Dual rate mobile data system

Abstract

A mobile data system that uses two significantly different data rates on the air interface is described. In a cellular system it is the conditions prevailing for a mobile terminal at the cell border that set the limit for a reasonable data rate. However, there are conditions in the cell, e.g., a stationary terminal close to the base station, where it is possible to use a higher data rate. A system is described that is designed for 12.5-kHz land mobile radio channels. The system uses a binary digital FM of GMSK type as the default transmission mode, but it switches to multilevel CPM when radio conditions are found to be good by the terminal. Considerations on the choice of the number of levels, and on the performance and complexity of the multilevel signaling, are given. Criteria for deciding when conditions are good enough for a rate increase are suggested.<>