The development and analysis of amplitude companded single sideband modulation techniques (acsb, companding, mobile radio, speech processing)
Philip Mark Wala · 1985
Increasing demand for spectrum has prompted a search for more efficient ways to use this limited resource. In particular, it has been suggested that the acute need for additional voice channels in the land mobile bands might be alleviated by the use of single sideband modulation with speech processing. A study was conducted to find ways of implementing a practical single sideband system in the land mobile environment, to optimize the voice processing configuration for a given application, and to investigate procedures for judging the effectiveness of different voice processing methods. Such techniques as amplitude and fequency companding, pre-emphasis, and clipping have been applied to a voice modulated single sideband system, and the effectiveness of those methods evaluated by means of mathematical analyses, intelligibility and isoprefence tests, and field and laboratory measurements. A model for a pilot referenced amplitude compandor has been derived, and the mathematical results compared with the results of human evaluations. In addition, the study has investigated the use of a pilot signal to provide automatic gain and frequency control, and fast-acting feed-forward signal regeneration (FFSR) of the sideband signal. The benefits of various pilot control techniques have been weighed against their reliability and the practicality of their implementation. The study has produced several generations of design, from the early narrowband radio prototypes and ACSB configurations using an above-band pilot, to digital signal processor implementations of feed-forward signal regeneration. It has been shown that single sideband can be implemented with higher spectral efficiency, and a quality of service equal to or better than that of existing FM systems. In addition, the effectiveness of various voice processing and voice quality analysis methods has been demonstrated. The research has led to designs which are capable of practical implementation and are now being readied for commercial production.