PGSLOT and SLOT_NUM
Definition: PGSLOT is an integer in the range from zero to decimal 2047 obtained from the hashing function used by a mobile to determine the paging channel slots assigned to it when it is operating in the slotted paging mode. A mo-bile can operate in the slotted mode only when it is in the Mobile Station Idle State. In the slotted mode, a mobile monitors the paging channel for one or two 80 msec time slots per slot cycle. The mobile can specify its preferred slot cycle, which sets the receiver duty cycle during the slotted mode.
SLOT_NUM are the paging channel slot numbers assigned to a mobile.
PGSLOT and SLOT_NUM
Example: The mobile first uses its hashing function to calculate a uniformly distri-buted random variable between zero and 2047. This number is PGSLOT. As-sume that PGSLOT equals 6. The mobile now specifies its preferred slot cycle. The minimum slot cycle is 1.28 seconds (16 slots) and the maximum slot cycle is 2048 slots of 80 msec each or 163.84 seconds (2.73 minutes).
Suppose the mobile selects a slot cycle time equal to the minimum time of 1.28 seconds. Then the slots assigned to the mobile are defined by the equa-tion
[ {t/4} -PGSLOT ] mod (16xT) =0 (1)
where t is the system time in frames, {t/4} denotes the largest integer less than or equal to t/4 , T is the slot cycle time expressed in units of 1.28 sec., given by 2i, where i is the slot cycle index. In our example, T equals 1, which corresponds to the slot cycle index i equal to zero. Substituting values into Eq. (1) yields the slots assigned to the mobile as
[ {t/4} -6 ] mod 16 =0 (2)
With the 20 msec frames used in IS-95, {t/4} is actually a slot number. The slots in the paging channel are numbered zero to 2047, and then the number-ing repeats. When t equals 24 frames (6 slots), Eq. (2) is zero signifying that the first slot to be monitored is slot number 6, which equals PGSLOT. The next time that Eq. (2) is satisfied will be when {t/4} equals 22, or in slot number 22. Eq. (2) will thereafter be satisfied when the slot numbers equal
6+16m, where m is an integer from zero to 127. With m equal to 127, the assigned slot number equals 2038. The next slot assigned after slot 2038 will be slot number 6 again.
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