Centralized wireless data networks with user arrivals and departures

A dynamic-user model for centralized wireless networks is studied, where users arrive with a certain file size and depart when the file is served by a central server. Although the exact analysis of dynamic-user systems can be complicated, it is shown that an approximate analysis can be performed in a time-scale separation regime where the file size is much larger than the time scale of service process fluctuation. A first-order approximation result is derived that shows that when file sizes are large, a complicated service process can be replaced by a simple constant-rate service process. The accuracy of the approximation is further improved through a second order approximation result that incorporates the effect of service variability. Variability in the service process is shown to reduce the effective service rate, leading to a quantification of the conventional heuristic that service variability degrades system performance.