Residual Synchronization Errors Research Articles

Quantification and mitigation of the effect of resynchronization errors in ultrasound sensor network for passive imaging in elastic plates.

The problem of signal desynchronization in passive imaging based on noise correlation for defect detection in elastic plates is investigated. Although a post-processing resynchronization process relying on the symmetry of noise correlation functions can be applied prior to the imaging algorithm, perfect synchronization might not be achieved experimentally. Effect of such residual synchronization errors on the defect detection performance is quantified as a function of their probability density function. A mathematical regularization process is then proposed to reduce the standard deviation of the resynchronization errors by a factor of N-1/N (N is the number of sensors), which results in a significant improvement in the detection performance. Finally, these theoretical results are validated through a simple flexural-wave propagation simulation.

Performance improvement of coherent optical chaos communication using probabilistic shaping.

We numerically investigate the effects of probabilistic shaping on the performance improvement of coherent optical chaos communication. Results show that the decryption bit-error ratio (BER) of the 16-ary quadrature amplitude modulation (QAM) signal decreases upon increasing the probabilistic shaping factor. It is predicted that the BER of 10-GBd 16QAM can be decreased by one order of magnitude. On the other hand, for the forward error correction threshold of the BER, the requirement for synchronization quality is no longer strict for successful decryption. This means that probabilistic shaping improves the system's tolerance to residual synchronization error. Thus, the transmission rate can be increased by approximately 30∼60%. The side effect of probabilistic shaping is that the valid masking coefficient range is narrowed.

Quantized control for finite-time synchronization of delayed fractional-order memristive neural networks: The Gronwall inequality approach

This paper is concerned with the finite-time synchronization (FTS) of delayed fractional-order memristive neural networks (FMNNs) by using quantized control. Firstly, two kinds of quantized controllers are designed to eliminate the residual synchronization errors that appear owing to the characteristics of memristive connection weights. Then, to derive α-dependent FTS criteria for drive–response FMNNs, the Gronwall inequality technique is used by combination with the direct estimation method. Compared with the existing results, the advantages of the derived synchronization criteria are discussed from the aspects of both theory and simulation. In addition, the relationships between the finite-time parameter and the quantization parameters are displayed. It reveals that there is a compromise between the admissible finite-time and the saved network bandwidth. Finally, two examples are given to illustrate the effectiveness of the obtained results.

Time Domain Channel Estimation and Equalization of CP-OTFS Under Multiple Fractional Dopplers and Residual Synchronization Errors

In the last few years, orthogonal time frequency space (OTFS) modulation has received significant attention as an alternative to OFDM especially for high mobilty scenarios. In this work, we develop a delay-Doppler domain embedded pilot based time domain channel estimation for cyclic prefix (CP)-OTFS in the presence of residual frame timing offset, carrier frequency offset and fractional multiple Doppler. One of the reasons for time domain processing is that the time domain channel representation is relatively more sparse as compared to its delay Doppler domain representation in the presence of residual synchronization errors. We also describe a time domain low complexity linear minimum mean square error (MMSE) equalization and successive interference cancellation (SIC) receiver for LDPC (low density parity check) coded CP-OTFS in this work. We further show the impact of residual frame timing offset, carrier frequency offset and fractional multiple Doppler on OTFS symbols. It is seen from the extensive Monte Carlo simulation results that the estimation and compensation methods presented here provide necessary resilience properties to OTFS. We bring out the tolerance of OTFS to such residual synchronization errors. It is further observed that the SIC is able to improve the performance of the system such that it almost matches that of the ideal knowledge based MMSE equalization. We also show the performance of RCP (reduced CP)-OTFS when used with the developed channel estimation and equalization algorithms. A unified signal processing flow for OTFS and orthogonal frequency division multiplexing (OFDM) is also described in this work to motivate studies on coexistence between the two as well as to encourage investigations on a seamless transition between OFDM and OTFS based systems for future adaptive air interface design.

