WiFi has become readily available in just about every indoor space, so it may seem like a logical default choice for indoor positioning systems, but it has security and accuracy setbacks. Nonetheless, despite WiFi’s downsides, with fingerprinting, sensor fusion, and security hardening, a WiFi positioning system is a good option for connecting indoor positioning systems.
Since the launch of the original iPhone, every person with a smartphone has been using WiFi signals to enhance their indoor positioning accuracy. What has changed since then is the level of accuracy that can be achieved through an indoor positioning system using WiFi. The heightened focus on location accuracy is set to continue as our technology standards, and solutions evolve.
In today’s (already) digitalized world, precise indoor location tracking using WiFi and indoor localization using WiFi are becoming increasingly common. The indoor WiFi positioning market is predicted to reach a value of approximately 19 billion dollars by 2030 on a global level. WiFi-based indoor positioning systems are being implemented in places we might not expect. These places go beyond the traditional industries like warehouses, airports, shopping malls, grocery stores, and hospitals. The use cases for WiFi-based positioning systems can now range from IoT monitoring and asset tracking to sending relevant marketing messages to nearby smartphones. Beyond all of these use, cases are a reliance on accurate location as a key component of a robust WiFi indoor positioning system.
When we think of location, we may automatically jump to thinking about Global Positioning Systems (GPS) or Global Navigation Satellite Systems (GNSS). GNSS systems are incredible systems that have been around since the late 1970s and are ideal for locating devices outdoors, getting down to ~5 meters in commercial devices. However, the whole GPS is great for providing location outdoors, its benefits are suppressed and even lost in any type of indoor environments like a building or warehouse. That’s where and why alternative location technologies such as WiFi positioning systems come into play.
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What is a WiFi-Based Positioning System?
WiFi describes a local wireless network that uses radio waves to communicate data. Typically from the internet. To be considered WiFi, the radio signal must use the IEEE 802.1 standard to communicate. There are multiple versions of WiFi as defined in the IEEE specifications, which include common ones such as 2.4 GHz and 5GHz frequency radio waves. WiFi is typically used to transfer large amounts of information. It has transfer speeds of up to several gigabits per second for certain versions.
With this in mind, WiFi positioning is a positioning system that uses techniques to locate a connected object or device. WiFi location uses already existing infrastructure and WiFi access points (APs) to calculate where a device is located. The device needs to be able to listen for the WiFi AP but does not need to connect to it. By analyzing the signal strength of multiple WiFi signals and knowing the location of those APs, WiFi-based positioning systems are able to determine the approximate location of the device.
WiFi typically has a short range, but the signal can be extended up to 150 meters. The accuracy generally depends on how many APs are nearby and the environment in which they are deployed. The more APs in a given area and the more precisely their position is known, the more accurate the location will be. WiFi can provide about 20m accuracy using existing crowdsourced WiFi infrastructure with no calibration. However, through calibration, surveying, and fine-tuning, WiFi positioning can achieve 5-8 meter accuracy in indoor environments.
How do WiFi-Based Positioning Systems Work?
There are multiple methods for monitoring indoor positioning using WiFi. The two primary methods are received signal strength (RSS) and fingerprinting. RSS of a WiFi signal is inversely proportional to distance. The MAC address is unique for each Wi-Fi router and the RSS provides a rough measurement of how far away the device is. Intuitively, a strong RSS would show that the user is close to that Wi-Fi router and a weak RSS would indicate that the user is far from the Wi-Fi router.
The challenge for indoor environments is that the signal strength is weakened as it passes through obstacles such as walls, furniture, or people’s bodies. Therefore, a weak RSS could imply that either the user is far away or that they may be close but there are obstacles in the way (e.g., walls or furniture).
There are two main ways WiFi MAC addresses and RSS can be used for WiFi positioning.
The first is Wi-Fi trilateration and the second is WiFi fingerprinting.
WiFi trilateration requires knowledge of the location of each WiFi router. Then, based on the RSS, it estimates the distance between the user and each visible WiFi router and calculates its position based on those distances.
WiFi fingerprinting can be used to significantly improve accuracy. Fingerprinting uses historical RSS information as well as known locations to determine the position of an asset given its current RSS values. Fingerprinting is highly dependent on the environment, so if a chair or table is moved, the fingerprint will need to be updated. In addition to RSS and fingerprinting, Angle of Arrival (AoA) and Time of Flight (ToF) can be used to determine location. AoA describes the angle at which a given Wi-Fi transmission was received and is calculated using something called a multiple-input multiple-output (MIMO) antenna, which clusters antennas together to increase range and throughput. MIMO antenna systems are common in some enterprise environments. Sometimes, systems use a combination of ToF and AoA, which can result in very accurate location. AoA systems have the additional concern that they need to be installed in a certain orientation to work correctly. They suffer from the same noise, sampling artifacts, and multipath channel effects as TOF does, but the requirement for clock synchronization is less of an issue.
While these methods are accurate, they require expensive equipment and methods such as multiple antennae and clock synchronization. Assembling the W-Fi fingerprint map can be time-consuming and requires a site survey, but tends to provide more accurate results than WiFi trilateration.
The Benefits of a WiFi Positioning System
Unlike other indoor positioning solutions such as BLE beacons or RFID, WiFi indoor positioning does not require additional hardware since most buildings already come equipped with WiFi access. Nearly all facilities already have Wi-Fi infrastructure installed, providing a base level of positioning capability without additional investment. Hardware solutions that must be manually deployed can be costly and time-consuming, especially if you have multiple facilities that require the capability. As a result, other technologies require a larger budget in both money and time in order to create an effective environment for indoor positioning.
WiFi-based indoor positioning systems can be scaled with little to no manual intervention. For instance, implementing Wi-Fi positioning in 25 warehouses compared to manually deploying BLE beacons or RFID in 25 warehouses saves a lot of time and resources. While Wi-Fi positioning provides instant-on capabilities, businesses have several options to improve the accuracy based on the use case requirements. A simple survey to map the precise locations of all Wi-Fi APs within a facility will improve the positioning accuracy of the system. If further accuracy is required, businesses have the option to deploy additional Wi-Fi access points within their facilities. While this does represent an additional expense, it does not require the customer to learn, deploy, and maintain yet another technology within their infrastructure. This can be accomplished as part of a general Wi-Fi infrastructure improvement project or by simply adding additional Wi-Fi access points in areas that require additional positional accuracy.
The Disadvantages of a WiFi Positioning System
The major disadvantage of a WiFi positioning system is the WiFi positioning accuracy. With accuracy at the higher end of 15 meters, it may not be as suitable for precise location applications, where Bluetooth excels by comparison with its 2-4m accuracy. However, accuracy can be as low as 2-3m with fingerprinting, a significant amount of WiFi access points, and/or combining tracking data with other technologies (also known as sensor fusion). Mapsted has developed the world’s most accurate, hardware-free indoor positioning system that doesn’t rely on the use of external sensors.
Another disadvantage of a WiFi positioning system is the threat of security breaches. WiFi is such a common technology that it has already experienced numerous hacks and resulting security patches. Security will always be a concern for WiFi, but given this, there will always be companies working to harden WiFi from malicious attacks.
WiFI positioning systems can be a viable solution for indoor location tracking if you’re willing to compromise on the accuracy. However, for a business office, shopping mall, hospital, university campus, airport, big-box store, or museum, more advanced and accurate technology, such as Mapsted should be used. While accuracy and security issues may hinder a WiFi positioning system, these drawbacks can be mitigated using techniques such as fingerprinting, sensor fusion, and security hardening. Hopefully, indoor tracking will be more prevalent given the widespread use of indoor localization using WiFI.