【摘要】：正交頻分復(fù)用是一種無(wú)線環(huán)境下的多載波調(diào)制技術(shù),它具有抗多徑衰落、抗干擾能力強(qiáng)和頻譜利用率高等特點(diǎn),是新一代移動(dòng)通信系統(tǒng)的核心技術(shù)之一。認(rèn)知無(wú)線電技術(shù)可以有效的解決頻譜資源閑置和浪費(fèi)的問(wèn)題,OFDM自身的優(yōu)點(diǎn)使其成為認(rèn)知無(wú)線電技術(shù)的最佳調(diào)制方式,不連續(xù)的正交頻分復(fù)用技術(shù)NC-OFDM應(yīng)運(yùn)而生,隨之產(chǎn)生的諸多關(guān)鍵問(wèn)題成為研究熱點(diǎn)。其中信道估計(jì)直接影響系統(tǒng)的通信品質(zhì)。基于導(dǎo)頻的信道估計(jì)由于其估計(jì)誤差小、收斂速度快、高傳輸速率等優(yōu)點(diǎn)成為主流的信道估計(jì)技術(shù),基于導(dǎo)頻的信道估計(jì)受到兩個(gè)方面的制約,一是信道估計(jì)器的設(shè)計(jì)；二是導(dǎo)頻序列的設(shè)計(jì),因此NC-OFDM系統(tǒng)導(dǎo)頻序列的設(shè)計(jì)研究具有十分重要的意義。本文詳細(xì)介紹了OFDM系統(tǒng)基本原理以及無(wú)線信道的傳輸特性,系統(tǒng)分析了最優(yōu)導(dǎo)頻序列設(shè)計(jì)的常用設(shè)計(jì)準(zhǔn)則和算法,針對(duì)稀疏信道環(huán)境,提出了NC-OFDM系統(tǒng)導(dǎo)頻序列位置和功率設(shè)計(jì)方法。針對(duì)傳統(tǒng)NC-OFDM系統(tǒng)信道估計(jì)導(dǎo)頻序列設(shè)計(jì)方法計(jì)算復(fù)雜度高、效率低下、數(shù)據(jù)利用率低的問(wèn)題,提出了一種NC-OFDM稀疏信道環(huán)境下導(dǎo)頻序列位置設(shè)計(jì)方法,該方法以最小測(cè)量矩陣互相關(guān)為目標(biāo)函數(shù),通過(guò)求解一個(gè)帶約束的最優(yōu)化問(wèn)題并簡(jiǎn)化搜索方法得到最優(yōu)導(dǎo)頻位置分布,該方法不僅在信道估計(jì)MSE上優(yōu)于傳統(tǒng)等間隔以及隨機(jī)搜索的導(dǎo)頻,在系統(tǒng)BER性能以及計(jì)算復(fù)雜度方面均有明顯改善。傳統(tǒng)OFDM系統(tǒng)的導(dǎo)頻功率分配方法通常考慮等功率限制或總發(fā)射功率限制因素,由于NC-OFDM的特殊性,該方法不能直接用于NC-OFDM系統(tǒng)導(dǎo)頻功率分配,為此,提出了一種NC-OFDM系統(tǒng)導(dǎo)頻子載波功率分配算法,該方法利用最小測(cè)量矩陣互相關(guān)準(zhǔn)則,并滿足以下幾種約束條件：干擾溫度約束、總功率約束、最大功率約束、子信道功率約束,通過(guò)求解多約束條件最優(yōu)化問(wèn)題得到最優(yōu)的導(dǎo)頻子載波功率分配。保證了信道的估計(jì)精度,提高了數(shù)據(jù)傳輸利用率,加強(qiáng)了系統(tǒng)的傳輸有效性和可靠性。與其他導(dǎo)頻序列設(shè)計(jì)算法相比,能夠有效降低系統(tǒng)誤碼率(BER, Bit Error Rate)和信道估計(jì)(MSE, Mean Squared Error),從而在整體上提高了系統(tǒng)性能。
[Abstract]:Orthogonal Frequency Division Multiplexing (OFDM) is a kind of multi-carrier modulation technology in wireless environment. It has the characteristics of anti-multipath fading, strong anti-interference ability and high spectrum efficiency. It is one of the core technologies of the new generation mobile communication system. Cognitive radio technology can effectively solve the problem of idle and wasteful spectrum resources. The advantages of OFDM make it the best modulation mode of cognitive radio technology. The discontinuous orthogonal frequency division multiplexing (NC-OFDM) technology emerges as the times require. Many key problems have become the focus of research. The channel estimation directly affects the communication quality of the system. Channel estimation based on pilot has become the mainstream channel estimation technology because of its small error, fast convergence and high transmission rate. The channel estimation based on pilot is restricted by two aspects, one is the design of channel estimator; The second is the design of pilot sequence, so the design of pilot sequence in NC-OFDM system is of great significance. In this paper, the basic principle of OFDM system and the transmission characteristics of wireless channel are introduced in detail. The common design criteria and algorithms of optimal pilot sequence design are analyzed systematically. The position and power design method of pilot sequence in NC-OFDM system is presented. Aiming at the problems of high computational complexity, low efficiency and low data utilization rate in traditional channel estimation pilot sequence design method for NC-OFDM systems, a pilot sequence position design method in NC-OFDM sparse channel environment is proposed. In this method, the minimum measurement matrix cross-correlation is taken as the objective function, and the optimal pilot position distribution is obtained by solving an optimization problem with constraints and simplifying the search method. This method not only outperforms the traditional equal-interval and random search pilots in channel estimation MSE, but also improves the BER performance and computational complexity of the system. Traditional pilot power allocation methods in OFDM systems usually consider equal power limit or total transmit power limiting factors. Because of the particularity of NC-OFDM, this method can not be directly applied to pilot power allocation in NC-OFDM systems. In this paper, a pilot subcarrier power allocation algorithm for NC-OFDM systems is proposed. The method uses the minimum measurement matrix cross-correlation criterion and satisfies the following constraints: interference temperature constraint, total power constraint, maximum power constraint, subchannel power constraint. The optimal pilot subcarrier power allocation is obtained by solving the multi-constrained optimization problem. The channel estimation accuracy is guaranteed, the data transmission efficiency is improved, and the transmission efficiency and reliability of the system are enhanced. Compared with other pilot sequence design algorithms, BER (BER, Bit Error Rate) and channel estimation (MSE, Mean Squared Error), can be effectively reduced, thus improving the overall performance of the system.
【學(xué)位授予單位】：東北大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TN925

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