Hi Folks,
There was some confusion regarding the
definition of virtual soft handoff and it would be beneficial if we can
all come to the same understanding of these terms. We can then discuss the
implications of these scenarios and backbone messages required to
implement these scenarios. Some of the HO scenarios are listed below.
Please comments on these such that we can come to a common
understanding.
All scenarios refer to a SS
which due to some trigger (load balancing at BS, geographical movement of
SS) disconnects from one BS (primary BS) and moves to the secondary
BS.
1. Hard Hand-Off:
The SS disconnects from the
primary BS and then reconnects to the secondary BS. At a time the SS is
either connected to the primary BS, not connected to any BS or connected
to the secondary BS.
2. Make before break (MBB HO)
While the SS is connected to
the primary BS, the SS also connects to the secondary BS and then
disconnects from the primary BS. At a time the SS is either connected to
the primary BS, connected to both the primary and the secondary BS, or
connected only to the secondary BS.
3. Virtual Soft Hand-Off
Same operation as
in (2).
4. Soft Hand-Off:
Same operation as in
(2).
As can be see scenarios 2,3 and 4 describe a very
similarly situation. The difference is in the type of macro diversity gain
obtained.
According to my
understanding:
1. Hard Hand-Off:
provides no diversity gain.
2. Make before break (MBB HO) provides no
diversity gain.
3. Virtual Soft
Hand-Off provides diversity gain by combining layer 2 information. This is
achieved by multicasting the same information through multiple BSs. On the
uplink the diversity gain is obtained by receiving the Layer 2 PDUs from
both the primary and secondary BS and using an appropriate combining
algorithm.
4. Soft Hand-Off: provides diversity gain by
combining PHY information (e.g. MRC of the OFDM/OFDMA signals). This is
again obtained by simultaneous multicast of downlink information from
multiple BS to obtain the downlink diversity and MRC the received OFDM
signals from different BSs at the central RNC to obtain the uplink
diversity.
Virtual Soft Handoff and soft handoff therefore
places different requirements on the backbone messages to be transferred
and also the information which needs to be shared to achieve the macro
diversity gain.
Please comment on this such that we have to same
basic understanding.
Regards,
-Raja
Hi
All,
I have the
following thoughts on HO process:
1. Since we are considering the
possibility of allowing SHO and fast BS switching HO, we adopt
an acitve set maintenance procedure regardless of the HO type (BBM, MBB
Hard HO, SHO or fast BS swiitching).
2. I
propose to change the current HO process defined in 16e to make it more
deterministic. With the current definition, the HO decision point could
be at the BS or the MSS, and any of the messages maybe or may not be
sent during a HO. I think this allows for too many possibilities, it's
hard to implement and maintain a state machine with so many
undeterminstic events. When operating and optimizing a larget
network, it would be easier to have a more defined HO procedure. I
propose we do the following:
a) The HO
decision point should be at the BS. The MSS can assist in the HO process
by reporting a list of recommaned target BS, but the BS directs to the
MSS to handover to a specific active set (the list of serving BS).
b) There is
a minimum pair of messages have to be sent during a HO: BS Handover
Command (or if we don't want to add a new message, we can just use BS
Handover Request to direct the MSS) and MS Handover Indication.
When the BS decides a HO should take place and chooses the new
active set, the BS should send BS Handover Command to the MSS.
When the MSS has performed the HO, the MSS should send MS Handover
Indication to indicate the status of the handover. The MSS can use this
message to Reject the HO if it has to.
c) For the
MSS assisted HO, the HO can be triggered by the MSS sending MS Handover
Request. However, this message doesn't have to result in HO. The
BS should send BS Handover Response just to stop possible
retransmission of MS Handover Request message. For BS triggered HO, the
BS just need to send BS Handover Command to start the HO
process.
d) I
believe no matter what type of HO we are supporting, we should use the
same HO process as defined above with possiblity different parameters
included in the message. i.e. For a HO with Level 3 backbone
communication, the BS Handover Command message can indicate skipping
certain steps when the MSS performing network entry at the target BS
(maybe just ranging necessary).
Just some
of my thought. Thanks.
Best
Regards,
Mary