Frequency Modulation

This paper outlines the applicative environment and sketches the technical details of an FM subcarrier technology called multipurpose radio communication channel (MPRC). This technology delivers data at maximum data rate of around 40 kbs using a proprietary codec algorithm, subsidiary communication channel (SCC). As a result it is possible to obtain video transmission in QCIF format at roughly 8/12 fps using 35 kHz of the 100 kHz available for a commercial FM radio station in Europe. In this way, it is possible to transmit video on FM radio together with the usual radio broadcasting. SCC is briefly described in its main characteristics

Among the family of pulse time modulation (PTM) techniques, square wave frequency modulation (SWFM) is particularly well suited to the transmission of high-quality wideband instrumentation and video signals such as MAC and high definition TV over optical fibres due to its attractive combination of performance and simplicity. This paper discusses aspects of SWFM and describes two experimental systems employing novel demodulators suitable for 5.5 MHz (PAL) and 12 MHz wide format MAC bandwidth systems respectively. >

An approach to watermarking digital signals using frequency modulation-'Chirp Coding'-is considered. The principles underlying this approach are based on the use of a matched filter to reconstruct a 'chirp stream'code that is uniquely robust. The method is generic in the sense that it can, in principle, be used for a variety of different signal (the authentication of speech and biomedical signals, for example). Further, by generating a bit stream that is signal dependent, chirp coding provides a method of self-authentication, ...

In this paper, the AM–FM modulation model is applied to speech analysis, synthesis and coding. The AM–FM model represents the speech signal as the sum of formant resonance signals each of which contains amplitude and frequency modulation. Multiband filtering and demodulation using the energy separation algorithm are the basic tools used for speech analysis. First, multiband demodulation analysis (MDA) is

We present a theoretical model developed for estimating the power, the optical signal to noise ratio and the number of generated carriers in a comb generator, having as a reference the minimum optical signal do noise ratio at the receiver input, for a given fiber link. Based on the recirculating frequency shifting technique, the generator relies on the use of coherent and orthogonal multi-carriers (Coherent WDM) that makes use of a single laser source (seed) for feeding high capacity (above 100 Gb/s) systems. The theoretical model has been validated by an experimental demonstration, where 23 comb lines with an optical signal to noise ratio ranging from 25 to 33 dB, in a spectral window of ~ 3.5 nm, are obtained.

This paper discusses a new implementation of a Gaussian minimum-shift keying (GMSK) modulator and demodulator on the European Space Agency (ESA)'s common deep-space receiver-the Intermediate Frequency Modem System (IFMS), which is a software radio based platform. The GMSK demodulator is needed for ESA's deep-space and near-Earth missions, starting with the Herschel-Planck satellites in 2008. The implementation requirements and hardware restrictions from the IFMS lead to the need for a significant simplification versus the optimum demodulation approach. In part, this can be achieved by using a demodulator based on the Laurent decomposition, yet further simplifications and changes to obtain a feasible implementation were necessary. The presented GMSK demodulator was directly implemented on the existing IFMS receiver without requiring any hardware changes. Measurements with the demodulator showed only a marginal technical degradation in the order of 0.1-0.3 dB for the chosen approach. Furthermore, for testing purposes, a GMSK modulator was implemented on the same platform.

ABSTRACT The Full Bridge converter topology modulated in phase shift is one of the most popular converters used to obtain high efficiency conversion, especially in high power and high voltage applications. This converter topology combines the simplicity of fixed frequency modulations with the soft switching characteristic of resonant converters but, if a diode rectifier is used as output stage, it suffers of severe overshoot voltage spikes and ringing across the rectifier. In this paper, a new regenerative active snubber is widely studied and developed to reduce this drawback. The proposed snubber is based on a combination of an active clamp with a buck converter used to discharge the snubber capacitor. The snubber gate signal is obtained by using those of the phase shift modulation.

