Reducing power consumption and per-hop latency are major challenges in Wireless Sensor Networks (WSNs), when network nodes or “tags” must be battery-powered. On the other hand, reducing transition overhead in RFID technology is crucial for efficient data collection and quick recognition of multiple tags. This chapter presents the method of analysis performed and explains the calculations used to evaluate the various performance behaviors based on the following mechanisms: (1) a duty cycle complying with the IEEE802.15.4 standard when assuming a fixed set of tags and free operating conditions. The system can be regarded as Reader Talk First (RTF), which is implemented during a tag collection process executed at the beginning of the system activation. (2) Wake-Up Mechanism, the tag transmits an identification packet to the reader and then waits for an Acknowledgment signal from the reader.
TopIntroduction
RFID is an automatic identification system that stores and remotely retrieves data from devices called RFID tags or transponders by using an interrogator (or reader) and a computer network (Wang et al., 2008). The emerging technology of RFID promises to be a more comprehensive approach to data collection, and one of its potential applications is the improvement of supply-chain operations, offering a more automated and informative alternative to barcode. More recently, the evident benefits of an RFID system over barcode systems have formed a preference for RFID in the retail industry. These benefits give increased automation because of the ability of RFID tags to be read without a visual line-of-sight, as well as their ability to accumulate more information than barcodes. Additionally, due to the suitability of RFID technology for locating and tracking objects, RFID has been recently applied to many location identification systems to detect the presence of tagged objects and/or people. Monitoring the system by way of an RFID reader is important for providing better and more efficient context-awareness services (Siadat & Selamat, 2008).
Furthermore, because reliable, sufficiently small and adequately low cost RFID tags can now be built, the reputation of RFIDs has lately been on the increase. Although the promise of RFID technology is thought to be great, its development has been slow because of anticipated implementation difficulties in areas such as signal quality and mobility in terms of spatiality when monitoring and tracking items in a large warehouse. In these cases the RFID mechanism is intrinsically unreliable and the system requires multiple read cycles for tag read efficiency. The necessity for modified RFID tag and reader devices to be made available is due to the high demand for these devices, with the goal of such a modification being the design of an RFID system capable of achieving a perfect network while being virtually invisible to the user.
However, research on efficient communication protocols for RFID-based systems has been rather limited in networked tag/reader environments, examples include systems for supply chain management, monitoring and controlling of large warehouses, and smart homes. Figure 1 (Lei & Zhi, 2006) shows architecture of networked smart nodes.
Figure 1. Architecture of networked smart nodes
The last decade has seen new developments for overcoming the limitations of RFID, enabling the technology to meet the growing demands of the modern world. Recent advances in wireless communication, processing capability, and memory technology have fueled increasing research and industrial activity on the subject of wireless sensor networks (WSN). RFID does not provide information about the condition of the detected objects; in contrast, WSNs not only provide information about the condition of the objects and the environment, but also enable multi-hop wireless communications (Callaway et al., 2002). Wireless sensors, also known as wireless sensor nodes or sensor nodes, have been making a significant impact on human daily life. Wireless sensors are the key that enables the technology for emerging cyber-physical systems, which would ultimately improve the quality of life (Shah &- Kumar, 2007). The RFID and WSNs are two complementary technologies; hence, an integrated implementation of these technologies expands their overall functionality in obtaining long-range and real-time information on the location and properties of objects and people. This extended coverage and effectively improved reliability can dramatically improve the read performance of an RFID system. Since WSN operates with low power consumption and low complexity, and since signal path loss is inversely related to range or distance.
In view of the above, there is a need for essential research on protocols and algorithms that can improve RFID-based WSN performance and thereby significantly benefit the emerging identification and monitoring applications.