基于CPM的高谱效恒包络导航信号调制方法

With the development of GNSS, the contradiction between the growing demand and the scarce frequency resources becomes more severe. The investigation on the modulation technique with high spectral efficiency is an efficient way to solve this problem. Considering the ranging accuracy, anti-interference performance, anti-multipath performance and the compatibility constraint, this project researches the definition of spectral efficiency applied to navigation signals and the assessment on the effective bandwidth and comprehensive effectiveness, and model the spectral efficiency. Based on these researches, the continuous phase modulation is introduced into the navigation signal design, and the trend graph for the combined effect is obtained to summarize the objective laws by quantitatively analyzing the effect of continuous phase modulation parameters on the spectral efficiency of navigation signals. The frequency pulse waveform is discretized, and compatibility constraints are introduced into the objective function by employing the penalty function. Then the optimal waveform is found out by numerical optimization, and the optimal modulation design based on joint modulation parameters and the optimal modulation pulse waveform is proposed. Finally, according to the typical application cases, the corresponding signal tracking schemes are designed and validated by simulation. This project can provide not only theoretical foundation and support for the navigation signal optimized designing, but also an alternative technical solution for the long term evolution of navigation system, which is significant for the construction and long term development of the Beidou system.

导航系统性能需求增长与频率资源紧缺之间的矛盾越来越突出，研究高谱效调制方式成为导航信号设计中亟待解决的问题。本项目综合考虑卫星导航系统对测距精度、抗干扰能力、抗多径性能的需求及频率兼容性约束，研究导航信号频谱效率的定义，提出导航信号有效占用带宽和综合效用的评估方法，并建立导航信号频谱效率模型。将连续相位调制方式引入导航信号设计，通过定量分析连续相位调制参数对导航信号频谱效率的影响，总结其客观规律，建立多参数联合影响趋势图；采用罚函数法将兼容性约束条件引入目标函数，并对频率脉冲波形进行离散化处理，然后通过数值优化的方法搜索最优波形；在此基础之上，提出联合调制参数和脉冲波形的最优调制设计方法。针对设计结果，结合典型应用需求设计相应的信号跟踪方案，并通过仿真验证。可为导航信号最优化设计提供理论基础和方法支撑，为导航系统长期演进提供可选的技术方案，对北斗系统的建设和长期发展具有重要的意义。

卫星导航系统在政治、经济、军事上具有重大战略意义，促使有实力的国家和地区竞相建设独立自主的全球或区域导航卫星系统，并且每个系统都呈现出多频点、多服务的发展趋势。快速增长的导航系统信号需求，与紧缺的频率资源之间的矛盾越来越突出，迫使导航信号设计更加注重频谱高效利用。本课题研究并提出了一系列提升导航频率资源利用效率的调制方法。首先，针对单一频带多路信号传输的需求，提出了一种准恒包络的多路相干联合调制方法，该方法允许任意调节分量信号幅度、相位及合路信号包络波动范围，获得满足约束条件的复合信号。与当前广泛使用的POCET调制方式相比，该方法增加了包络幅度维度的灵活性，可以引入微小的幅度波动减小无用交调分量的发射，提升频谱利用效率。其次，针对双频和多频多路信号传输的需求，分别提出了双频/多频多路恒包络相干联合调制方法。与同类技术相比，本课题方法不仅容许任意数目信号分量的幅度、相位配置，还增加了频率配置的灵活性。此外，针对带宽严重受限、带外辐射抑制要求高的导航信号传输需求，提出了一种通过联合波形优化提升频谱利用效率的GNSS恒包络调制方法。结果表明，在性能与已有方法相当的条件下，与相邻频带的兼容性可改善10dB以上。本课题的研究，扩展了卫星导航信号波形及复用设计的理论和方法，对高谱效导航信号调制技术进行了有益的探索，部分成果在工程实践中得到应用，可为卫星导航系统演进提供有效的技术手段。