1. John Ketchum, Bjorn A. Bjerke, and Irina Medvedev Qualcomm, Inc.
Month 2002
doc.: IEEE /xxxr0
July 2004
802.11n MIMO Link Performance: Some Simulation Results
John Ketchum, Bjorn A. Bjerke, and Irina Medvedev Qualcomm, Inc.
John Ketchum, et al., Qualcomm Incorporated
John Doe, His Company

2. Link simulation overview Preliminary simulation results:
Month 2002
doc.: IEEE /xxxr0
July 2004
Presentation Outline
MIMO system overview
Link simulation overview
Preliminary simulation results:
Throughput and PER performance with n channel B and rate adaptation (CC67)
PER vs. SNR performance in AWGN (CC59)
Hardware prototype summary
John Ketchum, et al., Qualcomm Incorporated
John Doe, His Company

3. July 2004
MIMO System Overview
2x2 – 4x4 MIMO-OFDM: enables multiplexing of up to 4 spatial channels
OFDM structure identical to a/g (i.e., 52 subcarriers)
802.11a/g constraint length 7, rate ½ convolutional code and punctured rates.
802.11a/g QAM modulations QAM
Additional rates adopted to provide increased spectral efficiency
Two approaches to spatial multiplexing:
Eigensteering:
Full CSI operation; Tx & Rx steering based on SVD decomposition per OFDM subcarrier
Spatial spreading:
Partial CSI operation; Rx-only spatial processing
Separate coding/interleaving per data stream
Interleaving over single OFDM symbol: identical to a/g
Closed-loop PHY rate adaptation based on observed Rx SNR
John Ketchum, et al., Qualcomm Incorporated

4. 4x4 MIMO Baseband System July 2004
John Ketchum, et al., Qualcomm Incorporated

5. Extended 802.11a/g Rate Set Used in Simulations
July 2004
Extended a/g Rate Set Used in Simulations
Efficiency (bps/Hz)
Data rate (Mbps)
Code rate
Modulation
0.5 6
1/2
BPSK
1.0 12
QPSK
1.5 18
3/4
2.0 24
16-QAM
2.5 30
5/8
3.0 36
3.5 42
7/12
64-QAM
4.0 48
2/3
4.5 54
5.0 60
5/6
6.0 72
256-QAM
7.0 84
7/8
John Ketchum, et al., Qualcomm Incorporated

6. Closed-Loop Rate Adaptation
July 2004
Closed-Loop Rate Adaptation
Forward link data rates determined by the STA and communicated to the AP. Rate adaptation algorithm determines the max. data rate supported per spatial stream, based on Rx SNR per subcarrier per stream computed from channel estimates.
Reverse link data rates determined by the AP and communicated to the STA. Rate adaptation algorithm identical to that operating in the STA.
John Ketchum, et al., Qualcomm Incorporated

7. Simulation of Spatial Multiplexing Using Tx & Rx Eigensteering
July 2004
Simulation of Spatial Multiplexing Using Tx & Rx Eigensteering
Common MIMO Training Sequence broadcast by AP once every SCAP (Scheduled Access Period) (…,t0,t3,…). Forward link (FL) channel coefficients estimated by STA receiver
FL Dedicated MIMO Training Sequence (steered) transmitted by AP at t1=0.5 ms, immediately followed by FL data PPDU
Reverse link (RL) Dedicated MIMO Training Sequence transmitted by STA at t2=1.5 ms, immediately followed by RL data PPDU
Transmit and receive steering vectors derived from most recent channel estimates
Closed-loop rate adaptation: FL and RL data rates determined based on receive SNRs observed in previous frames
John Ketchum, et al., Qualcomm Incorporated

8. July 2004
Simulation Sequence
Channel estimation and rate control occurs over three SCAPs (2.048 ms each)
First SCAP:
STA receives Common MIMO Training Sequence
Computes channel estimate
Transmits Dedicated MIMO Training Sequence (steered)
AP receives Dedicated MIMO Training Sequence
Computes estimate of receive & transmit steering vectors
Second SCAP:
AP sends Dedicated MIMO Training Sequence (steered)
STA makes FL rate selection based on received Dedicated MIMO Training Sequence
STA sends Dedicated MIMO Training Sequence (steered) with DL rate selection
AP makes RL rate selection based on received dedicated MIMO Training Sequence
Third SCAP:
AP sends data PPDU based on rate choice in previous SCAP
Includes RL rate selection
STA sends data PPDU
SCAP = Scheduled Access Period
John Ketchum, et al., Qualcomm Incorporated

