Third-order delay-locked loop: mean time to lose lock and optimal parameters

Noncoherent digital delay lock loops (DDLL) are suited for chip timing synchronisation in band-limited direct-sequence spread-spectrum (DSSS) demodulators. The diffusion approximation and the singular perturbation method are used in this paper to calculate the mean time to lose lock (MTLL) of the DDLL. Loop bandwidth optimisation for first order loop with severe Doppler is presented. A simple design rule for the loop bandwidth and a systematic approach for the loop threshold calculation are presented. Copyright © 2005 AEIT.

The delay-locked loop (DLL) is well suited to guarantee fine synchronization for direct-sequence spread spectrum systems. In fading channels the mean time to lose lock (MTLL) of a DLL is very important because a loss of loci during a makes a re-acquisition process necessary. Using a two state model for the fading channel and a modified DLL will improve the MTLL considerably. The modified DLL operates in two different modes: a normal tracking mode for good channel conditions, and a fade mode for bad channel conditions, i.e. during a deep fade. The modified DLL is more robust against bad channel conditions.

The Weibull distribution is a flexible statistical model for describing multipath fading channels in both indoor and outdoor radio propagation environments. The performance of noncoherent first- and second-order digital delay-lock loops (DDLLs) for direct-sequence spread-spectrum systems over Weibull fading channels is analyzed. Closed-form expressions for timing error transition probability density functions (PDFs) of Chapman-Kolmogorov (C-K) equations are derived, which are employed to drive the analytical expressions for the steady-state timing error PDF and the mean time to lose lock (MTLL). Moreover, the tracking performance of the DDLL in the presence of Doppler shifts is also examined.

The Global Positioning System (GPS) is a spread-spectrum system that employs direct-sequence spreading of the spectrum to achieve better ranging accuracy. Although GPS was originally conceived for use by the military in their missions, it has become an important utility for a number of civil and commercial applications. To facilitate improvement in the use of satellite navigation by the civilian users, for example aviation and terrestrial transportation systems, an additional signal called L5 is being added to the current GPS L1 signals. L5 is also a spread spectrum signal in which the spreading code rate is ten times the coding rate of the current coarse acquisition (C/A) codes on L1. Also, the code period is ten times longer than the L1 C/A codes. Higher coding rates and longer code periods are expected to help overcome some of the shortfalls of the C/A codes. An important consideration in the design of a spread-spectrum signal for code division multiple access (CDMA) applications such as in GPS is to select codes to minimize what is known as CDMA noise. The code selection process can be very tedious, depending on the number of codes needed and the number of codes available in a given code set. Code balance, autocorrelation sidelobe peak, cross-correlation peak, and spectral line distributions are some of the measures available in the code selection process, and these measures are not necessarily independent. In this paper we give the details of the code properties and the selection process used in our study. The suggested process can be applied to code selection in any other spread spectrum system

Srini Raghavan has over 25 years of experience in design, simulation and analysis of satellite communication systems, spread spectrum systems, and signal processing. Currently, he is supporting several communication systems and Global Positioning System (GPS)-related activities at The Aerospace Corporation, where he is a Senior Engineering Specialist. He has a B.S. and M.Tech. from India, and an M.S. and Ph.D. in Electrical Engineering from the University of MissouriRolla, and is a Senior Member of IEEE and a member of ION, Eta Kappa Nu and Sigma Xi. Jack K. Holmes is a Distinguished Engineer at The Aerospace Corporation in the Communication Systems Subdivision. He has over 40 year’s of experience in analysis, simulation, and design of communication and spread spectrum systems. He is author of the book entitled “Coherent Spread Spectrum Systems” and has published approximately 45 papers in the area of communications, synchronization, and GPS-related subjects. He has been heavily involved in the military side of the GPS Modernization effort since February 1997. He is currently the GPS Code Acquisition design risk assessment subteam leader for the GPS Modernization risk assessment team. Jack received his B.S., M.S., and Ph.D. degrees at UCLA in Electrical Engineering, and is a senior member of the IEEE and a member of ION, Tau Beta Pi, and Sigma Xi.

In inverse-GPS (Global Positioning System), intersymbol interference greatly influences the positioning error. The paper deals with a new interference canceller by means of which the error is reduced. The interference canceller which we propose is composed of a DLL (delay locked loop) and adaptive filter. Only a primary phase of a replica signal is estimated in DLL. Then, the exact wave is generated with the adaptive filter. The intersymbol interference error, which is caused and increased by the number of users, is decreased by the interference canceller which is the combined DLL and adaptive filter.

