1. Sept 2004
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: [CCA algorithm proposal for MB-OFDM]
Date Submitted: [9 Sept, 2004]
Source: [Charles Razzell, Yifeng Zhang] Company [Philips]
Address [1109, McKay Drive, San Jose, CA 95131, USA]
Voice:[ ], FAX: [ ],
Re: [ ]
Abstract: [Two algorithm proposals based on the same basic principle are evaluated for performance and complexity. Fast CCA is achieved requiring neither preamble correlation nor pre-existing, tight time and frequency synchronization. Initial estimations of algorithmic complexity are given.]
Purpose: []
Notice: This document has been prepared to assist the IEEE P It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P
C. Razzell, Y.Zhang, Philips

2. CCA algorithm proposal for MB-OFDM
Sept 2004
CCA algorithm proposal for MB-OFDM
C. Razzell, Y.Zhang, Philips

3. Sept 2004
Background
Previous proposals for MB-OFDM CCA have focused on time domain correlation of preamble
Energy detect may also be used as coarse detection for strong input signal
Ambiguity of media status appears when frame preamble is missing and SNR is low (close to sensitivity level)
Ambiguity of media status impacts MAC decisions, and may degrade the throughput
C. Razzell, Y.Zhang, Philips

4. Requirements CCA should be able to sense the media at any time
Sept 2004
Requirements
CCA should be able to sense the media at any time
The channel clear state should be sensed within a few micro seconds (within 3.75ms is the target)
CCA should be reliable at SNR as low as possible, and be robust in multipath channels
CCA should be reliable even in SOP environment
CCA implementation should be as simple as possible
C. Razzell, Y.Zhang, Philips

5. Scenarios analysis for CCA without preamble
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doc.: IEEE a
Sept 2004
Scenarios analysis for CCA without preamble
Two scenarios have been identified
Receiver is not time-synchronized to the channel Time-Frequency Interleaving (TFI) code
This is rarely a relevant case for media access, since timing must be known to access the media. It may, however, act as an aid to initial acquisition.
Receiver has at least coarse time synchronization for the relevant TFI code to be used
This is often the case after initial acquisition: a small amount of timing drift occurs depending on the time elapsed after the most recent successful burst reception.
C. Razzell, Y.Zhang, Philips
C. Razzell, Y.Zhang, Philips

6. Signal analysis for Case 1
Sept 2004
Signal analysis for Case 1
If the TFI channel timing information is not available to the receiver, the receiver has to stay at one channel to receive at least 1/3 of the symbols; otherwise, cases like hopping chasing could happen, and nothing will be received.
C. Razzell, Y.Zhang, Philips

7. Signal analysis for Case 1 (continued)
Sept 2004
Signal analysis for Case 1 (continued)
If receiver stays on one frequency channel, the signal will be gated by the channel selectivity.
C. Razzell, Y.Zhang, Philips

8. Proposed algorithm for case 1
Sept 2004
Proposed algorithm for case 1
A 128 moving average (MA) algorithm is proposed for this case. The sample power is calculated and MA over 128 samples. For a properly down-converted UWB symbol, the power MA over 128 samples is equivalent to frequency domain MRC, which maximizes the SNR at the MA output.
C. Razzell, Y.Zhang, Philips

9. Mathematical explanation of MA algorithm
Sept 2004
Mathematical explanation of MA algorithm
Received
UWB Symbol
Parseval’s theorem for Periodic signal
RHS is recognizable as
Frequency domain
maximal ratio
Combining (MRC)
C. Razzell, Y.Zhang, Philips

10. Sept 2004
MA based CCA detector
C. Razzell, Y.Zhang, Philips

11. MA based CCA detector description
Sept 2004
MA based CCA detector description
A peak detector will be used to find the peak of the MA output
A pre-determined threshold (Pth) is used to compare with the peak
A peak window is used to detect the periodicity of the peak (Pwindow)
A peak counter is used to count the number of peak occurred (Npeak)
Properly chosen Pth, Pwindow and Npeak can achieve optimal false alarm rate and missed frame rate
C. Razzell, Y.Zhang, Philips

