Study On Channel Estimation Algorithm Of Idma Systems

Interleave-division multiple-access (IDMA) is a recently proposed multiple access scheme, which employs random interleavers as the only method for user separation, different users have different interleavers. As a particular case of CDMA, it allows a low-cost Turbo-like multiuser detection (MUD) algorithm applicable to system with a large number of users, which is crucial for high-rate multiple access communication.IDMA significantly outperforms conventional CDMA in terms of spectral efficiency, maximized coding gain and simplification of receiver architecture. Thus, IDMA has been extensively studied. For instance, efficient generation method of interleavers for IDMA, analysis and optimization of IDMA performance, multicarrier IDMA systems, power allocation and so on. These discussions are all based on the assumption that the receiver has ideal channel state information (CSI). Thus, it is very important to study on the channel estimation algorithms for IDMA systems. This thesis concentrates on one of the key technologies of IDMA system, channel estimation algorithm .The main contributions of this thesis research are listed as following.(1) A new complex channel estimation approach based on the Expectation Maximization (EM) algorithm is proposed for the IDMA in this thesis firstly. The Turbo-like combination channel estimation is used in the proposed algorithm, which can get both amplitude and phase information of the complex channel. At the first iteration we use the pilot sequences to estimate the initial channel information. And the soft information from the IDMA signal detection is combined with the pilot information to refine the channel coefficients in the following estimation iterations.(2) We propose a channel estimation algorithm for the IDMA systems based on time-reverse (TR) technique, TDR-IDMA, which can accelerate the converge speed of multi-user detection (MUD) algorithm for IDMA systems. In the TDR-IDMA systems, the time-reversed version of channel impulse responses (TR-CIR) is used to perfume the pre-processing for the received signal to enhance the signal to interference and noise ratio (SINR). Therefore, we need the channel state information (CSI) from channel estimator at the receiver. The complex multi-path channel estimation based on the Expectation Maximization (EM) algorithm is proposed for the TDR-IDMA system.(3) A novel channel estimation approach based on the Evolutionary Game Algorithm (EGA) is proposed for the IDMA systems. As a stochastic optimization algorithm based on the non-cooperative games, EGA maps the search space of channel state information (CSI) and objective function of log-likelihood function to the strategy profile space and utility function of non-cooperative game respectively, and achieves the optimization objective by exploring the equilibrium points of the corresponding games.