In OFDM systems, link performance depends heavily on the estimation of symbol-timing and frequency offsets. Performance sensitivity to these estimates is a major drawback of OFDM systems. Timing errors destroy the orthogonality of OFDM signals and lead to inter-symbol interference (ISI) and inter-carrier interference (ICI). The interference due to timing errors can be exploited as a metric for symbol-timing synchronization. In this paper, we propose a novel method to extract interference components using a DFT of the upsampled OFDM signals. Mathematical analysis and formulation are given for the dependence of interference on timing errors. From a numerical analysis, the proposed interference estimation shows robustness against channel dispersion.

In this letter, we investigate the problem of feedforward timing estimation for burst-mode satellite communications. By analyzing the correlation property of frame header (FH) acquisition in the presence of sampling offset, a novel data-aided feedforward timing estimator that utilizes the correlation peaks for interpolating the fractional timing offset is proposed. Numerical results show that even under low signal-to-noise ratio (SNR) and small rolloff factor conditions, the proposed estimator can approach the modified Cramer-Rao bound (MCRB) closely. Furthermore, this estimator only requires two samples per symbol and can be implemented with low complexity with respect to conventional data-aided estimators.

Network coding on the physical-layer has recently been widely discussed as a potentially promising solution to the wireless access problem in a relay network. However, the existing research on physical-layer network coding (PNC), usually assumes that the symbol timing of the nodes is fully synchronized and hardly investigates the unavoidable symbol timing errors. Similar to many telecommunication systems, symbol timing plays a critical role in PNC and precise alignment has to be provided for the encoding. In this work, we propose a novel symbol timing algorithm with a low oversampling factor (samples per symbol) based on the a priori knowledge of the transmitted pulse shape. The proposed algorithm has the dual advantages of the low oversampling rate and high precision. The mean square error (MSE) performance is verified by simulations to be at least one order of magnitude better than that of the conventional optimum phase (OP) algorithm for a signal noise ratio (SNR) greater than 5dB.

In this letter, we propose a simple algorithm to jointly estimate the symbol timing offset (STO) and carrier frequency offset (CFO) of wireless body area network (WBAN) signals. The preamble specified in IEEE 802.15.6 WBAN is used to achieve an accurate timing and frequency estimation based on the differential correlation. Simulations demonstrate that the proposed joint estimation scheme can be effectively employed to get accurate STO and CFO estimate with less complexity.

In this letter, we present a low-complexity residual symbol timing offset (STO) estimation scheme in a long term evolution (LTE) downlink system. The proposed scheme is designed to estimate STO without a priori knowledge of cell-specific reference signals, which reduces the arithmetic complexity while maintaining a similar performance to the conventional algorithm.

In this letter, an improved residual symbol timing offset (STO) estimation scheme is suggested in an orthogonal frequency division multiplexing (OFDM) based digital radio mondiale plus (DRM+) system with cyclic delay diversity (CDD). The robust residual STO estimator is derived by properly selecting the amount of cyclic delay and a pilot pattern in the presence of frequency selectivity. Via computer simulation, it is shown that the proposed STO estimation scheme is robust to the frequency selectivity of the channel, with a performance better than the conventional scheme.

In this letter, we propose an integer carrier frequency offset (IFO) estimator in the presence of symbol timing error for an ultra-wideband multi-band orthogonal frequency division multiplexing (UWB MB-OFDM) system. The proposed IFO estimator uses frequency-domain spreaded data symbol which is provided in the MB-OFDM system. To demonstrate the accuracy of the proposed IFO estimator, comparisons are made with conventional estimators via computer simulation.

In this letter, a concept of virtual smart antenna (SA) is introduced for OFDM-based cellular systems with a frequency reuse factor equal to 1. A method of estimating intercell symbol timing offsets (STOs) from received OFDM signals impinging on virtual antenna is proposed for users at a cell boundary. Also, adaptive beamforming methods for virtual SA are proposed to reduce intercell interference (ICI) from adjacent base stations (BSs).

A robust joint symbol timing and fractional frequency offset estimator for OFDM systems in multipath fading channels is proposed based on cyclic shifting and autocorrelation properties of PN codes. A new timing metric is also introduced by considering the delay spread to improve the robustness of the estimator in the multipath fading channels.

