Experience with a multi-rate modem system for data transmission over 12.5 kHz land mobile radio

The mobile radio scene is moving inexorably towards digital transmission and it was deemed essential that one should gain some experience with the transmission of data over mobile radio systems, even though the principles can be taught based on almost unlimited textbooks. Previous experience on behalf of a public utility service had indicated that data transmission over PMR does not degrade as gracefully as the older established voice analog modulations and suggested that with data transmission one almost has two options: when the radio signal is good transmit the data at a fast rate, i.e. 4800 b/s; and when the radio signal is poor-wait until conditions improve, i.e. move to another site. The results presented tend to confirm this outlook. The third alternative is to employ intensive signal processing especially in multipath conditions.<>