Direct Sequence Spread Spectrum Research Articles

Structure of Spread Spectrum Telemetry Radio Link for LEO Small Satellite

The paper considers the design of telemetry radio link for low Earth orbit (LEO) satellites, particularly based on CubeSat format. A significant limitation of such spacecrafts are the available dimensions for antennas and the transmitting power, which leads to low energy level at the ground receiving point of transmitted signal. The article presents the physical level structure for data frame based on direct sequence spread spectrum technique, which allows for additional signal gain to achieve the required level of link performance. Using such principle also make possible to implement adaptive data rate control depending on dynamics in signal-to-noise ratio when the distance from the satellite to the ground point changes. For proposed data frame structure, an analysis of received information size during a communication session was carried out, which is parameterized on the maximum observable elevation angle of the satellite. The issue of datalink layer interaction between devices is also considered.

Chaotic Spread-Spectrum Communication: A Comparative Study between Chaotic Synchronization and Matched Filtering

This publication investigates the performance of demodulation methods utilized in spread spectrum chaotic communication systems, specifically matched filtering and chaotic synchronization. We conduct simulations and comparisons of three different communication systems: classic direct sequence spread spectrum (DSSS), chaotic signal fragment-based pseudo-chaotic spread spectrum (PCSS), and chaotic synchronization-based antipodal chaos shift keying (ACSK). These systems possess similar spectral and time domain characteristics, allowing us to shed light on their fundamental differences and limitations. Additionally, we assess the impact of frequency modulation (FM) on these modulation methods, as FM allows the creation of simplified non-coherent modulation schemes. Our findings, based on the analysis of bit error ratio (BER) curves, clearly demonstrate that the utilization of quantized waveforms for spreading confers a significant advantage over analogous, continuous-time spread spectrum systems. In addition, it is shown that the employment of chaotic synchronization instead of cross-correlation does not degrade the performance of the communication system and provides a more secure approach. In general, this research aims to enhance awareness regarding the distinct advantages and limitations associated with chaotic spread spectrum modulation methods.

Direct sequence spread spectrum (DSSS) signal detection based on eigenvalues local binary pattern residual network (EL-ResNet)

Direct sequence spread spectrum (DSSS) signal detection based on eigenvalues local binary pattern residual network (EL-ResNet)

Performance of the Direct Sequence Spread Spectrum Underwater Acoustic Communication System with Differential Detection in Strong Multipath Propagation Conditions

The underwater acoustic communication (UAC) operating in very shallow-water should ensure reliable transmission in conditions of strong multipath propagation, significantly disturbing the received signal. One of the techniques to achieve this goal is the direct sequence spread spectrum (DSSS) technique, which consists in binary phase shift keying (BPSK) according to a pseudo-random spreading sequence. This paper describes the DSSS data transmission tests in the simulation and experimental environment, using different types of pseudo-noise sequences: m-sequences and Kasami codes of the order 6 and 8. The transmitted signals are of different bandwidth and the detection at the receiver side was performed using two detection methods: non-differential and differential. The performed experiments allowed to draw important conclusions for the designing of a physical layer of the shallow-water UAC system. Both, m-sequences and Kasami codes allow to achieve a similar bit error rate, which at best was less than 10 −3. At the same time, the 6th order sequences are not long enough to achieve an acceptable BER under strong multipath conditions. In the case of transmission of wideband signals the differential detection algorithm allows to achieve a significantly better BER (less than 10 −2) than nondifferential one (BER not less than 10 −1). In the case of narrowband signals the simulation tests have shown that the non-differential algorithm gives a better BER, but experimental tests under conditions of strong multipath propagation did not confirm it. The differential algorithm allowed to achieve a BER less than 10 −2 in experimental tests, while the second algorithm allowed to obtain, at best, a BER less than 10 −1. In addition, two indicators have been proposed for a rough assessment which of the detection algorithms under current propagation conditions in the channel will allow to obtain a better BER.

Implementation of Underwater Electric Field Communication Based on Direct Sequence Spread Spectrum (DSSS) and Binary Phase Shift Keying (BPSK) Modulation.

