Chirp parameter plays an important role in the optical communication system. In this paper, we use a simple method to extact the chirp parameter, where the electroabsorption modulators (EAM) and broad-band Cr:YAG crystal-fiber are two main devices to be measured. A high-speed vector network analyzer (VNA) and a 50km non-zero-dispersion single-mode fiber (SMF) are used in this method. Modulating and detecting the optical power by the VNA signal, the chirp-parameters can be obtained by launching the chirped-optical signal into the SMF. It shows that this method is a reliable tool for analysis of chirp on fiber-based devices. Generally, EAMs have high-speed performance, however the chirp behavior still is a dominated factor on long optical fiber transmission. When changing the wavelength of input optical power and DC-bias applying on EAMs, the chirp parameters will be varied. Our measured results showed that the chirp parameters of the EAMs are in a low range of from ¡V1 to 1. These low values give an indication that it is quite useful for long-distance optical fiber transmission. We also measured the chirp parameter of Cr4+: YAG crystal fiber. Its ASE spectrum covers the whole communication wavelength (1300nm to 1600nm) and the absorption wavelength is in near-infrareds ranges (980nm to 1100nm). Therefore, this kind of materials can be potentially used for most of the telecommunication fields used today, like fiber-based optical amplifier, ASE, laser ¡K and so on. In order to further investigate the performance of Cr4+: YAG crystal fiber, the ASE, optical gain and the chirp behaviors are also measured in this paper.

Zugl.: Freiburg (Breisgau), Univ., Diss., 2008

Ulm, Univ. Diss., 2006.

No description available.

A digital modulation method using Chirp-Slope Keying (CSK) is developed for coherent underwater acoustic communications. Effective signal detection is a critical stage in the implementation of any communications system; we will see that CSK solves some significant challenges to reliable detection. This thesis is primarily based on analyzing the effectiveness of CSK through simulations using Matlab's Simulink for underwater communications. The procedure begins with modulating a chirp's slope by random binary data with a linear-down-slope chirp representing a 0, and a linear-up-slope chirp representing a 1. Each received symbol is demodulated by multiplying it with the exact linear-up-slope chirp and then integrating over a whole period (i.e., integrate and dump). This slope-detection technique reduces the need for the extensive recognition of the magnitude and/or the frequencies of the signal. Simulations demonstrate that CSK offers sturdy performance in the modeled ocean environment, even at very low signal-to-noise ratio (SNR). CSK is first tested using the fundamental communication channel, Additive White Gaussian Noise (AWGN) channel. Simulation results show excellent BER vs. SNR performance, implying CSK is a promising method. Further extensive analysis and simulations are performed to evaluate the quality of CSK in more realistic channels including Rayleigh amplitude fading channel and multipath.

In der vorliegenden klinischen Untersuchung wurden drei unterschiedliche Modelle zur Konstruktion von Chirp-Reizen untersucht und mit den bei der Standard-BERA traditi-onellen Klickreiz verglichen. Zwei Modelle zur Konstruktion der Chirp-Reize basieren auf bekannte Latenzverschiebungen frequenzspezifischer AEP: (ChNE) Daten von Neely et al. (1988) und (ChMD) Daten von Don et al. (2005). Das dritte Modell (ChDB) basiert auf Daten, die aus dem Cochlea-Modell von de Boer (1980) ermittelt wurden. An der Untersuchung nahmen 55 junge normalhörende Erwachsene teil. Von jedem wurden ASSR aufgezeichnet. Die Reize wurden bei zwei verschiedenen Reizpegeln, nämlich 30 und 50 dB nHL, mit einer Rate von 90/s den Probanden dargeboten.Die Auswertung erfolgte durch einen speziellen Auswertungsalgorithmus mit den identifi-zierten ASSR, nach deren Antwortamplitude, der Nachweiszeit und der Nachweisrate. In den Ergebnissen der Untersuchung zeigte sich, dass die Amplituden der Chirp-ASSR deutlich größer sind, als die der Klick-ASSR. Insgesamt konnten mit den Chirp-Reizen die kürzeste Nachweiszeit und die höchste Nachweisrate ermittelt werden. Es wurde gezeigt, dass alle drei Chirps effektiver sind als der Klick, sogar wenn die Chirps auf einem Pegel dargeboten werden, der um 20 dB niedriger ist als beim Klick. Trotz dieser offensichtlichen Rangfolge ist es nur bei 50 dB nHL möglich, statistisch die Effizienz des Don-Chirps gegenüber den zwei anderen Chirps zu demonstrieren. Die klinischen Ergebnisse zeigen, dass es von Vorteil ist, den Standardklick, der normaler-weise benutzt wird, um periphere auditorisch evozierte Antworten aufzunehmen, d. h. ABR und ASSR, durch einen optimierten Chirp-Stimulus zu ersetzen. / This study compares three different chirp-stimuli to a standard click stimulus where the ASSR is recorded from 55 younger people (age: 18-34 years) at two relatively low stimulus levels 30 and 50 dB nHL and with a stimulus rate of 90 / s. The chirps were constructed by three different estimates of the traveling wave delay that are based to increase the temporal synchronization between the contributing neural elements in the auditory periphery. One of the chosen chirps is based on latencies obtained from narrow-band ABRs described by the Don-data, in this study called ChMD, the second is based on latencies from tone burst ABRs by Neely et al. (1988), called ChNE, and the third is based on the cochlear model by de Boer (1980), called ChDB. The detection time [s] is significantly shorter and the detection rate [%] is higher in response to the three chirps than to the click. The response amplitudes are also higher by the chirps than by the click. It is shown that all three chirps are more efficient than the click even when the chirps are presented at a level which is 20 dB below the click. Despite this apparent ranking, only at 50 dB nHL it is possible to demonstrate statistically the efficiency of the Don chirp ChMD over the other two chirps. The results indicate that a chirp is a better choice than a click for the recording of early auditory evoked responses.

