偏轴下轨道角动量毫米波通信系统容量分析

轨道角动量(Orbital Angular Momentum, OAM)结合毫米波进行传输可以减少波束功率损耗,提高接收信号纯度,从而增大系统容量。但其必须保证收发两端天线平行共轴对齐,否则将严重影响接收端模态检测的准确性。针对这一问题,本文首先建立了一种OAM毫米波通信系统模型,其次结合OAM模态迁移特性,对横向轴偏移情形下的系统进行了信道建模,包括理论推导偏移下的模态功率分布以及构建信道传输矩阵。进一步基于该矩阵对系统容量进行了计算分析。仿真结果表明,OAM毫米波系统容量会随着偏移距离的增大而呈现下降趋势,并最终趋于稳定。同时发现当选用的模态群组的模态值较小或模态间隔较大时,系统容量受偏移影响相对小一些。为提高偏移场景下的系统性能奠定了理论基础。

Capacity Analysis of OAM Millimeter Communication System in the Off-axis Misalignment Case

Millimeter wave transmission combining with orbital angular momentum (OAM) can reduce the loss of beam power, improve the purity of the received signal, and thus increase the system capacity. During the transmission process, the antennas at the transmitter and receiver must be parallel and coaxial, otherwise the accuracy of mode detection at the receiver can be seriously influenced. In this paper, firstly the OAM millimeter wave communication system model is described, and then the channel modeling of the system is carried out based on the energy migration characteristics of OAM modes, including theoretical derivation of the power distribution between different OAM modes and construction of the channel transmission matrix in the case of the off-axis misalignment between the transmitter and receiver. Based on the transfer matrix, the system capacity is calculated and analyzed. The simulation results show that the capacity of OAM millimeter-wave communication system decreases and then keeps constant with the increase of lateral offset distance. And when the mode group with smaller modes or larger interval is selected by the system, the performance is less affected by the offset and the system capacity is larger. The results lay a theoretical foundation for the improvement of the system performance in the off-axis misalignment case.