PERFORMANCE EVALUATION METHOD OF TRELLIS-CODED MODULATION SCHEME WITHOUT UNIFORMITY

An encoder of a trellis coded modulation (TCM) is composed of a linear convolutional encoder followed by a mapper to channel signals. A new condition, under which the performance evaluation of the TCM is possib le based on the 2nu state error state transition diagram, is proposed, where nu is the number of delay elements in the convolutional encoder . There have been proposed three similar methods. This paper points ou t the restriction of the previous methods, and proposes a new method. The condition, under which the previous method is useful, is called un iformity, such as, the error weight profile is independent from the en coder state. When uniformity does not hold, we discuss to divide an er ror state into substates based on the coset decomposition of output ve ctors of the convolutional encoder. The coset is determined by the vec tor called coset selector. If the condition defined as equal dividing holds, the subdivided states can be merged and the performance can be evaluated based on the 2nu state transition diagram, even for the code s without uniformity. When the row rank of the transformation matrix, from the input vector of the encoder to the coset selector vector, is full, the equal dividing condition holds under the assumption of equal ly probable i.i.d. (independently identically distributed) input seque nce. For TCM schemes without uniformity (in the case, previous methods can not be applied), upper bounds of the bit error rate are evaluated by the proposed method and compared with the simulation results. The difference is less than 10% in the range of bit error rate < 10(-4).