1. Experiments with an 802.11n Radio Testbed
July 2005
doc.: IEEE / n
July 2005
Experiments with an n Radio Testbed
Date:
Authors:
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David Browne, UCLA UnWiReD Lab
David Browne, UCLA UnWiReD Lab

2. July 2005
doc.: IEEE / n
July 2005
Abstract
Present a software defined MIMO-OFDM testbed with n functionality.
Present a channel sounding scheme that can be integrated into n testbeds.
Demo simultaneous channel sounding and n measurements on the testbed via internet.
Present results from a measurement campaign in which a comparison was made between proposed n modem/codec schemes.
David Browne, UCLA UnWiReD Lab
David Browne, UCLA UnWiReD Lab

3. Experiments with an 802.11n Radio Testbed
July 2005
Experiments with an n Radio Testbed
U n W i R e D L a b
UCLA Wireless Research and Development
(in collaboration with STMicroelectronics)
Michael Fitz
David Browne, Weijun Zhu
David Browne, UCLA UnWiReD Lab

4. July 2005
Outline
Present a software defined MIMO-OFDM testbed with n functionality.
Present a channel sounding scheme that can be integrated into n testbeds.
Demo simultaneous channel sounding and n measurements on the testbed via internet.
Present results from a measurement campaign.
David Browne, UCLA UnWiReD Lab

5. MIMO-OFDM Radio Testbed
July 2005
MIMO-OFDM Radio Testbed
David Browne, UCLA UnWiReD Lab

6. MIMO-OFDM Radio Testbed
July 2005
MIMO-OFDM Radio Testbed
David Browne, UCLA UnWiReD Lab

7. MIMO-OFDM Radio Testbed
July 2005
MIMO-OFDM Radio Testbed
Radios
digital baseband
4 x 4 MIMO
fc = 2.4GHz
20MHz bandwidth
120Mbps throughput
3% EVM
internet control
David Browne, UCLA UnWiReD Lab

8. MIMO-OFDM Radio Testbed
July 2005
MIMO-OFDM Radio Testbed
Robots
spatial positioning
70cm x 70cm grid
1.59mm precision
LEGO
internet control
Antenna Arrays
variable geometry
dipoles, patches
compact MIMO arrays
David Browne, UCLA UnWiReD Lab

9. MIMO-OFDM Radio Testbed
July 2005
MIMO-OFDM Radio Testbed
Fair comparison of MIMO-OFDM signaling schemes
Multipath distortion
Phase noise
Frequency offset
Non-linear amplifiers
Antenna mutual coupling
...
Method:
simultaneous channel sounding and data transmission
David Browne, UCLA UnWiReD Lab

10. Field Test - Super Frame
July 2005
Field Test - Super Frame
Superframe Structure:
Up to 800us long.
One channel sounding packet.
Data packets with possibly different coding and modulation schemes.
Silence period between packets.
David Browne, UCLA UnWiReD Lab

11. Field Test - Super Frame
July 2005
Field Test - Super Frame
Assumption:
Channel characteristics does not change significantly over the super frame.
Advantage:
Possible to characterize data packet’s performance with the knowledge of channel environment.
Each scheme’s frame is self contained:
synchronization fields (similar to a)
preamble
payload information packet
David Browne, UCLA UnWiReD Lab

12. Field Test - General Frame Structure
July 2005
Field Test - General Frame Structure
802.11a Preamble for timing and frequency estimation.
Flexible structure for testing different MIMO-OFDM schemes simultaneously.
Implemented algorithms include Spatial multiplexing and space-time blocking coding, LDPC/BCC/Space-time trellis coding, etc. Many key algorithms related to the TGn proposals have been implemented and tested.
David Browne, UCLA UnWiReD Lab

13. Channel Sounding Packets
July 2005
Channel Sounding Packets
David Browne, UCLA UnWiReD Lab

14. July 2005
Outline
Present a software defined MIMO-OFDM testbed with n functionality.
Demo simultaneous channel sounding and n measurements on the testbed via internet.
Present a channel sounding scheme that can be integrated into n testbeds.
Present results from a measurement campaign.
David Browne, UCLA UnWiReD Lab

15. July 2005
David Browne, UCLA UnWiReD Lab

16. July 2005
Live Demo
David Browne, UCLA UnWiReD Lab

17. July 2005
Outline
Present a software defined MIMO-OFDM testbed with n functionality.
Demo simultaneous channel sounding and n measurements on the testbed via internet.
Present a channel sounding scheme that can be integrated into n testbeds.
Present results from a measurement campaign.
David Browne, UCLA UnWiReD Lab

