Business Technology Consulting

Successful Business with RFID, RTLS and Beyond

RTLS

RF RTLS

Sound (Ultrasound) Based RTLS

Optical (Infrared) Based RTLS

Regardless of RTLS type, its arrangement with monitoring sensors enables attaining the best results. If you want to locate objects that are on open air, there is nothing better solution than Global Positioning System (GPS) combined with means of wireless transmission of obtained coordinates. For an enclosed spaces (buildings without reception of satellites’ signals), the Wi-Fi (IEEE 802.11), UWB, Passive RFID RTLS (with Steerable Phased Array Antennas), Active RFID, Infrared (IR) and Ultrasonic RTLS are most popular solutions. Just remember, that varieties of errors are affecting location effectiveness and efficiency. The nature of errors relates to physics of selected methods and environment.
RTLS Technologies

Levels of Location accuracy are:

  • Zone level - object location within a group of rooms or a building floor
  • Room level - object location within a specific room
  • Base level - object location within in a specific sub-location inside a room

Building




Wi-Fi RTLS Map


Wi-Fi Tag
























UWB RTLS Map


UWB RTLS Tag




U-S RTLS Map


U-S RTLS Tag



IR RTLS Map


IR RTLS Sensors


IR RTLS Tag


RF RTLS

 Wi-Fi Based RTLS

RTLS solutions, based on IEEE 802.11 (Wi-Fi) - the tag-to-access point air interface, have location accuracy and resolution ~20 feet that depends on the AP installation density and the supporting Wi-Fi infrastructure. There are three relatively straightforward location-determining techniques in use:

  •      Time Difference of Arrival (TDOA) refers to the AP's received timing differences of the device's signal
  •      Received Signal Strength Indication (RSSI) refers to a device's signal strength measured by the access point
  •      Angle of Arrival refers to the highly directive antenna orientation

Probably RSSI method is more susceptible to environmental conditions than TDOA.

First two need an experimental confirmation of efficient transponder placement for each object type. Batteries last ~ 5 years for a repeat rate of 5 min. 

CHALLENGES & ISSUES

·         The multipath wave propagation that is common in building environments greatly lowering accuracy of all three methods

·         A simplified Time of Arrival technique requires the Transponder and the Receiver’s clocks synchronization

·         For Time Difference of Arrival (aka Three Dimensional Hyperbolic Positioning) a multipath propagation, noise and EMI/RFI are resulting in inaccurate intersections of the hyperbolas

·         The RSS requires installation of many 802.11 WLAN access points (AP)

·         TDOA and RSS systems need often calibration and their position estimation is not quite reliable

·         Angle of Arrival method requires a complex set of antenna arrays with locating accuracy proportional to number of antenna elements

·         The calculated location may appear entirely faulty

·         Systems can indicate incorrect location of the object real physical presence or

·         show an unreal movement


Ultra-Wideband Based RTLS

UWB RTLS occupy very wide spectrum from 3 to 10 GHz. They use a very short impulse to transmit data, so most reflected parasitic RF signals, having a longer pathway, arrive after the main signal. More often than not, this capability allows for overcoming a multipath problem. However, high multipath resilience comes together with low noise immunity because a receiver is sensitive to any interference in wide band.

UWB RTLS systems have high, ~ 1-foot location accuracy, high read rates and detection range of up to 100 feet. Transponders are practically insensitive to their placement and can have a battery life up to 8 years at minimum repeat rate 1 per second. UWB RTLS are capable of localizing of more than 1000 transponders in 1 second.

CHALLENGES & ISSUES

·         Worldwide UWB RTLS licensing is not available yet

·         UWB Technology for commercial applications is relatively new and immature


Sound (Ultrasound) Based RTLS

Ultrasound RTLS is usually a Radio–Ultrasonic Hybrid using time-of-flight (TOF) method. It utilizes a significantly lower sound propagation speed than RF wave and has a superior to a radio-only system accuracy performance.

CAPABILITY

·         100% room-level or sub-room level location accuracy

·         High immunity to electromagnetic noise and interferences

CHALLENGES & ISSUES

·         Method is typically applicable only to short-range line-of-sight systems

·         TOF systems depends on ultrasound speed that vitiates with air temperature and humidity

 







Optical (Infrared) Based RTLS 

Infrared (IR) based positioning systems use short-range transmissions of modulated IR light to send identity data from a tagged object to a fixed transceiver in a particular known location. It is relatively easy to focus light beam and direct it to assigned position. A transceiver linked to Wi-Fi detects a tag presence. This combination of IR and RFID or Wi-Fi helps to overcome limits associated with transmission range. 

Battery life expectancy for 3-10 seconds flash rate is 1 year for badges and 2 years for tags.  

CHALLENGES & ISSUES

·         IR System has significant costs of installation

·         100% room-level or sub-room level location accuracy

·         High immunity to electromagnetic noise and interferences

·         IR is safe and accepted worldwide