IEEE C802.16m-08/1045
Project
Title
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Medium Access Control Layer Aspects for E-MBS in IEEE 802.16m
Date
Submitted
2008 -09-05
Source(s)
Baowei Ji, Kaushik Josiam, Zhouyue Pi,
Farooq Khan, Sudhir Ramakrishna
Samsung Telecommunications America
1301 E. Lookout Dr
Richardson, TX 75082
Voice: 972-816-7000
E-mail:
bji, kjosiam@sta.samsung.com
*<http://standards.ieee.org/faqs/affiliationFAQ.html>
Re:
MAC aspects of enhanced MBS; IEEE 802.16m-08/033 Call for Contributions and Comments
on Project 802.16m SDD
Abstract
We provide an overview of our proposal for Medium Access Control (MAC) layer design to
enable E-MBS services in IEEE 802.16m. To that end, we describe an E-MBS specific protocol
architecture and describe various functional blocks. We describe methods for signaling,
initiation, registration and maintenance of E-MBS connections from a MAC layer perspective.
Purpose
For review and adoption by 802.16 TGm
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
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>.
Medium Access Control Layer Aspects for E-MBS in IEEE 802.16m
Baowei Ji, Kaushik Josiam, Zhouyue Pi, Farooq Khan, Sudhir Ramakrishna
Samsung Telecommunications America
Introduction
Multicast and Broadcast Services (MBS) in IEEE 802.16e standard[3] is a downlink only offering that provides
an efficient method to simultaneously transmit data to a group of users using common multicast connection
identifiers (CID). The next evolution of this standard, IEEE 802.16m has specified certain targets for
enhancements to the multicast and broadcast services, called Enhanced – MBS (E-MBS). To improve user
experience, the IEEE 802.16m System Requirement Document (SRD) [1] has set targets for both MBS spectral
1
IEEE C802.16m-08/1045
efficiency and maximum channel change interruption times in MBS.
The IEEE 802.16e standard prescribed that a BS capable of providing MBS service belong to a certain MBS
Zone. An MBS zone is formed by a group of BSs placed in geographical proximity, carrying the same MBS
content and is identified by a unique MBS_Zone ID. An optional macro-diversity mode that enabled singlefrequency network (SFN) operation is also allowed. In SFN, all BSs in the MBS zone simultaneously transmit
the same broadcast information in a time-frequency synchronized manner. For IEEE 802.16m, while we retain
the definition of MBS Zone, we intend to make SFN operation the default mode of E-MBS operatio
To meet the set targets in the SRD for E-MBS, we envision a downlink only E-MBS system operating in a widearea multi-cell SFN environment. In this proposal, we outline the medium access control (MAC) layer details
for the E-MBS system in IEEE 802.16m.
E-MBS Overall Network Architecture
Figure 1: E-MBS overall network architecture
Figure 1 shows the network architecture illustrating the various functional entities needed to enable E-MBS
service in IEEE 802.16m. The Access Services Network Gateway (ASN_GW) serves as a local point for all
network functions needed to provide radio access to an IEEE 802.16e/m subscriber. The primary function of the
ASN_GW with respect to E-MBS is the MBS zone management. In managing the various MBS zones, it is
responsible for transferring messages and content from the MCBCS server to the appropriate BS using Layer -3
(L-3) and maintains Layer 1 and Layer 2 connectivity with the MS. As illustrated in Figure 1, each BS capable
of E-MBS service can belong to one or more MBS zones and ASN_GW interfaces the BS with the appropriate
content from the MCBCS server for each zone.
