Phillip D. Rasky

Speech and channel coding for digital land-mobile radio

The joint development of a medium bit-rate speech coder along with an effective channel coding technique to provide a robust, spectrally efficient, high-quality mobile communication system is described. A subband coder operating at 12 kb/s is used; in the absence of channel errors, it provides speech quality comparable to current analog land-mobile radio systems. The coder design incorporates a unique coding of the side information to facilitate the use of forward-error-correction coding without the need to code the entire bit stream. The use of excessive overhead for redundancy is avoided while the harsh effects of frequent channels are mitigated. These techniques have been used in an experimental FDMA (frequency-division multiple access) digital land-mobile radio system. The combined speech and channel coder operates at 15 kb/s and provides intelligible speech at fading channel error rates up to 8%. >

An experimental slow frequency-hopped personal communication system for the proposed U.S. 1850-1990 MHz band

An operational, prototype 1.8 GHz personal communication system employing the access technique of slow frequency-hopped CDMA is described. This system was designed to permit true vehicular/portable mobility with larger cells than conventional PCS proposals would allow while providing for the existence of a lower-cost PCS which would be operable in truly pedestrian-only environments. In the paper, the modem architecture, algorithms, and performance are discussed. The system has been found to yield excellent performance on a variety of channels characteristic of expanded PCS environment at a reasonable level of hardware complexity.An operational, prototype 1.8 GHz personal communication system employing the access technique of slow frequency-hopped CDMA is described. This system was designed to permit true vehicular/portable mobility with larger cells than conventional PCS proposals would allow while providing for the existence of a lower-cost PCS which would be operable in truly pedestrian-only environments. In the paper, the modem architecture, algorithms, and performance are discussed. The system has been found to yield excellent performance on a variety of channels characteristic of expanded PCS environment at a reasonable level of hardware complexity.

Signal processing aspects of Motorola's Pan-European digital cellular validation mobile

An experimental hardware system designed to permit evaluation of the European Conference of Post and Telecommunication Administrations (CEPT) Group Speciale Mobile (GSM) air interface standard is described. The system is a two-way radio link which operates as a fully functional mobile radiotelephone and permits both objective (bit error rate) and subjective (speech codec quality) performance measurements to be made. A complete description of the mobile radio system along with key aspects of the signal processing algorithms used therein is provided and performance results of the system in the presence of co-channel interference and multipath fading are given.<<ETX>>

Frequency hopped systems for PCS

The application of frequency hopping methods to cellular and personal communication systems (PCS) is studied. The performance enhancements due to the use of frequency hopping (FH) is initially reviewed followed by a brief summary of previously designed cellular/PCS systems that have incorporated FH methods. A slow frequency hop (SFH) prototype (which incorporated a hybrid form of multiple access, in particular slow frequency hopping CDMA combined with time division multiple access (TDMA)) was developed for PCS applications is then described. Performance results using the SFH prototype in laboratory and field trials are provided. These results demonstrate the excellent performance that may be obtained in PCS environments using a SFH architecture which has a complexity level that is suitable for PCS implementation.<<ETX>>

Hybrid Slow Frequency-Hop/CDMA-TDMA as a Solution for High-Mobility, Wide-Area Personal Communications

In order to provide a full range of personal communication services with wide-area coverage and high mobility, a macrocellular complement to microcellular PCS is defined. This system was designed to permit true vehicular/portable mobility with larger cells than conventional PCS proposals would allow while providing for the existence of a lower-cost PCS which would be operable in truly pedestrian-only environments. This macrocellular system employs the multiple access technique of slow frequency hopping to provide robust transmission over the harsh mobile radio channel and to maintain high capacity despite the use of larger cells. This paper discusses the alternatives considered in the definition of this system,highlighting choices which allow significant reductions in complexity without compromising system performance. In addition, channel models for frequency-hop systems are discussed and verified with field data. Using these models, the performance and capacity of the macrocellular system have been estimated on a variety of channels characteristic of the expanded PCS environment. The system has been found to offer excellent performance at a level of complexity suitable for PCS implementation.

Field measurements of a prototype slow frequency hop personal communication system

A 500 kbps, high-mobility, personal communication system (PCS) employing slow frequency hopping (SFH) and time-division multiple access is investigated for the 1.8 GHz band. In order to verify the concepts which drove the system design and to characterize the SFH propagation environment, extensive field tests have been conducted with the prototype units. This paper summarizes the findings and draws conclusions on the effectiveness of the space, frequency, and time diversity. Results are presented for the forward and reverse transmission paths. On the forward path, both mobile and portable receiver antenna configurations have been examined. The complementary set of diversity techniques incorporated within the system has been found to allow robust operation even on the severe multipath fading channels characteristic of the expanded PCS propagation environment.