Stable communication technologies in complex waters are a prerequisite for underwater operations. Underwater acoustic communication is susceptible to multipath interference, while underwater optical communication is susceptible to environmental impact. The underwater electric field communication established based on the weak electric fish perception mechanism is not susceptible to environmental interference, and the communication is stable. It is a new type of underwater communication technology. To address issues like short communication distances and high bit error rates in existing underwater electric field communication systems, this study focuses on underwater electric field communication systems based on direct sequence spread spectrum (DSSS) and binary phase shift keying (BPSK) modulation techniques. To verify the feasibility of the established spread spectrum electric field communication system, static communication experiments were carried out in a swimming pool using the DSSS-based system. The experimental results show that in fresh water with a conductivity of 739 μS/cm, the system can achieve underwater current electric field communication within a 11.2 m range with 10-6 bit errors. This paper validates the feasibility of DSSS BPSK in short-range underwater communication, and compact communication devices are expected to be deployed on underwater robots for underwater operations.

Cyclostationarity of Communication Signals in Underwater Acoustic Channels

The effect of underwater acoustic propagation on the cyclostationary features of communication signals is modeled and analyzed. Two kinds of channels are considered: the multiscale-multilag channel, over which mobile and wideband acoustic systems usually communicate, and the dispersive channel resulting from low-frequency modal propagation in shallow water. It is shown that multiscale-multilag channels transform cyclostationary signals into a sum of velocity and acceleration-dependent time-warped cyclostationary processes. This time-warping is carefully taken into account to efficiently recover the cyclostationary features. On the other hand, it is found that low-frequency dispersive channels preserve the original periodicity but attenuate the shorter cycles and spread the correlations. To illustrate the theoretical results, applications with simulated and real data are also presented. Specifically, the problem of estimating time-varying Doppler scales is addressed for multiscale-multilag channels as well as the detection of signals with unique cyclostationary signatures. The example of blind symbol-rate estimation applied to covert communications in dispersive channels is also discussed. Special attention is paid to phase-shift keying (PSK), quadrature amplitude modulation (QAM), orthogonal frequency-division multiplexing (OFDM), and direct-sequence spread-spectrum (DSSS) signals. Accompanying supplementary material provides the MATLAB code used for the estimation and detection examples.

Is Direct Sequence Spread Spectrum Modulation Promising for AI-Based Design of 6G Networks?

Is Direct Sequence Spread Spectrum Modulation Promising for AI-Based Design of 6G Networks?

CBTC Security and Reliability Enhancements by a Key-Based Direct Sequence Spread Spectrum Technique

CBTC Security and Reliability Enhancements by a Key-Based Direct Sequence Spread Spectrum Technique

Integrating key generation and distribution with the quantum noise stream cipher system without compromising the transmission performance

We propose and experimentally demonstrate a secure quantum noise stream cipher transmission system that integrates key generation and distribution. At the stage of carrier phase recovery, the estimated phase noise is used to generate randomness keys without additional equipment. Based on direct sequence spread spectrum technology, we integrate the distributed keys with quantum noise stream cipher signals. The key distribution and encryption transmission can be completed simultaneously without occupying additional bandwidth or time slots. By changing the position of distributed keys in the encryption base, the BER performance of QAM/QNSC signals cannot be affected by the keys. Experimental results demonstrate that the 54.5 Mbps key distribution and 31 Gbps encryption transmission without OSNR penalty can be achieved simultaneously over a 120 km standard single-mode fiber.

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.

Reducing Bit Error Rate in WiMAX using Spread Spectrum Techniques in Comparison with OFDM based Modulations

This research investigated the Bit Error Rate (BER) performance of the WiMAX(Worldwide Interoperability for Microwave Access), a wireless system which uses IEEE 802.16 standard. For the implementation of OFDM model and analyzing the performance of WiMAX system using the Bit Error Rate (BER) and Signal to Noise Ratio (SNR) MATLAB software tool is used. We have used different adaptive modulation techniques such as QPSK, 16-QAM and 64-QAM and spread spectrum techniques such as FHSS (Frequency Hopping Spread Spectrum) and DSSS (Direct Sequence Spread Spectrum). In the current research the Bit Error Rate is improved by using spreading signals. Spread spectrum enables a signal to be transmitted across a frequency band that is much wider than the minimum bandwidth required by the information signal. The simulation results of this research show that FHSS and DSSS have given low BER at low SNR as compared to other modulation techniques.

