Power Level Difference Research Articles

Using power level difference for near field dual-microphone speech enhancement

In this contribution, a novel dual-channel speech enhancement technique is introduced. The proposed approach uses the dissimilarity between the power of received signals in the two channels as a criterion for speech enhancement and noise reduction. We claim that in near field conditions, where the distances between microphones and sound source are short, the difference in the received power levels at the two microphones is an estimate of the clean speech signal power. Then, apply this theory to present an optimum method for speech enhancement. Fortunately, the method has the ability to cope with problems such as transient noise and nearby microphones which are two of the main problems of the proposed dual-microphone speech enhancement techniques. Using objective speech quality measures and spectrogram analysis, we show that the proposed method results in improved speech quality.

Anti-collision algorithm with the aid of interference cancellation and tag set partitioning in radio-frequency identification systems

It is well known that an anti-collision protocol plays an essential role in the overall tag read time in radio-frequency identification systems because of the obstruction caused by tag collision. With an aim at speeding up the tag identification process, the authors propose an anti-collision algorithm, the spread partial-Q slot count (SPSC) algorithm, based on a slotted ALOHA code division multiple access technique along with tag set partitioning. A new packet structure is introduced preceded by a description of the mechanism of partition-wise identification process. In fact, according to received power levels, tags are partitioned into a certain number of groups. In the partition-wise identification process, tags belonging to two subsets are regrouped as a partition with a guarantee of having a uniformly largest received power level difference in a tag set so as to be interrogated by the reader simultaneously. The identification process for each partition is then operated sequentially. Indeed, tag set partitioning in conjunction with spread spectrum techniques could enable a simple multi-tag access detection scheme and improve system throughput as well. Simulations demonstrated that the SPSC algorithm outperforms some existing anti-collision algorithms in terms of throughput.

Fuzzy Inference System for Multiuser Detection in CDMA Systems

In this letter, multi user detection process in Code Division Multiple Access (CDMA) is performed by fuzzy inference system (FIS) and the bit error rate (BER) performance was compared with the single user bound, the matched filter receiver and neural network receiver. The BER performance of the matched filter receiver degrades as the number of the active users and the power level differences among the users increase. The neural network receiver needs the training process. Optimal receiver that has the best BER performance is too complex for practical application. The BER performance near the optimal case was obtained with the proposed receiver. The proposed receiver uses the FIS without training process and it has lower time complexity than the optimal receiver.

A new signal subspace processing for DOA estimation

We present a new subspace-based direction of arrival (DOA) estimation algorithm for narrow-band sources with high-resolution localization capabilities. The algorithm is based on the invariance property of noise subspace to power of emitters. We specifically compare the resolution of the proposed algorithm with the well-known high-resolution multiple signal classification (MUSIC) method. The proposed method performance is also superior to MUSIC algorithm in the case of correlated sources. Besides, the proposed algorithm is much less sensitive to the power level differences between adjacent sources compared to MUSIC, i.e., very weak sources in vicinity of strong ones can be resolved.

Postcanceling techniques for simultaneous broadcasting of analog fm and digital data

We consider simultaneous broadcasting of low-power digital data and analog FM and present reliable receivers for the digital data. Due to the relatively low power level of the digital data and the interference suppression capability of analog FM, standard analog FM receivers can reliably recover the analog FM audio signal. To recover the digital data, an extended Kalman filter front end is developed that exploits the capture capability of analog FM to reconstruct and postcancel the analog FM component from the received composite signal. Simulations are conducted with artificial analog FM signals, suggesting that postcanceling schemes can provide higher data rates than their precanceling counterparts, at a lower transmission delay penalty but higher digital receiver complexity. For analog FM to digital signal power level ratios in the range of 30-50 dB, the postcanceler digital signal recovery appears fairly robust, providing digital signal-to-noise ratios of 2-7.5 dB. The corresponding uncoded bit error rates strongly depend on the power level difference between the host analog FM and the digital data signal. In particular, at 260 kb/s and E/sub b//N/sub o/=10 dB they range between 1% to about 15%, and can be reduced to acceptable levels using standard channel coding techniques.

Electromyographic analysis of a human powered stepper cycle during seated and standing riding

This study examined the muscular activation patterns produced while riding the Step 'n Go, a tricycle powered by a reciprocating vertical motion and typically used by individuals with cognitive, orthopedic, and neuromuscular conditions. Seven normal, adult subjects were tested at three power levels (75, 100, and 125 W) during seated and standing riding. Eight lower extremity muscles were examined with surface electromyography. Results showed that the major power producing muscles for this device were the gluteus maximus, vastis lateralis and medialis, rectus femoris, and tibialis anterior. At the highest power level, peak and mean muscular activation in these muscles were substantially lower (17–38%) while riding standing compared to seated, and seems to reflect the benefit of body weight for power production while standing. At the lowest power level, the peak and mean muscle activation differences between positions were less remarkable, and in some cases the standing values were greater than seated. This suggests that significant muscular effort was required to maintain standing posture and balance when riding at low power levels. Individuals able to perform vastis lateralis and medialis intensive activities, such as the concentric portion of a squat or using a stepping machine (Stair Master), should be able to comfortably ride the Step 'n Go at low power levels.

