Showing papers on "Signal-to-noise ratio published in 2004"

Improved watershed transform for medical image segmentation using prior information

Abstract: The watershed transform has interesting properties that make it useful for many different image segmentation applications: it is simple and intuitive, can be parallelized, and always produces a complete division of the image. However, when applied to medical image analysis, it has important drawbacks (oversegmentation, sensitivity to noise, poor detection of thin or low signal to noise ratio structures). We present an improvement to the watershed transform that enables the introduction of prior information in its calculation. We propose to introduce this information via the use of a previous probability calculation. Furthermore, we introduce a method to combine the watershed transform and atlas registration, through the use of markers. We have applied our new algorithm to two challenging applications: knee cartilage and gray matter/white matter segmentation in MR images. Numerical validation of the results is provided, demonstrating the strength of the algorithm for medical image segmentation.

Channel aware decision fusion in wireless sensor networks

Abstract: Information fusion by utilizing multiple distributed sensors is studied in this work. Extending the classical parallel fusion structure by incorporating the fading channel layer that is omnipresent in wireless sensor networks, we derive the likelihood ratio based fusion rule given fixed local decision devices. This optimum fusion rule, however, requires perfect knowledge of the local decision performance indices as well as the fading channel. To address this issue, two alternative fusion schemes, namely, the maximum ratio combining statistic and a two-stage approach using the Chair-Varshney fusion rule, are proposed that alleviate these requirements and are shown to be the low and high signal-to-noise ratio (SNR) equivalents of the likelihood-based fusion rule. To further robustify the fusion rule and motivated by the maximum ratio combining statistics, we also propose a statistic analogous to an equal gain combiner that requires minimum a priori information. Performance evaluation is performed both analytically and through simulation.

Speckle reduction in optical coherence tomography by path length encoded angular compounding

Abstract: Speckle, a factor reducing image quality in optical coherence tomography ('OCT'), can limit the ability to identify cellular structures that are important for the diagnosis of a variety of diseases. The present invention allows for an implementation of an angular compounding, angular compounding by path length encoding ('ACPE') for reducing speckle in OCT images. By averaging images obtained at different incident angles, with each image encoded by path length, ACPE maintains high-speed image acquisition and implements minimal modifications to OCT probe optics. ACPE images obtained from tissue phantoms and human skin in vivo demonstrate a qualitative improvement over traditional OCT and an increased signal-to-noise ratio ('SNR'). Accordingly, apparatus probe catheter, and method are provided for irradiating a sample. In particular, an interferometer (5) may forward forwarding an electromagnetic radiation (10). In addition, a sample arm may receive the electromagnetic radiation, and can include an arrangement (20) which facilitates a production of at least two radiations (30, 40) from the electromagnetic radiation so as to irradiate the sample. Such arrangement can be configured to delay a first radiation of the at least two radiations with respect to a second radiation of the at least two radiations.

A fully integrated 24-GHz eight-element phased-array receiver in silicon

Abstract: This paper reports the first fully integrated 24-GHz eight-element phased-array receiver in a SiGe BiCMOS technology. The receiver utilizes a heterodyne topology and the signal combining is performed at an IF of 4.8 GHz. The phase-shifting with 4 bits of resolution is realized at the LO port of the first down-conversion mixer. A ring LC voltage-controlled oscillator (VCO) generates 16 different phases of the LO. An integrated 19.2-GHz frequency synthesizer locks the VCO frequency to a 75-MHz external reference. Each signal path achieves a gain of 43 dB, a noise figure of 7.4 dB, and an IIP3 of -11 dBm. The eight-path array achieves an array gain of 61 dB and a peak-to-null ratio of 20 dB and improves the signal-to-noise ratio at the output by 9 dB.

Diversity control in wireless communications devices and methods

Abstract: A wireless communications device (100) includes a primary radio frequency branch (134) and a diversity branch (136), which is enabled and disabled to balance performance and power consumption. Diversity mode operation of the device is controlled, for example, based on one or more of an estimated channel quality indicator, data reception, data rate, state or mode of the station, estimated signal to noise ratio of a pilot signal, battery power level, distance from a serving cell, among other factors.

