Analysis and performance of a hybrid multiple access scheme: IDMA/CDMA

Purpose - The purpose of this paper is to introduce the analysis and performance of a hybrid multiple access scheme which combines interleave division multiple access (IDMA) and code division multiple access (CDMA), referred to as IDMA/CDMA. With experimentations, the scheme can achieve good performance with simple user ends for the system. Design/methodology/approach - IDMA technique is employed as the uplink transmission and CDMA technique as the downlink transmission. The performance comparison of IDMA and IDMA/CDMA downlink is studied with Monte Carlo simulations to investigate the bit error rates. For IDMA/CDMA downlink, the signals are interleaved by random interleavers, spreaded by M-sequence and orthogonal Gold sequence, respectively, and then transmitted over an AWGN with BPSK modulation. Moreover, a channel estimation approach for IDMA based on expectation maximization (EM) algorithm is also presented. Findings - The multi-user detection (MUD) algorithm in uplink IDMA systems is much simpler than that used in traditional CDMA systems. It is also well known that the orthogonal spreading codes in CDMA can effectively help suppress the MM in the synchronized environments. But for the asynchronized application, the performance of CDMA systems will degrade due to the serious multiple user interference. According to traditional IDMA and orthogonal code division multiple access/IDMA signal detection algorithms, every UE has to detect all of the signals of other users for iterative detection. The advantages of IDMA and CDMA technologies can be utilized substantially. Originality/value - The proposed hybrid multiple access scheme can achieve a very simple chip-by-chip iterative MUD strategy at base station, and the simplified receiving operation at UE. On the other hand, this paper also evaluates channel estimation approach for IDMA based on EM algorithm.