Michael D. Kotzin

Speech quality improvement for voice coders and synthesizers

A harmonic signal is created from a limited spectral representation of a voice signal. The harmonic signal is combined with the at least a portion of the limited delayed spectral signal to provide a reconstructed speech signal having perceptually improved audio quality.

Reflectors and immersion lenses for detectors of diffuse radiation

The possibility of using reflectors or immersion lenses to enhance the output of detectors of diffuse (homogeneous and isotropic) radiation encountered in scatter communication systems is examined. Reflectors can yield no optical gain, whereas immersion lenses can provide gain equal to n2, where n is the index of refraction of the immersion medium. The conditions necessary to approach this theoretical maximum are examined from the point of view of geometrical optics. The general conclusions are verified by computer simulations for the spherical geometry. Experiments have been performed with spherical and hemispherical immersion lenses, thus confirming the theoretical predictions.

A duplex infra-red system for in-building communications

This paper discusses the application of optical links using indirect scatter to in-building portable communications. The design considerations for such systems are described, and the reasons for selecting a time division multiplexed approach with ON-OFF keying. Both analytical and experimental determination of the path loss for indirect scatter channels are discussed, and it is shown that about 85 dB of path loss can be expected for practical devices in representative office environments. A means for improving S/N in a pulsed system which is average power limited is described. An experimental system based on the above considerations was constructed consisting of a fixed base unit (and range extension repeaters), having essentially hemispheric field of view, and a portable unit having a radial transmitter and hemispheric receiver fields of view. The operation, construction, and performance of the prototype system is discussed.

Dead reckoning vehicle location using a solid state rate gyro

A solid state rate sensor based on the principle of inertia modulation has been evaluated for use in a dead reckoning vehicle location system using sparse signposts. The sensor consisted of a small, simply supported steel bar caused to vibrate at its resonant frequency. Rotation of the bar about its longitudinal axis induces vibration in a plane orthogonal to the driven motion whose magnitude is linearly related to the rotation rate and, upon integration, angular displacement. This output, together with distance-travelled estimates from the vehicle odometer was used to provide a semi-continuous estimate of vehicle position relative to a known initial location and heading. Cumulative errors due to sensor inaccuracies and drift were corrected by means of a grid of simulated radio sign-posts spaced at approximately half mile intervals over the test area. Field test of the experimental system yielded a worst case location error of 212 ft. at the 95% confidence level. Location accuracies of 134 ft./95% were obtained when corrections based on map trends were employed.

A novel spectrum efficient land mobile radio communication system

An experimental land mobile radio communication system which offers a significant improvement in spectrum efficiency over current analog 25-kHz FM radio is presented. Up to four voice channels are provided on a single 25-kHz spaced radio channel. A novel speech coding/constant envelope modulation technique is utilized along with a TDM/TDMA (time division multiplexing/time division multiple access) radio format. The system exhibits fully encryptable communication quality speech and improved sensitivity (range) while achieving adjacent channel splatter performance which meets the FCC mask for secure voice communications.<<ETX>>

A spectrum efficient speech processing method for land mobile radio systems

A method employing a novel combination of speech coding and channel modulation to provide improved spectrum efficiency for land mobile radio systems is described. The method employs a variant of the adaptive subband coding method and multilevel modulation which permits up to 4 TDM (time-division-multiplexed) voice channels to be carried by a single 25 kHz FM channel and more than 10 voice channels if an efficient linear modulation is employed. Details of the implementation show that the complexity required is modest. Comparison with current analog FM radio in terms of practically achievable performance in a mobile has shown that while the induced audible defects due to channel errors are quite different the overall performance is very comparable.<<ETX>>

The future noise environment at 800 MHz

Due to the relatively low noise environment which currently prevails in the 800 MHz spectrum recently allocated for land mobile radio systems, it is of considerable interest to determine the extent to which this situation is likely to deteriorate as the usage of the band grows. To this end, an extensive series of measurements of both noise level and received signal levels around 450 MHz has been conducted at a typical base station repeater site in the Chicago area, and the resulting data used to estimate the future noise environment at 800 MHz when this band reaches a similar level of maturity. In order to gather the data, a specialized scanning receiver system was constructed which sequentially samples the signal level on every channel over a 4 MHz band around 456 MHz while simultaneously monitoring the noise level on two unused channels near the middle of the band. During data collection each of the channels is sampled at a 6 Hz rate for a period of approximately 30 minutes during the midday peak of activity. This data, in conjunction with analytical models to convert it to equivalent 800 MHz data, has been used to estimate the probable noise level at 800 MHz in the future.