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Re: [STDS-802-16-MOBILE] [Handoff] Virtual Soft Handoff (Soft Swi tching)



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 
 
-----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
 
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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