| L-band signal spectrum congestion is becoming more and more serious,which makes it urgent to explore new frequency bands of satellite navigation services.In 2000,the International Telecommunication Union(ITU)divided the 5010 to 5030 MHz of the C-band into a new band for navigation services.This band has only 20 MHz bandwidth,which has extremely strict requirements for radiofrequency compatibility of adjacent service bands such as radio astronomy service(RAS)and microwave landing system(MLS).At present,the Cband navigation signal design is not yet mature,the C-band satellite navigation signal system in various countries is still in the research and exploratory stage,early research on C-band satellite navigation signals is both an opportunity and a challenge,efficient satellite navigation signal design can not only improve the performance of navigation system,but also avoid the spectrum overlap of adjacent service signals and maximize the sharing of spectrum resources.After analyzing the signal transmission characteristics of the C-band and the current global navigation satellite system(GNSS)signal modulation technology,this thesis demonstrates that the commonly used modulation signals in the L-band at this stage cannot meet the out-of-band compatibility constraints of the C-band,and tentatively applies the continuous phase modulation based on prolate spheroidal wave functions(CPM-PSWF)to the C-band navigation.On this basis,the multi modulation index is combined with CPM-PSWF for the first time,and after weighing the spectral compatibility of C-band signals and other navigation performance indicators,two candidate schemes are provided for the C-band navigation signal design of Bei Dou navigation satellite system,one is QM2PSWF(10)C=6 and h=0.5 signal based on CPM-PSWF modulation scheme,and the other is QM2PSWF(10)C=4 and h=[9/16,11/16]signal based on multi modulation index CPM-PSWF(Multi-h CPM-PSWF)modulation scheme.The main works of this thesis are as follows:(1)This thesis focuses on the transmission characteristics of L-band and C-band navigation signals,and expounds the performance advantages and disadvantages of C-band for satellite navigation.A transmission link model including free space loss,ionosphere and tropospheric loss and cloud rain fog attenuation is established,and the losses of C-band and L-band navigation signals in the transmission process under given conditions are calculated,and the power estimates of C-band and L-band satellite-ground links are given,the performance of Cband for satellite navigation is further described,which lays the corresponding theoretical foundation for the subsequent research of C-band signal modulation scheme.(2)It is demonstrated that the common modulation methods of L-band navigation signals at this stage are not suitable for C-band,summarize the out-of-band compatibility constraint requirements of C-band,and give the main principles of C-band modulation mode selection and signal design ideas.The mathematical models of common modulation techniques for L-band GNSS signals are derived,and the performance characteristics of modulation methods including binary phase shift keying(BPSK),binary offset carrier(BOC),multiplexed binary offset carrier(MBOC)and alternative binary offset carrier(Alt BOC)are analyzed.Through the evaluation of the compatibility index of the L-band navigation signal,the experimental simulation shows that directly moving the common modulation method of the L-band to the Cband cannot meet the strict out-of-band compatibility constraints of the C-band,and it is pointed out that when selecting C-band navigation signal,it is necessary to trade off between compatibility and other navigation performance indexes.(3)CPM-PSWF modulation is tentatively applied to C-band navigation,and the CPMPSWF signal with QM2PSWF(10)C = 6 and h= 0.5 is proposed as the candidate scheme of Cband navigation signal of Bei Dou navigation system.Firstly,the basic theory of CPM-PSWF modulation is described,and by studying the phase path of CPM-PSWF modulation signal,the spectrum superiority of CPM-PSWF modulation signal over classical CPM modulation signal is verified,and based on the in-depth study of the influence of key parameters on the power spectrum characteristics of CPM-PSWF signal,the optimization and preliminary screening of CPM-PSWF sub family are completed.Finally,the basic navigation performance indexes,such as compatibility,code tracking accuracy and anti-multipath performance,are evaluated.The CPM-PSWF signal with QM2PSWF(10)C=6 and h=0.5 is selected,which can alleviate the interference with RAS,MLS and C-band uplink signals to a certain extent and has the same compatibility with GMSK(10)signal adopted by Galileo satellite navigation system,but the Gabor bandwidth is larger and the average multipath error is smaller,and is more competitive than the current C-band non CPM-PSWF candidate navigation signal.(4)CPM-PSWF modulation scheme is combined with the multi modulation index for the first time,and the Multi-h CPM-PSWF signal with QM2PSWF(10)C=4 and h=[9/16,11/16] is proposed as a candidate scheme for the C-band navigation signal of Bei Dou navigation system.The influence of relevant parameters on the power spectrum characteristics of Multi-h CPMPSWF signals is mainly studied,and through the reasonable allocation of important parameters,the Multi-h CPM-PSWF subfamily comparable to the GMSK(10)signal compatibility can be obtained,and stronger code tracking and multipath resistance ability are possessed at the same time.The results show that the multi-h CPM-PSWF modulation applied to C-band satellite navigation has certain advantages in terms of multipath resistance,among which the code tracking performance of Multi-h CPM-PSWF signals with QM2PSWF(10)C=4 and h=[9/16,11/16] ranks first among all candidate signals,and the compatibility is slightly better than that CPM-PSWF signals with QM2PSWF(10)C=6 and h=0.5. |
PDF Full Text Request