The authors present a nonconventional joint data demodulation-pseudo-noise (PN) code tracking scheme for direct sequence (DS) spread-spectrum (SS) signals which solves problems of component imbalance and sensitivity with hardware simplicity and no performance degradation. An integrate-and-dump Costas loop is used for carrier recovery and data demodulation of the SS signal. Both data and carrier are then used to derive the baseband error signal of the code tracking loop. Moreover, a single passband correlator is used to perform the early-late correlation, leading to a hardware complexity equivalent to that of the tau-dither scheme, but without its loss in performance. Results of a thorough theoretical analysis of the system in an additive Gaussian noise (AWGN) environment are reported. They provide performance curves in terms of steady-state jitter and mean time to first lock loss. A superior jitter performance for low values of E/sub b//N/sub 0/ with respect to a traditional noncoherent delay lock loop (DLL) is shown, along with the potential gain of Manchester coding upon the more usual NRZ format.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The satellite transmits carrier signal to Global Positioning System (GPS) receivers suffered signal degradation in varied environmental conditions, from space through atmosphere to ground, especially due to the effects of multipath fading. In order to investigate the error performance of GPS signal transmission over multipath fading situations, a vector delay-locked tracking loop structure is applied to GPS receiver with the support of the Kalman filtering algorithms in this paper. The vector delay-locked tracking loop system is supported with receiver autonomous integrity monitoring (RAIM) and fault detection and exclusion (FDE) algorithm to prevent signal unlocked situation. Simulations of the satellite signal to GPS receiver over the multipath fading noise are investigated under three channel conditions: the additive Gaussian white noise (AWGN), Rayleigh fading noise, and Rician fading noise. The extended Kalman filter (EKF) algorithm is applied to improve the system performance. Analysis for various combinations of the above mentioned algorithms is studied and compared.

Navigation signals are the basis of satellite navigation systems, which determine the navigation systems' performance (such as tracking accuracy, anti-interference capability etc.), and are determined by some constraints (such as radio frequency resources, construction cost, technology level etc.). The aim of signal design is to select "proper" signals considering these above factors and make tradeoffs between performance and constraints. This paper will summarize the signal structure evolution of present satellite navigation and conclude some principles and issues which will be greatly valuable to our 2nd satellite navigation system. There's four main satellite positioning systems presently, the U.S. Global Positioning System (GPS), the Russian Global Navigation Satellite System (GLONASS), the Europe Galileo satellite navigation system and the Chinese BD-1 satellite positioning system. Among these systems, the signal characteristics of GPS and Galileo are good reference to our 2nd satellite navigation system. The improvement of GPS signals is a main aspect of GPS modernization. The aim of GPS modernization is mainly to modernize its signal structure so as to improve the whole systems' performance. The signal structure of Galileo has been revised for several times, and its present signal is the results of long time signal design. From GPS modernization and Galileo signals status, we can summarize some key specifications of navigation signals and some technologies to support these specifications. Based on this, we'll discuss some problems which should be attentive in our country's 2nd satellite navigation system and give some suggestions. This paper is organized into five sections. The first section will give a brief introduction of present satellite navigation system and their main features. Section two will review the GPS and Galileo signals structure evolution, including GPS modernization, Galileo signals status and the comparison of two systems' signals. In the third section, the relationship between signal parameters and system performance will be analyzed, including RF signal characteristics, modulation type, ranging code (such as code type, length and rate) and navigation data. In section four we will discuss some inspiration and technologies concerning our 2nd satellite navigation system, such as the use of multiple frequency signals (ionospheric delay estimation and carrier ambiguity resolution), pilot tones & dataless channel, binary offset carrier (BOC) modulation, and so on. The last section is conclusion, in which the whole paper will be retrospected and some useful conclusion will be given.

