Research On SWIPT In MIMO Systems

With the rapid development of wireless communication technology and the improvement of the wireless communications,the number of end devices are increasing rapidly,which has caused great charging demands.However,the traditional mobile devices still needs to be connected to the grid for recharging.Due to the limited battery life,frequent replacement or recharging has restricted the sustainable operation of the communication systems,and a large number of charging equipment also cause great pollution to the environment,therefore,new charging methods are urgently required.In order to solve this problem,wireless power transfer,which utilizes electromagnetic wave to transmit power,has received wide attention.Since wireless signals can also transmit information,simultaneous wireless information and power transfer(SWIPT)can make full use of the radio-frequency signals.In order to improve the efficiency of SWIPT in practical multi-antenna systems,the receiver needs to use the CSIT to perform beamforming.To obtain the CSIT,the receiver either send an uplink training sequence(TDD system)or feed back the channel state information(FDD system).However.the time-variant characteristics of the channel,the quantization error,and feedback error may lead to channel estimation error,and the CSIT acquisition may also cause some energy consumption and affect the system performance.In order to solve these problems,this paper proposes a spatial modulated wireless information and power transfer(SM SWIPT)system.For the massive MISO SWIPT system,a joint pilot length and PS/TS allocation optimization problem is formulated to obtain the maximum achievable rate.The main work and innovation of the paper are summarized as follows:(1)An SM SWIPT structure is proposed,and the achievable throughput is maximized by optimizing the power splitting factors.There are three open-loop MIMO schemes:spatial multiplexing,spatial diversity and spatial modulation.For the former two schemes,all the antennas are activated at the same time,thus it will consume more energy and cause co-channel interference.However,spatial modulation activates only one antenna(only one RF link)in one time slot,so it can reduce energy consumption and avoid co-channel interference.In this paper,a spatial modulated SWIPT system is designed and an iterative power splitting algorithm is proposed,which maximizes the achievable throughput under the constraints of energy harvesting threshold.By comparing with SIMO SWIPT and energy beamformed MIMO SWIPT,the SM SWIPT can achieve better energy-throughput performance under the same spectral efficiency.(2)An achievable Rate Maximization Problem for Massive MISO SWIPT with uplink channel estimation is formulated.For point-to-point Massive MISO SWIPT system,in time-division duplex mode,one coherent time is divided into uplink training and downlink transmission phases.It is considered that the pilot sequence needs to be sent to the transmitter for channel estimation and perform beamforming to combat with the channel fading,and two practical schemes:time switching(TS)and power splitting(PS)are adopted respectively at the receiver to decode information and harvest energy.Considering the harvested energy at the receiver during one coherent time for the information decoding and the pilot transmission at the next coherent time,we can maximize the achievable rate by optimizing the pilot length and the PS/TS factors under the energy constraints.In this paper,we propose a search algorithm that optimizes the pilot length and PS/TS factors,and shows the superiority of the algorithm by comparing the performance of the optimal pilot length with that of the fixed pilot length.