Research On Low Electromagnetic Radiation Signal Design Of Wireless Handheld Terminal

With the continuous development of mobile communication system,the functions of portable wireless communication devices such as mobile phones are becoming more and more powerful and complex,which is also more and more important to our daily life.However,the health impact of close use of portable devices has not been fully discussed.In order to limit users' excessive exposure to electromagnetic radiation,regulatory authorities in most countries set electromagnetic radiation thresholds based on Specific Absorptivity SAR(W/kg).SAR is a measure of human electromagnetic energy absorption.However,the design of portable devices usually pays little attention to SAR threshold,but more attention to transmission power limitation.This paper mainly studies how to design the system based on SAR constraints.Firstly,the channel capacity of large-scale MIMO is analyzed,and then the basic concept of SAR and the expression of SAR are introduced through modeling,which lays a foundation for the subsequent perfomathbfance analysis of the system.Secondly,a kind of SAR-based signal coding is introduced in the case of two antennas,and compared with traditional signal coding methods such as Alamouti coding,space division multiplexing and single antenna.A special codeword selected from a SAR curve can achieve better bit error perfomathbfance than the traditional one,but this coding method depends on the special SAR curve and does not have generality.Then the general situation is studied,that is,how to select codewords suitable for arbitrary SAR curve and make the decoding complexity acceptable.This paper mainly introduces a scheme of designing codewords by using specific codeword structure.Then the simulation analysis verifies the reasonableness of codeword design in general,so it can be applied to arbitrary Two-antenna equipment and can be used as a standard.It is suitable for industrial design.Then,the capacity of the system is maximized under both power and SAR constraints by means of signal covariance.In traditional signal design,only power limitation is considered and SAR limitation is neglected.Water injection method is usually used to solve the energy allocation of each antenna signal to maximize the channel capacity.When SAR constraints are placed in signal design,a scheme based on SAR constraints is introduced,and an effective optimization method is proposed for the scheme based on SAR constraints.The simulation results show that the traditional power regression method and the SAR constraints scheme are compared,and the superiority of the SAR constraints scheme is proved.Then,it is extended to the case of multiple SAR constraints.The representation of signal covariance is obtained by fixing dual variables through Lagrangian duality.Then it is proved that the original problem is a convex optimization problem,and the equivalence between the optimal solution of the original problem and the corresponding Lagrangian dual optimal solution is illustrated.Thus,the solution of the original problem can be obtained by solving Lagrangian dual optimal solution,mainly through sub-gradient.The method solves the optimal dual variables,and then obtains the detemathbfination fomathbf of signal covariance.Then the signal design method using beam forming is discussed.Beamforming originates from the concept of adaptive antenna.Signal processing at the receiving end can form the desired signal by weighting the signals received by multiple antenna elements.From the perspective of antenna pattern,this is equivalent to forming a beam pointing upward,and beamforming is equivalent to transmitting the same signal from each antenna at the transmitter to enhance the signal capacity.According to the idea of beamforming,the expression of channel capacity and the threshold of SAR are obtained firstly,and then the model of beamforming problem based on SAR constraints is obtained.According to the model,an optimized solution is introduced,which can satisfy the optimal conditions and simplify the complexity.Finally,the traditional scheme based on power regression and the scheme introduced in this paper are compared by simulation.Performance.Finally,the main work in this paper is summarized,some limitations of the study are pointed out,and the future work is prospected.