Spread Spectrum Signals Research Articles

Application of Arbitrary Position and Width Pulse Trains Signals in Ultrasonic Imaging: Correlation Performance Study

Ultrasonic imaging requires both the accuracy and the resolution. Conventional imaging systems use the pulse signals to accomplish the task. But the energy attainable with such signals is limited. Spread spectrum, compressible signals allow to achieve the wide bandwidth even using long durations. Conventional signals do not offer full flexibility or, like nonlinear frequency modulation signals, lack the ease of properties control. We suggest using novel spread spectrum signals generation technique: trains of pulses of arbitrary pulse width and position (APWP). It is expected that APWP should have properties similar to chirp (wide, controllable bandwidth) and both the single pulse (low correlation sidelobes) signals. Study presented here was aimed at evaluating the correlation properties of APWP signals. It indicates that application of APWP signals allows obtaining the properties better or close to those of the conventional signals. It can be concluded that APWP signals offer a new perspective in imaging applications.DOI: http://dx.doi.org/10.5755/j01.eee.19.3.2690

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Ultrasonic imaging requires both the accuracy and the resolution. Conventional imaging systems use the pulse signals to accomplish the task. But the energy attainable with such signals is limited. Spread spectrum, compressible signals allow to achieve the wide bandwidth even using long durations. Conventional signals do not offer full flexibility or, like nonlinear frequency modulation signals, lack the ease of properties control. We suggest using novel spread spectrum signals generation technique: trains of pulses of arbitrary pulse width and position (APWP). It is expected that APWP should have properties similar to chirp (wide, controllable bandwidth) and both the single pulse (low correlation sidelobes) signals. Study presented here was aimed at evaluating the correlation properties of APWP signals. It indicates that application of APWP signals allows obtaining the properties better or close to those of the conventional signals. It can be concluded that APWP signals offer a new perspective in imaging applications. DOI: http://dx.doi.org/10.5755/j01.eee.19.3.2690

A Deterministic Compressed GNSS Acquisition Technique

In the cold start of a Global Navigation Satellite Systems (GNSS) receiver, fast acquisition of the GNSS signal requires either an extensive usage of hardware resources for massive parallel correlators or a high computational complexity for fast Fourier transform (FFT) and inverse FFT operations. Because GNSS uses direct-sequence spread spectrum (DSSS) signaling with binary phase-shift keying (BPSK) or with BPSK and binary offset carrier, any GNSS signal can have a sparse representation so that the concept of compressed sensing can be applied to detect GNSS signals. To achieve a fast acquisition of the GNSS signal with a reduced number of correlators and low computational complexity, we propose a two-stage deterministic compressed GNSS acquisition technique using the Walsh-Hadamard matrix. The proposed technique makes fast acquisition possible for a receiver using a much smaller number of correlators than the conventional parallel-correlator-based technique, which requires much less computational complexity than the FFT-based technique. We provide complexity analysis of the proposed technique and compare the statistical performance of the proposed technique with other techniques applicable to the fast GNSS acquisition. The proposed technique is easy to implement and is the first compressed-sensing-based GNSS acquisition technique.

Least-Squares-Based Iterative Multipath Super-Resolution Technique

In this paper, we investigate the multipath resolution problem for direct sequence spread spectrum signals. To resolve multipath components arriving within a very short interval, we propose a new multipath super-resolution algorithm based on the iterative least-squares method. The proposed least-squares-based iterative multipath super-resolution (LIMS) algorithm exploits a triangular shaped auto-correlation function (ACF) of the pseudo-noise (PN) sequence and simplifies the least-squares parameter estimation procedure using iterative and algebraic operations. This results in an algorithm demanding low computational load with a high multipath resolution capability. It is also discussed that the LIMS algorithm can be applied for recursive multipath tracking of source localization systems, such as the global navigation satellite systems (GNSS). Simulation results show that the LIMS algorithm maintains its good performance even in a low [(C)/(N0)] or severe multipath interference conditions.

Hardware implementation for blind demodulation method for chaotic direct sequence spreadspectrum signals

In this paper, we design a field-programmable gate array (FPGA)-based hardware implementation for blind demodulation method for chaotic direct sequence spread spectrum (CD3S) signals. Both transmitter and receiver are designed. The transmitter can produce ten chaotic maps as the spreading sequence. In the receiver, the mathematic model of unscented Kalman filter (UKF) chaotic fitting is built and simplified for hardware implementation. The hardware structure of the receiver is based on this simplified model. For real time fitting different chaotic maps, a dynamic adjustment strategy of range-differentiating factor is proposed. The additove white Gausian noise (AWGN) and multipath channel experiments verify the anti-noise and anti-multipath performance of the UKF chaotic fitting method on one hand. On the other hand, the experiments verify the method can demodulate CD3S signals spread by all ten chaotic maps effectively.

