【摘要】：建立完備的星地測控網(wǎng)絡(luò)是各國大力發(fā)展航空航天工業(yè)的重要原因之一,不論是導(dǎo)航定位系統(tǒng),或是氣象遙感系統(tǒng),均屬于星地測控網(wǎng)絡(luò)的范疇。憑借出色抗干擾能力,直接序列擴(kuò)頻一直以來都是星地測控鏈路通信方式的首選。作為完成預(yù)定測控功能的前提,實(shí)現(xiàn)擴(kuò)頻信號的時頻同步非常關(guān)鍵。然而,特殊的通信環(huán)境和外部條件給接收信號帶來兩方面的影響:過長的通信距離與惡劣的信道使得接收信號功率大幅衰減,信噪比極低;衛(wèi)星的高動態(tài)特性使接收信號的多普勒效應(yīng)加劇。若不對接收信號進(jìn)行精確的時頻同步,整個測控業(yè)務(wù)將面臨失敗。為此,論文針對采用直接序列擴(kuò)頻的星地測控鏈路的時頻同步關(guān)鍵技術(shù)展開研究,主要包括:一、針對鏈路5s的捕獲時間要求以及最高達(dá)±150kHz的多普勒頻偏,調(diào)研偽碼捕獲的三種方法,選擇基于FFT的偽碼快速捕獲與多普勒頻偏一維搜索相結(jié)合,差分相干積分45次提高信噪比。通過對接收信號先頻偏預(yù)補(bǔ)償,然后進(jìn)行一次FFT運(yùn)算與一次IFFT運(yùn)算并差分相干積分45次后判決,在4.515s內(nèi)完成偽碼捕獲。二、針對偽碼相位抖動,根據(jù)經(jīng)典的偽碼跟蹤環(huán)路提出一種5路并行的偽碼跟蹤環(huán)路設(shè)計(jì)方案。通過給5條支路分別設(shè)置不同的偽碼偏移,取與接收數(shù)據(jù)相關(guān)運(yùn)算結(jié)果最大的支路作為最佳采樣支路,完成偽碼相位跟蹤,精度可達(dá)1/4碼片。三、針對多普勒頻偏預(yù)補(bǔ)償后的殘余頻偏,使用對調(diào)制數(shù)據(jù)不敏感Costas環(huán)進(jìn)行相位差的鎖定、補(bǔ)償并計(jì)算出頻差反饋至多普勒頻偏預(yù)補(bǔ)償。完成上述方案設(shè)計(jì)的Simulink仿真。四、基于軟件無線電平臺,完成星地測控鏈路高精度時頻同步關(guān)鍵技術(shù)驗(yàn)證。以FPGA芯片作為主要器件,Verilog作為編程語言,實(shí)現(xiàn)時頻同步關(guān)鍵技術(shù)板上測試,各模塊之間配合良好,能完成既定的功能。論文對特定條件下星地測控鏈路時頻同步關(guān)鍵技術(shù)進(jìn)行探究與驗(yàn)證,研究成果已工程實(shí)現(xiàn)并測試,具有實(shí)用價(jià)值,可為我國星地測控網(wǎng)絡(luò)建設(shè)提供參考與支持。
[Abstract]:It is one of the important reasons for the development of aerospace industry to establish a complete satellite-ground TT & C network. Both navigation and positioning system and meteorological remote sensing system belong to the category of satellite-ground TT & C network. Direct sequence spread spectrum (DSSS) is always the first choice of satellite-ground TT & C link communication mode by virtue of its excellent anti-jamming capability. As a prerequisite to complete the scheduled measurement and control function, the time-frequency synchronization of spread spectrum signals is very important. However, the special communication environment and external conditions have two effects on the received signal: the long communication distance and the bad channel make the received signal power attenuate greatly, and the signal-to-noise ratio is very low; The Doppler effect of the received signal is aggravated by the high dynamic characteristics of the satellite. Without accurate time-frequency synchronization, the whole measurement and control service will fail. Therefore, this paper studies the key technologies of time-frequency synchronization of satellite-ground TT & C link using direct sequence spread spectrum, including: first, aiming at the acquisition time requirement of link 5s and the Doppler frequency offset up to 鹵150kHz. This paper investigates three methods of PN code acquisition and selects the combination of fast PN code acquisition based on FFT and Doppler frequency offset one-dimensional search to improve signal-to-noise ratio (SNR) 45 times by differential coherent integration. The pseudo code acquisition is completed in 4.515s by precompensation of the received signal frequency offset, one FFT operation and one IFFT operation, and the differential coherent integration is 45 times later. Secondly, according to the classical pseudo code tracking loop, a 5 parallel pseudo code tracking loop design scheme is proposed for pseudo code phase jitter. By setting different pseudo code offsets to each of the five branches, the best sampling branch is the one with the largest correlation with the received data. The pseudo code phase tracking is completed, and the precision is as high as 1 / 4 code chip. Thirdly, for the residual frequency offset after Doppler frequency offset precompensation, the phase difference locking of Costas loop which is not sensitive to modulation data is used to compensate and calculate the frequency difference feedback to Doppler frequency offset precompensation. Finish the Simulink simulation of the above scheme design. 4. Based on the software radio platform, the key technology of high precision time-frequency synchronization of satellite-ground measurement and control link is verified. With FPGA chip as the main device and Verilog as the programming language, the key technology of time-frequency synchronization can be tested on board. This paper explores and verifies the key technologies of time-frequency synchronization of satellite-ground TT & C links under certain conditions. The research results have been realized and tested in engineering, which is of practical value and can provide reference and support for the construction of satellite-ground TT & C network in China.
【學(xué)位授予單位】：電子科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：V556;TN914.42

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