A flexible symbol-timing synchronization met-hod is a one that uses a common sampling clock to find synchronization points for radio communication systems that have different symbol rates. This method estimates synchronization points from state patterns calculated using the symbol rate, sampling clock, and number of observed symbols. Decreasing the number of state patterns is one of best ways to reduce the amount of device resources needed to store the patterns. In this paper, we propose a new pattern generation method in which the number of generated patterns does not increase when the sampling clocks of the communications systems are different. To show the feasibility of this method for symbol-timing synchronization, we analyzed a relationship between the number of samples and the number of state patterns and calculated the BER (bit error rate) in AWGN (additive white Gaussian noise) and one-path flat Rayleigh fading environments by computer simulation.

In this paper, a novel algorithm is presented for blind estimation of the symbol timing and frequency offset for OFDM systems. Time-varying frequency-selective Rayleigh fading multipath channel is considered, which is characterized by the power delay profile and time-varying scattering function and has high reliability for real-world mobile environment. The estimators exploit the intrinsic structures of OFDM signals and rely on the second-order moment rather than the probability distribution function of the received signals. They are totally optimum in sense of minimum mean-square-error and can be implemented easily. In addition, we have presented an improved approach which not only preserves the merits of previously proposed method, but also makes the estimation range of the frequency offset cover the entire subcarrier spacing of OFDM signals and the timing estimator be independent of the frequency offset.

We investigate the design of an interpolation filter of a multi-frequency time division multiple access (MF-TDMA) demodulator which is applied to digital video broadcasting-return channel system via satellite (DVB-RCS). We propose two interpolation filters for symbol timing recovery in a digital receiver where the input analog to digital conversion sampling clock is not synchronized to the transmitter symbol clock. The two proposed interpolation filters are designed by the least mean-square-error at the output of the receiver. Simulation results show that a performance improvement is achieved by employing the proposed interpolation filter.

In this paper, a modified Gardner's timing-error estimation algorithm is proposed for space-time block coding (STBC) schemes. In STBC schemes, the symbol timing-error can be estimated for each received antenna. The proposed algorithm is the diversity combining of all symbol timing-error estimates using Gardner's algorithm with the assumptions of identical channel delay of each SISO sub-stream. Simulation results show the proposed algorithm improves the symbol timing-error estimation performance through diversity gains. Estimation of symbol timing-error in multiple-input and multiple-output (MIMO) antenna systems is an another suitable area of application.

This paper proposes a novel synchronization method of jointly estimating symbol frame timing and carrier frequency-offset for Orthogonal Frequency Division Multiplexing (OFDM) signal operating in the burst mode which is usually employed in the wireless LAN communications systems. The proposed method enables a fast and accurate synchronization for the burst mode OFDM signal even under the presence of large frequency-offset, very low C/N and frequency selective fading environments by using only two preamble symbols inserted at the start of every burst frame. This paper presents the various computer simulation results to verify the performance of proposed synchronization methods both for symbol timing and carrier frequency.

A symbol timing synchronization method is proposed for the realization of a multi-mode and multi-service software radio receiver. The method enables an accurate search for the optimum symbol timing without any redundant hardware such as sampling rate conversion devices, when the system clock is non-integer times for the target systems' symbol rates. Accordingly, a multimode and multi-service receiver can set an arbitrary system clock for the target systems' symbol rates, and the number of A/D converters can be reduced to the minimum. Also, it may lead to a reduction of the implementation time for digital signal processing hardware, and reduce the burden on the memory in a multi-mode and multi-service software radio receiver, since no sampling rate conversion is needed. The effectiveness of the proposed method for use with a multi-mode and multi-service software radio receiver for future ITS services, which are GPS (Global Positioning System), ETC (Electric Toll Collection system), and Japanese PHS (Personal Handy-phone System) is assumed, and the supposed system is evaluated by computer simulation. The jitter performance under an AWGN (Additive White Gaussian Noise) environment is first simulated, and the necessary number of over-samples and observation symbols are defined by the value of jitter which gives a theoretical value of the BER, respectively. Moreover, the bit error rate performance under a fading environment condition where the attenuation of a signal level fluctuates more rapidly than in a noise environment is calculated, and it is shown that the proposed method enables an accurate search for the optimum synchronization timing caused by a cycle slip even if the signal level is quite low, and allows one handset to adopt a system clock for several systems.

This paper proposes a fast synchronization scheme with a short preamble signal for high data rate wireless LAN systems using orthogonal frequency division multiplexing (OFDM). The proposed OFDM burst format for fast synchronization and the demodulator for the proposed OFDM burst format are described. The demodulator, which offers automatic frequency control and symbol timing detection, enables us to shorten the preamble length to one quarter that of a conventional one. Computer simulation results show that the degradation in required Eb/N0 due to the synchronization scheme is less than 1 dB in a selective Rayleigh fading channel.