Design And Analysis Of The Opportunistic And Buffer Relying Based Multi-relay Cooperative Scheme

With the development of information technology, wireless mobile communications have played the more and more important roles in the social production and life. The fading caused by the characteristics of time-varying and non-stationary of wireless communication scenario severely affected the wireless communication quality. For decades, many scholars have been devoted to find the technology to resist the channel fading and have achieved a series of breakthroughs. Channel coding is a typical technology that can achieve almost error-free transmission by expanding the signal bandwidth. Turbo code and LDPC code are two especially efficient codes which can approximate the Shannon limit. However, as various kinds of wireless communication systems emerge one by one, the wireless spectrum resource has become more and more constrained. Consequently, how to use the spectrum efficiently has been another crucial problem except the channel fading resistance. MIMO technology can achieve the spatial diversity through multiple antennas equipped at the transmitter and receiver and can resist the channel fading without expanding the signal bandwidth. Meanwhile, using multiple antennas at the transmitter can achieve the spatial multiplexing, which can improve the data rate. In fact, due to the restriction of the volume and power, most wireless terminals are unable to equip multiple antennas, which limits the use of MIMO technology seriously. Cooperative communication has been proposed to provide a new idea, where the single antenna terminals can share their antennas and form virtual MIMO antenna arrays.How to forward the source information via the relay is one of the most crucial issues in cooperative commutation. Amplify and forward (AF), decode and forward (DF), and coded cooperation (CC) are three common cooperative protocols. And combining these protocols can achieve better performance at the cost of improving the complexity.In multi-relay cooperative communication systems, relay selection is another crucial problem. As an effective relay selection scheme, opportunistic relaying (OR) attracts many attentions. However, opportunistic relaying cannot use the best source to relay link and relay to destination link, which limits the performance improvement. Buffer relaying (BR) has been proposed to overcome the problem at the cost of delay and can further improve the system performance for time insensitive system.In this thesis, we are devoted to research the transmission optimization for multi-relay systems and try to improve system performance in terms of cooperative protocols and relay selection. We combine a high performance incremental hybrid decode-amplify-forward (IHDAF) protocol with opportunistic relaying and buffer relaying for systems in different situations, respectively. The main work can be summarized as follows:1) An opportunistic relaying based incremental hybrid decode-amplify-forward (OR-IHDAF) scheme which combines IHDAF protocol with OR is proposed in multi-relay scenario. The analytical expression of outage probability of the OR-IHDAF scheme is presented based on the probability density function (PDF) and cumulative distribution function (CDF). Computer simulations are given to vertify the theoretical analysis and the comparisons with other schemes are also provided.2) We analyse the bit-error rate (BER) performance of OR-IHDAF scheme. Due to the combination of complex protocol and relay selection, we propose a Taylor series expansion method instead of conventional method and finally obtain the theoretical BER result by finite iteration. Computer simulations are given to vertify the theoretical analysis and the comparisons with other schemes are also provided.3) The best relay selected by OR policy may be not available in some cases, resulting in the necessity of the selection for the Mth best relay. A different PDF from that in 1) is used in the theoretical analysis of the Mth best relay selection based IHDAF scheme and the simulation results are provided.4) For time insensitive system, we propose and research the infinite length buffer relaying based IHDAF (ILBR-IHDAF) scheme and finite length buffer relaying based IHDAF (FLBR-IHDAF) scheme. For the multi-factor eclectic problem that how the buffer element length is set for each relay will make FLBR-IHDAF scheme approximate ILBR-IHDAF scheme in terms of outage probability performance without too much hardware cost and too high delay, we provide the actual meaning conclusion via simulations. The comparisons between FLBR-IHDAF scheme and exsiting schemes are also provided.