47 research outputs found
Modeling and frequency tracking of marine mammal whistle calls
Submitted in partial fulfillment of the requirements for the degree of Master of Science at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2009Marine mammal whistle calls present an attractive medium for covert underwater
communications. High quality models of the whistle calls are needed in order to synthesize
natural-sounding whistles with embedded information. Since the whistle calls
are composed of frequency modulated harmonic tones, they are best modeled as a
weighted superposition of harmonically related sinusoids. Previous research with bottlenose
dolphin whistle calls has produced synthetic whistles that sound too “clean”
for use in a covert communications system. Due to the sensitivity of the human auditory
system, watermarking schemes that slightly modify the fundamental frequency
contour have good potential for producing natural-sounding whistles embedded with
retrievable watermarks. Structured total least squares is used with linear prediction
analysis to track the time-varying fundamental frequency and harmonic amplitude
contours throughout a whistle call. Simulation and experimental results demonstrate
the capability to accurately model bottlenose dolphin whistle calls and retrieve embedded
information from watermarked synthetic whistle calls. Different fundamental
frequency watermarking schemes are proposed based on their ability to produce natural
sounding synthetic whistles and yield suitable watermark detection and retrieval
Waveform-Diverse Stretch Processing
Stretch processing with the use of a wideband LFM transmit waveform is a commonly used technique, and its popularity is in large part due to the large time-bandwidth product that provides fine range resolution capabilities for applications that require it. It allows pulse compression of echoes at a much lower sampling bandwidth without sacrificing any range resolution. Previously, this technique has been restrictive in terms of waveform diversity because the literature shows that the LFM is the only type of waveform that will result in a tone after stretch processing. However, there are also many examples in the literature that demonstrate an ability to compensate for distortions from an ideal LFM waveform structure caused by various hardware components in the transmitter and receiver. This idea of compensating for variations is borrowed here, and the use of nonlinear FM (NLFM) waveforms is proposed to facilitate more variety in wideband waveforms that are usable with stretch processing. A compensation transform that permits the use of these proposed NLFM waveforms replaces the final fast Fourier transform (FFT) stage of the stretch processing configuration, but the rest of the RF receive chain remains the same. This modification to the receive processing structure makes possible the use of waveform diversity for legacy radar systems that already employ stretch processing. Similarly, using the same concept of compensating for distortions to the LFM structure along with the notion that a Fourier transform is essentially the matched filter bank for an LFM waveform mixed with an LFM reference, a least-squares based mismatched filtering (MMF) scheme is proposed. This MMF could likewise be used to replace thefinal FFT stage, and can also facilitate the application of NLFM waveforms to legacy radar systems. The efficacy of these filtering approaches (compensation transform and least-squares based MMF) are demonstrated in simulation and experimentally using open-air measurements and are applied to different scenarios of NLFM waveform to assess the results and provide a means of comparison between the two techniques
Decoding Electrophysiological Correlates of Selective Attention by Means of Circular Data
Sustaining our attention to a relevant sensory input in a complex listening environment, is of great
importance for a successful auditory communication. To avoid the overload of the auditory system,
the importance of the stimuli is estimated in the higher levels of the auditory system. Based on these
information, the attention is drifted away from the irrelevant and unimportant stimuli. Long-term
habituation, a gradual process independent from sensory adaptation, plays a major role in drifting
away our attention from irrelevant stimuli.
A better understanding of attention-modulated neural activity is important for shedding light on the
encoding process of auditory streams. For instance, these information can have a direct impact on
developing smarter hearing aid devices in which more accurate objective measures can be used to
re
ect the hearing capabilities of patients with hearing pathologies. As an example, an objective
measures of long-term habituation with respect to di erent level of sound stimuli can be used more
accurately for adjustment of hearing aid devices in comparison to verbal reports.
The main goal of this thesis is to analyze the neural decoding signatures of long-term habituation and
neural modulations of selective attention by exploiting circular regularities in electrophysiological
(EEG) data, in which we can objectively measure the level of attentional-binding to di erent stimuli.
