Study On The Novel Receivers For Future Mobile Communication Systems

With the development of universal mobile telecommunication systems, the number of subscribers is increasing rapidly and the service requirements are becoming diversified, which can not be satisfied by current mobile telecommunication systems. Therefore, future mobile communication systems with large system capacity and multimedia service support ability have absorbed much attention. To combat the technical obstacles, several new techniques have been innovated. In this dissertation, the focus is on the application of multiuser detection, smart antenna and Orthogonal Frequency Division Multiplexing (OFDM) techniques to the design of receivers for future mobile communication systems. The main contributions and original ideas included in the dissertation are summarized as follows.1. We investigate the problem of the design of an optimal OFDM receiver against unknown frequency selective fading. A fast convergent Monte Carlo receiver is proposed. The Markov chain Monte Carlo (MCMC) methods are employed for the approximate computation of bit posterior probability without channel estimation, which results in a substantial complexity reduction compared with the direct implementation of Bayesian symbol estimate. Moreover, no matrix inversion is needed with the use of the orthogonality of OFDM modulation and hence the computational load is again significantly reduced. Meanwhile, with the exploitation of the characteristic of OFDM systems, two methods are employed to improve the convergence rate and enhance the efficiency of MCMC algorithms. One is the integration of the posterior distribution function with respect to the associated channel parameters, which is involved in the derivation of the objective distribution function; the other is the differential coding for the elimination of the bimodality problem resulting from the presence of unknown fading channels. Thanks to the convergence acceleration tricks, the convergence rate is obviously improved and the performance approaches that of the optimal detection with unknown channel parameters.2. The multiuser detection for asynchronous DS-CDMA system with inter-cell interference and multipath fading is studied. The Gibbs sampler combined with the lineargroup-blind decorrelator is proposed as a novel nonlinear multiuser detector, which makes the Gibbs sampler applicable to the case of asynchronous CDMA systems in the presence of unknown interference and multipath fading. Furthermore, in a coded system the proposed detector is well suited for the Turbo detection. The proposed method has good near-far resistance and outperforms the linear group-blind decorrelator to a great extent.3. An OFDM receiver is designed to combat both frequency offset and cochannel interference, which involves the following two-staged procedure. First, the strong cochannel interference is effectively suppressed before frequency offset compensation. To this end, we propose to assign each user a spreading sequence in time domain and perform beamforming to suppress cochannel interference by aligning the data samples in proper order. Second, pilot symbols assisted frequency offset and channel least square estimation is achieved based on the output of the first stage. In particular, there is usually certain degradation in beamforming process due to the finite data samples, an iterative structure is used where signal waveform is reconstructed by exploiting the estimated parameters and subtracted from the beamformer input data sent to the next iteration. Simulation results show that within 2 or 3 iterations, the receiver has almost the same performance as the ideal receiver even in a heavily loaded system. The proposed receiver has a good near-far resistance and works well when the normalized frequency offset falls into the range of [-1/2,+1/2].4. The calibration of frequency response mismatch among antenna array channels is studied. A calibration method based on adaptive interference suppression is proposed, in which adaptive equalizers are employed for the compensation of channel mismatch. To mak...