Data link control protocols for wireless ATM access channels

Abstract

Describes data link control procedures for wireless ATM access channels based on a dynamic TDMA/TDD frame-work. The system provides integrated ATM services including available bit-rate (ABR) data and constant/variable bit-rate (CBR/VBR) voice or video through the addition of wireless-specific medium access control (MAC) and data link control (DLC) protocol layers between the physical and ATM network layers. The purpose of the DLC protocol layer is to insulate the ATM network layer from wireless channel impairments by selective retransmission of erroneous or lost cells before they are released to the ATM layer. The DLC methods described exploit the on-demand ABR burst transmission capability of the dynamic TDMA channel to retransmit unacknowledged cells in available slots not allocated to service data. Specific error recovery procedures are outlined for both (asynchronous) ABR and (isochronous) CBR services. For ABR, the DLC operation follows a group ACK/NACK based selective reject (SREJ) procedure on a burst-burst basis, without time limits for completion. For CBR, the retransmission procedure is constrained to complete within a specified time interval, so that isochronous delivery of cells to the ATM layer can be maintained. The proposed protocols have been validated using a software emulator which incorporates a choice of radio channel models, dynamic TDMA/TDD MAC, and ABR or CBR DLC. Numerical results show that the data link control protocols under consideration can significantly improve wireless ATM service quality over impaired radio channels for both packer data ABR and stream type CBR virtual circuits.