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The reader-to-tag collision problem occurs when multiple readers try to access the same tag simultaneously. The traditional collision avoidance techniques such as RTS (request to send) and CTS (clear to send) are not applicable because a reader may communicate with multiple tags simultaneously. In this paper, we introduce a collaborative communication protocol to avoid reader-to-tag collisions using TDMA and clustering approaches. The protocol targets the RFID-WSN static systems arranged in a square grid topology, which we can find in different RFID applications such as warehouse stocktaking, parking cars, agricultural fields, and libraries. In such simple topologies, the other proposed reader collision solutions for general use of RFID systems are not efficient since they cannot avoid all possible collisions, and worse of that, some of them are not even detectable, which is intolerable for stocktaking applications. Moreover, they are complicated and heavy in resources, while read throughput is limited. Our protocol presents a simple solution for simple RFID systems with better performances. To validate the proposed protocol, we presented a model using the Process Meta Language (Promela), which is executed under the simple Promela interpreter (SPIN) model checker to verify the protocol properties as deadlocks and livelocks. Also as a proof of concept, we have done a first-step performance analysis using the java runtime.