1. Design Tool for Spectrum Sensing of Cognitive Radio
5/15/2009
Jihoon Park

2. Spectrum Allocation Problem
Few spectrum slots are left to allocate.
Allocated spectrum is idle most time.
FCC allows use of allocated spectrum under following regulatory constraints
Minimum signal-to-noise ratio ()
Minimum probability of detection (PD,req)
Maximum detection delay (DD)

3. Idle Spectrum Detection
:detection (quiet) time
Freq.
Detection delay (DD)
:data transmission
Primary User
Primary User
Bandwidth open for use by the CR
Available Idle Bandwidth (Bav)
Detected idle Bandwidth (Beff)
Time
Quiet time
(TQT)
Available data transmission time
Cognitive Radios (CR) can use spectrum allocated to a primary users (PU) as long as it is idle i.e. unused by the PU
A key function is “detecting” if allocated spectrum is idle
Design Objective: Optimize detection efficiency
Maximize amount of idle bandwidth detected
Minimize quiet time (increases data transmission time)
Minimize cost of a design of the spectrum sensing

4. Spectrum Detection Efficiency
Detection Efficiency depends on MAC, PHY, radio, and control channel parameters
Sensing Radio:  (radio bandwidth)
Sensing PHY: TS , PFA
Sensing MAC:
 ,  : parameters determined by how to utilize bandwidth for detection process
 (Cooperation scale: #users who report the sensing results to cooperatively make a decision if a channel is idle)
Control channel: TR ,  (how to utilize bandwidth for reporting operation)
Traditional techniques optimize individual layers
Sub-optimal detection of idle bandwidth
Defined cross layer parameters
Fu : Bandwidth utilization factor
TQT : Quiet time
TD : Detection time
Defined cross layer efficiency model

5. Spectrum sensing design tool
Input
Cross Layer Parameters
Design Parameters
Regulatory specs
Minimum signal-to-noise ratio ()
Minimum probability of detection (PD,req)
Maximum detection delay (DD)
Network specs
Number of Cognitive Radio users (N)
Number of channels of primary users (nc)
Bandwidth of a PU channel (b)
Channel Model
(CR  PU)
Fu , TQT , TD
Control Chn. ( , TR )
Sensing MAC (Cooperation scale (), , )
Sensing PHY (TS, PFA)
Sensing Radio (BW ()) *
Output
Sensing PHY Parameters
Optimal sensing time (TS)
Optimal false alarm probability (PFA)
Performance
Optimized detection efficiency(D)

6. System Architecture Dedicated control channel / collaborative sensing
Fu = 1 , TQT = aTS , TD = aTS + bTR
a and b are determined by the parameters of the individual layers.
we focus on the effect of the following two parameters:
Bandwidth of the sensing radio (Implementation cost)
Cooperation scale (MAC complexity or power efficiency)
Freq.
: Sensing
Ded. CC TS TR
: Reporting
Sub-chn 1
: Dedicated CC
Sub-chn 2
Sub-chn 3
: Data channel
Sub-chn 4
TQT
TQT
Time TD DD TD

7. Trade-off between radio bandwidth and cooperation scale
=0.7 (cooperation of 7 users) =0.34 (6.8 MHz)
Param.
Values
PD,req
0.9 
-12 dB DD
2 sec b
200 kHz nc
100 N 10
=0.6 (cooperation of 6 users) =0.5 (10 MHz)
There are points at which high performance can be achieved with the low cost of radio and the low complexity of cooperation (or low power consumption)

8. Conclusion
The proposed design tool makes it possible for a designer to choose the design configuration of the best trade-off between implementation cost and power consumption.
For given network specs and regulatory specs, there exist design configurations which achieve high performance without wasting excessive cost and power.
The wideband architecture(high cost) does not perform better than the narrowband architecture (low cost) if many users cooperate for detection.