Performance analysis and design guidelines of a mobitex modem at 8 kb/s

Abstract

A modem intended to be interfaced to a 450-MHz or 900-MHz half-duplex, frequency-agile transceiver module with supporting microcontroller circuitry is discussed. The integrated radio modem unit will operate on the RAM Mobile Data USA Limited partnership packet radio networks in the US and the RAM Mobile Data Ltd network in the UK. The network uses a wireless protocol to provide a packet link between mobile or portable radio modems and fixed base stations arranged in a cellular pattern. The radio modems transmit a GMSK modulated datagram of no more than 7256 b at a 8000-b/s rate. The network allows 12.5 kHz channel spacing and a radio modem transmit power up to 10 W. RAM has been assigned 200 channel pairs in the US and 31 channel pairs in the UK frequency bands. Each radio modem handles roaming between base stations by automatically monitoring and selecting the best signal strength of all nearby cells.<>