相干接收圆偏振调制MIMO无线光通信系统理论与优化设计

Most the high speed free space optical (FSO) systems are based on the intensity modulation/direct detection (IM/DD) scheme, which are less resilient to the atmospheric turbulence and thus leads to phase fluctuation of the optical wavefront. By switching the modulation from intensity to polarization, the impact of atmospheric turbulence of the FSO links can be alleviated and the transmission data rate can be significantly increased compared to IM/DD FSO links. The main goal of this proposal is to systematically investigate the heterodyne circle polarization shift keying (CPOLSK) based FSO system by adopting the multiple-input-multiple-output (MIMO) technology over the atmospheric turbulence channel. In this scheme the vectorial property of propagating optical beams as well as coding digital bits on two rotation states of circle polarization can be utilized, which can be well maintained in long FSO transmission links, and is more resilient to the channel turbulence and the pointing error, thus offering lower bit error rate and improved link alignment and track-ability compared to IM/DD under the same channel conditions. The MIMO technique creates a large aperture at the receiver by deploying multiple smaller aperture receivers, which providing a striking approach to compensate for the turbulence induced fading. This research fundamental investigation of CPLSK based FSO systems will be carried out supported by experimental investigations. The results achieved from this project will provide the theoretical foundation and the key technology for high speed FSO communication systems in China.

随着高速激光通信的需求，针对现有强度调制/直接检测(IM/DD)的自由空间激光通信（FSO）系统可靠性低这一难题，本项目根据激光偏振态在大气中传输时稳定的特性，提出了一种基于圆偏振移位键控(CPOLSK)调制和相干接收的大气激光通信系统，并在此基础上引入多输入多输出(MIMO)技术，无需增加额外带宽和功率条件下提升信道容量或提升传输性能。该系统对发射功率和探测器件性能要求低，抗大气衰落能力强，可以降低大气湍流对通信系统性能的影响，提高通信系统的抗干扰能力并改善系统误码率。从通信系统综合性能方面考虑，CPOLSK系统要优于IM/DD系统。本项目将为我国高速激光通信系统在高谱效、高可靠传输等关键技术指标上提供重要的理论基础和技术储备。

随着大容量通信需求的迅速增加，目前基于射频载波的宽带移动通信面临带宽紧缺的问题，急需开发高频段资源满足大容量通信需求。自由空间激光通信(FSO)系统使用半导体光源，实现光信号在空间的高可靠高效传输，兼具免频谱许可证、抗电磁干扰等独特优势，满足未来宽带移动通信的需求，因此受到世界各国的重视。FSO系统大多采用强度调制/直接检测(IM/DD)方式，光信号在大气信道传输受到湍流和噪声干扰，严重影响了信息可靠传输，并增加了信道理论的复杂度和研究的难度。通过理论分析和实验相结合，本项目研究不同大气湍流效应对激光通信的影响机理和形式，并根据光偏振态在大气湍流信道传输的稳定性，提出基于圆偏振调制(CPOLSK)和相干接收的多输入多输出(MIMO)激光通信系统。与传统的IM/DD系统对比，该系统不仅具有较强的抗大气湍流干扰能力，而且在无需增加额外带宽和功率的条件下可提升信道容量和通信性能。本项目从激光信号与大气信道的作用机理、传输理论、资源优化三个层面展开研究，弄清大气随机信道对光信号的干扰效应，揭示无线光信道容量，提出有效抑制噪声的理论与方法，优化无线激光传输系统的多维资源，构建相应性能评估及典型应用演示平台。本项目开拓红外激光光谱资源，取得原创性研究成果。