Signal-to-noise Power Ratio Research Articles

Noise suppressing apparatus and noise suppressing method

Speech/non-speech determining section 103 makes a speech/non-speech determination of whether a speech spectrum is of a speech interval with a speech included or of a non-speech interval with only a noise and no speech included. Noise spectrum estimating section 104 estimates a noise spectrum based on the speech spectrum determined as the non-speech interval. SNR estimating section 105 obtains speech signal power from the speech interval and noise signal power from the non-speech interval in the speech spectrum, and calculates SNR from a ratio of two values. Based on the speech/non-speech determination and a value of SNR, suppression coefficient control section 106 outputs a suppression lower limit coefficient to spectrum subtraction section 107. Spectral subtraction section 107 subtracts an estimated noise spectrum from the input speech spectrum, and outputs a speech spectrum with a noise suppressed.

Frequency division multiplexing technique for composite ambiguity function approximation

Abstract In this paper, we propose a frequency division multiplexing (FDM) diversity waveform technique to achieve a delay-Doppler response that approximates the composite ambiguity function (CAF) in a multiple target scenario. First, a channel estimate based on maximum likelihood estimation (MLE) for each subband is provided, and the signal to noise power ratio (SNR) needed to achieve the specific variance requirement of the MLE is derived. Next, using the Doppler transformation, we show how to combine the output response of each subband undergoing a different Doppler shift. Then the CAF approximation of each detected target is derived based on the coherent CLEAN algorithm. Finally, the CAF approximation of all the targets is attained, having the improved delay-Doppler resolution and thus providing a way to resolve initially undetected targets using a recursive procedure.

Performance comparison of selection combining schemes for binary DPSK on nonselective Rayleigh-fading channels with interference

This paper is concerned with the error performance analysis of binary differential phase shift keying (DPSK) with differential detection over the nonselective Rayleigh-fading channel with selection diversity reception and with an additive, correlated, Gaussian interference process in each diversity channel. The fading process is assumed to have an arbitrary Doppler spectrum with arbitrary Doppler bandwidth. The selection schemes investigated are: 1) the selection combining (SC) scheme based on signal-to-noise power ratio (SNR); 2) the SC scheme based on signal-plus-noise (S+N); and 3) the SC scheme based on maximum output (MO). New, exact, closed-form bit-error probability (BEP) expressions are derived, and a performance comparison among the three SC schemes and combining diversity reception is given. The results obtained reduce to previously known results when the correlated interference process is absent, and when the fading process does not fluctuate over the duration of several symbol intervals. The results indicate that the performance of each scheme depends on the tradeoff between the number of diversity branches, the SNR, the interference level, and the correlation of the interference process. However, the SC-(S+N) scheme generally performs worse than the SC-SNR scheme, the SC-MO scheme and combining diversity reception scheme. The findings presented here are not only of fundamental theoretical value, but are also of practical interest to the designers of future mobile communication systems.

Radar detection and preclassification based on multiple hypothesis testing

This work presents a single-scan-processing approach to the problem of detecting and preclassifying a radar target that may belong to different target classes. The proposed method is based on a hybrid of the maximum a posteriori (MAP) and Neyman-Pearson (NP) criteria and guarantees the desired constant false alarm rate (CFAR) behavior. The targets are modeled as subspace random signals having zero mean and given covariance matrix. Different target classes are discriminated based on their different signal subspaces, which are specified by their corresponding projection matrices. Performance is investigated by means of numerical analysis and Monte Carlo simulation in terms of probability of false alarm, detection and classification; the extra signal-to-noise power ratio (SNR) necessary to classify once target detection has occurred is also derived.

