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Top1. Introduction
The RFID (Radio Frequency Identification) technology becomes more and more popular as a means for the identification and the automatic management of objects in a profitable way (Mahdin & Abawajy, 2012). The RFID automates many painful processes which were manually made previously (Guerrero & Bradley, 2010). We expect that the value of the market of the RFID increases up to 26 billion before 2016 (Das & Harrop, 2010). The RFID technology is one of the technologies of automatic identification, as well as the barcode or optical character recognition. The purpose of these technologies is to allow the identification of objects or individuals by machines.
The RFID technology has the peculiarity to work remotely, on the following principle: a reader emits a radio signal and receives in return the answers of tags which are in its coverage range (Pattabhiraman & David, 2008).
At least, an infrastructure RFID contains tags, readers and a middleware which constitutes the link between the material world and the software world (see Figure 1) (Fritz et al., 2010). Among the expected properties of the services offered by RFID systems is the following feature: the dependability.
Figure 1. Infrastructure of an RFID system (Fritz et al., 2010)
The “Dependability is the property of a system such that we can justifiably place our reliance on the service it delivers” (Laprie et al.,1995). Fault Tolerance (FT) (Algirdas, 1967; Tom & Lee, 1981; Jean et al., 2006) is a means to ensure the dependability.
Fault Tolerance can be defined as: “method which allows a system to fill its functions in spite of the faults which can affect its components, its conception or its interactions with men or other systems”.
A fault can be defined as a cause which can provoke an error. A failure of the system appears when the service provided by the system does not correspond to the realization of the function of the system. It is a transition of a correct service towards an incorrect service.
The redundancy is a technique too used and which ensures the dependability: Its principle is to add resources, of information, or time beyond what is necessary for the operation of the system.
There are four forms of redundancy: material, software, information, and time. The material redundancy is the most widespread form of redundancy because of the decrease of cost of the material and the minimization of the size of components. The passive material redundancy allows realizing the FT (Lala, 2001).
Middleware RFID plays a crucial role in the infrastructure by ensuring several tasks (transmits the data towards other systems, deals with the exchanges with the material…). The FT at the intermediate level consists of integrating the mechanisms of FT in the middleware (Farinaz et al., 2002).
Most work on FT were made and evaluated in the sensor networks WSN. Little work treated FT in RFID systems.
In (Fritz et al., 2010), the authors propose the evaluation of the system RFID by using the on-line test by considering a statistical parameter (Read-Error-Rate) to detect the RFID defective components. However, Reader Performance Monitoring can detect such failures, but without going further. It is not possible to determine whether the problem comes from the reader, the tags, or the environment (Rafik et al., 2012).
The authors in (Mahdin & Abawajy, 2012) presented mechanisms of detection of defective readers in RFID networks. They propose an approach based on the algorithm of the interval of fusion. The readings of the readers are merged together and an interval is generated accepted by the majority of the readers. The reader which is refused by the majority is considered defective.