# 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
### Actual Implementation at a Mail Facility  
The AMC, which is operated by the local governmental Post Office, is located next to the international airport of the city, has an area of about 100,000 square meters and handles an average of 700,000 mail items per day. The large area of the AMC, the tremendous volumes of mail items being sent to more than 180 cities across the world and the high air traffic at the international airport (around 1000 flight movements per day) all together create a very challenging task for the AMC to deliver mail items to their intended flights efficiently. One of the major operational problems was that the carts loaded with mail bags were densely staged at the AMC and the staff members were spending a very long time searching for the carts of the departing flights in this high-traffic environment. Figure 2 depicts shows the very crowded environment of the AMC, where the carts loaded with mail bags are densely staged within the facility, on a typical day. During the original practice, the staff members spent a significant amount of time reading the tags, which state the destinations of the mail bags, for finding the right carts of the departing flights. This not only was time-consuming, but also exhausted the staff members. For this reason, the AMC decided to adopt advanced information technologies to reduce the time of searching for carts and hence to increase their operational efficiency and throughput. The readers and tags used on this platform were developed by the Department of Electronic Engineering, the Chinese University of Hong Kong. In total, 68 positioning RFID readers were installed at various places of the AMC and 300 carts had an RFID tag affixed to it. The facility was zoned for cart staging and RFID readers were set up at the different corners of each zone. Therefore, there were at least four RFID readers used to locate each object to ensure a high level of positioning accuracy. Figure 3 shows several positioning RFID readers installed on a pillar of the facility. Figure 4 shows a display board, where an RFID communication module and an antenna module are installed. Figure 5 shows a cart for circulating mail bags, with the display board showing the abbreviation of the destination of the mail bags and a signal light to help the staff members to identify the carts. The positioning method adopted by this project was based on the angles of arrival  
Figure 2: The environment of AMC on a typical day. signals from the tags to the readers. A graphical illustration is shown in Figure 6. The staff members could also send a request using the mobile application via the RFID network to switch on the lights of the carts. This capability successfully assisted the staff at the AMC to locate carts in real time and could save them time from searching for the carts. The RFID system also stored the location data about the carts: at the time that a cart was located by an RFID reader, a time stamp and information about this transaction (e.g., the RFID tag ID and its coordinates of location) were stored into the legacy computer system of the AMC. The platform captured the data about the locations of the carts and these data have the following \"big data\" characteristics:  
* High transfer rate: Data were transferred automatically and continuously between the readers and the tags. The wireless communication data rate of the system was 250 kbps and the read rate in positioning was 40 tags per second. All the transmitted data were stored in the information system. * Volume: These high-speed locational data were captured and aggregated in the system. In total, there were more than 11 million records, excluding those of which the cart was staying at the same location point for a certain time duration, collected in the information system. * Accuracy: In total, 68 readers were installed at different places of AMC to achieve a high positioning accuracy for the cart locations.