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Passive RFID tags share a common channel and they use back-scattering modulation because of no self battery. It causes reader collision problems when signal from a reader interferes with signal from other readers. The evolving standards use CSMA based protocol called 'Listen Before Talk (LBT)' and FDMA based protocol called 'Frequency Hopping Spread Spectrum (FHSS)' to reduce reader collision problems. Moreover, these standards are not considered with real industry environment that a stationary reader and a mobility reader coexist with different operation methods and purposes in the same place. Therefore, we describe novel protocols to reduce reader collision problems by RSSI signal. They are mixed protocols between CSMA and TDMA based between a stationary reader and a mobility reader. Simulation results show that the proposed protocols improve RFID system performances.