18. Channel Sounding Popular Methods: Delay domain channel sounders
July 2005
Channel Sounding
Popular Methods:
Delay domain channel sounders
Correlation methods that estimate channel impulse response.
Swept frequency channel sounders
SISO hardware adapted to MIMO (virtual & switched arrays).
Require time synchronization.
Difficult to detect co-channel interference.
Do not utilize .11n radio architecture.
David Browne, UCLA UnWiReD Lab

19. Channel Sounding Proposed Scheme:
July 2005
Channel Sounding
Proposed Scheme:
Space-Frequency method suited to MIMO-OFDM.
Does not require time synchronization of TX and RX.
Integrated into testbed packet scheme.
Instantaneous channel capacity results.
reflects hardware and channel distortion experienced by packets.
Detects co-channel interference during a measurement.
David Browne, UCLA UnWiReD Lab

20. Channel Sounding The space-frequency signaling scheme …
July 2005
Channel Sounding
The space-frequency signaling scheme …
… and associated channel estimation algorithm.
David Browne, UCLA UnWiReD Lab

21. Channel Sounding Transmitter (2 x 2 Example) July 2005
David Browne, UCLA UnWiReD Lab

22. Channel Sounding Excitation Signal Synthesis… July 2005
David Browne, UCLA UnWiReD Lab

23. Channel Sounding Excitation Signal Spectra… July 2005
David Browne, UCLA UnWiReD Lab

24. Channel Sounding Space-Frequency Orthogonality … July 2005
David Browne, UCLA UnWiReD Lab

25. Channel Sounding Excitation Signal Waveform Poor PAPR … July 2005
David Browne, UCLA UnWiReD Lab

26. Channel Sounding Excitation Signal Waveform (good PAPR) … July 2005
David Browne, UCLA UnWiReD Lab

27. Channel Sounding Receiver (2 x 2 Example) July 2005
David Browne, UCLA UnWiReD Lab

28. Channel Sounding Orthogonal transformation by FFT… July 2005
David Browne, UCLA UnWiReD Lab

29. Channel Sounding Noise detection … July 2005
David Browne, UCLA UnWiReD Lab

30. July 2005
Channel Sounding
David Browne, UCLA UnWiReD Lab

31. Channel Sounding Signal detection … July 2005
David Browne, UCLA UnWiReD Lab

32. Channel Sounding Channel estimation … July 2005
David Browne, UCLA UnWiReD Lab

33. Channel Sounding Interference detection … Nominal Signal
July 2005
Channel Sounding
Interference detection …
Nominal Signal
Nominal Noise Floor
802.11b Interference Bluetooth Inteference
David Browne, UCLA UnWiReD Lab

34. Channel Sounding Advantages:
July 2005
Channel Sounding
Advantages:
Space-Frequency orthogonallity suited to MIMO-OFDM.
Signal periodicity → no time synchronization.
Low PAPR → max range and linear RF operation.
Utilizes n radio architecture.
Detection of co-channel interference
David Browne, UCLA UnWiReD Lab

35. System Benchtest on a 2x2 MIMO Channel Emulator…
July 2005
System Benchtest on a 2x2 MIMO Channel Emulator…
David Browne, UCLA UnWiReD Lab

36. Ideal Gaussian 2x2 MIMO Channel
July 2005
Ideal Gaussian 2x2 MIMO Channel
David Browne, UCLA UnWiReD Lab

37. Indoor Correlated Spatial Channel
July 2005
Indoor Correlated Spatial Channel
David Browne, UCLA UnWiReD Lab

38. Single Path Keyhole Channel
July 2005
Single Path Keyhole Channel
David Browne, UCLA UnWiReD Lab

39. July 2005
Outline
Present a software defined MIMO-OFDM testbed with n functionality.
Demo simultaneous channel sounding and n measurements on the testbed via internet.
Present a channel sounding scheme that can be integrated into n testbeds.
Present results from a measurement campaign.
David Browne, UCLA UnWiReD Lab

40. Field Tests Scenario: Indoor Office Environment
July 2005
Field Tests
Scenario:
Indoor Office Environment
Line-of-Sight & Non-Line-of-Sight
Variable TX power (-6dBm ~ 15dBm)
Linear array of dipoles
0.5 λ antenna spacing
11 x 9 positioning grid with λ/2 grid spacing
10 time separated measurements per grid point
David Browne, UCLA UnWiReD Lab