Channel Estimation on Individual Subcarrier Using Image Processing in Optical OFDM System

In an optical orthogonal frequency division multiplexing (OFDM) system, channel impairments, such as residual chromatic dispersion, residual synchronization error, and clock frequency offset, induce phase shifts over subcarriers. We propose a method of using image processing for phase channel estimation with negligible overhead, which is applicable to various subcarrier modulation formats. We conduct the experiment of 32-, 40-, and 48-Gbit/s direct detection optical OFDM with 16QAM, 32QAM, and 64QAM subcarrier modulation and simulation of 112-Gb/s coherent optical OFDM to verify this method and compare the results with those of the conventional method. Then, we investigate the effects of the numbers of required test phases and OFDM symbols with experimental data. We also present an approach of removing the inner part of constellation points to reduce the complexity.

Achieving Centimeter Accuracy Indoor Localization on WiFi Platforms: An Multi-Antenna Approach

Channel frequency response (CFR) is a fine-grained location-specific information in WiFi systems that can be utilized in indoor positioning systems (IPSs). However, CFR-based IPSs can hardly achieve an accuracy at the centimeter level due to the limited bandwidth in WiFi systems. To achieve such accuracy using WiFi devices, we propose an IPS that fully harnesses the spatial diversity in multiple-input-multiple-output WiFi systems, which leads to a much larger effective bandwidth than the bandwidth of a WiFi channel. The proposed IPS obtains CFRs associated with locations-of-interest on multiple antenna links during the training phase. In the positioning phase, the IPS captures instantaneous CFRs from a location to be estimated and compares it with the CFRs acquired in the training phase via the time-reversal resonating strength with residual synchronization errors compensated. Extensive experiment results in an office environment with a measurement resolution of 5 cm demonstrate that, with a single pair of WiFi devices and an effective bandwidth of 321 MHz, the proposed IPS achieves detection rates of 99.91% and 100% with false alarm rates of 1.81% and 1.65% under the line-of-sight (LOS) and non-LOS (NLOS) scenarios, respectively. Meanwhile, the proposed IPS is robust against environment dynamics. Moreover, experiment results with a measurement resolution of 0.5 cm demonstrate a localization accuracy of 1-2 cm in the NLOS scenario.

An adaptive scheme for chaotic synchronization in the presence of uncertain parameter and disturbances

Recently, several schemes have been proposed in the literature to synchronize chaotic systems. However, in most of these approaches, the presence of uncertain parameters and external disturbances were not considered. Motivated by the above consideration, this paper proposes an adaptive methodology to synchronize any chaotic system with unified chaotic systems, even if bounded disturbances are present. The proposed controller is composed of both variable proportional and adaptive control actions for guaranteeing the convergence of the residual synchronization error to zero in the presence of disturbances. Two possible modifications are considered: 1) only adaptive control action is implemented to overcome the well-known assumption of prior knowledge of upper bounds to compensate for the disturbances, and 2) the control gain of the proportional part is saturated, when the residual synchronization error has, practically, been removed. Lyapunov theory, in combination with Barbalat׳s Lemma, is used to design the proposed controller. Experimental simulations are provided to show the effectiveness of the proposed controller and its advantages, when compared with a recent work in the literature.

A Composite PN-Correlation Based Synchronizer for TDS-OFDM Receiver

In this paper, we presents a novel synchronizer dealing with carrier frequency offset (CFO), sampling frequency offset (SFO), as well as frame timing offset (FTO) in TDS-OFDM receiver. The proposed schemes are based on tracking the output waveform of a composite PN-correlator (CPC), which provides sufficient correlative gains to detect its peaks even in the presence of large CFOs. From the correlation peaks, we can extract useful information for estimating the synchronization offsets. CFO is recovered by a multi-stage CPC scheme, of which the parameters are adjustable for meeting the system's demands on the tracking range and accuracy. According to the inter-frame variations of correlation waveform, we estimate SFO for a large scale and correct SFO through an interpolator. Meanwhile, frame timing is investigated in this paper, and the analysis indicates a very fast and robust timing scheme is possible for TDS-OFDM receiver. The developed synchronizer is quite robust against a large CFO even in very adverse fading channels, and it is shown by computer simulation that the residual synchronization error has little effect on the performance of TDS-OFDM receiver.

