-----Original Message-----
From: Phillip Barber
[mailto:pbarber@BROADBANDMOBILETECH.COM]
Sent: Monday, June
07, 2004 3:22 PM
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
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