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为了在普遍存在的模拟电话型信道上进行可靠的高速数据传输,Ungerboeck提出了一种以“集合划分映射”为基础的格状编码调制技术,简称TCM。这种技术在不损失数据速率或不增加带宽的情况下,能大大改善同步数据线路的误码特性。本文在此基础上,给出了格状码的总体设计方法。作为一种新的传输方式,TCM技术已经在高速调制解调器中得到应用。在这些调制解调器中,接收端都采用软判决Viterbi算法进行译码。随着传输速率的增加,Viterbi译码器的复杂性迅速增长,给译码的实时处理带来很大的困难。本文提出一种简化的Viterbi译码算法,可以大大减少译码器的运算量。这不仅使高速实时译码的经济实现成为可能,而且缩小了运算的动态范围,使运算精度得到提高。计算机模拟证明:在加性白高斯噪声信道上,采用简化Viterbi算法的误码性能与原算法几乎完全相同。
For reliable high-speed data transmission over ubiquitous analog telephone channels, Ungerboeck proposed a trellis-coded modulation technique based on “set-division mapping”, referred to as TCM. This technique greatly improves the error characteristics of synchronous data lines without loss of data rate or with increased bandwidth. Based on this, this paper gives the overall design method of trellis code. As a new transmission method, TCM technology has been applied in high-speed modems. In these modems, the receiver uses the soft-decision Viterbi algorithm for decoding. With the increase of transmission rate, the complexity of Viterbi decoder increases rapidly, which brings great difficulties to real-time decoding. This paper presents a simplified Viterbi decoding algorithm, which can greatly reduce the computational complexity of the decoder. This not only makes high-speed real-time decoding of the economy possible, but also reduces the dynamic range of the operation, the computing accuracy is improved. Computer simulations prove that the error performance of the simplified Viterbi algorithm is almost the same as the original one in the additive white Gaussian noise channel.