# Fast and Effective Tag Searching for Multi-Group RFID Systems
###### Abstract  
In RFID-assisted applications, the customers often request to provide the tag searching service to determine which specific tags are present in the system. In practice, tags are usually divided into different groups to represent different categories or brands. We found that the traditional tag searching protocols are not very appropriate for multi-group RFID scenarios because they cannot ensure that the searching results of each group satisfy the predefined reliability requirements. Therefore, we develop a series of effective multi-group tag searching schemes. B-Search is a basic method that leverages the filter vector and the indicator vector to perform tag searching for each group sequentially. G-Search and A-Search are two parallel multi-group tag searching schemes. G-Search selects the longest frame length as the frame length of all groups, while A-Search can adaptively adjust the frame length of each group to improve the searching efficiency. We evaluate the performance of the proposed protocols through theoretical analysis and discuss the optimal parameter settings to minimize the execution time. Extensive simulations illustrate that both G-Search and A-Search can achieve fast and effective multi-group tag searching. RFID systems; tag searching; target tags; multi-group +
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a lot of tag searching algorithms [13; 14; 15; 16; 17], including iterative algorithms and segmented algorithms, which have greatly improved the efficiency of tag searching. Sometimes, tags are divided into different categories based on the type or brand of products to which they are attached. For the scenario, we may need to perform some operations for a certain category of tags. For example, the reader samples information, performs tag searching, and determines if a missing tag event occurs in a category. Typically, this scenario is referred to as the multi-group RFID system. In the system, researchers are most interested in the missing tag detection problem, and many effective multi-group missing tag detection protocols have been proposed [18; 19; 20]. The tag searching problem is much more complex and worthwhile. Obviously, the traditional tag searching focuses on studying single-group RFID systems, which is a special case of multi-group RFID systems. Currently, there is hardly a protocol which can effectively and pertinently solve the multi-group tag searching problem to ensure that the searching results in each group satisfy the predefined reliability requirements. To overcome this challenge, we deliver a comprehensive analysis on tag searching in multi-group scenario and investigate how to devise optimal tag searching algorithms. Of course, the three multi-group tag searching protocols we proposed are still appropriate in the single-group situation. The main contributions in our paper are summarized as follows:  
* We expand the application scenario of tag searching and systematically formulate the multi-group tag searching problem;
* We use the segmented tag searching protocol to solve the multi-group tag searching problem and develop B-Search protocol. All groups are searched sequentially. For tag searching within a group, the reader first performs the deactivation of non-wanted tags and then further performs the verification of target tags;
* Meanwhile, we propose two parallel multi-group tag searching protocols called G-Search and A-Search, respectively. G-Search selects the longest frame length as the frame length of all groups. A-Search can adaptively adjust the frame length of each group, thus improving the searching efficiency when the number of local tags and the number of wanted tags are different. * We conduct theoretical analysis to optimize the parameter settings of the three proposed protocols, and extensive simulations demonstrate that our best protocols can achieve fast and effective multi-group tag searching. The rest of our paper is organized as follows: Section 2 gives a brief overview of traditional tag searching protocols and multi-group missing tag detection protocols.