Integrated Satellite Communication And Navigation System Based On V-OFDM Modulation

With the enormous development of satellite communication system and satellite navigation system,their related applications have brought a great convenience to human production and life,while they are also facing the shortage of satellite spectrum resource,multipath propagation with deep fading,and a variety of issues to be urgently solved.At this stage,although satellite communication and satellite navigation are devoted to different fields,from the technical perspective,there is a close link between them.On one hand,the reliability of satellite communication is related to the anti-interference performance of the receiver and the symbol error rate(SER)of navigation message,thus affects the positioning accuracy of the receiver.On the other hand,satellite communication system is synchronized by estimating the time delay of the broadcast pilot signals,while the performance of symbol timing synchronization has a direct relevance to the reliability of satellite communication system.Therefore,under the background of the space-terrestrial network,it is of great significance to establish an integrated satellite communication and navigation system that can make full use of the space resource with multi-functional satellites.Having concerned the fundamental performance criteria on communication and navigation,i.e.,SER and positioning accuracy,considering further the spectral efficiency,peak-to-average power ratio(PAPR),system complexity and other factors,an integrated satellite communication and navigation system based on vector orthogonal frequency division multiplexing(V-OFDM)modulation is proposed in this dissertation.Some key technologies over the system,such as channel allocation,pilot symbol design,channel estimation,signal detection,symbol synchronization are further investigated,and a series of innovative research results have been achieved.Firstly,the dissertation investigates single-carrier frequency domain equalization(SC-FDE)and orthogonal frequency division multiplexing(OFDM),and then a generalized V-OFDM modulation model is provided,which builds a bridge between SC-FDE and OFDM in terms of intersymbol interference(ISI)level,PAPR,and transmitter/receiver complexities.The basic idea of V-OFDM is to convert an ISI channel to multiple vector subchannels where the vector size is a predesigned parameter and flexible.Since V-OFDM modulation may not collect full diversity for all subchannels,a constellation rotation matrix added at the transmitter enables all the subchannels to achieve full multipath diversity.In the design of the parallel rotated V-OFDM system easy for hardware implementation,the receiver can achieve the diversity gain as well as the coding gain with the optimization of constellation rotation angle.Under the broadband frequency selective fading channel,the dissertation makes a comprehensive comparison of different receiver with respect to SER and decoding complexity,and comes to a conclusion that the minimum mean square error receiver is suitable for the lower signal-to-noise ratio(SNR)scenarios,while the sphere decoding is suitable for the higher SNR scenarios.Then,the dissertation concentrates on the reliable transmission of the V-OFDM modulated satellite communication and navigation system.Considering a long distance between the satellite and terminal,a broadband frequency selective fading satellite channel is modelled with sparse multipath propagation.It is proved that the maximum multipath diversity order of a sparse channel is equal to the cardinality of remainder set of multipath time delay modulo vector size.By means of mathematical induction,the probability mass function of diversity order is theoretically derived for the stochastic channel.The partial intersection sphere(PIS)decoding receiver is proposed by exploiting of the sparse nature of the blocked channel matrix.With lower searching space,the decoding complexity decreases exponentially.It is the limit theorem of sphere radius that can balance the tradeoff between the SER and the decoding complexity.For the extreme case when the set of possible transmitted vectors is empty,which usually occurs at a low SNR,the weighted voting system makes a decision on the transmitted signal according to the set of symbol sequences inside the sphere radius generated in each iteration,which overcomes the drawback that the PIS decoding is unavailable for the lower SNR scenarios.In order to adapt to the rapid variation of satellite channel,the proposed PIS decoding with weighted voting can collect the maximum multipath diversity gain with reduced receiver complexity,which consequently,achieves the reliable transmission of service signal as well as navigation message.Finally,the dissertation concentrates on the precise positioning of the V-OFDM modulated satellite communication and navigation system.The comb-type pilot arrangement is designed that the pilot subchannels are uniformly spaced over the whole channel,where the pilot symbol vectors are optimized with the minimum mean square error(MSE)of channel estimation.On the other hand,the remaining subchannels allocated to transmit data symbols can achieve the maximum multipath diversity.The sparse inverse fast Fourier transform(SIFFT)is adopted for channel estimation where the key idea called "HashToBins" is significant to convert a higher dimensional inverse fast Fourier transform(FFT)to a lower one by employing two mathematical methods;permutation and flat window filtering.There is a fundamental connection between the channel estimation for the ideal noiseless/noise case and the exactly/approximately SIFFT.With the help of pilot signal,symbol synchronization usually involves two steps:acquisition and tracking.The coarse symbol timing synchronization is first implemented by shifting the starting point of the FFT sliding window,then the receiver accesses to the residual symbol timing synchronization by adjusting the estimation of propagation delay dynamically.The dissertation proposes the maximum likelihood estimation of multipath time delay based on Newton method,and derives the Cramer-Rao bound of the code tracking accuracy.For the satellite channel with Rician fading,an early-late gate based delay-locked loop timing correction is designed and easy to implement on hardware.The maximum likelihood positioning estimation,aimed at optimizing the three-dimensional coordinates of terminal directly without the cumulative error induced by the intermediate variable,is regarded as the global optimal solution.By means of the maximum likelihood positioning estimation,the receiver can collect the potential satellital diversity,and achieve the precise positioning of terminal.In summary,on the basis of comprehensive investigation of V-OFDM modulation,the broadband integrated satellite communication and navigation system is proposed in this dissertation,then the receiver with lower SER and lower MSE of the timing/delay estimation is designed accordingly.The proposed integrated satellite communication and navigation system based on V-OFDM modulation will lay the solid foundation of reliable transmission and precise positioning,toward the establishment of the space-terrestrial network continuously in depth.