Performance Analysis of Selected Cooperative Relaying Techniques

Abstract: Recently, cooperative communication has gained significant interest due to the fact that it exploits spatial diversity and provides capacity/performance gain over conventional single- input single-output (SISO) systems. A mobile node with single antenna can cooperate with a nearby mobile node having single antenna in multi-user environment to create the effect of virtual multiple antenna system. Hence, reducing the complexity associated with actual multiple antenna systems. Despite the small size and power constraints, a mobile node can still benefit from spatial diversity by employing cooperation, thus saving transmission power and increasing the coverage range of the network. In this thesis, we have selected some of relaying protocols, namely, amplify-and-forward, decode-and-forward, detect-and-forward, and selective detect-and-forward that are studied and implemented for two different relaying geometries, i.e. equidistant and collinear. Results are studied and compared with each other to show the performance of each protocol in terms of average symbol error probabilities. The considered system model has three nodes, i.e. source, relay, destination. Communicating nodes are considered to be half-duplex with single antenna for transmission and reception. The source, when communicating with the destination, broadcasts the information, which is heard by the nearby relay. The relay then uses one of the cooperation protocols. Finally, the relayed signal reaches the destination, where it is detected by maximal ratio combiner (MRC) and combined with the direct transmission for possible diversity gains. The transmission path or the channel is modeled as a frequency non-selective Rayleigh fading in the presence additive white Gaussian noise (AWGN). The effect of path loss has been observed on cooperation for collinear arrangement with exponential decay up to four. Considering equidistant arrangement, decode-and-forward shows good performance at high signal-to-noise ratio (SNR) while amplify-and-forward is very promising for very low SNR. A selective relaying scheme called selective detect-and- forward is also presented which outperforms its fixed counterparts for a wide range of SNR.