Presence Of Multiple Interference Research Articles

Beamforming Amplify-and-Forward Relay Networks With Feedback Delay and Interference

In this letter, we investigate the effect of feedback delay on the performance of a dual-hop amplify-and-forward (AF) relay network with beamforming in the presence of multiple interferers over Rayleigh fading channels. Specifically, we derive closed-form expressions for the outage probability (OP) and the symbol error rate (SER). Furthermore, to render insights into the effect of feedback delay and interference on the network performance, asymptotic OP and SER are also presented. These asymptotic expressions are very tight in the high signal-to-noise ratio regime, readily enabling us to obtain the diversity and coding gains of the considered network.

Performance Analysis of Dual-Hop AF Systems With Interference in Nakagami-$m$ Fading Channels

In this letter, we investigate the performance of dual-hop channel state information-assisted amplify-and-forward relaying systems over Nakagami-m fading channels in the presence of multiple interferers at the relay. Assuming integer fading parameter m, we derive closed-form expressions for the exact outage probability and accurate approximation for symbol error rate of the system. Furthermore, we look into the asymptotical high signal to noise ratio regime, and characterize the diversity order achieved by the system. All the analytical results are validated via Monte Carlo simulations.

Performance of three-level spectrally encoded spread-time CDMA in the presence of multiple interferences

In this study the authors present an in-depth study, analysis and discussion on maximum likelihood (ML)-based receiver for a typical spectrally encoded spread-time CDMA in the presence of multiple narrowband interference (NBI) signals in an additive white Gaussian noise channel. Furthermore, the authors demonstrate that by combining useful properties of ML-based receiver and three-level codes, that is, codes with values of −1, 0, +1, the authors can introduce a new strategy in which superior performance with respect to previous receiver structure based on two-level codes, that is, codes with values of −1, +1, can be attained. With the help of an example, the authors drive, first, the required signal-to-noise+interference power ratio (SNR) in a multiple access communication environment with multiple NBIs and, second, SNR attenuating parameter owing to multiple NBIs for two- and three-level codes. Finally, the authors relate the above parameters to a number of simple descriptive factors such as bit error rate. The results are validated by an extensive simulation on the aforementioned system.

Average Symbol Error Rate Performance of MIMO-MRC System with Multiple Interferers in Rayleigh Fading Channels

In this letter, we analyze the average symbol error rate (SER) performance for multiple-input multiple-output (MIMO) wireless communication links with transmit beamforming and maximum ratio combining (MRC), known as MIMO-MRC, in the presence of multiple interferers in Rayleigh fading channels. An upper bound and an approximation of the average SER for M-ary signaling and an exact average SER for some modulation formats are evaluated. Moreover, an exact closed-form expression of the average SER in an interference-limited environment is derived. The analytical results are confirmed by numerical simulations.

Performance analysis of MIMO-MRC system in the presence of multiple interferers and noise over rayleigh fading channels

In this paper, we analyze the performance of multiple-input multiple-output (MIMO) wireless communication links with transmit beamforming and maximum ratio combining (MRC), known as MIMO-MRC, in the presence of multiple interferers and noise over Rayleigh fading channels. First, exact closed-form expressions for the signal-to-noise-plus-interference-ratio (SINR) distribution are calculated, along with the outage probability of the SINR, and the moment generating function (MGF) of the SINR. Second, upper bound and approximation of the average symbol error rate (SER) for pulse amplitude modulation (PAM), quadrature amplitude modulation (QAM), and phase shift keying (PSK) with M-ary signaling are evaluated by using the MGF of the SINR. Third, an exact closed-form expression of the average SER for some modulation formats is derived. Finally, the analytical results are confirmed by numerical simulations.

Explicit Analytical Expressions for Outage and Error Rate of Diversity Cellular Systems in the Presence of Multiple Interferers and Correlated Rayleigh Fading

The outage probability of maximal ratio combining diversity with an arbitrary number of antennas in the presence of an arbitrary number of cochannel interferers and thermal noise is derived when the branch gains of the desired user signal and interfering signals experience Rayleigh fading and have the same correlation matrix. Two special cases, when the correlation matrix is equicorrelated and when the correlation matrix has different eigenvalues, are considered for both the equal-power cochannel interference case and the unequal-power cochannel interference case. Further, the average bit-error rate of a coherent binary phase-shift keying (BPSK)-modulated cellular system using maximal ratio combining diversity in cochannel interference and correlated Rayleigh fading is derived. The effects of the average signal-to-noise ratio (SNR) and the average signal-power-to-interference-power ratio on the system performance are examined.

