Simulation Research On IDMA System Based On OFDM

Multiple-access is one of the key techniques of wireless communication, and even an important sign of mobile communication generational changes. The core content is how to incise and distribute limited communication resources among multi-users, those who can share the resources without interfering one another. Along with the demands of unsymmetrical business, variable rate business and QoS, the significance of multiple-access technique is becoming higher thus draws more and more research interests. Based on Code Division Multiple Access (CDMA), Li Ping and his crew have proposed Interleave Division Multiple Access (IDMA) which distinguishes multi-users through chip level interleaving methods. This idea not only inherits many advantages from the former but also reduces complexity, is a new multiple-access method with wide foreground.OFDM, namely orthogonal frequency division multiplex, transmits information by multiple orthogonal carriers. It becomes research hotspot due to high system capacity with low ISI and narrow-band interference. OFDM is considered to be one of the core techniques of 4G mobile communication, is an ideal modulating technology which adapts to multimedia centered wireless wide-band high speed data transmission. Research on the combination of OFDM and new multiple-access methods is very significant towards future evolution of mobile communication techniques.This dissertation firstly summarizes research status of correlate techniques both domestic and overseas, and then introduces the fundamental principle and implementation of IDMA. The IDMA system model is presented with explanation for transmitter and receiver respectively. The chip-by-chip iterative multi-user detection is expatiated with emphasis on element signal estimate (ESE) algorithm and implementation. The influence of main parameters such as spreading length and iteration time to system performance are compared by simulation. On the foundation above, an OFDM based IDMA system model is constructed. The transmitter and receiver structures are introduced together with corresponding multi-user detection method. Simulation is done to investigate the bit-error-rate (BER) performance as well as a qualitative analysis to the possible cause. Later an OFDM-IDMA system associated with ARQ protocol is proposed. System performances including average transmission attempts and throughput are analyzed in theory. Simulation results show that ARQ protocol is able to improve system performances including BER, throughput and so on by means of retransmission combination.