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Single Burst Contention Resolution

Single Burst Contention Resolution. “Wireless Collision Detection” (“CSMA/CS”). Overview. Proposed new technology family for collision detection Uses OFDM modulation techniques Potentially provides better then 50% improvement in network efficiency Potential use in 802.11a and 802.11g.

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Single Burst Contention Resolution

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  1. Single Burst Contention Resolution “Wireless Collision Detection” (“CSMA/CS”) David Beberman, Corporate Wave Net, Inc.

  2. Overview • Proposed new technology family for collision detection • Uses OFDM modulation techniques • Potentially provides better then 50% improvement in network efficiency • Potential use in 802.11a and 802.11g David Beberman, Corporate Wave Net, Inc.

  3. CSMA/CA • Positive Acknowledgement • Collision time equals length of longest colliding data frame David Beberman, Corporate Wave Net, Inc.

  4. CSMA/CS • Positive Acknowledgement Optional in certain circumstances • Fixed short collision time David Beberman, Corporate Wave Net, Inc.

  5. Performance • IEEE 802.11 Wireless LAN: Capcity Analysis and Protocol Enhancement <0-7803-4386-7/98> • Packet transmit time = average length of packet + acknowledgement + (IFSs + backoffs) • Data transmit time = Packet transmit time + (Collision time x average collision percent) David Beberman, Corporate Wave Net, Inc.

  6. CSMA/CA vs CSMA/CSperformance graph David Beberman, Corporate Wave Net, Inc.

  7. CSMA/CA vs CSMA/CSperformance graph David Beberman, Corporate Wave Net, Inc.

  8. Current Solution: RTS/CTS • Performs contention resolution function • Used in larger sized packet transfers • Significant overhead due to total packet length of RTS and CTS David Beberman, Corporate Wave Net, Inc.

  9. What is needed? • Low network overhead contention resolution • Minimal implementation complexity • Minimal per node processing overhead • Fast collision detection at contending nodes David Beberman, Corporate Wave Net, Inc.

  10. Contention Symbol (“CSMA/CS”) • Channel Arbiter (“CA”) and nodes • Contention Symbol: single short OFDM burst • CA - fast collision detection algorithm • CA – single short OFDM burst response • OFDM burst length principally determined by propagation delay David Beberman, Corporate Wave Net, Inc.

  11. CSMA/CS How it works. David Beberman, Corporate Wave Net, Inc.

  12. Binary amplitude OFDM tones • implies: • Ignores all phase information • No synchronization information needed • Only requires overlap of orthogonal section of all received OFDM bursts David Beberman, Corporate Wave Net, Inc.

  13. Binary tone patterns • Set of linear independent basis vectors, example: • 1010, 0101, 0110, 1001, 0011, 1100 • Binary OR of two or more vectors from set, result not in set • Property: any vector with greater then ½ binary 1’s means OR of 2 or more vectors occured David Beberman, Corporate Wave Net, Inc.

  14. Multiple sets of vectors • 13 vectors of 4 bits each • Each vector random choice from set of 6 basis vectors • Resulting concatenated 52 bit vector • Very low probability of all 13 vectors identical from any two nodes. (Binomial probability distribution) David Beberman, Corporate Wave Net, Inc.

  15. Frequency Mapping • 52 bit binary vector mapped as binary on/off tones in 802.11 OFDM frequency map magnitudes • Discrete randomized phase rotations on a per tone basis. • Reduces opportunity for destructive phase interference between two signals David Beberman, Corporate Wave Net, Inc.

  16. OFDM burst transmission • Perform IFFT • Perform digital and analog modulation and transmission David Beberman, Corporate Wave Net, Inc.

  17. Burst reception at CA • Performs threshold power detection at defined sensitivity level • Waits for predefined propagation interval and guard interval • Captures OFDM burst • Performs analog and digital demodulation to baseband David Beberman, Corporate Wave Net, Inc.

  18. Burst reception at CA • Performs FFT on OFDM burst • Takes magnitude of complex frequency map elements • Creates binary vector using threshold value • Compares 13 sub vectors with set of basis vectors, using binary 1’s count • Collision detected in any single sub vector David Beberman, Corporate Wave Net, Inc.

  19. CA response • CA generates similar binary amplitude OFDM burst, consisting of: • Pattern A – collision detected • Pattern B – no collision detected David Beberman, Corporate Wave Net, Inc.

  20. Node receiving CA burst • Performs FFT on baseband signal • Thresholds magnitudes to create binary vector • Compares vector with known CA symbols • On no collision detected, waits for propagation delays, and transmits normal data frame David Beberman, Corporate Wave Net, Inc.

  21. Approximate Timing for 802.l1a • 4 uS frame + cyclic extension for propagation delays (< 1 uS per 100 meters) + cyclic extension for carrier sense delays at nodes (2 < uS ?) • Fixed wait between node burst and CA burst = (carrier sense delay) • 4 uS CA frame + propagation delay + carrier sense delay (carried forward) David Beberman, Corporate Wave Net, Inc.

  22. Approximate Timing for 802.11a • 16 uS for no collision detection • 14 uS for collision detected • Node transmits data frame after processing delays David Beberman, Corporate Wave Net, Inc.

  23. Comparison with RTS/CTS • RTS approximately 24 uS (54 MB) or greater • CTS approximately 24 uS (54 MB) or greater • 2 IFS = 32 uS • Total >= 80 uS for no collision detected • Total >= 49 uS for collision detected • CSMA/CS > 5 times faster data transmit turnaround • CSMA/CS > 3 times faster collision detection David Beberman, Corporate Wave Net, Inc.

  24. Comments • Constant fixed overhead suitable for all contention based traffic • Solves near/far power “capture” problem • Allows multiple infrastructure access points • Back compatible with 802.11 protocol David Beberman, Corporate Wave Net, Inc.

  25. Solutions For • Quality of Service • “Semi-soft” cell switching • Transmit power modulation • “Micro cells” • Inbuilding geolocation • Frequency offset error correction • Short duration burst noise David Beberman, Corporate Wave Net, Inc.

  26. Solutions For • Contention free operation periods • Collision detection in Ad hoc network operation David Beberman, Corporate Wave Net, Inc.

  27. Intellectual Property Statement • Corporate Wave Net, Inc. has multiple patents pending regarding the information presented. • CWN is willing to consider licensing of certain pending patents in its portfolio which are directed to and necessary for the implementation and practice of the technology presented for the purposes of IEEE standardization, on fair, reasonable and non-discriminatory terms and conditions to qualified applicants in accordance with IEEE patent policy David Beberman, Corporate Wave Net, Inc.

  28. Corporate Wave Net, Inc. David Beberman 104 Otis St. Ste. 29 Northboro, MA. 01532 P: (508) 351 – 9492 CWN1@world.std.com David Beberman, Corporate Wave Net, Inc.

  29. Carrier Sense Multiple Access with Contention Symbol CSMA/CS David Beberman, Corporate Wave Net, Inc.

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