9. Simulation Parameters
July 2004
Simulation Parameters
2x2 and 4x4 system configurations
IEEE n channel models B, D and E
IEEE n impairment models:
Time-domain channel simulator with 5x oversampling rate (Ts=10 ns)
Rapp nonlinear power amplifier model (IM1):
Total Tx power = 17 dBm; Psat = 25 dBm
2x2 backoff = 11 dB per PA; 4x4 backoff = 14 dB per PA
Carrier frequency offset : PPM (IM2)
Sampling clock frequency offset: PPM (IM2)
Phase noise at both transmitter and receiver (IM4)
100 channel realizations generated for each SNR point
In each channel realization the Doppler process evolves over three SCAPs to allow simulation of channel estimation, closed-loop rate adaptation and FL/RL data transmission in fading conditions
John Ketchum, et al., Qualcomm Incorporated

10. Simulation Parameters (cont’d)
July 2004
Simulation Parameters (cont’d)
Stopping criterion: 10 packet errors or 400 packets transmitted per channel realization
Targeted packet error rate performance: mean PER <= 1%
Simulation results:
2x2 and 4x4 systems
Packet size: 1000 B
Average throughput vs. SNR
Throughput distributions
Packet error rate distributions
Packet error rate vs. SNR in AWGN (“Fourier channel”)
John Ketchum, et al., Qualcomm Incorporated

11. 2x2 Simulation Results: Average throughput vs. SNR
July 2004
2x2 Simulation Results: Average throughput vs. SNR
John Ketchum, et al., Qualcomm Incorporated

12. 2x2 Throughput Distributions (Forward and Reverse Links)
July 2004
2x2 Throughput Distributions (Forward and Reverse Links)
John Ketchum, et al., Qualcomm Incorporated

13. 2x2 Packet Error Rate Distributions (Forward and Reverse Links)
July 2004
2x2 Packet Error Rate Distributions (Forward and Reverse Links)
John Ketchum, et al., Qualcomm Incorporated

14. 4x4 Simulation Results: Average throughput vs. SNR
July 2004
4x4 Simulation Results: Average throughput vs. SNR
John Ketchum, et al., Qualcomm Incorporated

15. 4x4 Throughput Distributions (Forward and Reverse Links)
July 2004
4x4 Throughput Distributions (Forward and Reverse Links)
John Ketchum, et al., Qualcomm Incorporated

16. 4x4 Packet Error Rate Distributions (Forward and Reverse Links)
July 2004
4x4 Packet Error Rate Distributions (Forward and Reverse Links)
John Ketchum, et al., Qualcomm Incorporated

17. Per-Eigenmode Data Rate Distributions
July 2004
Per-Eigenmode Data Rate Distributions
Distribution of data rates picked by the rate selection algorithm in a 4x4 system (Forward Link)
Independent data rates per stream (eigenmode)
SNR = 20, 30, 40, 50 dB
Legend:
0: Eigenmode does not support transmission
1: BPSK (0.5 bps/Hz)
2, 3: QPSK ( bps/Hz)
4, 5, 6: 16-QAM ( bps/Hz)
7, 8, 9, 10: 64-QAM ( bps/Hz)
11, 12: 256-QAM ( bps/Hz)
John Ketchum, et al., Qualcomm Incorporated

18. July 2004
4x4, Channel B, SNR = 20 dB
John Ketchum, et al., Qualcomm Incorporated

19. July 2004
4x4, Channel B, SNR = 30 dB
John Ketchum, et al., Qualcomm Incorporated

20. July 2004
4x4, Channel B, SNR = 40 dB
John Ketchum, et al., Qualcomm Incorporated

21. July 2004
4x4, Channel B, SNR = 50 dB
John Ketchum, et al., Qualcomm Incorporated

22. Packet Error Rate vs. SNR in AWGN
July 2004
Packet Error Rate vs. SNR in AWGN
2x2 and 4x4 Fourier matrix channels as specified by CC59
Perfect synchronization and channel estimation; no impairments
Fixed rates (rate adaptation turned off)
Simulation results obtained with the following rates:
BPSK, R=1/2 (6 Mbps per stream),
QPSK, R=3/4 (18 Mbps per stream)
16-QAM, R=3/4 (36 Mbps per stream)
64-QAM, R=3/4 (54 Mbps per stream)
256-QAM, R=7/8 (84 Mbps per stream)
Packet size: 1000 B
John Ketchum, et al., Qualcomm Incorporated

