Research Of Mimo Precoding In An N-Way Relay Network

The N-way relay system can exchange information among multiple users efficiently, with the total transmission time slots reduced efficiently as a result of multi-user diversity gain. However, the communication protocol in an N-way relay system is usually based on the "MAC-BC" process, and each receiver would receive interference from other users, which degrades the system performance seriously.In this thesis, two communication schemes in a MIMO N-way relay network are proposed, and the system performance of the two schemes are optimized via downlink precoding. The former is a communication scheme based on time division and multicasting, in which the uplink transmission process of each user is separated in different time slots, while the signal received by the relay is broadcast to all the users.The latter is a precoding scheme based on downlink interference cancellation, which is realized via the "MAC-BC" process. In this scheme, the relay would perform precoding based on the channel state information(CSI) it has got to cancel inter-user interference,and enables each user to acquire the information it needs.The total data rates of the two schemes are analyzed and optimized as well as the total energy efficiency. Simulation results show that through proper precoding in the downlink process, the total data rates in the former scheme gets improved to some extent, while the total data rates in the latter scheme is obviously higher than the one in the former scheme.Through precoding aimed at improving total energy efficiency in the downlink transmission process, the total energy efficiency both get notable improvements in the two schemes.The simulation results of the system performance in relation to the position of the relay shows that when the relay moves from the region center to the region edge, the achievable total data rates in the two schemes almost keep stable, while the achievable total energy efficiency present an obvious increase.