Bit error probability of trellis-coded quadrature amplitude modulation over cross-coupled multidimensional channels

Convolutionally encoded M-ary quadrature amplitude modulation (M-QAM) Systems operated over multidimensional Channels, for example dual-polarized radio Systems, are considered in this paper. We have derived upper bounds on the average bit-error probability for 4-QAM (QPSK) with conventional convolutional coding by means of a truncated union bound technique and averaging over the cross-polariza-tion interference by means of the method of moments. By modifying this technique, we have found approximate upper bounds on the average bit-error probability for bandwidth efficient trellis-coded QAM Systems. This is an extension of our previous work [1] that was based on one dominating error event probability as a Performance measure. Our evaluations seem to indicate that bandwidth efficient trellis-coded M-QAM schemes offer much larger coding gains in an interference environment, e.g., a cross-coupled interference Channel, than in a Gaussian noise Channel. In general, our findings point out that optimum codes for a Gaussian Channel are not optimum when applied in an interference environment. We note that a rate 1/2 convolutional code for example, with a code memory greater than two, if applied to two of the bits in each signal point representation, can be utilized with a simple decoder to greatly improve the Performance of a QAM signal in interference. Also, we have introduced a new concept referred to as dual-channel polarization hopping in this paper which can improve the System Performance significantly for Systems with nonsymmetrical interference.