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In this paper, a novel preamble structure, including a synchronization field (S-field) and a cell-search field (C-field), is proposed for orthogonal-frequency-division-multiplexing-based cellular systems. An efficient algorithm for downlink synchronization and cell search using the preamble is also proposed. The synchronization and cell-search process includes the initial symbol-timing estimation using continuously or, at least, periodically transmitted downlink signal, the frame detection, the fine symbol-timing estimation, the frequency-offset estimation using the preamble S-field, and the cell identification using the preamble C-field. Performance of each synchronization and cell-search step is analyzed and verified by computer simulation. The overall performance of the synchronization and cell search is then analyzed in terms of the mean acquisition time. It is shown that the proposed preamble with the corresponding synchronization and cell-search algorithm can provide a very robust synchronization and cell-search capability, even in bad cellular environments. [ABSTRACT FROM AUTHOR]

It has been well recognized that significant throughput gains can be leveraged in multiuser wireless communication systems by exploiting multiuser diversity with a smart scheduler. This scheduler collects channel state information (CSI) from all users and allocates the resources to the user(s) experiencing favorable channel conditions. However, for a frequency-division-duplex system with a large number of users, how to efficiently collect the required CSI will be a challenging task, especially when the feedback links are of limited capacity. In this paper, we propose a scheduling algorithm to exploit multiuser diversity with possibly imperfect one-bit channel state feedback. The basic idea is to define a threshold λ and let each user report one-bit information to the scheduler about the comparison between its measured channel fading level and λ. Correspondingly, the scheduler uses these feedback bits to classify all users into two sets and assigns the channel to one user belonging to the set experiencing favorable channel conditions. Several implementation schemes are developed by attacking the optimization of λ under different system configurations, covering both the case when the one-bit feedback is perfect and those when the one-bit feedback is imperfect. Computer simulations show that when the user number is large, say, more than ten users, the proposed scheduling supports significantly larger data rate over the round-robin scheduling, while in comparison with the optimum scheduling with complete CSI, the performance loss is limited if the one-bit feedback is of high reliability. In addition, our studies show that we can effectively enhance the robustness against feedback imperfectness by incorporating the feedback reliability into optimization of λ. [ABSTRACT FROM AUTHOR]