Performance Analysis of Optimum Interleaver based on Prime Numbers for Multiuser Iterative IDMA Systems

Performance Analysis of Optimum Interleaver based on Prime Numbers for Multiuser Iterative IDMA Systems

M. Shukla (Harcourt Butler Technological Institute, India) and Ruchir Gupta (Rohelkhand University, India)
DOI: 10.4018/jitn.2010070103
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Abstract

In recently proposed multiple access techniques like IDMA and OFDM-IDMA, the user separation is done by user specific interleavers in contrast to the conventional CDMA scheme, where user separation is assured with user-specific signature sequences. The user specific interleavers must demonstrate minimum probability of collision amongst each other in addition to other merits, including minimal consumption of bandwidth, least hardware for their generation, and least memory requirement. In this paper, the authors propose an interleaver based on prime numbers for the generation of user specific interleavers to remove the problem of high consumption of bandwidth. The simulation results demonstrate the optimal performance of prime interleaver (PI), which is based on prime numbers, apart from other merits in comparison to random and other interleavers.
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Introduction

By researchers, significant amount of research has been done in the field of wireless communication. The recently developed technique including iterative multi user detection (MUD) techniques for suppressing multiple access interference (MAI) (Liu, 2003; Ping, 2006) has also drawn their attention. Interleave division multiple access (IDMA) and OFDM-IDMA are the two multiple access (MA) schemes that make use of the iterative MUD efficiently, (Verdú, 1999). In IDMA, interleavers are being employed as the only means of user separation while in CDMA the signature sequences were designed to be means of user separation as the spreader provides no coding gain (Verdú, 1999). With even random interleavers, the IDMA system performs similarly and even better than a comparable CDMA system (Ping, 2006). IDMA outperforms CDMA in terms of better immunity to multiple access interference (MAI) and higher user count. IDMA also inherits the advantages of CDMA such as asynchronous transmission, diversity against fading and cross cell interference mitigation at a reduced cost of complexity (Verdú, 1999) and high data rate. This chip by chip turbo type detection technique in IDMA also reduces the complexity of receiver multi use detector (MUD) as compared to that used in CDMA system (Ping, 2006; Verdú, 1999).

The efficiency of IDMA system is dependent on the generation of various pseudo random interleaving patterns for each user. The system performance seriously degrades when the interleaving patterns are not orthogonal to each other i.e., the collision among the interleaving patterns is not minimum. These interleavers disperse the coded sequences so that the adjacent chips are approximately uncorrelated, which facilitates the simple chip-by-chip detection. In case of interleavers in IDMA systems, the parameters such as ease of generation, hardware required, bandwidth consumption during transmission, and memory requirement at transmitter and receiver end, may be vital parameters for generation of orthogonal interleavers. The greater the size of interleaver the more it consumes the memory and extra bandwidth for transmission, this becomes a greater problem when the number of users increase. In Ping (2006), random interleaver has been utilized in IDMA systems, while in Wu (2006), an efficient technique for interleaver generation in IDMA has been proposed in.

This paper is organized as follows. The following section presents the importance of interleavers in digital communication. Studies of relevant literature are presented. The mechanism of interleaving process is highlighted. The importance of interleavers in IDMA systems is also discussed. The next section focuses on available various orthogonal interleavers for IDMA scheme. The IDMA systems model is then duly explained. The motivation for the work and mechanism of propose prime interleaver and the numerical results are presented.

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