We study, in particular, the modulations of the instantaneous phase (IP) in event related potentials
(ERPs) over trials for di erent experimental settings. This is in contrast to the common approach
where the ERP component of interest is computed through averaging a su ciently large number of
ERP trials. It is hypothesized that a high attentional binding to a stimulus is related to a high level
of IP cluster. As the attention binding reduces, IP is spread more uniformly on a unit circle. This
work is divided into three main parts.
In the initial part, we investigate the dynamics of long-term habituation with di erent acoustical
stimuli (soft vs. loud) over ERP trials. The underlying temporal dynamics in IP and the level
of phase cluster of the ERPs are assessed by tting circular probability functions (pdf) over data
segments. To increase the temporal resolution of detecting times at which a signi cant change in
IP occurs, an abrupt change point model at di erent pure-tone stimulations is used. In a second
study, we improve upon the results and methodology by relaxing some of the constrains in order to
integrate the gradual process of long-term habituation into the model. For this means, a Bayesian
state-space model is proposed. In all of the aforementioned studies, we successfully classi ed between
di erent stimulation levels, using solely the IP of ERPs over trials.
In the second part of the thesis, the experimental setting is expanded to contain longer and more
complex auditory stimuli as in real-world scenarios. Thereby, we study the neural-correlates of
attention in spontaneous modulations of EEG (ongoing activity) which uses the complete temporal
resolution of the signal. We show a mapping between the ERP results and the ongoing EEG
activity based on IP. A Markov-based model is developed for removing spurious variations that can occur in ongoing signals. We believe the proposed method can be incorporated as an important preprocessing
step for a more reliable estimation of objective measures of the level of selective attention.
The proposed model is used to pre-process and classify between attending and un-attending states
in a seminal dichotic tone detection experiment.
In the last part of this thesis, we investigate the possibility of measuring a mapping between the
neural activities of the cortical laminae with the auditory evoked potentials (AEP) in vitro. We
show a strong correlation between the IP of AEPs and the neural activities at the granular layer,
using mutual information.Die Aufmerksamkeit auf ein relevantes auditorisches Signal in einer komplexen H orumgebung
zu lenken ist von gro er Bedeutung f ur eine erfolgreiche akustische Kommunikation. Um eine
Uberlastung des H orsystems zu vermeiden, wird die Bedeutung der Reize in den h oheren Ebenen
des auditorischen Systems bewertet. Basierend auf diesen Informationen wird die Aufmerksamkeit
von den irrelevanten und unwichtigen Reizen abgelenkt. Dabei spielt die sog. Langzeit- Habituation,
die einen graduellen Prozess darstellt der unabh angig von der sensorischen Adaptierung ist, eine
wichtige Rolle.
Ein besseres Verst andnis der aufmerksamkeits-modulierten neuronalen Aktivit at ist wichtig, um den
Kodierungsprozess von sog. auditory streams zu beleuchten. Zum Beispiel k onnen diese Informationen
einen direkten Ein
uss auf die Entwicklung intelligenter H orsysteme haben bei denen
genauere, objektive Messungen verwendet werden k onnen, um die H orf ahigkeiten von Patienten
mit H orpathologien widerzuspiegeln. So kann beispielsweise ein objektives Ma f ur die Langzeit-
Habituation an unterschiedliche Schallreize genutzt werden um - im Vergleich zu subjektiven Selbsteinsch
atzungen - eine genauere Anpassung der H orsysteme zu erreichen.
Das Hauptziel dieser Dissertation ist die Analyse neuronaler Dekodierungssignaturen der Langzeit-
Habituation und neuronaler Modulationen der selektiver Aufmerksamkeit durch Nutzung zirkul arer
Regularit aten in elektroenzephalogra schen Daten, in denen wir objektiv den Grad der Aufmerksamkeitsbindung
an verschiedene Reize messen k onnen.
