Cooperation And Coordination Mechanism In Interference Systems And Massive-MIMO Capacity Analysis In Hotspots

In wireless communication environment, interference between communication signals of different users usually limits system capacity. In this paper, we investigate several techniques in interference systems such as cognitive radio, interference alignment and massive MIMO. Our main works include:In cognitive system with active interference avoidance, we have designed a method of co-operative spectrum sensing with the target of energy efficiency. About the wireless local area network, we designed an MAC layer protocol on the basis of MIMO Interference Alignmen-t technique for some basic communication modes. This protocol make users achieve parallel communication and effectively manage the mutual interference. In the "hot spot" area, we an-alyzed the performance of massive MIMO, which is well known as suppressing interference between users through asymptotic orthogonal multi-user channels.In the first work, we proposed a new scheme of cooperative spectrum sensing:with avoiding interference to authorized users, we try to find the most suitable cooperative spectrum sensing accuracy degree of cognitive system, to get the best energy efficiency of the entire system in the complete communication process.At first, we formulate the energy-efficient cooperation problem for two special scenarios with Secondary Users in different distribution ranges. By determining how many Secondary Users to cooperate and which Secondary Users to cooperate in the spectrum sensing, the overall sensing and transmitting energy is minimized. Based on the theoretic analysis, a low-complexity heuristic algorithm is proposed to find the most appropriate set of cooperative Secondary Users corresponding to the minimal energy consumption. The simulation results show that the pro-posed algorithm can achieve a near-optimal performance.In the second work, a physical layer algorithm for all kinds of communication modes de-veloped from the X channel is derived based on the design results of an Interference Alignment algorithm on X channel with two-way data flow. In the meantime, for these communication pat-terns, control frames required in these new communication patterns are designed by us. Besides, protocol implementation process for each kind of communication mode is analyzed in this work.It enables users to realize the parallel communication by using Interference Alignment. In addition, through a certain design of scheduling, communication modes with higher multiplexing gains could be constructed, in order to improve the capacity of the networks.In the last work, we analyzed how to establish the mathematical model of user channels for local hotspots at first. And then, comparisons between characteristics of correlation of user channels in such a channel model and that of traditional multi-antenna systems are discussed by theoretical analysis and simulation verification respectively. In addition, impacts for capacity of a whole hotspot caused by these characteristics are also discussed.