In this work, we aimed to develop and evaluate multi-band outer volume suppression pulses for increased acceleration rates in simultaneous multi-slice accelerated cardiac MRI. MB-OVS pulses were constructed from a multi-band combination of two slab-selective saturation pulses and tested for various pulse shapes using Bloch simulation and phantom experiment. The MB-OVS pulses were interleaved between imaging pulses to ensure homogeneous suppression throughout the cardiac cycle/imaging window in vivo. Simultaneous multi-slice (SMS) CINE and first-pass myocardial perfusion scans with and without the proposed MB-OVS pulses were compared in terms of residual artifacts at high acceleration rates. Among the tested pulses, both Bloch simulation and phantom experiments showed that amplitude-optimized sinc pulses provided the best trade-off in suppression efficiency, the required B1+, SAR, and slab profile. CINE imaging with 5-fold SMS-OVS acceleration significantly outperformed imaging without MB-OVS, maintaining leakage-free image quality, even when adding 2-fold in-plane acceleration. SMS-OVS also enabled perfusion imaging in 9 slices with 1.7 × 1.7 mm2 resolution, achieving a 16-fold spatial-only acceleration while ensuring accurate contrast dynamics without leakage artifacts. Interleaved MB-OVS modules enabled thorough leakage artifact suppression in cardiac SMS-accelerated CINE and perfusion imaging, particularly at high acceleration rates. The proposed approach may be promising for unlocking further acceleration potential of SMS in cardiac imaging.

An enhanced coherent delay lock loop (DLL) is proposed for code tracking in direct sequence spread spectrum systems on multipath fading channels. By normalising the estimated tracking error for large values of the power of the tracked path, the proposed loop reduces most of the degradation caused by fading. Moreover, by subtracting an estimation of the multipath bias from the output of the coherent DLL, this enhanced scheme reduces most of the degradation caused by multipath interference.

A neural network (NN)-based delay-locked loop (DLL) for multipath mitigation in Global Positioning System (GPS) receivers is developed. The NN operates on equally-spaced samples of the autocorrelation function. The NN is trained using a statistical distribution model that takes into consideration multipath time delay and power attenuation. The performance of the proposed method is compared numerically and experimentally with three other conventional techniques: conventional early-minus-late DLL, narrow correlator, and high resolution correlator. It is demonstrated that the NN-based DLL produces smaller code phase root mean squared error compared to the three conventional techniques in high multipath environments.

The Global Positioning System (GPS) is a satellite navigation system and positioning that is owned and managed by the United States of America. This system is also designed to provide three-dimensional position and speed and information about time, continuously throughout the world without depending on time and weather, to many people simultaneously. The GPS module undergoes system expansion on low-cost devices by producing low-cost and energy-saving devices, including being able to provide L1 satellite data equivalent to geodetic GPS. This study shows whether low-cost U-Blox GPS can be equivalent to Hi-Target V60 geodetic GPS. The test was carried out by observing the four corners of the Geomatics Engineering volleyball field and PWK ITS using the RTK method. The results of GPS observations were carried out statistical tests to see if low-cost U-Blox GPS can be equivalent to GPS Geodetic Hi-Target V60.

Different attempts have been made to compare the performance of coded orthogonal frequency division multiplexing (COFDM) and a corresponding single carrier system employing a linear equalizer often by comparing the average bit error rates. The random coding technique is used to analyze the performance of these systems for signaling over piecewise constant channels. The probabilities that the cutoff rates are less than a desired rate are calculated and compared. It is shown that for low SNRs and low code rates, the cutoff rates of both systems are approximately the same. With an increasing SNR the cutoff rate for the linearly equalized system, however, converges faster to its maximum value than the cutoff rate for the COFDM system. Simulation results for the outage probability are presented for the two-ray Rayleigh fading channel with QPSK as the fundamental modulation technique. For code rates close to one or for uncoded transmission, the linearly equalized single carrier system substantially outperforms the COFDM system. For low to medium code rates COFDM and a linearly equalized single carrier system perform approximately identically.

The Georgia Institute of Technology is evaluating the feasibility and effectiveness of mileage-based pricing programs as transportation control measures. Incentives were provided to study participants who change driving behavior in response to cent per mile pricing (fixed pricing and pricing as a function of congestion level). In-vehicle Global Positioning System (GPS) devices were used to estimate distance traveled and driver behavior (e.g., speed and acceleration profiles). The accuracy of estimated mileage accrual speeds by road classification, and acceleration rates used in pricing algorithms, is paramount. Various data-smoothing techniques were applied to the instrumented vehicle GPS speed data, and performance of the algorithms was evaluated in minimizing the impact of GPS random error on speed, acceleration, and distance estimates. The conventional discrete Kalman filter algorithm was modified to enhance its ability to control GPS random errors. Each smoothing method produces different second-by-se...