Iterative Receiver Technologies In Wireless Communication Systems

Future broadband wireless communication systems will need to use advanced technologies to effectively deal with the detrimental time dispersive mobile radio environment. Use of the "turbo" principle to iteratively decode parallel or serial concatenated error correction codes has lead to performance closely approaching Shannon's theoretical channel capacity limit. This principle has also been used to improve the reliability of communications over a multi-path channel.This thesis addresses the issue of point-to-point reliable digital communications over a channel introducing inter-symbol interference (ISI), where the data to be transmitted is protected by an error correction code. The receiver in such a communication system faces two problems: that of mitigating the effects of ISI (equalization or detection) and that of decoding. The major contribution of this work is the study of an iterative receiver approach, which efficiently solves these two problems jointly.Firstly we provide the basical introduction of wireless communication systems, and introduce the related research about turbo code and turbo equalization at present. The main work in my thesis includes:Chapter 2 is a tutorial that gives a detailed explanation of the theory of turbo code and turbo equalization. Following this, this chapter provides a theoretical foundation of the algorithms derived in later chapters. At the end of this chapter, some simulation and analysis results are given.Depending on the well understanding of the iterative receiver, In the chapter 3, we utilize extrinsic information transfer(EXIT) chart to study the convergence behavior of iterative receiver and propose a modified iterative scheme for the data transmitted by more efficient way over inter-symbol interference (ISI) channels, then compare and analyze the performance for three equalization algorithms in this scenario: improved MAX-Log-MAP (I-MLM) algorithm, maximum a posteriori (MAP) algorithm and linear minimum mean-squared error (LMMSE) algorithm, named as MI-I-MLM, MI-MAP and MI-LMMSE respectively. As the result, the performance of MI-I-MLM is very close to MI-MAP and much better than MI-LMMSE while its computational complexity is much lower.Chapter 4 provides a modified iterative equalization (MIE) scheme based on precoding. Based on the good understanding of the performance of precoding and MI-I-MLM scheme, we exploit precoding in MI-I-MLM, and then find that the performance of precoded MI-I-MLM is obviously better than that of non-precoded and can even exceed the bound of an ISI-free channel in higher SNR, while its performance is lower than the one of non-precoded in low SNR. Therefore, we propose a novel scheme to get better performance by using a mixture of precoded and non-precoded scheme. Both analytical and simulation results demonstrate that the proposed novel scheme can achieve better performance without increase in computational complexity.Because Overlapped Code Division Multiplexing technology is a high frequency spectrum efficiency technology, we introduce the principle of encoder and decoder and simulate the system performance. And then, we analyze the system model which implements the OVCDM in ISI channel. Therefore, it is clear that benefits can be achieved by exploit the overlapped code.