Sequence Spread Spectrum Communication System Research Articles

The line-of-sight peak detection and tracking of underwater acoustic DSSS communications in the doubly spread channel

In the underwater acoustic (UWA) channel, the line-of-sight (LOS) path has the characteristics of stable magnitude and continuous phase, which is seldom affected by the surface/bottom reflection. Therefore, in the direct sequence spread spectrum (DSSS) communication systems, the receiver usually extracts the LOS path to recover the information bits and achieve the robust communication. However, the UWA channel is typically the doubly spread channel, i.e., multipath fast fading and non-uniform Doppler shifts, which seriously degrades the performance of extracting the LOS path by the conventional maximum energy method. Therefore, this paper proposes a LOS peak detection and tracking algorithm to extract the LOS path in the UWA DSSS communications. In the proposed algorithm, the candidate correlation peaks after de-spreading are firstly selected by the adaptive peak detection threshold. Then, according to the transmitter/receiver motion relationship, the Delay-Doppler joint state equation is established, and thus the nearest neighbor method adopting the Kalman filter is proposed to track the LOS path. Numerical simulation results demonstrate that the proposed algorithm has better processing performance in the doubly spread channels compared with the conventional method. Finally, the performance of the proposed algorithm is confirmed by the shallow water horizontal channel and deep sea vertical channel experiments.

Analytical Technique Leveraging Processing Gain for Evaluating the Anti-Jamming Potential of Underwater Acoustic Direct Sequence Spread Spectrum Communication Systems

This study proposes an analytical technique underpinned by processing gain to evaluate the anti-jamming potential of an underwater acoustic direct-sequence spread-spectrum (DSSS) communication system that employs a short-period pseudo-noise (PN) sequence. The processing gain comes from the symmetry of the coding, which provides a mechanism for separating desired signals from unwanted ones, and the apparent randomness of the coding, which suppresses interference and noise in the system. The robustness of such a system against wideband interference, partial-band jamming, and single-frequency interference is emulated. Outcomes suggest that, in comparison to a standard binary phase shift keying (BPSK) system, the DSSS system’s ability to resist wideband interference is limited, with only a marginal increase in immunity performance of approximately 0.5 dB. Contrarily, it suppresses partial-band jamming effectively, with the suppression level dependent on the interference bandwidth and its relative position concerning the signal carrier frequency. The influence of single-frequency interference on system performance depends similarly on its relative location relative to the signal carrier frequency. In all situations where the interference frequency offset is an integer multiple of the bit bandwidth, the system exhibits the worst performance when the frequency offset equals the bit bandwidth. Upon comparing resistance levels to identical power interferences targeted at the signal carrier frequency, our system demonstrates optimal resilience to single-frequency interference. In concordance with the empirical findings, the simulated results substantiate both the effectiveness and practicability of the proposed analytical method based on processing gain. Subsequently, this study contributes a novel perspective for evaluating the anti-jamming potential of DSSS systems.

Double-differential coded M-ary direct sequence spread spectrum for mobile underwater acoustic communication system

This paper presents a double-differential coded M-ary direct sequence spread spectrum (DD-MSS) underwater acoustic communication system to overcome problems of both low signal-to-noise ratio and severe Doppler effect. The system is very efficient in the challenging band-limited underwater acoustic channel and has many applications, particularly in which the transmitter and the receiver are mobile. Given that the bit error rate (BER) performance is unaffected, this scheme results in a significant improvement in the data rate compared to direct sequence spread spectrum (DSSS) communication systems. The MSS system uses M pseudo-random codes to represent k bits of information and offers advantages of a higher spectral efficiency and a lower energy consumption than the DSSS system. Both simulations and experiments are performed, and the results are discussed in the paper for the performance evaluation of the proposed scheme. The results demonstrate a better BER performance using the DD-MSS in a mobile environment.

Synchronization in DSSS system

AbstractDirect sequence spread spectrum (DSSS) communication systems offer huge performance focal points in perspective on their low probability of block, improved performance in multipath fading situations and their capacity to stay away from interference by spreading the signal over a wide bandwidth subsequently conveying the power. For the transmitted sequence to be effectively received and demodulated, the spreading sequence utilized at the receiver ought to be like that utilized in the transmitter. This paper uses MATLAB Simulink to show a technique for synchronizing the code clock at the receiver with the code clock at the transmitter. This fine arrangement procedure is known as code tracking.

