# Design and Implementation of a RFID Reader/Router in RFID-WSN Hybrid System
## 1 Introduction  
The aim of Internet of Things (IoT) is to integrate the physical and digital worlds seamlessly. The development of IoT also draws a lot of attention to the integration of different interconnecting technologies, such as Radio Frequency Indentification (RFID), Wireless Sensor Networking (WSN) and 5G networks. RFID is a non-contact automatic identification technology that can provide object level automatic identification. With the rapid development of RFID technology, the application of the systems based on RFID technology is widely used in different fields, such as logistics, civil affairs, transportation, civil aviation, security and identification. RFID is generally composed of three basic components: tags, readers and a PC reader. The tags, active or passive, communicate with readers wirelessly, while the readers communicate with PC reader with cable. WSN is a collection of nodes that can collect information of the physical world and transmit it as electrical signal. WSN provides a variety of real-time applications including medical, environmental, entertainment, military and security. WSN is generally composed of sensor nodes, routers, a coordinator and a PC server. Each sensor node contains one or more sensors, memory, power source and certain processing chips. The sensor nodes can communicate with routers directly or organize a multi-hop network to communicate with routers. All the information is transmitted to the PC server. The integration of RFID and WSN can extend the range of applications and also offers added value to the existing applications [1]. There is a proliferation of academic research and examples of implementations reported in the literature [2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14]. [PERSON] et al. [2] proposed a novel networkarchitecture and analyzed the energy consumption. [PERSON] et al. (2018) used a Proto Board, a Bridge Board and certain midware to integrate an RFID reader into a WSN to keep track of people. [PERSON] et al. (2018) used a WSN based ZigBee network with RFID tags as end nodes to improve the visibility in industrial environments. The integration of WSN and RFID involves the integration of hardware and software. In order to take advantage of WSN and RFID, the integration has three possible layouts: the integration of RFID tags with sensor nodes as shown in Figure 1a, the mixed integration architecture as shown in Figure 1b ([PERSON] et al., 2017; [PERSON] et al., 2018) and the integration of RFID readers with sensor nodes as shown in Figure 1c. For the first integration architecture, the end nodes can be traditional RFID tags, traditional WSN sensor nodes or a novel node that includes identification as well as more information captured by sensors ([PERSON] et al., 2018). For the third integration, the sensor node is equipped with a reader, which increases the power consumption of sensor nodes and pull down its efficiency ([PERSON] et al., 2017). For the second layouts, a smart station that incorporates RFID reader and WSN router is used so that RFID tags and sensors can coexist in the same network. The smart station is named as RFID reader/router because it works as a RFID reader as well as a WSN router ([PERSON] et al., 2017). The reader/router gathers both kinds of information from the end nodes and routes the information finally to the coordinator. The mixed integration uses both RF communication protocol (between RFID tags and RFID reader/router) and the ZigBee protocol (between sensor nodes and reader/router, between reader/routers). This makes the hardware and software design of the reader/router more challenging. In ([PERSON] et al., 2018), two separate micro-controllers were used respectively for RFID reader and ZigBee router, and that led to the waste of resources and the high cost. In ([PERSON] et al., 2018), a multi-protocol RFID reader system was implemented with a custom RFID reader board and a ZigBee mote, in addition with certain firmware. This reader can be used to construct an ad-hoc ZigBee network but not for general purpose.