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