DSSS Systems Research Articles

High Stability Code Tracking for Band-Limited DSSS Systems

High Stability Code Tracking for Band-Limited DSSS Systems

Novel Algorithm for Joint Channel Estimation and Spreading Sequence Detection in DSSS Systems

Novel Algorithm for Joint Channel Estimation and Spreading Sequence Detection in DSSS Systems

Novel Algorithm for Blind Estimation of Scramblers in DSSS Systems

In this paper, we propose a novel algorithm for blind estimation of a linear scrambler, which is a synchronous scrambler or a self-synchronous scrambler, in direct sequence spread spectrum systems and analyze its estimation performance. We first examine the statistics considering the linearity of the scrambled data and the repetition property of the spreading code. Based on this, we then propose an improved estimation algorithm for the feedback polynomial of the linear scrambler constituting a search process and a verification process of feedback polynomial candidates to determine the correct feedback polynomial of the scrambler. To validate the proposed algorithm, we show through computer simulations that the proposed algorithm outperforms the conventional algorithm in terms of estimation performance.

DETECTION OF THE DSSS SIGNAL WITH VARIABLE PN CODES USING THE ANN

- Direct sequence spread spectrum systems appeared and are used to protect the transmitted data DSSS Systems might be one of the solutions for reliable and secured communications. Also, it is one of the approaches used by signals for transmitting bandwidth larger compared to the satisfied frequency related to the original information. The communication systems of SS were vital to suppress interference, complicating the detection and processing of secure communications, the technology of spread spectrum (DSSS) has been initially created for military applications. In a traditional DSSS system, the PN code is the primary key to make the receiver recover the transmitted data. In this paper, by using the MATLAB R2020a is used to simulate the proposed system, it is considered that the transmitter sends data bits and wants to protect the sent data by making each bit send with a PN code consisting of 127 bits randomly without informing the receiver of that. here the artificial neural network (ANN) was used as a tool to find the PN code for each initial value of 7 flip-flops. so, the receiver could detect the transmitted data with BER =0.

On Radio Frequency Fingerprint Identification for DSSS Systems in Low SNR Scenarios

Radio frequency fingerprint (RFF) is an intrinsic hardware characteristic and has been employed for device identification. Its application in low signal-to-noise-ratio (SNR) has never been explored because its identification performance is greatly affected by the received signal quality. This letter proposes a novel RFF identification scheme for spread spectrum systems in low SNR scenarios. In the scheme, a signal preprocessing method, information data estimation-based stacking algorithm, is proposed, which leverages the repeated spreading sequences and stacks them together to eliminate the noise and interference effect. Simulation results demonstrate that the proposed scheme can achieve 98% identification rate when the received signal SNR is −15 dB and the length of spreading sequence is 1023.

Inherent diversity combining techniques to mitigate frequency selective fading in chaos-based DSSS systems

Analysis of communication systems with combiners, assuming flat fading channels, is well-known. However, this analysis for a chaos-based DSSS system with a frequency selective channel, giving proper mathematical model and derived expressions for the probability of error, practically does not exist. This paper presents the theoretical model of a chaos-based DSSS system assuming frequency selective channel that is composed of a primary channel and a number of secondary channels. In order to investigate the consequences of delays on signal transmission in these channels, this paper uses presentation of signals in discrete time domain and theoretical frame of discrete time stochastic processes. The channel is represented by a modified Saleh–Valenzuela model, which results in a number of delayed signal replicas at the receiver side. For the sake of explanation, the delays are assumed to remain in a chip interval. For the sake of comparison, the theoretical models and derived expressions are confirmed by the simulation of the system.

Time-Varying Single-Tone Jamming Suppression in DSSS Systems

Time-Varying Single-Tone Jamming Suppression in DSSS Systems

Noncoherent unitary space-time modulated DSSS systems in multipath channels

In this paper, in order to effectively apply unitary space-time modulation to the direct-sequence spread-spectrum multiple-access (DSSS-MA) networks, we propose a low-rate, noncoherent, unitary, and space-time modulated DSSS system supporting any number of transmit antennas based on Walsh matrices. The proposed scheme simultaneously performs bandwidth spreading and space-time coding and outperforms those using high-rate, conventional unitary space-time constellations. Furthermore, the proposed scheme allows for a simple detector structure based on fast Walsh transforms.

Suppression of Sinusoidal Frequency Modulation Interference in DSSS Systems

For the wideband nonstationary sinusoidal frequency modulation (SFM) interference in DSSS systems, the paper proposes a method to estimate partial parameters of the interference, and then an interference suppression algorithm is developed. The performance of the algorithm is analyzed. Simulations show that the algorithm can efficiently suppress the SFM interference.

