Trellis coded modulation for additive impulsive noise

Abstract

AbstractThis paper discusses the situation where the trellis coded modulation (TCM) is applied to the digital subscriber loop (DSL) using a balanced pair cable, and examines the effectiveness. The usual error‐correcting code cannot be applied successfully to the balanced pair since the loss increases with the increase of the transmission bandwidth. When TCM is applied, on the other hand, the transmission performance for the Gaussian noise can be improved without increasing the transmission bandwidth. The major factor deteriorating the performance in DSL, however, is the impulsive noise. From such a viewpoint, this paper examined the effectiveness of TCM for the impulsive noise.First, the probability density of the impulsive noise is derived from the measurement of the exiting DSL, and the channel capacity is calculated. It is shown that it is necessary and sufficient to double the transmitting symbols and to assign the produced redundancy to the error‐correction. This is the same as the known result for the Gaussian noise, but the coding gain by the ideal coding is 18 dB, which is larger than in the case of the Gaussian noise. The coding gain of 9 dB is obtained by the simulation using the 8‐state convolutional code, which is larger than 4 dB in the case of the Gaussian noise. The reason for this improvement is discussed from the viewpoint of the probability distribution of the noise and the signal mapping in the multidimensional signal space.