本文選題：非合作通信 + OFDM��； 參考：《西安電子科技大學(xué)》2014年碩士論文

【摘要】：非合作通信作為非授權(quán)接入的通信方式,是在不干擾合作通信雙方正常通信的條件下接入到合作通信系統(tǒng)的通信方式。在非合作通信方式下,由于發(fā)端信息未知性以及信道干擾的復(fù)雜性,設(shè)計出符合性能要求的方法來實現(xiàn)OFDM系統(tǒng)的定時和載波同步是非常困難的,同時也是非合作通信環(huán)境下OFDM系統(tǒng)解調(diào)的關(guān)鍵技術(shù)。因此本文針對非合作通信下的OFDM同步技術(shù)進(jìn)行了分析探討,主要涉及到基于循環(huán)前綴(CP)的OFDM系統(tǒng)載波頻率同步和基于偏置正交幅度調(diào)制(OQAM)的OFDM系統(tǒng)時頻聯(lián)合同步兩個方面,所取得的主要解決方案如下所示:1.針對非合作通信下的通信系統(tǒng)的要求,由于低信噪比下載波頻率同步性能不佳的情況,對基于循環(huán)前綴的OFDM系統(tǒng)載頻同步進(jìn)行了研究。通過分析接收端傅里葉變換后子載波信號幅度之間的關(guān)系,提出了一種多徑信道下OFDM系統(tǒng)載頻同步的方法,首先根據(jù)子載波信號之間的關(guān)系,初始構(gòu)造出幅度差值代價函數(shù);然后對其展開式推導(dǎo)消除無關(guān)項再次進(jìn)行化簡得到了基于幅度積的代價函數(shù);最后通過分析幅度積代價函數(shù)的特性,將其等效為一正弦函數(shù),進(jìn)而通過多項式內(nèi)插得到載波頻率偏移估計值。仿真實驗表明本文方法在低信噪比和多徑信道下?lián)碛辛己玫墓烙嬓阅?且計算復(fù)雜度較低。2.在非合作通信環(huán)境下,對基于OQAM調(diào)制的OFDM系統(tǒng)進(jìn)行系統(tǒng)符號定時和載頻的聯(lián)合同步研究。通過分析其信號的循環(huán)特性,提出了一種多徑信道下符號定時和載波頻率聯(lián)合同步方法。該方法首先推導(dǎo)并研究OFDM/OQAM信號的周期平穩(wěn)特性;其次通過對信號二階循環(huán)特性的分析,表明了加性噪聲對非零循環(huán)頻率處的循環(huán)量不產(chǎn)生干擾;然后通過利用兩對數(shù)值為偶數(shù)倍子載波間隔的循環(huán)頻率,基于循環(huán)特性可獨立得到符號定時偏移和載波頻率偏移的估計表達(dá)式;最后通過對收端信號二階循環(huán)累積量等的估計,從而得到符號定時偏移和載波頻率偏移的估計值。仿真結(jié)果表明了定時偏移和載波頻率偏移的估計不受到加性噪聲的影響,以及兩者之間估計的獨立性,與理論分析相吻合,同時仿真結(jié)果也表明了在多徑信道下該方法估計性能較好。
[Abstract]:Non-cooperative communication, as an unauthorized access mode, is a communication mode that can access cooperative communication system without interfering with the normal communication between the two sides of the cooperative communication. In non-cooperative communication mode, due to the unknown source information and the complexity of channel interference, it is very difficult to design a method to achieve timing and carrier synchronization in OFDM system. It is also the key technology of OFDM demodulation in non-cooperative communication environment. Therefore, this paper analyzes and discusses the OFDM synchronization technology in non-cooperative communication, mainly involves two aspects: carrier frequency synchronization based on cyclic prefix (CP) and joint time-frequency synchronization based on offset orthogonal amplitude modulation (OQAM). The main solution achieved is as follows: 1. To meet the requirements of non-cooperative communication systems, carrier frequency synchronization in OFDM systems based on cyclic prefix is studied because of the poor carrier frequency synchronization performance at low SNR. By analyzing the relationship between the amplitude of subcarrier signals after Fourier transform, a carrier frequency synchronization method for OFDM systems in multipath channels is proposed. Firstly, according to the relationship between sub-carrier signals, the cost function of amplitude difference is initially constructed. Then, the cost function based on amplitude product is obtained by simplifying the derivation and elimination of irrelevant terms, and the cost function is equivalent to a sinusoidal function by analyzing the characteristics of the cost function of amplitude product. Furthermore, the carrier frequency offset estimation is obtained by polynomial interpolation. Simulation results show that the proposed method has good estimation performance in low SNR and multipath channels, and its computational complexity is low. In non-cooperative communication environment, the joint synchronization of symbol timing and carrier frequency in OQAM modulated OFDM system is studied. By analyzing the cyclic characteristics of the signal, a joint symbol timing and carrier frequency synchronization method in multipath channel is proposed. The method first deduces and studies the periodic stationary characteristic of OFDM / OQAM signal, then through the analysis of the second order cycle characteristic of the signal, it shows that the additive noise does not interfere with the cycle quantity at the non-zero cycle frequency. Then, by using the cyclic frequency of double pairs of even times subcarrier spacing, the estimation expressions of symbol timing offset and carrier frequency offset can be independently obtained based on the cyclic characteristics. Finally, the second order cyclic cumulant of the receiver signal is estimated, and the second order cyclic cumulant of the receiver signal is estimated. Thus, the estimated values of symbol timing offset and carrier frequency offset are obtained. The simulation results show that the estimation of timing offset and carrier frequency offset is not affected by additive noise, and the estimation independence between them is consistent with the theoretical analysis. At the same time, the simulation results show that the performance of this method is good in multipath channel.
【學(xué)位授予單位】：西安電子科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：TN919.34

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