## 2 Related Work  
A large number of studies has been conducted in the last years with the aim of evaluating the performance of passive RFID systems. Most of them focused on suggesting new protocols and algorithms to improve the performance of RFID installations. The proposals cover a wide range of topics, with an emphasis in security, e.g., [7; 8; 9] and anti-collision protocols, e.g., [10; 11; 12; 13]. However, the vast majority of these proposals cannot be implemented in off-the-self readers, due to their high computational cost or due to incompatibilities with the current standards [14]. Hence, additional effort must be also devoted to study configuration and deployment techniques to achieve the best performance of RFID systems with the currently available commercial readers. In [15; 16; 17; 18] the authors performed several empirical studies to determine the factors that degrade performance and reliability of UHF RFID systems under EPC-C1G2 standard in a static scenario. In [15] the authors compute the read range by means of simulations, while in [16] the authors show how the bit error rate degrades the EPC-C1G2 performance. In [17], the authors experimentally validate the work in [15] and [16], and explore the extent to which reader configuration options, focused on the physical and medium access control layer can mitigate these factors. From the study, authors suggest that tuning physical layer operational parameters may increase the read rate up to a 33\(\%\). In [18] it is shown how the performance in EPC-C1G2 varies widely for different readers. Some works focus on analyzing the identification process of passive RFID systems. A relevant study is addressed by [PERSON] in [19], where the author characterizes the identification process of ISO-18000-6C standard [2] as a Markov chain, assuming a static scenario. The author found that the results matched an experimental evaluation using the old I-Code RFID system [20]. However, in [19] the author assumes that those tags already identified in previous frames keep on competing. This is not the case currently, since most FSA derived protocols, including EPC-C1G2, force identified tags to withdraw from the identification process. In [4] we study the identification performance in static scenarios, but also considering the dynamic frame-length procedure of EPC-C1G2, which is not widely implemented in the commercial readers. There are only a few works that address the mathematical analysis of the identification process in flow scenarios. In [21] and [6] we analyze the identification performance of RFID systems in scenarios characterized by an incoming flow of tags entering the coverage area of a reader, moving at constant speed (e.g., modeling a conveyor belt) and, considering that new tags can enter the workspace although other tags are still being identified. In [6] we provide a model based on dynamical systems for a general scenario where tags enter the checking area according to some arbitrary random arrival process and move with constant speed. With this model, the average tag loss ratio (tags lost per tags entering) can be computed. Moreover, assuming a fixed frame length identification procedure this model provides the optimal frame length for a given set of configuration parameters (speed, tag density and so on). Let us remark that these results can not be used in mixed scenarios, where new groups of tags do not enter in the reading area during the sojourn time. A work focused on mixed scenarios has been published [22], where a probabilistic model is provided for a conveyor belt carrying tags grouped in boxes. However, the main difference between [22] and this work is that, in the former the authors consider a dynamic frame length operation and provide a dynamic programming algorithm to optimally adjust the frame length based on their model. But, as stated previously, most commercial readers do not provide the dynamic frame capability and use FSA with a constant frame length. Therefore, the performance has to be improved by adjusting other system's parameters.