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Mehdi Abolfathi SDR Course Spring 2008
A Cognitive MAC Protocol for Ad Hoc Networks Mehdi Abolfathi SDR Course Spring 2008
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Overview Need for Spectrum Access Related Works
Access Scheme and Capacity PUs Constraints Sensing Techniques Statistical Channel Allocation Proposed combination
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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
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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
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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
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SU Access Schemes VX Scheme KS Scheme (Virtual-Xmit-if-Busy)
(Keep-Sensing-if-Busy)
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Collision Probabilities
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Primary User’s Statistics
Idle Time=Exponential Busy Time=General n Channels Modeled as a M/G/n Queue
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SU’s Maximum Capacity SU Packet Len. Dist. Mean PU Idle time
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SU’s Maximum Capacity
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PU’s Collision Probability
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Multiple SUs, one Channels
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Multiple SUs, one Channel
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“Random Sensing” vs. “All Sensing”
SU randomly selects a channel + Vitual Transmission All-Channel-Sensing: Each SU senses all channels + Virtual Transmission
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QoS of PU All-Channel-Sensing strategy does not improve the total spectral efficiency
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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
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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
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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
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Statistical Channel Allocation
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Successful Rate vs. Operating Range
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Successful Rate vs. Aggregation, m
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Proposed: “SCA” + “VX Scheme”
Identifying PU’s parameters, Historical Study Search for the maximum available rate Accessing the channel using the VX scheme
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“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.
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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)
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Questions ?
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