Performability analysis of a metropolitan area cellular network

We describe a model and associated metrics for evaluating the performability (performance + reliability) of a metro area network. The model extends over both the “wireline” backhaul and wireless (radio access) portions of the network, i.e. from the mobile telephony serving office (MTSO) to the users of wireless devices. The model captures failures of network elements in the backhaul, such as switches, network access and termination devices, uncertainty in the routing of fiber feeders, and failures of base station equipment in the radio access part. It also includes effects of path loss, interference, and traffic variability in the radio access, and represents the migration of wireless devices among cell sites in response to outages in the overall network. The last part of the model represents a population of (stationary) wireless users randomly distributed in a geographical area, but with density in accordance with measured cell site traffic. The model is analyzed with the “most probable states” method for performability evaluation to compute approximate probability distributions for metrics such as cell site disconnection due to failures in the backhaul, backhaul link utilizations, loss of coverage for wireless users, and a “service acceptability” metric. The results are useful for assessing the cost vs. performance of a cellular network design.