Spectrum Sensing in Cognitive Radio - Fading, Diversity and User

CooperationBy

Sanjeewa P. Herath

Examination Committee:1.Dr. R.M.A.P. Rajatheva (chairman),2.Prof. Kazi m. Ahmed,3.Dr. Poompat saengudomlert.

MASTER THESIS COMPETITION18TH May 2009

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

• Advantages– High speed internet, bandwidth– Low cost – Not using additional resources– Good QoS, Routing implementation

Conventional Licensed User (Primary User) NetworkUnlicensed User (Cognitive User) Access

• Solution: Allow cognitive user access

?

PU 1 PU 2PU 3 idle

CU 2CU 1

How to Detect?

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

PU Transmits Energy/PowerCU 2CU 1

The objective

• IEEE 802.22 – First cognitive radio standard– 90% detection reliability even when 0 dB signal-to-

noise ratio (SNR)

PU

CU

WALL

WAL

L

(2) LOW SIGNAL ENERGY

(1) MULTIPATH PROPAGATION

Very weak signal

PU Base Station

Diversity Combining

• Concept– Multiple copies of the same signal– Combine them

PU

CU

WALL

WALL

(1) MULTIPATH PROPAGATION

Very weak signal

PU Base Station

Remove Fading Effects

Contribution• Analysis of communication systems is complex• High chance of making mistakes

1. Theoretical analysis– PDF approach (new)– MGF approach (new)

2. Simulation Model (new)

• Solution: Two way analysis

Diversity Combining

Detection with MRC diversity (Rayleigh, False alarm probability 0.1, u=1)

Two way analysis

0 dB

More Diversity• Six different diversity techniques are

proposed– Motivation: Less complex, low cost solutions

• Proposed schemes1. Maximal Ratio (MRC) - 20% 2. Equal gain (EGC) - 16%3. Square-law (SLC) - 12%4. Square-law selection (SLS) - 10% 5. Selection (SC) - 11 %6. Switch-and-stay (SSC) - 2%

How far should we improve?

Required improvement by other means

Cooperative Detection

• Concept– PU assists CU to detects its presence – Tolerate capacity by PU

PU

CU

WALL

(2) LOW SIGNAL ENERGY

Very weak signalPU Base Station Improve signal strength

• Algorithm based solution– Convex optimization

• Based on IEEE 802.22 standard

Cooperative Detection

Cooperative Detection (2 Subcarriers, AWGN Nc

i={2,1}, Nbi={2,2})

Flexible

Low Data Rate

Industrial Contribution• 66% (out of 90%) is achieved– 30 % by energy detection– 20 % by diversity– 16 % by cooperation

• The rest of 24% by CU cooperation• Relax assumption– Channel estimation– User mobility

Future Work

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