Interleaver choice in Serially Concatenated Codes for soft real-time wireless speech transmission applications

The continuous investment in research and development of turbo codes, aimed at improving the overall system efficiency of wired/wireless electrical and optical communications networks, brings about a wealth of theoretical knowledge and practical industrial solutions. Turbo codes are Parallel or Serial Concatenation of Convolutional Codes (PCCCs and SCCCs respectively), which are also termed Parallel and Serially Concatenated Codes (PCCs and SCCs). In many cases, SCCs shown to have remarkable Bit-Error-Rate (BER) performance for BERs lower than 10^-5, unlike PCCs; therefore, they are widely used in modern wireless communication systems for realization of powerful Forward Error Correction (FEC). The most critical part in the design of SCCs is the interleaver design. Substantial increase in the Minimum Hamming Distance (MHD) between the legitimate permutations of the encoded bit sequence could be realized through an appropriate choice of the interleaver´s permutation pattern; hence, the corresponding BER performance is improved significantly through the lower bit error probabilities at moderate signal-to-noise ratios (SNRs) and lower error floor. In this correspondence, for the sake of practical utilization of SCCs in soft real-time Wireless Speech Transmission (WST) applications, the investigations on finding optimum interleaving type for SCCs are performed through the simulations.