Research On Diversity Theory Of Wireless Cooperative Relay System

In wireless cooperative relay system, relay and terminal equipment’s antennas are composed as "virtual antenna array", Multi-Input-Multi-Output (MIMO) system can extend cell coverage area, increase system capacity, improve frequency spectrum, and it is considered as the key technology of next-generation mobile communications. This paper lucubrates the diversity theory of cooperative relay system, from physical layer, link layer and route, it takes some theoretical innovation and experiment, takes some research on system capacity, error rate, link interrupt probability, and signal to noise ratio (SNR) performance. Based on these diversity theories, the theoretical architecture of wireless cooperative relay system has been improved more. This paper’s main work and innovation are as follows:1. Physical layer key technologies of cooperative relay systemFirst, a relay scheduling method which based on Markov chain is presented, a single relay node’s existing state is used to analyze its access behavior, then the users and relay nodes common status are taken as research foundation, and system’s balance equations are acquired, results show that this method can distribute relay nodes accessing reasonably, bandwidth resources are effectively used, and it keeps a lower interrupt probability. Second, we discuss multi-relay nodes selection problem. Aim at link breakage problem in cooperative diversity process, a stable link for relay selection algorithm is presented, we design a link survival time method, use backoff strategy to reduce data conflicts, this method greatly reduces selection failure probability, and effectively reduce link re-build time. Finally, according to relay system’s virtual antenna array, we present two source node precoding scheme which suitable for cooperative relay system, one is codebook design method which based on vector quantization (VQ), another one is distributed space precoding technology which based on QR Decomposition (QRD). In multi-antenna single-relay system precoding based on VQ research, we use the limited feedback idea, receiver sends parts of Channel State Information (CSI) to transmitter, then based on existing MIMO knowledge, the source node adds a time-domain precoding matrix. With minimal loss of mutual information as system optimization objective, we use VQ method to build a codebook, and together with average power distribution matrix to constitute the precoding matrix. Compare with tradition distributed precoding, the VQ precoding can acquire higher capacity gain and have good system bit error rate performance. In distributed space precoding technology which based on QRD, given the total transmitting power of all relay nodes, the distributed spatial precoder assigns different transmitting power to each relay node, all distributed precoder is equivalent to a spot on a sphere in multidimensional space. Based on maximize system capacity, we propose an improved particle swarm optimization (PSO) algorithm, which is used to evolve search. Results show that the distributed spatial precoding algorithm based on new PSO algorithm can enhance system capacity performance effectively. Compared to tradition QRD broadcast scheme, the distributed precoding can enhance about30%system capacity gain.2. Link layer key technologies of cooperative relay systemWe pay attention to the recent research focus of link layer, a power allocation algorithm with objective function to maximize system capacity is proposed, based on the convex optimization theory, we employ the ellipsoid algorithm to solve this problem, which could simplify the sub-gradient choosing steps and improving convergence stability, so that an optimized power allocation algorithm is obtained. Results show that this algorithm can effectively distribute power of each node with lower complexity, and ensure transmission capability of relay nodes in cooperative communication. Then, aim at orthogonal frequency division multiple access-decode forward (OFDMA-DF) relay system resource scheduling problems, we consider user access fairness factor, firstly introduce an improved analytic hierarchy process (AHP) method into OFDMA-DF resource scheduling model, presents an unite objective function of system subcarrier distribution, power distribution, transmission selection and relay selection, results show that this method comparing with tradition fair resource scheduling, it is a greater improvement in user fair access, and system performance has been improved greatly. In MAC layer, aim at wireless relay network multiple access collision problem, this paper presents a multiple random access protocol which relay nodes support, relay nodes store these collision data packets information, use digital signal processing technology, according to non-fading correlation coefficient to establish the linear simultaneou equations of restoring original data, solve it and restore the original packets, results show that compared with similar algorithms, system throughput has been significantly improved. This method doesn’t increase retransmission mechanism, save system resource. Due to the relay existence, it takes different path transmission, makes channel parameters uncorrelated. The receiver doesn’t need antennas or other hardware devices, and it still can acquire system diversity gain.3. Route layer key technologies of cooperative relay systemIn route design chapter, first we propose an original multi-path network model which based on graph theory analysis, use linear program theory to optimize this model, take analysis and solution. Then, we use the conclusion to select multi-path routing of practical relay network, base on this, we propose a multi-path routing algorithm which suit for general relay network, and establish an integrity source-destination multi-path routing protocol, results show that this method has30%performance gain compare with tradition single-path routing, and has good adaptability and network performance.