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Mehdi Abolfathi SDR Course Spring 2008

A Cognitive MAC Protocol for Ad Hoc Networks. Mehdi Abolfathi SDR Course Spring 2008. Overview. Need for Spectrum Access Related Works Access Scheme and Capacity Pus Constraints Sensing Techniques Statistical Channel Allocation Proposed combination. Cognitive Spectrum Access.

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Mehdi Abolfathi SDR Course Spring 2008

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  1. A Cognitive MAC Protocol for Ad Hoc Networks Mehdi Abolfathi SDR Course Spring 2008

  2. Overview • Need for Spectrum Access • Related Works • Access Scheme and Capacity • Pus Constraints • Sensing Techniques • Statistical Channel Allocation • Proposed combination

  3. Cognitive Spectrum Access • Basic idea • Sense the spectrum you want to transmit in • Look for “holes” or “opportunities” in time and frequency • Transmit so that you “don’t interfere” with the licensees

  4. Cognitive Spectrum Access • Goals • Dynamically control access (Tx/Rx, beam, power etc.) on each time/frequency such that network capacity is maximized • Constraints are honored • Capacity demands are met

  5. Related Works • Centralized and decentralized spectrum auction and brokerage • POMDP MAC protocol framework • A tri-band protocol, called the dynamic open spectrum sharing (DOSS) MAC

  6. SU Access Schemes VX Scheme (Virtual-Xmit-if-Busy) KS Scheme (Keep-Sensing-if-Busy)

  7. Collision Probabilities

  8. Primary User’s Statistics • Idle Time=Exponential • Busy Time=General • n Channels • Modeled as a M/G/n Queue

  9. SU’s Maximum Capacity SU Packet Len. Dist. Mean PU Idle time

  10. SU’s Maximum Capacity

  11. PU’s Collision Probability

  12. Multiple SUs, one Channels

  13. Multiple SUs, one Channel

  14. “Random Sensing” vs. “All Sensing” Random-Sensing: SU randomly selects a channel + Vitual Transmission All-Channel-Sensing: Each SU senses all channels + Virtual Transmission

  15. QoS of PU All-Channel-Sensing strategy does not improve the total spectral efficiency

  16. Multi-Band, Multi-User System • Multiple SUs has no loss/gain in terms of total throughput. • Sensing all the frequency bands does not improve the total throughput of SUs. • Dividing SUs into groups ≈ Scaled throughput

  17. Consraints • For the Primary User • Idle Time=Exponential • Busy Time=General • n Channels • Modeled as a M/G/n Queue SU Packet Len. Dist. Mean PU Idle time

  18. Constraints • G in “M/G/n” appears in: • Need for Sensing the Channel in KS or VX scheme • Capacity of SU decreases by the factor of

  19. Statistical Channel Allocation

  20. Successful Rate vs. Operating Range

  21. Successful Rate vs. Aggregation, m

  22. Proposed: “SCA” + “VX Scheme” • Identifying PU’s parameters, Historical Study • Search for the maximum available rate • Accessing the channel using the VX scheme

  23. “SCA” + “VX Scheme”, Benefits • Distributed calculation, Ad Hoc networks • Not to sense the channel in unnecessary occasions, Hardware savings. • Smart access to the channel. • Finding the best combination of the channels to achieve the maximum throughput. • Acting as an independent layer for upper layers by transparency in the case of busy channel.

  24. Questions

  25. Some Results • SU’s Capacity Bound: • Under the VX scheme, the SU achieves the maximum throughput when it transmits fixed length packets, i.e., L2 = l2.

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