Research On Multi-Way Relaying Channel With Single Relay

With the rapid development of wireless communication, the spectrum resource is becoming scare. The lack of spectrum resources restricts the rapid development of the wireless communication. It is hoped that the same spectrum resource can serve more than one users to improve the spectrum efficiency. The multi-antenna technique can not only get more diversity gain, i.e., more reliability, but also improve the system capacity. Cooperative relaying technique increases the coverage of the system, the data rate and reliability of the transmission links. Network coding technique deals with interference by making use of the interference instead of cancelling it. When the network coding is applied in the cooperative relaying channel, the signals can be transmitted in two-way relaying channel. Compared with the traditional one-way relaying channel, two-way relaying channel can improve the throughput and the spectrum efficiency of the system. The two-way relaying channel with network coding and MIMO technique has recently drawn great attention.This dissertation is an extension of the existing researches. First of all, the two-way relaying channel with two users is generalized to the multi-way relaying channel with multiple users, then the multi-way relaying channel is fully studied. The elimination of the interferences between different users is mainly focused on. And then some problems of the scenario with symmetric channels or asymmetric channels are investigated, and the corresponding solutions are proposed to improve the system performance. The main works and contributions of the dissertation are listed as following:1) The multi-way relaying channel system model is established, and the method for eliminating of the interferences between different users is proposed. Under the assumption that the perfect channel state informations can be known by each node, the precoding of the users and the relay can be designed jointly to align the signal space. With the assistance of network coding, the interference between different users is eliminated. The system symbol-error-rate performance is analyzed, and the diversity gain is obtained consequently. When the dimension of the signal space has redundancy, the selection of the precoding is discussed to obtain higher diversity gain. The theoretical analysis and the simulation results demonstrate the method of the precoding design and selection as well as the system performance.2) Some methods for reducing the computational complexity of signal processing at the relay are proposed, which is fit for the scenario with symmetric relaying channels. The signal received at the single relay is a mixture of the signals from multiple different users, the complexity of decoding and demodulation will be huge. Considering the scenario with symmetric channels, some methods are presented to reduce the computational complexity of signal processing at the relay. If the users do not use channel coding, a simple constellation mapping method is applied to reduce the signal points in the demodulation constellation at the relay. While the users use channel coding, the reduced trellis method is jointly applied with the constellation mapping to further decrease the computational complexity. A modified decoding scheme is proposed by omitting the decoding and re-encoding process, and the signals which will be broadcasted in next phase are decoded directly from the received signals. The complexity at the relay node is reduced by applying the above methods. Finally, the complexity of signal processing at the relay is analyzed, and simulation results demonstrate the system performance.3) An adaptive transmission scheme is proposed for the scenario with asymmetric relaying channels. The channels between users and the relay are different, and the capacity will be determined by the worse channel if the fixed modulation is applied. In order to make full use of the channels, an adaptive modulation scheme is proposed to realize the asymmetric transmission in the scenario with asymmetric channels. Each user can adaptively select the modulation according to their own channel. And at the relay, the buffer technique is applied to save the unmatched bit messages in the channels, meanwhile, a modified network coding and hierarchical modulation are used. The buffer size at the relay and the end-to-end through of the scheme are analyzed, and the simulation is provided to illustrate the performance of the proposed transmission scheme.