Performance of channel codec with channel state information (CSI) for the equalized cellular radio channels

The problem of deriving soft decisions for the convolutional decoder in the proposed time-division multiple access (TDMA) North American digital cellular system is examined. The equivalent bidirectional equalized mobile radio channel is derived. The analytical solution for the optimal bit likelihood calculation of π/4 shift QDPSK modulation is then derived for this channel. It is shown that error signal from the equalizer may be used to derive an estimate of the instantaneous SNR, which is required for the calculation of these metrics. The resulting soft decisions provide a decoded BER of 1% with 2 dB less power than that required for hard decisions