE-BLAST(MMSE-based OSIC)
DATA length
1000 Bytes for each stream
ADC
10bit-ADC
AGC
Common gain AGC
(power measurement is ideal)
Tsuguhide Aoki, TOSHIBA

9. PSDU=1000bytes for each,10bit-ADC
January 2004
BER/PER performance vs. average amplitude of SP in channel model B(NLOS)
PSDU=1000bytes for each,10bit-ADC
Tsuguhide Aoki, TOSHIBA

10. PSDU=1000bytes for each,10bit-ADC
January 2004
BER/PER performance vs. average amplitude of SP in channel model C(NLOS)
PSDU=1000bytes for each,10bit-ADC
Tsuguhide Aoki, TOSHIBA

11. January 2004
BER/PER performance vs. average amplitude of SP in channel model D(NLOS)
PSDU=1000bytes x 3,10bit-ADC
Tsuguhide Aoki, TOSHIBA

12. January 2004
BER/PER performance vs. average amplitude of SP in channel model E(NLOS)
PSDU=1000bytes x 3,10bit-ADC
Tsuguhide Aoki, TOSHIBA

13. Conclusions A new preamble structure with 2nd SP was examined.
January 2004
Conclusions
A new preamble structure with 2nd SP was examined.
Dynamic range of AGC is large compared with conventional preamble.
BER /PER performance can be improved.
Our preamble structure is effective to improve the performance of MIMO systems.
Tsuguhide Aoki, TOSHIBA