Air interface protocols for a national mobile data network

In 1990 the UK Government granted licences for national mobile data networks. This provided the opportunity for companies to implement mobile radio systems utilising hardware and protocols designed specifically for data-only transmission. The author provides an overview of the air interface protocols of one such network based on the Mobitex mobile data system. The network is a hierarchical structure. Sufficient intelligence is built into each node so that any message need only travel up the hierarchy as high as a common node. A radio modem (or mobile) communicates to the network using a UHF radio link to a base station. Data transmission is at 8 kbit/s using GMSK (gaussian minimum shift keying). The protocol operating on this link is called ROSI (radio signalling protocol) and this supports the transmission of small packets of data called MPAK