JPL's Wireless Communication Reference Website

Chapter: Network Concepts and Standards

Mobile Data and MultiMedia Networks

Data over Circuit-Switched Networks

In the early days of cellular radio, the only possible way to conduct data transmission over public mobile networks was to attach low-speed voice-band modems to analog radio telephone sets. Generally, this resulted in a poor performance due to the rapid signal fading and shadowing associated with mobile radio, the interference from adjacent cells and the frequent handoffs between base stations inherent in systems with moving users. Improvement by suitable error-correcting codes or data-link protocols is possible, but the data throughput of the narrowband radio voice channel remains small.

With the advent of digital systems, e.g. GSM, there is a popular belief that mobile computer communications will become easier, cheaper and better. While the circuit quality and data rate do indeed improve, a circuit-switched channel (supporting up to 9.6 kbit/s) is not well suited to any bursty data source, even if using digital transmission. Furthermore, call set-up procedures in GSM, requiring the exchange and sequentially processing of about 24 control messages, is prohibitively long for some computer applications. With sufficient error control, digital voice circuits are useful for transfer of batch data such as scheduled up- or downloading of files. On the other hand, dialling up (and paying for!) a real-time two-way circuit between end users is quite inefficient for the more frequent modes of mobile computer communications: electronic mail, interactive access to information services, EDI-type computer messaging, dispatch and other types of fleet management, and point-to-multipoint data 'broadcasting'. For the GSM packet data services, a number of applications for Road Transport Informatics are envisioned, such as traffic information, route guidance and fleet management. For such applications, the network features of classical packet switching appear desirable; i.e., non-blocking access for terminals and the ability to convert data rates and codes within the network. Wide-area flexibility and adaptability to serve computers and terminals with different functions and priorities may point towards dedicated mobile packet radio networks, which can bill by traffic volume, rather than by connect time. Such networks are also far more economic in the use of precious radio spectrum. This is a strong selling point in countries which charge operators for spectrum use or auction frequencies to the highest bidders.

Dedicated Data Networks

 

 

Wireless Local Area Networks

Satellite Systems

 

See also a discussion of early data systems in Germany.

Modacom

Mobile data networks operate in several European countries. Deutsche Bundespost Telekom announced in the Spring of 1993 that its experimental pilot mobile data network, Modacom, will be available for full operation in 80% of Germany by 1995. This wireless extension of Telekom's own public X.25 packet service to mobile computers such as Laptops, Notebooks and Palmtops suggests that (at least) one of the major GSM-operators in Europe has doubts about the competitiveness of the planned data transmission modes in the GSM network. Motorola's DataTAC technology, based on the RD LAP protocol for the logical radio link connection, was adopted by Deutsche Telekom for Modacom in Germany, by Hutchinson operating a mobile data service in the UK and Hong Kong, and by the ARDIS companies in the US and Canada.

Mobitex

Well ahead of the German Modacom network, the Scandinavian PTT- administrations in Sweden, Norway and Finland introduced the Mobitex Radio Data Standard. In the 1980's, Mobitex was supporting only a low-speed packet service at 1200 bit/s plus an emergency voice service, reflecting the initial use by police patrols, fire brigades and public utility services to exchange brief command-and-control messages with their headquarters. A decade later, the widespread acceptance of portable computers and the advent of more demanding commercial operators, including RAM Mobile Data in the US, have pushed the Mobitex data rate up - and the hybrid voice channel out: The 19,2 kbit/s data rate defined in is twice that foreseen in GSM. Mobitex- based networks have been introduced in the UK and the Netherlands by RAM, and in France by France Telecom, assisted by Bell South.

CDPD

Cellular Digital Packet Data coexists with the US cellular telephone system (AMPS / IS54). It can use temporarily vacant speech channels to transmit data.

Radio Broadcast Data System (RDS)

The RDS or RBDS system uses FM broadcast transmissions. It provides one-way communications only. Typical applications are in paging and road transportation.

Further Discussion of Wide-Area Mobile Data Systems

A brief description of the above systems has been compiled by Randy Katz in Acrobat format.

Theoretical aspects

Multiple Access in the uplink

Downlink



JPL's Wireless Communication Reference Website 1993, 1997.