Research On The Optimization Of Unique Factorization Signals In Noncoherent Massive MIMO Communication Systems

Ultra-Reliable Low-Latency Communication(URLLC)is one of the two application scenarios of the fifth-generation mobile communication for the mobile Internet of Things.Due to the stringent requirements for latency,the main feature of URLLC at the physical layer is the transmission of short data packets,which requires redesign the current signal transmission scheme of the physical layer.In particular,studying how to reduce the dependence of short data packet transmission on channel coding schemes with robust error correction capabilities and use resources other than time diversity to improve system reliability is of great significance to the realization of URLLC in 5G.Massive Multiple-Input Multiple-Output(MIMO)is one of the core technologies of the 5G physical layer.Its high space diversity resources and array gain can significantly improve the system's reliability under latency constraints.Therefore,it is considered to be one of the potential enabling solutions of URLLC.However,the coherent massive MIMO system will face the difficulties of significant pilot overhead and instantaneous channel state information(CSI)acquisition when transmitting short data packets.Non-coherent massive space-time modulation scheme can fully develop the space diversity gain of the multi-antenna systems without channel estimation operation,which is expected to solve the CSI acquisition problem.Given this,this dissertation aims to achieve ultra-reliable transmission of short data packets by optimizing the design of non-coherent space-time modulation schemes in massive MIMO systems.Specifically,the main contributions of this dissertation can be summarized as follows:(1)For the short data packet structure containing only two orthogonal frequency division multiplexing(OFDM)symbols in the 5G NR Node B protocol,we consider a massive Single-Input Multiple-Output(SIMO)uplink communication system.A single-antenna transmitter needs to send information to a base station deployed with a massive antenna array in such a system.The system's channel coefficient remains unchanged for two consecutive symbol periods,changing every two symbol periods.Aiming at the instantaneous CSI acquisition problem and the system's low reliability,a mapping scheme for Massive uniquely factorable constellation(MUFC)is proposed.With the multi-level coding and modulation method,a soft-decision MUFC symbol sequence detector is established based on the closed-form MUFC;then,a symbol sequence optimization framework is established based on the minimum Riemannian distance criterion.Following the idea of trellis coding,a specific mapping scheme of the MUFC constellation is given.The simulation results show that the designed mapping scheme can significantly reduce the system's bit error rate(BER).(2)In order to improve the system's spectrum efficiency and the number of users served,this dissertation further studies an effective uplink short data packet transmission scheme based on phase-shift keying(PSK)signals in the multi-user spatial multiplexing scenario.In the uplink,it is assumed that two single-antenna users send information to a base station deployed with a large-scale antenna array on the same time-frequency resource.The channel coefficients remain unchanged in two consecutive symbol periods and change independently every two symbol periods.In this system,both users use the PSK constellation to modulate the transmitted signal,and the constellation of one user can be obtained by rotating the PSK constellation of the other user.This paper proposes a non-coherent signal detector based on the Euclidean distance measurement criterion for such a system and signal model.Then,a signal optimization criterion based on Euclidean distance is proposed to establish a joint optimization framework of user transmit power and PSK constellation rotation angle.Finally,a linear search algorithm is used to solve the power allocation and rotation angles' optimal numerical solutions.The simulation results show that the proposed scheme can effectively improve the system's reliability while improving its energy efficiency.