Quality of service over wireless ATM links

Several technical issues must be resolved before ATM services can be efficiently extended to the wireless environment. Key issues include incorporating the characteristics of the time-varying wireless channel in the provisioning of the cell-level QoS, and improving the transport performance using error control mechanisms. We analyze the cell loss and delay performance over a wireless ATM link. We consider both cases of a single and multiplexed ATM connections. The link capacity fluctuates according to a fluid version of Gilbert-Elliot channel model. Traffic sources are modeled as on-off fluid processes. The analytical framework incorporates the effects of error control schemes (i.e., ARQ and/or FEC), which are used to improve the transport performance over the wireless link. For the single-stream case, we derive the mean delay and the cell loss rate (CLR) due to buffer overflow at the sender side of the wireless link. We also obtain a closed-form approximation for the corresponding wireless effective bandwidth. In the case of multiplexed streams, we obtain a good approximation for the CLR using the Chernoff-dominant eigenvalue (CDE) approach. The expressions for the CLR and effective bandwidth are then used to study the optimal FEC code rate that guarantees the requested QoS while maximizing the utilization of the wireless bandwidth. Numerical results and simulations are used to verify the adequacy of our analysis and to study the impact of error control on the allocation of bandwidth for guaranteed cell loss and delay performance