Modulation Parameter Estimation of LFM Interference for Direct Sequence Spread Spectrum Communication System in Alpha-Stable Noise

The linear frequency modulation (LFM) interference is one of the typical broadband interferences in direct sequence spread spectrum (DSSS) communication system. In this article, a novel modulation parameter estimation method of LFM interference is proposed for the DSSS communication system in alpha-stable noise. To accurately estimate the modulation parameters, the alpha-stable noise should be eliminated first. Thus, we formulate a new generalized extended linear chirplet transform to suppress the alpha-stable noise, for a robust time-frequency, transformation of LFM interference is realized. Then, using the Radon transform, the maximum value after transformation and the chirp rate according to the angle related to the maximum value are estimated. In addition, a generalized Fourier transform is introduced to estimate the initial frequency of the LFM interference. For the performance analysis, the Cramer–Rao lower bounds of the estimated chirp rate and the initial frequency of the LFM interference in the presence of alpha-stable noise are derived. Moreover, the asymptotic properties of the modulation parameter estimator are analyzed. Simulation results demonstrate that the performance of the proposed parameter estimation method significantly outperforms existing methods, especially in a low SNR regime.

Blind Estimation of Spreading Sequence and Data Bits in Direct-Sequence Spread Spectrum Communication Systems

At the transmitter of a Direct Sequence Spread Spectrum (DSSS) communication system, data bits are spread using a spreading sequence. To demodulate the transmitted data bits, the received signal should be de-spread using the same spreading sequence. However, there are many non-cooperative communication systems, where a receiver does not have the information on the spreading sequence. In such systems, to demodulate the transmitted data bits across a wide area, it is necessary to blindly estimate the spreading sequence at low Signal-to-Noise Ratio (SNR). Furthermore, for real-time processing, the computational complexity for the blind estimation should be minimized. In this paper, a novel algorithm is proposed to blindly estimate a spreading sequence and data bits based on turbo processing for both synchronous and asynchronous cases. The proposed algorithm can significantly improve the error rates of estimated data bits and the chips in the spreading sequence compared to an Eigen-Value Decomposition (EVD) based algorithm. Furthermore, compared to the EVD-based algorithm, the proposed algorithm drastically reduces the number of required multiplications.

Simulation and Experimental Study of Low Voltage Power Line Carrier Communication

This paper presents the simulation and experimental research of low-voltage power line carrier communication. The choice of communication method is an important factor in determining the communication quality of the communication system. For the communication mode of low-voltage power line as carrier, this paper prefers the direct sequence spread spectrum communication system as the communication method. In this paper, the simulation function is realized by establishing various parts of the system simulation model. The simulation reflects the stability of the direct sequence spread spectrum communication system and has strong anti-interference ability. In this paper, the spread spectrum communication method is used to simulate low-voltage power line communication in the laboratory environment, and good results are also obtained. The direct sequence spread spectrum communication system is a better choice for low voltage power line carrier communication.

Code Tracking of DSSS Signal over AWGN Channel

Abstract Direct sequence spread spectrum (DSSS) communication systems offer significant performance advantages in view of their low probability of intercept, improved performance in multipath fading environments and their ability to avoid interference by spreading the signal over a wide bandwidth hence distributing the power. For the transmitted sequence to be correctly received and demodulated, the spreading sequence used at the receiver should be similar to that employed in the transmitter. This paper utilizes MATLAB Simulink to demonstrate a method of synchronizing the code clock at the receiver with the code clock at the transmitter. This fine alignment process is knownas code tracking.

Effects of CW Interference on the BDS Receiver and Analysis on the Coupling Path of Electromagnetic Energy

The present research is carried out on the issue that the BDS (BeiDou Navigation Satellite System) receiver exerts some vulnerability to CW (continuous wave) interference. The analysis on the interference mechanism of navigation signal is implemented based on the model of direct sequence spread spectrum communication system while the method of parallel code phase search is employed to simulate the capture capability of the receiver under CW interference. In the CST-MWS, the simulation was made for the coupling path and electromagnetic energy into the navigation receiver, concluding that the antenna functions as the major obtained coupling path. On that basis, the RF radiation interference experiment for the antenna of the BDS receiver was conducted in the semi-anechoic chamber. In addition, the RF injection interference experiment was made on the basis of the power coupler. The sensitive frequency band of the receiver under the interference was obtained through the experiment. Furthermore, findings are made that the ratio of the output power of the RF signal generator under the RF irradiation method to the output power with the RF injection method takes no variation with change of the interference frequency. Therefore, The RF injection method can be used instead of RF irradiation method under CW interference in order to gain simplified experimental equipment, which provides a more professional theoretical basis for anti-interference research.

