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The design of an efficient MAC protocol is of paramount importance for the definition of a wireless ATM access. Such a protocol, together with an appropriate traffic scheduler, should guarantee the required QoS for ATM connections. In this paper, we describe the PRAS (polling and reservation access scheme), a TDMA-TDD based MAC protocol with fixed frame duration, using both reservation and polling techniques to assign transmission time slots. In PRAS, each frame consists of variable-length fields, which make the radio access suitable for variable traffic conditions. The scheduling algorithm uses a priority scheme based on the ATM service classes and the maxCTD (cell transfer delay) parameter. A selective-repeat (SR) retransmission procedure is also proposed to correct errored cells due to the noisy channel. Performance results, obtained by simulation, cover different environments and provide many warnings also useful for the in-progress specification activity carried out by the standardization bodies.