Research On Transmission And Detection Technology For TDR-IDMA Signal

Multiple access technique is one of the key techniques in cellular mobile communication systems,especially in personal communication systems.Theoretical research and practical experience show that code-division multiple-access (CDMA) systems based on non-orthogonal temporal or spectral resource have a higher spectral efficiency than time-division multiple-access (TDMA) systems based on orthogonal time-division or frequency-division multiple-access (FDMA) systems based on orthogonal frequency-division.Therefore, CDMA has been the key techniques in the third generation mobile communication system (3G), and has comprehensive applications in 3G systems.However, the capacity of CDMA systems is not maximized due to multiple access interference (MAI) in practical applications.MAI becomes severer with the increase of users.This affects the increase of capacity and spectral efficiency in 3G or future mobile communication systems.For addressing the complexity of multi-user detection (MUD) in CDMA systems, Prof. Liping proposes interleave-division multiple-access (IDMA).IDMA relies on interleaving as the only means to distinguish the signals from different users, different users have different interleavers. Thus the chip among the outputs of interleaver is approximately uncorrelated. This is the key of IDMA and this enables us to employ a very simple chip-by-chip (CBC) iterative MUD strategy in IDMA.IDMA is a new multiple access technique. IDMA has become one of the candidates for the air interface of fourth generation (4G) mobile communication systems due to its particular advantages.IDMA has attracted wide research attentions in China and abroad.The research shows that the iterative MUD algorithm in IDMA systems is much simpler than that used in traditional CDMA systems.Unfortunately, the convergence speed is very slow for the iterative MUD in IDMA systems and this directly affects the data transfer. The future mobile communication systems need high data rate.It is imperative for IDMA to enhance the convergence speed of iterative MUD.Interleaver is the only means to distinguish the signals from different users.According to the symmetrical feature between uplink and downlink, the processing method of uplink is directly used in downlink. This is feasible theoretically, but it is not optimal in practical. It does not meet the needs in system privacy, security, and economic costs for the receiver of downlink.For addressing above-mentioned problems, in this thesis,we propose a new transmission and receiving scheme for IDMA systems based on time-division duplexing (TDD) and time-reversal (TR) technique.We refer this system as time-division duplexing and time-reversal IDMA (TDR-IDMA).Our main contributions in this thesis research are as follows.1.According to the principle that the convergence of iterative MUD for IDMA degrades with the increase of user, we propose an efficient iterative MUD for IDMA systems based on TR technique. In this system, the time-reversed version of the channel impulse responses (TR-CIR) obtained from the uplink by TDD mode is used to process the received signal in the receiver at base station. By exploiting the weak correlations of channel impulse responses (CIR) for different users and multi-path, the signal to interference and noise ratio (SINR) at the beginning of turbo-like detection of IDMA becomes significantly higher than that of the traditional IDMA.As a result, considerably less number of iterations is needed for convergence in the proposed IDMA as compared with traditional IDMA.Our proposed technique effectively breaks the bottleneck of iterative MUD in IDMA receiver.2.To address the high complexity of user end receiver in IDMA,in this thesis,we propose a downlink transmission and receiving scheme for IDMA system based on time-division duplexing mode and time-reversal technique.The proposed scheme uses the time-reversed version of the channel impulse responses obtained from the uplink to pre-process the transmitted signal at base station. By exploiting the weak correlations of fading channels for different user ends (UEs),the spatial and temporal focusing of TR, as well as the multiple input-single output (MISO)configuration, it is helpful to alleviate the MAI, co-channel interference (CCI), and mitigate inter-symbol interference (ISI).It needs a simple one-finger receiver used at the UE.The UE can be simplified by canceling the iteration operation and removing the channel estimator from the receiver of UE to the receiver of the base station. Thus the data detection of the proposed scheme is rather simpler as compared with the traditional IDMA.In this thesis,we also propose a hybrid multiple access scheme which combines IDMA and CDMA to simplify the complexity of user end receiver. We employ IDMA technique as the uplink transmission and IDMA/CDMA technique for the downlink-transmission.For suppressing multiple user interference (MUI) in the downlink, the IDMA/CDMA hybrid scheme can cope with this issue with orthogonal spreading sequence as same as traditional CDMA systems.Thus iteration free receiving can be achieved at UEs.In the proposed scheme, random interleavers are used to distinguish different users in the downlink too.Each UE only requires the interleaver parameter and orthogonal sequences, which belongs to itself. The complexity of UEs in the proposed scheme is the same with that of the traditional CDMA systems.Thus the proposed scheme can share the advantage of IDMA and CDMA simultaneously.3.To resolve the high complexity of precoder in single-carrier IDMA frequency domain equalization (FDE), in this thesis,we propose a transmission and receiving algorithm for single-carrier IDMA system based on time reversal precoder and iterative LMMSE frequency domain equalization. That is transmission and receiving algorithm of single-carrier TDR-IDMA frequency domain equalization.Thus the complexity of transmitter is reduced and easy to implement. Finally, we give the performance comparison and analysis of single-carrier TDR-IDMA,single-carrier IDMA with water-filling precoder, single-carrier IDMA with optimal precoder, single-earrier IDMA with Proakis B channel based on iterative LMMSE frequency domain equalization algorithm.4.By exploiting the advantages of MUD in IDMA systems and Expectation Maximization (EM) algorithm, in this thesis,we develop a channel estimation approach for IDMA systems based on EM algorithm. The detection and evaluation algorithm of IDMA systems are also studied when there is the effect of channel estimation error. We design the method of overcoming the channel estimation error through the theoretic analysis of the effect of channel estimation error.