Noise canceling method and apparatus for the same

A noise canceler of the present invention is of the type including an adaptive filter for generating a pseudo noise signal, subtracting the pseudo noise signal from a received signal to thereby output an error signal, and sequentially correcting the filter coefficient of the filter in accordance with the error signal. A second adaptive filter produces a second pseudo noise signal and a second error signal. A first and a second power mean circuit each calculates the signal power of the respective signal. A divider performs division with the resulting two kinds of signal power, so that a signal-to-noise power ratio is estimated. A comparator compares the estimated signal-to-noise power ratio and a delayed version of the same and outputs greater one of them as an extended signal-to-noise power ratio. A step size output circuit corrects, based on the extended signal-to-noise power ratio and reference noise signal power output from a power mean circuit, a step size used to adaptively vary the filter coefficient of the first adaptive filter.

Bubbles in the sensing line of nuclear power plant pressure transmitters: the shift of spectrum resonances

Noise analysis is a valuable tool when applied to predictive maintenance problems in nuclear power plants. When focused to the capacitive pressure sensors it can detect the presence of undesirable bubbles in the sensing line. From the noise signal power spectrum density a resonant peak shifting towards the lower frequency region, due to bubbles appearance, is observed. In this work an explanation for the peak displacement is given; besides, a method to estimate the void fraction from the shift is developed. Both results benefit the on-line maintenance of pressure sensors without disturbing plant operation.

Theoretical analysis of system limitation for AM-DD/NRZ optical transmission systems using in-line phase-sensitive amplifiers

This paper shows the theoretically derived performance of single channel, amplitude modulation/direct detection optical transmission systems using in-line optical phase-sensitive amplifiers (PSA's). The calculations take into account the degradation of the signal-to-noise power ratio (SNR) and intersymbol interference (ISI) due to the distortion of transmitted signal pulses. The SNR is analyzed by considering not only amplifier noise and fiber loss but also noise enhancement by four-wave mixing in the transmission fiber. The ISI is estimated by eye-pattern degradation of the transmitted signal numerically calculated using the nonlinear Schrodinger equation. The regenerative repeater spacing of in-line PSA systems limited by SNR and ISI can be expanded by approximately 3 to 10 times that of in-line EDFA systems, in the case of |D|/spl les/0.1 ps/mn/km dispersion fiber systems transmitting a 40-Gb/s signal.

Recovery of antenna pattern loss in a search radar

An algorithm is presented for the maximisation of the signal-to-noise power ratio (SNR) at the output of a radar receiver when the target direction of arrival (TDOA) is unknown. The target detection is affected by receiver noise and clutter. The radar has a beam which is scanning with a priori known pattern. For the maximisation of SNR, the knowledge of TDOA would be needed; in practice, the TDOA is unknown and the detection is also affected by the so-called antenna pattern loss. In fact when the antenna pattern sweeps across the target, the received signal experiences an amplitude modulation in lieu of a constant amplitude. It is the purpose of this paper to exploit this modulation to estimate the TDOA and conceive a detection processor which recovers the antenna pattern loss.

Noise reduction method and filter for implementing the method particularly useful in telephone communications systems

Noise reduction using a digital signal processor includes receiving an input signal which may include a noise-corrupted information signal and/or a noise signal, filtering the noise-corrupted information signal to reduce noise content, and outputting a filtered information signal having the noise content reduced. The filtering includes estimating the spectral envelope of the noise-corrupted information signal amplitude using the formula: E(A|X,O;H1)*p(H1|X,O)+E(A|X,O;H0)*p(H0| H,O), where X is the spectral envelope of the amplitude of the noise-corrupted information signal, O is the spectral envelope of the noise signal power, H0 denotes the statistical event corresponding to a non-information interval, and H1 denotes the statistical event corresponding to an information interval.

Discrete-time method for signal-to-noise power ratio measurement

The measurement of signal-to-noise power ratio (SNR) is of fundamental importance in many areas of electrical engineering, such as communications, signal processing, tests and measurements, circuits and systems, etc. In this paper, we propose two algorithms for estimating the signal-to-noise ratio of a noisy sinewave from discrete-time data obtained by sampling the input signal. One algorithm is based on the estimation of the four parameters of the input sinewave. The second algorithm is based on estimating the average noise power by averaging the squared magnitude of the FFT bins attributed to the noise. Both methods show excellent performance. Simulation results indicate that the four-parameter method requires the input SNR to be at least 10 dB and the input signal frequency not exceeding one-third of the sampling frequency. On the other hand, the second approach, the spectrum averaging method, shows a remarkable robustness over a very wide range of normalized frequencies (with respect to the Nyquist frequency) and SNRs (well over 100 dB). This spectrum averaging method should prove to be very useful in a wide range of applications.

