北斗L/C双波段导航信号调制方式及性能评估

L/C dual-band navigation signal modulation mode and performance evaluation of BeiDou system

大间隔L/C双频段导航可显著提高定位精度和鲁棒性,将成为未来高精度卫星导航系统的发展趋势。为降低双频终端的复杂度,设计了一种通用调制方式,使其既满足L/C波段的频谱兼容性约束,又具有良好的导航性能。提出将正交频分复用-连续相位调制(OFDM-CPM)联合调制方式应用于L/C双波段导航。选取调制指数h=0.5、关联长度L与OFDM-CPM符号数一致的OFDM-CPM信号作为L/C双波段候选导航信号,设定双频频点,并对包括兼容性、码跟踪精度、抗多径干扰在内的基础导航性能指标进行评估。研究表明:在L波段,OFDM-CPM(15)具有优良的码跟踪性能和抗多径能力,且更易与其他候选信号共存;在C波段,OFDM-CPM(10)能很好兼顾C波段信号的带外约束性和导航性能要求,在码跟踪精度与抗多径干扰方面表现最佳,为未来北斗系统导航信号体制的设计提供一种选择。

Large interval L/C dual-band navigation can significantly improve positioning accuracy and robustness,and will become the development trend of high precision satellite navigation system in the future.To reduce the complexity of dual-frequency terminals,a universal modulation scheme is designed,which not only meets the spectrum compatibility constraints of L/C-band,but also has good navigation performance.A combination of Orthogonal Frequency Division Multiplexing-Continuous Phase Modulation(OFDM-CPM)is proposed for L/C dual-band navigation.OFDMCPM signals with the modulation index h=0.5 and the correlation length L consistent with the number of OFDM-CPM symbols are selected as L/C dual-band candidate navigation signals.Dual-frequency points are set,and the basic navigation performance indicators including compatibility,code tracking accuracy and anti-multipath interference are evaluated.The results show that in L-band,OFDM-CPM(15)has excellent code tracking performance and antimultipath ability,and is easier to coexist with other candidate signals.In C-band,OFDM-CPM(10)can well take into account the out-of-band constraint and navigation performance requirements of C-band signals,and has the best performance in code tracking accuracy and anti-multipath interference,providing a choice for the design of navigation signal system of BDS in the future.