23. July 2004
2x2 PER vs. SNR
John Ketchum, et al., Qualcomm Incorporated

24. July 2004
4x4 PER vs. SNR
John Ketchum, et al., Qualcomm Incorporated

25. Acquisition Performance
July 2004
Acquisition Performance
Probability of detection
Frequency estimate error variance
Frequency estimate error distributions
40 ppm timing and frequency GHz
1000 channel realizations, 20 trials per channel realization
John Ketchum, et al., Qualcomm Incorporated

26. Short Training Sequence Detection Performance in TGn Channels
Month 2002
doc.: IEEE /xxxr0
July 2004
Short Training Sequence Detection Performance in TGn Channels
John Ketchum, et al., Qualcomm Incorporated
John Doe, His Company

27. Frequency Estimation Performance in TGn Channels
July 2004
Frequency Estimation Performance in TGn Channels
John Ketchum, et al., Qualcomm Incorporated

28. Frequency Error CDF July 2004 SNR = 10 dB
John Ketchum, et al., Qualcomm Incorporated

29. MIMO WLAN Prototype July 2004
John Ketchum, et al., Qualcomm Incorporated

30. Qualcomm MIMO WLAN Prototype
July 2004
Qualcomm MIMO WLAN Prototype
Fully operational hardware prototype of n MIMO WLAN modem
Supports four antennas for Tx/Rx
Processing implemented in two Virtex-II Xilinx FPGAs
FPGA board has four channels that are digitized using four 12-bit A/D converters
All signal processing is real-time
IF sampled at 80 MHz is converted to complex baseband at 20 MHz sampling rate
FFT and spatial processing runs at peak rate of 250 kHz
Multiple parallel convolutional decoders run at 80 MHz clock to provide high-speed decoding
Fully operational hardware channel estimation and tracking
Supports stationary and low-mobility operation
Closed-loop rate control performs real-time rate adjustments
Performance matches results of detailed simulations
Operates in PCS band (1930 – 1950 MHz)
0 dBm per antenna Tx power to limit interference to PCS users per experimental license
John Ketchum, et al., Qualcomm Incorporated

31. MIMO WLAN Prototype July 2004
John Ketchum, et al., Qualcomm Incorporated

32. MIMO WLAN Prototype July 2004
John Ketchum, et al., Qualcomm Incorporated

33. MIMO WLAN Measured Performance
July 2004
MIMO WLAN Measured Performance
Measurements made in Qualcomm’s Concord MA offices
Renovated mill building with brick outer walls, sheet-rock on metal studs inner walls
41.2 m x 16.8 m, 3.2 m high floor-to-ceiling walls
Measured values indicate error-free physical-layer data rates achieved
All rates reflect communications between AP and stations
Measurements made at 1940 MHz
Measurement results extrapolated to 2.4 GHz and 5.25 GHz unlicensed bands
Data rates scaled to reflect operation in SNRs were modified to reflect 17 dBm total Tx power, and increased path loss at 2.4 GHz (1.6 dB) and 5.25 GHz (8.4 dB)
Resulting median/minimum physical layer data rates:
2.4 GHz: 310/198 Mbps
5.25 GHz: 225/120 Mbps
John Ketchum, et al., Qualcomm Incorporated

34. Measured PHY Data Rates
July 2004
Measured PHY Data Rates
John Ketchum, et al., Qualcomm Incorporated

35. Extrapolated PHY Data Rates
July 2004
Extrapolated PHY Data Rates
John Ketchum, et al., Qualcomm Incorporated

36. July 2004
Summary
Eigenvector steered mode supports high throughput operation in 2x2 and 4x4 configurations
Stable wideband spatial channels synthesized from eigenmodes easily support 256 QAM under full PHY impairments
High throughput eigenvector steering operation proven in hardware prototype
John Ketchum, et al., Qualcomm Incorporated