Complementary Coded Identical Code Cyclic Shift Multiple Access Under Asynchronous Frequency-Selective Fading Channels

A complementary coded code-division multiple-access (CC-CDMA) system is built on the direct sequence (DS) spread spectrum technique, which can suppress multipath interferences and multiple-access interferences due to the ideal correlation property of complementary codes (CCs). However, the DS spread spectrum technique will cause poor bandwidth efficiency; the CC-CDMA system suffers from serious interferences due to the ideal correlation of CCs may not be reconstructed at the receiver after passing through asynchronous frequency selective fading channels. In this paper, we propose a complementary coded identical code cyclic shift multiple access (CC-ICCSMA) system under asynchronous frequency selective fading channels, which allows multiple data streams to transmit in parallel by sharing one spreading code for improving the bandwidth efficiency. Considering the impact of interferences, we propose an ICCS matched filterbank to tackle the interferences, which can decode the data under all paths and achieve a high multipath diversity gain. Simulation results show that the proposed CC-ICCSMA system can achieve higher bandwidth efficiency than that of traditional CC-CDMA and can outperform the traditional DS-CDMA schemes in terms of bit-error rates and transmission rates.

Short-Block-Length Low-Density Parity-Check Codes-Based Underwater Acoustic Spread-Spectrum Communication System

Low-density parity-check (LDPC) codes are commonly used in communication systems to improve the system performance, but LDPC codes takes too long for decoding, making communication inefficient and unsuitable for short-frame data transmission methods. In underwater acoustic channels, spread-spectrum communication becomes an effective way to realize long-distance communication. This paper combines short-block LDPC codes with a direct sequence spread spectrum and soft spread spectrum in underwater acoustic communication, addressing the problem of the inapplicability of conventional LDPC codes. The applicability of the proposed method in this paper is verified through simulation tests and pool experiments. The results indicate that the proposed communication system achieves lower bit error rates compared to the classical coding methods used in underwater acoustic spread-spectrum communication systems under the same channel conditions.

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.

Enhancing Communication Security with 3DES and Spread Spectrum Technologies

As society moves towards the digital age, data security has become an increasingly important issue in wireless communication. To address this problem, the use of encryption techniques has become crucial. In this we studied the Triple Data Encryption Standard (3DES) from theory to practical application, and proposes a wireless spread spectrum system utilizing Direct Sequence Spread Spectrum (DSSS) technology, Quadrature Phase Shift Keying (QPSK) modulation, and 3DES encryption/decryption for secure and reliable data transmission. The system is able to efficiently recover the received signal, even in the presence of interference and noise, as demonstrated by the significantly lower Bit Error Rate (BER) of the received signal compared to the original transmitted binary sequence. The effectiveness of the system is demonstrated through simulation results, indicating that it offers a promising solution for wireless communication applications where secure and reliable data transmission is essential.

Multi-Access Techniques Comparison for Remote Lab System

Remote lab systems are one of the essential requirements for an increased academic productivity in the modern digital world. These systems support and facilitate effective migration from face-to-face classroom education to online education. Digital technology applications and processes are required to easily build a remote lab system. With the availability of multiple access techniques, users can comfortably share laboratory equipment among themselves. The sharing of resources using the remote lab system is highly required for a smooth deployment and implementation of online education. This paper therefore proposed and tested some techniques that combine Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) in remote lab systems. The tested techniques are Multi-Carrier Direct Sequence CDMA (MC-DS-CDMA), Multi-Tone CDMA (MT-CDMA), Multi-Carrier CDMA (MC-CDMA), and Spread Spectrum Multi-Carrier Multiple Access (SS-MC-MA). The first step proposed in this work had to do with the setting of the comparison criteria. At the second step, the solutions cited previously in the real equipment was tested and the best option that met the criteria was selected for the eLab system since the performance technique varies with the laboratory equipment characteristic. The four techniques that were tested demonstrated high performance in telecommunications and online laboratory systems. The implementation of these techniques will benefit universities in several ways, which include reduction of remote lab cost and optimization of sharing of online resources among users. This will further provide students with conducive learning environment by addressing the challenges of reservation and time slot limit. It is therefore recommended that MC-CDMA should be integrated into remote lab system.

Period Estimation of Spread Spectrum Codes Based on ResNet.