Cost-effective residual frame synchronization error cancellation for comb-type pilot-aided OFDM systems

A lot of conventional algorithms have tried to cancel the residual frame synchronization error (RFSE), which causes the performance degradation of channel estimation when using interpolation between pilot sub-carriers in comb-type pilot-aided OFDM systems. Among them, a tracking method has been attractive to provide good performance by eliminating the effects of RFSE. However, it requires high computational complexity because of its compensation process including many complex multiplications. In this paper, we propose a new method which significantly reduces computational costs by adjusting the starting point of FFT window in order to compensate for the RFSE. For the performance verification, we apply the proposed method to the IEEE 802.16e mobile WiMAX system and estimate its computational power compared to the tracking method. Simulation and implementation results show that the proposed algorithm has the performance similar to the tracking method and is very efficient for low power implementation in comb-type pilot-aided OFDM systems because it consumes only 40.5% of the tracking method's power.

PARTIAL SYNCHRONIZATION IN OSCILLATOR ARRAYS WITH ASYMMETRIC COUPLING

A new form of cluster synchronization is explored in cellular arrays of chaotic oscillators. Previously, it was shown in the literature that symmetries of the coupling topology with uniform interaction weights lead to several coexisting clusters of synchronized cells. In this study a new phenomenon is presented where highly asymmetric interaction weights can give rise to cluster synchronization regimes with partial synchronization. In addition, cluster or partial synchronization regimes corresponding to asymmetric interaction patterns can break the underlying symmetries of the network topology and boundary conditions at the expense of some residual synchronization error.

Residual Synchronization Error Elimination in OFDM Baseband Receivers

It is well known that an OFDM receiver is vulnerable to synchronization errors. Despite fine estimations used in the initial acquisition, there are still residual synchronization errors. Though these errors are very small, they severely degrade the bit error rate (BER) performance. In this paper, we propose a residual error elimination scheme for the digital OFDM baseband receiver aiming to improve the overall BER performance. Three improvements on existing schemes are made: a pilot-aided recursive algorithm for joint estimation of the residual carrier frequency and sampling time offsets; a delay-based timing error correction technique, which smoothly adjusts the incoming data stream without resampling disturbance; and a decision-directed channel gain update algorithm based on recursive least-squares criterion, which offers faster convergence and smaller error than the least-mean-squares algorithms. Simulation results show that the proposed scheme works well in the multipath channel, and its performance is close to that of an OFDM system with perfect synchronization parameters.

Ser performance evaluation and optimization of ofdm system with residual frequency and timing offsets from imperfect synchronization

This paper deals with the effects of residual timing and frequency offsets on the symbol error rate (SER) performance of an orthogonal frequency division multiplexing (OFDM) system. The synchronization of an OFDM system generally consists of a coarse frequency and timing acquisition stage and a refine stage. Due to the presence of Gaussian noise, channel distortions and implementation losses of synchronization and equalization algorithms, residual frequency and timing offsets always exist for an OFDM receiver. The residual frequency and timing offsets are proven to be Gaussian distributed, with their corresponding variances determined. The reception process of an OFDM signal with frequency and timing offsets is analyzed. A closed-form analytical result on the SER of an OFDM system with residual synchronization errors is derived. Computer simulations and analyses show that the frequency and timing offsets affect the OFDM subcarriers differently. With this observation, a new technique is proposed to minimize the SER of the OFDM systems by adjusting the distribution of transmission power among the subcarriers.

Getting synchronized with the metronome: Comparisons between phase and period correction

Most studies of synchronization have focused on how an established phase relationship between self-produced events (e.g., finger taps) and the clicks of a metronome is maintained when the metronome is regular or subject to unpredictable perturbations. Here we study how synchronization is initially established, using an experimental paradigm in which the metronome is activated after the subject has executed a series of self-paced finger taps. In Exp. 1, the metronome period was constant and equal to the mean of the self-paced inter-response intervals, whereas the initial phase difference of the metronome from the taps varied across trials. The synchronization error patterns could be predicted by a linear phase correction model. Experiment 2 involved both period and phase correction. The initial phase difference was constant, whereas the metronome period varied across trials. The observed synchronization error patterns suggest that the subjects achieved synchronization either by reacting to the second metronome signal or by aiming at the third metronome signal. The pattern of the residual synchronization errors was consistent with the linear phase correction model. These results support the notion that period and phase correction mechanisms are called for by different task variables and contribute differently to sensorimotor synchronization.