Hyperchaos-Based Spreading Codes Generator for DS-CDMA Communication Systems

In this paper, we propose a new hyperchaos-based spreading codes generator (HSCG) for multi-users direct sequence spread spectrum (DSSS) communication systems. For experimental validation, we implement the proposed generator in Xilinx FPGA Virtex-5 technology. Contrary to the traditional spreading codes, the proposed HSCG offers interesting statistical properties such as good autocorrelation, very small cross-correlation, no repetition of the generated spreading codes and high degree of security. In addition, the developed hardware architecture used for implementing the HSCG permits to generate simultaneously an infinite number of multi-length spreading codes with high hardware performances in terms of logic area consumption, throughput and latency. Real-time results are given for 32-, 64- and 128-bit chaotic spreading codes. All of these properties are validated and compared with that of classical codes (Gold sequences, Walsh–Hadamard) through bit error rate (BER) performance evaluation in a DS-CDMA system in AWGN and time-invariant multipath channels. With its interesting performances, the proposed HSCG is very useful for the next generations of mobile communication systems.

An underwater acoustic direct sequence spread spectrum communication system using dual spread spectrum code

With the goal of achieving high stability and reliability to support underwater point-to-point communications and code division multiple access (CDMA) based underwater networks, a direct sequence spread spectrum based underwater acoustic communication system using dual spread spectrum code is proposed. To solve the contradictions between the information data rate and the accuracy of Doppler estimation, channel estimation, and frame synchronization, a data frame structure based on dual spread spectrum code is designed. A long spread spectrum code is used as the training sequence, which can be used for data frame detection and synchronization, Doppler estimation, and channel estimation. A short spread spectrum code is used to modulate the effective information data. A delay cross-correlation algorithm is used for Doppler estimation, and a correlation algorithm is used for channel estimation. For underwater networking, each user is assigned a different pair of spread spectrum codes. Simulation results show that the system has a good anti-multipath, anti-interference, and anti-Doppler performance, the bit error rate can be smaller than 10−6 when the signal-to-noise ratio is larger than −10 dB, the data rate can be as high as 355 bits/s, and the system can be used in the downlink of CDMA based networks.

Acquisition of PN sequences using multilayer perceptron neural network adaptive processor for multiuser detection in spread‐spectrum communication systems

AbstractA non‐coherent serial acquisition scheme for direct sequence spread spectrum communication systems is analyzed and discussed in this paper. The adaptive thresholding based on constant false alarm rate and multilayer perceptron neural network (MLP‐NN) techniques are combined to improve the performance of code division multiple access systems. One of the most important problems in code acquisition of pseudo‐noise sequences for multiuser detection is the presence of interferences caused by the multiple access technique and multipath replicas. To solve this problem, an MLP‐NN is trained and adapted to work as a constant false alarm rate detector using the error back propagation gradient descendent algorithm. It is named MLP‐NN adaptive processor. The performance of this proposed algorithm is presented using the serial search acquisition system, which is chosen because of its simple hardware implementation. The performance of the MLP‐NN adaptive processor algorithm in homogeneous and non‐homogenous environments for additive white Gaussian noise and Rayleigh fading channels is evaluated via computer simulations. The obtained results are compared to other serial acquisition schemes using the cell‐averaging adaptive processor, the order statistics adaptive processor, and the automatic censoring adaptive processor algorithms.

Jammer suppression in spread spectrum communication using novel independent component analysis approach

Spread spectrum communications is an increasingly popular technique for use in diversity of systems. They are based on signaling schemes which greatly expand the bandwidth of the transmitted spectrum relative to the information bandwidth. Though, the gain is sufficient for proper performance of the system in most of the cases, additional interference suppression capability is needed when interference plays a dominant role. A novel adaptive scheme for jammer mitigation in Direct Sequence Spread Spectrum communication (DSSS) systems using independent component analysis (ICA) is proposed in this paper. This blind separation method provides jammer mitigation and recovers the data sequence from Binary Phase Shift Keying (BPSK) modulated signal as they arrive in a blind fashion. Extraction of the transmitted sequence from the received sequence is done with improved convergence speed compared to existing ICA algorithms. Simulations are carried out to illustrate the achieved performance of the proposed scheme for variable sequence lengths and different values of jammer power. The merits and limitations of the proposed ICA assisted jammer suppression scheme in comparison to Fast ICA assisted one are also discussed. The proposed method provides better SNR value compared to simple DSSS, Fast ICA based DSSS and other interference suppression schemes presented in the literature.