An Improved Adaptive Tracking Algorithm based on Iteration and Discriminator Optimization for Burst DSSS Signals

To enhance the pseudo-range measurement performance based on code synchronization of burst Direct Sequence Spread Spectrum (DSSS) signals, a new adaptive tracking algorithm based on iteration is proposed. After a forward tracking based on initial values provided by acquisition or coarse tracking, a backward estimation is adopted to get more precise initial values. Based on these precise initial values, forward tracking is carried out again. By performing forward tracking and backward estimation iteratively, a more and more precise tracking result can be achieved. At the beginning of each tracking, code discriminator optimization is carried out considering the precise of initial carrier and code phase. For the convenience of optimization, a performance evaluation algorithm of dot-product power code discriminator for band limited signal is proposed. Compared with several existing tracking algorithms which exploit received signal only once, simulation results show the superiority of our proposed iterative tracking algorithm, under data-aided and non-data-aided conditions respectively.

Excitation signal's influence on ultrasonic transit time flow meter's performance

Ultrasonic flow meter performance was analyzed. Ultrasound transit time was used for flow rate estimation. Time of flight was measured using cross correlation processing. Simultaneous channels excitation was used. Ultrasonic signals were excited using low voltage (4V pp) signal generator, received signals were amplified 30 dB and simultaneously acquired by 100 Ms/s 10 bit analog-to-digit converters. Subsample delay estimation was used. Flow rate was varied from 10 l/h to 200 l/h. Measurement channel diameter 8 mm was used. It is complicated to obtain the unbiased reference signal for correlation processing. Various combinations of signals travelling in measurement channel were used for cross-correlation processing. Performance of correlation function and time of flight estimator variance were studied. Variable gain amplifier usually is used for signal dynamic range matching to A/D converter input. Gain influence on time of flight was a subject to study. It has been concluded that gain control introduces systematic errors in time of flight estimator. Influence of the temperature of electronics (pulser, receiver, A/D converter, reference clock etc.) and ultrasonic transducers on the delay estimator was studied. It was concluded that the major temperature-related systematic error comes from the pulser. Performance of the meter was studied when narrowband and spread spectrum signals were used for ultrasound excitation across temperature and flow rate range. It has been concluded that spread spectrum signal allows for better zero flow stability over temperature and lower time of flight variation.

Comparison of spread spectrum and pulse signal excitation for split spectrum techniques composite imaging

Ultrasonic imaging of composites was investigated. Glass and carbon fiber reinforced plastic produced by resin transfer molding and prepreg forming were analyzed. In some of the samples air bubbles were trapped during RTM (resin transfer molding) process and interlayer gaps were present in prepreg technology samples. One of the most expected techniques to apply in such case is the Split Spectrum processing. On the other hand such signals require specific processing to reliably reconstruct the temporal position of the defect reflection. Correlation processing can be used for signal compression or Wiener filtering can be applied for spectral content equalisation. Pulse signals are simple to generate, but lack the possibility to alter the signal's spectrum shape. Spread spectrum signals offer a powerful tool for signal energy over frequency band increase and resolution enhancement. CW (continuous wave) burst has high energy but lacks the bandwidth needed for SSP (spread spectrum processing). The aim of the investigation was to compare the performance of the above signals in case of composite imaging, when various Split Spectrum Processing techniques are used with preceding Wiener processing for spectral content compensation. Resulting composite signals and images obtained are presented. Structural noise removal performance was evaluated as Receiver Operating Characteristics (ROC).

Chaotic modulation‐based spread spectrum communication using complex dynamics of chaotic DC–DC current mode controlled boost converter

ABSTRACTAmple amount of research has been done for analysing nonlinear phenomenon in power electronics converters. Application of chaotic power electronics converters in spread spectrum communication in recent times is catching interest. This paper proposes a methodology for using chaotic current mode‐controlled DC (Direct Current)–DC (Direct Current) boost converter in spread spectrum communication. A noncoherent receiver is developed. For this, an Adaline‐based adaptive filter is designed to recover the message from spread spectrum signal at the receiver end. The proposed Adaline‐based receiver is tested by transmitting various types of message signals while considering white noise at different signal‐to‐noise ratio. For designing noncoherent receiver‐based chaotic communication, use of power electronics converters is expected to play a vital role in the future. Copyright © 2012 John Wiley & Sons, Ltd.