12. MA based CCA detector performance
Sept 2004
MA based CCA detector performance
C. Razzell, Y.Zhang, Philips

13. MA based CCA detector performance
Sept 2004
MA based CCA detector performance
C. Razzell, Y.Zhang, Philips

14. MA based CCA detector performance
Sept 2004
MA based CCA detector performance
C. Razzell, Y.Zhang, Philips

15. MA based CCA detector performance
Sept 2004
MA based CCA detector performance
C. Razzell, Y.Zhang, Philips

16. MA based CCA detector performance
Sept 2004
MA based CCA detector performance
C. Razzell, Y.Zhang, Philips

17. MA based CCA detector performance
Sept 2004
MA based CCA detector performance
C. Razzell, Y.Zhang, Philips

18. Complexity of MA based CCA
Sept 2004
Complexity of MA based CCA
Since MA is calculated sample by sample, it needs only 5 multipliers, 5 adders and size 128 buffer, and results in modest gate count.
C. Razzell, Y.Zhang, Philips

19. Signal analysis for Case 2
Sept 2004
Signal analysis for Case 2
If TFI channel timing information is coarsely available to the receiver, the receiver can follow the assigned frequency/time sequence and almost all the symbols can be down-converted to base band.
C. Razzell, Y.Zhang, Philips

20. Signal analysis for Case 2 (continued)
Sept 2004
Signal analysis for Case 2 (continued)
If TFI timing information is coarsely available to the receiver, due to ZP, the signal can be looked as the product of a continuous random signal with a 3.2MHz square wave clock
C. Razzell, Y.Zhang, Philips

21. Proposed algorithm for case 2
Sept 2004
Proposed algorithm for case 2
A symbol based cross-correlation (CC) algorithm is proposed. By using symbol by symbol cross correlation of the input signal and a 3.2MHz sinusoid, the existence of UWB signal can be detected.
C. Razzell, Y.Zhang, Philips

22. Mathematical explanation of CC algorithm
Sept 2004
Mathematical explanation of CC algorithm
Instantaneous power of received UWB signal, remove impact from frequency offset
Remove DC to enhance 3.2MHz frequency component, N is number of samples per period
Cross correlation with 3.2MHz sinusoid
C. Razzell, Y.Zhang, Philips

23. Sept 2004
CC based CCA detector
C. Razzell, Y.Zhang, Philips

24. CC based CCA detector description
Sept 2004
CC based CCA detector description
Several symbols (Nsym) are used to provide averaged CC output
A pre-determined threshold (Pth) is used to compare with the CC output
Properly chosen Pth, and Nsym can achieve good false alarm rate and missed frame rate
A counter can be used to count the number of contiguous CC outputs which are larger than Pth. This will enhance both the false alarm rate and missed frame rate performance.
C. Razzell, Y.Zhang, Philips

25. CC based CCA detector performance
Sept 2004
CC based CCA detector performance
C. Razzell, Y.Zhang, Philips

26. CC based CCA detector performance
Sept 2004
CC based CCA detector performance
C. Razzell, Y.Zhang, Philips

27. CC based CCA detector performance
Sept 2004
CC based CCA detector performance
C. Razzell, Y.Zhang, Philips

28. CC based CCA detector performance
Sept 2004
CC based CCA detector performance
C. Razzell, Y.Zhang, Philips

29. CC based CCA detector performance
Sept 2004
CC based CCA detector performance
C. Razzell, Y.Zhang, Philips

30. CC based CCA detector performance
Sept 2004
CC based CCA detector performance
C. Razzell, Y.Zhang, Philips

31. CC based CCA detector performance
Sept 2004
CC based CCA detector performance
C. Razzell, Y.Zhang, Philips

32. Complexity of CC based CCA
Sept 2004
Complexity of CC based CCA
Since CC is also calculated sample by sample, it needs only 5 multipliers, 5 adders and size 64 buffer (due to the symmetric property of sinusoid), which has even less gate count compared with MA.
C. Razzell, Y.Zhang, Philips

33. Comparison of two schemes
Sept 2004
Comparison of two schemes
Comparison parameters
MA algorithm
CC algorithm
Channel dependency
Robust
False alarm rate
Relatively low
Relatively lower
Detection duration
3.75ms
Sensitivity to TFI sync
piconet identify capability
Low
High
SOP tolerance
Mid
Complexity
Very low
Very low, and lower than MA algorithm
C. Razzell, Y.Zhang, Philips

