扩展谱通信GLRT：联合的信道估计、均衡和符号检测

发布时间：2018-06-08 01:50

本文选题：扩展谱 + CDMA　；参考：《浙江大学》2014年博士论文

【摘要】：本文瞄准不确实信道下的有效、可靠通信,以信号处理、信息理论和传播物理为支柱,在广义似然比检验(Generalized Likelihood Ratio Test, GLRT)框架下,进行联合的信道估计、均衡和符号检测,以设计扩展谱码分多址(Code Division Multiple Address, CDMA)水下空时阵通信系统。扩展谱调制,在发射端,将待传输的信息用与所传输的信息相独立的伪随机码扩展成为宽带信号,即使信号所占用的带宽远远超过所传信息的必需带宽；在接收端,使用完全相同的码进行同步相关／匹配接收以解扩,进而恢复所传送的信息。固有冗余伪随机码的引入不仅使发射信号为大时间带宽乘积信号,而且还让发射信号呈现类噪声性,以至于扩展谱通信具有抗干扰、低截获、高隐蔽等特性。在多用户通信中,还可在每一发送信号中叠加不同的伪随机码来区分彼此,形成CDMA技术。扩展谱调制在实现形式上主要分为直接序列扩展谱和跳频扩展谱两种。直接序列扩展谱利用伪随机码调制相移键控(Phase Shift Keying, PSK)信号进行谱的扩展；跳频扩展谱是在一个发射信号间隔内,按照伪随机码在一组预先规定的频隙上随机选择一个或数个频隙。与无扩展调制方式相比,扩展谱调制是以宽带谱为代价来提高系统的可靠性的,利用CDMA技术,尽管相对于单用户扩展谱通信而言,谱有效性／每码片的总容量得到了提高,但采用随机扩展的CDMA技术相对于确定性扩展的CDMA技术／无扩展多用户时的谱有效性仍存在损失。水声通信中,我们面临的海洋波导环境,特别是浅海波导环境,由于其边界及介质起伏效应,造成时延和多普勒扩展及其变化严重,致使经海洋介质传播的声信号呈现出时间和频率选择性衰落。其次,海洋信道还存在多用户干扰、有意干扰及带宽严重受限等问题。因此,要想实现远距离且有效可靠的水下通信必须采用空时阵通信。时域模糊度函数在大时间带宽乘积波形下低旁瓣,且波形“越乱越好”,时间上波形频率无序寻求时延-多普勒集中。因此,本文在调制器端施加伪随机码以发射信号,解调器端利用同步伪随机码解调接收信号。利用空时对偶性,空域模糊度函数在大空间带宽乘积阵形下低旁瓣,且阵形“越乱越好”,空间上阵几何取向无序寻求阵响应向量集中。因此,本文收发端均采用“伪随机”双螺旋线阵(Double Spiral Line Array, DSLA)来作收发波束形成,以实现有效接收和有效照射。借助于信号的几何表征和信号空间分析,在发射信号先验等可能情况下,最小差错概率准则导出的白高斯信道下的最佳符号检测器为最大似然检测器或最小距离检测器,相应的接收机为相关接收机及其等效的匹配滤波器。实际水声通信中,反映信道传播变化的测量模型中会存在未知参数如信道,因此,若采用先对未知参数作估计,然后选择最有可能的假设,则构成GLRT检测器,其表现为：联合的信道估计、均衡和符号检测。为了跟踪信道变化,应采用自适应均衡／滤波,如基于递归最小二乘(Recursive Least Square, RLS)的均衡／滤波。先验信息与数据信息具有相加性,在基于数据信息的基础上,根据信道的空时演化特性构建状态-空间模型,然后在GLRT框架下,利用序贯贝叶斯滤波——卡尔曼／质点滤波将先验信息规则化地嵌入到算法设计中,通过反馈,改善迭代过程的收敛,形成宽容性处理方法。为了设计低复杂度扩展谱CDMA序贯GLRT空时阵通信系统,本文首先着重对空时匹配滤波／时反技术进行了研究,提出了循环平稳时反技术、时反-正交空时块编码技术和时反波束形成技术。鉴于被动时反是时+空处理,本文又提出采用空时联合的阵处理方法——空-时最小均方误差(Minimum Mean Square Error, MMSE)来进一步提高通信系统的可靠性。然后,本文将时反和空-时MMSE分别与卡尔曼／质点滤波相结合设计了低复杂度的单载波／多载波扩展谱CDMA水下空时阵通信系统。本文的研究内容按三个部分展开。第一部分：水声通信源-信道和空-时四维阵扩展谱GLRT;第二部分：单载波扩展谱通信GLRT;第三部分：多载波扩展谱通信GLRT.在第二三部分又有层次地对两个子内容进行研究：(1)时反扩展谱通信GLRT;(2)空-时MMSE扩展谱通信GLRT.最后,仿真和实验数据分别证实了上述研究内容的可行性。
[Abstract]:This article aims at the effective and reliable communication under the uncertain channel, with signal processing, information theory and communication physics as the pillar, under the framework of Generalized Likelihood Ratio Test (GLRT), the joint channel estimation, equalization and symbol detection are used to design the extended spectrum code division multiple access (Code Division Multiple Address, CDMA). Underwater space-time array communication system.
Extended spectrum modulation, at the transmitter, the information to be transmitted is extended into a wideband signal with a pseudo random code independent of the transmitted information, even if the bandwidth occupied by the signal is far more than the required bandwidth of the transmitted information; at the receiving end, the same code is used to carry out the synchronization phase close / match reception to despread, and then restore the transmission. The introduction of inherent redundant pseudorandom code not only makes the transmitting signal a large time bandwidth product signal, but also makes the transmitting signal present noise like, so that the spread spectrum communication has the characteristics of anti-jamming, low interception and high concealment. In the multiuser communication, the different pseudo random codes can be superimposed on each sending signal to distinguish each other. CDMA technology is formed.
The spread spectrum modulation is divided into two kinds: direct sequence spread spectrum and frequency hopping spread spectrum. The direct sequence extension spectrum is extended by pseudo random code modulation phase shift keying (Phase Shift Keying, PSK). The frequency hopping spread spectrum is in a set of signal intervals, in a set of predetermined frequency gaps according to pseudorandom code There is a random selection of one or several frequency gaps. Compared with the non extended modulation, the extended spectrum modulation improves the reliability of the system at the cost of the broadband spectrum. Using the CDMA technology, the spectrum effectiveness / the total volume of each chip is improved compared to the single user extended spectrum communication, but the CDMA technique with random expansion is relative accurate. The spectral efficiency of the CDMA technology extended by nature is not lost.
