Trellis decoding of linear block codes in digital mobile radio

Word error rate (WER) performance with soft decision decoding of linear block codes using a trellis is investigated for noncoherent FSK (frequency-shift keying) in a Rayleigh fading channel. The received signal envelopes corresponding to each bit of the code are sampled and used for estimating reliability of the bits. Hamming (7,4) code is used for WER performance evaluation by means of computer simulation and laboratory experiments. The simulation results show that required SNR to obtain a WER of 10＾ for trellis decoding is about 5 dB lower than that for minimum distance decoding with 1-bit error correction when (maximum Doppler frequency) × (bit interleaving degree)/(bit rate) >= 0.2. The effect of n-bit A/D conversion in signal envelope sampling is also investigated. A simplified trellis decoding algorithm, in which the hard decision output of a bit with the envelope sample greater than the threshold value is accepted as correct, is presented for complexity reduction