Handoff - Huawei Airbridge BTS3606A Technical Manual

Technical Manual
Airbridge BTS3606A CDMA Base Station
The system transmits at the maximum allowed rate through the Control Channel
(CC).
The AT first transmits at 9.6 kbps, and then increases the rate gradually according
to the Reverse Activity Bit (RAB) sent by the AN.
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4.2 Handoff

When the MS/AT moves out of the current serving cell/sector or the conversation
quality deteriorates to an unacceptable degree, the MS will be handed off to another
cell/sector to maintain the ongoing conversation.
If the handoff of MS/AT to another cell/sector helps to improve the conversation quality
and network performance, it is also possible to trigger the handoff procedure.
Different from the CDMA2000 1x, the 1xEV-DO introduces virtual soft handoff function
to the forward link.
I. Soft handoff
The soft handoff happens between neighboring cells which serve on the same
frequency and belong to different BTSs. The two different BTSs can belong to the same
BSC, or two different BSCs connected with A3/A7 interface.
In the soft handoff procedure, the MS maintains the connection with the previous cell till
it establishes the communication with the new cell. The MS can establish radio links
with multiple cells, select and combine data received from these links to improve the
conversation quality and reduce call drops.
II. Softer handoff
The softer handoff happens between neighboring sectors that serve on the same
frequency and belong to the same BTS. It is a special case of soft handoff.
Since the MS establishes radio links with multiple sectors under the same BTS, the
BTS can combine the diversity signals received by its sectors from the MS.
Therefore, the conversation quality during softer handoff is better than that of soft
handoff.
III. Virtual soft handoff (only applied to the 1xEV-DO forward link)
The AT monitors all pilot signals in the Active Set and selects the best as its serving
sector. Then, it receives signaling messages and data from the selected sector. This
process is called virtual software handoff.
If the RAB sent by all sectors in the Active Set is 0 and when a certain
condition is met, the AT multiples the rate every other 26.67 ms until the rate
reaches the maximum allowed rate.
If the RAB sent by at least one sector in the Active Set is 1, the AT decreases
the rate by half when a certain condition is met.
4-3
System Description
Chapter 4 Main Functions