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Re: [STDS-802-16-MOBILE] [Handoff] Some additional thoughts on Ha ndover process



Title: [STDS-802-16-MOBILE] [Handoff] Comments / contribs deferred/rejected/withdrawn in Shenzhen to be considered by handoff adhoc
Dear Folks
 
I have two coments on Raja's view
 
1) I'm not sure Hard HO canot give a diversity gain, it just give a single Active set which has only one target BS, not multiple, but in terms of MSS view, if the MSS selects one BS from multiple BSs transmitting some signals and the communication pass temporarily disconnected, it would be Hard HO so that the MSS can take diversity gain little bit.
 
2) Regarding Virtual Soft HO, I do not understand how does L2 combines the L2 PDU..in my understanding it is impossible. L2 and higher layer cannot have the multiple same PDUs from the PHY.
 
3) I think we don't need to clarify and separate the BBM and Hard HO, the Hard HO and soft HO are designated terminologies which has been used in CDMA world regarding soft combining of the signal in PHY. In generally, BBM and MBB would be common terminologies for IEEE802.16e
 
Thanks
-----Original Message-----
From: owner-stds-802-16-mobile@listserv.ieee.org [mailto:owner-stds-802-16-mobile@listserv.ieee.org]On Behalf Of Raja Banerjea
Sent: Wednesday, June 09, 2004 1:56 AM
To: STDS-802-16-MOBILE@listserv.ieee.org
Subject: Re: [STDS-802-16-MOBILE] [Handoff] Some additional thoughts on Ha ndover process

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
 
 
 
-----Original Message-----
From: Mary Chion [mailto:mchion@ZTESANDIEGO.COM]
Sent: Tuesday, June 08, 2004 8:30 AM
To: STDS-802-16-MOBILE@listserv.ieee.org
Subject: Re: [STDS-802-16-MOBILE] [Handoff] Some additional thoughts on Handover process

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