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

Clock and carrier recovery are very critical in high speed digital wireless communication for achieving high data rate with low packet error rate. In this paper, we propose a linear estimator for both clock and carrier recovery in a direct sequence spread spectrum (DSSS) communication system and show that this is also the maximum likelihood (ML) estimator. We present simulation results to illustrate the convergence of the estimator under different multipath channel conditions.

A novel method of multipath diversity signal combination is proposed for mobile direct sequence spread spectrum (DS-SS) communications. Multiple transmissions are made for each spread signal. Each transmission is independently delayed and amplified in the complex domain according to the delay profile and the estimated path strength of the channel. This is done to facilitate reception of a signal at the mobile unit which is already a RAKE combination of the multipath signals. This method is called a pre-RAKE combination system because the RAKE combination function is performed pre-transmission. Using this method the size and complexity of the mobile unit can be kept to a minimum. The pre-RAKE method retains the advantages of diversity reception in a multi-path fading environment. An examination of the SNR for the traditional RAKE and the pre-RAKE systems and computer simulations show that the performance of the pre-RAKE system is equivalent to that of the RAKE system. >

This study introduces the group delay and its characteristics in satellite channel, meanwhile, the model of the impact of group delay ripple on performance of direct sequence spread spectrum communication system is established and simulated for analysis. The simulation results indicate the specific impact of group delay ripple on system, as well as the impact of group delay ripple on the transmission and reception signals in the spread spectrum communication system. For transmission signals in the spread spectrum system, the group delay ripple can worsen the EVM and Eye-diagram of spread spectrum signal, cause signal distortion and the deterioration of noise tolerance. For the reception performance of the spread spectrum system, the group delay ripple has little effect on the spread spectrum acquisition using incoherent accumulation and energy judgment, but it can cause a deterioration in the error performance of the reception signal. For example, when relative group delay increases from 0.011 to 0.9, the error performance decreases by about 2 dB. When designing satellite spread spectrum communication systems, power resources are extremely precious, it is necessary to consider the impact of group delay on the communication system, and take certain measures to reduce the impact of group delay ripple to the system.

The performance of a direct sequence spread spectrum (DS/SS) communication system in land mobile satellite channels is evaluated with experiments. Field test results in the L-band with the ETS-V satellite are presented, in which the use of a multibit-quantized coherent matched filter receiver improves the initial acquisition and the bit error rate performances. The bit error rate characteristics in urban and suburban environments are found to agree with those of non-SS BPSK (binary phase-shift keyed) on a nonselective Rician fading channel.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

With the development of nondestructive detection, the emerging testing techniques provide new challenges to signal analysis and interpretation approach applied to the inspection evaluation. Some researchers have developed the methods that focus on feature analysis of detected signals. This article presents a new feature analysis by the Independent Component Analysis (ICA) approach to evaluate the defects tested by the pulsed eddy current (PEC) technique. ICA is a high-order statistics technique used to separate multi-unknown sources, which has been successfully applied to facial image identification and separation of the components of 1D signal. In this article, the ICA approach is utilized to project the response signals of various defects into the independent components (ICs) feature subspace by signal representation model. Dependent on the selected ICs, each defect is represented by different projected coefficients, which are proposed to discriminate and classify the defects that belong to three categories. The improved ICA model is proposed to improve the classification of two similar categories of single defects: metal loss and subsurface defects. The evaluation using the series of experimental data has validated the classification of single defects and the defects with lift-off effect by our ICA approach. The comparison with Principal component analysis (PCA)–based approach further verified the better performance of the ICA-based model.

In this paper we consider blind interference mitigation in direct sequence spread spectrum communication system under intentional jamming. Belouchrani et al. (2000) present a general framework in which blind source separation (BSS) techniques are utilized to enhance conventional detection. However, only second order statistics were utilized which makes the scheme vulnerable to temporally uncorrelated information or jamming signals. In this paper we remove this disadvantage by utilizing BSS based on independent component analysis (ICA). Numerical examples are given to evaluate achieved performance gains.

As digital systems grow rapidly in complexity and sophistication, the educational process must provide future developers with experience that incorporates advanced development tools and modem design techniques. However, this cannot be achieved at the expense of relevant theory and traditional design methods on which modem methods are based. Hence, the learning experience must efficiently combine emphasis on classical design principles with an exposure to state-of-the-art tools and techniques. This student project demonstrates the use of hardware description language design with programmable logic devices to develop a digital system of significant complexity, while introducing the basic principles of spread spectrum communications. After 20 years, this latter technology still remains a modern digital approach to reliable communications, and provides a practical and challenging educational application. This paper summarizes the design and full system hardware implementation of a baseband digital direct sequence spread spectrum communication system for classroom demonstration. The system configuration includes a serial transmitter with pseudorandom spreading routine, a receiver with despreader, and other diagnostic equipment.

For direct sequence (DS) spread spectrum communication systems with differential phase-shift keying (DPSK) modulation, we have calculated low autocorrelation sidelobe pseudo noise (PN) sequences. We constructed a matched filter comprising localized layered structure on a quartz crystal to obtain low matching loss. As a result of the sequences and the construction, 14 dB (6 dB improvement on that of the conventional sequences) peak vs sidelobe of correlated output signal and 9 dB lower loss than that of a conventional filter was achieved. We have applied these matched filters to SS rf-modem units for weak-power digital communications. In these modem units high data rate (1 Mbps), long communication distance (about 20 m) and low current (210 mA when received) performances are obtained.

