Modeling LTE/UMTS Deployment with Patchy Coverage

LTE is currently considered by many wireless operators as their next generation technology. During a transition phase, LTE will be deployed as an overlay on an existing wireless technology, which acts as an underlay. It is expected that initial LTE deployment will be patchy with coverage holes. In this paper, we model and analyze the impact of dual-technology deployment on signaling load at critical network elements. We consider a case, known as without ISR, where a location update is executed when a UE moves between an overlay and an underlay and another case, known as with ISR, where a location update is made only when a new tracking area or routing area is encountered by a UE. Given a fixed total area of coverage holes in an overlay, our result shows that update rate increases as a square root of the number of coverage holes without ISR while it is virtually constant with ISR.