Delta Modulation Systems For Voice Communication

Digital systems are of major importance in modern communications. This research investigates the minimum clock (bit) rate of a commercially available delta modulator/demodulator needed to transmit intelligible voice signals. Intelligible voice and music signals were recovered using a clock rate as low as 6 Kbits/sec. (Author).

A variable bit width delta modulator (VBWDM) demodulator was designed, built and tested to achieve voice and music communication using a bandlimited channel. Only baseband modulation is applied to the input signal. Since there is no 'clock' used during the digitizing process at the modulator, no bit synchronization is required for signal recovery in the receiver. The modulator is a hybrid design using 7 linear and 3 digital integrated circuits (IC), and the demodulator uses 2 linear ICs. A lowpass filter (LPF) is used to simulate the channel. The average number of bits sent over the channel is measured with a frequency counter at the output of the modulator. The minimum bandwidth required for the LPF is determined according to the intelligibility of the recovered message. Measurements indicate an average bit rate required for intelligible voice transmission is in the range of 2 to 4 kilobits per seconds (kbps) and between 2 to 5 kbps for music. The channel 3 dB bandwidth required is determined to be 1.5 kilohertzs. Besides the hardware simplicity, VBWDM provides an option for intelligible digitized voice transmission at very low bit rates without requiring synchronization. Another important feature of the modulator design is that no bits are sent when no signal is present at the input which saves transmitter power (important for mobile stations) and reduces probability of intercept and jamming in military applications. Keywords: Voice communication, Delta modulation, Analog-to-digital converter, Bit rate, Variable bit width, Hard limiter, DM, VBWDM, Radiofrequency wave propagation, Theses. (JG).

This book is intended for students and professionals who are interested in the field of digital signal processing of delta-sigma modulated sequences. The overall focus is on the development of algorithms and circuits for linear, non-linear, and mixed mode processing of delta-sigma modulated pulse streams. The material presented here is directly relevant to applications in digital communication, DSP, instrumentation, and control.

A way to increase jamming immunity and to decrease the intercept probability of a communication system is to use spread spectrum (SS) techniques. In this report a frequency hopping SS system (transmitter and receiver) is presented. This system is designed, built, and tested to send and receive digitized voice by utilizing a single chip delta modulator/demodulator. The report describes the circuitry employed, lists the important parameters of the system and includes photographs of various waveforms. The recovered audio is of good quality using digital data rates as low as 25 kilobits per second. A hopping rate of 100 hops per second is used in the design. (Author).

Innovations in Telecommunications, Part A contains the proceedings of the symposium on "Innovations in Telecommunications" of the International Symposium Series held in Kuwait in April 1981 and sponsored by the Kuwait Foundation for the Advancement of Science. The symposium provided a forum for reviewing advances in research, development, demonstration, design, manufacture, field testing, and application in the field of telecommunications. Both the state of the art and the cutting edge of technology in telecommunications are given emphasis. Comprised of 17 chapters, this book is arranged in five major sections: signal processing; devices and microfabrication techniques; terrestrial communications; satellite communication; and applications. The discussion begins with an assessment of trends in electronic information transfer, followed by a description of a bandwidth- and power-efficient modulation system that combines convolutional encoding and phase modulation. Subsequent chapters deal with voice processing techniques; image processing for communication; developments in switching; and devices such as those for transmission and delta modulation. The final section is devoted to terrestrial communications and covers microwave systems, mobile and lightwave communications, and coaxial cable systems for land and sea. This monograph will be of interest to those in the telecommunications industry.

A way to increase jamming immunity and to decrease the intercept probability of a communication system is to use spread spectrum (SS) techniques. In this report a frequency hopping SS system (transmitter and receiver) is presented. This system is designed, built, and tested to send and receive digitized voice by utilizing a single chip delta modulator/demodulator. The report describes the circuitry employed, lists the important parameters of the system and includes photographs of various waveforms. The recovered audio is of good quality using digital data rates as low as 25 kilobits per second. A hopping rate of 100 hops per second is used in the design. (Author).

An introductory, graduate-level look at modern communications in general and radio communications in particular. This seminal presentation of the applications of communication theory to signal and receiver design brings you valuable insights into the fundamental concepts underlying today's communications systems, especially wireless communications. Coverage includes: AM, FM Phase Modulation, PCM, fading, and diversity receivers. This is a classic reissue of a book published by McGraw Hill in 1966.