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