Time-Based Vs. Proximity-Based Asset Tracking — Comparing Applications

“Where is my stuff?!” For just about every organization in every industry, this question is a central challenge—and if you know the answer, it has the potential to yield enormous value. To answer this question, businesses are using their real-time data to analyze trends and patterns in asset use while gaining better control over their resources and operations. That’s why implementing asset tracking is a priority for so many organizations today. I wrote a piece on how vital location tracking is for supply chain management. There are important nuances to the "time-based vs. proximity-based asset tracking" discussion, which I aim to clarify in this post.

Those businesses that are likely to see the greatest success are knowledgeable about the types of asset tracking technology—i.e., time-based vs. proximity-based asset tracking—and have designed a solution that properly matches their business needs. In what follows, I hope to clarify the nuances between these modes of asset tracking for you, so that you can be better informed when thinking about your next asset tracking Applications.

Two Categories Of Asset-Tracking Technology

A: Time-based asset location systems

Asset-tracking technologies measure time differently. Some systems calculate location using time because time is distance. If you know the speed of light and the speed of sound, you can measure how long it takes a signal to travel from one place to another, and use those signals to calculate location.

The most common way to calculate location via time is called "time difference of arrival (TDOA)." TDOA involves sending signals to multiple reception points and comparing the time difference in receiving them. This is how some of the newer WiFi-based positioning systems and ultra-wide-band systems work.

TDOA systems require a significant indoor infrastructure investment. They also require a lot of calibration—all of the receivers must have the exact same time (to the nanosecond) for TDOA to be effective. The method is considered the gold standard of location accuracy, but not every organization wants or needs such precise location positioning, making the expense unjustifiable.

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B: Proximity-based Asset Location Systems

Proximity-based asset tracking is based on received signal strength. Essentially, it asks the question, “Who is my loudest neighbor?” From the received signal strength we can infer how close the asset is.

In a more technical sense, it works like this: A tag using Bluetooth advertises every 30 milliseconds or so to a number of different receivers, all of which “hear” that tag’s advertisement and send that data up to the cloud. The location of the tag can be determined based on the meshing of the various signal strengths.

Proximity-based location solutions can accurately pinpoint locations within about 100 square feet, making them ideal for Applications that don’t require exact locations. They are also inexpensive to implement because they don’t require costly infrastructure. Moreover, you can use low-cost beacons.

The one downside of this architecture is that all of the raw data must flow constantly up to a server in order to determine location. There are, however, proximity-based asset tracking solutions that overcome this problem by essentially working in reverse.

In one such solution, instead of the tags being connected to the cloud, they are capable of calculating only their own position and sending it periodically to a nearby access point using Bluetooth (think edge computing). That access point is then connected to the cloud. This type of solution reduces the amount of data being transmitted and improves accuracy (because you can put many more low-cost reference points in a room than you could with other technologies).

Selecting The Right Technology For Your Asset Tracking Applications

For many business Applications, proximity-based location knowledge is sufficient. Here are some examples:

• In construction, proximity-based tracking is being used to track prefabricated assemblies that are built offsite and then delivered to the job site. The implementation solves the problem of assemblies getting lost on-site since assemblies are sometimes delivered before workers are ready to use them.
• In consumables, companies are using the technology to deliver supplies (oil, paper, etc.) to enterprises or industrial environments. Specifically, they use it to track the life cycles of those supplies, from their movement inside a fulfillment center to end-user delivery. Optimizing delivery and inventory like so offers tremendous opportunities for savings.
• In logistics, manufacturers are using proximity-based asset tracking to keep eyes on the movement of pallets from when suppliers initially deliver them throughout that pallet's "life cycle" in the plant or warehouse. Doing so eliminates inefficiencies and speeds up production capability.
• Proximity-based location is being used by businesses that travel to residences and businesses for service calls, in order to ensure no expensive equipment is left behind at the site. The IoT deployment saves money associated with having to replace lost equipment.

Very few Applications require the pinpoint precision associated with time-based asset tracking solutions. One such example, however, would be "human factors research," in which you need to know exactly how people are moving around within a particular space—in near real time. Another instance in which pinpoint precision would be useful is for shelf-level inventory management.

It's not always clear which to choose among the different types of asset tracking technology, but there are resources, including this article, to guide you.

When More Than One System Is Needed

Many business Applications are complex and require more than one type of technology. My point is that it's not always a black and white debate: "time-based vs. proximity-based asset tracking." In other words, it's not always one or the other. Often, the best solution comes from combining different location tracking technologies. Such a strategy not only provides seamless indoor and outdoor asset-tracking, it also helps businesses design a solution that meets their cost targets while still satisfying their needs.

A typical customer scenario would use a low-cost tag both indoors and outdoors:

Indoors, a Bluetooth Low Energy (BLE) transceiver tag wakes up, listens to the BLE references around it, and calculates where it is located based on those references. It then transmits that information to a BLE access point. A gateway (cellular, LoRa, or WiFi) picks up those messages and is responsible for sending that information back to the cloud.

This solution is inexpensive to implement, because the tags themselves are just simple BLE devices, as are the reference point beacons. It also doesn’t require lots of access points in an area to pick up those transmissions—a single access point can cover hundreds of square meters.

When this tag gets put on a truck, there’s another BLE access point it can connect to, sending it location information. This cellular-connected AP knows it’s position from GPS (or cell ID or WiFi location database) and can send that data back out via cellular LTE-M.

If you don’t own the truck, however, you may not be able to install your own infrastructure in it for tracking. This necessitates another infrastructure—one where the tag itself has the ability to talk to the wider network. This tag would have a BLE receiver and an LTE-M radio in it to send data out; it could also have a WIFi receiver. When the tag is indoors, it can read out the BLE reference points and send those out via LTE. Inside a truck, it can use the LTE-only location; or, if the truck is parked in a parking lot or driving near a WiFi access point, the tag can also grab that data and report it out to further refine the accuracy. It’s an indoor/outdoor solution that’s both cost-efficient and data-efficient because the tag is only transmitting through LTE-M when it’s moving.

Conclusion

The number of business Applications for asset tracking is growing. From an operational standpoint, having more control over the whereabouts of your assets translates to savings and productivity gains. But the added value of an asset tracking solution can be compromised by choosing a tracking technology that’s not properly suited for the task.

One that costs too much or is overly complex will be a challenge to implement, making it harder to realize the full benefits of asset tracking. Pinpoint the problem you’re trying to solve, do your homework on asset tracking technology, and talk to as many solution providers as possible to get a broad view of your options. Doing so will ensure you get the outcome you expect. We outlined some of these challenges and how best to make decisions in your asset-tracking initiative in a recent AirFinder whitepaper.