發(fā)布時間：2018-04-18 11:00

  本文選題：水聲通信 + 正交頻分復(fù)用��； 參考：《哈爾濱工程大學》2014年博士論文

【摘要】：水聲信道的多徑時延會引起嚴重的碼間干擾;水聲信道的窄帶寬、快速時變性及水下通信設(shè)備和水介質(zhì)的相對運動等因素會產(chǎn)生明顯的多普勒效應(yīng);水聲信道的介質(zhì)構(gòu)成、水體運動形式及水下環(huán)境的復(fù)雜性等因素會造成大的水下噪聲。水聲信道的上述特點最終導致了水聲信號的嚴重失真和快速衰減。因此如何解決水聲通信系統(tǒng)中與多徑現(xiàn)象、多普勒效應(yīng)及水下噪聲相關(guān)的問題,已成為水聲通信領(lǐng)域所面臨的重要課題。正交頻分復(fù)用(OFDM)技術(shù)是一種多載波并行傳輸技術(shù),由于其不但具有良好的抗多徑性能和高的頻譜利用率,而且可以根據(jù)信道條件對子載波進行靈活調(diào)制及功率分配,因而已被廣泛應(yīng)用于陸上無線電磁通信和水聲通信系統(tǒng)中。與陸上無線電磁通信相比較,將OFDM技術(shù)應(yīng)用于水聲通信系統(tǒng)中會出現(xiàn)更為嚴重的問題。首先,OFDM信號容易出現(xiàn)高的峰均比(PAPR),這更加不利于水下無線低功率通信設(shè)備的正常使用;第二,OFDM系統(tǒng)對于載波頻率偏移非常敏感,而水聲信道中顯著的多普勒效應(yīng)更容易導致這種頻偏;另外,由于水聲信道的時變特性和高噪聲,要求OFDM系統(tǒng)在進行相干解調(diào)時,信道估計器不但要有更好的信道跟蹤能力以滿足系統(tǒng)實時性的要求,而且還要有更強的抗噪聲能力。因此,解決高峰均比、多普勒頻移及信道估計等相關(guān)問題是OFDM水聲通信系統(tǒng)所面臨的重要任務(wù)。本文結(jié)合水聲信道和水聲通信設(shè)備的特點,針對OFDM水聲通信系統(tǒng)中出現(xiàn)的高峰均比、多普勒頻移及信道估計等相關(guān)問題作了進一步的研究,以提高水聲通信系統(tǒng)的高速實時處理性能為目標,提出了創(chuàng)新算法,并通過理論分析和計算機仿真驗證分析了這些算法的性能。論文的主要研究工作包括以下四部分:首先,分別從帶寬、噪聲、多徑及多普勒效應(yīng)等方面分析介紹了水聲信道的特性;再針對上述特性對水聲信道進行了建模和仿真;最后概括了 OFDM水聲通信系統(tǒng)的優(yōu)缺點,并提出了信號的峰均比、多普勒頻移及信道估計等三個與OFDM水聲通信系統(tǒng)密切相關(guān)的問題。其次,考慮到水下無線通信設(shè)備的低功率特點,在傳統(tǒng)限幅算法的基礎(chǔ)上,針對限幅噪聲問題對OFDM水聲通信系統(tǒng)的峰均比進行了研究,提出了一種計算復(fù)雜度較低的降低限幅噪聲的新算法。該算法對超過限幅門限的數(shù)據(jù)采用分段式的不同的限幅幅度,再用限幅記錄保存這一處理結(jié)果,然后接收端可以利用這一記錄恢復(fù)相應(yīng)數(shù)據(jù)的原始幅度。從而大幅降低限幅噪聲對于系統(tǒng)性能的影響。理論分析和仿真結(jié)果均表明,這種限幅算法在較低誤碼率的前提下能夠有效提升水聲發(fā)射機功率放大器的工作效率。第三,針對OFDM水聲通信系統(tǒng)對于多普勒頻移敏感的問題,從多普勒因子(DSF)估計、采樣率轉(zhuǎn)換及載波頻移(CFO)估計三方面提出了一種多普勒頻移估計和補償?shù)男滤惴āＪ紫仍诮邮斩藢�接收�?shù)據(jù)進行過采樣,然后利用線性調(diào)頻信號估計出多普勒因子的初值;再利用上述過采樣數(shù)據(jù)結(jié)合多普勒因子的估計初值,通過線性插值的方法進行采樣率轉(zhuǎn)換;最后根據(jù)系統(tǒng)精度要求,以上述多普勒因子估計初值作為中心數(shù)據(jù),列出若干多普勒因子的候選值,結(jié)合空載波能量代價函數(shù)對多普勒因子進行快速搜索實現(xiàn)二次估計,以完成由多普勒效應(yīng)引起的載波頻移(CFO)的估計。通過理論及計算機仿真對新算法的性能進行了分析,結(jié)果表明該算法和傳統(tǒng)的多普勒頻移估計及補償算法相比具有較低的運算復(fù)雜度,能夠有效改善OFDM水聲通信系統(tǒng)的多普勒頻移問題。最后,結(jié)合水聲信道的快速時變性和高噪聲特性,針對頻域最小二乘(LS)信道估計算法(性能受噪聲影響大)和離散傅立葉變換(DFT)算法(性能受空載波影響大)各自的誤差問題,提出了一種LS-DFT聯(lián)合信道估計新算法。首先在頻域?qū)�導頻子載波進行LS信道估計,再通過DFT對上述LS導頻信道估值作降噪處理,得到另一組頻域?qū)ьl信道估值,然后將兩組導頻信道估值作誤差對比和數(shù)據(jù)替換,取誤差較小者組成一組新的導頻信道估值,最后在頻域作線性插值運算,以獲得數(shù)據(jù)子載波處的信道估值。無論是理論分析還是計算機仿真結(jié)果,均表明這種聯(lián)合信道估計算法能有效克服LS算法和DFT算法各自的缺點,且該算法能以小的計算復(fù)雜度從整體上有效提升OFDM水聲通信系統(tǒng)信道估計的實時性能和抗噪聲性能。
[Abstract]:Multipath underwater acoustic channel will cause serious intersymbol interference; narrow bandwidth of underwater acoustic channel, fast time-varying and underwater communication equipment and water medium relative motion and other factors will have Doppler effect; composition of underwater acoustic channel medium, water sports and water environmental factors such as the complexity of the cause the underwater noise. The characteristics of underwater acoustic channel eventually led to a serious and rapid attenuation of underwater acoustic signal distortion. So how to solve the underwater acoustic communication system with multipath effect, Doppler effect and underwater noise related issues, has become an important task in the field of underwater acoustic communication. Orthogonal frequency division multiplexing (OFDM) technology is a parallel multi carrier transmission technology, because it not only has good anti multipath performance and high spectrum utilization, but also flexible modulation and power allocation according to the channel condition of sub carrier Therefore, has been widely used in terrestrial wireless electromagnetic communication and underwater acoustic communication system. And the wireless electromagnetic communication compared to the application of OFDM technology in underwater acoustic communication systems, there will be more serious problems. First, the OFDM signal is easy to appear the high peak to average ratio (PAPR), which is not conducive to the normal the use of low power wireless communication equipment under water; second, OFDM system is very sensitive to carrier frequency offset, and the Doppler effect in the underwater acoustic channel is more likely to result in the frequency offset; in addition, due to the time-varying characteristics of underwater acoustic channel and high noise, the requirement of OFDM system in coherent demodulation, channel estimator not only have better tracking capability to meet the real-time requirement of the system, but also has stronger anti noise ability. Therefore, to solve the problems related to the high peak to average ratio, Doppler frequency shift and channel estimation in OFDM underwater acoustic communication system An important task facing. Combining