C80216m_08/995
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
Multi-Carrier Supported Handover Procedures
Date
Submitted
2008-09-05
Source(s)
Inuk Jung, Youngsoo Yuk, Ronny
Yongho Kim, Kiseon Ryu
Voice: +82-31-450-1856
E-mail: cooper@lge.com
LG Electronics Inc.
Re:
MAC: Multi-Carrier Operation; in response to the TGm Call for Contributions and Comments
802.16m-08/033 for Session 57
Abstract
This contribution describes HO procedures for Multi-carrier support
Purpose
To be discussed and adopted by TGm for use in the IEEE 802.16m SDD
Notice
Release
Patent
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Multi-Carrier Supported Handover Framework
Inuk Jung, Youngsoo Yuk, Ronny Yongho Kim and Kiseon Ryu
LG Electronics
1 Introduction
For reducing the total HO latency and satisfying the 802.16m’s SRD 30ms HO interruption time, the MS may
utilize Multi-carrier operation for HO operation if capable. In the last session, there were some HO frameworks
introduced using Multi-carrier support and have given some examples of possible scenarios. Here, we propose a
Multi-carrier supported HO framework, which describes each procedure with considerations to efficiently
support full utilization of multiple carriers during HO.
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2 General Multi-Carrier Handover Framework
The general HO framework with Multi-carrier support is not different from the conventional HO procedures.
The multiple carriers are in support of some or all parts of signaling of the generic HO procedure. Hence, the
Multi-carrier support may provide support in HO preparation and execution phases.
In Fig. 1, a very generic exemplar scenario of Multi-carrier supported HO is shown. Assuming that MS and
BS’s have three RF carriers, the MS uses its RF1 and RF2 carriers for continuous data transmission with the
Serving BS and performs HO ranging signaling using RF3 to access the Target BS. By being served through
RF1 and RF2 by Serving BS and performing HO signaling through RF3 with the Target BS, any present data
traffic may be continuously served without interruption or delay.
Serving BS
Target BS
MS
RF1
RF2
RF3
RF1
Ranging,
Scanning,
Network entry
data traffic
RF1
RF2
RF2
RF3
RF3
Figure 1. General Multi-carrier example scenario.
However, to manage such multiple carrier supported HO signaling, the MS need to acquire certain
information of when to signal at what HO procedure with what carrier and so forth. Therefore, each carrier
needs to be scheduled and configured through negotiation between the MS and the Target BS via the Serving
BS.
On such basis, we designed some scenarios and description for HO preparation and execution phases in terms
of Multi-carrier management throughout this proposal.
3 Description of Multi-Carrier Handover Procedures
As mentioned before, the Multi-carrier HO preparation and execution procedures are proposed in this
document. For the HO preparation phase, we considered a solution for scenarios where all carriers are currently
in use with the Serving BS, and thus, have no idle (vacant) carrier for ranging or network entry with the Target
BS. Further along of the above scenario, the re-configuration of MS’s carriers (primary, secondary carriers) at
the Target BS during HO execution is described in means of providing continuous service of any past data
communication that were held with the old Serving BS. The next few subsections give more insight of them.
3.1 Multi-Carrier Handover Initiation
To achieve maximum throughput and best channel quality, the MS would try to utilize all carriers available.
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Hence, at the time of HO trigger, the MS may not have an idle carrier that may be used for HO. In such a case,
there are two possible ways to provide HO: Hard handover by forcing disconnection of one or more carriers to
perform HO ranging with TBS, which will incur HO interruption time, and Seamless HO by scheduling carrier’s
open connections to make a carrier available for HO ranging etc, by merging the carriers connection with
another carrier. The latter case is preferred, since no or minimal HO interruption is incurred, which is a critical
requirement and most important factor in HO.
MS
SBS
f1 f2 f3
f1 f2
TBS
f3
f1
f2
f3
HO-REQ
data={A,B}
data={C,D}
HO-RSP
select TBS
Make s1 carrier
available by
moving A,B
contexts to s2
data={A,B}
data={A,B,C,D}
Access TBS temporary p2 carrier
(e.g Fast ranging, code ranging)
RNG-RSP
Disconnect
from SBS
p – primary carrier
s1 – first secondary carrier
s2 – second secondary carrier
Figure 2. Multi-Carrier Handover Initiation procedure with ‘Carrier Merge’ operation
First, a carrier is chosen to perform HO ranging with the Target BS through negotiation. If the specific carrier
has no data transmission with the Serving BS, it may be used for HO ranging right away. Nevertheless, if it has
connection with active data transmission with the Serving BS, the data contents need to be scheduled and the
connection needs to be closed in proper manner. As shown in Fig. 2, after choosing the carrier (f2) for ranging,
its content {A, B} are re-scheduled to be served by carrier f3. We define this as a ‘carrier merge’ operation,
since the contents (connection, data etc) of two carriers are merged at one carrier.
3.2 Multi-Carrier HO Execution
After acquiring an idle carrier, it is used to access the Target BS’s ‘temporary carrier’. The temporary carrier
serves as an initial BS access point during HO, which may also be used for initial entry. The temporary carrier is
fully configured to serve all the information to the MS required during HO execution. The MS is given
information of the temporary carrier at HO preparation time from the Serving BS through negotiation via HOREQ/RSP messages. An example describing the usage of the temporary carrier is shown in Fig. 3.
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C80216m_08/995
Serving BS
Mobile Station
frame
RF1
SCH (preamble)
s
in u
primary carrier
SFH
secondary carrier
(fully configured)
SFH
secondary carrier
(partially configured)
e
SFH
se
in u
RF2
SFH
additional SI
SFH
Target BS
RF3
SFH
(idle)
TB
(ra S acc
ng
ing ess
)
SFH
primary carrier
SFH
primary carrier
SFH
Temporary (needs to
be fully configured)
Figure 3. General view of HO execution with Multi-Carrier support using ‘Temporary carrier’
There are three scenarios of action by the MS during HO execution for re-configuration of its primary and
secondary carriers at the Target BS for service continuity.
