Research
Enhancing Transmission Capacity of a Cognitive Radio Network by Joint Spatial-Temporal Sensing with Cooperative Communication Strategy
In static cognitive radio network a secondary transmitter communicates directly with a secondary receiver only when the spectrum is not occupied by any primary user. The secondary user has to stop its transmission when no spectrum holes exist. To improve the transmission capacity, in this paper we approach to combine cognitive radio network with cooperative communication strategy employing spatial sensing as well as temporal sensing. In our proposed scheme when primary user is active, a secondary user transmits to another secondary user via a relay channel. By enabling the use of both the direct and relay channels, the transmission performance of the secondary system can be improved significantly. Our information-theoretic analysis as well as numerical results show that the proposed scheme significantly reduces the average symbol error probability compared to schemes based on pure temporal or spatial sensing.
BER Performance Evaluation of a Cooperative Wireless Communication System with CDMA Implementation of Fixed Relaying Protocols
In this paper, we investigate a comprehensive study on a simulated cooperative wireless communication system with implementation of code division multiple access (CDMA) technique under Decode-and-Forward (DAF) and Amplify-and- Forward (AAF) relaying protocols. The system under investigation incorporates two digital modulations (BPSK and QPSK) with five major types of signal combining schemes as Equal Ratio Combining (ERC), Fixed Ratio Combining (FRC), Signal-to-Noise Ratio Combining (SNRC), Maximum Ratio Combining (MRC) and Enhanced Signal-to-Noise Combining (ESNRC). Results of BER simulation in AWGN and Raleigh fading channels show that the system provides better performance in AAF relaying protocol as compared to DAF whatever the signal combining scheme is used. In DAF relaying protocol, the system shows most satisfactory performance in SNRC and QPSK digital modulation in comparison with worst case in ERC. In AAF relaying protocol, a much better system performance is achieved in FRC and QPSK digital modulation as finding worst performance in ERC. Information about the average quality shows performance benefits, and a rough approximation about the variation of the channel quality increases the performance even more. The best system performance is achieved when the relay is at equal distance from the sender and the destination or slightly closer to the former.