Blind Residual Carrier Frequency Offset and Timing Offset Estimation Using Improved Minimum Output Variance Approaches in Uplink MC-CDMA Systems

This paper deals with blind residual carrier frequency offset (CFO) and timing offset (TO) estimation based on minimum output variance (MOV) criterion without devoting training sequence and pilot symbol for uplink multicarrier-code division multiple access (MC-CDMA) systems. It has been shown that the performance of MOV estimator is degraded because the effect of noise and wideband spread-spectrum signals. In conjunction with spreading code-aided and subspace projection techniques, we present an improved code-aided MOV (ICMOV) estimator to achieve the high accuracy estimate for the noisy case. Due to more accuracy residual CFO estimate can provide more accuracy residual TO estimate, this paper also present a decision-directed ICMOV (DD-ICMOV) approach to improve the estimation performance of ICMOV estimator. Computer simulations are provided for illustrating the effectiveness of the proposed approaches.

Non-cooperative detection of weak spread-spectrum signals in additive white Gaussian noise

A semi-blind method based on principal component analysis and sequence synchronisation is proposed to detect direct sequence spread-spectrum signals in a non-cooperative setting under low signal-to-noise ratio conditions. The intercepted signal is segmented to form a detection matrix from which a feature is extracted through cyclic shifting. Signal detection is then performed using a test statistic based on this feature. The carrier frequency and sequence duration of the signal to be detected are assumed known. Theoretical analysis and a computer simulation study show that the performance of the new detection method is superior to classic energy detection in an additive white Gaussian noise channel.

Efficient Spectrum Sharing in the Presence of Multiple Narrowband Interference

In this paper, we study the spectrum usage efficiency by applying wideband methods and systems to the existing analog systems and applications. The essential motivation of this work is to define the prospective coexistence between analog FM and digital Spread Spectrum systems in an efficient way sharing the same frequency band. The potential overlaid Spread Spectrum (SS) system can spectrally coincide within the existing narrowband Frequency Modulated (FM) broadcasting system upon several limitations, originating a key motivation for the use of the FM radio frequency band in many applications, encompassing wireless personal and sensors networks. The performance of the SS system due to the overlaying analog FM system, consisting of multiple narrowband FM stations, is investigated in order to derive the relevant bit error probability and maximum achievable data rates. The SS system uses direct sequence (DS) spreading, through maximal length pseudorandom sequences with long spreading codes. The SS signal is evaluated throughout theoretical and simulation-based performance analysis, for various types of spreading scenarios, for different carrier frequency offset ({\Delta}f) and signal-to-interference ratios, in order to derive valuable results for future developing and planning of an overlay scenario.

Blind joint information and spreading sequence estimation for short-code DS-SS signal in asynchronous and synchronous systems

The problem of blind despreading of short-code direct sequence spread-spectrum signal in asynchronous or synchronous system is considered. A novel blind estimation algorithm for time offset, spreading and information sequences is presented in this paper. Firstly, the received signal is divided into two-information-period-length temporal vectors overlapped by one-information-period and accumulates these vectors one by one to form the accumulated matrix. The algorithm exploits an unbiased estimation of user’s time offset to realize synchronization blindly, and an operation of singular value decomposition is applied to the intercepted matrix, which is intercepted from the accumulated matrix according to user’s time offset. Lastly, the spreading sequence is recovered from a right singular vector blindly; therefore, the shortcomings of traditional algorithms, such as phase ambiguity when make use of two vectors to form the spreading sequence, are avoided. And the information sequence is then recovered blindly from the left singular vector. Simulation results show that the new method is capable of retrieving time offset, the spreading and information sequences with higher accuracy than previous methods.

Simultaneous remote transfer of accurate timing and optical frequency over a public fiber network

In this work, we demonstrate for the first time that it is possible to transfer simultaneously an ultra-stable optical frequency and precise and accurate timing over 540 km using a public telecommunication optical fiber network with Internet data. The optical phase is used to carry both the frequency information and the timestamps by modulating a very narrow optical carrier at 1.55 μm with spread spectrum signals using two-way satellite time transfer modems. The results in terms of absolute time accuracy (250 ps) and long-term timing stability (20 ps) well outperform the conventional Global Navigation Satellite System or geostationary transfer methods.

