Research On Spectrum Sharing In Dense Heterogeneous Wireless Environment Based On Polarization Signal Processing

The innovation of wireless network infrastructure is regarded as the key role of satisfying the exponentially increasing needs of network capacity with spectrum resource shortage and limited potential of capacity improvement by air interface technologies.Through densely deploying small cells within the coverage of existing macrocells,wireless environment becomes dense and heterogeneous with enhanced coverage and capacity,which becomes the major form of future wireless communication systems.However,due to the dense deployment of small cells accessing the spectrum of macrocells,severe interference problem arises including cross-tier interference between macrocells and small cells and co-tier interference among small cells.Spectrum sharing in cognitive radio is an effective means to solve the interference problem by allowing small cells(cognitive networks)to reuse the licensed spectrum of macrocells(primary networks)while avoiding harmful interference to macrocells.Traditional spectrum sharing technologies utilize spectrum opportunities in time,frequency,space,power,range and code domains,which face the challenge of decreasing resources in dense heterogeneous wireless environment.Except for the above resource domains,polarization,an essential property of signal,is an important and under-utilized resource domain.Based on polarization signal processing,this thesis exploits polarization resource for spectrum sharing to realize the coexistence between cognitive and primary networks at the same time,frequency and space,which can achieve spectrum efficiency enhancement of dense heterogeneous wireless environment.This thesis is supported by Chinese National Nature Science Foundation Project“Sensing and utilization of polarization resource in dense heterogeneous wireless environment"(No.61571062).To solve interference problem and improve overall system capacity of dense heterogeneous wireless environment,the research work exploits new theories and methods of spectrum sharing based on polarization signal processing in heterogeneous cellular networks,dense small cell networks and dense heterogeneous cellular networks.The main research work of this thesis are summarized as follows:(1)The related research on dense heterogeneous wireless environment,traditional spectrum sharing technologies and polarization signal processing based spectrum sharing are summarized and analyzed.Firstly,the current studies of dense heterogeneous wireless environment are summarized whose capacity increase is limited by severe interference problem.Secondly,the related research on spectrum sharing in cognitive radio are reviewed,where the problem of decreasing available resources are pointed out.Then,polarization signal processing technologies are classified with emphasis on polarization signal processing in wireless communication networks.In the end,the existing polarization signal processing based spectrum sharing technologies are summarized,and the feasibility and benefits of polarization signal processing based spectrum sharing in dense heterogeneous wireless environment are analyzed.(2)Considering the cross-tier interference between macrocell and small cell in heterogeneous cellular networks,the thesis proposes polarization-based spectrum sharing method and polarization-power domain collaborative spectrum sharing method to realize the coexistence between macrocell and small cell.Based on the utilization of polarization resources,the polarization-based spectrum sharing method is firstly proposed while avoiding harmful interference to macrocell.Then,the polarization-power domain collaborative spectrum sharing method is proposed with consideration of transmit-power constraint of small cells,which achieves higher spectrum efficiency than polarization-based spectrum sharing method by utilizing additional power resources.(3)For the co-tier interference problem among co-channel deployed small cells in dense small cell networks,this thesis exploits spectrum opportunities in polarization domain and other resource domains,and builds the polarization-based spectrum sharing model.Then,the polarization-other domain collaborative spectrum sharing scheme is proposed to increase the degrees of freedom in dense small cell networks.Theoretical and simulation analysis show that,compared with traditional spectrum sharing schemes,the proposed scheme can achieve higher system capacity and lower energy consumption in dense small cell networks.(4)In view of both cross-tier interference and co-tier interference in dense heterogeneous cellular networks,this thesis utilizes available spectrum opportunities in multiple resource domains with consideration of interference avoidance to macrocell.A polarization-other domain collaborative spectrum sharing scheme in dense heterogeneous cellular networks is proposed for the coexistence between macrocell and densely-deployed small cells.Theoretical and simulation analysis show the great potential of joint utilization of polarization resource and other domains for capacity enhancement in dense heterogeneous cellular networks.In summary,this thesis innovatively proposes the exploration of polarization resources and polarization-other domain collaborative spectrum sharing,and makes a systematic study on polarization signal processing based spectrum sharing in heterogeneous cellular networks,dense small cell networks and dense heterogeneous cellular networks.The research findings will have certain reference meanings for spectrum efficiency enhancement of future wireless communication systems.