34. Sept 2004
Conclusions
Two CCA schemes for systems missing preamble detection is proposed
Both schemes provide reliable detection (detect rate > 90%) within 3.75us, regardless of channel condition, at SNR > -2 dB.
With SOP, the MA shows robust performance while CC shows acceptable performance
CC method also shows robust performance to the TFI synchronization condition.
Both schemes can be realized with moderate complexity.
C. Razzell, Y.Zhang, Philips

35. Simulation setup and conditions
Sept 2004
Supporting materials
Simulation setup and conditions
C. Razzell, Y.Zhang, Philips

36. Sept 2004
Simulation setup
C. Razzell, Y.Zhang, Philips

37. Simulation condition for MA scheme in different channels
Sept 2004
Simulation condition for MA scheme in different channels
12 UWB symbols(3.75ms) are used for CCA detection
Pth = 1.3
Window size is 90 samples
Number of frames simulated for each SNR is 20000
100 channel realization are used, therefore, 200 frames per channel realization
Peak counter > 1 for a valid detection
The complex channels are normalized such that the shadowing effect is excluded.
C. Razzell, Y.Zhang, Philips

38. Simulation condition for MA scheme in SOP environment
Sept 2004
Simulation condition for MA scheme in SOP environment
12 UWB symbols (3.75ms) are used for CCA detection
Pth = 1.3
Window size is 90 samples
CM4 is used as multipath channel, number of frames simulated for each SNR is 20000, 100 channel realization are used, therefore, 200 frames per channel realization
Peak counter > 1 for a valid detection
The complex channels are normalized such that the shadowing effect is excluded.
There are two piconets in the system, piconet 1 is the designated signal with TFI pattern 1 2 3; piconet 2 is the interference with hopping pattern 1 3 2
C. Razzell, Y.Zhang, Philips

39. Simulation condition for MA scheme in SOP environment (continued)
Sept 2004
Simulation condition for MA scheme in SOP environment (continued)
SNR = 0 dB
piconet 1 and 2 has different relative phase shift that reflects the unsynchronized effect
piconet 2 and 1 has different power level at receiver input, defined as ISR. ISR = -1dB means the power of interference piconet 2 is 1 dB lower than that of piconet 1 at receiver input.
C. Razzell, Y.Zhang, Philips

40. Simulation condition for SOP environment (continued)
Sept 2004
Simulation condition for SOP environment (continued)
Phase misalignment is represented by number of samples in the simulation plot, sampling rate is 1/2112MHz
C. Razzell, Y.Zhang, Philips

41. Simulation condition for CC scheme in different channels
Sept 2004
Simulation condition for CC scheme in different channels
12 UWB symbols (3.75ms) are used for CCA detection
Pth = -12.5dB
Number of frames simulated for each SNR is 20000
100 channel realization are used, therefore, 200 frames per channel realization
The complex channels are normalized such that the shadowing effect is excluded.
Ideal frequency hopping synchronization
C. Razzell, Y.Zhang, Philips

42. Simulation condition for CC scheme in SOP environment
Sept 2004
Simulation condition for CC scheme in SOP environment
12 UWB symbols (3.75ms) are used for CCA detection
Pth = -11.9dB
CM4 is used as multipath channel, number of frames simulated for each SNR is 20000, 100 channel realization are used, therefore, 200 frames per channel realization
The complex channels are normalized such that the shadowing effect is excluded.
There are two piconets in the system, piconet 1 is the designated signal with hopping pattern 1 2 3; piconet 2 is the interference with hopping pattern 1 3 2
SNR = 0 dB
piconet 1 and 2 has different relative phase shift that reflects the unsynchronized effect
piconet 2 and 1 has different power level at receiver input, defined as ISR. ISR = -1dB means the power of interference piconet 2 is 1 dB lower than that of piconet 1 at receiver input.
C. Razzell, Y.Zhang, Philips

43. Sept 2004
Simulation condition for CC scheme with imperfect hopping synchronization
12 UWB symbols (3.75ms) are used for CCA detection
Pth = -11.9
CM4 is used as multipath channel, number of frames simulated for each SNR is 20000, 100 channel realization are used, therefore, 200 frames per channel realization
The complex channels are normalized such that the shadowing effect is excluded.
SNR = 0 dB
Timing illustration is given on next slide…
C. Razzell, Y.Zhang, Philips

44. Sept 2004
Simulation condition for CC scheme with imperfect hopping synchronization
Phase misalignment is represented by number of samples in the simulation plot, sampling rate is 1/2112MHz
C. Razzell, Y.Zhang, Philips