A digitally enhanced 1.8-V 15-bit 40-MSample/s CMOS pipelined ADC

Abstract: A 1.8-V 15-bit 40-MSample/s CMOS pipelined analog-to-digital converter with 90-dB spurious-free dynamic range (SFDR) and 72-dB peak signal-to-noise ratio (SNR) over the full Nyquist band is presented. Its differential and integral nonlinearities are 0.25 LSB and 1.5 LSB, respectively, and its power consumption is 400 mW. This performance is enabled by digital background calibration of internal digital-to-analog converter (DAC) noise and interstage gain errors. The calibration achieves improvements of better than 12 dB in signal-to-noise plus distortion ratio and 20 dB in SFDR relative to the case where calibration is disabled. Other enabling features of the prototype integrated circuit (IC) include a low-latency, segmented, dynamic element-matching DAC, distributed passive input signal sampling, and asymmetric clocking to maximize the time available for the first-stage residue amplifier to settle. The IC is realized in a 0.18-/spl mu/m mixed-signal CMOS process and has a die size of 4mm/spl times/5 mm.

A cascaded continuous-time /spl Sigma//spl Delta/ Modulator with 67-dB dynamic range in 10-MHz bandwidth

Abstract: This paper presents the design of a 2-2 cascaded continuous-time sigma-delta modulator. The cascaded modulator comprises two stages with second-order continuous-time resonator loopfilters, 4-bit quantizers, and feedback digital-to-analog converters. The digital noise cancellation filter design is determined using continuous-time to discrete-time transformation of the sigma-delta loopfilter transfer functions. The required matching between the analog and digital filter coefficients is achieved by means of simple digital calibration of the noise cancellation filter. Measurement results of a 0.18-/spl mu/m CMOS prototype chip demonstrate 67-dB dynamic range in a 10-MHz bandwidth at 8 times oversampling for a single continuous-time cascaded modulator. Two cascaded modulators in quadrature configuration provide 20-MHz aggregate bandwidth. Measured anti-alias suppression is over 50 dB for input signals in the band from 150 to 170 MHz around the sampling frequency of 160 MHz.

Embedding carrier phase recovery into iterative decoding of turbo-coded linear modulations

Abstract: In this paper, we introduce a low-complexity carrier phase estimation algorithm to be integrated into the data decoder of a turbo-coded modem employing a linear modulation. The estimator is based on a pseudo-maximum-likelihood approach and makes iterative use of soft decisions provided by the soft-in/soft-out decoders within the overall turbo-decoding scheme. In doing so, iterative decoding and carrier phase recovery go together iteration after iteration in a "soft decision-directed" mode. This allows performing reliable blind phase estimation and almost ideal coherent detection for values of the signal-to-noise ratio down to a few decibels only, and without the need to resort to narrowband phase-locked loops with large acquisition time. Performance in terms of mean estimated value, root mean-squared estimation error, and overall decoder bit-error rate as derived by simulation are also reported.

Second-order asymptotics of mutual information

Abstract: A formula for the second-order expansion of the input-output mutual information of multidimensional channels as the signal-to-noise ratio (SNR) goes to zero is obtained. While the additive noise is assumed to be Gaussian, we deal with very general classes of input and channel distributions. As special cases, these channel models include fading channels, channels with random parameters, and channels with almost Gaussian noise. When the channel is unknown at the receiver, the second term in the asymptotic expansion depends not only on the covariance matrix of the input signal but also on the fourth mixed moments of its components. The study of the second-order asymptotics of mutual information finds application in the analysis of the bandwidth-power tradeoff achieved by various signaling strategies in the wideband regime.

Power allocation for regenerative relay channel with Rayleigh fading

Abstract: Cooperative relaying is considered as an effective way to combat Rayleigh fading, to offer better quality of communication link or channel capacity. From the perspective of information theory, channel capacity depends on the SNR of the received signal, therefore, how to allocate transmit power between transmitter and relay to achieve maximum SNR at the receiver or maximum channel capacity is an important issue. In general, there are two types of relaying system, i.e. non-regenerative and regenerative systems. This paper puts emphasis on the power allocation (PA) of regenerative systems. Based on a 2-hop relaying channel suffering from Rayleigh fading, with and without diversity, an adaptive PA scheme is proposed, under transmit power constraints, to keep the system running at the optimum level. Numerical results indicate that with the proposed PA scheme, the system performance not only outperforms that of the direct transmission system, but also obtains the maximum channel capacity or SNR of the relaying system.

