Research On Multiple Access Technology Of Downlink In High Mobility Wireless Networks

With the development of electronic information technology and the advancement of communication technology,future warfare will gradually evolve into joint all-domain operations.Military forces will develop towards joint clustering,giving rise to integrated combat clusters based on different combat functions.Meanwhile,combat equipment in the battlefield environment,such as cruise missiles and fighter jets,are often in a state of high-speed movement,with their speeds reaching up to 500 km/h,1000 km/h,and even 2 to 3 Mach.Combat units,reconnaissance units,command units,and others simultaneously connect to the network.The central command center needs to transmit control information to multiple high-speed moving units or unit clusters simultaneously during operations.In the context of high-speed mobility,extensive access of various units and unit clusters,as well as the demand for high-throughput information transmission from the operational center to each unit and unit cluster,research is conducted on multiple access technologies for the downlink in high-mobility wireless networks.In the downlink of high-mobility wireless networks,the simultaneous connection of a large number of units poses challenges to system spectral efficiency and throughput.NetworkCoded Multiple Access(NCMA),as a type of Non-Orthogonal Multiple Access(NOMA),benefits from the gains brought by Physical-layer Network Coding(PNC).While ensuring high spectral efficiency,it can further enhance the system’s throughput.However,the existing NCMA implements equal power allocation among different users,which does not meet the flexibility requirements in modern battlefields where different units have varying priorities and communication quality needs.Moreover,equal power allocation NCMA experiences severe overlapping of superimposed constellation points when applied in the downlink,leading to a decrease in system throughput.In addition,the high Doppler spread caused by the high-speed movement of units constrains the throughput of NCMA systems.By employing Orthogonal Time Frequency Space(OTFS)waveforms,the adverse effects of high Doppler spread can be effectively mitigated.On the other hand,the presence of multi-user interference can significantly impact the information transmission from the operational center to various units.By deploying multiple antennas at both the operational center and individual units,a Multi-Input and Multi-Output(MIMO)system is formed,and the effective elimination of multi-user interference is achieved through the use of transmitter precoding.However,under the OTFS waveform framework,signals are processed in the Delay-Doppler(DD)domain.Existing transmitter precoding algorithms incur excessively high computational complexity when executed in the DD domain,posing challenges to the practical deployment of downlink high-mobility wireless networks.This paper addresses the aforementioned issues and conducts in-depth research on the throughput improvement techniques for traditional NCMA in the downlink,throughput enhancement techniques for NCMA in high-speed mobility scenarios,and low-complexity precoding techniques for multi-user NCMA in high-speed mobility scenarios.The main objective is to provide crucial support for the Chinese military to gain a strategic advantage in future warfare.The key tasks are summarized as follows:(1)In response to the throughput degradation and the challenges of achieving flexible deployment in the traditional downlink NCMA,we propose a new strategy for downlink NCMA based on power allocation.This strategy involves allocating different power to different users by analyzing the impact of power allocation coefficients on the error performance of the PNC decoder and the Multi-User Decoder(MUD).Distribution different power levels to signals for different users allows for the adjustment of the amplitudes of different constellation points to optimize the Euclidean distance between overlapping constellation points,this improvement enhances the joint decoding performance of PNC decoder and MUD,ultimately boosting the system throughput.Simultaneously,with the objective of maximizing the overall system throughput,appropriate power allocation coefficient is selected.Simulation results demonstrate that the proposed new strategy for downlink NCMA based on power allocation significantly enhances the joint decoding performance of PNC decoder and MUD,leading to an improvement in overall system throughput.(2)To address the throughput limitations of NCMA in high-speed mobility scenarios,we design a downlink OTFS-NCMA system architecture and propose a transmission strategy denoted as OTFS-NCMA with joint Amplitude-Phase design(OTFS-NCMA-AP).This strategy is based on amplitude-phase joint optimization to enhance the performance of downlink OTFS-NCMA system.This transmission strategy involves an analysis of the impact of power allocation coefficients and relative phase offset on the downlink OTFS-NCMA system.It derives an upper bound expression for the error probability in the physical layer processing of NCMA decoder.With the assistance of a genetic algorithm,it jointly adjusts the power allocation coefficients and relative phase offset of constellation points to minimize the error probability upper bound,enhancing the overall system throughput in high-mobility scenarios.Simulation results confirm the effectiveness of the downlink OTFS-NCMA system in high-speed mobile scenarios and demonstrate the gains achieved by the proposed OTFSNCMA-AP transmission strategy in terms of throughput improvement.(3)To address the issue of high complexity in NCMA multi-user precoding algorithms in high-speed mobility scenarios,we design a NCMA-enabled downlink multi-user MIMOOTFS system.Additionally,a low-cost,low-complexity precoding algorithm is proposed.This algorithm leverages the properties of OTFS channel matrices in the DD domain and transforms the Singular Value Decomposition(SVD)problem of high-dimensional matrices into multiple lower-dimensional SVD decomposition problems.While effectively eliminating multi-user interference,a significant reduction in the number of floating-point computations required during the precoding execution process is achieved.Simulation experiments demonstrate the capacity of the NCMA-enabled downlink multi-user MIMO-OTFS system to support numerous users,and the outstanding performance of the proposed low-complexity precoding algorithm.