本文選題：水聲通信 + 正交頻分復用　； 參考：《哈爾濱工程大學》2014年碩士論文

【摘要】：伴隨著海洋事業(yè)的壯大,水下通信業(yè)務繁忙,發(fā)展網(wǎng)絡化水聲通信刻不容緩。其中,水下網(wǎng)絡多用戶通信已逐漸成為水聲通信研究的熱點。擴頻(Spread-Spectrum,SS)技術作為一種抗干擾和抗衰落能力強的通信技術,發(fā)射功率低、可靠性高、保密性好,具有廣泛的應用。正交頻分復用(Orthogonal Frequency Division Multiplexing, OFDM)技術是一種抗頻率選擇性衰落能力強、頻譜利用率高、傳輸速率高的通信技術,將其與擴頻技術相結合應用于水下通信,能大大增加系統(tǒng)的抗干擾和抗衰落能力,對于水下多用戶通信的發(fā)展具有深遠意義。本文主要研究OFDM擴頻技術在水聲通信中的應用。論文最初對擴頻技術、OFDM技術的基本原理進行了理論分析,并研究了擴頻與OFDM結合的三種方式,分析了頻域擴頻MC-CDMA、正交MCDS-CDMA和多音DS-CDMA的實現(xiàn)過程,通過仿真驗證了頻域擴頻的優(yōu)越性,該擴頻方式充分利用了頻率分集增益,抗多徑衰落能力更好。擴頻通信技術抗多徑干擾能力強,適用于較低信噪比條件,并且具有很好地組網(wǎng)能力。本文在實現(xiàn)直接序列擴頻與OFDM結合的基礎上,研究了循環(huán)移位擴頻OFDM技術和組合擴頻OFDM技術,這兩種技術擁有更高的通信速率。仿真驗證了無循環(huán)前綴的OFDM擴頻系統(tǒng)仍可以保持高效可靠的解碼。在水聲通信中,空間的變化對水聲信道沖激響應函數(shù)影響甚大,這使得不同空間位置上的水聲信道的沖激響應函數(shù)具備弱相關性。利用水聲信道的這一物理特性,將時間反轉鏡技術用于多用戶水聲通信中,以聚焦期望用戶,屏蔽非期望用戶實現(xiàn)空分多址。本文構建基于時間反轉鏡技術的OFDM擴頻多用戶水聲通信系統(tǒng),實現(xiàn)了多個用戶的可靠通信。然后提出差分OFDM擴頻技術,差分技術在接收端采用差分相干解調的方法,削弱水聲衰落信道引起的性能下降問題,不需要相干解調和信道估計,提高系統(tǒng)的頻帶利用率,降低系統(tǒng)的復雜度和計算量,將其結合OFDM擴頻技術應用于多用水聲通信中,能建立穩(wěn)健的通信系統(tǒng)。本文對所研究的算法進行了計算機仿真實驗和水池試驗驗證,結果表明:擴頻技術與OFDM技術相結合提高了水聲通信系統(tǒng)的性能,實現(xiàn)了高質量點對點水聲通信和多用戶水聲通信。
[Abstract]:With the development of ocean business, underwater communication business is busy, so it is urgent to develop network underwater acoustic communication. Among them, underwater network multi-user communication has gradually become the hot spot of underwater acoustic communication research. As a kind of communication technology with strong anti-interference and anti-fading ability, spread spectrum SS (spread Spectrum) technology has a wide range of applications, such as low transmission power, high reliability and good confidentiality. Orthogonal Frequency Division Multiplexing (OFDM) is a kind of communication technology with strong anti-frequency selective fading ability, high spectral efficiency and high transmission rate. It can greatly increase the anti-interference and anti-fading ability of the system, and has far-reaching significance for the development of underwater multi-user communication. This paper mainly studies the application of OFDM spread spectrum technology in underwater acoustic communication. At the beginning of this paper, the basic principle of spread spectrum technology and OFDM technology is theoretically analyzed, and three ways of combining spread spectrum with OFDM are studied, and the realization process of spread spectrum MC-CDMA, orthogonal MCDS-CDMA and multi-tone DS-CDMA in frequency domain is analyzed. The superiority of spread spectrum in frequency domain is verified by simulation. The spread spectrum method makes full use of frequency diversity gain and has better anti-multipath fading ability. Spread spectrum communication technology has strong ability to resist multipath interference, is suitable for low signal-to-noise ratio (SNR), and has good networking ability. Based on the combination of direct sequence spread spectrum (DSSS) and OFDM, the cyclic shift spread spectrum OFDM technology and the combined spread spectrum OFDM technology are studied in this paper. These two technologies have higher communication rate. Simulation results show that OFDM spread spectrum system without cyclic prefix can still be decoded efficiently and reliably. In underwater acoustic communication, spatial variation has a great influence on the impulse response function of underwater acoustic channel, which makes the impulse response function of underwater acoustic channel have weak correlation. Based on this physical property of underwater acoustic channel, the time reversal mirror technique is used in multi-user underwater acoustic communication to focus on the desired users and shield the non-expected users to realize space-division multiple access (SDMA). In this paper, the OFDM spread spectrum multi-user underwater acoustic communication system based on time reversal mirror is constructed, and the reliable communication of multiple users is realized. Then the differential OFDM spread spectrum technique is proposed, which adopts differential coherent demodulation at the receiver to weaken the performance degradation problem caused by underwater acoustic fading channel, without the need of coherent demodulation and channel estimation, so as to improve the frequency band efficiency of the system. In order to reduce the complexity and computational complexity of the system, a robust communication system can be established by applying OFDM spread spectrum technology to multi-purpose underwater acoustic communication. In this paper, computer simulation experiments and tank experiments are carried out to verify the proposed algorithm. The results show that the performance of underwater acoustic communication system is improved by the combination of spread spectrum technology and OFDM technology. High-quality point-to-point underwater acoustic communication and multi-user underwater acoustic communication are realized.
【學位授予單位】：哈爾濱工程大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TN929.3;TN929.53

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