Flow Rate Measurements Using Flow-Induced Pipe Vibration

Abstract: This paper focuses on the possibility of a non-intrusive, low cost, flow rate measurement technique. The technique is based on signal noise from an accelerometer attached to the surface of the pipe. The signal noise is defined as the standard deviation of the frequency averaged time series signal. Experimental results are presented that indicate a nearly quadratic relationship between the signal noise and mass flow rate in the pipe. It is also shown that the signal noise - flow rate relationship is dependant on the pipe material and diameter.

Quantitative study of high-dynamic-range image sensor architectures

Abstract: Analysis of dynamic-range (DR) and signal-to-noise-ratio (SNR) for high fidelity, high-dynamic-range (HDR) image sensor architectures is presented. Four architectures are considered: (i) time-to-saturation, (ii) multiple-capture, (iii) asynchronous self-reset with multiple capture, and (iv) synchronous self-reset with residue readout. The analysis takes into account circuit nonidealities such as quantization noise and the effects of limited pixel area on building block and reference signal performance and accuracy. Examples that demonstrate the behavior of SNR in the extended DR and implementation and power consumption issues for each scheme are presented.

Synchronization analysis for UWB systems with a low-complexity energy collection receiver

Abstract: This paper presents analysis of a synchronization scheme for a low complexity, noncoherent ultrawideband (UWB) receiver. The receiver has very low complexity and the synchronization scheme does not increase drastically the complexity. A theoretical formula that helps in the definition of the preamble length is proposed and its validity provided for reasonable signal to noise ratio (SNR). The performance is examined in terms of probability of synchronization for both AWGN and Saleh-Valenzuela channel models. The synchronization results together with the BER performance show the suitability of this simple receiver structure for low cost devices in sensor networks.

Optical performance monitoring using nonlinear detection

Abstract: A definitive goal for optical performance monitoring in an optical communications network is to provide comprehensive signal quality information in a cost-effective manner. This paper explores in detail the possibility of using nonlinear optical detection to achieve this goal. Sensitive nonlinear detection techniques commonly used in the field of ultrafast optics are applied to the problem of performance monitoring and are shown to allow quantitative measurements to be made of quantities such as accumulated chromatic dispersion, polarization-mode dispersion impairment, optical signal-to-noise ratio, and extinction ratio. Experiments performed on a 40-Gb/s transmission system demonstrate the immediate viability of this approach for measuring these quantities of interest at practical optical power levels.

A modified a priori SNR for speech enhancement using spectral subtraction rules

Abstract: The letter addresses the problem of single-channel speech enhancement using a spectral subtraction method. The proposed approach is directed toward finding a self-adaptive averaging factor to estimate the a priori SNR. Performance of the modified averaging factor is evaluated using conventional spectral-subtraction algorithms in which the averaging factor is otherwise kept as a constant. Improved results are obtained in terms of speech quality measures for various types of noise and at different SNR levels when the proposed time-frequency varying averaging factor is adapted in the conventional subtraction rules.

Design optimization of a piezoresistive pressure sensor considering the output signal-to-noise ratio

Abstract: Piezoresistive sensors often suffer from poor signal-to-noise ratios, limiting their use for measuring small pressure differentials. As the pressure range is reduced, and the sensitivity of the sensor increased, the effect of noise on the output signal becomes the limiting factor in the sensor design. In this paper, the optimization of the design to enhance the signal-to-noise ratio of a piezoresistive-type pressure sensor is performed considering different noise components commonly present with these types of sensors. The optimal design for the cases of constant voltage and current is achieved by maximizing the performance index, which is defined as the output signal versus noise. The output voltage and noise are separately analyzed and experimentally tested with respect to the geometric parameters of the piezoresistor and the applied voltage and current. Brownian, Johnson and flicker (1/f) noises are modeled, the latter two of which are dominant for piezoresistive sensors operated at low frequencies to dc. The experimental results show that the optimal design with respect to the resistor length, and number of turns is significantly different when noise is considered. For the special case of the piezoresistive sensor tested, the flicker noise required more turns and longer active elements than if only the effective and non-effective resistances were considered. The optimal Vout/Vnoise was over twice that of the sensor designed maximizing Vout alone.