Proposal of coherence multiplexed optical communication system using balanced receiver and its application for space transmission

AbstractVarious types of theoretical studies and experimental work are being performed on coherence multiplexed systems in which multiplexing of the signal light is done by using the time incoherence of a semiconductor laser light. In this paper, the balanced receiver that uses the balanced mixer type photodetector is proposed for coherence multiplexed communication system and signal‐to‐noise power ratio (SNR) and bit‐error rate are theoretically derived. Moreover, the application of a coherence multiplexed system for space transmission is studied and the system which transmits reference light and signal light by polarization multiplexing is proposed. Moreover, the polarization diversity balanced receiver that is presented can remove the effect of polarization mismatch between the transmitter and receiver. Since both of the proposed systems are removed, then a signal‐signal beat noise (a large problem in conventional receiver using single photodetector) creates a drastic improvement in the SNR. Moreover, theoretical analysis of the receiver using an optical amplifier is performed and it is shown that there is an optimum value of spectral linewidth for obtaining the maximum SNR.

Bandwidth efficient QPSK in cochannel interference and fading

The performances of QPSK in the presence of cochannel interference in both nonfading and fading environments are analyzed. Three approaches for representing the cochannel interference are investigated. These are a precise error probability method, a sum of sinusoids (sinusoidal) model, and a Gaussian interference model. In addition to determining precise results for the performance of QPSK in cochannel interference, we examine the validity of these two interference models in both additive white Gaussian noise (AWGN) environments and in different flat fading environments; Rayleigh, Ricean, and Nakagami. Nyquist pulse shaping is considered and the effects of cross channel ISI produced by the cochannel interference are accounted for in the precise interference model. Also accounted for are the random symbol and carrier timing offsets of the interfering signals. Two performance criteria are considered. These are the average bit error rate and the interference penalty. The latter is defined as the increase in signal-to-noise power ratio (SNR) required by a system with cochannel interference in order to maintain the same BER as a system without interference. Attention is given, in particular, to the outdoor microcellular fading environment. In this environment, the fading experienced by the interfering signals may be represented by a Rayleigh-fading model while the fading experienced by the desired signal may be represented by a Ricean or a Nakagami-fading model. >

Microdiversity on rician fading channels

-The performance of an L-branch equal gain (EG) combiner on slow and nonselective Rician fading channels is analyzed. Two performance criteria are considered; the probability distribution of signal-to-noise power ratio (SNR) at the output of the EG combiner and the average bit error rate (BER). Matched filter receivers are considered for two binary modulation formats, coherent phase shift keying (NCFSK). Results using both maximal ratio combing (MRC) and selection diversity combining (SC) are presented for comparison. Our results show that from a feasibility and practical tradeoffs point of view, the performance of an EG combiner may be a good as that of a MR combiner. The effects of gain unbalance between branches of the EG combiner on the probability distribution of SNR and on the bit error rates are also investigated.

Analysis of DPSK error rate due to multipath delay spread

The intersymbol interference (ISI) produced by multipath channel delay spread can be approximated as Gaussian noise. The equivalent average signal-to-noise power ratio (SNR) is defined. Very simple expressions for average bit error rate (BER) due to delay spread are derived for linear quaternary DPSK (QDPSK) transmission with differential detection over mobile radio Rayleigh fading channels.

