Large Estimation Range Research Articles

A Background Correlation-Based Timing Skew Estimation Method for Time-Interleaved ADCs

This paper presents a correlation-based all-digital background estimation method for timing skew mismatches in time-interleaved analog-to-digital converters (TI-ADCs). Exploiting the first-order approximation of an autocorrelation function of the digital output of each Sub-ADC, the timing skew mismatch between adjacent channels is identified, which can be used for analog or digital correction methods. The proposed estimation method has a low computation complexity and a simple implementation structure, because it basically only requires multiply-accumulate and average operations. In addition, the proposed method is not limited in the number of channels, does not need any pilot injection, is basically suitable for any bandlimited analog input signal, possess a large estimation range of mismatches and is immune against gain and offset mismatches to a certain extent. Simulation results of a four-channel TI-ADC behavioral model and measurement results from a commercial 12-bit 3.6-GS/s TI-ADC show the effectiveness and superiority of the proposed estimation method.

Data-Aided Frequency Offset Estimation for CE-OFDM Broadband Satellite Systems

In recent years, the constant-envelope orthogonal frequency-division multiplexing (CE-OFDM) has been considered as a candidate waveform in broadband satellite systems as it has a 0-dB peak-to-average power ratio (PAPR). However, the carrier frequency offset (CFO) estimation scheme for CE-OFDM broadband satellite systems directly affects system performance. In this paper, we analyze the network architecture and the propagation environment of CE-OFDM broadband satellite systems, and we propose a data-aided CFO estimation strategy based on the frequency domain pilot symbols. The Cramer–Rao bound (CRB) of our CFO estimator is given by mathematical analysis, and the effect of the number of pilot symbols on the estimation performance is analyzed. The pilot symbol-based CFO estimator is composed of a phase demodulator and a discrete Fourier transform (DFT) module, and it can obtain a large estimation range under a small pilot overhead. The simulation results show that the CE-OFDM broadband satellite systems can achieve a good bit error rate (BER) performance by using the proposed strategy to estimate and compensate the CFO.

Carrier Frequency Offset Estimation for BPSK Signals in Coherent Optical Communications

In this paper, a algorithm which is used for carrier frequency offset (CFO) estimation is proposed in coherent optical communications system with binary phase-shift keying (BPSK) modulation. The proposed algorithm utilizes the frequency divider to broaden the range of the estimation algorithm. In a 5-GBaud coherent BPSK system, simulation results show that when 12dB signal-to-noise ratio (SNR) and 512 samples are utilized, a 8 frequency divider can expand the range of the frequency offset estimation from [-0.5GHz, +0.5GHz] to [-4GHz, +4GHz] and the CFO estimation error can be obtained less than 5MHz. The paper presents a novel algorithm that features the large estimation range for carrier frequency offset while estimation error is not enlarged. The experimental results verified the effectiveness of the proposed algorithm.

A novel joint timing/frequency synchronization scheme based on Radon–Wigner transform of LFM signals in CO-OFDM systems

A joint timing and frequency synchronization method has been proposed for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) system in this paper. The timing offset (TO), integer frequency offset (FO) and the fractional FO can be realized by only one training symbol, which consists of two linear frequency modulation (LFM) signals with opposite chirp rates. By detecting the peak of LFM signals after Radon–Wigner transform (RWT), the TO and the integer FO can be estimated at the same time, moreover, the fractional FO can be acquired correspondingly through the self-correlation characteristic of the same training symbol. Simulation results show that the proposed method can give a more accurate TO estimation than the existing methods, especially at poor OSNR conditions; for the FO estimation, both the fractional and the integer FO can be estimated through the proposed training symbol with no extra overhead, a more accurate estimation and a large FO estimation range of [−5 GHz, 5GHz] can be acquired.

Joint CFO and SFO Estimator for OFDM Receiver Using Common Reference Frequency

In this paper, we propose a maximum likelihood method for jointly estimating carrier frequency offset (CFO) and sampling frequency offset (SFO) in receivers for orthogonal frequency division multiplexing signals. The proposed estimator exploits the fact that a single source (such as a crystal oscillator or voltage controlled oscillator) is typically used in modern wireless receivers to provide a reference frequency for both the sampling clock and the radio frequency synthesizers. The proposed CFO estimator is capable of a large CFO estimation range (i.e., more than half of intercarrier spacing) without extending the length of the training sequence. The Cramer–Rao lower bound (CRLB) of the variance of the estimated joint CFO and SFO is derived and compared to the CRLBs of the CFO and SFO estimators in the literature. More importantly, the proposed method is validated on a real-time wireless test bed.