Exact Performance Analysis of Optimum Combining With Multiple Interferers in Flat Rayleigh Fading

This letter provides a comprehensive overview and extension of recent results on outage probabilities and bit-error rates (BER) for optimal combiners in the presence of multiple interferers and additive noise. Desired signal and interferers are subject to flat Rayleigh fading and all channels are independent. In addition to summarizing previous work, this letter also derives the BER for a wider range of modulations than previously considered. We show that previous approximate results on the equal power interferer case where the number of interferers is less than the number of antenna elements can be made exact in a straightforward way. Finally we extend previous work on the single and double interferer case to the general case of arbitrary numbers of interferers.

Characteristics of detection of a radio signal of unknown duration in the presence of multiple interference with unknown parameters

The paper describes the structure and characteristics of new maximum-probable algorithms for detection of radio signals in the presence of multiplicative and additive interference with different rates of a priori indeterminacy.

Speech perception in noise with a two-sensor frequency-domain minimum-variance (FMV) beamforming algorithm

The performance of a two-sensor based, frequency-domain minimum-variance beamforming algorithm (FMV) to extract a signal in the presence of multiple interferers was evaluated. Speech reception thresholds (SRT) and speech intelligibility measures were obtained from listeners with normal hearing or with mild-to-moderate sensorineural hearing loss. Word and sentence length stimuli were processed through the FMV algorithm, directional microphones alone, or with a simple delay-and-sum beamformer. Listener’s ratings of speech intelligibility, percent of words repeated correctly, and threshold for words and sentences in the presence of four competing signals showed the FMV to provide significant performance benefits across different listening environments.

Outage probability with MRC in presence of multiple interferers under Rayleigh fading channels

Closed-form analytical expressions are derived for the outage probability of predetection maximal ratio combiner (MRC) diversity reception with M branches in Rayleigh fading channels. This formulation is obtained in the presence of white Gaussian noise and Q interferers, without restrictions regarding the power, number or distribution parameters of interferers.

Beamforming with collocated microphone arrays

A collocated microphone array, including three gradient microphones with different orientations and one omnidirectional microphone, was used to acquire data in a sound‐treated room and in an outdoor environment. This arrangement of gradient microphones represents an acoustic vector sensor used in air. Beamforming techniques traditionally associated with much larger uniformly spaced arrays of omnidirectional sensors are extended to this compact array (1 cm3) with encouraging results. A frequency–domain minimum‐variance beamformer was developed to work with this array. After a calibration of the array, the recovery of sources from any direction is achieved with high fidelity, even in the presence of multiple interferers. SNR gains of 5–12 dB with up to four speech sources were obtained with both indoor and outdoor recordings. This algorithm has been developed for new MEMS‐type microphones that further reduce the size of the sensor array.

Average error probability of digital cellular radio systems using mrc diversity in the presence of multiple interferers

The performance of digital cellular radio systems employing maximal ratio combining diversity is analyzed in a flat-fading channel with cochannel interference and additive white Gaussian noise. It is assumed that the desired signal may experience Rice fading (due to the presence of a line-of-sight component), while the interferers are Rayleigh-faded and may have similar or dissimilar average powers. Exact expressions are derived for the average symbol-error probability of M-ary phase-shift keying modulation in the presence of multiple independent Rayleigh-faded interferers.

Using cross-frequency cost functions for broadband source localization and environmental inversion

Cost functions that are constructed by coherently summing (model-to-data) correlations over hydrophone pairs and frequency have been used successfully for source localization [E. K. Westwood, J. Acoust. Soc. Am. 91, 2777–2789 (1992)] as well as source localization and environmental inversion [Neilsen, J. Acoust. Soc. Am. (to be published)]. Although the coherent sum is usually taken over the same frequency for both data and model, it is shown that summing over other regions of the fdata⊗fmodel space is also useful and may facilitate more efficient source localization. It is shown that lines of constant fdata/fmodel correspond to different source bearings. Although looking along lines of constant fdata/fmodel can be used as a crude form of spatial filtering, a new non-plane-wave spatial filter is also constructed that helps localize sources in the presence of multiple interferers. The spatial filter employed uses the environmental model to construct its set of basis functions and is therefore theoretically capable of spatially filtering in full 3-D as opposed to just bearing, as is done in adaptive beamforming.

A two-microphone dual delay-line approach for extraction of a speech sound in the presence of multiple interferers.

