Analysis of sampling and quantization effects on the performance of PN code tracking loops

It has been reported that a smart antenna can improve bit error rate (BER) performance significantly in a mobile communications system (Tanaka, S. et al., IEEE JSAC, vol.18, no.8, p.1495-504, 2000). However, the smart antenna has not been applied and analyzed much for the pseudonoise (PN) code tracking loop, which is one of the important aspects in spread spectrum communications receivers. We present a performance analysis of a first order PN-code tracking loop with a smart antenna under a frequency selective fading environment, and show that the smart antenna can also improve the PN code tracking loop significantly, compared to a single antenna element system. We employ the root mean square (RMS) error and mean time to lose lock (MTLL) of the PN code tracking loop as performance criterion.

A modified pseudonoise (PN) code tracking loop is proposed for direct-sequence spread-spectrum communications in the fast fading channel and strong interference environment. First, to formulate the problem we analyze PN code autocorrelation character in the fast fading channel and strong interference. Then the modified PN code tracking model using limited-length curve fitting algorithm is developed to improve the tracking performance. Analytical expressions of the curve fitting algorithm are derived and then confirmed by means of extensive computer simulation results. In addition, utilizing a DS/BPSK experimental system, several simulation results for PN code tracking performance are also presented in this paper. Very attractive behaviors obtained using the proposed technique are verified.

In an effort to transmit information over communication channels that contain both Gaussian and non-Gaussian noise components, military and commercial applications frequently rely upon the use of direct sequence spread spectrum (DSSS) techniques. Whilst DSSS is an interference tolerant modulation scheme, situations may be encountered when the processing gain offered by the pseudonoise (PN) spreading code is inadequate. Enhancements to the interference immunity of a DSSS system can be accomplished through the use of signal processing techniques that suppress unwanted interference prior to despreading. To date, the majority of interference suppression techniques developed for DSSS applications, have concentrated on improving detector performance exclusively, and perfect synchronisation between transmitter and receiver is assumed. However, the process of PN code acquisition and tracking within a DSSS receiver is arguably one of the most critical functions within the receiver structure since, if it fails to operate correctly, the wanted signal will not be successfully recovered. An evaluation of the benefits of any interference suppression technique within a DSSS receiver would not be complete without considering at least one level within the synchronisation hierarchy. We examine the improvements in receiver performance, when the process of PN code tracking and detection employs a novel wavelet packet denoising (WPD) procedure for a variety of non-Gaussian channel scenarios.

This paper proposes an algorithm that improves the mean code acquisition time using an energy estimation mode (EEM) and dwell time values from direct-sequence spread spectrum (DS-SS) System. Until recently, DS-SS System has been used in many areas from Wireless LAN, cellular phone, and GPS to telecommunication. Meanwhile, the development of reducing of pseudonoise (PN) code acquisition time, the core technique of DS-SS system, is continuously explored. The algorithm in this paper added the EEM before a search mode (SM) from the conventional PN code acquisition system, which is composed of a SM and a verification mode (VM). In the EEM, dwell time and threshold values are determined for use in the SM and the VM depending on the correlation energy. This paper applies the proposed technique under Rayleigh-fading channel in performing a simulation of PN code acquisition time by a mathematical modeling to evaluate the proposed algorithm. Numerical results show that the proposed method improves the detection performance and the rejection performance of false code phases not only in the VM but also in the SM. Furthermore, the proposed algorithm reduces the mean code acquisition time by maximum 29% than the conventional algorithm.

This paper considers sequence acquisition in direct-
\nsequence spread-spectrum (DS/SS) systems that use Gold
\nsequences as the multiple access pseudonoise (PN) sequence.
\nWhen long PN sequences are used, the design of an acquisition
\nscheme requires the characteristics of partial correlation of PN
\nsequences. For ease of analytic design, the partial correlation
\nof Gold sequences is approximated using a piecewise linearized
\nupper bound model. Since the acquisition of PN sequence in direct-
\nsequence code-division multiple access (DS-CDMA) systems
\ncan be formulated as testing two simple hypotheses, we apply fixed
\nsample size (FSS) and sequential tests to detection of phase alignment.
\nWhen a sliding correlator-type structure is employed for
\nthe acquisition scheme, the acquisition performance of Gold-sequence-
\nbased DS-CDMA systems is analyzed and compared to
\nthat of -sequence-based systems. Analytical results show that
\nthe use of Gold sequences requires a mean acquisition time quite
\ncomparable to the use of -sequences. Finally, analytical results
\nare verified by computer simulation.

