Dual Mode Satellite/Cellular Modem Can Ensure Reliable SCADA Connectivity

Cellular data connectivity is  pervasive and cost effective and seeing increasing use in SCADA Applications. Due to the nature of cellular data communications technology; cellular connectivity alone may not provide adequate reliability in critical SCADA applications; however cellular connectivity backed up by satellite connectivity can provide the necessary reliability.  Field experience with the SCADALink SAT120 and SAT130 Dual Mode Satellite/Cellular Modems with cellular as primary link with fail-over to satellite shows that dual mode connectivity can provides cost effective and high reliability solution for fixed and mobile SCADA applications.

Cellular Communication Challenges

Due to the nature of cellular data communications technology, loss of  cellular connectivity can occur due to:

• Path Fade
• Network Changes
• Network Failures
• Natural Disasters
• Network Overload
• Cellular Repeater Relocation

Path Fade

Cellular RF paths  can be obstructed by terrain and foliage. Many cellular based SCADA sites will not have direct line of site RF paths due to limited antenna height.  The paths will most times have a goodl signal. These RF paths can be affected by wet foliage, or atmospheric temperature inversion causing reduced cellular signal strength and connectivity loss.

Network Changes

Cellular providers will change network topology, tower configurations, and cellular service without notifying subscribers.  This can affect remote site connectivity for cellular based links.

Network Failures

Network outages can be caused by equipment failure, human error, or malicious  actions causing cellular data communications outages. The complexity of cellular networks increases chances of problems.

Natural Disaster Outages

Natural disasters such as hurricanes, floods, fires, and snowstorms can damage the cellular infrastructure, affecting cellular connectivity in local and wider areas.

Network Overload

Cellular Networks can be overloaded by traffic spikes during emergency situations or special events causing cellular data communication service interruptions in given areas.

Cellular Repeater Relocation

Cellular data communication sites that  have relied on cellular signal improvement provided by by a cellular repeater may be affected when the repeater is relocated.

Satellite Connectivity Provides Availability

Satellite based connectivity on the Geosynchronous Inmarsat network provides a highly stable data link since a direct RF path will be  less affected by terrestrial obstructions and weather.  A satellite based network effectively has a lower number of hops can would have higher availability, however will have higher connectivity costs.

Dual Mode Connectivity Balances Availability & Cost

SCADALink SAT120 and SAT130  Modems with dual mode satellite/cellular connectivity can provide the best of both worlds. At sites with marginal cellular RF path, the satellite link can provide connectivity during cellular RF fading.   Most of the time when cellular connectivity is available, providing high speed and lower latency connection at lower costs.