41. July 2005
Field Tests
David Browne, UCLA UnWiReD Lab

42. July 2005
Capacity vs. SNR
David Browne, UCLA UnWiReD Lab

43. July 2005
Capacity vs. SNR
David Browne, UCLA UnWiReD Lab

44. Capacity vs. SNR >10 000 data measurement points.
July 2005
Capacity vs. SNR
> data measurement points.
Error statistics binned by SNR (left) and Capacity (right).
SNR does not expose trend we expect (too few points).
Capacity plot better at exposing the error rate profile.
David Browne, UCLA UnWiReD Lab

45. Capacity vs. SNR Capacity is better suited to characterizing MIMO
July 2005
Capacity vs. SNR
Capacity is better suited to characterizing MIMO
performance in field measurements
Accounts for both SNR and channel structure.
Fewer degrees of freedom → fewer data points needed.
David Browne, UCLA UnWiReD Lab

46. Field Test - Compared Schemes
July 2005
Field Test - Compared Schemes
Experimental Modem/Codec Parameters:
2 x 2 and 2 x 3 data signaling
4 x 4 channel sounding.
WWise LDPC and BCC,
Rate 1/2, 2/3, 5/6.
16QAM and 64QAM.
MIMO Preamble based on Hadamard Sequence.
Pilot Tones (Orthogonal w.r.t different TX channels).
1000 information bytes per data packet.
David Browne, UCLA UnWiReD Lab

47. Field Test - Observation Perspectives
July 2005
Field Test - Observation Perspectives
LDPC vs. BCC
LOS vs. NLOS
2RX vs. 3RX
Plotting against capacity vs. SNR
Hardware Limitation
David Browne, UCLA UnWiReD Lab

48. Field Test Results - LDPC vs. BCC (1)
July 2005
Field Test Results - LDPC vs. BCC (1)
LDPC significantly outperforms BCC, especially at high rate.
David Browne, UCLA UnWiReD Lab

49. Field Test Results - LDPC vs. BCC (2)
July 2005
Field Test Results - LDPC vs. BCC (2)
BCC shows a much higher error floor than LDPC.
David Browne, UCLA UnWiReD Lab

50. Field Test Results - LOS vs. NLOS (1)
July 2005
Field Test Results - LOS vs. NLOS (1)
Comparison not obvious when plotting PER against capacity.
David Browne, UCLA UnWiReD Lab

51. Field Test Results - LOS vs. NLOS (2)
July 2005
Field Test Results - LOS vs. NLOS (2)
LOS suffers performance degradation at higher SNR compared with NLOS except with the highest rate mode.
David Browne, UCLA UnWiReD Lab

52. Field Test Results - 2 RX vs. 3 RX (1)
July 2005
Field Test Results - 2 RX vs. 3 RX (1)
Performance difference is significant when plotting against SNR.
David Browne, UCLA UnWiReD Lab

53. Field Test Results - 2 RX vs. 3 RX (2)
July 2005
Field Test Results - 2 RX vs. 3 RX (2)
Performance is very close for most of test modes when plotting against the capacity.
Indicating that capacity is a better choice of measure of channel.
David Browne, UCLA UnWiReD Lab

54. Field Test Results - Hardware Limitation
July 2005
Field Test Results - Hardware Limitation
Maximum SNR achievable is about 32 ~ 34 dB on the testbed.
David Browne, UCLA UnWiReD Lab

55. Field Test Conclusions
July 2005
Field Test Conclusions
Capacity better suited to characterizing MIMO performance in measurement campaigns than SNR .
LDPC outperforms BCC.
LOS performance degradation observed.
Direct comparison of how close n performs compared to the achievable channel capacity.
David Browne, UCLA UnWiReD Lab

56. July 2005
Conclusion
Presented a software defined MIMO-OFDM testbed with n functionality.
Presented a channel sounding scheme that can be integrated into n testbeds
Demoed simultaneous channel sounding and n measurements on the testbed via internet.
Presented results from a measurement campaign.
David Browne, UCLA UnWiReD Lab

57. July 2005
References
W. Zhu, D.W. Browne, M.P. Fitz, "An Open Access Wideband Multi-Antenna Wireless Testbed with Remote Control Capability", IEEE TridentCom, February 2005.
D. W. Browne, W. Zhu, and M.P. Fitz, "A Signaling Scheme and Estimation Algorithm for Characterizing Frequency Selective MIMO Channels," IEEE Vehicular Technology Conference, May 2005.
D. W. Browne, M. Manteghi, M. P. Fitz, Y. Rahmat-Samii, "Antenna Topology Impacts on Measured MIMO Capacity," IEEE Vehicular Technology Conference, September 2005.
David Browne, UCLA UnWiReD Lab