Under the software environment of MATLAB/Simulink, the communication system of direct sequence spread spectrum (DSSS) is dynamically modeled and simulated over a new practical Rayleigh channel, and the relationship curves of the bit error rate (BER) with the signal-to-noise ratio (SNR) of DSSS communication systems are presented. It is analyzed that DSSS system can effectively overcome multipath fading in multipath Rayleigh Fading Channel (RFC). In addition, the anti-multipath fading performance improved by the way of increasing pseudo noise (PN) code length is better than that by the way of increasing the spread spectrum gain in the condition of strong multipath fading.

We propose a closed-loop noncoherent Pseudo-Noise (PN) acquisition scheme for Direct-Sequence Spread-Spectrum (DS/SS) systems using an auxiliary sequence, previously used for coherent acquisition. The proposed scheme consists of an alignment detection and a VCC loop for updating the local PN signal and the direction of update. The performance of the proposed scheme is obtained by simulation and compared with the noncoherent fixed-dwell serial scheme. Results show that the proposed scheme acquires approximately three to four times faster than the conventional noncoherent serial scheme.

A rapid acquisition scheme for direct-sequence (DS) spread-spectrum packet radio systems using PN matched filters is described. The system operates in burst mode, with limited permitted time for synchronization using a fixed length preamble at the beginning of each data burst. Multiple PN codes are available for acquisition at the first portion of the preamble. The second portion of the preamble consists of several PN codes which are modulated with a marker. The receiver may achieve code acquisition anywhere within the first portion of the preamble. Since it is not known a priori in which of the several code periods acquisition will occur, coincidence detection is done using the marker for frame synchronization. The analysis shows that the scheme yields better performance than some other previous schemes in packet radio systems. >

In this paper, the performance of a decision-feedback coherent code tracking loop for pilot-symbol-aided (PSA) direct-sequence spread-spectrum systems, considering the effect of both symbol and channel estimation errors, is analyzed. An analytical closed-form expression on the steady-state jitter variance in additive white Gaussian noise (AWGN) environments using the linear analysis model is first derived. Then, the upper and lower bounds of the jitter variance in fading environments are obtained based on the analysis of the loop bandwidth variation according to the input signal level. Finally, a second-order coherent tracking loop is designed, and its performance in both AWGN and fading environments is evaluated, along with verification by computer simulations. It is demonstrated that analytical results are very close to the simulation results in AWGN environments and that the jitter variance in fading environments is located between analytical upper and lower bounds with its position depending on the fading rate.

Adaptive filtering is a widely used technique in active noise control (ANC). In order to make the adaptive filter in an FXLMS (filtered-x LMS) ANC system stable, the reference signal must pass through an estimation filter whose phase response is within /spl plusmn/90/spl deg/ of the phase of the secondary path. In this paper, we study the quantization effects on the filter phase response and the relationship between the phase response and the location of the zeros and poles. In addition, we propose a filter structure and nonuniform quantization method in which we quantize the filter coefficients so they each contain a small number of nonzero bits, based on the distance of the zeros/poles to the unit circle, to guarantee that the /spl plusmn/90/spl deg/ allowable phase deviation is met - greatly reducing the implementation cost. We combine these ideas with that of multiplierless implementations of adaptive FIR filters to realize an efficient active noise control using field programmable gate arrays or other digital hardware.

The landscape of Global Navigation Satellite Systems (GNSS) signals is undergoing significant change. The parallel development of new, more robust and versatile signals along with two new GNSS systems with global reach is having a dramatic impact on the development of GNSS receivers. Receiver manufacturers are continually developing and implementing unique signal acquisition and tracking algorithms, advanced integrity monitoring algorithms, advanced multipath mitigation algorithms and a host of other enhancements in an effort to improve the performance of GNSS receivers and make their products stand out in a crowded field. The objective of this research is to develop a methodology for comparing the pseudorandom noise (PRN) code tracking performance of various receivers. While the overall performance of a receiver depends on many more factors, effective PRN code tracking is fundamental to the operation of a GNSS receiver. The methodology developed in this research requires three fundamental measurements from the receiver under test – code pseudorange, carrier pseudorange and carrier-to-noise-density ratio (C/No). These measurements are generated by all GNSS receivers but may not always be available to the user. Therefore, this methodology can only be performed on receivers that output these values. This methodology might be useful as a tool to evaluate the suitability of various receivers in certain environments or applications (e.g., weak signal environments, high dynamic environments, unfriendly radio frequency (RF) interference environments, etc.) and also as a means of comparing the relative performance of receivers in those environments or applications. Expectations for the research were that the data collection and analysis techniques would generate code loop tracking jitter plots that closely tracked with theoretical curves. In addition, it was expected that different receivers would yield slightly different jitter plots giving them a unique “signature.” Finally, it was expected that some receivers might incorporate scalar code tracking loops and others might incorporate vector tracking loops. The methodology was developed and refined using three receivers from three popular manufacturers, each with a unique set of capabilities. Raw data was collected from each receiver and processed using purpose built algorithms to estimate the code loop tracking jitter for each signal for each receiver. The code loop tracking observations for each of the three receivers tested were compared with theoretical curves generated using closed form equations published in previous papers. In most cases, the data compared favorably. However, there were some significant outliers that are worthy of additional research and analysis. In addition, the jitter plots for one receiver tested indicated that it used scalar code tracking loops and the jitter plots for the other two receivers indicated that they use vector tracking loops. It appears to be possible to determine if a receiver uses scalar tracking loops or vector tracking loops based on the jitter estimates generated in this research. This research indicated that the methodology might be a useful tool for 2 characterizing GNSS receivers and, eventually evaluating their performance in various environments. However, more data collection and analysis is required to further validate and refine the methodology. Also, more analysis of the signals that yielded “non-conforming” jitter plots should be examined in more detail.

