Equalization and combining techniques for distributed space time trellis codes on co-operative networks

Fading severely affects wireless communications performance, causing large variations in signal strength as a function of the user position. Spatial diversity is an effective way to combat fading while keeps the bandwidth efficiency unaltered. To exploit the spatial diversity, multiple antennas have to be equipped at the transmitter and/or the receiver. However, it is difficult to place multiple antennas onto a mobile terminal or a sensor node due to the size limit and the hardware complexity. It is shown recently that the spatial diversity can be exploited if cooperation is adopted among the users. The resulted transmission scheme is referred to as the cooperative diversity. The main objective of the paper is to improve the performance of the distributed space-time trellis code (DSTTC) protocols by using different equalization techniques at different channels namely AWGN, slow fading, fast fading and quasi-slow fading. Various relay selection techniques are employed for AAF protocol in order to improve its performance. Relay selection is based on the received SNR at the relay and receiver, decoding capability of the relay, forward and backward channel quality of the relays and the harmonic mean of the channel magnitude. To reduce the effects of inter symbol interference and inter channel interference various equalizations such as zero forcing which uses the inverse channels at the receiver, minimum mean square error which tries to minimize the mean square error between the source data and received data at the receiver and the maximum likelihood tries to estimate the signal which is maximum likelihood to the source signal. Co-operative Maximum Ratio Combining scheme uses the weighting factor for each channel and the co-operative alamouti forms the orthogonal matrix at the receiver by receiving the signals of real and complex at different time slots.