Tag collision is one of the most significant limitations of the RFID systems. Current anti-collision algorithms process the problem in medium access control layer as an estimation of the collided tags number. This process requires retransmission of the RN16 sequence, and hence the discarding of signals in the PHY layer. This letter shows how to use the physical signal in order to decode collided tags. The contributions of this letter are as follows: 1) a simulation model of the Ultra High Frequency RFID system using a Nexxim circuit in conjunction with a system designer using Ansoft Designer simulator platform; 2) a proposed edge transition scheme to recover collision and decode tag signals. This scheme permits us to decode collision signal of three tags, which increases the system throughput from 0.37 (slotted Aloha) to 1.37; 3) an experimental setup that was able to collect and decode the real collision tag signal thanks to our proposed edge transition scheme.