# RFID Technology for Management and Tracking: e-Health Applications
## 2 System Architecture  
### Radio Frequency Identification (RFID) Hardware and Considerations about Signal Propagation  
As outlined in Table 2, the main advantage of UHF RFID over HF RFID systems is the capability of providing longer reading distances, thus minimizing the need for approaching items to the readers. Conventional UHF RFID antennas and readers can provide a reading distance up to 6-7 m far from the antenna even in NLOS and multipath conditions, so a single UHF RFID antenna is enough to provide coverage within a hospital room. UHF RFID-based systems for management and tracking applications consist of [12; 13]: (i) a set of UHF antennas; (ii) one or several RFID readers; (iii) a computer that manages the RFID readers; and (iv) UHF RFID tags attached to the items to be tracked. While the cost of a RFID tag is less than 0.05 EUR, UHF antennas are within the range of 20-200 EUR (depending on their specifications and requirements), and UHF RFID readers are in the range of 200-1100 EUR also depending on their specifications and performance. The use of antenna hubs enables increasing the number of antennas that can be controlled by a single RFID reader, thus cutting down the cost of the overall system. Typical specifications/performances of a reader involve the number of tags read per second, or the number of UHF antennas that can be controlled. RFID antennas are placed to provide a coverage area within a place of interest, for example around the beds in hospitalization rooms (4-5 m\({}^{2}\)). It is important to avoid coverage areas overlapping to ensure that RFID tags are detected by just one antenna. Another source of error is the presence of multipath [23; 24], especially in indoor scenarios like the one illustrated in Figure 1. Under normal operation conditions, only those items within the coverage area of the RFID antenna are detected. However, multipath can result in the detection of RFID tags beyond the coverage area of the antenna (_in-channel_ interference [25]). To overcome this problem, the following solutions can be adopted: (i) reducing the power transmitted by the RFID antenna while ensuring that the minimum level to detect RFID tags is achieved within the coverage area; (ii) using antennas whose radiation pattern fit the area of interest, thus minimizing reflections. For example, directive antennas are considered in the example shown in Figure 1 to provide coverage around the beds. The use of directive antennas also contributes to mitigate multipath contributions. To illustrate the influence of the antenna radiation pattern, Figure 2a shows the main cuts of the radiation pattern of a RFID antenna [26], that has around 80\({}^{\circ}\) \(-\)3 dB beamwidth in both planes (resulting in \(\sim\)8.1 dBi directivity). Given the radiation pattern, it is possible to obtain an estimate of the coverage area considering propagation losses (_Att_). These losses are estimated according to a log-distance path loss model. Among the different methodologies and models proposed for indoor channel characterization [27; 28], the International Telecommunication Union Radiocommunication Sector (ITU-R) path loss definition [29] has been selected as a trade-off between accuracy and complexity (1):  
\[Att(R)(\text{dB})=20\;log_{10}(f)+nlog_{10}(R)+Lf-28\;\text{dB} \tag{1}\]  
where \(f\) is the working frequency (in MHz) of the UHF RFID system (868 MHz in Europe), \(R\) is the distance from the transmitter to the tag, \(n\) is the path loss exponent (20 for free-space propagation, 33 for an indoor environment such as the one described in this contribution), and _Lf_ accounts for signal attenuation when passing from one floor to another (_Lf_ = 0 dB in this case, as the RFID reader and RFID tags are on the same floor). Figure 1: Example of non-desired RFID tag read due to multipath (_in-channel_ interference). Item tagged with tag #A is within the coverage area of RFID antenna #1, while item tagged with tag #B is located outside the coverage area. Green arrows represent desired interrogation/response.