Block interleaving for soft decision Viterbi decoding in OFDM systems

In this paper, frequency and time interleaving algorithms used for soft decision Viterbi decoding for OFDM systems, performed on frequency-selective and time-selective channels respectively, are investigated. To achieve optimal performance in terms of the bit error rate (BER), the size of the interleavers must be specified depending on the properties of the channel and the characteristics of the code. Under these aspects, new frequency- and time interleaving algorithms are proposed. To get the lowest BER, we have found that the frequency interleaving length should be chosen in the range of the decoding constraint length. On the other hand, the time interleaving depth should be derived from the coherence time of the channel.