【摘要】：由于擴(kuò)頻通信具有保密性好,抗干擾性強(qiáng)的特點(diǎn),因此在各個(gè)領(lǐng)域內(nèi)倍受關(guān)注,至今,擴(kuò)頻通信技術(shù)已經(jīng)被非常廣泛的運(yùn)用在軍事、民事、和商業(yè)領(lǐng)域。擴(kuò)頻通信系統(tǒng)雖然優(yōu)點(diǎn)眾多,運(yùn)用廣泛,但是相比于普通的通信系統(tǒng),擴(kuò)頻通信系統(tǒng)的硬件結(jié)構(gòu)和軟件算法更為復(fù)雜,這限制了擴(kuò)頻通信技術(shù)的發(fā)展。在擴(kuò)頻通信系統(tǒng)中,只有發(fā)送端用于擴(kuò)頻的偽隨機(jī)序列與在接收端用于解擴(kuò)頻的偽隨機(jī)序列相同,且相位也完全相同的條件下才能正確的解擴(kuò)頻得到發(fā)送信息序列。目前如何保證發(fā)送端偽隨機(jī)序列與接收端的偽隨機(jī)序列的同步問題是擴(kuò)頻通信系統(tǒng)中最為關(guān)鍵的技術(shù),也是本文的研究出發(fā)點(diǎn)。本文從擴(kuò)頻碼的特點(diǎn)出發(fā),首先介紹了直接擴(kuò)頻通信信號(hào)的模型,接著介紹了在直擴(kuò)通信中常用的偽隨機(jī)碼類型,最后著重介紹了在直擴(kuò)通信中長(zhǎng)、短周期擴(kuò)頻碼的捕獲算法。在短周期偽隨機(jī)碼的捕獲方法中,由于短周期碼速率慢,數(shù)據(jù)量少,可以進(jìn)行直接捕獲。本文推導(dǎo)了采用匹配濾波器和快速傅里葉變換算法代替滑動(dòng)相關(guān)算法的原理,兩種算法在不同程度上提高了捕獲速度,但是二者對(duì)于多普勒頻率過于敏感,且算法不能直接移植到超長(zhǎng)周期偽隨機(jī)碼的捕獲上,有一定的局限性。在超長(zhǎng)周期或無周期偽隨機(jī)碼的相位捕獲方法中,著重介紹了基于分組折疊相加、分組均值,以及二者綜合的三種算法。基于分組折疊相加的算法是把偽隨機(jī)碼折疊并相加,使其增大一次相關(guān)的搜捕范圍。分組均值算法是采用分多個(gè)組,然后再組內(nèi)多個(gè)點(diǎn)求平均值轉(zhuǎn)化為一個(gè)點(diǎn),這樣在相關(guān)點(diǎn)數(shù)一定的條件下,增大了搜捕范圍。綜合算法則是綜合了二者的優(yōu)勢(shì),使捕獲速度進(jìn)一步加快。但由于綜合算法的多普勒頻率補(bǔ)償有誤差,不能完全去掉多普勒對(duì)相關(guān)峰值的影響且在去模糊階段有冗余,本文提出了一種新的算法,用信號(hào)序列傅里葉變換后循環(huán)移位代替多普勒補(bǔ)償數(shù)值,并在去模糊階段采用基于二分的查找算法,通過matlab仿真分析,新算法在一定程度上提高了偽碼相位的捕獲性能。
[Abstract]:Spread spectrum communication has been widely used in military, civil and commercial fields since it has the characteristics of good security and strong anti-interference, so it has been paid more and more attention in various fields, so far, spread spectrum communication technology has been widely used in military, civil and commercial fields. Although the spread spectrum communication system has many advantages and is widely used, the hardware structure and software algorithm of the spread spectrum communication system are more complex than the ordinary communication system, which limits the development of the spread spectrum communication technology. In the spread spectrum communication system, only when the pseudorandom sequence used by the transmitter is the same as the pseudorandom sequence used for despreading the spectrum at the receiving end, and the phase is exactly the same, can the transmission information sequence be obtained correctly. At present, how to ensure the synchronization between the pseudo-random sequence at the transmitter and the pseudo-random sequence at the receiving end is the most important technology in the spread spectrum communication system, and it is also the starting point of this paper. Starting from the characteristics of spread spectrum code, this paper first introduces the model of direct spread spectrum communication signal, then introduces the type of pseudo random code commonly used in direct spread spectrum communication, and finally introduces the acquisition algorithm of long and short period spread spectrum code in direct spread spectrum communication. In the acquisition method of short-period pseudorandom code, it can be directly captured because of the slow rate of short-period code and the small amount of data. In this paper, the principle of using matched filter and Fast Fourier transform (FFT) instead of sliding correlation algorithm is deduced. The two algorithms improve the acquisition speed to some extent, but they are too sensitive to Doppler frequency. Moreover, the algorithm can not be directly transplanted to the acquisition of ultra-long period pseudorandom codes, which has some limitations. In the phase acquisition method of extra-long period or non-periodic pseudorandom codes, three kinds of algorithms based on the addition of packet folding, the mean of packets and the combination of them are introduced emphatically. The algorithm based on the addition of packet folding is to fold and add pseudo random code to enlarge the range of one-time correlation search. The grouping mean algorithm is divided into multiple groups, then the average value of multiple points in the group is transformed into a point, so that under the condition of certain correlation points, the search range is enlarged. Synthesis algorithm is to synthesize the advantages of the two, so that the capture speed is further accelerated. However, due to the error in the Doppler frequency compensation of the synthetic algorithm, the influence of Doppler on the correlation peak can not be completely removed and there is redundancy in the deblurring phase. A new algorithm is proposed in this paper. The Doppler compensation value is replaced by the cyclic shift after Fourier transform of signal sequence, and the binary-based search algorithm is adopted in the phase of de-ambiguity. The new algorithm improves the acquisition performance of pseudo-code phase to a certain extent by matlab simulation analysis.
【學(xué)位授予單位】：電子科技大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TN914.42

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本文編號(hào)：2450107