Analysis of diffuse optical wireless channels employing spot-diffusing techniques, diversity receivers, and combining schemes

Abstract: In this letter, the performance of an indoor optical wireless spot-diffusing system using various multibeam transmitter configurations, in association with direction diversity and combining techniques, is assessed and compared under the impact of multipath dispersion and ambient light noise through theoretical analysis and computer simulation. Computer simulation for three different multibeam transmitter configurations and a conventional diffuse transmitter is carried out. Diversity receiver and wide field-of-view (FOV) receiver configurations are evaluated in conjunction with the proposed configurations. For the diversity-detection case, a receiver comprising an array of narrow FOV detectors (three and seven segments) oriented in different directions is used to maximize the collected signals and minimize noise. A novel line-strip multibeam system (LSMS) is investigated with single and diversity receiver configurations, and is compared with other spot-diffusing methods. Combining schemes, including selection combining, maximum ratio combining, and equal gain combining are employed for the presented configurations. Our results indicate that the performance improvement obtained through the use of LSMS with a three-direction diversity receiver is about 20 dB signal-to-noise ratio enhancement over the conventional diffuse system, and 26 dB when combining techniques are used. Root mean square delay-spread performance for the proposed configurations, at different positions on the communication floor, are also evaluated and compared.

Scaling trends of on-chip power distribution noise

Abstract: The design of power distribution networks in high-performance integrated circuits has become significantly more challenging with recent advances in process technologies. As on-chip currents exceed tens of amperes and circuit clock periods are reduced well below a nanosecond, the signal integrity of on-chip power supply has become a primary concern in the integrated circuit design. The scaling behavior of the inductive and resistance voltage drops across the on-chip power distribution networks is the subject of this paper. The existing work on power distribution noise scaling is reviewed and extended to include the scaling behavior of the inductance of the on-chip global power distribution networks in high-performance flip-chip packaged integrated circuits. As the dimensions of the on-chip devices are scaled by S, where S>1, the resistive voltage drop across the power grids remains constant and the inductive voltage drop increases by S, if the metal thickness is maintained constant. Consequently, the signal-to-noise ratio decreases by S in the case of resistive noise and by S/sup 2/ in the case of inductive noise. As compared to the constant metal thickness scenario, ideal interconnect scaling of the global power grid mitigates the unfavorable scaling of the inductive noise but exacerbates the scaling of resistive noise by a factor of S. On-chip inductive noise will, therefore, become of greater significance with technology scaling. Careful tradeoffs between the resistance and inductance of the power distribution networks will be necessary in nanometer technologies to achieve minimum power supply noise.

A two-step noise reduction technique

Abstract: The paper addresses the problem of single microphone speech enhancement in noisy environments Common short-time noise reduction techniques proposed in the art are expressed as a spectral gain depending on the a priori SNR In the well-known decision-directed approach, the a priori SNR depends on the speech spectrum estimation in the previous frame As a consequence, the gain function matches the previous frame rather than the current one which degrades the noise reduction performance We propose a new method, called the two-step noise reduction (TSNR) technique, which solves this problem while maintaining the benefits of the decision-directed approach This method is analyzed and results in voice communication and speech recognition contexts are given

Outage performance for maximal ratio combiner in the presence of unequal-power co-channel interferers

Abstract: Outage probability for maximal ratio combining (MRC) is usually tackled in the framework of Rayleigh or Nakagami faded co-channel interferers with equal power, which allows for the treatment of the total interference power as a single gamma distributed variable to simplify the analysis. The more general case with unequal-power co-channel interferers is formulated and solved differently in this paper ending up with simple closed-form solutions for Rician/Rayleigh and Nakagami/Rayleigh channel models.

Feedback stabilization over signal-to-noise ratio constrained channels

Abstract: There has recently been significant interest in feedback stabilization problems over communication channels, including several with bit rate limited feedback. Motivated by considering one source of such bit rate limits, we study the problem of stabilization over a signal-to-noise ratio (SNR) constrained channel. We discuss both continuous and discrete time cases, and show that for either state feedback, or for output feedback delay-free, minimum phase plants, there are limitations on the ability to stabilize an unstable plant over an SNR constrained channel. These limitations in fact match precisely those that might have been inferred by considering the associated ideal Shannon capacity bit rate over the same channel.

