| In order to meet the demand of both military and civilian users for high-speed and stable transmission of satellite communications, it is quite important and imperative to establish a new generation low earth orbit(LEO) satellite mobile communication system with high transmission rate and high spectral efficiency. Among the key technologies of the next generation of satellite mobile communication, orthogonal frequency division multiplexing (OFDM) with high spectral efficiency, high-speed data transmission rate, flexible carrier allocation strategy and good compatibility with the terrestrial communication system, has become a key technology and research hotspot. Although OFDM has lots of advantages, OFDM that uses the orthogonal subcarriers has a high sensitivity to carrier frequency offset. So, in the 5rd Generation wireless communication system (5G), as a multi- carrier candidate technology,universal filtered multi-carrier (UFMC) replaces OFDM to solve the problem of its frequency offset sensitivity. Therefore, this paper takes the new generation LEO satellite mobile communication system as the research object, and has a detailed research and comparison on OFDM and UFMC multi-carrier technology applied in this scenario. The main research results are shown as follows:(1) As LEO satellite running speed is fast and its orbit is low, when it communicates with the terrestrial terminal, it will generate a large Doppler frequency shift, greatly impact on the demodulation of the receivers and dramatically reduce communication quality. In order to improve the ability of anti-Doppler frequency offset of LEO satellite mobile communication system, a good Doppler frequency offset estimation and compensation algorithm plays an important role. For the design idea of primary synchronization signal (PSS) sequence in long term evolution (LTE) system, this paper introduces a kind of mature and stable estimation scheme with good performance of LTE system in detail,which is Doppler frequency offset estimation algorithm based on PSS.This algorithm takes advantage of Fourier transformation-hold and good autocorrelation characteristics of Zadoff-Chu (ZC) sequence to complete fractional frequency offset and integer frequency offset estimation and compensation. The simulation results based on OFDM and UFMC system:in the Doppler rate range of -7.5kHz/s ?+7.5kHz/s, the normalized frequency offset estimation range of Doppler frequency offset estimation algorithm based on PSS sequence is [-62, 62] and the actual frequency offset estimation range is [-930KHz, +930KHz]. Then, bit error rate(BER) performance is good after using this algorithm. Further more, this scheme ensures the accuracy of the link detection and play an important role for OFDM and UFMC system applying in LEO satellite mobile communication.(2) Non uniform motion between LEO satellite and terrestrial terminal causes Doppler shift variation with time and results in Doppler rate. Larger Doppler rate is the same as the Doppler shift, which has a serious impact on the performance of the communication system.Therefore, in order to stably and effectively apply UFMC in LEO satellite mobile communication system, this paper proposes Doppler rate estimation algorithm based on ZC sequence. This algorithm is based on the principle that Doppler rate is second order difference of the phase,takes advantage of Fourier transformation-hold characteristic of ZC sequence of UFMC signal in frequency domain and estimate Doppler rate by conjugate multiplication of native ZC sequences and received ZC sequence three times. The simulation results based on UFMC system: the normalized Doppler rate estimation range is (-0.5,0.5) and the actual Doppler rate estimation range is (-57.6GHz/s, 57.6GHz/s).This algorithm improves accuracy and stability of the link detection and makes guidance and reference to the application of UFMC technology in LEO satellite senario. |
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