A novel sampling synchronization scheme for OFDM-based system with unified reference clock
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RESEARCH
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A novel sampling synchronization scheme for OFDM-based system with unified reference clock Zhuo Sun*, Tao Peng and Wenbo Wang
Abstract Due to the constraint of cost and size for mobile wireless communication terminals, many orthogonal frequency division multiplexing (OFDM)-based systems required the same crystal driving the sampling and the channel frequencies, which leads to the challenge of a more comprehensive sampling clock synchronization scheme needed. In this article, the effect of sampling clock error on the system performance was analyzed by dividing it into sampling clock frequency offset (SFO) and sampling timing error (STE) firstly. After that, we proposed a two-stage scheme of sampling clock synchronization based on theoretical derivation: the preliminary SFO was jointly acquired with the carrier frequency offset by using the improved preamble-aided algorithm firstly, the timing drift resulted from residual SFO and STE was tracked based on a phase looped lock in the second stage. The deviation properties of the estimation were achieved theoretically, which reveals that both the estimating variances of SFO and timing drift are in inverse proportion to signal-to-noise ratio and grow linearly by the number of total subcarrier. The results of the simulation show that the proposed synchronization scheme can introduce preferable tracking and robust synchronizing performance for this kind of OFDM-based system. Keywords: System synchronization, Sampling clock error, Joint estimation, PLL, Timing drift
1. Introduction Underwater acoustic channels are characterized by severe bandwidth limitations, long inter-symbol interference (ISI) spans, and large Doppler spreads, which lead to significant challengers for reliable communications. Owning to the advantages of high spectral efficiency and robustness against channel fading, orthogonal frequency division multiplexing (OFDM) has been applied in modern communication system extensively such as WLAN, WiMAX, LTE, and DVB-T. OFDM is also a good alternative transmission scheme for underwater communication that both remedies the problem of ISI and provides low complexity solutions. However, OFDM is sensitive to inter-carrier interference (ICI) caused by channel variations. Underwater channels vary fast due to the large ratio of the platform motion relative to the sound propagation speed. Even with stationary transmitters and receivers, significant ICI could still exist due to wave action and water motion. One of the solutions for eliminating ICI is to estimate and correct * Correspondence: [email protected] Key Laboratory of Universal Wireless Communications, Ministry of Education, Beijing University of Posts & Telecommunications, Beijing, China
the frequency shift adaptively in the synchronization procedure. Therefore, the synchronization scheme for OFDM system used in underwater communications is a critical issue [1]. The sampling clock synchronization in an OFDM system is to mitigate the sampling clock errors due to the mismatch of the cryst
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