Speech enhancement with missing data techniques using recurrent neural networks

Abstract: This paper presents an application of missing data techniques in speech enhancement. The enhancement system consists of two stages: the first stage uses a recurrent neural network, which is supplied with noisy speech and produces enhanced speech; whereas the second stage uses missing data techniques to further improve the quality of enhanced speech. The results suggest that combining missing data technique with RNN enhancement is an effective enhancement scheme resulting in a 16 dB background noise reduction for all input signal to noise ratio (SNR) conditions from -5 to 20 dB, improved spectral quality and robust automatic speech recognition performance.

Quantifying variability in neural responses and its application for the validation of model predictions

Abstract: A rate code assumes that a neuron's response is completely characterized by its time-varying mean firing rate. This assumption has successfully described neural responses in many systems. The noise in rate coding neurons can be quantified by the coherence function or the correlation coefficient between the neuron's deterministic time-varying mean rate and noise corrupted single spike trains. Because of the finite data size, the mean rate cannot be known exactly and must be approximated. We introduce novel unbiased estimators for the measures of coherence and correlation which are based on the extrapolation of the signal to noise ratio in the neural response to infinite data size. We then describe the application of these estimates to the validation of the class of stimulus-response models that assume that the mean firing rate captures all the information embedded in the neural response. We explain how these quantifiers can be used to separate response prediction errors that are due to inaccurate model assumptions from errors due to noise inherent in neuronal spike trains.

Magnetic Resonance Sounding: New Method for Ground Water Assessment

Abstract: The advantage of magnetic resonance sounding (MRS) as compared to other classical geophysical methods is in its water selective approach and reduced ambiguity in determination of subsurface free water content and hydraulic properties of the media due to the nuclear magnetic resonance (NMR) principle applied. Two case examples are used to explain how hydrogeological parameters are obtained from an MRS survey. The first case example in Delft (the Netherlands) is a multiaquifer system characterized by large signal to noise ratio (S/N = 73), with a 24 m thick, shallow sand aquifer, confined by a 15 m thick clay layer. For the shallow aquifer, a very good match between MRS and borehole data was obtained with regard to effective porosity n(e) approximately 28% and specific drainage S(d) approximately 20%. The MRS interpretation at the level deeper than 39 m was disturbed by signal attenuation in the low resistivity (approximately 10 omega(m)) media. The second case of Serowe (Botswana) shows a fractured sandstone aquifer where hydrogeological parameters are well defined at depth > 74 m below ground surface despite quite a low S/N = 0.9 ratio, thanks to the negligible signal attenuation in the resistive environment. Finally, capabilities and limitations of the MRS technology are reviewed and discussed. MRS can contribute to subsurface hydrostratigraphy description, hydrogeological system parameterization, and improvement of well siting. The main limitations are survey dependence upon the value of the S/N ratio, signal attenuation in electrically conductive environments, nonuniformity of magnetic field, and some instrumental limitations. At locations sufficiently resistive to disregard the signal attenuation problems, the MRS S/N ratio determines how successfully MRS data can be acquired. Both signal and noise vary spatially; therefore, world scale maps providing guidelines on spatial variability of signal and noise are presented and their importance with respect to the MRS survey results is discussed. The noise varies also temporally; therefore, its diurnal and seasonal variability impact upon the MRS survey is covered as well.

Effect of carrier frequency offset on OFDM systems for multipath fading channels

Abstract: The paper presents an exact analysis of the effect of the carrier frequency offset on orthogonal frequency division multiplexing (OFDM) systems for a general multipath fading channel. As is well known, the carrier frequency offset attenuates the desired signal and causes intercarrier interference, thus reducing the signal-to-noise ratio (SNR). The SNR degradation due to the carrier frequency offset is evaluated by deriving the exact SNR expression in the presence of the carrier frequency offset. The SNR analysis can be used for the design of a practical OFDM system in determining how small the frequency offset should be in order to maintain the SNR degradation to negligible levels.

Distance-Based Decision Fusion in a Distributed Wireless Sensor Network

Abstract: Target classification fusion problem in a distributed, wireless sensor network is investigated. We propose a distance-based decision fusion scheme exploiting the relationship between sensor to target distance, signal to noise ratio and classification rate, which requires less communication while achieving higher region classification rate when compared to conventional majority-vote-based fusion schemes. Several different methods are tested, and very encouraging simulation results using real world experimental data samples are also observed.