Jammer mitigation in DS-CDMA array system using independent component analysis

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.

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.

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. >

Signal estimation from functional magnetic resonance imaging data (fMRI) is a difficult and challenging task that involves carefully chosen models that can be validated by domain experts. Blind source separation (BSS) techniques such as principal component analysis (PCA), independent component analysis (ICA), and tensor decomposition have been proposed for estimating the task-fMRI signals. However, few studies have investigated their efficacy for classifying different tasks. This paper proposes yet another novel method to validate the signal estimation using predictive performance of the methods. Three commonly used BSS techniques are used for estimating signals (spatio-temporal maps) from task-fMRI. The dataset (consisting of 4 tasks) is taken from the Human Connectome Project (HCP). The extracted temporal signals are used to train a classifier that classifies two different tasks. For a binary classification, a Constrained-PARAFAC tensor decomposition achieves 92% accuracy for differentiating gambling vs. relational tasks. In addition, results for other binary task classifications are also presented. Overall, the proposed Constrained-PARAFAC performs better in prediction performance compared to PCA and ICA.

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

Under the software environment of MATLAB/Simulink, the communication system of direct sequence spread spectrum (DSSS) is dynamically modeled and simulated over a new practical Rayleigh channel, and the relationship curves of the bit error rate (BER) with the signal-to-noise ratio (SNR) of DSSS communication systems are presented. It is analyzed that DSSS system can effectively overcome multipath fading in multipath Rayleigh Fading Channel (RFC). In addition, the anti-multipath fading performance improved by the way of increasing pseudo noise (PN) code length is better than that by the way of increasing the spread spectrum gain in the condition of strong multipath fading.

We address the problem of Blind Source Separation (BSS) of superimposed signals in situations where one signal has constant or slowly varying intensities at some consecutive locations and at the corresponding locations the other signal has highly varying intensities. Independent Component Analysis (ICA) is a major technique for Blind Source Separation and the existing ICA algorithms fail to estimate the original intensities in the stated situation. We combine the advantages of existing sparse methods and Kernel ICA in our technique, by proposing wavelet packet based sparse decomposition of signals prior to the application of Kernel ICA. Simulations and experimental results illustrate the effectiveness and accuracy of the proposed approach. The approach is general in the way that it can be tailored and applied to a wide range of BSS problems concerning one-dimensional signals and images (two-dimensional signals).

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."

The effects of filtering in transmitters on the bit error performance of a binary asynchronous direct sequence spread spectrum communication system are examined in a multiple access environment. Computer simulations are carried out to evaluate the effects of non-linear phase Chebyshev and Butterworth filters and linear phase Bessel, Gauss and Nyquist roll-off filters. The performance degradation of the system is compared and discussed in terms of the BT product of the filter or the transmitted spectrum. >

Performance of a direct sequence spread spectrum communication system operating in an impulsive noise and multipath channel is evaluated using computer simulation techniques. The results indicate that the direct sequence spread spectrum receiver tends to convert the block error pattern in to random error pattern and further application of convolutional coding with Viterbi decoding gives substantial improvement in performance. Balanced Gold codes are found to perform better than Gold codes and m-sequences.

In the field of camera-based photoplethysmography the application of blind source separation (BSS) techniques has extensively stressed to cope with frequently occurring artifacts and noise. Although said techniques can help to extract the cardiac component from a mixture of input sources, permutation indeterminacy inherit to BSS techniques often introduces inaccuracies or requires manual intervention. The current contribution focuses on methods to automatically select the cardiac component from the output of BSS techniques applied to camera-based photoplethysmograms. To that end, we propose simple Markov models to describe and subsequently identify cardiac components. It is shown that good results can be obtained by combining different simple Markov models.

This paper discusses a new surface acoustic wave (SAW) device implementation of a weighted stepped chirp code signal for use in direct sequence spread spectrum communications systems. The theoretical performance of the code signal is evaluated including the following figures of merit: compression ratio, peak sidelobe level, integrated sidelobe level, processing gain, and probability of error. The design considerations for the SAW device implementation of the code signal are discussed including the effects of intersymbol interference. Experimental results are presented for 8 different SAW devices examining the effects of code length (9 or 13 chips), weighting (uniform, cosine-squared, and Hamming), and sampling on the performance of the code signal.

In this paper, a technique will be described which uses multiple surface acoustic wave (SAW) devices in parallel to reduce the acquisition time of a direct sequence spread spectrum communication system. Analysis of system performance in both the search and the lock modes will be presented, and considerations relevant to actual hardware implementation will be discussed.

A new technique for direct sequence spread spectrum communication system synchronization is presented. This technique is based on the pseudorandom sequence decomposition and partial correlation of the component sequences. Correlator self noise power spectal density, signal to noise ratio degradation and acquisition time performance are analyzed. It is shown that considerable reduction of the average time to acquire synchronization can be achieved using the suggested technique.

The performance of a Direct Sequence Spread Spectrum Communication system in actual land mobile satellite channel is evaluated with experiments. Field test results in L-band with the ETS-V satellite are presented, in which the use of a multi-bitquantized Coherent Matched Filter receiver improves the initial acquisition and the bit error rate performances. The BER characteristics in urban and suburban environments are found to agree with that of nonSS BPSK on a non-selective Rician fading channel.