# Real-Time Location-Positioning Technologies for Managing Cart Operations at a Distribution Facility
## 4 Case Study: Tracking of Carts in a Large and High-Traffic RFID-Enabled Air Mail Centre
### Discussion  
Our project team learned some lessons from the implementation of this RFID-enabled locating system. The technological challenge of the project was that the angles of arrival signals from the tags to the readers might not be exact due to various factors. For example, the accuracy can be affected by the metallic walls, blockage of signals, movements of tags, other movements of objects within the facility, interferences from other electrical devices, etc. Moreover, the indoor channel fading effects might also cause severe communication failures at some particular locations. Therefore, our project team used multiple readers to locate each tag and conducted a site survey for more than a year to figure out the proper locations for installing the readers for the best positioning performance. In the site survey, the project team had done a series of experiments to ensure a high positioning accuracy, including: (i) measuring antenna pattern of every positioning reader; (ii) performance test of the estimated angles of arrival signals; (iii) performance test of the readers in different  
Figure 11: The total distance traveled by all tagged carts in different hours.  
Figure 12: The average speed of all tagged carts in different hours.  
positions and environments; and (iv) weight assignments to the readers for calculation of location based on the accuracy. More specifically, two key techniques for positioning accuracy improvements are:  
1. Positioning by angles of the tagged object from more than three receivers for a smaller confident zone
2. Filtering receivers by ignoring the signals from receivers which did not lie within the confident zone  
As reported by other studies (e.g., [31; 39]), return on investment (ROI) is the biggest concern of companies and organizations about the adoption of advanced technologies. In this project, the benefits and value of adopting RFID to locate the carts for more efficient operations at the AMC could not be directly converted to monetary value. Therefore, our project team tried various methods to reduce the cost of establishing this RFID-enabled locating system. For example, our team developed RFID tags, the middleware and the mobile application in-house; reduced the power required to operate the system (e.g., the display board was turned on only when a signal request was sent from the mobile application); and replaced the original 6-inch E-Ink display board of 800 \(\times\) 400 resolution with the 5.2-inch LCD display board of 128 \(\times\) 280 resolution. The cost of the new version of RFID tags was then reduced by one-third. Furthermore, the AMC was also able to secure a grant from a funding agency to financially support this project on integrating innovation and advanced technologies for real-life applications in the industry. Our project team also had very frequent meetings and on-site visits at the AMC to ensure that the user requirements were correct and the solutions for locating objects within the facility were feasible.