FRAME_OFFSET Definition: FRAME_OFFSET is the frame offset of the current traffic channel, expressed as a multiple of 1.25 msec. Recall, that the frames in IS-95 are 20 msec in duration. Therefore, every 2 seconds exactly 100 frames occur. Also every 2 seconds an even numbered second of GPS and IS-95 time occurs. However, a frame may not begin at every even numbered GPS or IS-95 second. Rather, the frame may start some multiple of power control groups or increments of 1.25 msec after the even numbered seconds. The number of such 1.25 msec offsets relative to the even-numbered-seconds marker is called the frame offset. The FRAME_OFFSET is sent to the mobile on the Channel Assignment Message. USE YOUR BROWSER "BACK" BUTTON TO RETURN © 1999 DR. ERNEST SIMO - SPACE2000 FRAME_OFFSET Application: The FRAME_OFFSET could be zero if the frame start time is synchronous with the even numbered system seconds. On the other hand, the time delay could be as large as (20-1.25) msec or 18.75 msec. In units of 1.25 msec, the maximum offset is 15. Hence, FRAME_OFFSET can range from zero to 15 inclusively. FRAME_OFFSET is therefore sent as a 4 binary-bit word. When the FRAME_OFFSET does not equal zero, the base station is said to be using staggered forward traffic channel frames. The forward and reverse traffic channels are offset by the same amount. Since a mobile receiving forward-link traffic at different frame offsets cannot combine the frames coherently, different frame offsets require a hard CDMA-to-CDMA handoff. USE YOUR BROWSER "BACK" BUTTON TO RETURN © 1999 DR. ERNEST SIMO - SPACE2000 FRAME_OFFSET Example: USE YOUR BROWSER "BACK" BUTTON TO RETURN © 1999 DR. ERNEST SIMO - SPACE2000

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