Synchronization & Channel Estimation Algorithms For Broadband Wireless Communication Systems

The future broadband wireless communication systems are expected to provide ubiquitous, high-reliability, and high-data-rate mobile multimedia transmission. Orthogonal frequency division multiplexing (OFDM), single carrier frequency domain equalization (SC-FDE) and multiple antennas technique are efficient techniques to achieve this goal. The estimation of the synchronization and channel parameters with multipath fading is a crucial task in broadband wireless comunication systems. With the development of the integrate circuit technique, the ability of processing of the chips are improved rapidly and some complicate algorithms can be implemented online. As a result, more high-performance algorithms with appropriate complexity can be pursued. In the future broadband wireless communication systems, it is hope that the parametrizaed solutions yield optimal or close to optimal performance in different radio conditions. From the point of view of the optimization of entire systems, the correlated parameters should be estimated jointly. Furthermore, the limiting performance of estimation in various environments is also the important issue which need be addressed in broadband wireless communications. This dissertation is devoted to the design and analysis of timing synchronization, carrier frequency offset (CFO) and channel parameter estimation algorithms in broadband wireless communications. The main contributions of the dissertation are as follows:A propagator based closed-form blind CFO estimation algorithm for OFDM systems is proposed. This method utilizes the propagator obtained from data matrix and the diagonal loading technique to make it possible to have better performance even if only using one or two OFDM blocks. Furthermore, the range of the CFO estimation which can be handled is overall transmission spectral. Simulation results show that the performance of proposed algorithm is better than that of ESPRIT-like algorithm in the case of small samples.We present a maximum likelihood (ML) based cost function which can estimate timing, CFO and channel jointly for OFDM systems and derive three estimation algorithms in different cases from it. The algorithms are based on pilot subcarriers. First, joint IFO, timing and channel estimation is considered. Both the IFO and the timing offset can be obtained by using the fast fourier transform (FFT) and one-dimension (1-D) search and the channel estimation is followed. In the case of unknown channel order (UCO), we replace the channel order by the length of cyclicprefix (CP). The simulation results show that the replacement of channel order by the length of CP leads to the negligible loss in terms of the word error rate (WER) of systems. Secondly, we simplified the algorithm when there is no CFO. This leads to a novel timing estimation algorithm in multipath fading. In the case of UCO, we employ the zero-padding (ZP) in the front of OFDM symbol to eliminate the wide plateau caused by replacement of channel order. Finally, we design the pilot as two identical halves in time domain and abtain a joint FFO and timing estimation algorithm. We find that the essential of FFO estimation of Schmidl & Cox algorithm (SCA) is ML estimation. Computer simulations show that the estimation performance of the proposed algorithms outperforms some others.A maximum likelihood (ML) based algorithm is proposed to jointly estimate the frequency-selective channels and the CFO in MIMO-OFDM by using pilot subcarriers. The proposed algorithm is capable of dealing with the CFO range overall transmission spectral. Furthermore, we present a scheme for tracking the CFO and channel parameters in time-vary channel by exploiting the finite alphabet (FA) property of the transmitted symbols. The cases with timing error and unknown channel order are also discussed. The Cramer-Rao Lower Bound (CRLB) for the problem is developed to evaluate the performance of the algorithm. Computer simulations show that the proposed algorithm can exploit the gain from multi-antenna to improve effectively the estimation performance and achieve the CRLB in high signal-noise ratio (SNR). The proposed tracking method has also high tracking performance in typical urban channel model.Subspace-based channel estimation methods for ZP-SC-FDE systems by exploiting the zero-padding are developed. The methods can estimate frequency-selective channel blindly by exploiting the zero-padding. Sufficient condition for identifiability is presented. The estimation algorithms in frequency domain and time domain are presented respectively and the equivalence of two algorithms is also proved. The performance of the method is better than that of conventional oversampling methods, and it is robust to over-estimated channel order.We develop the CRLB of CFO in smart antenna systems and analyze the contributions of the numbers of both the array elements and pilot symbols for pilot-assisted CFO estimation quantitatively. A new algorithm for pilot-assisted CFO estimation in the presence of co-channel interference (CCI) is presented with the help of adaptive array weighted structure. However, neither adaptive weight nor array manifold was needed in the final algorithm. Furthermore, computer simulations showthat the proposed algorithm can fully exploit the gains from elements and pilots and reject the effect of CCI effectively...