with the characteristics of underwater acoustic channel and underwater acoustic communication equipment, for OFDM in underwater acoustic communication system PAPR, made further research on issues related to the Doppler shift and the channel estimation, in order to improve the speed of real-time underwater communication system can reason as the goal, put forward the innovative algorithm and analysis of the performance of these algorithms through theoretical analysis and computer simulation. The main research work of the thesis includes the following four parts: first, from the bandwidth, noise, multipath and Doppler effect analysis and introduces the characteristics of underwater acoustic channel; and then according to the characteristics of underwater acoustic channel modeling and simulation; finally summarized the advantages and disadvantages OFDM underwater communication system, and puts forward the PAPR and is closely related to the three and OFDM underwater acoustic communication system and channel estimation of Doppler frequency shift. Then Considering the characteristics of low power, wireless communication equipment under water, based on the traditional algorithm of amplitude limit, aiming at limiting the noise problem of OFDM underwater acoustic communication system PAPR is studied, a new algorithm is proposed for low complexity to reduce the clipping noise. The algorithm adopts segmented different limiting amplitude of the data exceeds the limit threshold, and limiting record the results of this treatment, then the receiver can recover the corresponding data of the original amplitude using this record. To reduce the effect of clipping noise on system performance. Theoretical analysis and simulation results show that this algorithm can limit to effectively enhance the acoustic transmitter power amplifier at low bit error rate under the premise of efficiency. Third, for OFDM underwater acoustic communication system sensitive issue for the Doppler frequency shift, from the Doppler factor (DSF) estimation, sampling rate Conversion and carrier frequency offset (CFO) estimation and propose a new algorithm of Doppler frequency shift estimation and compensation in three aspects. First, in the receiver to receive data over sampling, and then use the estimated initial Doppler factor of linear FM signal; and then use the over sampling data combined with initial estimates of the Doppler factor, sampling the rate of conversion by linear interpolation method; finally, according to the accuracy requirement of the system, the data center to initial estimates as Doppler factor, Doppler factor lists a number of candidate values, combined with the empty carrier energy cost function for quick search to achieve two times to estimate the Doppler factor, carrier frequency to complete the shift caused by the Doppler effect (CFO) estimation through the performance of the new algorithm theory and computer simulation are analyzed. The results show that the algorithm and the Doppler frequency shift estimation and compensation algorithm It has low computational complexity and can effectively improve the Doppler frequency shift of the OFDM underwater acoustic communication system. Finally, combined with the acoustic channel fast time-varying and high noise characteristics based on frequency domain least squares (LS) channel estimation algorithm (performance affected by noise) and the discrete Fu Liye transform (DFT) algorithm (performance by the air carrier effect of their error), proposed a new LS-DFT joint channel estimation algorithm. Firstly, the pilot subcarriers in the frequency domain for LS channel estimation, and then through the DFT on the LS pilot channel estimation of noise reduction processing, get another set of frequency domain pilot channel estimation, and then two groups of pilot channel estimation error comparison and data substitution error is smaller consisting of a new set of pilot channel estimation, the linear interpolation in the frequency domain, to obtain data subcarrier channel estimation. Both theory analysis and calculation The simulation results show that the joint channel estimation algorithm can effectively overcome the shortcomings of LS algorithm and DFT algorithm, and the algorithm can effectively enhance the real-time performance and noise immunity of OFDM underwater acoustic communication system in a small computational complexity.

【學位授予單位】：哈爾濱工程大學
【學位級別】：博士
【學位授予年份】：2014
【分類號】：TN929.3
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本文編號：1768083