Development of Signal Processing Systems for Digital Recording

改进记录码信息密度的基本概念有：(1)增加无直流特性，以限制串扰和直流漂移；(2)尽可能大地设置T_<min>，以减少码间干扰的影响，其中T_<min>为记录波形中两个连续极性变化之间的时间间隔；(3)从系统设计上考虑，增加信道容量，使其成为几个约束参数的函数。虽然在这方面已经提出了许多记录代码，但很少有出版物对代码进行分类。我们介绍了有限自动机模型，作为编码规则的理论描述和促进各种拟议代码之间的性能比较的有用工具。调频码是世界上最著名和最强大的码之一，本文对调频码及其族码进行了研究，以期对记录码的系统化有一个基本的认识。结果表明，一些常规码与调频族码是一致的。数字记录系统中信号的再现过程不要求是记录过程的倒数函数。为此，我们采用部分响应（Partial Response， PR）系统均衡检测信号，采用Viterbi算法代替逐位解码方法。我们还假设附加噪声是有色的。结果表明，有效信噪比和误码率均有显著提高。

The basic concepts for the imformation density improvements in recording codes are summarized as follows:(1) to include DC-free property in order to restrict cross-talk and dc wandering, (2) to set T_<min> as large as possible in order to reduce the influence of intersymbol interference, where T_<min> is the time separation between two successive polarity changes in recording waveform, (3) to incease channel capacity as a function of several constaint parameters with respect to system design.Although a lot of recording codes are already proposed in this respect, there have been few publications with classification of the code. We introduced the finite automaton model as a useful tool for theoretical description of the coding rule and for facilitation of performance comparison among various proposed codes.FM code, one of the most famous and powerful codes, and its family codes have been investigateds to obtain fundamental insights for systematization of recording codes. It turns out that some conventional codes are identified with FM family codes.The reproduction process of signals in digital recording systems is not required to be a reciprocal function of recording process. For this reason, we adopted Partial Response(PR) systems for equalizing the detected signal and Viterbi algorithm in stead of bit-by-bit decoding method. We also assumed additive noise to be colored. As the results, significant improvements on both effective signal-to-noise ratio and bit error rate are performed.