| This dissertation deals with wireless communications using cooperating relay nodes. Specifically, this dissertation relaxes two restrictive conditions ubiquitous in the current literature. First, the assumption that relay nodes can perform complex calculations is lifted. Demodulate-encode-forward (DEF) is a low-complexity relaying scheme where the relay is asked only to demodulate, not decode, a source transmission. The implementation of DEF and various methods that can be used with DEF to improve the performance while satisfying the hardware complexity limitations are detailed here. Second, we remove the assumption that the relays either transmit the complete source codeword or not transmit at all. When relays have limited resources, each relay may only be able to transmit part of the source codeword. Fractional cooperation, which allows nodes to transmit a fraction of the source codeword, is proposed and analyzed. Fractional cooperation is also very flexible because coordination between relaying nodes is not required.;A third contribution of this dissertation is the use of the union-Bhattacharyya bound (UBB) to analyze relay networks. The bound has the significant advantage of accounting for the specifics of the system parameters and coding scheme used. The UBB is shown here to provide an effective and efficient scheme for relay selection, performance prediction, and system design. It can also be used to distribute relay resources in order to optimize the total energy consumed and error rate performance. A sub-optimal distributed algorithm that can be used to solve the optimization problems is introduced. |