BER evaluation for phase and polarization diversity optical homodyne receivers using noncoherent ASK and DPSK demodulation

An analysis of the performance of phase diversity receivers using amplitude-shift keying (ASK) and differential phase-shift keying (DPSK) is presented. Both (2*2) and (3*3) multiport receivers are investigated. Asymptotic methods are used to estimate the bit error rate (BER) and signal-to-noise power ratio (SNR) dependence for each type of the receiver. The analysis favors the squarers as the demodulators for ASK whose performance approaches that of the ideal heterodyne detector in the limit of large SNR. A modification of the ASK ((3*3)) receiver which cancels the local oscillator intensity noise is proposed. Receivers which comprise polarization and phase diversity techniques are also investigated for both ASK and DPSK. Their performance is independent of the polarization state of the received signal, and the value of SNR required to obtain the BER of 10/sup -9/ is only a few tenths of a decibel greater than that needed by the phase diversity receivers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Performance of an ADPCM/TASI system for PCM speech compression

This paper contains a summary of performance measurements for a digital speech interpolation (DSI) system called adaptive differential PCM with time assignment speech interpolation (ADPCM/ TASI). This system is used to compress the output of two or more T1 PCM terminals into a bit rate normally requited by one such terminal. The performance measurements presented are as follows. 1) Signal-to-noise power ratios (SNR) for a 1004 Hz tone signal measured by a transmission impairment measuring test set (TIMS). 2) Idle channel noise performance measured by a TIMS. 3) SNR for speech measured by actual computation. These measurements were made for a variety of traffic loading conditions, and a number of different input power levels. The ADPCM/TASI system was constructed by using an AMD 2900 bit slice microprocessor architecture, but was designed to operate on only one speech channel. The presence of other active channels was simulated programatically. The performance of the system when voice band data signals occupy some of the T1 channels is discussed and is reflected in the measurements. An audio tape was made to demonstrate the subjective performance of the system with and without errors in the transmission medium. The objective performance of the system is compared to the D3 channel bank specifications.

SNR Performances for Cascaded Hard Limiting Repeater System

A conventional coaxial CATV system consists of a cascade of many linear or / and nonlinear repeaters ( or amplifiers ) . The output signal-to-noise power ratio ( SNR ) performance in a cascaded linear amplifier system is evaluated by the well-known noise figure . On the other hand, the output SNR performance in nonlinear systems is generally complicated due to the nonlinear behavior of signal and noise , and particularly for cascaded nonlinear repeater systems there has been no analysis of the total output SNR . Therefore , it is of interest to investigate the relations between the output SNR at the final stage and the input SNR at the first stage in cascaded nonlinear repeater systems

Optimum Processing of Antenna Array Signals in the Presence of Discrete Noise Sources

Previous formulations of the signal-to-noise power ratio (SNR) of an antenna array are shown to fail when a number of monochromatic discrete noise sources smaller than the number of elements in the array are considered in the formulation. It is shown how the performance of the array with respect to SNR may, nevertheless, be optimized using a gain maximization procedure The derivation of the theory is carried out in terms of network parameters defined at the input terminals of the array elements. Mutual coupling effects are taken into account. Numerical and experimental results are also presented to illustrate how this technique can be physically implemented.

Coding for suppression of noise and interference in airborne PCM telemetering systems

For the transmission of data from aircraft and missiles to a ground station, compact, lowpower equipment in the air is mandatory, but considerable complexity can be acceptable for the receiver. To transmit data reliably with low transmitter power under conditions of noise and interference normally encountered in air-to-ground transmissions, one may apply noise suppressing coding techniques such as PCM. In standard PCM a signal consists of a sequence of pulses with positive or negative amplitude, and the signals are detected by sampling the amplitudes and ascribing the value +1 to a positive amplitude and the value −1 to a negative amplitude. An improvement of about 7 db in signal-tonoise power ratio over this system may be obtained by using a detection method based on correlation. The received signal is multiplied by a certain function, and the integral of this product taken over the length of the whole signal assumes the value +1 or −1. For each bit of information in the signal a different multiplying function is used. A signal with eight bits of information will thus be represented by eight integrals of value +1 or −1 each. This “integration system” behaves — as far as noise is concerned-like an “amplitude sampling system” having a bandwidth equal to one half times the pulse rate. Since amplitude sampling systems usually are operated with five times that bandwidth in order to keep the filter distortions sufficiently low, the gain of 7 db mentioned above is obtained.