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Phil,
Irving and All
I am a
bit confused by discussion on definition of soft / v.soft / hard etc.
handovers.
There
is a "soft handover" in 3GPP spec, in all details, PHY and MAC and
L3.
There
is no [known to me] common definition of "soft handover for any imaginable
mobile network".
So 3GPP/"soft handover" is not a family name, it
is a given name.
To the
best of my knowledge, there is no PHY/MAC specifications related to
"macrodiversity" =
procedure when SS simultaneously receives data from
[transmits to] more than one BS.
So
what is the utility of classification based on usage of
macrodiversity?
Concerning context transfer prior to the HO, it can be done under
existing MAC/PHY definitions.
I
would appreciate creating a list of possible HO scenarios [transfer of the
context, then HO or opposite etc.];
then
different names may be assigned to
different scenarios.
Vladimir
This is the mechanism I originally envisioned
when devising HO methodology language and structure in the document.
Supporting this mechanism would be much easier than re-writing the document to
support a macrodiversity/synchronized transmission Soft HO mechanism.
But we should be aware that any macrodiversity benefit will be lost using this
mechanism.
On a related note, this is what I was talking
about when discussing differentiating concept ('Soft Handoff') from the
specific mechanism used to achieve that concept or enhance reliability (pre-HO
context transfer, fast-switching, macrodiversity, etc...). The EVDO
mechanism is referred to as 'Virtual Soft Handoff' yet has no element of
macrodiversity--the primary criteria cited by the group on the June 3
conference call as defining 'Soft Handoff' (by the way, we should be using
'handover' here, not 'handoff').
I once again reiterate these
definitions:
Hard-handover: a handover occuring without
transfer of MSS service and operating context prior to MSS network re-entry at
the new attachment point
Soft-handover: a handover occuring with transfer
of MSS service and operating context prior to network re-entry at the new
attachment point such that the MSS enjoys persistent context and
continuity of service across handover
Soft-handover with macrodiversity: a handover
occuring with transfer of MSS service and operating context prior to MSS
network re-entry at the new attachment point, with two or more BS providing
synchronized transmission of MSS downlink data during the handover interval,
such that the MSS enjoys persistent context and continuity of service across
handover
Thanks,
Phil
----- Original Message -----
Sent: Sunday, June 06, 2004 10:51
PM
Subject: [STDS-802-16-MOBILE] [Handoff]
Virtual Soft Handoff (Soft Switching)
Hi,
Soft Handoff provides gains for
real-time transmission application, thus, we strongly support it being
accepted in the standard.
However, system complexity may
increase dramatically and H-ARQ may need to be turned off to support Soft
Handoff. For non-real-time transmission, the loss may outweigh the benefit
by using soft Handoff.
Therefore, in cdma2000 1XEV-DO
system, virtual soft handoff (or soft switching) is used instead of Soft
Handoff.
In virtual soft handoff (or soft
switching), only one BS in the active list with the best pilot strength
transmits at any moment.
We think it will provide the
following benefit:
1. It provides diversity gain by
allowing fast switching of data transmission from BS to another
BS.
2. It can fit into both OFDM and
OFDMA PHY layer without much change
3. Since only BS is transmitting
at any given time, the schedule of the BS can be more flexible and
optimized than in SHO (no data synchronization issue to worry
about)
4. It can easily support data
connection with H-ARQ
5. It won't take up additional
air link capacity/resource as in SHO case.
We would like to propose the
virtual soft handoff coexist with soft handoff in the standard to provide
more flexibility.
Any opinion?
Best regards,
Irving
Wang, Ph. D.
Director,
Standards
& 3G
Technologies
ZTE San
Diego
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