Pulse Duration Modulation (PDM) Voice Modems.
Abstract
Satellite communication to aircraft imposes severe restraints on received signal power and, consequently, received signal-to-noise ratio. In order to provide reliable, tactical quality voice communication and maximize the traffic capacity of a given satellite repeater, optimum use of the available satellite power must be made. The PDM voice modulation techniques has demonstrated considerable advantage over competitive constant-envelope modulation techniques, in functioning under severely constrained received signal-to-noise ratios. This report analyzes in detail the modulation process, describes the implementation, and describes the test results of the subject PDM modems. A 5 to 7 dB signal-to-noise ratio advantage was realized, permitting communications with gradual degradation, rather than precipitous thresholding as normally encountered in narrow-band FM techniques. Highly intelligible 'tactical' voice quality at a carrier-to-noise density ratio of 43 dB-Hz was achieved with 'hang-on' gradual degradation to 38 dB. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1970
- Accession Number
- AD0873396
Entities
People
- Frank Chethik