To obtain the receive diversity of timing acquisition, the cooperative processing of multiple distributed received antennas is considered in this paper. In the flat Rayleigh channels, we assume two remote antennas at the base station for receiving the signal transmitted from the mobile station with a single antenna. By utilizing the coverage range of each remote antenna, a constraint is exploited to associate the time-delays from the mobile station to the two remote antennas. With this constraint, we propose a maximum likelihood-based cooperative timing acquisition method to improve the probability of correct acquisition for each remote antenna. Also, a lower bound of the probability of correct acquisition is derived to evaluate the performance of the proposed method. Compared to the independent timing acquisition, the analysis and simulations show that the probability of correct acquisition for each remote antenna can be improved by the cooperation of the two remote antennas.
[Show abstract][Hide abstract] ABSTRACT: Equipped with an adaptive beamformer, existing adaptive array code acquisition still relies on the correlator structure. Due to the inherent property of the associated serial-search scheme, its mean acquisition time is large, especially in strong interference environments. In this paper, we propose a novel adaptive filtering scheme to solve the problem. The proposed scheme comprises two adaptive filters, an adaptive spatial and an adaptive temporal filter. With a specially designed structure, the spatial filter can act as a beamformer suppressing interference, while the temporal filter can act as a code-delay estimator. A mean squared error (MSE) criterion is proposed such that these filters can be simultaneously adjusted by a stochastic gradient descent method. The performance as well as the convergence behavior of the proposed algorithm are analyzed in detail. Closed-form expressions for optimum filter weights, optimum beamformer signal-to-interference-plus-noise ratio (SINR), steady-state MSE, and mean acquisition time are derived for the additive white Gaussian noise (AWGN) channel. Computer simulations show that the mean acquisition time of the proposed algorithm is much shorter than that of the correlator-based approach, and the derived theoretical expressions are accurate.
IEEE Transactions on Signal Processing 10/2007; 55(9-55):4567 - 4580. DOI:10.1109/TSP.2007.893916 · 2.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Orthogonal frequency division multiplexing (OFDM) is a popular method for high data rate wireless transmission. Its capability of turning a frequency-selective channel into a parallel collection of frequency flat subchannels has attracted huge interest from the research community as well as the industry. Multiple input and multiple output (MIMO) configuration is also a hot topic for the merit of an increased diversity gain and/or a higher system capacity. In this contribution, a novel timing synchronization method is proposed for the distributed MIMO-OFDM configuration. The performance of this proposed scheme is evaluated by simulations. The simulation results show that the proposed method offers an accurate estimation on the different time delay caused by the distributed transmitters of the MIMO-OFDM system
Proceedings of the 63rd IEEE Vehicular Technology Conference, VTC Spring 2006, 7-10 May 2006, Melbourne, Australia; 01/2006
[Show abstract][Hide abstract] ABSTRACT: In this contribution we investigate both Differentially Coherent (DC) and Non-Coherent (NC) code acquisition schemes in the Multiple Input Multiple Output (MIMO)-aided Direct Sequence-Code Division Multiple Access (DS-CDMA) downlink, when communicating over uncorrelated Rayleigh channels. It is demonstrated that the employment of multiple transmit antennas has a detrimental impact on the achievable diversity gain at typical operational Signal-to-Interference plus Noise Ratios (SINR), as the number of transmit antennas is increased, regardless whether single-path or multi-path scenarios are considered. Our findings suggest that increasing the number of transmit antennas in a MIMO-aided CDMA system results in increasing the Mean Acquisition Time (MAT) by as much as an order of magnitude, when the SINR per chip value is relatively low. The main reasons for the performance trends are plausible, since we have to reduce each individual MIMO element's signal power for maintaining the same total power as in a single-antenna system and this will be further justified by information theoretic considerations in the NC MIMO-aided scenarios considered.
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