ARTIN currently implement pilot projects for indoor localization and monitoring of hospital facilities. We co-operate with selected suppliers of HW, such as Sewio, Infsoft and kontakt.io. Our suppliers are able to deliver complete solutions including software and connection on other business systems.
Many modern electronic devices nowadays require positioning. The most typical example are ubiquitous smartphones in conjunction with GPS technology for external localization. Currently, external localization is something that is used with obviousness but there is also a growing need to locate devices within buildings where it is not possible for GPS to be used. The devices that use internal localization can be wireless electronic ‘toys’ such as smart watches, home appliances or professional transport drones on automated production lines. Since the possibilities of this technology are wide, we can expect growth of the whole segment in the future (e.g., navigation software, marketing applications and monitoring systems).
Engineers who are currently developing these smart devices are facing the challenge of selecting the correct technology. Could it be that the best solution is to use Wi-Fi or Bluetooth technology that is widely used or would it be more advantageous to select an alternative wireless technology such as UWB (Ultra-Wideband)? What are the pros and cons? The following article will try to explain the differences.
Indoor localization based on Bluetooth technology
Localization using Bluetooth technology received attention after Apple introduced iBeacon with Apple using BLE (Bluetooth Low Energy) in iBeacon. The goal of iBeacon technology is to provide rough indoor localization so this technology doesn’t provide accurate localization. iBeacon simply detects just two distances ‘in range’ and ‘close’ based on the level of signal.
Some companies started to use BLE technology for accurate positioning although the major problem of this technology is that the distance is measured by signal level. Signal level is not accurate indicator of distance. Sometimes weakening of signal can be caused by interference. If, for example, we put a concrete barrier between the transmitter and the receiver, we definitely weaken the signal without altering the distance. A typical condition would be in a hall with concrete columns.
One of the solutions is ‘foot printing’ of an area. In this solution there are transmitting nodes strategically placed and for every square meter of area there is an exact measured signal level from all the nodes with knowledge of the exact position. Based on this information, a default database will be created with well-known signal levels and locations. When one enters into the area, a tag will measure the signals and attempt to locate the nearest match in the default database, the closest match is considered as the current position.
Although there countless variations of algorithms for ‘foot printing’ areas, it is important to comprehend that that all of these solutions do not solve the core of problem. This is just workaround.
Indoor localization based on Wi-Fi technology
Before Apple introduced iBeacon technology, Wi-Fi was the main solution for indoor localization. Nowadays it is the widespread indoor localization technology for Android smartphones, often with a combination of BLE technology. The main advantage of Wi-Fi technology is its massive usage in public areas and also in households.
The principle of Wi-Fi localization is the same as that for Bluetooth – measuring of signal strength. This principle has also the same weaknesses as BLE. For Wi-Fi one of the possible solutions is the use of alternative algorithms and measuring distance via the measuring time of the signal flight (ToF, Time of Flight) or time of the arrival signal (ToA, Time of Arrival). This technology could not currently be used through the existing infrastructure because this algorithm needs a different hardware against typical access points.
The difficulty of measuring Wi-Fi or Bluetooth signal strength is its inherent structure and narrow band. In figure one there is a demonstration of how difficult it can be for threshold measurement of signal with sin wave and noise. Narrow bands aren’t suitable for measuring time of the arrival signal.
Inaccuracy of measurement is also caused by a multi-path effect. Multipath occurs when a signal can be spread by more paths to its destination, this is caused when a receiver gets multiple reflected signals with lower amplitude and delay. This effect makes it impossible to measure the correct amplitude and arrival time. Figure two shows the multi-path effect.
Indoor localization based on Ultra-Wideband technology
Standard UWB (IEEE 802.15.4-2011) was created to solve problems with the above technology. This standard uses very short bursts of wideband signals which can be seen in figure three.
Short bursts of wideband signals with a fast rising and falling edge allows easy measurement time of the arrival of signal. The distance between two UBW devices can be measured by using this signal more precisely than the previous technology (BLE, Wi-Fi). Another advantage is the interference immunity of these signals. In figure four one can see UWB signal in interfered band.
UWB signals are also resistant against the multi-path effect because the time of duration signal is very short and pulse is strong (similarity with Dirac impulse).
The main difference between UWB and the other technologies is its ability to measure the precise time of signal arrival and also its resistance against interference. In real conditions UWB is possible to measure a position with an accuracy of 5 – 10 cm. Accuracy with Wi-Fi or Bluetooth is approximately 5 meters.
What are pros and cons of each technology?
Accuracy of position measurement is much better with UWB technology (5 – 10 cm) against the other technologies such as Wi-Fi or Bluetooth (approx. 5 m).
Important parameter is power consumption, where UWB and Bluetooth have an advantage over Wi-Fi. Power consumption is critical because localization service will be mainly used on portable devices with limited power capacity.
Another important parameter is the ubiquity of technologies. There is great advantage for Wi-Fi and Bluetooth because these technologies can be found everywhere against that of UWB.
Overall it is not possible to choose the overall winner because there are many pros and cons for each technology. Choosing the right one has to be considered based on many factors (price, implementation on existing infrastructure, etc.).