| 摘要 |
A turbo coded communication system includes a gray scale mapper in a transmitter for generating a symbol constellation of modulated signals points that can be separated by boundary lines in the constellation space into bitwise groups of zero bits and one bits where the shortest distance from a boundary line to received value in the constellation space indicates the bitwise soft metrics that is computed using a set of bitwise soft metric equations are a function of the minimum distance using closed form algebraic equations in turbo decoding receiver. In the case of quadrature amplitude modulation (QAM), the bit boundary lines are predetermined by a minimum distance in the constellation space for a specified M-ary modulation, so that, the soft metric equations are only a function of the received signal value for providing efficient computation of the bitwise soft metric.
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