In order to more effectively monitor and interfere with enemy signals, it is particularly important to accurately and efficiently identify the intercepted signals and estimate their parameters in the increasingly complex electromagnetic environment. Therefore, in non-cooperative situations, it is of great practical significance to study how to accurately detect direct sequence spread spectrum (DSSS) signals in real time and estimate their parameters. The traditional time-delay correlation algorithm encounters the challenges such as peak energy leakage and false peak interference. As an alternative, this paper introduces a Pseudo-Noise (PN) code period estimation method utilizing a one-dimensional (1D) convolutional neural network based on the residual network (CNN-ResNet). This method transforms the problem of spread spectrum code period estimation into a multi-classification problem of spread spectrum code length estimation. Firstly, the In-phase/Quadrature(I/Q) two-way of the received DSSS signals is directly input into the CNN-ResNet model, which will automatically learn the characteristics of the DSSS signal with different PN code lengths and then estimate the PN code length. Simulation experiments are conducted using a data set with DSSS signals ranging from -20 to 10 dB in terms of signal-to-noise ratios (SNRs). Upon training and verifying the model using BPSK modulation, it is then put to the test with QPSK-modulated signals, and the estimation performance was analyzed through metrics such as loss function, accuracy rate, recall rate, and confusion matrix. The results demonstrate that the 1D CNN-ResNet proposed in this paper is capable of effectively estimating the PN code period of the non-cooperative DSSS signal, exhibiting robust generalization abilities.

Intelligent Search Strategy for Doppler Frequency Based on Fuzzy Logic in DSSS Signal Acquisition

This study focuses on Doppler frequency search strategy for signal acquisition in direct sequence spread spectrum (DSSS) systems. According to DSSS signal accumulation energy vibration characteristics, the whole two-dimension search region can be divided into non-vicinity region, transition region and vicinity region. If only one search strategy is used for the whole region, it is difficult to balance the frequency search times and the frequency estimation accuracy. To solve the above problem, this study proposes an intelligent Doppler frequency search (IDFS) strategy. A fuzzy logic (FL) controller with two sets of fuzzy parameters is utilized to adjust the frequency search step size in the non-vicinity region and vicinity region, respectively. In the non-vicinity region, by jointly considering signal amplitude and code phase to design the fuzzy parameters of the FL controller, the IDFS strategy can reduce the frequency search times while reducing frequency false detection caused by abnormal change of signal energy. In the vicinity region, the fuzzy parameters are designed based on our previous work which aims to achieve higher frequency estimation accuracy. The effectiveness of the IDFS strategy is evaluated through Monte Carlo simulations. Simulation results show that the proposed intelligent search strategy can reduce the frequency search times while ensuring frequency estimation accuracy compared to other existing search strategies. Moreover, the proposed search strategy can reduce false detection in the non-vicinity region.

Cell-Straddling Robust-Fast Cross-Correlation Mitigation via MMSE Filter for DSSS Signals

Existing cross-correlation mitigation algorithms based on the minimum mean square error (MMSE) criterion can effectively suppress multiple access interference (MAI) but suffer from high complexity and modeling grid mismatch. In this work, we propose a cell-straddling robust-fast cross-correlation mitigation (CSR-FCCM) algorithm with two improvements. First, CSRFCCM combines the two-dimensional joint iterative adaptive filtering with interference cancellation, which significantly reduces the number and computational cost of complex amplitude MMSE filters. Second, two discriminators are designed to estimate the straddling offset of delay and frequency for the direct sequence spread spectrum (DSSS) signal. The mismatch problem can be ameliorated by substituting estimated straddling offsets into the signal model, which further improves the MAI mitigation effect. The effectiveness of the CSR-FCCM is verified by simulations using 1023- and 63- length Gold codes. Simulation results show that CSR-FCCM has a better MAI mitigation performance and a lower complexity than the open-loop MAI mitigation algorithms, including 2D-JIAF, and RSR-APC.

Fast acquisition method using modified PCA with a sparse factor for burst DS spread-spectrum transmission

To improve the acquisition speed and inbound capacity of the ground station in a burst direct-sequence (DS) spread-spectrum transmission system, an acquisition method based on a modified parallel code-phase acquisition (PCA) scheme is proposed. By taking advantage of the sparsity of the acquisition result with PCA in the time domain, we introduce the sparse factor to handle the signals via sparsification and apply the sparse recovery algorithm to search and estimate the acquisition result. The computational complexity, mean acquisition time, and relationship between the inbound capacity and acquisition performance are provided. We theoretically analyse the effect of the sparse factor on the acquisition performance. The estimation errors verify our analysis, and simulations show that the acquisition time of our proposed method outperforms that of advanced PCA by 1.2–4.0 times; additionally, the inbound capacity increases by 6.2–36.7%.