Polling- and contention-based schemes for TDMA-TDD access to wireless ATM networks

The design of an efficient MAC protocol is of paramount interest for the de finition of a wireless ATM (WATM) access. In the case of TDMA-TDD WATM acce ss, the current trend in the standardization bodies is to adopt frames of f ixed duration, whose slots are shared among uplink and downlink connections under the control of a MAC scheduler located in the base station. In this paper, we first compare polling and contention techniques, in order to iden tify the best access scheme to serve ATM connections. Then, since the knowl edge of the queue status of the portable terminals can be used by the centr alized scheduler to increase the efficiency of the slot assignment procedur e, we propose different algorithms to code the buffer occupancy status. Mor eover, we compare their performance by considering two different scenarios; the first loaded with ON-OFF sources served by nrt-VBR ATM connections, an d the second with TCP/IP sources served by UBR ATM connections. The results show the superiority of the contention access and the advantages of the bu ffer status notification for the scheduler at the base station.