1. Mehdi Abolfathi SDR Course Spring 2008
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 KS Scheme (Virtual-Xmit-if-Busy)
(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”
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 Idle Time=Exponential Busy Time=General n Channels
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. References
[1] Opportunistic Spectrum Access in Cognitive Radio Networks, Senhua Huang, Xin Liu, and Zhi Ding, MOBIHOC 2008, Phoenix, AZ, US
[2]Decentralized Cognitive MAC for Opportunistic Spectrum Access in Cognitive Ad Hoc Networks, Qing Zhao, Lang Tong, Ananthram Swami, and Yunxia Chen, IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 25, NO. 3, APRIL 2007
[3] Decentralized Cognitive MAC for Opportunistic Spectrum Access in Ad Hoc Networks: A POMDP Framework, Qing Zhao, Lang Tong, Ananthram Swami, and Yunxia Chen, IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 25, NO. 3, APRIL 2007
[4] Multiband Ad Hoc Cognitive Radio for Reducing Inter System Interference, Takeo Fujii, Yukihiro Kamiya, Yasuo Suzuki, The 17th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC 2006)

25. Questions ?