Limiting Self-Propagating Malware Based On Connection Failure Behavior Through Hyper-Compact Estimators

Self-propagating malware (e.g., an Internet worm) exploits security loopholes in software to infect servers and then use them to scan the Internet for more vulnerable servers. While the mechanisms of worm infection and their propagation models are well understood, defense against worms remains an open problem. One branch of defense research investigates the behavioral difference between worm-infected hosts and normal hosts to set them apart. One particular observation is that a worm-infected host, which scans the Internet with randomly selected addresses, has a much higher connection-failure rate than a normal host. Rate-limit algorithms have been proposed to control the spread of worms by traffic shaping based on connection failure rate. However, these rate-limit algorithms can work properly only if it is possible to measure failure rates of individual hosts efficiently and accurately. This paper points out a serious problem in the prior method. To address this problem, we first propose a solution based on a highly efficient double-bitmap data structure, which places only a small memory footprint on the routers, while providing good measurement of connection failure rates whose accuracy can be tuned by system parameters. Furthermore, we propose another solution based on shared register array data structure, achieving better memory efficiency and much larger estimation range than our double-bitmap solution.

The New Mathematical Model of Motion Compensation for Stepped-Frequency Radar Signal

When a stepped-frequency radar is used to obtain the high-resolution range profile (HRRP) of high-speed target, accurate speed estimation and motion compensation must be considered. Therefore, in this paper, a novel mathematical method is presented for estimating the target speed. Firstly, the pulse Doppler method is used to calculate the initial estimation value. Secondly, based on the initial estimation value, the minimum entropy method is used to calculate the coarse estimation value. Finally, based on the coarse estimation value, the minimuml1-Norms method is used to calculate the accurate estimation value. The numeric simulation results confirm that this new method is effective and predominant, which has a much higher estimation accuracy in a low SNR and a much larger estimation range of target speed. The final estimation value can be used to well compensate for the influence of target speed on HRRP.

Data-Aided Parameters Estimation of Satellite-Based AIS Signals

Aiming at the problem of poor accuracy and small range of frequency estimation in the area of satellite-based AIS signals, this paper presents a novel data-aided estimation method based on the autocorrelation and DFT. The algorithm determines the principal value and the expansion of the frequency and then acquires high-precision estimation by data fitting. Based on that, other parameters can be estimated. Computer simulations were used to illustrate better estimation accuracy and a large estimation range.

A Novel Non-Data-Aided Frequency Estimation Algorithm for M-PSK Signals

This paper deals with the problem of carrier frequency estimation for MPSK symbols. We present a novel non-data-aided method by introducing a step factor into an earlier estimation algorithm to reduce the computational complexity with little loss of the estimation accuracy. We also make some comparisons with earlier algorithms. From the results of simulations, we make the conclusion that the new method can separate the estimation range and the estimation accuracy, and avoid the weakness of reaching large estimation range at the expense of estimation accuracy.

Improved Code-Aided Symbol Timing Recovery with Large Estimation Range for LDPC-Coded Systems

We present an improved code-aided symbol timing recovery method for low-density parity-check (LDPC) coded systems, which comprises two supporting algorithms: 1) a coarse estimation by utilizing a cost function, the mean absolute value of soft output of the LDPC decoder and 2) a fine estimation based on the Expectation-Maximization (EM) algorithm with a simple maximization step. With low computational complexity, this proposed algorithm can achieve symbol timing recovery at low signal-to-noise ratio (SNR) with large estimation range, eliminating the biased results of many algorithms for large timing offset values. Simulation results for the case of 8-PSK system with (1944,972) LDPC code show that the root-mean-square-error (RMSE) performance of the proposed algorithm approaches the modified Cramer-Rao lower bound (MCRB) at Eb/No=4dB, and the bit-error-rate (BER) curve is very close to that of ideal synchronization.

An improved algorithm for blind carrier frequency estimation with burst MPSK transmissions

This paper presents an improved non-data-aided algorithm for carrier frequency estimation for burst M-ary PSK signals when modulation order M and training symbols are unknown. Unlike data-aided estimation, a phase clustering algorithm is used first to estimate M and modulated information is removed by a variable interval linear phase unwrapping. Then, a high-order correlation algorithm with proper correction is present, which reduces the probability of phase ambiguity and promotes anti-noise capability of the estimation. Simulations are given to analyze the unbiased estimation range, and the asymptotic performance and symbol number are needed to compare with the former algorithms. The new algorithm has a large estimation range close to the theoretical maximum value for non-data-aided estimation and has a better performance than earlier non-data-aided techniques for large frequency offset, low signal-to-noise ratio, and limited symbol numbers.

A Simplified Carrier Frequency Offset Estimation Algorithm for Burst Digital Transmission

In this letter, we present a carrier frequency offset estimation method for burst digital transmission, by introducing a step factor into an earlier estimation algorithm to reduce the computational complexity, with little loss of the estimation accuracy. Performance simulations show that this method can separate the estimation range and accuracy, avoiding the weakness of reaching large estimation range at the expense of estimation accuracy.

