Research On The Cooperative Schemes And Resource Optimization Allocation In Wireless Cooperative Communication

Multiple input multiple output (MIMO) technique can overcome the limitations of multi-path fading in radio channels, and therefore holds the potential to drastically improve the capacity and reliability in future wireless communication system. However, due to size, cost or hardware complexity limitations, it may be difficult for a wireless terminal to support multiple antennas. Recently, cooperative diversity technique, which is based on user cooperation and relay cooperation etc, has emerged as a promising technique and received considerable interests. The essence of this technique lies in that single-antenna terminals in a multi-user scenario are allowed to share their antennas and other resources through distributed transmission and processing so that a virtual multi-antenna transmitter is achieved, and hence reap the spatial diversity benefits of the virtual MIMO system. Focusing on the design of cooperative schemes and resource optimization allocation strategies in the cooperative diversity fields, the solutions for particular scenarios are introduced and further analyzed from theoretical and simulation aspects. The main contribution of this work can be summarized as follows:1. The design issues of cooperative schemesTo solve the resource inefficiency of the traditional two-user cooperative schemes which require the users to relay on orthogonal sub-channels, several improved cooperative schemes combined with distributed space-time code (DSTC) and distributed precode (DP) techniques are proposed when the destination is configured with single and multiple antennas, respectively.For the single-antenna destination scenario, 1) An amplify-and-forward based DSTC (AF-DSTC) cooperative scheme is proposed, which utilizes the orthogonal characteristic of space-time block code (STBC) to make cooperative users relay on the shared channel resources so that the spectral efficiency of the classical AF cooperative scheme can be improved. Simulation results show that the proposed scheme can achieve full diversity order in the high signal-to-noise ratio (SNR) regimes. 2) A decode-and-forward based DSTC (DF-DSTC) cooperative scheme is proposed, which adopts the same idea of AF-DSTC scheme. The upper and lower bounds of outage performance and the closed-form bit error rate (BER) expression of binary phase shift keying (BPSK) signal are derived. The theoretical results demonstrate that the full diversity order does exist in the high SNR regimes, and further validated by simulation results.For the multi-antenna destination scenario, 1) The DF-DSTC cooperative scheme under the single-antenna destination scenario is extended. Assume there exists a user that originates the cooperation, the new DF-DSTC scheme indicates that when both users fail to decode the other, the originator should retransmit its own information so that its performance is no worse than direct transmission. When M-ary phase shift keying (MPSK) constellation modulation is employed at the user and m(m≥1) antennas are configured at the base station, the upper and lower bounds of system BER performance are derived and verified by simulations. 2) A decode-and-forward based DP (DF-DP) cooperative scheme is proposed, which utilizes the multi-antenna characteristic at the destination to make the preprocessed relay signals transmitted on the shared channel resources, so that the spectral efficiency and reliability of the traditional DF cooperative scheme can be improved simultaneously. With the virtual two-input multiple-output channel decomposed into two orthogonal sub-channels in the vector space, a precoding scheme is proposed under the minimum BER criterion. Simulation results show that the proposed scheme is effective in improving the BER performance and has a low feedback overhead.2. The optimization issues of resource allocationFocusing on the cooperative partner selection and power allocation issues, the solutions to"When to cooperate","Whom to cooperate with"and"How to allocate the power"are presented for particular scenarios of interests.1) The optimal power allocation and partner selection algorithms for quadrature modulation cooperative schemes with fixed and selective relays are investigated. The closed-form expressions of the BER performance are derived for both cooperative schemes, in terms of the inter-user channel and uplink channel statistics and a scalable power factor. Then OPA algorithms are devised to optimize the power allocation between the local and relayed signals under the minimum BER criterion. By joint consideration of the partner selection and OPA algorithm, the partner locations specified by various cooperation gains are determined, and then a simple sub-optimal partner selection algorithm is proposed, i.e, the best partner should be located nearest to the midway between the source and the destination from the source side. Simulation results show that the proposed resource optimization algorithms are superior to the unoptimized algorithms by significantly reducing the BER and improve the cooperative gain, which is also useful to simplify the practical partner choice process.2) An optimal power allocation (EPA) algorithm is proposed for the cooperative scheme based on rotation code. The upper bound of the end-to-end system symbol error rate (SER) is first derived using the Chernoff bound, and then under the total power constraint, the power factor is obtained to minimize the SER bound according to the average channel gains. The power allocation information is transmitted to cooperative users through feedback channels, so that the system source utilization can be improved. The effectiveness of the proposed OPA algorithm is verified by simulations. Furthermore, the effect of various partner selection algorithms on the system performance are also investigated.