本文選題：多輸入多輸出正交頻分復(fù)用 + 導(dǎo)頻信道估計(jì)　； 參考：《南京航空航天大學(xué)》2017年碩士論文

【摘要】：隨著現(xiàn)代社會(huì)對(duì)移動(dòng)通信服務(wù)需求的迅速增長(zhǎng),頻譜資源日趨緊張,未來(lái)可靠高速的無(wú)線通信首先要實(shí)現(xiàn)大容量、高速率和高頻譜利用率。OFDM技術(shù)由于頻譜利用率高、實(shí)現(xiàn)復(fù)雜度低、抗多徑衰落等優(yōu)點(diǎn),在寬帶通信中得到廣泛的應(yīng)用。同時(shí),MIMO技術(shù)充分利用空間資源,在無(wú)需占用額外頻譜資源以及增加發(fā)射功率的前提下,有效提升系統(tǒng)的信道容量和頻譜利用率。因此,MIMO技術(shù)與OFDM技術(shù)的結(jié)合能夠同時(shí)發(fā)揮兩種技術(shù)的優(yōu)勢(shì),有利于系統(tǒng)容量及頻譜利用率的提升。第四代移動(dòng)通信系統(tǒng)中已經(jīng)將MIMO-OFDM技術(shù)作為數(shù)據(jù)傳輸?shù)暮诵募夹g(shù)方案,很大程度上提升了用戶的通信體驗(yàn)。由于MIMO-OFDM無(wú)線通信系統(tǒng)中,信道傳輸環(huán)境復(fù)雜,因此信道估計(jì)是通信系統(tǒng)可靠運(yùn)行的關(guān)鍵,同時(shí)空時(shí)解碼、相干解調(diào)、恢復(fù)初始數(shù)據(jù)等操作也需要盡可能準(zhǔn)確的信道狀態(tài)信息,因此,本文主要研究MIMO-OFDM無(wú)線通信系統(tǒng)中的信道估計(jì)算法。本文針對(duì)MIMO-OFDM系統(tǒng),首先根據(jù)無(wú)線信道的統(tǒng)計(jì)特性和衰落特性,建立了頻率選擇性衰落和非頻率選擇性衰落MIMO信道模型;然后結(jié)合OFDM技術(shù)利用多載波并行傳輸信號(hào)的特點(diǎn),建立MIMO-OFDM系統(tǒng)數(shù)據(jù)傳輸模型;接著推導(dǎo)了LS、DFT以及MMSE三種經(jīng)典信道估計(jì)算法,均仿真實(shí)現(xiàn)。算法改進(jìn)部分,本文針對(duì)DFT算法中最大時(shí)延長(zhǎng)度內(nèi)仍存在噪聲以及最大時(shí)延長(zhǎng)度需要提前獲取的不足,創(chuàng)新提出了基于循環(huán)前綴的改進(jìn)DFT算法,用循環(huán)前綴長(zhǎng)度代替最大時(shí)延長(zhǎng)度,并設(shè)置門(mén)限值獲取循環(huán)前綴長(zhǎng)度內(nèi)的信道主要路徑,從而提升了經(jīng)典DFT算法的估計(jì)精度;同時(shí),本文針對(duì)LS算法和DFT算法結(jié)果中每一徑上存在噪聲的不足,創(chuàng)新提出了基于指數(shù)平滑算法的改進(jìn)LS和DFT信道估計(jì)算法,利用指數(shù)平滑算法對(duì)信道估計(jì)的結(jié)果做優(yōu)化,從而減少信道每一徑上的噪聲,提升估計(jì)精度。仿真實(shí)驗(yàn)結(jié)果表明,基于循環(huán)前綴的改進(jìn)DFT算法提升了經(jīng)典DFT算法的估計(jì)精度,同時(shí)避免了經(jīng)典DFT算法中獲取最大時(shí)延長(zhǎng)度的問(wèn)題;指數(shù)平滑算法對(duì)LS、DFT算法的估計(jì)結(jié)果進(jìn)行優(yōu)化,減少信道每一徑上的噪聲,有效提升了經(jīng)典LS、DFT算法的估計(jì)精度,且改進(jìn)算法僅需增加少量計(jì)算復(fù)雜度,易于實(shí)現(xiàn)。
[Abstract]:With the rapid growth of the demand for mobile communication services in modern society, the spectrum resources are becoming increasingly tight. In the future, the reliable and high-speed wireless communication must first achieve large capacity, high rate and high spectrum efficiency. OFDM technology is due to the high spectrum efficiency. Because of its low complexity and anti-multipath fading, it has been widely used in broadband communication. At the same time MIMO technology makes full use of space resources and improves the channel capacity and spectral efficiency of the system without requiring additional spectrum resources and increasing transmission power. Therefore, the combination of MIMO technology and OFDM technology can bring into play the advantages of the two technologies at the same time, which is conducive to the improvement of system capacity and spectrum efficiency. MIMO-OFDM technology has been taken as the core technology of data transmission in the fourth generation mobile communication system, which greatly improves the user's communication experience. In MIMO-OFDM wireless communication system, the channel transmission environment is complex, so channel estimation is the key to reliable operation of communication system. At the same time, space-time decoding, coherent demodulation, recovery of initial data and other operations also need as accurate channel state information as possible. Therefore, this paper mainly studies the channel estimation algorithm in MIMO-OFDM wireless communication systems. For MIMO-OFDM system, firstly, according to the statistical and fading characteristics of wireless channel, the MIMO channel models of frequency-selective fading and non-frequency-selective fading are established, and then the characteristics of multi-carrier parallel transmission signal are combined with OFDM technology. The data transmission model of MIMO-OFDM system is established, and then three classical channel estimation algorithms, LS- DFT and MMSE, are derived and realized by simulation. In order to solve the problem that the maximum delay length still exists in the DFT algorithm and the maximum delay length needs to be obtained in advance, an improved DFT algorithm based on cyclic prefix is proposed in this paper. The maximum delay length is replaced by cyclic prefix length, and the main channel path within the cyclic prefix length is obtained by setting the threshold value, which improves the estimation accuracy of the classical DFT algorithm. Aiming at the deficiency of noise in every path of LS algorithm and DFT algorithm, an improved LS and DFT channel estimation algorithm based on exponential smoothing algorithm is proposed in this paper, and the result of channel estimation is optimized by exponential smoothing algorithm. In order to reduce the channel noise on each path, improve the estimation accuracy. The simulation results show that the improved DFT algorithm based on cyclic prefix improves the estimation accuracy of the classical DFT algorithm and avoids the problem of obtaining the maximum delay length in the classical DFT algorithm. The exponential smoothing algorithm optimizes the estimation results of the LSN DFT algorithm, reduces the noise in every path of the channel, effectively improves the estimation accuracy of the classical LSN DFT algorithm, and the improved algorithm only needs a small amount of computational complexity, which is easy to implement.
【學(xué)位授予單位】：南京航空航天大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TN929.5

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