Research On Polarization Alignment Technology For Cognitive Heterogeneous Cellular Network

As a new wireless network architecture,cognitive heterogeneous cellular network(CHCN)can achieve seamless coverage and performance improvement of edge users by deploying multiple types of cognitive small cells at the same frequency within the coverage of traditional macro cell.CHCN can also solve the problems of the fast-growing network capacity and the shortage of spectrum resource.However,the multi-source interference and the complex interference scenerios seriously reduce the reliability of the signal transmission in CHCN,which become the most important factors that restrict the network performance.The traditional interference suppression technologies avoid or eliminate the interference by using the resources provided by the dimension of time domain,frequency domain,spatial domain and power domain.But with the densification of the network quantity and the complexity of the architecture,the available resources of degrees of freedom(DoFs)are also limited and the traditional methods can not cope with the conditions of complex network state and various interference scenerios.Therefore,this thesis exploits the spectrum opportunities provided by the signal polarization domain resources and the cooperative resources in polarization domain and other domains,and analyzes the characteristics of interference in different scenarios of CHCN,as well as studies the polarization interference alignment technology based on the interference alignment theory.The cross-tier interference between macro cell and small cell and the co-tier interference between small cells in CHCN are suppressed efficiently which makes the coexistence of macro cell and small cells come true.The communication reliability of small cells is improved and further the performance of CHCN is improved.This thesis is supported by Chinese National Nature Science Foundation Project"Sensing and utilization of polarization resource in dense heterogeneous wireless environment"(No.61571062).Focusing on different interference scenarios in CHCN,the polarization interference alignment techniques in closed subscriber group(CSG)access mode and open subscriber group(OSG)access mode are studied.The main contents are as follows:1.The current situation and interference problems of CHCN,traditional interference alignment(IA)techniques and polarization signal processing techniques are reviewed and analyzed.Firstly,the features of heterogeneous cognitive wireless environment are summarized revealing the development potential of CHCN,and the causes of interference are analyzed.Secondly,demonstrating the current research situation of IA,it is necessary to use its efficient interference suppression ability to solve the multiple interference problems of CHCN obviously.Finally,the polarization information processing technology is summarized,and the feasibility of polarization IA in CHCN is analyzed.This lays a theoretical foundation for further research.2.Considering the closed subscriber group access mode in CHCN,there is serious cross-tier interference between macro cell and small cell which reduces the transmission quality of them.So,a polarization cross-tier IA(PXIA)optimization model is established according to interference processing criteria for underlay spectrum sharing.Secondly,based on polarization mismatch theory and LA principle,a transcevier non-cooperative algorithm is proposed.The optimal transmitting polarization state,receiving polarization state and transmission power are derived.Then,the PXIA algorithm flow is summarized while the block diagram of algorithm transceiver based on polarization signal processing is proposed.Finally,the simulation verifies the PXIA algorithm significantly improves the bit error rate(BER)performance and the reliability of small cell transmission without affecting the BER performance of macro cell and the optimal system sum rate.The BER performance of the small cell is increased to twice that of the existing algorithm when signal-to-noise ratio(SNR)is 10 dB.3.In the open subscriber group access mode of CHCN,in addition to the cross-tier interference between macro cell and small cells,the serious co-tier interference between small cells can not be ignored.Considering that the cooperation between polarization domain and spatial domain provides more resources of DoFs to deal with more interference,a system and signal model based on Hadamard product is established.Still according to the interference processing criterion for underlay spectrum sharing,a polarization-spatial based IA model is established.Then considering the optimization of different networks,two iterative algorithms are proposed.Orthogonal projection based polarization-space interference alignment(OP-PSIA)ensures the minimum effect to macro cell and interference constrained polarization-space interference alignment(IC-PSIA)maximizes the performances of small cells if permitted.Based on the orthogonal projection filtering and IA,the polarization-spatial processing matrices of the transmitter and receiver are derived.Finally,the simulation results show that the performance of the two algorithms is different in two kinds of network configurations,and validate that the performances of the proposed two algorithms are generally better than those of the existing algorithms.