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

摘要

A modem intended to be interfaced to a 450-MHz or 900-MHznhalf-duplex, frequency-agile transceiver module with supportingnmicrocontroller circuitry is discussed. The integrated radio modem unitnwill operate on the RAM Mobile Data USA Limited partnership packet radionnetworks in the US and the RAM Mobile Data Ltd network in the UK. Thennetwork uses a wireless protocol to provide a packet link between mobilenor portable radio modems and fixed base stations arranged in a cellularnpattern. The radio modems transmit a GMSK modulated datagram of no morenthan 7256 b at a 8000-b/s rate. The network allows 12.5 kHz channelnspacing and a radio modem transmit power up to 10 W. RAM has beennassigned 200 channel pairs in the US and 31 channel pairs in the UKnfrequency bands. Each radio modem handles roaming between base stationsnby automatically monitoring and selecting the best signal strength ofnall nearby cells