It is difficult to divine a single specific trend in the wireless modem industry, because this market is so application-driven and the possibilities inherent in remote data transfer are endless. Applications vary with each customer.

As with a chameleon, a wireless data modem can adapt to be what the user wants it to be. It may be used for many applications that require monitoring, remote control, position location and other information transfer.

Applications exist in every industry from transportation to mining, environmental monitoring and citywide surveillance. There are mobile applications such as safety devices for lone workers, the elderly and hospital patients. Plus, demand is increasing for fleet management in which thousands of wireless modems provide position location information for buses, taxicabs and construction equipment. There are exotic applications, such as the wireless sensors that are being placed under the Dead Sea, off the coast of Turkey, to provide early warning of seismic activity.

To handle all of those different applications in varied locations, wireless modems must be manufactured to meet challenges in distance, terrain and harsh environments. In fact, modems, today, are designed to deal with greater distances, rough terrain of all kinds and increased data throughput needs.

Also like a chameleon, the wireless data modem must be able to change its stripes to continue to meet users' needs. Satel's most recent modems are totally programmable - in terms of power, data throughput, channel spacing and frequency - to be adapted to the system even if the application changes.

Distance

As the local radio network grows in terms of distance, enhancements need to be implemented in the modem's transmitter, receiver and antenna. A network configuration with wireless modems is also helpful in providing transmission over increased distances.

The Satelline-3AS Epic radio modem includes a high-power 10 W transmitter and two receivers, which are designed to provide a diversity of functions. Because of the powerful transmitter, the coverage is better than before and the distances between the stations can be remarkably further.

With the diversity receiver, the modem selects the best signal from the ones received in distinction to the two different points. Thus, it can improve the reliability of the connection where there is much reflection and fading. These new characteristics make it possible to more than double the distances between the modems compared to the existing Satelline-3AS radio modems.

Terrain

Wireless modems in a repeater/slave network may also meet challenges provided by hilly terrain. For any radio modem in the network to act as a repeater, it must be able to pass information to the next modem. To do this, Satel included message routing in the software of the Satelline-3AS, designed to relay the message forward toward its ultimate address. The message routing function is independent of the user's protocol, and the network needs only one radio channel.

Message routing in the network can be organised in two different ways: In the Source Mode, the routing control is restricted to a few points called master stations. A routing chain can consist of a maximum of 16 hops. The network may include mobile stations, which can communicate with several routing stations. In the Virtual Mode, the routing information is distributed throughout the network. The number of successive repeaters is unlimited. Mobile stations cannot, however, use the routing service.

It is not necessary to have a direct visual connection between the master station and the moving substation, because the radio signal transmits by reflecting from buildings and terrain such as hills. Fading occurs, however, when the radio signals reflect from several objects to the receiving antenna. After reflecting from different objects, the signals meet the antenna at different phases. At worst case, two equally strong signals of opposite phase cancel each other out and thus cause fading.

In connections that are only based on reflections, the reliability of the signal receiving is dependent on the position of the receiving antenna, even ones fairly close to the base station. If the two antennas of the diversity receiver are set at least three-quarter of a wavelength apart from each other, the message can always be received by one of the receivers, if not both.

Harsh environments

Any modem that one considers must be built well to protect against the rain, heat, snow and other environmental hazards. Satel has chosen a casing made of powder-painted aluminium, plus they also use a durable weatherproof housing made of plastic.

Applications

The applications of Satel radio modems include transfer of data concerning monitoring, remote control, GPS navigation and innumerable other purposes. Communication through radio modems is fully transparent. Built-in RS232/485 interfaces make them directly compatible with most user protocols. In a city environment, the coverage of a radio modem connection varies from a few kilometres up to 19 km, depending on the antenna arrangements, the terrain, buildings and other obstacles to the radio signals.

Direct data throughput needs

Applications vary and may require small amounts of data or a great amount of information. A remote control application that is simply a wireless on-off switch would not need a high data throughput. Many new applications call for more data at a faster rate. Many companies now rely on remote access to their headquarters' central database and access to the Internet, both of which produce increased streams of data.

To serve customers' increased data needs, Satel built much faster data throughput capability into its modems, for example: 19,2 Kbps on a 25 kHz channel and 9,6 Kbps on a 12,5 kHz channel. On the other hand, it has other modems that are much slower, providing up to 4,8 Kbps on a 25 kHz channel, to serve other needs.

Many applications exist for low-power modems

The company also offers low-power radio modems that are used to transfer alarm messages from the object to the control centre. A pair of radio modems with 0,5 W of transmitter power is sufficient to establish a connection between two points up to 30 km.

Satelcode is a compact 0,5 W radio modem for unidirectional transfer of alarm information. It is equipped with eight current loop inputs for connecting various kinds of alarm sensors. Satelnode is a code receiver capable of handling a maximum of 64 000 times eight, contact signals, from the Satelcode or other alarm transmitters. The received alarm messages are transferred to the master computer through an RS232 interface.

Only a couple of radio modems are needed to set up remote monitoring systems or alarm systems for the protection of private property. By increasing the number of alarm transmitters the alarm system can be scaled up to cover thousands of control objects.

Other modems are made to be used in mobile applications. The Satelmate pocket transmitter and Satelsafe wrist transmitter are used for occupational safety of lone workers and as a personal aid and safety device for elderly and patients in hospitals. The two receiver models differ in the ways (alarm loop or relay output) the alarm information is forwarded.

Conclusion

This evolution of wireless data modems operating over greater distances, through all kinds of rough terrain and with increased data throughput is controlled by the users. The applications, which seem to multiply daily, also are a result of users' changing needs.

Satel's customers have always been its best source of advice. When asked for opinions, customers have always responded and given the information needed to provide the products they need. In the future, wireless modems will continue to evolve depending on users' changing communication needs. It is truly the chameleon of the private wireless world.