Das Ziel dieser Studie war die Untersuchung frequenzspezifischer laufzeitkorrigierter Stimuli (Chirp-Reize). Die Stimuli hatten mittlere Frequenzen von 500 Hz, 1 kHz, 2 kHz und 4 kHz und eine Bandbreite von einer Oktave. Es wurden drei verschiedene Modelle zur Laufzeitkorrektur untersucht. Diese stützen sich auf verschiedene Schätzungen der Laufzeitverzögerung der Wanderwelle in der Kochlea. Modell 1 basiert auf von schmalbandigen AEP ermittelten Latenzen (Don et al., 2005). Modell 2 wurde auf der Basis des Kochleamodells von de Boer (1980) erarbeitet und Grundlage für Modell 3 sind frequenzspezifische Latenzen von Tonbursts AEP (Neely et al., 1988). Die Stimuli wurden an einem Kollektiv von 50 Erwachsenen mit Hilfe der Ableitung von Hirnstammpotentialen bei Lautstärkepegeln von 30 dB nHL und 50 dB nHL untersucht. Die Auswertung der Ergebnisse erfolgte an Hand von Nachweisraten und -zeiten. Insgesamt kann festgestellt werden, dass unabhängig von der Testfrequenz sowohl 30 dB nHL als auch 50 dB nHL die nach Modell 1 generierten Stimuli effizienter als die anderen beiden Modelle sind. Es ist zu erwarten, dass die Anwendung der darauf basierenden Stimuli zu einer genaueren Bestimmung der objektiven frequenzspezifischen Hörschwelle führt als bisherige Verfahren. / The aim of this study was the investigation of time-corrected chirp stimuli based on cochlea traveling wave delays for frequency-specific stimulation. The stimuli had average frequencies of 500 Hz, 1 kHz, 2 kHz and 4 kHz and a bandwidth of one octave. Three different models of correction of the cochlea traveling wave delay were studied. These are based on different estimations of the temporal dispersion in the cochlea as given by the traveling time. Model 1 is based on narrow-band ABR latencies (Don et al., 2005). Model 2 was elaborated in accordance with a cochlea model by de Boer (1980). Model 3 originates from frequency-specific latencies from tone burst ABR (Neely et al., 1988). The stimuli were investigated in 50 normal-hearing adults by recording EEGs at stimulus levels of 30 and 50 dBnHL, respectively. The evaluation of results was according to detection rate and detection time. The overall outcome indicates that the stimulus given by model1 is more efficient than by the other models , independent of frequency and stimulus level (i.e., 30 or 50 dBnHL). Therefore, it can be expected that the use of these stimuli will give better results than earlier methods for the objective determination of the frequency hearing threshold.

No description available.

No description available.

In this thesis, a computationally efficient method for detecting a whistle and capturing it using a 4 microphone array is proposed. Furthermore, methods are developed to efficiently process the data captured from all the microphones to estimate the direction of the sound source. The accuracy, the shortcoming and the constraints of the method proposed are also discussed. There is an emphasis placed on being computationally efficient so that the methods may be implemented on a low cost microcontroller and be used to provide a heading to an Unmanned Ground Vehicle. / MS / As humans, we rely on our sense of hearing to help us interact with the outside world. It helps us to listen not just to other people but also for sounds that maybe a warning for us. It can often be the first warning we get of an impending danger as we might hear a predator before we see it or we might hear a car brake and slip before we turn to look at it. However, it is not merely the ability to hear a sound that makes hearing so useful. It is the fact that we can tell which direction the sound is coming from that makes it so important. That is what allows us to know which direction to turn towards to respond to someone or from which direction the sound warning us of danger is coming. We may not be able to pinpoint the location of the source with complete accuracy but we can discern the general heading. It was this idea that inspired this research work. We wanted to be capable of estimating where a sound is coming from while being computationally efficient so that it may be implemented in real time with the help of a low cost microcontroller. This would then be used to provide a heading to an Unmanned Ground Vehicle while keeping the costs down.