Study of the Interference Rejection Based on ATF in DSSS

A novel, adaptive time-frequency interference rejection for suppressing the interference in Direct Sequence Spread Spectrum communication systems is studied in this paper. For a time-localized interference, excision is performed in the time domain. When a frequency domain excision is decided, an adaptive sub-band transform is employed. The most proper sub-spectral split is defined according to the spectrum of the received signal. This joint treatment of time and frequency domains overcomes the performance limitations of the fixed transform-based excision algorithms. The paper presents the performance evaluation of the rejection technique via the analytical and computer simulation tools. It is found that the analytical performance tools match up with the computer simulation results. It is also shown that the proposed adaptive time-frequency interference rejection consistently outperforms the existing interference excision techniques in the literature.

A two-step MF signal acquisition method for wireless underground sensor networks

Signal acquisition plays a critical role on the bit error rate (BER) of a direct sequence spread spectrum (DS/SS) communication system working with low frequency. In this paper, we propose a new signal acquisition method. The acquisition process includes coarse matched filter (MF) location in the first stage and an accurate MF acquisition as a verification mode for the second stage. The performance metrics, including mean acquisition time (MAT) and power consumption, are accuracy. The results indicate that when the signal-to-noise ratio (SNR) keeping consistent, the MAT of the proposed method is less than the original one. When the SNR is around -5dB, the system mismatch rate is about 5:6 x 10-4, which takes only one percent of those achieved in the original acquisition algorithms. The two-step MF acquisition method is stable except its power consumption being a little higher than the original method.

The Design and Implementation of Spread Spectrum Communication System

The main research content of this article is to design a direct sequence spread spectrum communication system based on software radio technology. In this paper, design of spread spectrum receiver system directly to intermediate frequency sampling signal processing, after internal processing directly output transmission baseband signal information.

Research of Anti-Multipath Interference Capability in Direct Sequence Spread Spectrum Communication System by Simulation

The effects of multipath fading with time delay longer or shorter than one chip interval on DSSS system are mathematically and experimentally researched. Simulation results indicate that DSSS system can efficiently overcome multipath fading in multipath Rayleigh Fading channels. And the spreading gain is not the higher the better, it must be chosen reasonably.

Research on the Equivalence of Pulsed Interference Signal and CW Signal in DSSS Communication System

Pulsed interference signal and pure frequency continuous wave (CW) jamming signal have the same effect on performance of bit error rate (BER). Due to equivalence, we can effectively simplify the complex of the direct sequence spread spectrum (DSSS) communication system. The equivalence will be simulated by the software SystemView in systematic level.

Fast Time-Recursive Block Correlators for Pseudorandom Sequences

Correlators for pseudorandom sequences are used in direct sequence spread spectrum communication systems for signal synchronization and identification of transmitters. Implementation aspects of these correlators are critical for real-time processing of signals. This paper presents fast correlator structures in time domain which significantly reduce redundant operations using time-recursive and block processing. The approach can be extended to other applications which use correlations with both binary and non-binary sequences.

Multicomponent Chirp-like Jammer Excision in DSSS Communication Systems Using Hilbert-Huang Hough Transform

A novel and efficient approach for multicomponent chirp-like jammer excision in direct sequence spread spectrum (DSSS) communication systems using Hilbert-Huang Hough (HH-H) transform is proposed, which is the generalization of marginal Hilbert spectrum. The approach iteratively decomposes the received signal into intrinsic mode functions (IMFs) and applies Hilbert transform to each IMF to yield Hilbert spectrum (HS), by which the embedded jammers can be well concentrated in the time-frequency plane along their instantaneous frequency laws. By performing Hough transform over the HS and searching peaks in the parameter space, parameters estimation and components reconstruction of the multicomponent chirp-like jammer are implememted. Simulation results are presented showing performance comparison between the proposed method and the fractional Fourier transform (FrFT) based method in the case of two chirp-like jammer components. DOI: http://dx.doi.org/10.11591/telkomnika.v11i4.2372