Spread Spectrum Signals Research Articles

Spectrally shaped generalized MC-DS-CDMA with dual band combining for increased diversity

A new multicarrier spread spectrum modulation scheme is proposed in this paper. This scheme uses sinusoidal chip waveforms to shape the spectrum of each subcarrier of a multicarrier direct sequence spread spectrum (DS-SS) signal. As a result, each subcarrier has two distinct spectral lobes, one a lower sideband (LSB) and the other an upper sideband (USB). By properly selecting the parameters of the sinusoidal chip waveforms, the two sideband signals can be made to undergo independent fading in a dispersive fading channel. These two independently-faded sideband signals, when combined at the receiver, provide diversity gain to the system. Our analysis and simulation results show that by properly selecting the chip waveform parameter and the intersubcarrier frequency separation, the bit error ratio (BER) performance of the proposed scheme is superior to that of the conventional MC-DS-CDMA system in dispersive fading channels. In addition, spectral sidelobes are naturally reduced by our scheme.

A low-complexity algorithm for fast acquisition of weak DSSS signal in high dynamic environment

The initial acquisition of direct-sequence spread-spectrum (DSSS) signal transmitted in bursts by ground terminals at satellite-borne receiver poses an engineering challenge. We propose a low-compl...

Composite spread spectrum signals with uniform amplitude envelope for satellite radio-navigation systems

A method for generating the composite spread spectrum signals of satellite radio-navigation system based on linear equilibrium and nonequilibrium multiplexing of components is proposed to ensure the uniform amplitude envelope of a resultant signals. This makes it possible to solve the main problem of the given systems related to the low energy efficiency of signal amplification in the satellite radio receiver due to the substantial peak factor of an emitted signal.

Long‐term integration based on two‐stage differential acquisition for weak direct sequence spread spectrum signal

Fast acquisition in space telemetry and telecontrol communication system is challenged significantly by the high dynamic and low signal-to-noise ratio. Increasing the dwell time to obtain better acquisition sensitivity, based on two-dimensional time-frequency search, is impossible because of resource limitation in receiver. To tackle these problems, this study proposes a two-stage differential acquisition (TSDA) algorithm. The differential coherent integration is employed by the first stage of TDSA to extend integration time, during which keystone transform and fast Fourier transform are used to compensate the linear code phase drift and obtain high accumulation gain. The carrier-frequency offset is estimated in terms of the code phase difference between the two parts of received signal divided by the second stage of TSDA in which the two-dimensional searching process is avoided. The proposed TSDA algorithm and the traditional acquisition methods are compared under the same acquisition time and typical parameters of S-band space telemetry and telecontrol communication system. Simulation results demonstrate that the proposed TSDA algorithm attains a higher acquisition probability and better acquisition sensitivity than the traditional acquisition methods.

Detection of the Beginning of the Communication Session at Networking with Time-Varying Channels

Определены требования к вероятности ложных обнаружений для формирования решающей статистики системы синхронизации по задержке при приеме широкополосных сигналов. Приведены требования к надежной фиксации границ начала сеанса связи при значительном времени ожидания сеанса связи. Предложены методы выбора лучей для выполнения требований по надежности вхождения в синхронизм.

Radar-Communication Integration Based on MSK-LFM Spread Spectrum Signal

At present, with the progress and innovation of technology, the radar communication dual function wave has become a hot research at home and abroad. Excellent integrated waveform can make full use resources of combat platform, reduce the size of equipment, and realize the actual functionality of the reality of the battle-field without affecting the radar communication func-tion. The MSK-LFM dual-function wave is a typical representative; it is based on LFM, through the MSK modulation to achieve the integration function. This paper proposes a scheme of combining the spread spectrum technology with the MSK-LFM waveform based on the previous literature. The simulation results show that the waveform envelope is more stable and the energy is more concentrated. With the introduction of spread-spectrum technology, the new waveform ambiguity function graph is much closer to the thumbtack than the traditional MSK-LFM waveform.

Design of a TDOA location engine and development of a location system based on chirp spread spectrum.