Deployment of wireless sensor networks (WSNs) with a large number of nodes have reinstated interest in spread spectrum (SS) technologies as they allow to establish multiple access for nodes with simple hardware and limited power budget. Chaotic spreading is one of the still insufficiently explored areas which can lead to higher security and lower multiple access interference (MAI). This research is intended to bring new information about the performance of binary direct sequence spread spectrum (DSSS) and frequency hopping spread spectrum (FHSS) communication systems which employ chaos-based spreading codes and compare them against classical systems employing m-sequences. Unlike existing research, this investigation is based on the simulation of passband communication systems with up/down-conversion and respective filtering. Performance comparison in terms of bit error ratio (BER) versus signal-to-noise ratio (SNR) at the different number of users and MAI dependence on carrier frequency offset among users in case of additive white Gaussian noise (AWGN) channel are presented. Obtained results highlight several scenarios where chaotic-sequences-based binary DSSS and FHSS systems have advantages over classical solutions.

To address the inability to quantitatively analyze the performance of the direct sequence spread spectrum (DSSS) communication system in the presence of short-period pseudo-noise (PN) sequences, this study derives the interference components resulting from correlation processing of single-frequency interference. Given the short period of the spread spectrum sequence used in underwater acoustic systems, a theoretical expression is proposed for analyzing the anti-single-frequency interference performance of DSSS communication systems in underwater acoustics. This expression combines the interference power output by the system to enable quantitative analysis. Simulations are conducted to validate the accuracy of the theoretical expression. The results reveal that the interference sequence generated by correlation processing assumes either a direct current (DC) or sinusoidal distribution. The bit error rate (BER) of the system is influenced by signal-to-interference ratio (SIR), interference frequency offset, phase deviation, and the structure of the spreading code itself. The BER exhibits regular variation with changes in the interference phase. In all working conditions where the interference frequency offset is an integer multiple of the bit bandwidth, single-frequency interference with a frequency offset equivalent to the bit bandwidth has the greatest impact on the system. The concise theoretical expression presented in this study has significant practical value as it allows for quick prediction of variation in the anti-single-frequency interference performance of underwater acoustic DSSS communication systems using short-period PN sequences.

The problem treated in this paper is monocomponent nonstationary interference excision in direct sequence spread spectrum (DSSS) communication systems by means of the local polynomial Fourier transform (LPFT). First, the interference is optimally concentrated in the time-frequency (t-f) plane and then its t-f signature is removed via a binary mask. The LPFT receiver is derived in matrix form and its optimization is performed, having in mind an influence of the binary mask on the received signal. The conventional (suboptimal) and the optimal LPFT receiver performances are compared by means of simulations carried out on the received signal corrupted by different FM types of interferences. The short-time Fourier transform (STFT) receiver is considered as a special case of the LPFT receiver and its performance is assessed simultaneously with the LPFT receiver, both in conventional and optimal case.

Summary form only given, as follows. On page 1398 of the above paper (ibid., vol. COM-28,Part II,pp. 1389-1398, Aig. 1980), the Acknowledgment was published incorrectly. The correct Acknowledgment is as follows: "ACKNOWLEDGMENT The authors would like to thank Prof. C. Ziegler for generating the numerical results, and J. Bartow and S. Hall for their helpful suggestions."

In this letter, the weighted fractional Fourier transform (WFRFT) is performed on the chaotic sequence to enhance the security of the chaotic direct sequence spread spectrum (CD3S) communication, and a WFRFT-CD3S system that spreads the information bits through the WFRFT-chaotic sequence is proposed. In the proposed system, the transmitter scrambles the phase space trajectory of the chaotic sequence through WFRFT and make the distribution of the transmitted signal be Gaussian-like. The receiver synchronizes the WFRFT-chaotic sequence through bidirectional correlation search and demodulates the information through the synchronized local WFRFT-chaotic sequence. Simulations are implemented to evaluate the security performance, synchronization performance, and demodulation performance of the proposed system.

The time-frequency (TF) filter design of non-stationary signals especially chirp signals are studied in the fractional domain. The design of TF/ linear time variant (LTV) filter is implemented as a non-overlapping short time fractional Fourier transform (STFRFT). The first step of our method involves detecting the presence of a multi component linear FM interference and correctly estimating its orientation in the time-frequency plane using cross spectral estimation of signal parameter via rotational invariant technique. This paper introduces a novel algorithm to excise single and multicomponent chirp-like interferences in direct sequence spread spectrum (DSSS) communication. The proposed method excises the interference with high interference power condition, and technique could be easily extended to any kind of chirp interference with little modification

Remote labs have become popular learning aids due to their versatility and considerable ease of utilisation as compared to their physical counterparts. At Makerere University, the remote labs are based on the standard Massachusetts Institute of Technology (MIT) iLabs Shared Architecture (ISA) - a scalable and generic platform. Presented in this paper is such a lab, addressing the key practical aspects of Direct Sequence Spread Spectrum (DSSS) communication. The lab is built on the National Instruments Educational Laboratory Virtual Instrumentation Suite (NI ELVIS) with the Emona Digital and Analog Telecommunications Experimenter (DATEx) add-on board. It also incorporates switching hardware. The lab facilitates real-time control of the equipment, with users able to set, manipulate and observe signal parameters in both the frequency and the time domains. Simulation and data Acquisition modes of the experiment are supported to provide a richer learning experience.