By Tracy Cozzens
A system that tracks and monitors valuable high-risk assets for defense and commercial customers has received certification from Iridium Communications, increasing the system’s accuracy and effectiveness. The Iridium constellation of low-Earth satellites provides voice and data services for areas not served by terrestrial communication networks.
The Global Sentinel System, by Cubic Global Tracking Solutions, tracks and monitors assets with two-way, redundant encrypted communications. The system provides up to 2,000 unique geozones for each Global Sentinel device to control precise reporting rules along the supply chain. It can monitor asset conditions including temperature, humidity, light sensing, motion, and container door status.
The latest generation of Cubic’s Global Sentinel System provides continuous global coverage by incorporating the Iridium 9602 short-burst-data transceiver. “As an Iridium partner for the past seven years, we’ve worked closely to integrate the Iridium 9602 transceiver into Cubic’s fifth generation of products,” said Mary Ann Wagner, president of CGTS.
Wagner said Cubic relies on Iridium to provide real-time low latency reporting on customers’ assets in areas where other modes of communication are unavailable. This capability allows for continuous global coverage for reliable secure reporting of asset position, status, and event alerts. “This is essential because of the critical nature of the assets we are tracking and monitoring for our Department of Defense and commercial customers,” Wagner said.
Power-Saving GPS. GPS also plays an important role. With the flexibility derived from geozone attributes for GPS, Cubic can provide an optimum balance between position accuracy and power management.
Cubic’s devices take full advantage of GPS receiver circular error probable (CEP) estimates to set accuracy limits for reporting, explained Randy Shepard, vice president of technology innovations for CGTS. While higher position accuracy may be a challenge for battery-powered units operating for years between servicing, it is often necessary to avoid false alarming for events like route deviation where position accuracy is important.
“One of the unique features of Cubic’s devices is the aggressive manner in which we manage power for all device functions including GPS,” Shepard said. “Using the geozones that are remotely reconfigurable on the device, GPS accuracy and response time can be controlled as a function of geozone.
“As an example, for our current GS-5B receiver used for global tracking and monitoring of shipping containers, the initial default dwell time to capture GPS position is 60 seconds. Our experience is that from a cold start we get a normal lock in less than 45 seconds. The maximum acceptable CEP is 100 meters. If a CEP of less than 100 meters is not received, we do not update position. If a CEP of less than 100 meters is received, we wait up to an additional 60 seconds to improve the CEP. Once a CEP of 10 meters or less is received, the position is captured and the GPS receiver turned off. Again, all four of these parameters are remotely reconfigurable for each of the 2,000 user-defined geozones.”
The other GPS receiver parameter that is configurable as a geozone attribute is whether power is maintained on the receiver to retain satellite ephemeris data. If the position update interval for a geozone is more often than every 15 minutes, data back-up power is usually maintained on the GPS receiver and the satellite ephemeris data is retained. This provides and effective warm start for the GPS and usually results in a much quicker initial position lock, which saves overall power.
To provide real-time asset tracking worldwide, Cubic’s Global Sentinel System relies on a variety of transmission links to communicate the positioning and status of an asset. Based on the location of the asset, the system selects whichever link is the most cost-effective for data transmission. This includes wireless mesh networking, cellular, or the ubiquitous global two-way coverage of the 66-satellite Iridium constellation. The Global Sentinel System relies on the Iridium network’s ability to eliminate blind spots when the asset is out of range of other routing methods.
