미래 무선통신시스템을 위한 IDMA기반의 다중사용자 접속

Abstract

A new multiple access scheme called Interleave Division Multiple Access (IDMA), which is a special case of CDMA, was recently proposed as a spread spectrum multiple access scheme. In an IDMA scheme, users are distinguished by different chip-level interleaving methods instead of by different signatures as in a conventional CDMA scheme. A special benefit of IDMA is that it allows a very simple chip-by-chip iterative multiuser detection strategy and per user cost of this algorithm is independent of the number of users. Moreover, the advantages of combining FEC and spreading lead to improved cellular performance and also increase the throughput. The main contributions of this thesis are listed below. In the first contribution, we propose a method to improve the performance of the conventional IDMA scheme with a high level of signal refinement via an oversampling method for user chip-level data at the receiver. This oversampled data gives additional redundancy for the transmitted signal that is used to minimize the noise power and thus helps to suppress inter-symbol interference (ISI) with reduced multiple access interference (MAI). This signal refinement offers the improved bit-error rate (BER) performance of the system. In the second contribution, we propose novel memory efficient interleavers for user separation in the IDMA scheme. The proposed interleavers called Matrix Helical Scan Interleaver (MHSI) and Primitive Element based Interleaver (PEI), can be generated using a few parameters that exhibit reasonable randomness in the interleaving pattern, and improve the BER performance of the IDMA scheme. In particular, these are attractive in the practical implementation as the number of simultaneous users increases. In the third contribution, we propose an IDMA-based multiuser access scheme called User-data Division Multiple Access (UDMA) scheme that employs user data as the spreading sequence for user separation with a chip-by-chip iterative multiuser detection strategy. As such, this spreading sequence is not only as random as user data and independent of current symbols, but also dynamically changes from one symbol to another according to the user data. Therefore, this spreading sequence makes unwanted detection of the data by unintended receivers practically impossible. Also, in the UDMA scheme, identical interleavers are used and thus do not require to store all interleaving patterns. In the final contribution, we improve the performance of the IDMA scheme over frequency selective fading channel. We propose an IDMA based multiuser access scheme with large receiver MIMO (LR-MIMO), that is, LR-MIMO-IDMA scheme. This scheme provides superior performance for the IDMA scheme over frequency selective fading channel, and further enhances bandwidth efficiency by reducing the repetition length of the IDMA scheme.