Research On The Key Technologies In Wireless Communication Systems Based On Time Reversal

The temporal focusing property of time reversal(TR)in wireless communication system can compress the channel delay spread,reduce the inter-symbol interference and increase the channel capacity of the system.With the development of mobile communication system,wireless powered communication which combines energy transmission system and information transmission system has been researched widely.Energy transmission system with TR technique can precisely and wirelessly transfer power to the target without knowing its position.This dissertation aims to increase the channel capacity of the TR information transmission system and the energy efficiency of the wireless powered communication system,and has researched the antenna systems at the transmitter or receiver and the spatial channel response which have significant impacts on the channel capacity and energy transmission efficiency.Firstly,the theoretical model of the wideband carrier modulated communication system based on TR technique is built,and it has been verified that channel correlation can reduce the channel capacity of TR system as well as make the probability distribution of the channel capacities more concentrated.When multiple antennas are allocated within limited space in realistic carrier modulated communication system,mutual coupling effect and channel correlation can inevitably arise,the channel capacity of the system will also be affected.This dissertation has built the numerical model of wideband TR system,and the the improvement of the channel capacity with TR technique has been verified.The channel correlation matrix is derived from antenna mutual coupling matrix and the cumulative probability distribution function of the channel capacity is calculated,it has been theoretically derived and numerically verified that antenna mutual coupling effect can reduce the random variation of the channel capacity with the channel response in TR system.Based on this conclusion,the deployment of the antenna system can be realized properly according to the system index when the TR carrier modulated communication system is designed.Secondly,the joint antenna and channel network model in the pulse radio ultrawideband(UWB)communication system based on TR technique is built,and measurement results show that the temporal dispersion effect of the UWB antenna can reduce the channel capacity and anti-interference performance of the system.Due to the pulse distortion effect caused by the terminal UWB antenna,and the transmitted pulse is used as the template to do coherent demodulation at the receiver,the antenna effect must be considered when evaluating the system performance.Thus the joint UWB antenna and channel model is built,and its correctness has been verified by simulation,this model can be used to evaluate the performance of the arbitrary UWB system based on TR technique.Furthermore,by using three different pairs of UWB antennas to build the system and do the experimental measurements,it have been demonstrated that TR technique can improve the channel capacity of the pulse radio UWB system and the dispersion effect of UWB antenna can reduce the channel capacity and anti-interference performance of TR system.This research has provided solution for the selection of antennas in the pulse radio UWB system based on TR technique.Finally,large scale energy transmitting array based on TR technique and wideband energy transmitting array which can optimize power allocation and adjust radiation mode based on channel response are designed for the usage in the wireless powered communication system.The spatial focusing property of TR can transfer energy to the target when its position is unknown.The large scale energy transmission array based on TR technique is built in this dissertation,by the comparison of theoretical analysis and numerical simulation,the unparalleled advantage of TR technique compared with the direct power transmission scheme is obvious when the number of antenna is large and the distance of the user is relatively near.Aiming for the different received power caused by near or far distances of users,a low-complexity power balance algorithm is proposed.Considering that optimal spatial linear transmission with single-tone and optimal rectification efficiency with multi-tone,for the maximization of energy transmission efficiency,the energy allocation of subcarriers must be compromised between channel response and the rectifier.Thus the joint optimization model of spatial channel and nonlinear rectification circuit is built and the optimal energy allocation scheme is solved.Furthermore,the time modulation array which can adaptively adjust its radiation modes is proposed for the wideband wireless energy transmission,and the radiation efficiency of different radiation modes and the rectification efficiency of each subcarrier are calculated,respectively.This research has provided very referential scheme for the design of energy transmitting array either in narrowband or wideband wireless powered communication systems.