Research On Signal Processing Technology In Intelligent Reflecting Surface Assisted Communication Systems

With the perpetual progress of communication technology,the usage of wireless devices increases rapidly,the data traffic in wireless network increases rapidly,and the network resources are constantly consumed,which puts forward higher requirements for the communication systems,such as extremely low-power communication and high-mobility communication.The fifth generation mobile communication technology(5G)has been unable to satisfy the growing demand.There is an urgent need to develop the next generation of wireless communication technology to address these challenges.Therefore,intelligent reflecting surface(IRS)has emerged as a revolutionary new technology,which is expected to become one of the key technology of future the sixth generation mobile communication technology(6G).IRS is a two-dimensional surface composed of programmable metamaterials.By connecting intelligent controller,it can independently control the amplitude and phase of each reflecting element to change the direction of the incident signal,thus realizing the active reconstruction of the wireless environment.The introduction of IRS makes wireless channel complex,then channel estimation cannot be carried out by traditional methods.However,channel estimation is an indispensable part of communication systems.Therefore,it is very important to design a reasonable channel estimation scheme for the IRS assisted communication systems.In addition,since the future network will be a network integrating communication,sensing and computing,and wireless localization is an important technology to realize sensing,it is also very important to deploy IRS to assist joint communication and localization,which is a frontier research topic.In view of these research directions,this paper mainly studies the channel estimation scheme in IRS assisted communication systems and the implementation scheme of IRS assisted integrated communication and localization.The main contributions of this paper are as follows:(1)To deal with the problem of signal interference and channel change in the IRS assisted communication systems,a two-stage channel estimation scheme is proposed.In order to better estimate the channel,channel estimation scheme is divided into two stages.In the first stage,only the direct channel is estimated,and the classical least square(LS)method is used to estimate the channel.In the second stage,the null space of the direct channel is applied to eliminate the interference and Kalman filter is used to estimate the reflecting channel while the direct users communicate with the base station(BS).The simulation results show that the proposed scheme has satisfactory channel estimation accuracy and its bit error rate is lower than that of the existing scheme,which demonstrates the effectiveness of the proposed scheme.(2)In view of the limitation of the number of users in the proposed channel estimation scheme,a user grouping scheme based on QR is proposed.In the proposed scheme,direct users are divided into the primary user group and the secondary user group according to the signalto-noise ratio of users at the receiver.The primary user group continues to communicate with BS through direct links due to high signal-to-noise ratio,while the secondary user group mainly communicates with BS through reflecting links.In the proposed scheme,direct users can be grouped according to the estimation of direct channel,and the reflecting channel can be estimated according to the grouping results.The simulation results show that the bit error rate of the proposed grouping scheme is lower than that of the random grouping scheme,which confirms the advantages of the proposed scheme.(3)Aiming at the wireless localization scheme design in IRS assisted communication systems,a joint communication and localization scheme based on multiple signal classification(MUSIC)is proposed.In the proposed scheme,the received signal is projected onto the orthogonal space of the IRS-BS channel to obtain the direct signal without interference,and the direction of arrival(DOA)of the direct link is estimated by the MUSIC algorithm.Then,the estimation of direct channel is obtained according to the estimated DO A,and the received signal is projected onto the orthogonal space of the direct channel.The MUSIC algorithm is used again to get the DOA of user-IRS link.Finally,according to the two DOA estimations,the location information of users is recovered,so as to locate users.According to the location results,the receiver can be designed to better complete the signal decoding and realize better communication between users and BS.The simulation results show that the proposed scheme has good positioning effect and communication performance,which verifies the availability of the proposed scheme.