Implementation of Co-Operative Diversity and Space Time Coding In Wireless Networks

A Wireless Ad-hoc network is an autonomous and self-organizing network without any centralized controller. Cooperative communication is a technique used to increase the reliability and the quality of service (QoS), coverage area range. Space time coding and spatial diversity schemes enhances the performance of the wireless networks. Such networks can be used in military communications and have lot of prospective for civilian applications, to include commercial and educational use, calamity management, road vehicular network etc. In this paper, Decode and Forward with Cooperative diversity and the Alamouti Space Time coding with cooperative diversity has been evaluated, which are primarily used to relay multiple-input multiple-output communications in distributed clustered two hop relaying network. In Decode and Forward Cooperative diversity, an Ad-hoc network consisting of a source, a destination and a third station as a relay is analyzed with Rayleigh flat fading channel by using different combining techniques. Combining techniques such as Equal Ratio Combining (ERC), Maximum Ratio combining (MRC) and Fixed Ratio Combining (FRC) with cooperative diversity have been compared. From the comparison of three combining techniques it is found that FRC improves system performance by reducing the BER. In Alamouti Space Time coding, a 2x2 Alamouti coding has been implemented with the cooperation of two relays with Stanford University Interim (SUI) channel. The data is modulated using Binary Phase Shift Keying (BPSK) and Quadrature Phase Shift Keying (QPSK). Simulation results show that, in order to achieve BER of Cooperative diversity with DAF protocol at relay and FRC at the receiver reduces the SNR by 6dB as compared to that of a single link transmission. Alamouti Cooperative space time coding reduces the SNR by 8dB in order to achieve the BER of as compared to that of Alamouti space time coding. The location of relay in between source and the destination has high influence on the performance of the network. MATLAB is used to evaluate the bit error rate for the Cooperative wireless communication.