Research On Distributed Precoding Technplogies In Multi-Relay Systems

Relay communication systems are considered as one of the most promising networks for future wireless telecommunication technologies due to its capability of providing effective spatial diversity gain. It has become one of the hottest research points recently. In cellular systems, assistance of relay nodes will enhance the connectivity between a base station (BS) and mobile stations (MS) which are located at the edge area of the cell. In ad-hoc scenarios, the use of relay nodes will increase the connection range between the BS and MS. Thanks to its array and diversity gains, the relaying technologies improve the channel capacity linearly. Because of the similarity of the relaying and MIMO (multiple input multiple output) technologies, the application of pre-coding into the cooperation systems will be the one of the most potential techniques to improve the spectral efficiency in the future.This paper is about the research of the application of distributed pre-coding in multiple relay systems. The first chapter will introduce the main categories of the distributed pre-coding relaying technologies after a brief overview of the future technologies. The third chapter discusses research on the multi-stream broadcasting mode. Double-sided filters are proposed to obtain the inter-node diversity gain. A new algorithm which improved the application of QR decomposition in multi-relay systems will be proposed. Its superiority will be proved by the simulations.The third chapter is about research on multi-stream unicasting mode in which the source node transmits different data streams to each relay node with the downlink multi-user pre-coding. The papers existing did have done some research work on this mode, but none of these pay noticed the interferences caused by the multiple streams, which will decrease the system capacity. In the fourth chapter, we propose two unicasting modes which can suppress the interference more effectively. The first one suppresses the interference signals at the source node by performing orthogonal multi-user pre-coding. The second one conducts the interference suppression at relay nodes by designing proper receiving filters. In addition, a new algorithm about relay selection will be introduced in this chapter. The existing papers have proposed some algorithms about relay selection. These algorithms can achieve maximum capacity, but they need to have all the channel information which means too much feedback overhead for the system. To reduce the overhead without lose of the capacity; this paper will propose an algorithm which feedback part of the channel information instead the whole. Numerical results will show the advantages of our proposed schemes.In the end of this paper, there will be a conclusion about the work I have done and a discussion about the next steps in the future.