Location based services (LBS) provided by wireless sensor networks have garnered a great deal of attention from researchers and developers in recent years. Chirp spread spectrum (CSS) signaling formatting with time difference of arrival (TDOA) ranging technology is an effective LBS technique in regards to positioning accuracy, cost, and power consumption. The design and implementation of the location engine and location management based on TDOA location algorithms were the focus of this study; as the core of the system, the location engine was designed as a series of location algorithms and smoothing algorithms. To enhance the location accuracy, a Kalman filter algorithm and moving weighted average technique were respectively applied to smooth the TDOA range measurements and location results, which are calculated by the cooperation of a Kalman TDOA algorithm and a Taylor TDOA algorithm. The location management server, the information center of the system, was designed with Data Server and Mclient. To evaluate the performance of the location algorithms and the stability of the system software, we used a Nanotron nanoLOC Development Kit 3.0 to conduct indoor and outdoor location experiments. The results indicated that the location system runs stably with high accuracy at absolute error below 0.6 m.Electronic supplementary materialThe online version of this article (doi:10.1186/s40064-016-3632-0) contains supplementary material, which is available to authorized users.

On the performance of low-rate wireless correlation-delay-shift-keying system

The performance of a correlation-delay-shift-keying (CDSK) system for low data-rate applications in wireless communications is studied in this paper. In the transmitter, the low-rate data modulates the chaotic spreading sequence by means of a CDSK modulator at baseband. By using a RF modulator, the baseband CDSK-modulated signal is up-converted into a RF passband signal which is then transmitted on the antenna. These modulators allow the transmitter to be able to adjust flexibly the chip period compared with bit duration and locate the transmitted signal at a desired or allocated RF band. The receiver performs in turn the corresponding RF and CDSK demodulations to recover the data. A wireless channel affected by noise, fading, multipath, and delay-spread in the context of low-rate and short-range transmission of the chaotic spread-spectrum signals is described. Schemes for the transmitter and receiver under the impact of the wireless channel are then developed. Bit-error-rate (BER) performance is analyzed with the use of both theoretical derivation and numerical integration. Simulated performance is shown in comparison with the corresponding analyzed ones, where the effect of the spreading factor, modulation delay, and the number of transmission paths on the BER is fully evaluated. Our findings show that the low-rate CDSK system can exploit the multipath nature of wireless channels for improving the BER performance.

Compressive Sampling for Detection of Frequency-Hopping Spread Spectrum Signals

In this paper, methods for detection of frequency-hopping spread spectrum (FHSS) signals from compressive measurements are proposed. Rapid switching of the carrier frequency in a pseudorandom manner makes detection of FHSS signals challenging. Conventionally, FHSS detection is performed by scanning small segments of the spectrum in a sequential manner using a sweeping spectrum analyzer (SSA). However, SSAs have the inherent risk of missing the transmitted signal depending on factors such as the rate of hopping and scanning. In this paper, we propose compressive detection strategies that sample the full FHSS spectrum in a compressive manner. We discuss the use of random measurement kernels as well as designed measurement kernels in the proposed architecture. The measurement kernels are designed to maximize the mutual information between the FHSS signal and the compressive measurements. Using a mixture-of-Gaussian model to represent the FHSS signal, we derive a closed-form gradient of the mutual information with respect to the measurement kernel. Theoretical analysis and simulation results are provided to compare different systems. These results demonstrate that the proposed compressive system with random measurement kernels is not subject to the performance limitations suffered by SSAs when their scanning rates are low and designed adaptive measurement kernels provide enhanced detection performance compared to random ones.

Whole-Region Hybrid Search Algorithm for DSSS Signal Acquisition

The conventional hybrid search algorithm for direct sequence spread spectrum (DSSS) signal acquisition terminates once a decision variable exceeds the detection threshold. Therefore, a spurious “hit” declared before the search reaches the cell where the target signal is located avoids any possibility of a correct detection. This behavior increases the probability of false detection, especially in abnormal scenarios, such as when in the presence of interfering signals. To improve the probability of correct detection under a constant false-alarm rate criterion, this paper proposes an advanced hybrid acquisition scheme, whose search area is extended to the whole Doppler frequency and code phase delay uncertainty region. To reduce the mean acquisition time (MAT) increment resulting from this increased search area, both parameters of a Tong detector and the detection threshold are adaptively customized, according to a signal-to-noise ratio estimate obtained during the search operation. In addition, analytic expressions for the detection probability and false-alarm probability are derived. The most prominent advantage of the proposed method is that it can reduce the false detection probability noticeably, with little increase in resource utilization, and an acceptable MAT. The validity of this algorithm is verified, both theoretically and through simulation. The proposed algorithm is particularly suitable for DSSS signal acquisition when in the presence of either multiple access interference or continuous wave interference.

