Performance of network-coded cooperative MIMO systems with antenna selection over Rician fading channels

Multiple-input multiple-output (MIMO) systems, which are based on the idea of obtaining antenna diversity gain by deployment of physical antenna arrays at the receiver and transmitter, have become one of the leading technologies in meeting today's increasing communication demands due to the significant capacity increases they offer. However, exploiting a large number of antennas in wireless terminals causes significant increase in the cost and complexity of the system. In the antenna selection technique proposed to solve this problem, antennas in the receiver and/or transmitter that maximize the system performance are selected and used in transmission. Many studies exist in the literature that show that antenna selection technique can solve the size, cost and complexity increase problem encountered in MIMO systems. Another approach that provides antenna diversity gain in wireless communication systems is the cooperative diversity technique, in which the transmission between the source and the destination is assisted by neighboring terminals called relays. The leading signal processing strategies used in relay terminals of cooperative wireless networks can be classified as analog relaying (AR) and digital relaying (DR). In the DR technique, which is focused on in this master thesis, the relay terminals retransmit the received signal to the destination after decoding it. Performance losses due to the detection errors at the relays are the most important problem encountered in DR-based wireless cooperative networks. Many different techniques have been proposed in the literature to combat this problem called error propagation such as maximum likelihood (ML) detection, cooperative maximum ratio combining (C-MRC), selective relaying (SR), log-likelihood ratio (LLR) transmission and virtual noise (VN) based detection. Network coding technique is based on the idea that relay terminals obtain new packets by combining the signals they receive and is exploited to increase the spectral efficiency of cooperative wireless communication systems. Multiple access relay channel (MARC) is one of the leading applications of cooperative wireless network coding, where multiple users transmit their independent data to a common destination with the help of a relay terminal. In this master thesis, the performance of a DR-based MARC structure consisting of two users, one relay and one destination was obtained by simulation results over Rician fading channels where multiple antennas are located at the terminals. A three-phase transmission protocol in which the users transmit in the first two phases and the relay forwards the network encoded data packet in the third phase is considered and it is assumed that direct links exists between the users and the destination. In the antenna selection criteria utilized in this master thesis, only one antenna has been selected and activated at the corresponding receiver and the transmitter terminals. In order to combat the performance losses due to the error propagation problem, the maximum likelihood (ML) decision rule has also been employed where the erroneous transmission probability from the relay is considered at the destination. It has been shown by simulation results that the examined system model provides diversity gain.