This paper describes algorithms for signal extraction for use as a front-end of telecommunication devices, speech recognition systems, as well as hearing aids that operate in noisy environments. The development was based on some independent, hypothesized theories of the computational mechanics of biological systems in which directional hearing is enabled mainly by binaural processing of interaural directional cues. Our system uses two microphones as input devices and a signal processing method based on the two input channels. The signal processing procedure comprises two major stages: (i) source localization, and (ii) cancellation of noise sources based on knowledge of the locations of all sound sources. The source localization, detailed in our previous paper [Liu et al., J. Acoust. Soc. Am. 108, 1888 (2000)], was based on a well-recognized biological architecture comprising a dual delay-line and a coincidence detection mechanism. This paper focuses on description of the noise cancellation stage. We designed a simple subtraction method which, when strategically employed over the dual delay-line structure in the broadband manner, can effectively cancel multiple interfering sound sources and consequently enhance the desired signal. We obtained an 8-10 dB enhancement for the desired speech in the situations of four talkers in the anechoic acoustic test (or 7-10 dB enhancement in the situations of six talkers in the computer simulation) when all the sounds were equally intense and temporally aligned.

Human performance in a multisource environment with a frequency-banded minimum-variance beamforming algorithm

The effectiveness of a newly developed signal-processing algorithm to extract speech in the presence of multiple interferers was evaluated through intelligibility ratings from normal- and hearing-impaired listeners. Sentences were presented with competing speech and multitalker babble (MTB) at four different SNRs to groups of individuals with sensorineural hearing loss and normal hearing. The sentences and competition had been processed through a real-time, frequency-banded minimum-variance beamforming (FBMVB) algorithm in multitalker environments (Lockwood et al., 1999). Competing messages and MTB were simulated at +22 and +45 azimuths relative to the target source. Each target sentence with competing messages was submitted to the FBMVB algorithm to yield a set of 24 ‘‘processed’’ and 24 ‘‘unprocessed’’ sentences per SNR condition. Listeners rated the intelligibility (0%–100%) of the target sentences and repeated the last word of each sentence. Results from the ratings and the word recognition scores show improvement for every listener when the ensemble speech and competition were processed through the FBMVB algorithm. Results from these experiments indicate the advantage of the algorithm in selective extraction of speech in complex environments. Continued evaluation of the algorithm under real-room conditions is in progress. [Work supported by R21DC04840 ONR N00014-99-1-0612.]

Multi-Window Classical Least-Squares Multivariate Calibration Methods for Quantitative ICP-AES Analyses

The advent of inductively coupled plasma atomic emission spectrometers (ICP-AES) equipped with charge-coupled device (CCD) detector arrays allows the application of multivariate calibration methods to the quantitative analysis of spectral data. We have applied classical least-squares (CLS) methods to the analysis of a variety of samples containing up to 12 elements plus an internal standard. The elements included in the calibration models were Ag, Al, As, Au, Cd, Cr, Cu, Fe, Ni, Pb, Pd, and Se. By performing the CLS analysis separately in each of 46 spectral windows and by pooling the CLS concentration results for each element in all windows in a statistically efficient manner, we have been able to significantly improve the accuracy and precision of the ICP-AES analyses relative to the univariate and single-window multivariate methods supplied with the spectrometer. This new multi-window CLS (MWCLS) approach simplifies the analyses by providing a single concentration determination for each element from all spectral windows. Thus, the analyst does not have to perform the tedious task of reviewing the results from each window in an attempt to decide the correct value among discrepant analyses in one or more windows for each element. Furthermore, it is not necessary to construct a spectral correction model for each window prior to calibration and analysis. When one or more interfering elements were present, the new MWCLS method was able to reduce prediction errors compared to the single-window multivariate and univariate predictions. The MWCLS detection limits in the presence of multiple interferences are 15 ng/g (i.e., 15 ppb) or better for each element. In addition, errors with the new method are only slightly inflated when only a single target element is included in the calibration (i.e., knowledge of all other elements is excluded during calibration). The MWCLS method is found to be vastly superior to partial least-squares (PLS) in this case of limited numbers of calibration samples.

Approximation of outage probability on Nakagami fading channels with multiple interferers

A distribution of the signal-to-interference ratio (SIR) has been obtained on Nakagami fading channels using an approximation proposed by Nakagami, thus simplifying the analysis of outage probabilities in the presence of multiple interferers with arbitrary fading parameters.

Outage probability of cellular radio systems using maximal ratio combining in the presence of multiple interferers

In mobile radio systems, antenna diversity is used to combat fading and reduce the impact of cochannel interference. We derived a new expression for probability density functions of the signal-to-interference-plus-noise ratio and apply it to analyze the outage probability (OTP) for a maximal ratio combining diversity system when multiple cochannel interferers are present. Numerical results showing the impact of the number of antenna elements, the number of cochannel interferers, and signal-to-noise ratio on the OTP are presented. Simulation results validating the analytical results are also presented.