Mobile phone signal

From inside a building with thick walls or of mostly metal construction (or with dense rebar in concrete), signal attenuation may prevent a mobile phone from being used.

There may also be gaps where the service contours of the individual base stations (Cell towers) of the mobile provider (and/or its roaming partners) do not completely overlap.

This phenomenon, which is also common in other VHF radio bands including FM broadcasting, may also cause other anomalies, such as a person in San Diego "roaming" on a Mexican tower from just over the border in Tijuana, or someone in Detroit "roaming" on a Canadian tower located within sight across the Detroit River in Windsor, Ontario.

The volume of network traffic can also cause calls to be blocked or dropped due to a disaster or other mass call event which overloads the number of available radio channels in an area, or the number of telephone circuits connecting to and from the general public switched telephone network Areas where mobile phones cannot transmit to a nearby mobile site, base station, or repeater are known as dead zones.

Dead zones can be filled-in with microcells, while picocells can handle even smaller areas without causing interference to the larger network.

A similar system can be set up to perform inmate call capture,[2] which prevents cellphones smuggled into a prison from being used.

These systems must be carefully designed so as to avoid capturing calls from outside the prison, which would in effect create a dead zone for any passersby outside.

In the event of a disaster causing temporary dead zones, a cell on wheels may be brought in until the local telecom infrastructure can be restored.

One reason for a call to be "dropped" is if the mobile phone subscriber travels outside the coverage area—the cellular network radio tower(s).

[clarification needed] Another common reason is when a phone is taken into an area where wireless communication is unavailable, interrupted, interfered with, or jammed.

They have attempted to address the complaint in various ways, including expansion of their home network coverage, increased cell capacity, and offering refunds for individual dropped calls.

In GSM networks, ASU maps to RSSI (received signal strength indicator, see TS 27.007[3] sub clause 8.5).

In LTE networks, ASU maps to RSRP (reference signal received power, see TS 36.133, sub-clause 9.1.4).

The Active Set Update is a signalling message used in handover procedures of UMTS and CDMA mobile telephony standards.