Research On Effective Transmission Techniques In Cooperative Networks

MIMO has become the necessary technique in 3G and future mobile communication system. However, employing multiple antennas in a terminal is difficult due to its limited size and limited complexity. To overcome this problem, cooperative diversity based on user cooperation was proposed. In cooperative networks, users form a virtual antenna network by sharing their own antennas, where the diversity gain is obtained to combat the multipath fading in wireless channels. This dissertation investigates effective transmission techniques in cooperative networks, the main contents of which are described as follows.Chapter 1 introduces the research backgrounds, main research contents and structures of the dissertation.Chapter 2 discusses related techniques in cooperative networks, including some diversity combining methods, cooperative diversity, automatic repeat-request (ARQ) technique and another two techniques which can reduce the transmitter complexity, i.e., distributed video coding (DVC) and compressive sensing (CS).Chapter 3 proposes three propositions with regard to the non-zero derivative on the zeros of probability density function (PDF). Based on the Derivative Theorem of Laplace transform, Proposition 1 gives the first non-zero derivative on the zeros of PDF. To the maximum of multiple independent random variables, Proposition 2 derives the first non-zero derivative on the zeros of corresponding PDF. Proposition 3 considers the maximum of multiple independent minimum, and derives the first non-zero derivative on the zeros of corresponding PDF, where minimum means the minimun of two independent random variables. Using these propositions, three relaying protocols are analyzed, and the respective formulas of bit error probability at high signal-to-noise ratio (SNR) are derived. To simplify the performance development of the third protocol, the two-hop link is transformed into an equivalent on-hop link, and Lamber W function is used to get the bounds of equivalent SNR. The theoretical results in this chapter apply for the systems with arbitrary relays, and apply for the systems under multiple fading channels, such as Rayleigh and Nakgami-m channels. In addition, simulation results are provided to verify the theoretical results, and the performance of different protocols is compared.Chapter 4 analyzes the frame error probability (FEP) of hybrid ARQ (HARQ) systems and cooperative ARQ (CARQ) systems over Nakagami-m channels, where coherent equal gain combining is used at the receivers to combine the multiple retransmission versions. To simplify the performance development, the approximation of the product of two independent Nakagami-m random variables is developed, which is then extended to derive the approximation of the product of two independent maximum Nakagami-m random variables. In addition, the first approximation is compared with an existed approximation scheme in three aspects, which affirms the advantages of the former. Based on these two approximations, the FEP performance is derived for various protocols at high SNR, i.e., two protocols in HARQ system, two protocols in CARQ systems with one relay, and one protocol in CARQ systems with two relays. Simuulation results are provided to verify the theoretical results, and verify the advantages of CARQ protocols when compared with traditional HARQ protocols and cooperative diversity protocol. Moreover, based on the tradeoff between throughput and complexity, more practical protocols are suggested.Chapter 5 designs a new transmitter structure with low complexity in cooperative networks. This structure adopts two effective transmission techniques, i.e., DVC and CS, which reduces the complexity of the transmitter. Based on the fact that different CS measurements are distributed identically, this sub-sampling structure enjoys several merits when compared with traditional fully-sampling structure. Specifically, these merits are lower implementation complexity, lower transmission rate without performance degradation and higher robustness to packet loss. Simulation results under erasure channels are provided, which verify the above theoretical analysis. In addition, some simulations under noisy and fading channels are presented. Chapter 6 concludes this dissertation, and presents some future work.