With
Handover power boost (HOPB), the handover command is sent by the BSC/BTS to the
MS on maximum configurative power. Handover command includes information about
which uplink power the MS shall use in serving cell. The MS then acknowledges
the handover command using maximum configurative power. In case of a HO
failure, the HO failure message is also sent on maximum configurative power.
When handover power boost is triggered, normal regulation is inhibited until
the MS has received the handover command. The BTS ignores all BTS or MS power
orders sent by the BSC in the serving cell until the MS has acknowledged the handover
command.
The
speech/channel coding and interleaving in GSM is very robust. A small number of
bursts/frames can be lost without speech degradation (the number depends on the
error distribution). Power Control should therefore also be used for
connections close to the cell border. Since the signaling for the handover
procedure (for example Handover Command) is more critical and error-sensitive,
it should be sent on maximum power in order to maximise the handover
performance.
HOPB
is useful when the SS quickly drops, for example when the MS moves around a
street corner. In this case, due to the system delay and the limited up-regulation
speed, the signaling would be sent on a too low power without HOPB. Thus in
order to maximise the probability of a successful handover, Handover Power
Boost should be used.
Since
the maximum configurative power is only used for a short time before the
handover, activating HOPB has a minor impact on the overall interference level
in the network.
Note
that HOPB only improves the HO performance if power control is activated.
Handover
power boost is activated by setting the state variable HPBSTATE.