The phase vocoder is a well established tool for time scaling and pitch shifting speech and audio signals via modification of their short-time Fourier transforms (STFTs). In contrast to time-domain time-scaling and pitch-shifting techniques, the phase vocoder is generally considered to yield high quality results, especially for large modification factors and/or polyphonic signals. However, the phase vocoder is also known

This work focuses on presenting a novel high efficiency channel encoding for transmitting acoustical signals in the hope of improving wireless underwater communication. Yet, water puts a damper on communication capacity, slowing down the signal propagation and creating background noise and echoes. For thus systems and methods for implementing a control channel, e.g., in underwater communication system, are presented below. Aspects of the channel structures used to implement the control channel described herein, can improve error detection capabilities, reduce decoding complexity, and increase transmission efficiency. In certain aspects, transmission efficiency can be increased through using CRC encoding. A circular trellis check and Viterbi decoding can also be used to increase efficiency and maintain error detection capabilities. Symbol Error Rate (SER) can be reduced in embodiments described herein over that of tail-biting convolutional coding with a CRC. Furthermore, error detection offered by Reed Solomon encoder can well compensate underwater noise. Additionally, the encoder packet size can be fixed in order to facilitate decoding and reducing receiver complexity.

Pulse compression is used in radar systems to improve range resolution while maintaining a high duty cycle. In addition to practical implementation constraints, the key issues for the selection of a pulse-compression waveform are mismatch loss, peak / integrated range sidelobes, and Doppler tolerance. While much progress has been made in the design of nonlinear frequency modulated (FM) chirp waveforms satisfying these requirements, the corresponding performance for binary phase-coded waveforms is often inadequate. In order to improve the range sidelobes achieved with phase-coded waveforms, specially designed mismatched pulse compression filters can be used. Several such approaches have been described in the literature since 1959. This paper review these techniques and highlight a particular approach using infinite impulse response (IIR) filters, which has received little attention in the past. Using this technique the performance for a number of binary phase codes of different length have been determined and their Doppler tolerance is investigated.

In this study, Auditory Steady State Responses (ASSR) to 100 μsec clicks and 4 msec cochlear chirps are recorded in adult subjects at repetition rates of 20 to 100 Hz in 10 Hz increments. Response characteristics of ASSRs are compared in the frequency domain. Results show that response amplitudes to both stimuli peak in the proximity of 40 Hz and 80 Hz, but chirps generate responses with larger amplitudes at all repetition rates. The responses at 40 Hz repetition rates for both clicks and chirps are larger than the corresponding responses at 80 Hz stimuli in awake adults. The 40 Hz responses, however, show greater variability than the 80 Hz responses depending on the subject's state of consciousness. The predictions of the ASSR waveforms at each repetition rate were then synthesized by superimposing the suitably shifted Middle Latency Response (MLR) waveforms that were recorded during the same session with a stimulus repetition rate of 10 Hz for both click and chirp recordings. ...

Series compensation of transmission lines using fixed series capacitors can cause sub-synchronous resonance (SSR) between electrical and mechanical systems. This phenomenon leads to severe damages to turbine generator shafts. Thyristor controlled series compensator (TCSC) is one of the FACTS devices which can be utilized to damp electromechanical and sub-synchronous oscillations. This device can perform flexible series compensation and SSR damping. The effect of different parameters of the TCSC is studied using complex torque coefficient method. Open loop and closed-loop constant current and constant power control methods are simulated using PSCAD/EMTDC software package. First IEEE benchmark model for sub-synchronous resonance studies and a complete model of TCSC is used to analyze the effect of different parameters and control structure on the SSR damping capability of the TCSC.

https://ieeexplore.ieee.org/document/9021056/

......................................................................................................................................................................In this paper, we investigate the use of chirp spread spectrum signaling over air-ground channels. This includes evaluation of not only the traditional linear chirp, but also of a new chirp signal format we have devised for multiple access applications. This new format is more practical than prior multiuser chirp systems in the literature, because we allow for imperfect synchronism. Specifically we evaluate multiuser chirp signaling over air-ground channels in a quasi-synchronous condition. The air-ground channels we employ are models based upon an extensive NASA measurement campaign. We show that our new signaling scheme outperforms the classic linear chirp in these air-ground settings.