Wir untersuchen insbesondere die Modulation der Momentanphase (engl. Instantaneous phase, IP)
in ereigniskorrelierten Potenzialen (EKPs) in verschiedenen experimentellen Settings. Dies steht
im Gegensatz zu dem traditionellen Ansatz, bei dem die interessierenden EKP-Komponenten durch
Mittelung einer ausreichend gro en Anzahl von Einzelantworten im Zeitbereich ermittelt werden. Es
wird vermutet, dass eine hohe Aufmerksamkeitsbindung an einen Stimulus mit einem hohen Grad
an IP-Clustern verbunden ist. Nimmt die Aufmerksamkeitsbindung hingegen ab, so ist die Momentanphase
uniform auf dem Einheitskreis verteilt. Diese Arbeit gliedert sich in drei Teile. Im ersten
Teil untersuchen wir die Dynamik der Langzeit-Habituation mit verschiedenen akustischen Reizen
(leise vs. laut) in EKP-Studien. Die zugrundeliegende zeitliche Dynamik der Momentanphase und
die Ebene des Phasenclusters der EKPs werden durch die Anpassung von zirkul aren Wahrscheinlichkeitsfunktionen
(engl. probability density function, pdf) uber Datensegmente bewertet. Mithilfe
eines sog. abrupt change-point Modells wurde die zeitliche Au
osung der Daten erh oht, sodass signi
kante Anderungen in der Momentanphase bei verschiedenen Reintonstimulationen detektierbar
sind.
In einer zweiten Studie verbessern wir die Ergebnisse und die Methodik, indem wir einige der Einschr
ankungen lockern, um den gradualen Prozess der Langzeit-Habituation in das abrupt changepoint
Modell zu integrieren. Dazu wird ein bayes`sches Zustands-Raum-Modell vorgeschlagen. In den zuvor genannten Studien konnte erfolgreich mithilfe der Momentanphase zwischen verschiedenen
Stimulationspegeln unterschieden werden. Im zweiten Teil der Arbeit wird der experimentelle
Rahmen erweitert, um komplexere auditorische Reize wie in realen H orsituationen untersuchen zu
k onnen. Dabei analysieren wir die neuronalen Korrelate der Aufmerksamkeit anhand spontaner
Modulationen der kontinuierlichen EEG-Aktivit at, die eine zeitliche Au
osung erm oglicht. Wir
zeigen eine Abbildung zwischen den EKP-Ergebnissen und der kontinuierlichen EEG-Aktivit at auf
Basis der Momentanphase. Ein Markov-basiertes Modell wird entwickelt, um st orende Variationen
zu entfernen, die in kontinuierlichen EEG-Signalen auftreten k onnen. Wir glauben, dass die
vorgeschlagene Methode als wichtiger Vorverarbeitungsschritt zur soliden objektiven Absch atzung
des Aufmerksamkeitsgrades mithilfe von EEG-Daten verwendet werden kann. In einem dichotischen
Tonerkennungsexperiment wird das vorgeschlagene Modell zur Vorverarbeitung der EEG-Daten und
zur Klassi zierung zwischen gerichteten und ungerichteten Aufmerksamkeitszust anden erfolgreich
verwendet.
Im letzten Teil dieser Arbeit untersuchen wir den Zusammenhang zwischen den neuronalen Aktivit
aten der kortikalen Laminae und auditorisch evozierten Potentialen (AEP) in vitro im Tiermodell.
Wir zeigen eine starke Korrelation zwischen der Momentanphase der AEPs und den neuronalen
Aktivit aten in der Granularschicht unter Verwendung der Transinformation
Modem design for digital satellite communications
The thesis is concerned with the design of a phase-shift keying system for a
digital modem, operating over a satellite link. Computer simulation tests and
theoretical analyses are used to assess the proposed design.
The optimum design of both transmitter and receiver filters for the system to be
used in the modem are discussed. Sinusoidal roll-off spectrum with different roll-off
factor and optimum truncation lengths of the sample impulse response are designed
for the proposed scheme to approximate to the theoretical ideal. It has used an EF
bandpass filter to band limit the modulated signal, which forms part of the satellite
channel modelling. The high power amplifier (HPA) at the earth station has been
used in the satellite channel modelling due to its effect in introducing nonlinear AMAM
and AM-PM conversion effects and distortion on the transmitted signal from the
earth station. The satellite transponder is assumed to be operating in a linear mode.
