Over a decade ago GPS World covered the introduction of the first battery-powered asset tracking device that operated over satellite networks, the AXTracker (“Going the Distance,” October 2003). More than ten years later, the technology has proven the market, and opened new markets. Battery powered tracking devices today are used for the expected, like enterprise asset tracking for trailers, containers, and field equipment, to the unexpected like tracking sea currents, ranging sheep, and weather balloons.
The newest products are dramatically smaller, have much longer battery life, and pack accelerometers and Bluetooth for mobile phone connectivity and wireless sensor interface. Yet power management, cellular and satellite communications, and environmental ruggedness remain the technical challenge.
Advances have occurred in rechargeable technologies, largely driven by cellular telephones, military and automotive, but advances in primary batteries for industrial use are limited. Environmental operation is the problem. It remains extremely difficult to produce a primary cell that retains power for a decade while exposed to industrial temperature extremes. Global GPS tags for industrial use must operate in industrial temperature ranges of -40 C to + 85 C (-40 to + 185 F) while limiting self-discharge to enable operation over many years. Primary cells providing utility over the industrial temperature range with low self-discharge rates remain the same as available ten years ago. LiMnO2 (lithium/manganese dioxide) and Li-SOCl2 (lithium-thionyl chloride) are still the leading chemistries.
Lessons learned from field deployments have produced quality improvements and better field longevity and yield. Not all AA batteries with the same paper specifications survive equally, so developers must be wary. Through power reductions in satellite communications and GPS technology discussed below, the asset tag of today can enjoy a volumetric and cost reduction for batteries while achieving the same service duration.
GSatellite Network Technology
Ten years ago, the available global commercial satellite machine-to-machine (data) networks included Iridium, Orbcomm, INMARSAT and Globalstar. Though several of the satellite network service providers are replacing retired satellites, the technology remains unchanged and developers are left with the same choices today as ten years ago. Each satellite network offers different strengths and weaknesses for specific M2M field applications with different power budgets required. The AXTracker of a decade ago utilized the Globalstar simplex capability specifically because of the power budget profile for data delivery. From a satellite network power perspective, the limitations of one-way (field to cloud) satellite solutions employed by that first tracker continue to out-weigh other satellite network offerings.
In order to utilize the available satellite networks, the asset tag must integrate satellite communication circuitry. In a world of continuous technology improvements, the satellite transceiver evolution has been slow. Over the past decade most of the major satellite network providers have next-generation transceivers. However, the new technology has only marginally improved the power issues for battery-powered industrial GPS tags. For example, Iridium’s first OEM transceiver, the 9601, required peak power of 7.5W, with average power of 1.8W. Their latest transceiver, the 9603, is much smaller physically but still requires the same 7.5W peak, though average power is now 1W. Average power for an Iridium data packet delivery is the measure of the power used over message transmit and receive as well as idle times while accessing the satellite network. This average power for Iridium is the parameter used for calculating message delivery per a given battery capacity but peak power must also be supplied in any design that seeks to use the data service. Orbcomm and INMARSAT technology have similar power budgets due to their communications handshake requirements to access the network. For these systems, it remains difficult to source this power capacity and peak current requirements at -40C environmental temperature using batteries only.
Similar power improvements are available in the Globalstar simplex system. The Globalstar system is different than the other commercial M2M satellite networks in that data is merely transmitted one-way from the GPS tag to the network, thus removing the power needs for handshaking with the network to deliver data. The STX1 radio transmitter of eleven years ago required a whopping 6W during transmit, but thankfully was soon replaced with the STX2 radio transmitter. The STX2 is still the primary simplex transmitter in use today and requires 1.65W during the one-way short-packet bursts. The much lower and short duration requirements for power were, and are, the deciding factor for network selection for the original battery operated GPS tag. Today, the Geoforce MYTE radio transmitter embedded in the GT1 and GT0 devices requires 1.1W peak, an 82% reduction from the short-lived STX1 and a 33% reduction from the STX2. For simplex service, the peak power is used to calculate message delivery per available battery capacity since there are no network access or receive power requirements. Ten years of simplex transmitter evolution and size reduction enable fundamentally smaller asset tags while providing a 30% to 40% reduction in power required for satellite data delivery.
Improvements here have made the greatest power budget impact for tag developers, greatly reducing the total power and current required to ascertain a location. GPS chipsets of ten years ago would kill today’s smartphones in hours. The newest GPS cores operate at much lower voltages and operating currents. The GPS engine of the first AXTracker operated at 3.3V and required 70 mA operating current for an average cold-fix time of 45 seconds (10.4 Wsec of battery power). Geoforce’s GT1 and GT0 embed the Origin Spider GPS module that incorporates the SiRFstarIV GPS chipset. This GPS engine operates at 1.8V with 37 mA operating current and an average cold-fix time of 35 seconds (2.3 Wsec). Even for challenging GPS field deployments, this represents a conservative 75 percent power reduction for location determination.
