Harold P. Stern

A comprehensive model for voice activity in conversational speech—development and application to performance analysis of new-generation wireless communication systems

Proposed new wireless communication systems such as third generation cellular and PCN will utilize speech inferpolation, disconnecting the user from the spectral resource during pauses in speech in order to reduce radiated emissions and improve spectral efficiency. An accurate model of the on-off characteristics of conversational speech is thus necessary to analyze system performance, particularly if the system utilizes a time and/or frequency division multiple access technique. Previously developed speech activity models are deficient because they either do not reproduce short silent pauses of less than 200 ms. (representative of the silence gaps between syllables or words) or else they do not replicate the dynamics between the two conversing parties. Starting with the P.T. Brady model and developing appropriate modifications, this paper formulates a simple, accurate, comprehensive 8-state Markov model for voice activity in conversational speech. The new model can easily be incorporated into simulations or analyses assessing the performance of various new-generation wireless networks, thus improving the accuracy of the performance assessments.

A voice activity detection algorithm for communication systems with dynamically varying background acoustic noise

Speech can be modeled as short bursts of vocal energy separated by silence gaps. During typical conversation talk-spurts comprise only 31.5% of each partys speech and the remaining 68.5% is silence. Communication systems can achieve significant gains in spectral efficiency and energy efficiency by disconnecting the users from the spectral resource during the silence periods. This paper develops a simple, efficient, and robust voice activity detection (VAD) algorithm to work in a mobile or portable environment exhibiting dynamically varying background noise. The VAD uses probabilistic distances based on the energy content, the periodicity, the stationarity and the spectral distribution within the low frequency band to decide if the presented speech frame is speech or silence.

A model for generating on-off patterns in conversational speech, including short silence gaps and the effects of interaction between parties

The six-state model for on-off characteristics of conversational speech established by Brady (1969) does not consider pauses in speech shorter than 200 ms. Such an omission is significant since new-generation speech interpolation systems will utilize these short pauses as well as the longer periods of silence. This paper proposes modifications to the Brady model to represent the effects of the short pauses while preserving the effects of the longer silences and the dynamics of the interaction between speaking parties. The modified Brady model provides a tool for more accurately assessing the performance of new-generation wireless communication systems. >

An adaptive propagation prediction program for land mobile radio systems

This paper describes the development of an adaptive RF propagation prediction program for land mobile radio systems. The program, which allows the user to specify transmitted signal strength, carrier frequency, base station antenna height, and mobile vehicle antenna height also provides the information necessary to determine a level of confidence for its predictions. In lieu of detailed topographical data (which is unavailable for many regions), the program makes use of data files containing the results of received signal strength measurements previously taken within the geographic region of interest at various locations, various carrier frequencies (measurements were taken at 453, 922, 1310, 1430, and 1920 MHz), and various base station antenna heights. This paper concludes by providing examples of results illustrating the performance of the adaptive propagation prediction program, showing that the proposed program yields significant improvement in propagation prediction and level of confidence when compared to currently available tools.

Design issues relevant to developing an integrated voice/data mobile radio system

Dynamically integrating voice and digital data over common radio channels for mobile applications is discussed in that it is expected to provide significant increases in flexibility and efficiency over systems which handle voice and data separately. Various design issues related to developing an integrated voice/data mobile radio system are discussed, including high-speed digital RF modulation in a mobile environment, statistics for the talkspurt/silence gap composition of speech, encoding techniques, and voice and data traffic statistics.<<ETX>>

Transmission policies and traffic management in multimedia wireless networks

We consider multimedia wireless networks in environments where traffic characterizations and traffic rates are generally time‐varying. For such networks we propose a CDMA transmission policy, in conjunction with a moving boundaries concept induced by a traffic monitoring high‐level protocol. The proposed transmission/traffic management technique is analyzed and numerically evaluated.

Design and performance analysis of an advanced, narrowband integrated voice/data mobile radio system

Private land mobile communications have experienced significant demand for increased capacity and for new services, but congestion within the currently allocated 450 and 800 MHz bands has severely limited the capability of present generation systems to meet this demand. This paper proposes a narrowband integrated voice/data mobile radio system which triples current voice traffic capacity and simultaneously provides capacity for mobile data communications such as mobile data terminals, automatic vehicle location, and mobile facsimile by utilizing the silence gaps inherent in speech. The system is designed to fit within the narrowband 25 kHz channels in the 450 and 800 MHz frequency bands, and thus the system can replace existing private land mobile radio systems with minimum impact. The centerpiece of the system design is an evolutionary multiplexing and access control technique known as Packetized Data, Voice Dedicated (PDVD) Burst Switching which allows transmission of data within the silence gaps inherent in speech. Simulation results for various voice and data traffic loads show the flexibility and efficiency of the proposed narrowband integrated voice/data mobile radio system. >

Efficient dynamic synchronous machine simulation with harmonics

Within this paper, an efficient procedure for the dynamic simulation of faulted synchronous machines operating in the presence of harmonics is presented. The algorithm employs steady-state frequency domain techniques for simulation of the transmission system sequence networks and time domain methods for synchronous machines represented in the odq frame of reference. The procedure affords greater accuracy than conventional fault analysis techniques based strictly on steady-state methods, yet requires far less computational time than full system dynamic simulations such as those using the EMTP.

An instructional module for engineering ethics

This paper describes a short (3 class-hour) module developed to teach engineering ethics. The module has been designed for simple integration into a standard technical course, minimally impacting existing curricula and effectively introducing the need for engineering ethics, the key components in an engineering code of ethics, and resources for help in resolving ethical conflicts. Case studies are used, showing directly how certain ethical issues relate to the practice of engineering and prompting lively in-class discussions. Using cooperative and active learning techniques, the class develops its own code of engineering ethics and compares their code to the professional society codes within their discipline. Test data shows that after taking the module, students are more capable of stating the key components of an engineering code of ethics and are more knowledgeable concerning resources available for resolving ethical dilemmas. Testing also shows that the students have a high awareness of the issues involved in engineering ethics and that, after taking the module, they are significantly more confident concerning their ability to address ethical conflicts in their future professional practice.

Fixed cell assignment for forward link in broadband wireless networks

This paper proposes a new allocation method, called the fixed cell assignment, which provides wireless Internet access by employing time division multiple access transmission for the forward link in broadband (10 Mbit/s) wireless networks. The system is configured with directional base station antennas and omnidirectional mobile antennas, with each cell divided into six sectors, and sectors numbered in the same order for every cell. Access is controlled based on availability and sector number, and half the sectors in each cell reuse the same spectrum with power control mitigating the effects of co-channel interference. Performance is evaluated using both analytic techniques and computer simulation for the maximum capacity tradeoffs.