Different phase-shift keying signals such as differentially encoded quaternary
phase-shift keying (DEQPSK), offset quaternary phase-shift keying (OQPSK) and
convolutionally encoded 8PSK (CE8PSK) signals are analysed and discussed in the
thesis, when the high power amplifier (HPA) at the earth station is operating in a
nonlinear mode. Convolutional encoding is discussed when applied to the system
used in the modem, and a Viterbi -algorithm decoder at the receiver has been used, for
CE8PSK signals for a nonlinear satellite channel. A method of feed-forward
synchronisation scheme is designed for carrier recovery in CE8PSK receiver.
The thesis describes a method of baseband linearizing the baseband signal in
order to reduce the nonlinear effects caused by the HPA at the earth station. The
scheme which compensates for the nonlinear effects of the HPA by predistorting the
baseband signal prior to modulation as opposed to correcting the distortion after
modulation, thus reducing the effects of nonlinear distortion introduced by the HPA.
The results of the improvement are presented.
The advanced technology of digital signal processors (DSPs) has been used in the implementation of the demodulation and digital filtering parts of the modem
replacing large parts of conventional circuits. The Viterbi-algorithm decoder for
CE8PSK signals has been implemented using a digital signal processor chip, giving excellent performance and is a cost effective and easy way for future developments
and any modifications,
The results showed that, by using the various studied techniques, as well as the
implementation of digital signal processor chip in parts of the modem, a potentially
more cost effective modem can be obtained
Digital modems for mobile systems
Digital modems for mobile system
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Study of continuous-phase four-state modulation for cordless telecommunications. Assessment by simulation of CP-QFSK as an alternative modulation scheme for TDMA digital cordless telecommunications systems operating in indoor applications
One of the major driving elements behind the explosive boom in wireless revolution is the advances in the field of modulation which plays a fundamental role in any communication system, and especially in cellular radio systems. Hence, the elaborate choice of an efficient modulation scheme is of paramount importance in the design and employment of any communications system. Work presented in this thesis is an investigation (study) of the feasibility of whether multilevel FSK modulation scheme would provide a viable alternative modem that can be employed in TDMA cordless communications systems. In the thesis the design and performance analysis of a non-coherent multi-level modem that offers a great deal of bandwidth efficiency and hardware simplicity is studied in detail. Simulation results demonstrate that 2RC pre-modulation filter pulse shaping with a modulation index of 0.3, and pre-detection filter normalized equivalent noise bandwidth of 1.5 are optimum system parameter values. Results reported in chapter 5 signify that an adjacent channel rejection factor of around 40 dB has been achieved at channel spacing of 1.5 times the symbol rate while the DECT system standards stipulated a much lower rejection limit criterion (25-30dB), implying that CP-QFSK modulation out-performs the conventional GMSK as it causes significantly less ACI, thus it is more spectrally efficient in a multi-channel system. However, measured system performance in terms of BER indicates that this system does not coexist well with other interferers as at delay spreads between 100ns to 200ns, which are commonly encountered in such indoor environment, a severe degradation in system performance apparently caused by multi-path fading has been noticed, and there exists a noise floor of about 40 dB, i.e. high irreducible error rate of less than 5.10-3. Implementing MRC diversity combiner and BCH codec has brought in a good gain.Higher Education Ministr
Applications of FM Noise Radar Waveforms: Spatial Modulation and Polarization Diversity
