IEEE C802.16m-09/0123
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
Clarification for Ranging during HO Preparation
Date
Submitted
2008-1-5
Source(s)
Chun-Yen Wang, ITRI
Chun-Yuan Chiu, ITRI
Chie-Ming Chou, ITRI
Fang-Ching (Frank) Ren, ITRI
Richard Li, ITRI
Wern-Ho sheen, NCTU/ITRI
Re:
Call for Comments on Project 802.16m System Description Document (SDD)
Abstract
This contribution clarifies some problems about ranging during HO preparation
Purpose
For discussion and approval by TGm
Notice
Release
Patent
Policy
Voice:
E-mail: ChunYen@itri.org.tw
richard929@itri.org.tw
This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It
represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for
discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material
contained herein.
The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution,
and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name
any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole
discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The
contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.16.
The contributor is familiar with the IEEE-SA Patent Policy and Procedures:
<http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and
<http://standards.ieee.org/guides/opman/sect6.html#6.3>.
Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and
<http://standards.ieee.org/board/pat>.
Clarification for Ranging during HO Preparation
Chun-Yen Wang, Chun-Yuan Chiu, Chie-Ming Chou, Fang-Ching (Frank) Ren, Richard Li
ITRI
Wern-Ho sheen
ITRI/NCTU
1.
Introduction
1
IEEE C802.16m-09/0123
AMS
Serving ABS
Target ABS
AMS
HO Initiation (for MS initiated HO)
Serving ABS
Target ABS
HO Initiation (for MS initiated HO)
Make a HO decision
Make a HO decision
HO REQ
Pre-ranging notification
T1
HO REQ
CDMA Ranging Code
HO RSP
HO Command
HO RSP
T1
HO Command
CDMA Ranging Code
T3'
RNG-RSP
(parameters in RNG-RSP)
(parameters in RNG-RSP)
RNG-REQ
T2
CDMA allocation IE
T3
RNG-REQ
T4
RNG-RSP
T4
RNG-RSP
Resume user data transmission
Resume user data transmission
(a) HO interruption time: T1+T2+T3(+T4)
(Ranging during network re-entry)
(b) HO interruption time: T1+T3’(+T4)
(Ranging during HO Preparation)
Fig. 1. Comparison of HO interruption time
In this section, we briefly introduce the HO procedure for the case in which ranging is performed during HO preparation.
Fig. 1(a) presents the original HO procedure, and Fig. 1(b) shows the case where the ranging is performed during HO
preparation phase. As shown in Fig. 1(b), when a handover decision is made, the serving BS may sends a “Pre-ranging
notification” message which contains some information to the MS for performing pre-ranging process. For example, this
message may include the target BS identifier, a reserved CDMA ranging code, and an idle period. The idle period (e.g.,
T1) is used to assure that no data is scheduled to the MS during the pre-ranging process. This idle period can be
scheduled by the serving BS with the knowledge of the incoming HO ranging opportunities in the target BS.
In response to receiving the pre-ranging notification message, the MS initiates the pre-ranging process by sending the
assigned CDMA ranging code to target BS in the provided idle period. Moreover, the MS sends the reserved ranging
code and then goes back to the serving BS immediately without a need of waiting for RNG-RSP message. That can
shorten the UE detaching time from the serving BS (i.e., the assigned idle time T1). In the meanwhile, the serving BS and
target BS negotiates with each other in order to prepare the handover (i.e., HO REQ and HO RSP). Hence, the target BS
can respond the calculated MS’s UL timing adjustment information through these Inter-BS handover preparation
messages. In addition, it is worth noting that the target BS can also attach an UL grant resource information for the MS to
send the RNG-REQ message after it detaches from the old serving cell. And this information can also be applied by the
serving BS to determine the starting time that the MS switches to the target BS, so the handover interruption time can be
further shortened (i.e., T3’ can be further shortened). Besides, since MSs can perform the pre-ranging procedure in
parallel with the other handover process, it is expected to reduce the overall handover duration time.
Finally, the serving BS sends a HO_Command message with handover starting time and some information about target
cell to the MS. After expiry of starting time in HO_Command message, the MS detaches from the old serving cell and
sends a RNG-REQ message to notify the target BS in the pre-allocated UL grant resource, which completes the handover
procedure in the MS side.
In conclusion, ranging during HO preparation allows MSs performing non-contention based ranging process to avoid
collision. Furthermore, the MS can send its CDMA ranging code to target BS and return to its serving BS immediately
2
IEEE C802.16m-09/0123
without waiting for RNG-RSP response from the target BS. Thus, it is clear that the overall handover interruption time
can be reduced. Furthermore, since MSs can perform this procedure in parallel with the other handover preparation
process, the overall handover duration is expected to be further shortened. As a consequence, we propose to capture the
proposed text into the IEEE 802.16m system description document (SDD) [1].
2.
Problem Clarification
In conventional 16eRev2, Association with level 1 and level 2 are specified to reduce the HO interruption time. However,
association is performed during scanning phase, so it may come out with the following problems:
Q1: Prior to HO preparation, a BS may or may not become a target, therefore any pre-ranging may not be useful if this
BS does not eventually become an HO target
Q2: Even if a BS becomes a target, the information obtained during pre-ranging may be completely stale by the time the
HO happens.
Nevertheless, this contribution suggests to perform ranging during HO preparation which is not the same as association
procedure, because association is performed during scanning phase. Moreover, these questions described above do not
exist for the case when pre-ranging is performed during HO preparation phase. For Q1, since 16m agrees to adopt the
network-controlled HO, which BS will become the target BS can be determined in HO preparation phase. As for the Q2,
since the time interval between HO preparation and HO execution is short, the information (e.g., timing offset) obtained
from pre-ranging is absolutely valid after detaching from the old serving BS. Thus, we suggest that ranging during HO
preparation should be supported to further reduce HO interruption time.
References
[1]
802.16m-08/003r6, “The Draft IEEE 802.16m System Description Document”
Proposed Text
The following text is proposed to be captured in the IEEE 802.16m system description document (SDD).
------------------------------------------------------- Start of the proposed text -----------------------------------------------[Add the following text on page 38, line 20]
10.3.2.2.2 HO preparation
The target ABS may obtain AMS information from the serving ABS via backbone network for HO optimization.
Ranging with target ABS may be performed during HO preparation. If ranging with target ABS not performed
prior to or during HO preparation, dedicated ranging resource (e.g. code, channel, etc.) at target ABS may be
reserved for the AMS to facilitate non-contention-based HO ranging.
-------------------------------------------------------- End of the text ------------------------------------------------------
3