The Power of Where: Locating IoT Devices
This is the second blog in the "Power of Where" series, authored by Brian Salisbury, VP of Product Management at Comtech Telecommunications Corp. Did you miss Part 1? Read it now!
One of the great promises of the Internet of Things (IoT) is that data will be captured automatically by a broad range of smart “Things” that will be distributed everywhere. Even today, an incredible amount of data is already being created and captured by sensors. The number of these sensors that are connected to the Internet is also growing rapidly every day. Machine learning and artificial intelligence platforms will consume this data and take actions on our behalf, as well as create amazing insights to help us make the world a better place. But many of those actions and insights won’t be that useful without the context of location included with the data. This is what we mean by the “Power of Where.”
This posting is the second in a series on this topic, in which we will discuss how location is typically determined, and why many traditional approaches don’t work that well in IoT use cases. In our upcoming third post we will share our thoughts on a different approach for location for IoT, and how it can conserve energy, minimize device memory requirements, reduce communication bandwidth, and support a broad range of networks. We welcome your feedback and questions, and invite you to share your insights and experiences on the subject.
There are many methods that can be used to determine the location of devices, and there are different requirements for the quality of that location estimate based upon the use case. There are also many different types of IoT devices, and some of those differences are important factors in determining the best approach for locating those devices. All of the methods we discuss here use radio signals, which we refer to as “Signals of Opportunity”, since to use them the device must be equipped to receive them, and they must be present at that location.
Let’s start with a method that everyone knows about: GNSS, of which the best known version is GPS.
This method is based on receiving radio signals from a constellation of satellites that are orbiting the Earth, and calculating the device position based on differences in the time those signals arrive at the device. The device needs a receiver and antenna to pick up those signals, and since they travel such a great distance and are weak by the time they reach the device, this method works best outdoors in areas where the device has a clear view of the sky. When a GNSS receiver is first powered on, it needs to scan for the satellite signals, “lock” onto them, and start measuring the timing data received. This, along with capturing key GNSS data, can take anywhere from a few 10’s of seconds up to several minutes, and consumes power from the device battery. One popular method for reducing this “cold start” time is to provide assistance data to the device, so that the receiver only scans for the satellites that are overhead. This method does require the device to obtain fresh assistance data at least every few days, so the reduced cold start time comes at the cost of increased communication usage and may require some method of knowing roughly where the device is (for example, what state or province) in order to provide the corresponding assistance data. The precision of the GNSS-based position will generally be 3 to 10 meters in open sky scenarios, which is quite useful in a variety of applications.
Pros: generally good precision of position estimation, can operate without connection to any network
Cons: added cost and power consumption of GNSS circuits and antenna, poor performance indoors and certain outdoor locations (e.g., urban canyons)
Two methods that can be used for IoT devices that have Cellular or Wi-Fi data connectivity involves using the communication signals for the added purpose of position calculation.
The simplest Cellular method is based upon having the device scan for Cellular signals and their signal strengths. That information is then sent to a Location Server, where the position calculation is performed using a database of Cellular transmitter locations as a reference. The Location Server then provides the device position to the application. No additional radio circuits and minimal additional software are needed in the device for this method, since it uses the Cellular radio that is already there and the process is not complicated. The precision of the position estimate will typically range from 300 to 3,000 meters which may not meet the requirements of some applications.
There are ways to further improve Cellular-based positioning. For example, one can use neighbor cells (if available) and signal strength to improve the position estimate. Also, one can use the same serving and neighbor cells along with timing information and accurate knowledge of the Base Station Antenna location to further increase the position estimate accuracy to a typical range of 100 to 500 meters. This method, however, typically requires a Cellular Carrier sourced Base Station Almanac with accurate tower information and a synchronized network.
Pros: no additional radio needed in device, broadly available coverage
Cons: less precise location, dependent on quality of reference database
The massive growth in Wi-Fi Access Point (AP) deployments in recent years has created a great opportunity for using Wi-Fi signals for locating devices. While Wi-Fi is mostly used for indoor connectivity, many cities are deploying APs for outdoor use. Further, the signal levels needed for positioning purposes are well below those needed for reliable data communication, which means that this method works indoors and in many urban and suburban outdoor areas as well. The device scans for Wi-Fi signals which are sent to the Location Server, where the position calculation is performed using a database of Wi-Fi AP locations as a reference. Location precision of 10 to 50 meters is typical, depending on the density and geometry of the APs. For indoor applications, an enhanced method can be used leveraging previously surveyed measurements of the Wi-Fi signals correlated with locations of those measurements. The generalized Wi-Fi measurements in the global Wi-Fi database are enhanced with these surveyed measurements resulting in precision that is typically 3 to 8 meters.
Pros: no additional radio needed in device, broadly available urban and suburban coverage, particularly indoors
Cons: dependent on quality of reference database
With one or more of the methods described above, most types of IoT devices can be located. Certain applications and use cases require precise location, while others are less demanding. If the business model supports it, a device that combines GNSS, Cellular and Wi-Fi measurement capabilities can provide location under almost any circumstance, and the selection of which method to use at which time can be optimized for the trade-offs of power consumption, bandwidth utilization, and precision. In reality, such a device may be too expensive for many applications so just using one or two of the three methods is more likely.
GNSS (or GPS) is a good choice for IoT devices with higher battery capacity that are used primarily in outdoor environments, and where the use case requires precise position estimates. Such devices probably also include cellular modems for connectivity, which can also support less precise position estimates when the device is indoors and may also be used to deliver assistance data to enhance the efficiency of the GNSS receiver.
Cellular is a good choice for IoT devices that use a cellular modem for connectivity, and need to be located with lower precision in both outdoor and indoor environments.
Wi-Fi is a good choice for IoT devices that need to be located with moderate precision in both indoor and urban outdoor environments. The connectivity for these devices may also be provided by Wi-Fi, or alternative radio types such as LoRa can be used.
Brian Salisbury is VP Product Management at Comtech Telecommunications Corp, which is an mbed Partner. Comtech Telecommunications Corp. designs, develops, produces and markets innovative products, systems and services for advanced communications solutions. Comtech sells products to a diverse customer base in the global commercial and government communications markets. Comtech believes it is a leader in most of the market segments that it serves.