Run‐length method for determining the segmentation length based on the segmentation long‐code blind estimation

In this study, the blind despreading of long-code direct sequence spread spectrum signals (LC-DSSS) is considered. Qiu et al. presented a heuristic segmentation-based method to estimate the spreading code of LC-DSSS signals, which divided the received signal into far shorter temporal windows than the symbol duration, then spreading code was reconstructed from these short windows by computing the related covariance matrices. However, Qiu et al. did not consider the criterion of determining the segmentation length. By combining the matrix perturbation theory and run length property, the authors propose a run-length method for determining the segmentation length based on the segmentation idea, and this method can also be applied to long-code direct-sequence code division multiple access (LC-DS-CDMA) signals. Monte Carlo simulations for both LC-DSSS signals and LC-DS-CDMA signals are presented to demonstrate the effectiveness of the proposed method.

Performance Enhancement of a Multichannel Uncoordinated Code Hopping DSSS Signaling Scheme Using Multipath Fading Compensator

In this paper, a multipath fading compensator(MFC) has been introduced and demonstrated to reduce the signal distortion which arose due to Doppler effect, multipath propagation and self-interference for a multichannel uncoordinated code hopping direct sequence spread spectrum (UCH-DSSS) signaling in underwater communication. The bit error rate (BER) performance analysis of the proposed system obtained both analytically and using P-Spice circuit simulation model with and without jamming signal is presented. It is observed that the BER is independent of the frequencies (used in focused acoustic field (FAF) experiments FAF-06 and FAF-05) and is also less than those of the previous works. Oscilloscope traces indicate that the experimental waveform of the proposed four-channel UCH-DSSS transceiver is almost close to those obtained using P-Spice circuit simulation. The experimental values of BER measured by BER meter also matched well with the BER obtained theoretically. Noise margin and distortion performance also are analyzed from the eye pattern which shows that noise margin and distortion also are independent of frequencies (used in both FAF-06 and FAF-05) and the bandwidth of operation of FAF-06 is [Formula: see text]5.5 times more than that of FAF-05.

Analysis of protection technologies radio fire alarm systems against unauthorized access

There is currently a growth of radio channel fire alarm. One of their main disadvantage is the vulnerability of the communication channel to the data being compromised. The authors, based on our analysis and fuzzy logic unit, identified the most tamper-proof wireless technology fire alarm to give a quantitative evaluation of the security level. The most secure technologies from complex threats (view, substitution, interception, jamming) include technologies based on spread-spectrum signals (based on the technology of random sequences and ultra-wideband signals) and are the least secure cryptographic techniques (simulation protection device). It's the necessity of further research aimed at improving the security of the radio fire alarm. A promising development is seen systems with technologies to protect the radio channel based on spread-spectrum signals (based on the technology of random sequences and ultra-wideband signals).

Blind estimation of pseudo‐random codes in periodic long code direct sequence spread spectrum signals

An estimation method of pseudo-random (PN) codes in the periodic long code direct sequence spread spectrum signals using a pair of spreading code and scrambling code [i.e. long scrambling code direct sequence spread spectrum (LSC-DSSS)] is investigated in this study. Via the investigation of properties of triple correlation function (TCF) of m-sequences, the existence of common peaks in the TCFs of different m-sequences is proved, and the corresponding relationship between common peaks and primitive polynomials is further investigated. Four theorems are proposed as supplements of triple correlation theory and a novel estimation algorithm of the PN codes in LSC-DSSS signals is put forward on the basis of the theorems. With certain carrier frequency and chip rate of spreading code, this algorithm first eliminates the influence of information codes through delay-and-multiply operation. Then the TCF of signal is calculated, and the two PN codes in signal are successfully estimated finally by searching and using the common peak coordinates in the TCF. Simulation results show that the proposed algorithm exhibits excellent performance in estimating PN codes in LSC-DSSS signals.

