Research On 5G Mobile Communication And Wireless Power Transfer

In recent years,with the rapidly increasing demand of medium service,the fifth generation(5G)mobile communications,which can improve the data rate and spectrum efficiency,have become a hot research topic in communication field.Millimeter wave communications can provide large available spectrum and achieve high data rate by multiplexing gain.Due to the short wavelength,millimeter wave transceiver can be equipped with more antennas.Full duplex communications can obtain high spectrum efficiency through simultaneous transmis-sion and reception using the same frequency band at the same time.Thus,millimeter wave communications and full duplex communications have become the 5G key technologies.At the same time,wireless power transfer,which can harvest energy from radio frequen-cy signal,has been a new solution to reduce the energy consumption and achieve green communications.Traditional energy harvesting,which can scavenge energy from natural sources,can not be controlled and thus hardly provides stable power supply for wireless net-works.The radio frequency signal can carry both information and energy,wireless power transfer,which has attracted much attention recently,can harvest energy from radio frequen-cy signal,provide stable energy and reduce energy consumption.In addition,cooperative relay technology can divide a long transmission distance into several short transmission dis-tances,which can effectively reduce the path loss and energy consumption.Wireless sensor networks can employ the cooperative relay to improve energy efficiency and prolong the lifetime.This thesis first studies the millimeter wave communications and full duplex com-munications to increase the data rate and spectrum efficiency of mobile communications.Then,we apply the wireless power transfer and cooperative relay to wireless sensor net-works,which can improve the energy efficiency.The contribution of the dissertation can be summarized as follows:1.To study the performance of millimeter wave communications,we establish a three-dimensional multiple input multiple output(MIMO)channel model.which is based on u-niform linear antenna array(ULA).First,utilizing the channel orthogonality,the optimal antenna separation corresponding to the achievable maximum capacity is derived.The ex-pression of optimal antenna separation demonstrates the relationship between the capacity and the antenna separation,carrier frequency,antenna number and the distance between the transmit and receive antenna arrays.Then,we analyze the performance variations caused by the increasing antenna number and the deviation of antenna separation,respectively.The in-creasing antenna number will increase the channel power gain,but not the channel freedom.Finally,to minimize the ULA length for millimeter wave communication system with max-imum capacity,we formulate the ULA length minimization problem and derive the optimal solution,which satisfies(i)the length of the transmit ULA is equal to that of the receive ULA and(ii)the transmit and receive ULAs are in the same plane and the line connecting centers of the transmit and receive ULAs is perpendicular to both the transmit and receive ULAs.Furthermore,we analyze the influence of orientation deviation on ULA length.2.By analyzing time and power allocations,we study the power efficiency maximization of wireless-powered full-duplex relay(WFR)systems,where the entire transmission process can be partitioned into wireless power transfer phase(WP)and full-duplex relay informa-tion transmission phase(FP).For WFR systems with same source transmit power,where the source transmit powers of WP and FP are same,we first prove that the power efficiency is a strictly concave function over the time-switching factor,and an optimal time allocation scheme is proposed to maximize the power efficiency.Then,for the given time-switching protocol,the optimal power allocation strategy is obtained by analyzing the derivative of the power efficiency with respect to the transmit power.Finally,we propose the joint power and time allocation scheme.For WFR systems with different source transmit power,where the source transmit powers of WP and FP are different,the optimal time allocation scheme and optimal power allocation strategy are derived by studying the derivative of the power effi-ciency.Furthermore,the joint power and time allocation scheme is proposed to maximize the power efficiency.3.We propose the single power relay based wireless decode-and-forward information trans-mission,where the information and power relay can decode and forward information from the user to the access point(AP),and assist the wireless power transfer from the AP to the user.For the relay systems with power splitting(PS)protocol,the closed form expression of the optimal PS factor is derived to maximize the capacity from the user to the AP.For the relay systems with time switching(TS)protocol,we propose the time allocation scheme to obtain the optimal TS factor,which maximizes the capacity.Note that the capacity of decode-and-forward based relay systems is determined by the minimum received signal-to-noise ratio(SNR)between the relay and AP,which significantly complicates the capacity maximization problem and makes our study nontrivial.4.We investigate the performance of multiple power relays based wireless decode-and-forward information transmission,where all the information and power relays can decode and forward information from the user to the AP,and assist the wireless power transfer from the AP to the user.The relay employs the PS protocol to coordinate the received signal energy for information transmission and energy harvesting.By converting the multi-relay system capacity maximization problem into a convex optimization problem,the distributed power allocation(DPA)scheme is obtained to maximize the capacity.In multi-relay sys-tems,all the relays can receive the signals from AP and user,spatial diversity of the relays can effectively increase the capacity without extra power.