Abstract

The maximum a posteriori (MAP) decoding algorithm for convolutional codes is reformulated in terms of probabilities and log-likelihood ratios. This is shown to be a precise circuit description of an analog decoder in terms of currents and voltages which inspires different circuit designs. I. INTRODUCTION Recently several proposals for analog decoders were made in [1], [2], [3], [4], [5], which is in contrast to common practice where decoding is performed by digital processors. The implementation of `soft-in/soft-out' decoders which accept soft input from the demodulator and deliver soft output for the information bits require that soft values are processed throughout the decoder [6]. Such decoders are useful for serial or parallel concatenated decoding schemes, e.g., `turbo'-decoding. In the digital domain the soft values are represented by a hard decision for the corresponding bit combined with additional quantized reliability information about the decision. Especially in combination...

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