IEEE C802.16m-07/248
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
Neighbor BS Coordination via MS
Date
Submitted
2007-11-07
Source(s)
Gang Shen, Kaibin Zhang, Wei Ni, Wei
Zou, Jimin Liu, Shan Jin
Alcatel-Lucent Research and Innovation
Voice: + 86-21-50554550-7167
Fax: + 86-21-50554554
mailto: gang.a.shen@alcatel-sbell.com.cn
Re:
IEEE 802.16m-07/040 Call for Contributions on Project 802.16m SDD
Abstract
To allow MS forward BS’s control information to its neighbor BS
Purpose
For 802.16m discussion and eventual adoption for SDD
Notice
Release
Patent
Policy
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
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Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and
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Neighbor BS Coordination via MS
Gang Shen, Kaibin Zhang, Wei Ni, Wei Zou, Jimin Liu, Shan Jin
Alcatel-Lucent
1. Introduction
With the technical development targeting IMT-Advance, neighboring BS coordination becomes more and more
important and frequent for the exchange of some control information, channel information, request / response
messages, etc. This coordination is necessary with enhancement of some existing techniques and the adoption of
some new advanced techniques, such as fast handover, network MIMO, collaborative MIMO, interference
cancellation, fractional frequency reuse, multicast and broadcast service (MBS). For example, in the handover
procedure, the serving BS has to negotiate with neighboring BSs for the potential candidates of target BS to
check whether the neighboring BS would like to accept the moving MS or not. The serving BS is required to
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send pre-notification request message to the neighboring BS with MS static context, and the neighboring BS
sends back a response message, including the service level predication, estimated HO time and HO optimization
parameters. Upon handover completion, the target BS also sends the serving BS a notification that it is now
hosts the MS in order that the serving BS releases the resources allocated to the MS. Another example is
neighboring BS coordination for interference cancellation. Some time-frequency scheduling information should
be exchanged between neighboring BSs for the purpose of interference cancellation or resource reuse. The strict
latency requirement is raised for neighboring BS control coordination. A small latency can reduce possible
service interruption and improve the performance.
Fig. 1 Neighboring BS coordination for control information exchange
In the existing neighboring BS coordination method, control information exchange is exchanged via backbone.
For example, neighboring BS exchanges pre-notification request / response messages via backbone for
handover. Although backbone is suitable for massive data transmission, the latency for control information
exchange between neighboring BS via backbone is not predictable, depending on neighboring BS locations and
which NCMS they belong to. The total latency on backbone may include transmitting delay, routing / switching
delay, and IP encapsulation / encapsulation delay. And the delay will be much longer if IP routing is involved.
2. Neighbor BS Coordination via MS
This document proposes a BS-BS coordination scheme via MS. A MS is located within the overlapped coverage
of neighboring BSs, who identify this MS for their coordination.
In this method, one BS sends control information to the MS first, and then MS forwards the received control
information to the neighboring BS, as illustrated in Fig.2. Thus the control information exchange is conducted
via MS, instead of via backbone with unpredictable routing and latency. The channel for coordination between
MS and BS is assigned in advance. It could be dedicated or shared control channel. Exchanged control
information may be encrypted, and it is transparent to MS. MS does not decode it to get the data contents. It just
simply forwards what it receives from one BS to the designated neighbor. The BS coordination via MS is
proposed suitable for short and time-critical information exchange between neighboring BSs. Massive
information exchange is still transmitted via backbone. Compared to legacy BS coordination via backbone, the
latency of this control information exchange is low and predictable.
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Neighboring BS coordination
via MS
Neighbor BS
Serving BS
MS
Neighboring BS control message exchange



MS is located in the overlapped coverage area of two BSs
MS just simply forwards one BS’s control message to its neighboring BS
MS does not decrypt the control message
Fig. 2 Neighboring BS control information exchange via MS
3. Common Control Channel
A common control channel is shared by multiple BSs, where MS uplink control message transmission through
this common control channel can be monitored and received by multiple BSs, as illustrated in Fig.3. So
neighboring BS can easily and quickly get some MS’s information (SINR, HO request …) directly, instead of
achieving this information from MS’s serving BS via backbone. The common control channel is used for the
MS located within the overlapped coverage area of several BSs. It is established such that a common timefrequency area is shared by multiple involved BSs. It can be taken as an uplink broadcast such that MS
broadcast its message to multiple BSs, fully using the signal broadcast feature without extra bandwidth
consumption.
MS may use the common control channel to unicast the message to one BS, or multicast / broadcast the message
to several BSs simultaneously. MS identifies its communication partner in the control message by BS ID. It may
identify one, several or all involved BS as the communication target. If a BS receives a message without its own
ID as destination, it omits it.
Only MS located at the overlapped coverage area of multiple BSs have common control channel, as only this
MS can communicate to / from multiple BSs. Different MS may have its own common control channel, or
several MSs share one common control channel. Downlink common control channel is also possible, where
neighboring BS may transmit control message to the involved MS.
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Common control channel
BS
BS
BS
Control message
Fig. 3 Common control channel
4. Example in Fast Handover
This section gives a possible improvement of fast handover with the introduction of the common control
channel and neighbor BS coordination. Fig.4(a) illustrates the procedure of legacy MS handover. Although MS
is located within the coverage and direct communication distance of candidate target BS, its static context and
handover intention are still firstly received and forwarded by its own BS. It may cause some unnecessary
message exchange and latency between the serving BS and the target BS.
Fig.4(a) illustrates a possible improvement with control message exchange using common control channel. MS
first transmits HO request with its static context. As this message is transmitted through the common control
channel, it can be received by it own BS as well as its neighboring BSs. The neighboring BS who would like to
accept the moving MS will feedback a response at once, including the service level predication, estimated HO
time and HO optimization etc. MS gets the feedbacks from other BSs, and evaluates its handover targets. And
then sends its handover preference as well as neighboring BS feedback information to its serving BS. The
serving BS responds HO -Rsp to MS, and sends a notification message for handover.
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MS
Serving BS
Target BS
MOB_MSHO_REQ
HO pre-notification request
Possibly experience routing, IP
encapsulation / decapsulation...
HO pre-notification response
MOB_BSHO_RSP
Fig. 4 (a), Legacy handover procedure
MS
Serving BS
Target BS
MOB_MSHO_REQ
Target BS HO-Req
MOB_MSHO_REQ with target BS feedback
MOB_BSHO_RSP
Fig. 4 (b), Fast handover with the common control channel and neighbor BS coordination
5. Text Proposal in SDD TOC
x.x.x Neighbor BS coordination
Neighbor BSs exchange control information for coordination.
This coordination information can be forwarded via the MS located in the overlapped coverage area of two or
more neighboring BSs.
x.x.x Common control channel
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A common control channel is shared by multiple BSs, where the MS exchanges control messages with multiple
involved BSs.
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