Study On Equalization Technology Of Millimeter Wave Communication Systems

In recent years,with the development of digital multimedia services and the popularization of smart terminal devices,the requirements for the transmission rate and signal bandwidth of wireless communication technologies have been rapidly increasing,and the traditional wireless communication technologies have been unable to meet people's needs gradually.60GHz-millimeter-wave communication system has become a research focus in recent years due to its rich spectrum resources,high transmission rate,strong anti-interference ability and high security.This paper mainly studies the equalization technique in 60GHz-millimeter-wave communication system,including the equalization of linear channel and nonlinear channel.Because the zeroforcing algorithm and the fixed-point algorithm involved in this paper need to know the channel characteristics,this paper also discusses related channel estimation algorithms.Firstly,a brief introduction of millimeter-wave communication system is given.The common channel model for the millimeter-wave communication system is described from two aspects of large and small scale respectively,including path loss and shadow fading.Next,the channel characteristics and frame structure of the IEEE 802.11 ad standard are introduced in detail.Secondly,the linear channel equalization is introduced.The reason of the intersymbol interference leads to a balanced technology,and a brief description of the classification of equalization techniques is given.Based on the Wiener filter,the tap coefficients of the zero-forcing equalizer in the time-domain are deduced and the adaptive equalizer is derived based on the LMS criterion.Then according to the characteristics of the channels in the CM1 and CM2 modes in the IEEE 802.11 ad standard,they are respectively equivalent to a simple quasistatic Rice channel and a Rayleigh channel.Finally,the performance of the two equalization algorithms under two modes of channels is analyzed by simulation.Simulation results show that the two equalization methods can achieve good results,and the adaptive algorithm is slightly better than the zero-forcing equalization algorithm.Thirdly,considering the influence of nonlinear power amplifier,the problem of equalization of nonlinear channel is studied.This article briefly introduce the channel model of nonlinear system,including Volterra model,Wiener model,Hammerstein model and memory polynomial model and so on.Then,the problem of equalization of nonlinear channel is abstracted as the problem of the fixed-point equation,and its solution is obtained by successive approximation.Then the LMS-based adaptive algorithm is generalized to the nonlinear channel.Finally,the Wiener model and the Hammerstein model are chosen as examples to simulate the performance of the two equalization algorithms.Simulation results show that compared to zero-forcing equalization and general LMS adaptive equalization,the fixed-point algorithm and the modified LMS algorithm have significantly improved system performance.At last,the issue of channel estimation is discussed in view of the need to know the channel characteristics in both zero-forcing and fixed-point equalization.The linear channel estimation is accomplished by using the autocorrelation of Gray complementary sequences.The Wiener model and the Hammerstein model are taken as examples to derive the least square method for nonlinear channel estimation.Next,the performance of the two channel estimation methods is analyzed by simulation.The simulation results show that the linear channel estimation based on Golay complementary sequences can achieve close performance to the ideal channel estimation.For the nonlinear channel,based on the least square estimation method,the performance under the Hammerstein model is significantly better than that of the Wiener model.On that basis,the effect of the equalization algorithm on the non-linear power amplifier at the sending end of the millimeter-wave system is discussed by simulation.The results show that the fixed-point algorithm and the modified LMS adaptive algorithm can effectively reduce the adverse effect of power amplifier nonlinearity on the transmission performance of millimeter-wave communication systems.