Spread-Spectrum Continuous-Phase-Modulated Signals for Satellite Navigation

Spread-spectrum continuous-phase-modulated (SS-CPM) signals are investigated with application to satellite navigation. In particular, focus is devoted to the special subclasses of SS-CPM with semi-integer modulation index h greater than one. This constitutes a novelty with respect to traditional navigation signal design on one hand (which is based on direct-sequence spread-spectrum (DS-SS) signals with rectangular pulse) and with traditional communication SS-CPM with h>;1 on the other. Main output is that setting the modulation index h<;1 to semi-integer values allows the SS-CPM signals to behave like having subcarriers, exactly in the same way as it happens for the binary offset carrier (BOC) modulation. The main advantage is that CPM ensures a constant envelope at the transmission side, thus being appealing when these features are required at the system level. After a description of signal properties, focus is devoted to ranging code synchronization, by exploitation of the theory on time-delay estimation (TDE). A few delay-lock loop schemes are also presented, based on an offset quadrature phase-shift keying (OQPSK) approximation of the signal at the receiver side, achieved by Laurent's decomposition at the receiver side. Proposed loops performance are analyzed in terms of Cramer-Rao bound (CRB), rms tracking error, and multipath robustness. An application of SS-CPM for a two-rate-service scheme is proposed.

Sound speed measurement with direct-sequence spread spectrum signal combining time of flight and phase shift

Increasing demands for high accuracy and rapid measurement of sound speed have prompted the development of portable sound velocimeter in oceanography. Generally, sound speed can be established by CTD or TD (Time Delayed) method respectively. CTD method suffers from errors of corresponding sensors and application range of the converting equations. TD method, sing-around technique representative, is widely used in portable velocimeter. The accuracy of TD is proportional to receiving SNR and signal length. The duration of tone burst in convenient sing-around is limited by multi-echo, thus only a few valid data can be utilized. To address the problems, DSSS (Direct-Sequence-Spread-Spectrum) signal in continuous form is adopted to extract the TD directly, with which sound speed could be established related to laboratory derived equations, Del Grosso’s equation representative. Based on this method, two separate transducers were deployed with constant distance. Cross-correlation between received and transmitted (orthogonal form) signals is computed. Combine Time-of-Flight and Phase-Shift, the TD can be derived by two processes, the peak detecting of cross-correlation envelope and carrier phase estimating. Theoretic analyses and experiments indicate that the accuracy with DSSS relates to the period of PN sequence, the frequency of chip, and the linearity characteristic of electronic circuits and transducers.

Parameter Estimation of the Direct Sequence Spread Spectrum Signal Based on Time-Smoothing Cyclic Periodogram

The direct sequence spread spectrum (DS-SS) signal is a typical kind of LPI signals widely-used in the modern digital communication system, and it is difficult to be detected for its statistical characteristic similar to noise. An algorithm for estimating the code rate, carrier frequency of DS-SS signals was proposed using time-smoothing cyclic periodogram instead of cyclic spectrum according to cyclostationary feature of DS-SS signal to improve the precision of parameter estimation. The estimation performance was analyzed for the cyclic spectrum by time-smoothing cyclic periodogram from the tapering points in the case of limited data length. Simulation results showed that the proposed algorithm is effective.

Detection Performance Analysis and Parameter Design Method of DSSS Signal Acquisition Algorithm Based on the MAX/TC Criterion

For the acquisition of week direct sequence spread spectrum (DSSS) signal in dynamic environment, an acquisition algorithm using MAX /TC criterion on bi-dimensional search region in noncoherent integrations is proposed. Detection performance of the proposed acquisition algorithm is deduced and the deduced formulas are simple and practicable. Based on these formulas, parameter design method is given for low signal-to-noise ratio (SNR). Computer simulation results demonstrate the correctness of the conclusion and effectiveness of parameter design method.

An Improved Re-Sampling Interpolation Algorithm for Base-Band Signal Shaping Filtering

Research on shaping filtering algorithms in wireless communication systems has important practical value. Based on the digital base-band shaping filter, which is widely used in the area of software radio, an improved re-sampling filtering algorithm is proposed in this paper. By the design of truncated raise cosine filter, the continuous sequence of digital spread-spectrum signal can be restored. The piecewise parabola interpolation filter is established to carry out the signal re-sample, and the Farrow implementation structure is adopted to reduce the calculation cost. The algorithm is validated through the experiment using simulated and true signals respectively, which demonstrate that not only the out band power of frequency division multi signals can be effectively suppressed, but also the steadiness of re-sampling signals is improved during the dynamic environment.

Research on Detection Method of Direct Sequence Spread Spectrum Signals

Direct Sequence Spread Spectrum (DSSS) Communication has been widely applied in Personal communications network, WLAN, the third-generation mobile communications, satellite communications systems, military tactics communications and etc, thanks to the DSSS signals’ strong anti-interference ability, low probability of being intercepted and outstanding multi-access communication ability. At the same time, the Problem of estimating Signals has been of great research interest with the development of wind-band weak signals processing and communication antagonism. A new effective detection method of DSSS is proposed, combined the method of wavelet transformation with cycle spectral correlation approach, from the perspective of jamming in non-cooperation condition, and a simulation result of signals--BPSK is given.