Wei-Lung Mao

A new fuzzy bandwidth carrier recovery system in GPS for robust phase tracking

Fast carrier recovery loops are essential in high-dynamic global positioning system receivers. A new digital phase-locked loop (DPLL) system incorporating a fuzzy bandwidth controller (FBC) is presented in this letter. The FBC provides a time-varying bandwidth and adjusts the loop filter coefficients to improve DPLL tracking capability. When the phase error or phase difference error becomes large in the presence of significant accelerations, the loop bandwidth increases adaptively and performs rapid locking. Simulation results show that our receiver does achieve a superior performance over conventional tracking loops in terms of shorter settling time and wider frequency ramp range, while preventing the occurrence of cycle slipping.

Design of adaptive all-pass based notch filter for narrowband anti-jamming GPS system

The application of an adaptive all-pass based notch filter (ANFA) for the narrowband interference suppression in Global Positioning System (GPS) is proposed. The GPS that provides accurate positioning and timing information has become a commonly used navigation instrument for many applications. The adaptive notch filter is used to accurately estimate the narrowband jamming in real-time. It is based on all-pass filter with the Gaussian-Newton algorithm that can significantly improve the convergence rate by incorporating the so-called Hessian matrix. Simulation results show that the ANFA achieves a better performance than conventional linear predictors in terms of signal to noise ratio (SNR) improvement and mean square prediction error (MSPE) on the narrowband interference rejection in the GPS receiver.

An artificial neural network-based scheme for fragile watermarking

This paper proposes an artificial neural network based fragile watermarking scheme. Our method can detect tampering, locate where the tampering has occurred and recognize what kind of alteration has occurred. The experimental results have proven that our method is indeed effective.

New Acquisition Method in GPS Software Receiver with Split-Radix FFT Technique

Acquisition is the first step in the signal processing section of a Global Position System (GPS) receiver. It detects the presence of a GPS signal received by antenna and provides estimates of code phase and Doppler frequency to the tracking loops. Three acquisition methods in frequency-domain processing are compared, i.e., namely radix-2, split-radix-2/4 and split-radix 2/8 FFTs. The expectancy of the split-radix algorithm is increasing the acquisition efficiency. It is shown that the split-radix-2/8 FFT can save 25% of data loads and stores compared with split-radix-2/4 FFT. The modified Tone detector is applied to enhance the probability of detection. Finally, the acquisition functions are developed in software architecture running on PC.

Acquisition of GPS Software Receiver Using Split-Radix FFT

Acquisition is the first step in the signal processing section of a Global Position System (GPS) receiver. It detects the presence of a GPS signal received by antenna and provides estimates of code phase and Doppler frequency to the tracking loops. Three acquisition methods in frequency-domain processing are compared, i.e., namely radix-2 FFT, split-radix-2/4 FFT and. The expectancy of the split-radix algorithm is increasing the acquisition efficiency. It is shown that the split-radix-2/8 FFT can save 25% of data loads and stores compared with split-radix-2/4 FFT. In order to simulate the overall system in an efficient way, the acquisition functions are developed in software architecture running on PC.

A Novel Loop Filter Design for Phase-Locked Loops

A new loop filter design method for phase locked loops (PLLs) is presented, which employs multi-objective control technique to deal with the various design objectives: small noise bandwidth, good transient response (small settling time, small overshoot), and large gain and phase margins. Trade-off among the conflicting objectives is made via recently developed convex optimization skill in conjunction with appropriate adjustment of certain design parameters. One salient feature of the proposed method is that it allows one to specify the filter poles in advance, including the special case of PI form filter. Moreover, the proposed method is applicable to PLL of any order. Numerical simulation on nonlinear PLL model is performed which demonstrates the effectiveness of the proposed method.

Equalization and Interference Cancellation with MIMO THP for 10GBASE-T

Unlike 1000BASE-T system, the far-end crosstalk (FEXT) must be suppressed by at least 20 dB to meet the high speed transmission requirement for 10GBASE-T. Without FEXT cancellation, the average decision-point signal-to-noise ratio (DP-SNR) can degrade by 3 dB. This paper presents a multi-input multi-output Tomlinson-Harashima precoding (MIMO THP) technique to equalize the channel and to cancel the FEXT interference. Besides, the corresponding training method to deal with delay skew among channels and the arrangement of different step-size in least mean square (LMS) adaptive algorithm are proposed as well. Simulation results show that delay skew compensation and step-sizes arrangement can improve DP-SNR by 4.59 dB and 1.62 dB, respectively. The proposed MIMO THP architecture improves the DP-SNR by 2.75 dB than The tenative decision based approach.

Design of Peak-finding Algorithm on Acquisition of Weak GPS Signals

GPS is the system combined CDMA technique and trilateration to obtain precision position information. The main goal of this paper is design of high-sensitivity receiver on acquisition of weak GPS signals. A new peak-finding algorithm is developed to search the C/A code phase in the FFT-based correlation domain. This method can estimate the peak location accurately and provides a faster performance in the software-based signal acquisition. The integration time deciding algorithm is also utilized to enhance the capability of waveform search under indoor environments. Simulation results demonstrate that our proposed scheme can acquire the GPS signal efficiently under the power level of-155 dBm in frequency domain processing.

Design of a Robust Multi-Channel Timing Recovery System With Imperfect Channel State Information for 10GBASE-T

The interdependence among multiple channels and the interaction between timing and equalization loops bring new challenges to the design of a multi-channel symbol timing recovery (STR) system for 10GBASE-T. In addition, the nonlinear Tomlinson-Harashima precoding (THP) technique used in the 10GBASE-T system is vulnerable to the imperfect channel state information (CSI). In this paper, we address the problem of timing inaccuracy caused by imperfect CSI and the problem of extracting correct timing information in the presence of channel-interdependence and loop-interaction for 10GBASE-T. This paper proposes a novel averaged-sampling-phase (ASP) hybrid STR scheme, which aligns the sampling clock phase of a single phase-locked loop (PLL) with an average value of the timing information provided by each wire pair so that the impact of the noisy timing information resulting from the imperfect CSI and the timing jitter of the single PLL is reduced. Moreover, a three-phase timing recovery strategy based on our architecture is also designed to correctly extract the timing information and effectively mitigate the loop-interaction. Simulation results demonstrate that the proposed multi-channel STR provides a complete loop-timed solution for 10GBASE-T and achieves a superior performance over conventional approaches in terms of robustness and timing jitter.

A Novel Baud-Rate Timing Error Detector Design for Baseband Transmission System Using Tomlinson-Harashima Precoder

Extraction of correct timing error information is very important for high-speed digital transmission systems. In this letter, a novel effective-data-sequence-based timing error detector (EDS-TED) is presented for a baseband transmission system using nonlinear Tomlinson-Harashima precoding (THP), such as 10GBASE-T. The key idea of our TED is to minimize the mean square error between the received and desired EDS, rather than between the transmitted data signals. This formulation can exploit the autocorrelation between the EDS signals and extract the timing information embedded in the received signal. Moreover, the proposed architecture can lead to a simple and feasible circuit implementation. Simulation results show that a timing loop based on the proposed EDS-TED achieves a superior performance over traditional TED in terms of the peak-to-peak jitter and the TED gain.