A novel Timing and Frequency Synchronization Technology for OFDM System

Due to its high spectrum efficiency and good ability in coping with multi-path fading, orthogonal frequency division multiplexing (OFDM) technology has attracted considerable attention from researchers. However, OFDM system is very sensitive to symbol timing offset and carrier frequency offset, so accurate timing synchronization and frequency synchronization are necessary to OFDM system. This paper discusses on OFDM synchronization technology based on training symbol. OFDM synchronization algorithms based on training symbol are investigated, and two algorithms are proposed. An improved algorithm is proposed aimed at resolving training symbol redundancy and timing metric plateau in Schmidl algorithm. The training symbol in this algorithm is conjugated symmetrical and repeated. The timing metric has a sharp peak and eliminates the plateau. Both integral and fractional frequency offset estimation employ the same training symbol, and therefore the system overhead is saved and the complexity is degraded. The second algorithm proposed in this paper does not just improve symbol timing method or frequency offset estimation method. It is a complete set of solution project of OFDM synchronization. A new training symbol with special structure is designed, and a new joint symbol timing and frequency synchronization algorithm is presented based on this symbol. New frequency offset estimation algorithms are characteristic of large estimation range and high accuracy. At the same time, timing synchronization can produce a sharp peak, through which we can find where the OFDM symbol starts. The simulation results show that the performance of the synchronization algorithms proposed here is better than that of conventional methods.

A Blind Estimation Algorithm of Synchronization Parameter for OFDM Signals Based on Auto-correlation Matrix

An algorithm using auto-correlation matrix of received data for OFDM timing and carrier frequency offset estimation is presented in this paper. The algorithm does not need training data. Fractional frequency offset tracking and frame synchronization are implemented by minimizing the modular sum of off-diagonal elements and diagonal elements whose position is corresponding to virtual carrier’s number respectively. Integral frequency offset is estimated exactly based on the position movements of diagonal elements. Mathematical derivation is also provided in the paper. The simulation results show that the proposed algorithm has a large estimation range and a high resolution.

Frequency Offset Estimation with Improved Estimation Range in UWB-OFDM Systems

In this letter, we address a carrier frequency offset (CFO) estimator with a large estimation range for ultra-wideband multi-band orthogonal frequency division multiplexing (UWB MB-OFDM) systems. We find by simulations that the proposed CFO estimator yields an improved estimation range, maintaining the same estimation performance and complexity in comparison with the conventional estimator.

A Method to Extend the Estimation Range of the Existing Time-Domain Doppler Centroid Estimators

In this letter, we use the summation-by-parts formula as a simple tool to extend the estimation range of a certain class of the already existing correlation-based Doppler centroid estimators. The resulting estimators are as robust as the original ones but cover a much larger estimation range of about 50% of the pulse-repetition frequency. Two examples with simulations are provided to demonstrate the benefits of the proposal.

Robust frequency offset estimator for OFDM over fast varying multipath channel

Presented is a robust carrier frequency offset (CFO) estimation algorithm suitable for fast varying multipath channels. The proposed algorithm estimates CFO both in time-domain and frequency-domain using two carefully designed sequences. This novel technique possesses high accuracy as well as large estimation range and works well in fast varying channels.

Improved maximum likelihood frequency offset estimation based on likelihood metric design

For emerging high data-rate communication systems in highly dispersive channels such as ultrawideband (UWB) systems, possible frequency offsets could be larger than the estimation range of the existing methods using training signals with identical parts or repetitive training signals (i.e., the training signals are composed of several identical subblocks or are obtained by repeating a training subblock for several times). This paper presents a novel improved maximum likelihood frequency offset estimator which can handle at least twice the estimation range of the existing methods using training signals with identical parts and achieves a better estimation performance. Based on the likelihood metric, a new design metric is introduced which is a pair-wise error probability (PEP) between the correct frequency offset point and a trial frequency offset point. The proposed PEP metric gives more theoretical insights on the performance of practical maximum likelihood estimators. How to design the PEP to achieve both a larger estimation range and a better estimation performance in fading channel environments is also presented and the corresponding estimator implementation is described.

A Novel Frequency Offset Estimation Method for OFDM Systems With Large Estimation Range

In this paper, we proposed a novel frequency synchronization method which has larger estimation range than conventional method proposed by Tufvesson. A two steps frequency offset estimation method is performed in the new method. In the first step the received signal is correlated with local training sequence to eliminate the influence of training sequence which makes the estimation range of frequency offset is independent of period of the repeated data in the training sequence. The received signal is correlated with its delay in the second step to obtain the fine estimation of frequency offset. Precise estimation can be achieved in the proposed method than Tufvesson's method. The period of the repeated data in the training sequence determines the estimation range of the frequency offset in the conventional method, while in the new method they are irrelevant. Tens of subcarriers spacing can be estimated by the new method. The new method can be used in other cases as long as a known sequence is transmitted, which will introduce valuable flexibility in training sequence design. The validity of the algorithm is verified in AWGN channel and multipath fading channel.

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.