# Tag-to-Tag Interference Suppression Technique Based on Time Division for RFID
## 1 Introduction  
Recent advancements in digital electronics, signal processing, and wireless communications have given rise to low-cost and low-power automatic wireless sensor systems, which allow non-contact and non-line-of-sight reading of data using electromagnetic signals. Radio-frequency identification (RFID) is an important building block for the Internet of Things (IoT), which helps to connect the status of a physical object to the Internet by capturing meaningful data in order to trace and share information [1, 2]. It has become a key technology that spans a wide range of applications such as asset management, supply chains, and construction. An RFID system consists of a reader (interrogator), a tag (transonder), and middleware software that helps with data processing from the tag to the reader using RF signals [3, 4]. Tags are classified as passive, semi-passive, and active depending on their functionality. Since a passive tag is not equipped with a power source, it requires energy from the reader in order to send back the re-modulated signal containing its ID information [4, 5]. RFID communication based on backscatter tag signals depends on various factors including the power of the signal, the radar cross section (RCS) of the tag, and propagation loss.  
For example, the RFID tags used in the construction industry for materials management suffers a lot from interference signals originating from neighboring tags, which ultimately results in the tag-to-tag collision problem. In order to minimize data collisions caused by neighboring tags, in this paper, we propose an anti-collision algorithm based on the time-division (TD) technique. In the TDtechnique, each tag's response is differentiated by a specific time interval that corresponds to that particular tag for the transmission of data to the reader within the same reader-coverage area. Therefore, a data frame is divided into several timeslots, each of which is assigned to individual tags, and the reader can read all of the tags in chronological order [6]. Furthermore, the data frame considered in this paper includes the preamble frame, which helps with the channel estimation, signal-to-noise ratio (SNR) estimation, synchronization, etc. When transmitting data from a tag to the reader, the tag sends the preamble data before transmitting its main ID information to broadcast the destination of the tag information. After the reader receives the preamble data, it records TD slots for the data transmission corresponding to tags. In RFID applications, the TD method is required to group tags using the same time slot such that they only transmit within a specific time interval. In this paper, we compare the performance of the proposed TD method to the conventional method without the consideration of interference suppression and anti-collision technology and the CDMA technique based on the gold-code sequence, which spreads the tag backscatter signals to separate the signals of each individual tag. To verify the performance of our system, we perform our simulation in various reader interrogation zones.  
The rest of the paper is organized as follows. Section 2 describes the RFID collision problems, and discusses and analyzes some previous works related to the collision problem. In Section 3, we present details of the received signal model employed in this study. In Section 4, we introduce the proposed TD solution for the anti-collision problem for a single reader, while in Section 5, we present a performance analysis of the proposed method in terms of bit error rate (BER) and frame error rate (FER). Finally, in Section 6, we conclude the paper.