27 June 2019

Bluetooth for RTLS: Coverage vs Range

Since the introduction of Bluetooth 4.0 (Bluetooth Low Energy or BLE), which includes location-oriented specific profiles, Bluetooth technologies have become very valuable for location-based applications. The technology is well suited to both Received Signal Strength Indicator (RSSI) and Angular-based measurement methods for Real-Time Location Systems (RTLS). Unfortunately, the deployment of Bluetooth solutions is hindered by a common misconception about the technology: that Bluetooth is just a Wireless Personal Area Network (WPAN) technology and the distance between the transmitter and receiver is restricted to about 10 meters. When we hear the word Bluetooth, we immediately think of common consumer applications such as Bluetooth headphones and speakers that have limited ranges. However, Bluetooth radio technologies are not restricted to 10 meters.

A Bluetooth radio is able to communicate at 1Mbps or faster for a distance of up to 10 meters. But, if the throughput requirements are lowered, for instance by using small radio packets like the BLE Advertising packet format, then the communication range can increase to hundreds of meters. In other words, the communication distance between transmitter and receiver is inversely proportional to the bit rate, so the smaller the communication rate (in bps) the longer the range. To see the extended range for yourself, have a look at this video of a RuuviTag transmitting a BLE radio packet to a standard unmodified phone as the receiver: https://www.youtube.com/watch?v=wRpW2KIPfVo.

In order to grasp the versatility of Bluetooth for advanced location-based applications, we need to understand two key concepts: communication range and coverage area. Let’s take a look at these concepts in the context of the Quuppa Intelligent Locating System™.

Communication Range

The communication range is the distance that the signal can be transmitted between devices.

Communication range is affected by several factors such as the bit rate described above and the conditions in the environment where the communication occurs. Large and open spaces with no obstacles provide Line of Sight (LoS) conditions with long communication ranges. Environments where signals need to bounce from or pass through obstacles such as walls provide non-Line of Sight (NLoS) conditions, which can significantly reduce the communication range. Quuppa Locators have a range of approximately 100 to 300 meters (depending on the Locator type, see https://quuppa.com/technology/products/ for more information, and device orientation) in LoS conditions and about 30 to 100 meters in NLoS conditions.

Figure 1. The maximum communication range for Quuppa Locators is 100-300 meters in Line of Sight (LoS) conditions. Please note that this image is a demonstration of the concept of communication range, not an example of an actual installation. Not to scale.

Calculating the communication range enables us to identify the so-called Detection Area, so the space around a Locator in which a tag’s transmitted signal can be received by the system. The Detection Area is used for presence detection, the simplest form of positioning, where we just need to know that a tag exists somewhere within the Locator’s range.

Some examples of communication range in different environments:

  • The Quuppa LD-6L Locator can receive a signal from a tag that is located approximately 30 to 50 meters away in environments like hospitals or offices, with walls and other obstacles, if it is mounted onto the ceiling.
  • The Quuppa LD-7L Locator can receive a signal from a tag that is located approximately 70 to 120 meters away when deployed in logistics or industrial environments with fewer obstacles. The communication range can be even longer (up to 300 meters) if the solution is deployed in large open spaces such as outdoors.

Coverage Area

The coverage area is the area or footprint in which the location of a tracked tag can be calculated.

Quuppa Locators can measure the Angle-of-Arrival (AoA) of the signals for tags within a certain coverage area. The system uses these measurements to calculate the location of the tracked tags. Assuming that the Locator is flat-mounted onto the ceiling, we can imagine that the coverage area is like a spotlight, a cone which widens with distance from the Locator. We can divide this spotlight cone into three levels of positioning accuracy. Tags that fall within the central green-coloured cone (the High-Accuracy Area) can be tracked accurately, even to sub-meter level accuracy. Tags inside the yellow-coloured cone (the Low-Accuracy Area) can be tracked but with less accuracy. The location of tags in the red-coloured area (Detection Area) cannot be tracked but presence detection is still possible. It is worth noting that the coverage area is always smaller than the detection area and the communication range.

 

 

Figure 2. The accuracy of a tag’s calculated location depends on the coverage area that it is in. Please note that this image is a representation of the coverage range of a single Locator, while actual installations typically include multiple Locators. Not to scale.

To get the best coverage for continuous tracking, Locators should be installed so that their coverage areas intersect at least in the low-accuracy areas. This way the measurements from multiple Locators can be combined, increasing the accuracy and consistency of the tracking results.

An assessment of the physical dimensions of the space (area size and ceiling height) and the type of environment that it is (confined, semi-confined or open) is the first step in determining how many Locators are needed to ensure that the combined Locator coverage is green for the whole area of interest. The next step is to fine tune the deployment plan by including further parameters such as the placement of the tags on the tracked objects, the speed of motion and physical obstacles in the environment. Quuppa has developed dedicated software application tools for planning (Quuppa Site Planner – QSP) and simulating (Quuppa System Simulator – QSS) deployment scenarios. These tools aim to improve tracking performance estimates used during the early stages of the project execution.

Some examples of how coverage areas affect end solutions:

  • The coverage area level (green, yellow or red) does not need to be uniform throughout the deployment environment. The distance between Locators can be varied depending on the tracking accuracy needs of different spaces within the deployment environment.
  • In order to accurately track the location of a tag, for example during a sports event, Locators are installed to ensure the maximum visibility of the tracking area. This level of redundancy, where each locator can see the majority of the playing field, ensures that any given tag can be tracked accurately at any given time because it is always within a High-Accuracy Area.
  • Although Quuppa’s LD-6L and LD-7L Locators have the same coverage area, the LD-7L is typically selected for sites with ceiling heights of over 10 meters because of its superior angular resolution. This enables sub-meter accuracy even when mounted further away from the tracking area.

In summary, we can see that a combination of communication range and coverage area is key to achieving the best possible positioning results to meet the requirements of the use case. Confusing the two concepts could also significantly affect the results of any implementation. Each use case needs to be assessed individually to see how many Locators are needed, how they should be positioned, which Locator (LD-6L or LD-7L) is best for the site conditions and what level of accuracy is accurate enough (see more on this topic: https://quuppa.com/location-data-how-accurate-is-accurate-enough).

BLE is much more than just short-range communication. It is a versatile technology that has great potential for RTLS and IoT solutions.

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