Ultrasonic System Models for Pulse Trains Excitation Tuning

Quality of the ultrasonic imaging depends on probing signal. Application of the spread spectrum (SS) signals offers significant advantage over conventional signals: higher signal-to-noise ratio can be achieved and spectral content can be programmed. Yet, such SS signals like chirp and coded sequences suffer for the sidelobes which are induced by compression processing. Arbitrary position and width pulse (APWP) trains is a new class of SS signals which are expected to maintain advantages of the square pulse and the SS signals. Usual approach of SS signals application does not assume signal optimization. The novelty of the APWP approach is the optimization of the APWP train accounting of the signal transmission through system. In order to speed up the optimization iterations, a mathematical model of the APWP signal transmission through ultrasonic system is needed: instead of doing the iterations in real environment, those can be accomplished mathematically, using the system transmission model in order to sustain the experiment conditions. The development of the transmission model of the system is presented; the models are compared using the correlation properties. The results of the investigation are presented. DOI: http://dx.doi.org/10.5755/j01.eie.22.2.9815

Coding Versus Spreading for Narrowband Interference Suppression

The use of active narrowband interference (NBI) suppression in direct-sequence spread-spectrum (DS-SS) communications has been extensively studied. In this paper, we address the problem of optimum coding–spreading tradeoff for NBI suppression. With maximum-likelihood (ML) decoding, we first derive upper bounds on the error probability of coded systems in the presence of a special class of NBI, namely, multitone interference with orthogonal signatures. By employing the well-developed bounding techniques, we show that there is no advantage in spreading, and hence, a low-rate full-coding approach is always preferred. Then, we propose a practical low-rate turbo-Hadamard coding approach, in which NBI suppression is naturally achieved through iterative decoding. The proposed turbo-Hadamard coding approach employs a kind of coded spread-spectrum signaling with time-varying spreading sequences, which is sharply compared with the code-aided DS-SS approach. With a spreading sequence of length 32 and a fixed bandwidth allocated for both approaches, it is shown through extensive simulations that the proposed turbo-Hadamard coding approach outperforms the code-aided DS-SS approach for three types of NBI, even when its transmission information rate is about five times higher than that of the code-aided DS-SS approach. The use of the proposed turbo-Hadmard coding approach in multipath fading channels is also discussed.

ACE-BOC: dual-frequency constant envelope multiplexing for satellite navigation

In the signal design of new generation global navigation satellite systems, there is a strong demand for multiplexing multiple binary spreading signals on two adjacent frequencies into an integrated signal with a constant envelope. In this paper, a dual-frequency constant envelope multiplexing (DCEM) technique with high-design flexibility based on subcarrier waveform reconstruction, named asymmetric constant envelope binary offset carrier (ACE-BOC), is presented. This multiplexing technique can be seen as a generalized alternate BOC. It can combine four or fewer independent, bipolar, direct sequence spread spectrum signals onto two sidebands of a spectrum-split integrated signal, where each sideband consists of two or fewer signals with arbitrary power ratio modulated onto the quadrature components. The design principle, diversified generation methods of ACE-BOC signals, as well as the characteristics in both time and frequency domains are investigated. Multiplexing efficiency and receiving performance of this signal are also analyzed. Analysis with typical examples shows that, for both transmitters and receivers, ACE-BOC signals have multiple processing forms. Compared with existing DCEM methods, ACE-BOC has much higher design flexibility in the number of signal components, power ratio among components, hardware complexity of both transmitters and receivers, and spectrum compatibility. Such high-level design flexibility provides system designers great room in signal scheme optimization for varied navigation applications in the future.

