Research On Energy Efficiency Optimization In Cellular Networks Based On Polarization Signal Processing

With the development of mobile Internet services,data traffic will grow rapidly in the future,and energy consumption in cellular networks will continue to increase.The sustainable development of mobile communication industry through green communication has become an inevitable developing trend.Also,the International Telecommunication Union(ITU)proposed an expectation of 100-fold of increase for the network energy efficiency(EE)in its 5G vision.The conventional EE optimization technology utilizes multiple radio resources such as time domain,frequency domain,and spatial domain to improve the EE performance for the cellular networks.In addition to the above wireless resources,polarization,an essential property of signals,is also an important resource that can be utilized.Faced with the contradiction between green sustainable development and high energy consumption,polarization signal processing can be regarded as an effective way to enhance the EE of cellular networks.This thesis is supported by the National Natural Science Foundation of China Project "Research on power amplifier energy efficiency based on cognitive and polarization signal processing"(No.61271177).This thesis focuses on the key issues which prevent the EE promotion of cellular networks,such as the high energy consumption of power amplifier(PA),high energy consumption of multiple radio frequency(RF)chains,as well as how to effectively use the power of interference signals.This thesis then exploits the performance advantages of polarization signal processing,in order to deal with the PA nonlinearity,reduce the number of necessary RF chains,and control the received strength of the vector signal.Also,the feasibility of combining polarization domain resources and with other domain of wireless resources is investigated,and a series of novel EE optimization theories and methods are proposed.The detailed research and achievements of this thesis can be summarized as follows:(1)The related work on EE optimization technology in cellular networks and polarization signal processing methods are reviewed and analyzed.Firstly,the existing energy efficient techniques are divided into four categories,shown as component level solution,network planning and deployment,energy transmission and harvesting,and multi-domains of resource allocation.The related research on each category of energy efficient techniques are also summarized.Secondly,polarization signal processing technologies are reviewed with an emphasis on depolarization effects and its application in wireless communication.Finally,the advantage and challenge of EE optimization based on polarization signal processing are summarized,which is the foundation for this thesis.(2)Focusing on the problem of high energy consumption caused by the PA nonlinearity,an adaptive polarization-QAM modulation(APQAM)scheme is proposed.EE can be promoted considering the fact that polarization state is not affected by the PA nonlinearity,while QAM has better EE performance in the linear region of PA.Firstly,the EE optimization model of PA is described.Secondly,a full-band as well as a sub-band APQAM schemes are proposed for the AWGN channel and the depolarization channel,respectively.Finally,the performance of the APQAM scheme is evaluated with channel estimation error to testify its robustness.The analysis and simulation results show that the proposed scheme can significantly improve the EE performance of PA by more than 50%.(3)Aiming at the problem of high circuit power consumption caused by the large number of RF chains,a joint polarization-spatial precoding(JPSP)scheme is proposed.Considering the orthogonality between the dual-polarized antennas,the polarization information and the spatial information in the channel can used to design precoding methods respectively,as limited base station antennas are selected to receive pilot signals,in order to estimate completed channel state information.As a result,the number of necessary RF chains can be reduced significantly.Simulation results show that,the proposed scheme can increase the EE performance without incurring huge array gain loss by increasing the polarization domain degree of freedom to the system.(4)Concentrating on the problem of how to effectively use the power of interference signals,a polarization adaption reception(PAR)scheme is proposed to enhance the EE performance of Simultaneous Wireless Information and Power Transfer(SWIPT)system.By joint utilizing the polarization match and mismatch methods,EE can be enhanced by designing distinct PAR algorithms for different kinds of users.While polarization mismatch reception method is designed for the information decoding users to eliminate interference,polarization match reception method can be used for the energy harvesting users to receive the resultant vector signals which are composed of both the desired signals and the interference signals.Simulation results verify the importance of the combination of polarization domain resources with spatial domain resources,and the EE performance of the SWIPT system can be promoted significantly.