单载波频域均衡技术的研究

发布时间：2018-10-04 21:05

【摘要】：单载波频域均衡(Single Carrier Frequency Domain Equalization,SC-FDE)技术是一种抵抗频率选择性衰落信道中由多径时延引起的码间串扰的技术。与传统单载波时域均衡技术相比,SC-FDE技术由于采用频域均衡,具有较低的计算复杂度,与OFDM(Orthogonal Frequency Domain Modulation)技术相当;与多载波OFDM技术相比,SC-FDE技术由于采用单载波传输,峰均功率比较低,不需要昂贵的线性放大器,并且对载波频偏的敏感度也大大低于OFDM技术,对同步精度要求较低。因此,该技术目前广泛应用于宽带系统中,如空中接口标准IEEE 802.16,移动宽带无线接入IEEE802.20工作组,以及3GPP LTE的上行链路。但是,SC-FDE技术也存在一些缺点,其频谱利用率不高,且无法利用频率分集等。除此之外,传统的SC-FDE系统在多径信道下,不能充分利用信道的多径分集,使得信道容量下降。针对这些问题,研究人员提出了SC-FDE技术与多输入多输出(Multiple-Input Multiple-Output,MIMO)系统的结合,并有很多研究将STBC(Space-Time Block Coding)和SFBC(Space-Frequency Block Coding)等发射分集方案应用在SC-FDE系统中,从而使SC-FDE系统获得空间分集、时间分集和频率分集增益。由于SC-FDE系统的发射信号是在时域进行的,因而不能直接应用SFBC方案。在基于SFBC设计的SC-FDE发射分集方案中,需要首先利用傅里叶变换(Discrete Fourier Transform,DFT)将时域信号变换到频域,进行SFBC设计,之后再利用IDFT(Inverse Discrete Transform,IDFT)将编码后的信号变换到时域进行发送。该方案涉及到多个傅里叶变换,其计算复杂度较高。而离散Hartley变换(Discrete Hartley Transform,DHT),作为一种与傅里叶变换类似但计算复杂度较低的变换,可以被应用于该方案中。本文首先对SC-FDE的技术背景和发展状况进行了相关研究,分析了无线通信系统的衰落信道,建立SC-FDE系统模型,并与OFDM系统模型作了相应的比较。在SC-FDE系统中,研究了基于DFT的STBC和SFBC发射分集方案,理论分析推导,并通过仿真实验进行了验证。为了降低传统的基于DFT的SC-FDE系统的计算复杂度,本文提出了基于DHT的SFBC SC-FDE系统。针对DHT只能调制实数信号,以及不能像DFT一样直接将信道矩阵对角化等问题,进行了详细的叙述和分析,并提出了相应的解决方案。本方案通过将二维复数调制信号的实部和虚部分别进行离散Hartley变换,再合并,使信号从时域变换到频域,进行SFBC设计,实现了DHT调制复数信号。再利用DHT矩阵的互补特性,将信道矩阵对角化,从而实现单抽头的频域均衡。文章的最后,通过分析和仿真证明,与传统的基于傅里叶变换的单载波频域均衡系统相比,本算法在高信噪比的情况下,可以获得更好的性能,并且使得接收机端的计算复杂度降低了将近一半。另外,由于离散Hartley变换的正变换和逆变换是相同的变换,因而可以使用完全相同的硬件和程序来实现调制和解调,降低了系统的硬件成本。
[Abstract]:Single carrier frequency domain equalization (Single Carrier Frequency Domain Equalization,SC-FDE) is a technique to resist inter-symbol crosstalk caused by multipath delay in frequency-selective fading channels. Compared with traditional single-carrier time-domain equalization technique, SC-FDE technology has lower computational complexity and is comparable to OFDM (Orthogonal Frequency Domain Modulation) technology because of frequency domain equalization, and SC-FDE technology has lower peak-to-average power compared with multicarrier OFDM technology because of single-carrier transmission. There is no need for expensive linear amplifiers, and the sensitivity to carrier frequency offset is much lower than that of OFDM technology, and the synchronization accuracy is low. Therefore, this technology is widely used in broadband systems, such as the air interface standard IEEE 802.16, the Mobile Broadband Wireless access IEEE802.20 working Group, and the uplink of 3GPP LTE. However, SC-FDE technology also has some shortcomings, its spectrum efficiency is not high, and can not use frequency diversity and so on. In addition, the traditional SC-FDE system can not make full use of multipath diversity in multipath channel, which makes the channel capacity decrease. To solve these problems, researchers proposed the combination of SC-FDE technology and multi-input multiple-output (Multiple-Input Multiple-Output,MIMO) system, and many studies have applied STBC (Space-Time Block Coding) and SFBC (Space-Frequency Block Coding) to SC-FDE system, so that SC-FDE system can obtain spatial diversity. Time diversity and frequency diversity gain. Because the transmitted signal of SC-FDE system is carried out in time domain, SFBC scheme can not be applied directly. In the SC-FDE transmit diversity scheme based on SFBC, it is necessary to transform the time domain signal to the frequency domain by using the Fourier transform (Discrete Fourier Transform,DFT (Discrete Fourier Transform,DFT), and then to design the SFBC using IDFT (Inverse Discrete Transform,IDFT) to transform the encoded signal into the time domain for transmission. This scheme involves multiple Fourier transforms, and its computational complexity is high. The discrete Hartley transform (Discrete Hartley Transform,DHT), which is similar to Fourier transform but with low computational complexity, can be applied to this scheme. In this paper, the technical background and development of SC-FDE are studied, and the fading channel of wireless communication system is analyzed. The SC-FDE system model is established and compared with the OFDM system model. In the SC-FDE system, the STBC and SFBC transmit diversity schemes based on DFT are studied, the theoretical analysis and derivation are carried out, and the simulation results are verified. In order to reduce the computational complexity of the traditional SC-FDE system based on DFT, a SFBC SC-FDE system based on DHT is proposed in this paper. Aiming at the problem that DHT can only modulate real signal and can not directly diagonalize the channel matrix as DFT, this paper gives a detailed description and analysis, and puts forward the corresponding solution. In this scheme, the real part and the imaginary part of the 2-D complex modulation signal are transformed into discrete Hartley transform, then combined, the signal is transformed from time domain to frequency domain, and the SFBC is designed, and the complex DHT modulation signal is realized. The channel matrix is diagonalized by using the complementary characteristic of DHT matrix, and the frequency domain equalization of single tap is realized. Finally, through analysis and simulation, it is proved that compared with the traditional single-carrier frequency-domain equalization system based on Fourier transform, the proposed algorithm can achieve better performance in the case of high SNR. And the complexity of the receiver is reduced by nearly half. In addition, because the forward transformation and inverse transform of discrete Hartley transform are the same transformation, the same hardware and program can be used to realize modulation and demodulation, which reduces the hardware cost of the system.
【学位授予单位】：大连工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TN911.5

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