PCS uses the DCCH to provide a sleep mode during which phones can turn off much of their circuitry until they need to wake up, at predetermined intervals, to receive system messaging. This feature greatly increases the battery life, thereby increasing the standby time of phones. Standby time is the time a wireless phone is idle; that is, the phone is on, but no calls are being placed or received.

Operating Principle

An idle phone camps on the DCCH. The phone checks for incoming calls every few milliseconds and then reenters the sleep mode. This differs from a phone using an ACC, where an idle phone must monitor the control channel constantly, wearing down the battery.

The system messages received by the phone can be pages (for either a voice call or PCS messaging) or broadcast messages (for example, updates about cell changes or neighbor lists) carried on the downlink DCCH. The phone needs to decode the downlink information only at intervals on its predetermined paging slots or on the broadcast slots if the broadcast information changes. In this manner, the phone has extended periods of time in which it can power down some of its circuitry and sleep between paging opportunities.

Current Consumption and Sleep Periods

Figure 6 depicts ACC versus DCCH battery current consumption and indicates the phone's sleep-mode periods on the DCCH. The time spikes in the DCCH segment of the drawing are representative of the predetermined paging slots.

Figure 6. Current Consumption and Sleep Periods