Spectrum Sensing in Cognitive Radio
- Fading, Diversity and User
Cooperation
By
Sanjeewa P. Herath
E xa m i n a t i o n C o m m i t t e e :
1 . D r. R . M . A . P. R a j a t h e v a ( c h a i r m a n ) ,
2 . P r o f. K a z i m . A h m e d ,
3 . D r. Po o m p a t s a e n g u d o m l e r t .
MASTER THESIS COMPETITION
1 8 TH M a y 2 0 0 9
Wireless access & Cognitive Radio
• Wireless access – high demand
– Every one with mobile phones
– Demand: High speed internet, TV, on-line movie
• But, the available radio resource is very limited
• Solution: Allow cognitive user access
CU 1
PU 1
CU 2
PU 2
PU 3
idle
Unlicensed
UserUser
(Cognitive
User)
Access
Conventional
Licensed
(Primary
User)
Network
• Advantages
– High speed internet, bandwidth
– Low cost – Not using additional resources
– Good QoS, Routing implementation
?
How to Detect?
CU 1
CU 2
PU Transmits Energy/Power
Detection by Cognitive Users
• Measure the energy content
– Can use in CDMA, 3G, Wi-Max, 4G/OFDMA etc
– Guaranteed security to primary users
– Cost effective, simple in structure, less hardware
The objective
W
A
L
L
PU Base Station
(2) LOW SIGNAL
ENERGY
Very weak signal
CU
(1) MULTIPATH
PROPAGATION
PU
• IEEE 802.22 – First cognitive radio standard
– 90% detection reliability even when 0 dB signal-tonoise ratio (SNR)
Diversity Combining
W
A
L
L
PU Base Station
Remove Fading Effects
Very weak signal
CU
(1) MULTIPATH
PROPAGATION
PU
• Concept
– Multiple copies of the same signal
– Combine them
Contribution
• Analysis of communication systems is complex
• High chance of making mistakes
• Solution: Two way analysis
1. Theoretical analysis
– PDF approach (new)
– MGF approach (new)
2. Simulation Model (new)
Diversity Combining
Two way analysis
0 dB
Detection with MRC diversity
(Rayleigh, False alarm probability 0.1, u=1)
More Diversity
• Six different diversity techniques are
proposed
– Motivation: Less complex, low cost solutions
• Proposed schemes
1.
2.
3.
4.
5.
6.
Maximal Ratio (MRC) - 20%
Equal gain (EGC) - 16%
Square-law (SLC) - 12%
Square-law selection (SLS) - 10%
Selection (SC) - 11 %
Switch-and-stay (SSC) - 2%
How far should we improve?
Required improvement by other means
Cooperative Detection
PU Base Station
W
A
L
L
(2) LOW SIGNAL
ENERGY
CU
Improve
Verysignal
weak strength
signal
PU
• Concept
– PU assists CU to detects its presence
– Tolerate capacity by PU
• Algorithm based solution
– Convex optimization
• Based on IEEE 802.22 standard
Cooperative Detection
Flexible
Low Data Rate
Cooperative Detection
(2 Subcarriers, AWGN Nci={2,1}, Nbi={2,2})
Industrial Contribution
• 66% (out of 90%) is achieved
– 30 % by energy detection
– 20 % by diversity
– 16 % by cooperation
Future Work
• The rest of 24% by CU cooperation
• Relax assumption
– Channel estimation
– User mobility
Contribution to Academia (7)
1) Sanjeewa Herath, Nandana Rajatheva,``Analysis of Equal Gain Combining
in Energy Detection for Cognitive Radio over Nakagami Channels,“ IEEE
GLOBECOM `08, pp. 1-5, Nov.-Dec. 2008, USA.
2) Sanjeewa Herath, Nandana Rajatheva, Chintha Tellambura,``On the
Energy Detection of Unknown Deterministic Signal over Nakagami
Channels with Selection Combining,“ IEEE CCECE `09, May 2009,
Newfoundland, Canada.
3) Sanjeewa Herath, Nandana Rajatheva,``Analysis of Diversity Combining in
Energy Detection for Cognitive Radio over Nakagami Channels,"Accepted
for IEEE Int. Conf. ICC `09, Jun. 2009, Germany - to appear.
4) Sanjeewa Herath, Nandana Rajatheva, Chintha Tellambura,``Unified
Approach for Energy Detection of Unknown Deterministic Signal in
Cognitive Radio over Fading Channels,“Accepted for IEEE Int. Conf. ICC
`09, Jun. 2009, Germany - to appear.
5) Sanjeewa Herath, Nandana Rajatheva, Poompat Saengudomlert,
``Primary and Cognitive User Cooperation in Detection,“ Submitted for
IEEE GLOBECOM '09, Nov.-Dec. 2009, USA.
Contribution to Academia (7)
1) Sanjeewa Herath, Nandana Rajatheva, Chintha Tellambura,``Performance
Analysis of Square Law, Switch and Stay Diversity Techniques for Energy
Detection over Nakagami Fading Channel,” In preparation to be
submitted to IEEE Transactions on Communications.
2) Sanjeewa Herath, Nandana Rajatheva, Chintha Tellambura,``Energy
Detection of Unknown Deterministic Signal in Fading and Diversity
Reception,”In preparation to be submitted to IEEE Transactions on
Communications.
Thank You
Master Thesis
Telecommunication FoS, AIT
18th May 2009