Systems that capture and process analog signals must first acquire them through an analog-to-digital converter. While subsequent digital processing can remove statistical correlations present in the acquired data, the dynamic range of the converter is typically scaled to match that of the input analog signal. The present paper develops an approach for analog-todigital conversion that aims at minimizing the number of bits per sample at the output of the converter. This is attained by reducing the dynamic range of the analog signal by performing a modulo operation on its amplitude, and then quantizing the result. While the converter itself is universal and agnostic of the statistics of the signal, the decoder operation on the output of the quantizer can exploit the statistical structure in order to unwrap the modulo folding. The performance of this method is shown to approach information theoretical limits, as captured by the rate-distortion function, in various settings. An architecture for modulo analog-to-digital conversion via ring oscillators is suggested, and its merits are numerically demonstrated.
The use of wireless implanted medical devices (IMDs) is growing because they facilitate monitoring of patients at home and during normal activities, reduce the discomfort of patients and reduce the likelihood of infection associated with trailing wires. Currently, radiofrequency (RF) electromagnetic waves are the most commonly used method for communicating wirelessly with IMDs. However, due to the restrictions on the available bandwidth and the employable power, data rates of RF-based IMDs are limited to 267 kbps. Considering standard definition video streaming requires data rates of 1.2 mbps and high definition requires 3 mbps, it is not possible to use the RF electromagnetic communications for high data rate communication applications such as video streaming. In this work, an alternative method that utilizes ultrasonic waves to relay information at high data rates is introduced. An advanced quadrature amplitude modulation (QAM) modem with phase-compensating, sparse decision feedback equalizer (DFE) is tailored to realize the full potential of the ultrasonic channel through biological tissues. The proposed system is tested in a variety of scenarios, including both simulations with finite impulse response (FIR) channel models, and real physical transmission experiments with ex vivo beef liver and pork chop samples as well as in situ rabbit abdomen. Consequently, the simulations demonstrated that video-capable data rates can be achieved with milimetersized transducers. Real physical experiments confirmed data rates of 6.7, 4.4, 4 and 3.2 mbps through water, ex vivo beef liver, ex vivo pork chop and in situ rabbit abdomen, respectively.
The performance of remotely-controlled (RC) vehicles in recreational activities, such as RC cars, boats, planes and drones, has increased dramatically with the increased energy density of lithium polymer and Nickel metal hydride battery technologies. As a result, RC cars capable of land speeds in excess of 100 mph are available in hobbyist-class vehicles. This work presents an experimental and analytical setup for measuring the land-, water-, and air-speed of such RC vehicles using passive signal processing of acoustic recordings of the vehicles in operation. The high-efficiency DC brushless motors used in these platforms emit strong harmonic structure that can be efficiently measured with Doppler-tracking. The harmonic structure of the recorded acoustic signals allow passive velocity estimation using quasi-periodic signal detection and period estimation techniques based on pitch detection methods in the time and frequency domain. Preliminary results yielded successful velocity recovery based on Doppler tracking using a pilot signal, and demonstrated the correlation between the speed profile of the vehicle and acoustic harmonics. Future work will include an analytical model and set of experiments for passive velocity measurement suitable for high school and undergraduate physics laboratory exercises.
Acoustic communication has been gaining traction as an alternative communication method in nontraditional media, such as underwater or through tissue. Acoustic propagation is known to be a nonlinear phenomenon; nonlinear propagation of acoustic waves in soft tissues at biomedical frequencies and intensities has been widely demonstrated. However, the effects of acoustic nonlinearity on communication performance in biological tissues have not yet been examined. In this work, nonlinear propagation of a communication signal in soft tissues is analyzed. The relationship between communication parameters (signal amplitude, bandwidth, and center frequency) and nonlinear distortion of the communication signal propagating in soft tissues with different acoustic properties is investigated. Simulated experiments revealed that, unlike linear channels, bit error rates increase as signal amplitude and bandwidth increase. Linear and decision feedback equalizers fail to address the increased error rates. When tissue properties and transmission parameters can be estimated, receivers based on maximum likelihood sequence estimation approach the performance of an ideal receiver in an ideal additive white Gaussian noise channel.
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