The power budget rule of thumb ten years ago was 20 percent went into idle sleep current, with the remaining 80 percent split roughly equally between satellite communications and GPS location determination. Improvements in satellite transmitter and GPS power technology have shifted the power budget ratio to 40 percent satellite communications and roughly equal power between idle sleep current and GPS location determination, for a net overall power reduction of roughly 33 percent. This means that the tag of today can last 50 percent longer than the tracker a decade ago with the same battery capacity. Alternatively, today’s tracker can have 33 to 50 percent fewer batteries to achieve the same service life depending on operational configuration.
What about Cellular?
Ten years ago cellular M2M systems were as much in their infancy as satellite systems. The advance of cellular telemetry tracking systems has exploded far faster than satellite systems for powered fleet-type assets, yet there are far fewer battery-powered cellular systems than satellite today. Two primary contributing technology factors impede the introduction of battery-powered cellular systems: network availability and network power requirements. Cellular tracking services have good availability as long as the asset operating area greatly overlaps consumer cellphone service. International and industrial applications have lower cellular regional overlap. As a result, battery powered cellular asset tracking devices remains a niche market.
Even if network coverage is acceptable, power budget asserts real technical problems for the developer. Cellular transceivers have similar power requirements as two-way satellite network, with high peak currents and relatively long network access dwell times. A multi-year, industrial temperature GPS asset tag operating over cellular is similar to a two-way satellite, requiring large capacity primary batteries, or rechargeable configurations that require frequent access to line power. For this reason, these battery-powered cellular asset tag technologies are seeing slower market insertion, leaving unpowered, industrial and international asset management applications to simplex satellite solutions.
The largest product evolution observed in battery-powered asset tag technology is industrial packaging. Electronic and battery technology has remained fundamentally unchanged, however the packaging of these devices has changed significantly. Over the past ten years, the GPS asset tag has transitioned through many design and package iterations, all seeking to improve the reliability and service life of the industrial tag. Conflicting use-case requirements have contributed to field failures. Customers often demand features similar to commercial electronics systems such as rechargeable or replaceable batteries, or connectivity of remote sensors. While these features are highly desirable, they also lead to field failures in rugged, industrial environments. Chief among environmental failures is water intrusion.
Customer expectations for wired sensor connectivity or battery replacement require connectors for wiring or panels to access the battery compartment with gaskets to prevent water intrusion. The stressors of industrial, multi-year fielded devices are unlike consumer electronics systems. Industrial tags are subjected to directed pressure washing, often at forces sufficient to cut plastic. And unlike commercial electronic systems, the industrial tags see the full temperature range of automotive-grade electronics while still providing compartments for battery replacement (something that most automotive electronics products do not require). Beyond liquid water intrusion, many products succumb to water vapor intrusion that subsequently condenses inside the device due to large temperature swings. Gaskets designed to prevent water are less able to prevent passage of small amounts of atmospheric vapor due to a vacuum created on temperature drop. The effect is easy to visualize if we apply the ideal gas law, PV = nRT where P is pressure, V is volume and T is temperature (n and R are constants). For a given volume inside the tag, the pressure changes proportionally with temperature, thus a tag that experiences a drop in temperature will also experience a drop in relative pressure and will pull in minute amounts of water vapor, which over time will condense and cause product failure.
Several obvious solutions exist, starting with removal of internal air volume through encapsulation (potting). Encapsulation seeks to take V to zero, thus making the device impervious to vapor intrusion caused by temperature swings. Additionally gaskets can be removed at the tradeoff of inaccessible batteries.
Putting It All Together
The Geoforce GT0 leverages over a decade of lessons learned. It incorporates the smallest, lowest power simplex transmitter, salvaging 33% of power required for satellite communications. It also uses the Origin Spider GPS module, which includes the latest SiRFstarIV GPS chipsets, harvesting 50% of the power for location fixes. The GT0 also incorporates the latest circular polarized antenna technology from Tallysman, with unparalleled performance compared to previously available commercial patch antennas.
The combined antenna design and power savings enable the GT0 to require only half of the batteries with an 85% reduction of device volume to achieve the same or better field service life compared with the tracker of ten years ago. The lower volume alone reduces the risk for water intrusion, but the risk is further reduced by the use of encapsulation and non-replaceable batteries. The GT0 is therefore fully sealed, disposable and encapsulated. This packaging concept makes the GT0 extremely rugged and impervious to directed water or water vapor intrusion. Thus, the GT0 is truly in a class of its own. The technology advancements and lessons learned over the past decade have enabled mechanical footprint and volumetric reduction of the global, battery-powered GPS asset tag.
The GT0 combines the smallest, lowest power satellite and GPS engines with innovative packaging to create the smallest, industrial-grade global satellite asset management tag available anywhere, setting the bar for size, value and performance.
Asset managers today need more than dots on a map. They need asset utilization metrics that provide actionable information for improving operations. Knowing where an asset is and where it is moving is sometimes enough, and for these applications GPS enabled, battery-powered tags provide supreme value. New tags provide the value of track and trace, but also can relay data from nearby sensors using short-range Bluetooth wireless interfaces. This capability will evolve the utility of yesterday’s global tag, closing the gap from location only toward satellite-based telematics, but that is a story for another day.