Transmission edge filters for power equalization of EDFA's

We propose and demonstrate the use of transmission edge filters based on apodized linearly chirped fiber Bragg gratings for providing power equalization among different wavelength channels in an erbium-doped fiber amplifier module. The filters we fabricated provide a dynamic range of /spl ap/13 dB, an amplitude variation of /spl plusmn/0.5 dB from an ideal linear edge, and negligible group delay in transmission. Using the grating filters, we demonstrate power equalization, with no observed variation in signal levels after compensation, for three WDM signals having >6-dB difference in power levels before amplification. Our technique can also be extended to provide active power equalization by incorporating a feedback loop.

Non-Linear Behaviour in Commonly Used Non- Polar Dielectrics at Microwave Frequencies in Space RF Components

In space RF communications payloads, it is increasingly required that high-power multi-channel transmitters and broadband receivers have shared, or closely adja-cent RF feeds. Because of the large power level difference between the transmit and receive signals and the limitation of frequency allocation, harmonics genera-tion due to passive non-linearities in the high-power transmission path can be a se-rious problem. This paper describes how to determine the signal levels and dominant mechanisms associated with non-linear dielectric behaviour in this con-text. A novel measurement system for testing dielectric samples is described and measurement results are provided for commonly used microwave dielectrics.

Measurement and analysis of pump-dependent refractive index and dispersion effects in erbium-doped fiber amplifiers

In a doped fiber, at wavelengths close to an absorption, the refractive index, and hence the dispersion, is expected to be a strong function of wavelength, as described by the Kramers-Kronig relationship. Furthermore, this spectral variation itself will be a function of pumping. This paper describes an accurate and sensitive experimental determination of the pump dependence of the refractive index in an erbium-doped fiber amplifier. A Mach-Zehnder interferometric measurement is described where only one arm is comprised of doped fiber. Particular attention is paid to accounting for the significant difference in power levels in the two arms and the effects of polarization and incoherent light. The measured refractive-index change matches well with that theoretically predicted. The pumped and unpumped dispersion of the amplifier are calculated. While the extra dispersion is of similar magnitude to that of silica fiber, the impact on long telecommunications systems is likely to be negligible. However, this extra dispersion may be important in shorter systems such as soliton lasers. Given the good agreement between theory and experiment, the variation of dispersion with fractional inversion is calculated from absorption and gain measurements. The presence of codopants is known to alter the absorption and emission spectra; the effect on the dispersion is calculated, and a near linear dependence on germanium concentration is observed.

Structure-borne noise transmission through ship stanchions

Stanchions provide a path for structure-borne noise transmission from a noise source space on one level to noise sensitive spaces on another level in commercial and combatant surface ships. Measurements of structure-borne noise from one level to an adjacent level were made with and without a stanchion in place in the laboratory full-scale model of ship compartments at Hopeman Brothers. Measured data of the structure-borne noise transmission loss across the stanchion and the difference in the airborne sound power levels radiated into the compartments with and without the stanchion in place are presented. Results of statistical energy analysis (SEA) are compared to measured data. Methods for reducing structure-borne noise transmission through stanchions are suggested.

Analysis of an XPD event at 30 GHz measured with ATS-6

Power level and phase difference of two linearly polarized, wanted and unwanted, 30-GHz signals transmitted by ATS-6 during its European campaign are measured. The analysis of a cross-polar discrimination (XPD) event reveals the possibility of improving XPD by a simple rotation of the feed systmn. The procedure applied could be self-adaptive where the phase difference between both components could serve as the variable criterion.

Cavity Phase Dependent Frequency Shifts in Cesium Beam Frequency Standards

The influence of the atomic velocity distribution in cesium beam atomic frequency standards on the frequency shift due to Ramsey cavity phase difference is discussed. The atomic resonance is shifted and its shape distorted to a degree dependent not only on the exciting power level and cavity phase difference, but also on the actual velocity distribution which exists in the standard. Calculations carried out for the NRC 2.1 metre primary standard show that, for the velocity distribution which probably exists in this standard, the resonance distortion gives rise to a power dependence of the frequency shift of about an order of magnitude less than that expected for a Maxwellian velocity distribution in the beam. Experimental measurements tend to support this result.