Fluid analysis of delay and packet discard performance for QoS support in wireless networks

Providing quality-of-service (QoS) guarantees over wireless links requires thorough understanding and quantification of the interactions among the traffic source, the wireless channel, and the underlying link-layer error control mechanisms. We account for such interactions in an analytical model that we use to investigate the delay distribution and the packet discard rate (PDR) over a wireless link. Our analysis accommodates the inherent autocorrelations in both the traffic source as well as the channel error characteristics. An on-off fluid process is used to model the arrival of packets at the transmitter. These packets are temporarily stored in a first-in-first-out (FIFO) buffer before being transmitted over a channel with a time-varying and autocorrelated service rate. Using fluid analysis, we first derive the distribution for the queueing delay at the transmitter. As part of this analysis, we solve a fundamental fluid problem, namely, the probability distribution for the workload generated by a two-state fluid source over a fixed time interval. We then use the delay analysis to derive the PDR at the receiver. A closed-form expression for the effective bandwidth subject to a delay constraint is provided as a function of the source, channel, and error scheme parameters. This expression enables fast assessment of the bandwidth requirement of real-time traffic over QoS-based wireless networks. Numerical results and simulations are used to verify the adequacy of the analysis and to study the interactions among various system parameters.