Semi-Blind Reception Using Joint Channel Estimation in IDMA Systems

Abdelkrim Hamza, Ali Kazem, Gérard Salut

CNRS, LAAS, 7 Avenue du Colonel Roche, Toulouse, France; Univ. de Toulouse, LAAS, Toulouse, France.
LCPTS Laboratoire de Communication et du Traitement du Signal, FEI-USTHB, Alger, Algérie.

DOI: 10.4236/ijcns.2012.57053                

Abstract

In this paper a bi-directional system based on linear channel estimation and data detection using turbo detection algorithm is proposed. By combining channel estimation with an iterative chip-by-chip detection process (inner loop) in an iterative way (outer loop), communications performance can be further increased. We present results on blind reception in case of Interleave Division Multiple Access (IDMA) system when the channel coefficients are unknown. We develop a low-complexity iterative joint channel/code estimation method. The philosophy of the turbo processing is the iterative exchange of related information which yields a substantial improvement of the overall system performance. We analyze the achievable performance of the iterative system proposed. Simulation results demonstrate the efficiency of the proposed algorithms.

Keywords

Channel Estimation; IDMA; Multiuser Detection

1. Introduction

The present paper proposes a semi-blind channel estimation method, based on conditional Gaussian particle algorithm for IDMA systems, to track varying channel coefficients. The performance of Code Division Multiple Access (CDMA) systems is mainly limited by Multiple Access Interference (MAI) and Inter Symbol Interference (ISI). Chip-level interleavers for user separation can separate different users without spreading within the CDMA framework. An interleaver based multiple access scheme has also been studied in [1,2] for high spectral efficiency, improved error performance and low receiver complexity. This paper concerns transmission and detection principles using interleavers as the only means for user separation, incorporating principles developed in [3,4]. Interleave Division Multiple-Access (IDMA) systems communication is one of the most promising technologies for high data rate wireless networks. IDMA inherits many advantages from CDMA, in particular, diversity against fading and mitigation of the worst-case other-cell user interference problem. Furthermore, IDMA allows a very simple chip-by-chip iterative Multi User Detection (MUD) strategy [5]. The normalized MUD cost (per user) can be made independent of the user number. From the receiver point of view the unknown channel degrades the accuracy of symbol detection. This can be eliminated using estimation methods on Channel State Information (CSI). Channel coefficient estimation is usually performed using known training sequences which are periodically transmitted (for instance, at the start of each frame), implicitly assuming that the channel does not vary between two training sequences. An iterative procedure to track the channel variations by refining the channel coefficients in a semi-blind manner is proposed. The paper is organized as follows: section 2 introduces the IDMA system and settles the various notations. Section 3 recalls the Chip by Chip (CBC) algorithm and its application on IDMA system, as well as channel estimation. This section presents also, the new detection system based on semi-blind channel estimation. Finally, section 4 illustrates the performance of the proposed algorithm through simulation results. Section 5 concludes the paper.

2. IDMA System Model

IDMA Transmitter and Receiver Structures are shown in

Figure 1 for the multiple access scheme under consideration with K simultaneous users, with perfect channel knowledge. The input data sequence d_k of user-k is spread by a length C spreading sequence, generating a coded sequence c_k = [c_k(1); …; c_k(j); …; c_k(J)]T , where J is the frame length. The elements in c_k are referred to as coded bits. Then c_k is permuted by an interleaver π(k), producing the vector x_k = [x_k(1); …; x_k(j); …; x_k(J)]^T. We

Conflicts of Interest

The authors declare no conflicts of interest.

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