Two possible radar application spaces are explored through the exploitation of highdimensional nonrecurrent FM-noise waveforms. The first involving a simultaneous dual-polarized emission scheme that provides good separability with respect to co- and cross-polarized terms and the second mimicking the passive actuation of the human eye with a MIMO emission. A waveform optimization scheme denoted as pseudorandom optimized (PRO) FM has been shown to generate FM-noise radar waveforms that are amenable to high power transmitters. Each pulse is generated and optimized independently and possesses a non-repeating FM-noise modulation structure. Because of this the range sidelobes of each pulse are unique and thus are effectively suppressed given enough coherent integration. The PRO-FM waveform generation scheme is used to create two independent sets of FM-noise waveforms to be incorporated into a simultaneous dual-polarized emission; whereby two independent PRO-FM waveforms will be transmitted simultaneously from orthogonal polarization channels. This effectively creates a polarization diverse emission. The random nature of these waveforms also reduce cross-correlation effects that occur during simultaneous transmission on both channels. This formulation is evaluated using experimental open-air measurements to demonstrate the effectiveness of this high-dimensional emission. This research aims to build upon previous work that has demonstrated the ability to mimic fixational eye movements (FEM) employed by the human eye. To implement FEM on a radar system a MIMO capable digital array must be utilized in conjunction with spatial modulation beamforming. Successful imitation of FEM will require randomized fast-time beamsteering from a two-dimensional array. The inherent randomness associated with FEM will be paired with the PRO-FM waveforms to create an emission possessing randomness in the space and frequency domains, called the FEM radar (FEMR). Unlike traditional MIMO, FEMR emits a coherent and time varying beam. Simulations will show the inherent enhancement to spatial resolution in two-dimensional space (azimuth and elevation) relative to standard beamforming using only the matched filter to process returns
LOFT instrumentation definition study Final report, 28 May - 28 Nov. 1969
Flight test instrumentation requirements for interim scale models of low frequency radio telescope
Design and Optimization of Physical Waveform-Diverse and Spatially-Diverse Radar Emissions
With the advancement of arbitrary waveform generation techniques, new radar transmission modes can be designed via precise control of the waveform's time-domain signal structure. The finer degree of emission control for a waveform (or multiple waveforms via a digital array) presents an opportunity to reduce ambiguities in the estimation of parameters within the radar backscatter. While this freedom opens the door to new emission capabilities, one must still consider the practical attributes for radar waveform design. Constraints such as constant amplitude (to maintain sufficient power efficiency) and continuous phase (for spectral containment) are still considered prerequisites for high-powered radar waveforms. These criteria are also applicable to the design of multiple waveforms emitted from an antenna array in a multiple-input multiple-output (MIMO) mode. In this work, three spatially-diverse radar emission design methods are introduced that provide constant amplitude, spectrally-contained waveforms implemented via a digital array radar (DAR). The first design method, denoted as spatial modulation, designs the radar waveforms via a polyphase-coded frequency-modulated (PCFM) framework to steer the coherent mainbeam of the emission within a pulse. The second design method is an iterative scheme to generate waveforms that achieve a desired wideband and/or widebeam radar emission. However, a wideband and widebeam emission can place a portion of the emitted energy into what is known as the `invisible' space of the array, which is related to the storage of reactive power that can damage a radar transmitter. The proposed design method purposefully avoids this space and a quantity denoted as the Fractional Reactive Power (FRP) is defined to assess the quality of the result. The third design method produces simultaneous radar and communications beams in separate spatial directions while maintaining constant modulus by leveraging the orthogonal complement of the emitted directions. This orthogonal energy defines a trade-space between power efficiency gained from constraining waveforms to be constant amplitude and power efficiency lost by emitting energy in undesired directions. The design of FM waveforms via traditional gradient-based optimization methods is also considered. A waveform model is proposed that is a generalization of the PCFM implementation, denoted as coded-FM (CFM), which defines the phase of the waveform via a summation of weighted, predefined basis functions. Therefore, gradient-based methods can be used to minimize a given cost function with respect to a finite set of optimizable parameters. A generalized integrated sidelobe level (GISL) metric is used as the optimization cost function to minimize the correlation range sidelobes of the radar waveform. System specific waveform optimization is explored by incorporating the linear models of three different loopback configurations into the GISL metric to match the optimized waveforms to the particular systems