Spread spectrum techniques in wireless communication

This article discusses about spread-spectrum technique, the goal is to deliberately spread the transmitted electromagnetic energy in the frequency domain and receive the user data signal using the same pseudo random code used in the transmitter. Critical advantages of DSSS systems are related to their ability to provide secure communication and be robust against continuous time narrow band jamming with low spectral density power.

M-ary spreading-code-phase-shift-keying modulation for DSSS multiple access systems

Code shift keying (CSK) was proposed to increase the transmission efficiency of DSSS systems, and to overcome the spreading gain versus data rate limitation. However, CSK modulation provides no multi-access capability, and degrades the flexibility of a spread spectrum system. In this work, a generalized M-ary DSSS modulation scheme, spreading code phase shift keying (SCPSK), is proposed to improve the system flexibility, and to provide the multi-access capability. This scheme involves switching the spreading code phase in accordance with the incoming data. The union bound of the symbol error probability, in an AWGN channel exposed to multi-user interference, are derived for performance evaluation. Furthermore, the performance of M-SCPSK in a multipath fading channel is investigated via simulation and compared with the conventional DSSS-BPSK scheme.

Performance of a digital code tracking loop for DSSS systems in the presence of Doppler shift

The authors present a low-complexity non-coherent tracking loop based on the gravity of energy window (GEW). Expressions for the proposed tracking loop in a multipath fading channel with Doppler shift environment are derived. The stationary probability density function (PDF) of the phase error and the root-mean-square (RMS) tracking error are obtained by computer simulation. Statistical simulation results show that the new tracking loop can provide much better performance than the conventional non-coherent delay lock loop (DLL) in the presence of Doppler shift.

Code acquisition schemes using antenna arrays for DS-SS systems and their performance in spatially correlated fading channels

We propose parallel and serial code-acquisition schemes using antenna arrays for initial acquisition of direct-sequence spread-spectrum signals, which can lower substantially the range of detectable signal-to-noise ratio (SNR) as compared to the corresponding conventional schemes with a single antenna. The proposed schemes use the sum of all the single-antenna decision samples from antenna arrays, corresponding to an identical subsequence of a given pseudonoise code as a decision variable in order to enhance SNR of the resulting signal. We analyze the mean acquisition time performance under an additive white Gaussian noise channel and spatially correlated time-varying flat Rayleigh fading channels by deriving the expressions for the probabilities of detection, missing, and false alarm. We consider two extreme cases of spatial fading correlation among antenna arrays, the case of uncorrelated diversity antennas and the case of perfectly correlated antennas. From numerical results, we see that the acquisition performance of the proposed schemes using antenna arrays becomes improved continually as the number of antennas increases and the performance improvement depends on the degree of spatial fading correlation.

HOS and GA based interference rejection in DS SS communication systems

A new interference rejection filter based on Higher Order Statistics (HOS) and Genetic Algorithm (GA) is introduced. The advantages over the adaptive filters based on second-order statistics or gradient algorithm are shown through computer simulation.

The application of modified lapped transform domain median filter to narrow—band interference excision in DSSS systems

AbstractA novel communication receiver which uses lapped transform (LT) incorporating modified median filter (MMF) algorithm is designed for narrow—band interference (NB1) excision. Comparing to traditional Fourier Transform, LT has longer basis vectors, less spectral leakage, thus better frequency resolution. The LT domain MMF algorithm takes full advantages of the direct sequence spread spectrum signal, as well as the characteristics of LT, performs the transform domain filtering twice. The first filtering locates the position of interference and mitigates most of them. The second filtering was performed in a small neighborhood of the located interference. So LT domain MMF algorithm can completely mitigate the interference without distorting the desired signal. Simulation results demonstrated the improved BER performance and increased robustness of our approach.

Adaptive wavelet packet transform-basednarrowband interference canceller in DSSS systems

A new adaptive narrowband interference (NBI) rejection method based on wavelet packet transform in DSSS systems is presented. The interference is well located in the course of wavelet packet decomposition, and excised in proper domain in synthesis procedure.

Comments on "Narrow-band interference rejection using real-time Fourier transforms

In their paper on narrow-band interference excision in DS-SS systems D. Davidovici and E.G. Kanterakis (ibid., vol.37, p.713-22, 1989) concluded that excision need not improve the bit-error rate at high-interference levels. It is argued that while this conclusion follows from the specific cases examined, it does not apply to more realistic spread-spectrum system designs.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>