A block coded modulation method for variable-rate data transmission

Abstract

We describe a block-coded modulation method producing variable data-transmission rate using a one-sided link. This method uses signal points that are added to the normal signal constellation of the digital modulation (e.g., QPSK, 16QAM). The different numbers of the bits are assigned to the added points. This is the basis for changing the transmission rate. However, the Euclidean distance becomes quite short and the bit error rate performance is severely degraded. To avoid this, a multilevel block code is constructed using these signal points. The signal points are set-partitioned. We can lengthen the Euclidean distance of the code with this modified signal constellation. To demodulate the signal we use the Viterbi algorithm of the block-coded modulation for maximum likelihood decoding. The trellis diagram used for the Viterbi algorithm is the same as that used for trellis-coded modulation. We evaluated the method by using computer simulations, and showed that it results in both a large coding gain and variable-rate data transmission.