In traditional feedback structure of direct sequence spread spectrum (DS-SS) receiver, delay lock loop is a prevailing approach to estimate the timing error. However, in burst communication, it is hard for DLL to be in transient state or lock the signal with high accuracy. In this paper, an efficient feedforward PN code timing recovery scheme is proposed for DS-SS systems. The received signal after the chip-matched filter is two times over-sampled. The characteristics of DS-SS signal are explored to make the synchronization scheme efficient and simple in such a low sampling rate. Three sets of correlation values with different timing offsets are stored to estimate the code timing and carrier phase error. With very low computational complexity, the proposed scheme can make the performance approaches to the DS- SS systems with ideal synchronization in an AWGN channel.

One of the most important problems to be solved in Direct Sequence Spread Spectrum systems is to achieve a robust acquisition of the pseudo noise sequence. In multiuser time-varying environments this fact becomes even more important because acquisition and tracking performance can heavily degrade communication reliability. In this paper a new neural network estimator is presented, and it is compared to the performance of a fuzzy logic acquisition estimator [11] and stability acquisition estimator [16] in the multiresolutive acquisition system. The new neural network acquisition estimator improves the results for both fuzzy logic and stability estimators, through the estimation of the probability of being acquired and the signal to noise ratio for single user and multiuser communication.

Spread spectrum signals are widely used for secure communications, as well as for multiple access interference (MAI).They have many interesting properties, including low probability of interception.Indeed, direct sequence spread spectrum systems (DSSSS) use a periodical pseudo-random sequence to modulate the baseband signal before transmission.Interception of DSSS signals is a difficult task due to the hiding of the PN sequence, especially if the accompanied noise is non-Gaussian and the channel is frequency selective.In this paper, a receiver is proposed to intercept asynchronous direct sequence code division multiple access (DS-CDMA) signals received from different users and estimate the PN sequences of each one of them.The signals are assumed to be transmitted over frequency selective fading channel and contaminated with Class-A impulsive noise.The proposed interception receiver is based on Independent Component Analysis (ICA), the pseudo random sequences is estimated from the eigenvector subspace in case of single path.In multipath situations, the estimation is the overlapped form of the pseudo random sequences, a triple correlation function (TCF) is introduced to eliminate the influence of multipath.The performance of proposed receiver is evaluated in terms of the number of correct estimated codes for m-sequence over typical urban channel in presence of impulsive noise.The results show that the interception receiver performs is 100% code estimation at -8dB signal to noise ratio.

Parallel correlation in direct-sequence spread spectrum system allows faster and more reliable coarse acquisition. However, the power consumed becomes significant especially for receivers that employ a large number of parallel correlators. In this paper, the power efficiency of various parallel correlator architectures is explored assuming baseband sampled signals of two samples per chip. Active correlators placed in parallel that use both two's complement and sign-magnitude accumulators are first presented. A functionally equivalent M-parallel passive correlators are then studied. In this approach, the baseband sampled signals are passed through a tapped delay-line. Each tap is then multiplied by a stationary reference pseudonoise code and summed using a binary tree network. The passive correlators are generally more power efficient compared to both types of active correlators, especially for large M values. Further reduction in power consumption is possible by splitting the tapped delay-line into even and odd delays and summing using two smaller binary tree adders. This proposed architecture consumes significantly less power compared to all other architectures. The power dissipation of M-parallel correlator architectures are evaluated for M = 8, 16, 32 using TSMC 0.35-µm CMOS technology at 3.3V supply voltage.