Date post: | 21-Dec-2015 |
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Overview
• Need for Spectrum Access• Related Works• Access Scheme and Capacity• Pus Constraints• Sensing Techniques• Statistical Channel Allocation• Proposed combination
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
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
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
Primary User’s Statistics
• Idle Time=Exponential • Busy Time=General• n Channels
Modeled as a M/G/n Queue
“Random Sensing” vs. “All Sensing”
Random-Sensing: SU randomly selects a channel + Vitual Transmission
All-Channel-Sensing: Each SU senses all channels + Virtual Transmission
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
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
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
Proposed: “SCA” + “VX Scheme”
• Identifying PU’s parameters, Historical Study
• Search for the maximum available rate
• Accessing the channel using the VX scheme
“SCA” + “VX Scheme”, Benefits
1. Distributed calculation, Ad Hoc networks
2. Not to sense the channel in unnecessary occasions, Hardware savings.
3. Smart access to the channel.
4. Finding the best combination of the channels to achieve the maximum throughput.
5. Acting as an independent layer for upper layers by transparency in the case of busy channel.