Research On Performance Of Channel Estimation In Massive Wireless Access And Modulation Technology Based On Multi-scale Spatial Fractal Characteristics

With the large-scale deployment of the fifth generation(5G)mobile communication system,the access and high-rate data transmission requirements of wireless devices increase rapidly.The channel estimation is an important support for wireless access in mobile communication systems.Normally,channel state information(CSI)is estimated by the pilot signal.In the massive wireless access scenarios,a large number of access requests lead to a rapid increase in pilot overhead,which increases the system load seriously.High-order modulation is one of the crucial technologies for high-rate wireless transmission,quadrature amplitude modulation(QAM)can achieve high-rate data transmission without additional bandwidth.In the research of massive access and high-rate data transmission of 5G mobile communication systems,it is generally considered that the coverage boundary of 5G cellular networks is a regular polygon.However,the coverage boundary of cellular networks is irregular actually,and shows fractal self-similarity in multi-scale space.It is a considerable challenge to reduce the pilot overhead of channel estimation in massive wireless access and improve the calculation accuracy of the symbol error rate(SER)of QAM by utilizing the fractal characteristics of the channel.The main contributions of this paper are summarized as follows:Firstly,based on the self-similarity of the fractal channel in multi-scale space,a channel estimation scheme for multi-terminal power control in massive wireless access scenarios is proposed.In the proposed scheme,the part of CSI is sampled to estimate all CSI between the base station and terminals,which can reduce the access pilot overhead and solve the shortage of pilot resources in terminals.Moreover,in order to save power consumption,terminals adjust their transmitting power according to the CSI estimated by the proposed scheme.The simulation results show that the pilot overhead and the power consumption of the proposed scheme can be reduced.Then,a new calculation method of the SER of 64-QAM is proposed.Based on the fractal theory,the SER of 64-QAM considering fractal channel characteristics is derived.The simulation results show that the calculation accuracy of the proposed method is improved compared with the traditional method.In summary,by utilizing the statistical fractal characteristic in angular scales of the coverage boundary of actual cellular networks,the pilot overhead in channel estimation is significantly reduced,and the calculation accuracy of the SER in 64-QAM is significantly improved in this paper.This paper provides some new ideas for the application of the fractal theory in the wireless communication field.