RTLS Series - All RTLS systems are not created equal II.
In the last post, we looked at the different types of available RTLS systems. This week we will take a look at one that uses RSSI for location calculation.
In an RSSI system, the distance between a tag (attached to an object or person) and a reader is determined by converting the value of the signal strength at the reader into a distance measurement based on the known signal output power at the tag and on a particular path-loss model.
The advantage of RSSI RTLS system is that this is usually a lower cost solution which can utilize existing WiFi infrastructure; however it is not as accurate as other techniques. The main problem is that the RSSI changes exponentially when the distance increases. Therefore any deployment requires a dense infrastructure of RF sensors if high accuracy is desired, which often increases cost and deployment complexity. This technique requires a precise channel behavior model and is sensitive to channel inconsistency.
IDENTEC SOLUTIONS’ RTLS system uses a different technique, much faster and more precise. IDENTEC’s RTLS utilizes the double sided two-way ranging, which measures time of flight between a tag and a node, rather than the signal strength. The values are gathered from a range with at least three nodes and are then transmitted to a reader connected to a positioning engine - which calculates the tag position. The advantages of this type of ranging is it increases accuracy (new ranging data which is constantly gathered and processed by the tag improve the accuracy of the tag’s position) and increases location speed.
The whole system can be also supplemented by using RTLS enabled handhelds for on the go location and marker loops for precise location of assets in fixed zones, which creates a comprehensive solution for location of assets in any situation.
by
Eva Zeisel