In underwater acoustic communication, we face the marine waveguide environment, especially the shallow sea waveguide environment. Due to its boundary and medium fluctuation effect, the time delay and Doppler expansion and its change are serious. The acoustic signals transmitted through the ocean media show time and frequency selective fading. Secondly, there are multi user interference and intentional interference in the ocean channel. And the bandwidth is severely limited. Therefore, space time array communication must be used to achieve long distance and reliable underwater communication.
The time domain ambiguity function is low sidelobe in the large time bandwidth product waveform, and the waveform is "more chaotic, the better", and the time waveform frequency disorder seeks time delay - Doppler concentration. Therefore, this paper applies pseudo random code to transmit signal at the modulator end and demodulates the received signal using synchronous pseudorandom code.
By using space-time duality, the spatial ambiguity function is low sidelobe under the large space bandwidth product formation, and the formation is "more chaotic, the better", and the space array geometry orientation is disordered to seek the array response vector concentration. Therefore, the transceiver ends of this paper use "pseudo random" double spiral linear array (Double Spiral Line Array, DSLA) for sending and receiving beamforming. Effective reception and effective irradiation.
With the aid of geometric representation and signal spatial analysis of signals, the best symbol detector under the minimum error probability criterion derived from the minimum error probability criterion is the maximum likelihood detector or the minimum distance detector, and the corresponding receiver is the related receiver and the equivalent matching filter. In the letter, there will be unknown parameters such as channel in the measurement model that reflects the variation of channel propagation. Therefore, if the unknown parameter is estimated first and then the most probable hypothesis is selected, the GLRT detector is composed of the joint channel estimation, equalization and symbol detection. In order to track channel changes, adaptive equalization / filtering should be used. For example, equalization / filtering based on recursive least squares (Recursive Least Square, RLS). The priori information and data information are additive. Based on the data information, the state space model is constructed based on the spatial time evolution characteristics of the channel. Then the sequential Bayesian filtering, Calman / particle filter, will be used in the GLRT framework. The information is regularly embedded in the algorithm design, and the feedback process is adopted to improve the convergence of the iterative process and form a tolerance processing method.
In order to design a low complexity extended spectrum CDMA sequential GLRT space-time array communication system, this paper first focuses on the study of space-time matched filtering / time inverse technology, and proposes a cyclostationary time inverse technology, time inverse orthogonal space-time block coding and time inverse beamforming. The joint array processing method, Minimum Mean Square Error (MMSE), is used to further improve the reliability of the communication system. Then, a low complexity single carrier / multicarrier extended spectrum CDMA space time array communication system is designed by combining time and space time MMSE with Calman / particle filter, respectively. The research content of this paper is carried out in three parts. The first part: the underwater acoustic communication source channel and the space-time four-dimensional array extension spectrum GLRT; the second part: the single carrier spread spectrum communication GLRT; the third part: the multi carrier spread spectrum communication GLRT. studies the two sub content in the two or three part again: (1) the inverse spread spectrum communication GLRT; (2) empty. Time MMSE spread spectrum communication GLRT. finally, simulation and experimental data confirm the feasibility of the above research contents.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TN929.3

【参考文献】