Research On Interference Alignemnt In Wireless Network

In order to improve the spectrum utilization, frequency reuse factor one is widelyused in the wireless systems. But that networking lead to the existence of blind spotand hot spot in the real communication system. The “two spot” can affect theperformance of the system seriously. So several program have been advanced to solvethe problem that caused by the blind spot and the hot spot, mostly used methods arePicocell technology and cooperative relay technology. To some extent that technologycan resolve the “two spot” problem, but at the same time those technology alsoincrease the cells of the network. Such that multi-cell interference and Co-ChannelInterference (CCI) have become a key factor constraining the system capacity。For thepurpose of suppressing the interference and improving the cell-edge throughput of thesystem，anti-jamming technology is very important in the multi-cell wireless network。As a realization of anti-jamming technology，interference alignment (IA) attractswide attention，which can obtain the optimal transmitting degree of freedom(DoF) andmax the capacity of the network。We first research the traditional IA algorithm basedon ideal interference channel，but the channel matrix in that algorithm must fullranked, which limit the applications of the traditional algorithm. For that reason weintroduce a ranks constrained interference alignment, which can have a wide range ofapplications. The simulation shows the performance of the IA is very well, but thecomplexity is also very high. So based on the rank constrained rank minimization IAalgorithm, we propose an optimized IA scheme and derive the up-bound of thecapacity in this paper. Simulation results show that the presented IA scheme caneffectively reduce the implementation complexity and the performance of theoptimized IA is well.Then we put the IA into the real communication network, such as HeterogeneousNetwork (HetNet) composed of Macrocell and Picocell and LTE-A system. As we allknow, HetNet will play an important role in future cellular system, and it has potentialto drastically improve the capacity of wireless network。But with the deployment ofPicocells, the co-channel interference (CCI) is more and more serious in theheterogeneous network。Thus，interference suppression is very meaningful for HetNet.In this paper, based on the muticell IA algorithm，we propose an optimized IA schemefor HetNet. Simulation results show that the presented IA scheme can improve thecapacity of HeNet and reduce the implementation complexity。In order to improve theLTE-A system throughput, cooperative relay technique is proposed in3GPP R8specification。However，the deployment of a large number of relay nodes will lead serious co-channel interference (CCI)。So interference suppression in the LTE-Anetwork is very meaningful for the future wireless communication。In this paper, anoptimized low rank IA scheme based on the cooperative relay for LTE-A network isproposed。Simulation results show that the presented IA scheme can improve thecapacity of LTE-A network and reduce the implementation complexity。In this paper, a further analysis for the IA performance in multi-cell with delayedchannel state information is introduced. The signal processing and propagation willbring delay into the system. The delay results in the fact that the signal at the basestation could not be aligned perfectly, and then the receiver could not remove themulti-cell interference completely. So we investigate the performance of multi-cell IAin presence of delayed interference channel in this paper。Simulation results show thatthe delayed channel state information seriously decreases the performance of IA，especially in present of high SNR。The analysis results might be useful for the designof the systems to some extent.