摘要
在通信盲接收中,研究在码元数目较少时的参数估计技术和盲均衡技术具有重要的理论意义和实用价值。本文从实用角度出发,重点研究了在接收数据只有数十至数百个码元的情况下,如何有效地进行码元速率估计和盲均衡。本文主要工作和成果如下:
首先,针对基于二阶非线性变换估计码元速率方法在码元数目较少和信号冗余带宽较小时性能较差的缺陷,提出先滤除信号低频分量,再进行二阶非线性变换的方法。理论推导证明该改进措施有效地提高了该类算法在码元数目少和冗余带宽小时的性能,仿真实验验证了该结论。针对K.C.Ho小波变换估计码元速率方法现存缺陷,本文提出先去除载频,再进行小波变换估计码元速率的方法。该方法较好地克服了小波变换方法的缺陷,使其在码元数目较少时的性能得到较大提高,仿真实验验证了该结论。
其次,针对码元数只有数十至数百个时,对数据进行盲均衡存在的困难,本文研究了在Bussgang类算法中重复使用短数据段的方法。本文分析了重复使用短数据段方法有效的原因,并研究了影响重复使用短数据段方法盲均衡效果的若干因素,得出了Bussgang类算法实现均衡所需要码元数量的结论,即通过重复使用短数据段方法,部分Bussgang类算法能够在数十至数百个码元的级别实现有效均衡,这与基于二阶统计量的盲均衡方法所需要的数据量相当。
第三,针对通信盲接收系统中要求盲均衡算法计算量低、适应性强、需要数据量少的特点,本文设计了新型盲均衡算法。本文首先研究了Bussgang类算法的收敛本质,并由此提出了Bussgang算法统一的代价函数。根据该代价函数得到一类设计新型Bussgang算法的方法。本文据此设计了几种新型算法,仿真实验验证了这些算法的收敛性能。结合这几种新型算法的优点,本文设计了一种组合算法。该组合算法具有计算量低、适应性强、需要数据量少等优点,能够满足通信盲接收系统对盲均衡算法的需要。该算法已应用到实际系统。
最后,基于软件无线电原理,本文集成了所提出的算法,并完成了软、硬件系统设计,成功研制了一套通信盲接收样机系统。
In communication blind receiver, it’s of great significance to study how to estimate signal’s parameters and achieve blind equalization form short data series. Based on field project, this dissertation focus on the symbol rate estimation and blind equalization techniques from short data series (from several decades to several hundreds symbols). The main work and the results are summarized as follows:
Firstly, aiming at the symbol rate estimation method by second nonlinear transform showing poor performance in the case of short data and less spectrum redundancy, a modified algorithm was introduced: Filtering the received series first by a high pass filter, then applying second nonlinear transform. The analyses shows that the modified algorithm improved the performance of the original algorithm greatly in the case of short data and less spectrum redundancy. Simulation also verified the conclusion. K.C.Ho’s symbol rate estimation method by wavelet transforms show some defects and instability, the reason which induced these defects was analyzed in this dissertation, and then a modified algorithm was introduced: Removing the residual carrier frequency, and then applying wavelet transform. This method get rid of the defects of the original method thoroughly, improved the performance of the wavelet method in the case of short data series. Simulation verified the conclusion.
Secondly, aiming at the difficulty of blind equalization by short data in length of several decades to hundreds, the short data series reusing method in Bussgang algorithm was analyzed in this dissertation. First of all, the reason why the short data series reusing method to be effective was analyzed, and then the facts which will influent the effect of reusing short data series in Bussgang algorithm was analyzed. By these analyzing results, some conclusions were got about how many data the Bussgang algorithm needed to achieve equalization: By reusing short data series, some Bussgang algorithms can achieve equalization by only several decades’data, which is close to the L.Tong’s method.
Thirdly, blind receiver put many requirements to blind equalization method, such as less computing consuming, less data consuming, and common adaptability to all kinds of communication signal. A new equalization method was designed in this dissertation to meet this requirement. First of all, the essence of Bussgang algorithm’s convergence was studied, and the conclusion was got that Bussgang algorithm is one kind of the Minimum Entropy algorithm. By this conclusion the common cost function of Bussgang algorithm was put forward. This common cost function also indicates a new way to design new Bussgang algorithm. Some new Bussgang algorithms was designed according to this method, simulation has verified the convergence of these new algorithms. Combining the merits of these new algorithms, a dual-mode blind equalization algorithm was designed. This dual-mode algorithm shows some excellent performance: less computing consuming, less data consuming, and great adaptability to many kind of communication signals, which makes it meet to the requirement of blind receiver well. This new dual-mode algorithm has been used in communication blind receiver.
Finally, based on software radio techniques, a communication blind receiver was designed, which integrated the algorithms designed by this dissertation.
引文
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