Research On Multi-Antenna Transmission Under Large-Scale Fading Environment

With the rapid development of wireless communication technology and the people's increasing demands for wireless applications, higher speed, better reliability and wider usage have become important indicators of next generation of wireless communication networks. The outdating core network architecture of wireless communication network is gradually becoming the main obstacle of reaching higher speed and reliability. In order to overcome these defects, modern wireless communication network system combines multi-antenna and cooperative transmission schemes. Multi-antenna diversity can improve speed and stability of the link between the base station and mobile terminals. Using cooperative transmission technology can effectively solve the problem of cell edge coverage and improve overall network reliability. Meanwhile, introducing cooperative transmission scheme can significantly increase the transmission distance and reduce the number of hops, which can lower power consumption of the system.We address the transmission of a multi-antenna base-station in a multi-hop network of single-antenna nodes. These nodes will form multiple groups according to their positions and we focus on the downlink between base-station and first-hop groups. Multiple independent data streams will be sent from base-station and each group in first hop should decode its corresponding data and relay to next-hop group through cooperative transmission among different users. Such problem is a combination of spatial multiplexing and multicasting. However, existing algorithms hardly do well on the combination of multi-antenna downlink and cooperative transmission according to the characteristics of cooperative transmission, and fail to make specific optimization on the downlink from base station. According to above problems, this paper focuses on the characteristics of multi-antenna downlink and cooperative transmission. Through the study on the structure of network system, we raise a scheme of finding available nodes around using spectrum sensing algorithm and deciding whether it is feasible to build receiving cluster with these nodes. We also compare the performances of different algorithms through theoretical analysis and simulation. Comparing with current upper layer protocol based cluster building scheme, using sensing algorithm enables us to know the current network topology better. During the practical implementation, sensing algorithm based cluster building scheme can be applied together with the current one so as to assist the upper layer protocol to build receiving cluster.According to the defects of current downlink algorithms, we put forward a new optimization algorithm for the downlink between base-station and first hop clusters. We identify the key factor affecting transmission success rate according to characteristics of practical network and design the entire optimization process based on these key factors. Through the comparison between optimization algorithm proposed in this paper and other existing algorithms, the system performance is enhanced significantly.On the level of project implementation, we conduct the study on enablement constraints, focusing on the impact of sample delay on channel estimation error and overall system performance. We derive the correlation curves among sample delay, channel estimation error and system performance and prove them quantitatively through theoretical analysis, simulation and hardware verification. This result provides the project design with theoretical reference and is able to show the design standards with given requirements of system performance, which is quite meaningful to project implementation.