Abstract: A method and apparatus reduces current consumption of a mobile communication unit, such as a cellular or mobile telephone that communicates with a base station by disabling a temperature controlled crystal oscillator and a code generator while the mobile communication unit is in a sleep mode of operation, thereby reducing the sleep mode current consumed by the mobile communication unit. Prior to entering sleep mode, the mobile communications unit stores the state of the code generator and disables the temperature controlled crystal oscillator. Upon waking from sleep mode, the mobile communication unit calculates what the state of its code generator would have been if its temperature controlled crystal oscillator had not been disabled, and uses this calculated state to achieve synchronization with a code generator in the base station.

Abstract: A unique method for supervising a cellular telephone call between a base station and a radio telephone of a TDMA cellular communications system includes the steps of determining (304) that the assigned time slot is expected to be received within a predetermined amount of time; detecting the presence of the assigned time slot (306) within the predetermined amount of time; detecting the presence of the assigned DVCC when the assigned time slot is detected (308); incrementing a bad slot counter (316) [if] responsive to the assigned time slot is not detected within the predetermined amount of time or [if] responsive to the assigned DVCC is not detected; and terminating the communication (322) [if] when the bad slot counter reaches a predetermined maximum value. A good slot counter is incremented (310) when the assigned DVCC is detected in a burst.