Multi-h C波段导航信号调制方式及性能评估

Multi-h C-band Navigation Signal Modulation and Performance Evaluation

近年来,L波段(1164~1610 MHz)频谱拥挤日渐严重,我国北斗卫星导航系统可用资源明显不足,基于频谱资源的不可再生性,探索研究新频段迫在眉睫。鉴于目前C波段导航信号设计尚不成熟,各国对C波段卫星导航信号体制也都还处于探索研究阶段,我国有必要预先开展C波段卫星导航信号研究。处于C波段中5010~5030 MHz的卫星导航信号具有较少的频谱干扰、较低的电离层误差等显著优势,但仅有的20 MHz带宽对诸如射电天文业务(Radio Astronomy Service,RAS)和微波着陆系统(Microwave Landing System,MLS)等相邻业务频段的射频兼容性要求极为严苛。首先提出将多调制指数(Multi-h)的正交频分复用-连续相位调制(Orthogonal Frequency Division Multiplexing-Continuous Phase Modulation,OFDM-CPM)联合调制方式应用于C波段卫星导航;其次,在分析关键参数对Multi-h OFDM-CPM信号功率谱特性影响后,选取关联长度L为64、调制指数h为0.5的单调制指数(Single-h)OFDM-CPM(10)信号和h为[1/16,3/16]的Multi-h OFDM-CPM(10)信号作为C波段候选导航信号;最后,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,OFDM-CPM调制方式能很好兼顾C波段信号的带外约束性和导航性能要求,OFDM-CPM(10)h=[1/16,3/16]信号在所述各个基础导航性能指标上均表现最佳,在兼容性方面能弥补OFDM-CPM(10)h=0.5信号的略微不足。然而考虑到多调制指数会增加接收机复杂度,因此在C波段导航中,只有当接收机采用低复杂度检测算法时,Multi-h OFDM-CPM信号才会是比Single-h OFDM-CPM信号更佳的选择。

In recent years,the spectrum congestion of the L-band(1164~1610 MHz)has become increasingly serious.Moreover,the available resources of the BeiDou Navigation Satellite System in our country are obviously insufficient.Based on the non-reproducibility of spectrum resources,it is imperative to explore new frequency bands.Because C-band navigation-signal design is not yet mature,and many countries are still investigating C-band navigation-signal systems,it is necessary for our country to conduct a study of C-band navigation signals.Satellite navigation signals at 5010~5030 MHz in the C-band have significant advantages,including less spectral interference and lower ionospheric errors,but the 20 MHz bandwidth has strict requirements for radio frequency compatibility with adjacent service bands such as those of the Radio Astronomy Service and Microwave Landing System.This study first investigated the application of the combined orthogonal frequency division multiplexing-continuous phase modulation(OFDM-CPM)method based on multiple modulation indices(multi-h)for C-band satellite navigation.Then,after analyzing the influences of key parameters on the power spectrum characteristics of a multi-h OFDM-CPM signal,a single-h OFDM-CPM(10)signal with a correlation length(L)of 64 and modulation index(h)of 0.5 and a multi-h OFDM-CPM(10)signal with a correlation length(L)of 64 and h of[1/16,3/16]were selected as C-band candidate navigation signals.Finally,basic navigation performance indices were evaluated,including the compatibility,code tracking accuracy,and anti-multipath performance.The study found that OFDM-CPM modulation could take into account both the out-of-band constraints and navigation performance requirements of C-band signals,and OFDM-CPM(10)signals with h=[1/16,3/16]had the best performance,as shown by the above basic navigation performance indices.In terms of compatibility,it could make up for the slight deficiency of OFDM-CPM(10)signal with h=0.5.However,considering that the multiple modulation index will increase the complexity of the receiver,the multi-h OFDM-CPM signal is a better choice than the single-h OFDM-CPM signal for C-band navigation only when the receiver adopts a low-complexity detection algorithm.