Architecture that facilitates the broadcast of a custom signature message to one or more portable wireless devices that enter an associated area of coverage. Ingress and egress buffers are disposed in input and output line cards to maintain the history of transmitted cells. An overlay error is then determined between the first and second structures by analyzing the measured optical signals at the plurality of incident angles from the periodic targets using a scatterometry overlay technique based on the predefined offsets without using a calibration operation. A terminal manages the packet filters.