Advanced Relaying Methods for One-Way and Two-Way Communication

In wireless communication, relays are devices that receive and forward radio signals. Relays are attractive as they can increase the coverage of cellular networks. Moreover, relays improve the robustness of the wireless radio communication as they create additional signal paths. In this thesis, we propose novel schemes for oneand two-way communication in wireless relay networks. We aim to select the optimum relaying parameters by meeting two different design goals. The first goal is to minimize the transmit power where we assume constraints on the signal quality at the receivers. The second goal is to maximize the signal quality where we assume that the transmit power is limited. For one-directional communication, we propose schemes for communication over frequency selective radio channels that lead to inter-symbolinterference (ISI). First, we consider a multi-antenna source that transmits individual data streams to multiple destinations via multi-antenna relays. The proposed relaying scheme mitigates ISI as well as multi-user interference by using linear filters at the relays. Moreover, we demonstrate that linear precoding at the source efficiently improves the signal quality at the destinations. Then, we show that the latter scheme with a single source and multiple destinations includes the multi-user peer-to-peer (p2p) relaying scheme as a special case. In the p2p scheme, multiple source terminals transmit messages to multiple destination terminals via a network of relays. The simulation results demonstrate that increasing the relay filter length substantially improves the signal quality at the destinations. For relay networks with frequency-flat channels, we propose a novel multicasting scheme where a single source transmits common information to multiple destinations. The relays use the amplifyand-forward (AF) protocol to scale and adjust the phases of their received signals by using weight coefficients. To increase the number of degrees of freedom in the system, a rank-two beamforming method is used to create two communication links from the source to each destination. We propose an iterative algorithm that computes the relay weights and the optimal transmit power of the source and the relays. For bi-directional two-way AF relay communication, we first consider a single user pair. We analytically compare three different bi-directional schemes by their maximum rate.