I just thought people
might find the UMTS handover definitions useful (or maybe they will just
confuse things): http://www.umtsworld.com/technology/handover.htm.
According to the UMTS
definitions, what Phil calls Hard-handover would be called a non-seamless hard
handover (break before make)
Phil’s Soft-handover,
in the UMTS world, would be called seamless Hard handover (make before
break).
Phil’s “Soft-handover
with macrodiversity” is simply called soft-handover because it includes macro
diversity by definition. As far as I know that is also consistent with
3GPP2.
To the best of my
knowledge, UMTS does not currently have a “virtual soft handover (soft
switching) although there is nothing to preclude
it.
Brian
From: Phillip
Barber [mailto:pbarber@BROADBANDMOBILETECH.COM]
Sent: Monday, June 07, 2004 8:22
AM
To:
STDS-802-16-MOBILE@listserv.ieee.org
Subject: Re: [STDS-802-16-MOBILE]
[Handoff] Virtual Soft Handoff (Soft
Switching)
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
----- 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