The Design of New Modified Block and Matched S-Random Interleavers for Turbo Codes

Abstract

Abstract-It is known that one of the essential building blocks of turbo codes is the interleaver and its design using random, semi-random (S-Random) and deterministic permutations. In this paper, two new types of turbo code interleavers, Modified Block S-Random (MBSR) interleaver and Modified Matched S-Random (MMSR) interleaver are proposed. The design algorithm for the new interleavers is described in depth, and the simulation results are compared to the two new interleavers with different existing interleavers based on the BER (Bit Error Rate) performances of the turbo codes. Through the simulation, we find a better performance of the MBSR interleaver than random and practical interleavers.In addition, the performance of MMSR interleaver is close to the code matched interleaver at different frame sizes and with less complex design.Index Terms-Interleaver, semi random, turbo codes, weight distribution. I. INTRODUCTIONA typical turbo code (TC) was first introduced in 1993 by Berrou et al.,[1] as a class of near channel capacity achieving codes. This turbo code is constructed by concatenating two parallel convolutional codes via an interleaver as shown in Fig. 1. The interleaver is an indexing function given by a permutation of bits index in the information frames with N frame length that plays a crucial role in the turbo codes architecture. Interleaver has three main functions: a) it constructs a long code from small memory convolutional codes by permuting the input bits such that the two constituent encoders are operating on different order input bits. b) Provides "scrambled" information data to the second constituent encoder to decorrelate the inputs of the two decoders, so that an iterative suboptimum decoding algorithm based on "uncorrelated" information exchange between the two constituent decoders can be applied. c) It changes theweight distribution of turbo codes such that, the overall weight for the generated codeword depends on how the outputs from the two constituent encoders are teamed together.The main two properties characterize any interleaver are the interleaver spreading property which is the distance between adjacent bits before interleaving, and the randomness property that provides a non-fixed indexing function which is a good factor for correction in the iterative decoding. Turbo code interleaver types have been Manuscript received May 31, 2014; revised July 17, 2014. This work was supported in part by College of Electronic and Information Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, ChinaThe authors are with the Nanjing university of Aeronautics and Astronautics, College of Electronic and Information Engineering, Nanjing (e-mail: thms78@gmail.com, saqibejaz@gmail.com).extensively studied in different ways, and they fall into two main classes: Random interleavers and Deterministic interleavers. A random interleaver is simply a random permutation with new positions produced by an indexing function based on the uniform probability distribution. While in majo...

Interleaving Gains for Receive Diversity Schemes of Distributed Turbo Codes in Wireless Half–Duplex Relay Channels

“…Nevertheless, it fails to break many combined lower-weight sequences that appears in several consecutive rows. To solve such problem, MBSR interleaver [12] designed to combine both columns and rows reordering technique with S-random interleaving constraint (spreads elements positions such that any two elements within a window of size S will not be located in a window of size S in the interleaved sequence). This algorithm increases the interleaver ability to break input bad sequences.…”

“…For this purpose, we first introduce the use of Modified Block S-Random (MBSR) and MMSR interleavers in [12] compared with practical and random interleavers [13], [14] to show the interleaving effect on both Distributed Turbo Codes (DTC) and Distributed Multiple Turbo Codes (DMTC) schemes. Secondly, we have conducted a series of numerical simulations to study the effect of using MBSR and MMSR interleavers at the relay comparing our results with using different other interleavers.…”