Why GPS is not an answer to Indoor Positioning?GPS is our lifesaver. It’s one of those techniques which has long back has gained acceptance as a part and parcel of our lives. It undoubtedly comes handy for locating an unknown place, navigating our way through an unknown route. If you have used GPS multiple times, you must have faced situations where your GPS couldn’t differentiate between lanes which are a few meters apart. That’s because GPS accuracy is limited to 5 meters at the best possible scenario. This accuracy is further hindered by atmospheric conditions, obstacles etc. This was just the horizontal accuracy, vertical is even worse. The probability of getting an accurate spatial coordinate with GPS is too low to consider using it in indoor positioning. GPS signals get further weaker inside a closed building. GPS still is the best when it comes to outdoor positioning, but we must embrace the newer technologies for our indoor applications. These technologies are - RFID, Wifi, Bluetooth Low Energy, Zigbee and Ultra Wideband (UWB). We are already familiar with Bluetooth, so why not use Bluetooth Low Energy? Here’s why not -
When and when not to use BLE/WiFi/Zigbee?BLE has gained huge popularity since the introduction of iBeacon technology by Apple in 2013. When it comes to ‘proximity detection’, iBeacon serves well by sensing whether a device is within the range of the beacon or not. It can even tell whether an object is ‘close’ or ‘far’ by measuring the signal strength. But, the catch here is that a low signal strength wouldn’t always mean that an object is ‘far’, it can also mean that there’s some obstacle in the way. Among all the available technologies, BLE is the least expensive one. It requires fewer devices and is energy efficient too. But, as good and easy to use it sounds, there are certain compromises you would have to make if you use BLE. Its operating frequency is 2.4GHz, which is the most crowded band, thus, making it susceptible to interferences. In this regards, Zigbee and Wifi can also be ruled out, as they too operate at 2.4GHz. Secondly, it uses RSSI (also used by Wifi and Zigbee) and Triangulation method for tracking and positioning. RSSI or ‘Received Signal Strength Indication’ doesn’t always give an accurate result as a result of path loss, fading and shadowing effect. Moreover, measurement of signal strength is also impacted by the relativity of the object. Among BLE, Wifi and Zigbee, Wifi has the least accuracy of 5-10 meters and is a bit expensive compared to the other two. Moreover, it consumes significantly higher power than UWB. Now, coming to the most important part. As has been mentioned earlier that, both Bluetooth and Wifi operates on the same frequency of 2.4GHz. And both utilize the technique of expanding a narrowband signal to a wideband signal, known as Spread Spectrum Signal Technology. It is needless to say that narrowband radio signals are highly prone to noise, multipath propagations etc. There are some more imitations of BLE -
- Beacon batteries have a finite life.
- Blind spots are hard to eliminate.
- Signals from Beacons can be easily reflected or absorbed, thus it’s data can be highly inaccurate.
- BLE has a shorter range.
- BLE cannot transmit a large amount of data.
- Beacons can sometimes delay a device detection.
Why RFID will soon be replaced by UWB?RFID or ‘Radio Frequency Identification’ can be either passive or active. Passive RFID is the most commonly used and finds its applications in airport security checkpoints for luggage tracking or as an anti-theft measure in libraries etc. Due to its low range and large size, it is not a feasible option for live tracking. Due to the high presence of RF energy, RFID is also not a preferred option for the medical industry. RFID readers have the ability to identify items from a quick scan, thus making it suitable for airport security checks and theft identification. As evident, with its low accuracy, the current RFID technology is not the right way to implement RTLS. Probably, when used alongside, Zigbee, it can act as one, which could further complicate the process.
“According to forecast reports from IndustryARC, UWB technology is expected to acquire the fastest growth due to the growing demand for personal & asset tracking. It is expected to surpass the other technologies by 2023.”
Ultra Wideband Technology to the rescueThere’s a reason for UWB to be slightly expensive as compared to its counterparts. UWB can give an accuracy of 5-10 cms. Isn’t accuracy the most important consideration in RTLS? As per IEEE 802.15.4-2011 std., UWB technology uses short bursts of radio impulses with incisive rises & drops, making it easily measurable. UWB’s operating frequency is 3.1 - 10.6GHz, thus, reducing the probability of any interference. Another important aspect of UWB is that, it uses ToF (Time of Flight), TWR (Two Way Ranging), TDoA (Time Difference of Arrival), AoA (Angle of Arrival) techniques etc. to compute the position of the object, which enhances its precision and enables it to make exact measurements.
“Time of Flight (ToF) is the travel time of a radio signal from a single transmitter to a single receiver.”Some notable properties of UWB are as follows -
- High Precision
- Less to no interference with other devices
- Not prone to multipath propagation
- Power efficient transceivers
- Not prone to noise due to the nature of the signals in the form of a train of impulses