We consider the scattering of a narrow pulse wave beam by a randomly rough surface with a complex local scattering indicatrix. Analytical expressions are found for the mean received power for a ...normal distribution of heights and slopes of the surface in two cases: where the direction to the receiver is close to the direction of mirror reflection and where the direction to the receiver is very different from the direction of mirror reflection. It is shown that in these two cases the echo pulse is very different in shape and is controlled by the parameters of the source and receiver, the sounding scheme, and the variance of heights of a rough surface. The received power is strongly dependent on the width of the local scattering indicatrix, and the form of this dependence is determined by the angles of illumination and reception. The analytical expressions for the mean received power are in good agreement with the results of numerical calculations.PUBLICATION ABSTRACT
Advanced computing devices equipped with various wired and wireless network capabilities, built-in microphones and audio capture devices are becoming increasingly popular. At the same time, ...sophisticated signal processing algorithms for hands-free acoustic human-machine interfaces are being developed. Those algorithms are currently restricted to dedicated audio hardware, in part because they require perfectly synchronized audio data. Naive attempts to use the available audio devices for microphone array processing in a distributed wireless setting fails due to the algorithms' sensitivity to deviations in the sampling rates of the distributed devices. We propose a synchronization scheme, which combines the microphones of different spatially distributed computing devices to an acoustic ad-hoc network. The proposed scheme is capable to significantly compensate the sampling rate deviations of the different audio capture devices and we show that, as an example, blind source separation performs well with the synchronized data of distributed acoustic sensors.
We propose to use a set of general purpose computing (GPC), communication and multimedia devices such as laptops, tablets, PDAs, smart phones, audio recorders, and camcorders as a distributed array ...signal processing system. A novel scheme is developed to synchronize input and output sampling for a network of distributed multi-channel audio sensors and actuators. IEEE 802.11 wireless network is used to deliver the global clock and data streams to distributed GPC platforms, while an interrupt timestamping mechanism is employed to distribute the common clock between I/O devices. Adaptive statistical processing is applied to reduce the effect of timing errors inevitable on real-life platforms. A prototype of distributed array is implemented based on Intel®Centrino™laptops and experimental results demonstrate a precision in A/D and D/A synchronization better than 50 μs (a couple of samples at 48 kHz).
We present a novel algorithm to automatically determine the relative three-dimensional (3-D) positions of audio sensors and actuators in an ad-hoc distributed network of heterogeneous general purpose ...computing platforms such as laptops, PDAs, and tablets. A closed form approximate solution is derived, which is further refined by minimizing a nonlinear error function. Our formulation and solution accounts for the lack of temporal synchronization among different platforms. We compare two different estimators, one based on the time of flight and the other based on time difference of flight. We also derive an approximate expression for the mean and covariance of the implicitly defined estimator using the implicit function theorem and approximate Taylors' series expansion. The theoretical performance limits for estimating the sensor 3-D positions are derived via the Crame/spl acute/r-Rao bound (CRB) and analyzed, with respect to the number of sensors and actuators, as well as their geometry. We report extensive simulation results and discuss the practical details of implementing our algorithms in a real-life system.
With the proliferation of pervasive computing in digital home and office environment there is an increasing demand for hands-free audio and video interfaces. Microphone arrays are already present on ...desktops and mobile computers, and camera arrays are in transition from being highly sophisticated prototypes to become affordable consumer devices soon. Thanks to increasing CPU power of general-purpose computers and higher bandwidth in wired and wireless networks, it now becomes possible to perform array signal processing of audio using networked sensors, actuators and computers. This paper presents components of a prototype system developed to support hands-free audio capture for audio recording and voice recognition based on multiple wirelessly networked laptops with onboard microphone arrays. Several key technologies demonstrated in this system include: 1) time synchronization scheme for distributed audio input devices that uses wireless network; 2) localization algorithms to reconstruct the geometry of audio sensors and speakers in a room; 3) cascaded beamforming algorithms for signals captured by distributed microphone arrays. This paper discusses both theoretical and practical aspects of mapping array signal processing algorithms on a distributed network of general-purpose computers with integrated audio sensors. Our experimental results demonstrate great potential of distributed audio arrays for hands-free command-and-control when compared to an array located on a single platform
Summary form only given. We propose a new paradigm for implementations of audio array processing algorithms on a network of distributed general-purpose computers. In contrast to current existing DSP ...processor-based solutions, our approach offers new possibilities for advanced array signal processing by enabling the usage of general-purpose computing platforms with their superior computational and storage resources. We demonstrate that synchronization of sensors is essential for acoustic blind source separation (BSS) algorithms, and we propose a synchronization scheme that enables BSS on distributed, wirelessly networked computers and can easily be implemented on existing hardware.
An on-the-fly laser method for measuring wind velocity in the atmosphere using the time correlation analysis is considered. It is shown that measuring the size of aerosol inhomogeneities and adaptive ...choice of the measuring base in accordance with the criterion obtained allow an increase in the accuracy of on-the-fly measurements of wind velocity by correlation lidars.
A "continuous" error detection scheme based on arithmetic coding ideas is analyzed. The results show significant gains of the proposed scheme over conventional block error detection codes (e.g., CRC) ...for automatic repeat request (ARQ), forward error correction (FEC) and hybrid ARQ schemes.
The possibility of modifying oxidized asphalt by performing polycondensation of maleic anhydride with aliphatic amines of various chemical structures in the dispersion medium was considered. The ...influence of the reactant structures and reaction conditions on the physicomechanical and structural-rheological properties of the polymer-modified asphalt was examined.
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