Frequency-domain Synchronization Research Articles

Frequency-domain synchronization of structural health monitoring data

Since the advent of structural health monitoring (SHM), vibration analysis has been one of the most popular strategies for yielding modal information of structures, such as eigenfrequencies and mode shapes. As a result of the relatively high sampling rates adopted in vibration analysis, obtaining accurate modal information requires absolute synchronization of structural response data. Despite the advances in sensing technologies and synchronization protocols, synchronization discrepancies in structural response data may occur due to drifting in internal clocks of independent data acquisition units. Particularly in wireless SHM, in which each wireless sensor node essentially operates as an independent data acquisition unit, mitigating clock drifting has been an area of intensive research. This paper addresses the issue of data synchronization from a physics-based perspective, aiming to add an additional synchronization check at the post-sampling stage. Specifically, a frequency-domain synchronization approach is reported, which builds upon the relationship between time lags in structural response data and the cross spectral density phase angles. Validation tests are conducted using simulations of a multi-degree-of-freedom oscillator and data collected from a full-scale road bridge, demonstrating the capability of the approach to estimate time lags between SHM data even in the presence of non-proportional damping, thus overcoming a common limitation of other synchronization methods. The frequency-domain synchronization approach is intended to complement synchronization protocols in extracting accurate modal information.

Effective Time, Frequency, and Sidelink Synchronization for Cellular Device-to-Device Communications

This article proposes an efficient time, frequency, and sidelink synchronization algorithm for device-to-device communication in a long-term evolution system. To end this, the proposed synchronization scheme uses both the structure of cyclic prefix and sidelink synchronization signals. By performing cyclic prefix mode and primary sidelink synchronization signal detection in the time domain, the performance of the frequency-domain synchronization receiver, including carrier frequency offset and sidelink identity detection, is improved. To assess the usefulness of the proposed synchronization method, the mean square error and the detection probability are theoretically derived. Simulation results show that the proposed synchronization scheme achieves robust detection of carrier frequency offset, symbol timing offset, cyclic prefix mode, and sidelink synchronization signal in a time-frequency doubly selective fading channel.

Signal Design for Reduced Complexity and Accurate Cell Search/Synchronization in OFDM-Based Cellular Systems

This paper proposes a variant of the frequency-domain synchronization structure specified in the long-term evolution (LTE) standard. In the proposed scheme, the primary synchronization signal used in step-1 cell search is the concatenation of a Zadoff-Chu (ZC) sequence and its conjugate (as opposed to only the ZC sequence in LTE). For step-2 cell search, we propose a complex scrambling sequence requiring no descrambling and a new remapped short secondary synchronization signal that randomizes the intercell interference (as opposed to the first/second scrambling sequence and swapped short signals in LTE). Through a combination of analysis and simulation, we demonstrate that the proposed synchronization signals lead to lower searcher complexity than LTE, a lower detection error rate, a shorter mean cell search time, and immunity toward a frequency offset.

Synchronization of MIMO OFDM systems by perfect complete generalized complementary orthogonal loosely synchronous code groups

This article proposes a time/frequency synchronization algorithm in the multiple input multiple output (MIMO) systems, in which the perfect complete generalized complementary orthogonal loosely synchronous code groups are used as the synchronization sequence. The synchronization algorithm is divided into four stages: 1) synchronization in time domain by signal autocorrelation; 2) synchronization in frequency domain by fast Fourier transform (FFT); 3) multipath dissociation using coherent detection and fine time synchronization; 4) fine frequency offset estimation by phase rotation. As per the perfect complete generalized complementary orthogonal loosely synchronous code groups, the cross-correlation and out-of-phase auto-correlation for any relative shift between any two codes is always zero. This ideal property makes the time/frequency synchronization algorithm simple and efficient. The simulation results show that even in the multipath fast fading channel with low signal noise ratio (SNR), the MIMO system can get synchronized both in the time domain and frequency domain with high stability and reliability.

An algorithm for frequency-domain synchronization of the transmit-receive devices of a system with orthogonal frequency division multiplexing

The basic reasons for desynchronization of the receiving and transmitting devices of a system with orthogonal frequency division multiplexing (OFDM) are studied. An algorithm for estimation of the parameters of frequency-domain synchronization of an OFDM system is developed. The algorithm is optimal in accordance with the maximum likelihood criterion. Block diagrams of circuits for the estimation of the desynchronization parameters according to the quasi-optimal algorithm are constructed.

On the Synchronization Techniques for Wireless OFDM Systems

The latest research works on the synchronization scheme for either continuous transmission mode or burst packet transmission mode for the wireless OFDM communications are overviewed in this paper. The typical algorithms dealing with the symbol timing synchronization, the carrier frequency synchronization as well as the sampling clock synchronization are briefly introduced and analyzed. Three improved methods for the fine symbol timing synchronization in frequency domain are also proposed, with several key issues on the synchronization for the OFDM systems discussed.

Carrier Frequency Recovery Technique in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) systems are highly sensitive to carrier frequency errors. In this paper, a new method utilizing pilots to do frequency synchronization in frequency domain is proposed with large estimation range. It needs no such prerequisite assumption that a perfect symbol timing synchronization [IEEE Transactions on Communications 42 (1994) 2908; 45 (1997) 1613] has been done before performing integer carrier frequency synchronization. Also, a new adjusting model for fine carrier frequency is proposed. Simulation and performance analysis show that our overall frequency estimator has high accuracy. The corresponding FPGA circuit through test in high definition TV (HDTV) prototype in Team of Expert Engineering Group (TEEG) in China proves its availability and feasibility.

Orthogonal frequency division multiplex synchronization techniques for frequency-selective fading channels

The effect of time-domain and frequency-domain synchronization errors is quantified in the context of various coherently and noncoherently detected 1, 2, and 4 bits/symbol OFDM constellations, in order to demonstrate the wide applicability of the techniques proposed for mitigating the bit error rate (BER) performance degradations inflicted. A reference symbol is proposed and a range of correlation techniques are suggested for coarse and fine synchronization. Their performance is studied over time-dispersive Rayleigh fading channels, with the conclusion that the proposed synchronization techniques result in virtually unimpaired BERs over the range of wideband channels investigated in comparison to a perfectly synchronized system.

Prolog to adaptive multicarrier modulation: a convenient framework for time-frequency processing in wireless communications

A historical perspective of orthogonal frequency-division multiplexing (OFDM) is given with reference to its literature. Its advantages and disadvantages are reviewed, and its performance is characterized over highly dispersive channels. The effects of both time- and frequency-domain synchronization errors are quantified, and a range of solutions proposed in the recent literature are reviewed. One of the main objectives of this review is to highlight the recent thinking behind adaptive bit allocation and turbo coding in the context of OFDM. This paper concludes with a wide-ranging throughput comparison of the schemes discussed herein under the unified constraint of a fixed target bit error rate of 10/sup -4/.

Adaptive multicarrier modulation: a convenient framework for time-frequency processing in wireless communications

A historical perspective of orthogonal frequency-division multiplexing (OFDM) is given with reference to its literature. Its advantages and disadvantages are reviewed, and its performance is characterized over highly dispersive channels. The effects of both time- and frequency-domain synchronization errors are quantified, and a range of solutions proposed in the recent literature are reviewed. One of the main objectives of this review is to highlight the recent thinking behind adaptive bit allocation and turbo coding in the context of OFDM. This paper concludes with a wide-ranging throughput comparison of the schemes discussed herein under the unified constraint of a fixed target bit error rate of 10/sup -4/.