How spread spectrum could spread

Traditionally, telemetry and SCADA data radio users have opted for narrowband licensed channels, primarily for protection from possible interference sources and the security of bandwidth for critical infrastructure.

In Australia, narrowband users have been reluctant to consider the publicly accessible bands such as the 900 MHz and 2.4 GHz (spread spectrum) ISM bands through an aversion to invest in a band that might be free today but congested down the track.

Trends around the world, and especially in North America, suggest a move towards spread spectrum radio systems. In the US market, licensed radio channels are at saturation levels and many SCADA and telemetry users have little choice but to deploy a spread spectrum solution.

Unlike narrowband channels that operate on a fixed frequency pair, spread spectrum operates by having all the radios in a group move (hop) between predetermined sequences of channels.

In Australia, the typical licensed telemetry model allows for a central base or repeater communicating to remote stations within a 30 km radius.

Unfortunately, it is rare that user operations fit neatly into a circle. Therefore, if stations are outside this radius a new licence (if available) would need to be purchased, with all the typical infrastructure costs associated with setting up a base site.

An option for rectifying this is to create a hybrid system. The logical solution is an extension of the main network using spread spectrum radio products.

This is particularly useful if the outlying stations are following a watercourse or pipelines where several store and forward radios could be deployed to bring this spur back in to the main system.

In doing this the importance of having a dedicated narrowband frequency within the busier 30 km licensed limit is covered. As most spurs from the main system can be achieved with short distance (1–5 km) store and forward radios, the likelihood of other spread spectrum systems causing interference is noticeably reduced, especially if directional antennas are used.

The lure of a spread spectrum radio network with its flexibility and simple deployment is enhanced by the added features that these data radio modems provide.

Features like dual ethernet and serial interfacing allow for more control and connectivity of the network.

Trends in recent years have seen the increased merging of the radio and IT worlds as ethernet connectivity makes it possible to obtain the bandwidth required to negotiate ethernet traffic.

This brings significant benefits in data throughput with speeds of 256 and 512 Kbps available for around the -100 dBm at 1x10

Paul Harriss is the Australian sales manager of Trio DataCom, a manufacturer of data radio modems. He holds tertiary qualifications in radio, electronics and IT. He has over 30 years<0x0219> experience within the radio industry.