onse will directly impact overall system efficiency. They may also be additional 'policy' issues to consider, for example the charge state of the battery and external or internal operating temperatures. Peripheral devices such as displays (one of the largest power-consuming items in most present appliances), also use adaptation by responding to changes in ambient light level or by decreasing frame rates, resolution and colour depth in response to a changed operational requirement. 21.6 Examples of Adaptation in Present Mobile Broadband Systems Adaptation has always been an inherent part of cellular network design. First-generation analogue cellular networks used receive signal strength measurements to determine power and edge of cell handover thresholds (an intelligent use of observed information). Second-generation networks made the handset work harder in that the handset compiles a measurement report that is a composite of received signal level and received signal quality (bit error rate and bit error probability). This is sent to the radio network controller that in turn makes power control and handover decisions. The handset is instructed to look at up to 6 base stations, its own present serving base station and five 'neighbour' handover candidates though there is support for more extended measurement reporting (up to ten base stations) in more recent releases. Power control is implemented within a relatively relaxed duty cycle of 480 milliseconds, though optional enhanced (120 millisecond) and fast (20 millisecond) power control is now supported. So in these examples, the adaptation process is the combined function of power control and handover. The scale of power control is typically about 25 dB (first generation) or 30 to 35 dB in second-generation systems, the rate is either 480 milliseconds, 120 milliseconds or 20 milliseconds and the resolution is typically half a dB. The context is provided by the measurement report. Note that overall system efficiency is determined directly by the accuracy of the meas