Case 1: MS’s available carrier accesses Target BS’s temporary carrier. Temporary carrier is configured
to serve as primary carrier. Secondary carriers are configured through the newly assigned primary carrier.
Case 2: MS’s available carrier accesses Target BS’s temporary carrier. MS’s Primary carrier (other than
temporary carrier) is assigned through the temporary carrier through negotiation.
Case 2-a: MS initiated – MS preference for power, mobility or coverage etc.
Case 2-b: BS initiated – load balancing, channel quality etc.
Secondary carriers are configured through the newly assigned primary carrier.
Case 3: Before accessing Target BS, MS’s available carrier is assigned a primary carrier at Target BS
through negotiation with Target BS vial Serving BS (backhaul). Secondary carriers may also be assigned
in such pre-negotiated manner, or can be assigned at the Target BS through the primary carrier.
In Fig. 4, a procedural description is shown for scenario 1. After HO initiation and preparation, the MS
accesses the temporary carrier (RF2 of Target BS) with its RF2 while being served by the Serving BS with RF1.
Here, the temporary carrier is assigned as the primary carrier of MS after the ranging procedure.
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MS
Mobile Station
RFcarriers
SFH
RF2
SFH
SFH
primary carrier
Select
TBS
SFH
secondary 1 carrier
(fully configured)
SFH
secondary 2 carrier
(partially configured)
HO
- IN
SCH (preamble)
D
additional SI
(idle)
RF3
SFH
B_
RF1
HO-RSP
MO
frame
Serving BS
RF carriers
Ra
ng
ing
Ra
ng
in
res
po
n se
Target BS
RF carriers
g
(su
cce
ss)
SFH
primary 1 carrier
SFH
primary 2 carrier
(temporary carrier)
SFH
primary 3 carrier
Figure 4. An example of Multi-Carrier Handover Execution procedure for scenario 1.
Another procedural scenario for scenario 2 is given in Fig. 5 for easier comprehension. Along the time line,
middle axis, the MS access the Target BS’s temporary carrier with its RF2. However, this time, after the ranging
is done, the temporary carrier assigns a carrier different from itself as the primary carrier for MS. Since carrier
may have different configurations, such system information needs to be given to the MS, which is done through
the temporary carrier. Hence, a very short data exchange will be done for carrier change to acquire any extra
information of the newly assigned primary carrier. If no such system information is needed to be exchanged, the
MS may directly access the primary RF carrier. The △BCH in the figure relates to such system information,
which includes only the different configuration parameters of the temporary carrier.
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MS
Mobile Station
RFcarriers
SFH
RF2
SFH
SFH
primary carrier
Select
TBS
SFH
secondary 1 carrier
(fully configured)
SFH
secondary 2 carrier
(partially configured)
O-I
N
SCH (preamble)
D
additional SI
MO
RF1
HO-RSP
B_
H
frame
Serving BS
RF carriers
(idle)
RF3
SFH
Ra
ng
ing
Ra
ng
in
res
po
Target BS
RF carriers
g
SFH
primary 1 carrier
SFH
primary 2 carrier
(temporary carrier)
SFH
primary 3 carrier
n se
ΔB
(su
cce
resou CH of p1
ss)
rce a
lloc. &
at p1
Figure 5. An example of Multi-Carrier Handover Execution procedure for scenario 2.
4 Conclusion
For minimum HO interruption time, the MS may utilize secondary carriers for concurrently maintaining
service with the Serving BS and performing HO procedures with the Target BS. Descriptions for Multi-carrier
supported HO are described in this proposal, including HO preparation and execution.
References
[1] IEEE 802.16m-08/003r4, Draft IEEE 802.16m System Description Document, 2008-07-29
Text Proposal for the IEEE802.16m SDD
============================== Start of Proposed Text ================================
19.x MAC procedures for Multicarrier Support
19.x.1 Multi-carrier Handover Procedures
19.x.1.1 Multi-carrier Handover Preparation
A secondary carrier for HO execution is made available for performing HO execution with Target BS through
negotiation between MS and the Target BS via Serving BS. If no available secondary carriers are present, the
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contents (e.g. connection, sessions, data traffic) of a specified carrier are merged with another carrier to
release any activity of it and prepare to access the Target BS.
19.x.1.2 Multi-carrier Handover Execution
During HO Execution, the MS need to re-configure its primary and secondary carriers at the Target BS for
continuous service provision. The following are three possible scenarios and actions described:
Case 1: MS’s available carrier accesses Target BS’s temporary carrier. Temporary carrier is configured
to serve as primary carrier. Secondary carriers are configured through the newly assigned primary carrier.
Case 2: MS’s available carrier accesses Target BS’s temporary carrier. MS’s Primary carrier (other than
temporary carrier) is assigned through the temporary carrier through negotiation. The selection of
primary carrier may be initiated either by MS or the Target BS.
Case 2-a: MS initiated – MS preference for power, mobility or coverage etc.
Case 2-b: BS initiated – load balancing, channel quality etc.
Secondary carriers are configured through the newly assigned primary carrier. Any information
regarding the primary carrier, carrier specific system information that the MS is unaware of, is
provided through the temporary carrier.
Case 3: Before accessing Target BS, MS’s available carrier is assigned a primary carrier at Target BS
through negotiation with Target BS vial Serving BS (backhaul). Secondary carriers may also be assigned
in such pre-negotiated manner, or can be assigned at the Target BS through the primary carrier.
============================== End of Proposed Text =================================
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