Application of Alamouti Coding to Two-Way Relaying

In wireless communications systems, large scale fading (i.e., path-loss and shadowing) can significantly attenuate the transmitted signal power and consequently degrade the wireless link quality between two nodes. One cost-effective solution to the problem of large scale fading is to use a relay. A relay is an access point that is used to assist two nodes in exchanging their messages and to improve the link quality between them. Recently, the use of multiple antenna techniques with relaying has attracted the attention of many researchers, and it has been shown that the combination of multiple antennas and relaying can significantly improve the system performance.In this thesis, we study the performance of two-way relaying (TWR). We limit our study to the case where the nodes and the relay are equipped with only two antennas and they use Alamouti coding for transmission. We consider different TWR schemes using Alamouti coding. Firstly, we integrate Alamouti coding with the traditional four-phase relaying scheme, in which eight time slots are required to exchange four symbols between the nodes, and the relay uses the detect-and-forward (Det&F) strategy to re-transmit the received symbols. Secondly, we use Alamouti coding in three-phase relaying. In this scheme the nodes require three phases (i.e., 6 time slots) to exchange their symbols, and the relay uses either the XOR-and-forward (X&F) strategy or the Det&F strategy. Lastly, we combine Alamouti coding with two-phase relaying scheme, in which the nodes require two phases (i.e., 4 time slots) to exchange their symbols. In this scheme, the relay uses minimum mean square error detection to estimate the transmitted symbols from the nodes, and it uses either the X&F strategy or the Det&F strategy to broadcast the combined symbols.We derive closed-form expressions of the average end-to-end bit error rate for these schemes for the case when M-QAM with Gray mapping is used. In the derivation, we assume the channel is modeled as Rayleigh fading channel, and it is assumed to be perfectly known to the receiver. To confirm our analysis, we compare the analytical results with simulation results, and it is shown that the analytical and simulation results have an excellent agreement.