Amplitude‐adaptive spread‐spectrum data embedding

In this study, the authors consider additive spread-spectrum (SS) data embedding in transform-domain host data. Conventional additive SS embedding schemes use an equal-amplitude modulated carrier to deposit one information symbol across a group of host data coefficients which act as interference to SS signal of interest. If there is a flexibility of assigning different amplitudes across symbol bits, the probability of error can be further reduced by adaptively allocating amplitude to each symbol bit based on its own host/interference. In this study, they present a novel amplitude-adaptive SS embedding scheme. Particularly, symbol-by-symbol adaptive amplitude allocation algorithms are developed to compensate for the impact from the known interference. They aim at designing the SS embedding amplitude for each symbol adaptively in order to minimise the receiver bit-error-rate (BER) at any given distortion level. Then, optimised amplitude allocation for multi-carrier/multi-message embedding in the same host data is studied as well. Finally, they consider the problem of amplitude optimisation for an ideal scenario where no external noise is introduced during embedding and transmission. Extensive experimental results illustrate that the proposed amplitude-adaptive SS embedding scheme can provide order-of-magnitude performance improvement over several other state-of-the-art SS embedding schemes.

Use of Matched Filter in Direct Sequence Spread Spectrum Techniques

Objectives: The protection of signal against jamming is accomplished using Spread Spectrum (SS) techniques. In this research paper, noise rejecting property of the matched filter and Binary Phase Shift Keying (BPSK) modulation is used in Direct Sequence Spread Spectrum (DSSS) system for secure communication. Methods/Statistical Analysis: Here, DSSS system has been developed and simulated using C-programming language on windows platform. In order to perform the simulation, different parameters are initialized and message bits are generated by random function. With the help of binary message signal and PN sequence, a SS signal is generated which is modulated using BPSK modulation technique at the transmitter side. In the channel, noise/jamming signal is added to the transmitted signal. Then the received signal is demodulated using coherent BPSK receiver (i.e., correlation receiver) and matched filtering is followed by despreading the demodulated signal at the receiver side. Finally, the received binary message bits are detected by threshold detector and various parameters such as input SNR, output SNR, probability of error are calculated. Findings: It has been found that matched filter is a linear filter which has a noise rejection property (means jamming signals can be treated just like other random noise) and hence provides signal security. This particular property of matched filter is used in DSSS communication. As far as matched filter is concerned, it cannot remove the total effect of interference but still the waveforms can be detected in the presence of noise/jamming signal. So, a matched filter receiver is supposed to be an ideal receiver for a signal which is corrupted by AWGN/jamming signal. Here, an average probability of symbol error decreases because it maximizes the output signal to noise ratio. These parameters are supposed to be the most important factors that determine the efficiency of performance of the system. Applications: DSSS systems using matched filter are strong contender for mobile and personnel communications, due to their very large user handling capacity. They also have better transmission quality and capability by incorporating wireless services such as data, short transaction messages, and multimedia etc.

Bounds for Low Probability of Detection for Underwater Acoustic Communication

Most military underwater activities require stealth operations, and hydroacoustic transmissions might temper the mission. For this reason, military underwater acoustic transmission aims for low probability of detection (LPD). LPD communication systems are characterized by low transmission power and reception at low signal-to-noise power ratio (SNPR). As a side effect, LPD decreases acoustic noise pollution. In this paper, we study the LPD capability of underwater acoustic communication (UWAC) systems. We consider an interceptor with target false alarm and detection probabilities and a legitimate receiver with required detection and packet error probabilities. For the interceptor, we focus on an energy detector and calculate the minimal SNPR which satisfies its required performance. For the legitimate communication link, we consider spread-spectrum signaling with several modulation techniques, and calculate the minimal required SNPR to allow reliable detection and decoding of a data packet. Based on these minimal SNPR terms and using bounds on power attenuation in the channel, we quantify the LPD capability of the system and analyze the effect of channel and communication parameters. We also present results from a sea trial conducted in the Saanich Inlet off the coast of Vancouver Island, where we conducted LPD experiments for different transmission powers and carrier frequencies. We provide bounds for the minimal bandwidth and maximal transmission rate for LPD communication. Our results also show that LPD UWAC performs better in shallow and warm water, and for transmission at low carrier frequencies.