L/C双频段联合导航信号中通用调制方案研究

General modulation scheme for L/C dual-frequency combined navigation signal

为缓解L频段卫星导航信号日趋拥挤的问题,国际电联(ITU)将5 010~5 030 MHz的C频段分配给导航业务,客观上使L与C频段联合导航成为可能。调制方案是导航信号体制设计中的关键环节,设计一种能满足各波段要求的通用调制方案,可有助于降低多频终端的复杂度,加快多波段联合导航的实用化进程。本文针对北斗(BDS)B3信号的频点分布,设计一种L和C频段的双频组合模型,提出将连续相位调制(continuous phase modulation,CPM)作为上述频段的通用调制方案。仿真结果表明:相比于现有调制方案,CPM具有较高的频谱利用率,在码跟踪精度、抗多径、兼容性方面有一定的优势,可满足C频段严格的兼容性约束条件,使各波段中通用信号设计成为可能,为未来北斗卫星导航信号调制方案的设计提供新思路和可行性论证。

To ease the already overcrowded radio spectrum in the L band,the C band(5 010~5 030 MHz)was allocated by the international telecommunication union(ITU)to the navigation service,which makes it possible to combine navigation of the L and C frequency bands.The modulation scheme is the core part of the design of signal structure,and it is necessary to design a general modulation scheme that meets the requirements of all bands,reduces complexity of the multi-frequency terminal,and accelerates the practical course of multi-band combined navigation.Aimed at the distribution of frequency points of(BDS)B3 signal,this paper designs a double-frequency combination model of the L and C bands,and proposes to take continuous phase modulation(CPM)as the general modulation scheme for the above bands.In comparison with the prevailing scheme,simulation results indicate that CPM has high spectral efficiency.In addition,it has advantages in terms of tracking accuracy,multipath mitigation,and compatibility.Furthermore,it also satisfies stringent constraints required for the C band and makes general signal design possible.This paper therefore provides a new concept and provides a feasible demonstration of the future BDS signal modulation scheme.