In a typical cellular wireless communication system, a wireless carrier operates a radio access network (RAN) comprising a number of base transceiver stations (base stations) or other such access points positioned at various locations throughout a region. Each base station includes an antenna or antenna arrangement that radiates to define one or more coverage areas such as a cell or cell sectors. Further, each base station may be coupled with other RAN infrastructure to ultimately provide a connection with a transport network such as the public switched telephone network (PSTN) or the Internet. With this arrangement, when a wireless communication device (WCD) is positioned within one of the RAN coverage areas, the WCD can engage in air interface communication with the base station serving the coverage area and in turn with other served WCDs or with entities on the transport network.
In practice, a WCD such as a cell phone, portable computer or other wirelessly equipped device will regularly monitor pilot signals emitted by base stations in various coverage areas, in search of a coverage area having a strongest pilot signal. The WCD will then “idle” in that coverage area, monitoring overhead air interface channels to obtain system information and any applicable page messages, and awaiting a network or user directive to initiate a communication such as a voice call or data session. When the WCD then seeks to initiate a communication, the WCD may transmit an access probe message to the base station serving that coverage area. In response, the RAN may then assign air interface traffic channel resources and/or take other action to establish a connection so that the WCD may proceed with the communication.
If a WCD is very far away from a base station when the WCD engages in an active communication (e.g., voice call or data session) via the base station, both the WCD and the base station will need to communicate with particularly high transmission power. Such high powered transmissions can consume a disproportionate amount of base station power resources and can interfere with other communications being carried out in the coverage area and perhaps in adjacent coverage areas. To help avoid or minimize those problems, a base station or its supporting RAN infrastructure may be programmed to reject communication requests from WCDs that are considered too far away from the base station, such as farther than a particular “cell radius” from the base station.
To facilitate this, in certain systems, a WCD will include within its access probe information that indicates how far away the WCD is from the base station. For instance, the WCD may include in its access probe a measurement of pilot signal delay (e.g., chip delay), i.e., how long it takes a pilot signal from the base station to reach the WCD, which would correlate with a distance between the base station and the WCD. The RAN may then compare the indicated distance with a cell radius threshold to determine whether to allow the requested communication to be established. If the RAN determines that the indicated distance is within the cell radius, then the RAN may grant the request. However, if the RAN determines that the indicated distance is beyond the cell radius, then the RAN may reject the request.