本文關(guān)鍵詞： 正交頻分復(fù)用 同步誤差 符號定時同步 載波頻率同步　出處：《天津理工大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：甚高頻數(shù)據(jù)交換系統(tǒng)(VHF Data Exchange System,VDES)是在船舶自動識別系統(tǒng)(Automatic Identification System,AIS)上發(fā)展起來的新一代海事通信系統(tǒng),可以有效緩解現(xiàn)有AIS的數(shù)據(jù)通信壓力,能夠全面提升水上無線數(shù)據(jù)通信的能力。VDES允許多種編碼速率和調(diào)制方式,可以在系統(tǒng)規(guī)模和業(yè)務(wù)可用性上提供更多的靈活性。VDES在特定信道內(nèi)可以采用正交頻分復(fù)用技術(shù)(OFDM)。在VDES中衛(wèi)星通信的接收信號可能會存在信道傳輸時延較大、多普勒頻偏等問題,這些可能會造成OFDM信號的符號定時偏差和載波頻率偏差。本文主要是對OFDM的符號定時同步算法和載波頻率同步算法進行研究。文中對經(jīng)典同步算法進行了仿真分析,針對現(xiàn)有算法的不足之處對OFDM同步技術(shù)進行了研究。主要研究內(nèi)容包括:(1)針對基于循環(huán)前綴的最大似然(ML)估計方法在低信噪比和多徑信道環(huán)境下符號定時不準確和頻偏估計的精度低等問題,本文設(shè)計了一種由兩個相同部分構(gòu)成的循環(huán)前綴結(jié)構(gòu)并引入了一種定時度量函數(shù),去除了符號間干擾(ISI)的影響。該算法和ML算法相比,實現(xiàn)了在低信噪比和多徑信道中良好的定時性能,并且提高了頻偏估計的均方誤差(MSE)性能和估計范圍。(2)針對現(xiàn)有OFDM頻率同步算法存在的同步精度不高,估計范圍較小等問題,本文提出了基于實訓(xùn)練序列的頻率同步算法。根據(jù)時域訓(xùn)練序列結(jié)構(gòu)的共軛對稱性求出小數(shù)倍頻偏,利用接收端頻域訓(xùn)練序列的循環(huán)移位估計整數(shù)倍頻偏。該算法擴大了小數(shù)倍頻偏估計的范圍,小數(shù)倍頻偏估計在低信噪比下有較好的MSE性能;該算法提高了整數(shù)倍頻偏的正確檢測率。(3)針對現(xiàn)有OFDM同步算法存在的同步精度不高,在低信噪比環(huán)境下定時容易出錯等問題,本文提出了一種基于訓(xùn)練序列的OFDM時頻同步算法。根據(jù)時域訓(xùn)練序列結(jié)構(gòu)中存在的共軛特性進行符號定時偏差估計,這種符號定時同步算法去除了循環(huán)前綴對定時的影響,實現(xiàn)了準確定時。根據(jù)時域訓(xùn)練序列中存在的相位差求出小數(shù)倍載波頻偏,在頻域根據(jù)循環(huán)移位估計出整數(shù)倍頻偏。本文頻率同步算法的MSE性能良好,整數(shù)倍頻偏正確檢測率較高。
[Abstract]:VHF Data Exchange system VDES is a new generation maritime communication system developed on the automatic Identification system of ship identification, which can effectively relieve the pressure of data communication of the existing AIS. The ability to fully enhance wireless data communications on water. VDES allows for a variety of coding rates and modulation methods. It can provide more flexibility in system size and service availability. VDES can adopt orthogonal frequency division multiplexing (OFDM) technique in a specific channel. In VDES, the received signals of satellite communication may have some problems such as long channel transmission delay, Doppler frequency offset and so on. This paper mainly studies the symbol timing synchronization algorithm and carrier frequency synchronization algorithm of OFDM. Aiming at the shortcomings of the existing algorithms, the OFDM synchronization technology is studied. The main research contents include: 1) aiming at the maximum likelihood (MLL) estimation method based on cyclic prefix, the symbol timing is inaccurate in low SNR and multipath channel environment. Problems such as low accuracy of sum frequency offset estimation, In this paper, a cyclic prefix structure consisting of two identical parts is designed and a timing metric function is introduced to remove the influence of ISI). The algorithm is compared with ML algorithm. Good timing performance in low signal-to-noise ratio and multipath channel is realized, and the mean square error (MSE) performance and estimation range of frequency offset estimation are improved. (2) aiming at the existing OFDM frequency synchronization algorithms, the synchronization accuracy is not high and the estimation range is small, etc. In this paper, a frequency synchronization algorithm based on real training sequence is proposed, and the fractional double frequency offset is obtained according to the conjugate symmetry of the structure of the training sequence in time domain. The integer frequency-doubling offset is estimated by cyclic shift of the training sequence in the frequency domain of the receiving end. The algorithm expands the range of the fractional frequency-doubling offset estimation, and the fractional frequency-doubling offset estimation has better MSE performance under low SNR. This algorithm improves the correct detection rate of integer frequency-doubling offset. Aiming at the existing OFDM synchronization algorithms, the accuracy of synchronization is not high, and the timing is prone to make mistakes in the environment of low signal-to-noise ratio (SNR). In this paper, a OFDM time-frequency synchronization algorithm based on training sequence is proposed. The symbol timing deviation is estimated according to the conjugate characteristics of the time-domain training sequence structure. The symbol timing synchronization algorithm eliminates the influence of cyclic prefix on timing. Accurate timing is achieved. The fractional carrier frequency offset is calculated according to the phase difference in the time domain training sequence, and the integer frequency doubling offset is estimated in the frequency domain according to the cyclic shift. The MSE performance of the frequency synchronization algorithm in this paper is good. The detection rate of integer frequency doubling deviation is high.
【學(xué)位授予單位】：天津理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：U675.7;TN929.53

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