Statistical Analysis of Interference in Asynchronous MC-CDMA Systems

Two major sources of interference affect asynchronous MC-CDMA systems, i.e. multiple access interference due to subcarriers with the same frequency (MAI) and multiple access interference due to subcarriers with different frequency (ICI). Both MAI and ICI are generally modelled as zero-mean Gaussian random variable and their power has been previously been derived in the case of uniformly distributed timing offsets. In this paper, we derive an expression of the conditional power of the MAI and ICI as a function of timing offset. The advantage is that the interference power can then be derived for various distributions of the timing offsets. We then apply the expression to calculating the MAI and ICI power for two different distributions of timing offsets, i.e. uniform distribution and Poisson distribution. Finally, we propose a statistical model for asynchronous MC-CDMA systems that will simplify the computer simulation process of these systems. It is based on modelling the asynchronous system with a synchronous system followed by additive noise representing the MAI and ICI. The model is validated by comparing the BER at the output of the asynchronous system and the model

MULTIPLE ACCESS INTERFERENCE REDUCTION FOR DS-CDMA IN THE PRESENCE OF RAYLEIGH FADING

This paper proposes an alternative transmission structure to the existing direct-sequence code division multiple access (DSCDMA) technique in order to alleviate the decision variable from a substantial portion of the multiple access interference (MAI) incurred over an asynchronous slow varying Rayleigh fading channel. The proposed technique uses a dual frequency switching system that shifts lagging interference components to an alternative frequency band thus reducing the degree ofMAI incurred in the considered symbol-by-symbol matched _lter recovery. Bit-error rate (BER) performance comparisons are offered for the use of both Gold andWalsh-Hadamard (WH) codes. The proposed technique successfully reduces the amount of MAI experienced, however, this reduction comes at the cost of an increased bandwidth

REDUCTION OF MULTIPLE ACCESS INTERFERENCE IN MC-CDMA IN THE PRESENCE OF RAYLEIGH FADING

A new technique is proposed that offers significant reduction of multiple access interference (MAI) encountered in asynchronous multicarrier code division multiple access (MC-CD MA) detection. Using a dual frequency switching component at the transmitter enables the removal of a portion of unwanted interference signals from the decision variable. Biterror rate (BER) comparisons are shown for the use of both Gold and Walsh-Hadamard (WH) spreading sequences. The proposed switching technique clearly outperforms the existing MC-CDMA technique, however, additional bandwidth is required

Enhanced Forensic Speaker Verification Using a Combination of DWT and MFCC Feature Warping in the Presence of Noise and Reverberation Conditions

© 2013 IEEE. Environmental noise and reverberation conditions severely degrade the performance of forensic speaker verification. Robust feature extraction plays an important role in improving forensic speaker verification performance. This paper investigates the effectiveness of combining features, mel frequency cepstral coefficients (MFCCs), and MFCC extracted from the discrete wavelet transform (DWT) of the speech, with and without feature warping for improving modern identity-vector (i-vector)-based speaker verification performance in the presence of noise and reverberation. The performance of i-vector speaker verification was evaluated using different feature extraction techniques: MFCC, feature-warped MFCC, DWT-MFCC, feature-warped DWT-MFCC, a fusion of DWT-MFCC and MFCC features, and fusion feature-warped DWT-MFCC and feature-warped MFCC features. We evaluated the performance of i-vector speaker verification using the Australian Forensic Voice Comparison and QUT-NOISE databases in the presence of noise, reverberation, and noisy and reverberation conditions. Our results indicate that the fusion of feature-warped DWT-MFCC and feature-warped MFCC is superior to other feature extraction techniques in the presence of environmental noise under the majority of signal-to-noise ratios (SNRs), reverberation, and noisy and reverberation conditions. At 0-dB SNR, the performance of the fusion of feature-warped DWT-MFCC and feature-warped MFCC approach achieves a reduction in average equal error rate of 21.33%, 20.00%, and 13.28% over feature-warped MFCC, respectively, in the presence of various types of environmental noises only, reverberation, and noisy and reverberation environments. The approach can be used for improving the performance of forensic speaker verification and it may be utilized for preparing legal evidence in court

Estimation of the hysteresis value for handover decision algorithms using Bayes criterion

In mobile radio communications, inter-cell handover is the process whereby a call in progress is maintained while the mobile unit passes through different cells. Current handover decision algorithms compare the difference between the received signal strengths from different base-stations to a hysteresis value. The proposed paper is a contribution towards an optimal estimation of the hysteresis value using Bayes criterion [1]. An expression of the threshold value h is derived in terms of the standard deviation sigma of the log-normal shadowing affecting the received signals and the ratio eta between the a priori probability of handover and probability of no handover. The performance of the handover decision algorithm is evaluated in terms of the probability of false alarm, or probability of unnecessary handover, and probability of detection, or probability of successful handover

Localisation de sources large bande par des méthodes de régularisation

Cet article présente deux nouvelles méthodes de localisation de sources large bande, basées sur un même principe: la régularisation. L'estimation de paramètres à partir de données de durée assez courte peut être améliorée par les techniques de régularisation qui apportent une information à priori sur ces paramètres. Nous appliquons de deux manières différentes, quoique liées, ces techniques pour l'estimation des angles d'incidence de sources arrivant sur un réseau linéaire de capteurs équidistants. La première solution utilise un filtrage de Kalman dans un espace d'état indexé par la fréquence, tandis que la seconde repose sur l'emploi de paramètres de régularisation ou hyperparamètres pour connecter entre eux deux critères quadratiques à minimiser

Complex-lag polynomial Wigner-Ville distribution

This paper introduces a fourth order polynomial Wigner-Ville distribution (PWVD) which uses complex time lags to achieve optimal energy concentration for signals with non-linear FM laws. It is shown that the new complex-time fourth order PWVD provides an unbiased estimate of the instantaneous frequency of signals with polynomial phases up to order four

Estimating the velocity of mobile stations in macro-cellular systems using the ACF of the received signal IF

This paper presents a novel method for estimating the velocity of a mobile station (MS) in a typical macro-cell. The proposed estimator uses the auto-correlation function of the instantaneous frequency (IF) of the received signal at the MS antenna. The performance of the proposed estimator in the presence of shadowing, additive noise, and non-isotropic scattering is studied analytically. It is proved that, unlike existing velocity estimators, the IF-based estimator is robust to shadowing

Ricean K-factor estimation in mobile communication systems

We propose an estimator for the Ricean K-factor which has applications in mobile communication systems. The estimator is based on the statistics of the instantaneous frequency (IF) of the received signal. Using simulations, we show that the proposed estimator is robust to shadowing and its mean-square error (MSE) is significantly lower than that of the envelope-based estimators