A New Block S-Random Interleaver for Shorter Length Frames for Turbo Codes

In this paper, we have proposed a new design of interleaver based on S-random and block interleaver. The characteristics of both block and S-random interleaver are used by this proposed interleaver. There is a large influence of free distance in turbo codes due to interleaving as it lowers the error floor. The free distance of turbo codes can be increased by designing interleaver with high spread. In this case, the overall spreading factor is increased significantly for smaller length frames also. The simulations results are compared with full S-random interleavers. The bit error rate performance of proposed interleaver for Turbo codes is much better than full s-random interleaver at the cost of small delay

A New Block S-Random Interleaver for Shorter Length Frames for Turbo Codes

In this paper, we have proposed a new design of interleaver based on S-random and block interleaver. The characteristics of both block and S-random interleaver are used by this proposed interleaver.  There is a large influence of free distance in turbo codes due to interleaving as it lowers the error floor. The free distance of turbo codes can be increased by designing interleaver with high spread. In this case, the overall spreading factor is increased significantly for smaller length frames also. The simulations results are compared with full S-random interleavers. The bit error rate performance of proposed interleaver for Turbo codes is much better than full s-random interleaver at the cost of small delay

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

This paper proposes the interleaving gain in two different distributed turbo-coding schemes: Distributed Turbo Codes (DTC) and Distributed Multiple Turbo Codes (DMTC) for half-duplex relay system as an extension of our previous work on turbo coding interleaver design for direct communication channel. For these schemes with half-duplex constraint, the source node transmits its information with the parity bit sequence(s) to both the relay and the destination nodes during the first phase. The relay received the data from the source and process it by using decode and forward protocol. For the second transmission period, the decoded systematic data at relay is interleaved and re-encoded by a Recursive Systematic Convolutional (RSC) encoder and forwarded to the destination. At destination node, the signals received from the source and relay are processed by using turbo log-MAP iterative decoding for retrieving the original information bits. We demonstrate via simulations that the interleaving gain has a large effect with DTC scheme when we use only one RSC encoder at both the source and relay with best performance when using Modified Matched S-Random (MMSR) interleaver. Furthermore, by designing a Chaotic Pseudo Random Interleaver (CPRI) as an outer interleaver at the source node instead of classical interleavers, our scheme can add more secure channel conditions

On the Design of Turbo Codes

This thesis is about Turbo codes - codes constructed via parallel concatenation of two recursive convolutional encoders linked by an interleaver. The focus of the work is on the understanding and design of Turbo codes. This includes thorough investigation of central components that influence Turbo code performances, such as the constituent encoders and the interleaver, as well as the procedure of iterative decoding. The investigations are carried out for transmission on additive white Gaussian noise channels. Two aspects that influence the performance of Turbo codes are considered: (1) code properties, in terms of Hamming distance spectra, and (2) decoding properties, in terms of the performance of iterative decoding. It is asserted that both these aspects are influenced by both the choice of interleaver and the choice of constituent encoders. An interleaver design algorithm based on these observations is presented. Furthermore, guidelines for the choice of constituent encoders are outlined. As regards the interleaver, it can be designed to result in both good code- and decoding properties. In contrast, the choice of constituent encoders involves a trade off between the two. A measure that comprises the interleaver properties influencing the performance of iterative decoding is presented. This measure is called Iterative Decoding Suitability (IDS), and it is derived using a model that approximates correlation properties of decoder inputs and outputs. The aspect of trellis termination of Turbo codes is also investigated. It is demonstrated that with proper interleaver design, very competitive error rate performances is obtained also without trellis termination. In addition, it is demonstrated that the 'error-floor' that Turbo codes are claimed to suffer from at medium- to high signal-to-noise ratios can be significantly lowered by proper combination of constituent encoders and interleaver design

Joint interleaver design for multiple turbo codes

The outstanding performance of turbo codes at low signal-to-noise ratio is deteriorated in the error-floor region, due to the low values of the free distance of turbo codes. Interleaver design for turbo codes can improve the minimum distance of the code, by eliminating low-weight input sequences that result in low-weight codewords. Interleaver can also be designed to improve the performance of the sub-optimal iterative decoding methods. While the relating criteria to satisfy these conditions are known, we are not able to find an interleaver that fulfills all these conditions in reasonable time. In this thesis, we have proposed a Joint interleaver design methods , for multiple turbo codes, where we have at least three constituent codes and two interleavers to design. In our proposed methods each interleaver is designed to satisfy some of the conditions and the other conditions are satisfied by the other interleaver. This will decrease the load on one interleaver to satisfy all the conditions at the same time and enable us to satisfy tougher conditions. It is shown that the proposed Sequential joint interleaver design converges very fast and can satisfy very tough conditions, which means better performance at error-floor region of the turbo code

On the Theory and Performance of Trellis Termination Methods for Turbo Codes

The performance of a turbo code can be severely degraded if no trellis termination is employed. This paper investigates the implications of the choice of trellis termination method for turbo codes, and explains the origin of the performance degradation often experienced without trellis termination. An efficient method to derive the distance spectrum of turbo codes for different trellis termination methods is presented. Further, we present interleaver design rules that are tailored to each termination method. Using interleavers designed with these restrictions, we demonstrate that the performance difference between various termination methods is very small, including no trellis termination at all. For example, we demonstrate a turbo code with a 500-bit interleaver that exhibits no sign of an error floor for frame error rates as low as 10-8, even though no trellis termination is employe

Space-time coding techniques with bit-interleaved coded modulations for MIMO block-fading channels

The space-time bit-interleaved coded modulation (ST-BICM) is an efficient technique to obtain high diversity and coding gain on a block-fading MIMO channel. Its maximum-likelihood (ML) performance is computed under ideal interleaving conditions, which enables a global optimization taking into account channel coding. Thanks to a diversity upperbound derived from the Singleton bound, an appropriate choice of the time dimension of the space-time coding is possible, which maximizes diversity while minimizing complexity. Based on the analysis, an optimized interleaver and a set of linear precoders, called dispersive nucleo algebraic (DNA) precoders are proposed. The proposed precoders have good performance with respect to the state of the art and exist for any number of transmit antennas and any time dimension. With turbo codes, they exhibit a frame error rate which does not increase with frame length.Comment: Submitted to IEEE Trans. on Information Theory, Submission: January 2006 - First review: June 200