2
IEEE C802.16m-08/1045
E-MBS Air-Interface Protocol Structure
Figure 2: E-MBS Air-Interface Protocol Structure
The air interface protocol architecture for E-MBS is illustrated in Figure 2. The functional blocks describe both
the data plane and control plane of the E-MBS capable BS. The E-MBS protocol structure is a logical structure
that describes MAC operations for E-MBS and complements the IEEE 802.16m protocol structure described in
the SDD [2]. Since E-MBS is designed primarily to be an open loop SFN system, a lot of functional blocks
like interference management, ranging, link adaptation, scheduling described for the control plane in the unicast
MAC protocol structure might not be required for E-MBS. Therefore, the proposed protocol structure is
optimized for E-MBS and requires close interaction with the unicast protocol structure. In fact, the functional
blocks on the left size of Figure 2 represent the control plane of the unicast protocol structure (Figure 9 in the
current SDD).
The data plane for E-MBS is similar to the data-plane of unicast service except there is no ARQ functional
block in E-MBS. In the control plane, E-MBS MAC operates in parallel with the unicast MAC. Unicast MAC
could operate independently from E-MBS MAC. E-MBS MAC may operate differently depending on whether
unicast MAC is in active mode or idle mode, especially during inter-EMBS-zone handover.
The E-MBS MAC consists of the following functional blocks:
3
IEEE C802.16m-08/1045
E-MBS Zone Management: This block manages the configuration of E-MBS zones. A BS could belong to
multiple E-MBS zones. All the BS of the same E-MBS zone should operate in the single frequency network
(SFN) mode.
E-MBS Operation Configuration: This block decides the best way to deliver E-MBS flow to a MS in its cell.
The BS could transmit the E-MBS flow using unicast channel if there is a few numbers of MS interested in that
E-MBS flow. The BS could transmit the same content to multiple MSs in the single –BS broadcast mode.
Otherwise, the BS shall operate in SFN mode.
E-MBS Service Management: This block manages E-MBS service registration / de-registration and session
start / update / termination, and the BS is responsible for forwarding the data for registration/termination from
and to the E-MBS server.
E-MBS Mobility Management: This block manages the handover when a MS crosses the E-MBS zone
boundary. The handover could be triggered irrespective of when the MS is in active or idle mode in unicast
MAC.
E-MBS-Unicast Interactivity: While E-MBS happens only in downlink, this specification also includes
methods allowing the MS to interact with the BS regarding E-MBS flow. These interactions are strictly unicast.
E-MBS Control Signaling: This block broadcasts the E-MBS scheduling and logical-to-physical channel
mapping to facilitate E-MBS receiving and power saving. This also helps when E-MBS may have its own frame
structure in cases where dedicated carriers are used for E-MBS.
E-MBS Operation Mode
The primary usage of E-MBS in 16m systems is broadcasting mobile TV. In case of broadcast, SFN operation
shall be the default operating mode. For multicast, if all users are in one cell, the operation mode is single-BS
broadcast. However, if multiple BSs are involved in multicasting and all are located in the same geographical
area, then SFN is the preferred operating mode.
E-MBS Procedures
1. E-MBS Service Registration/ De-registration: There are multiple options available for the subscriber to
register for E-MBS service. The registration could happen on a different interface not related to E-MBS
MAC. The subscriber could use unicast signaling for registration / de-registration of E-MBS service or a
different interface such as R-2 for registration. The signaling for this procedure should be transparent to the
BS because the registration and de-registration happens between the MS and E-MBS flow server. The
messages that the MS uses to register/maintain the E-MBS service should be specified if the registration
goes through the BS. As shown in Figure 3, message EMBS_REG_REQ( ) indicates the requirement for
registration or de-registration of a certain E-MBS service. Message E_MBS_ REG_RSP( ) indicates the
response which could be of acceptance or reject. The MS maintains a timer after sending EMBSREG_REQ( ) to take further action if it does not receive EMBS_ REG_RSP( ) within the period. Message
EMBS_ REG_ACK( ) is generally operational. However, the MS is required to send this message if
required by the EMBS-server possibly for accounting purposes.
4
IEEE C802.16m-08/1045
BS
MS
EMBSServer
EMBS_REG_REQ( )
EMBS_REG_RSP( )
EMBS_REG_ACK( )
Figure 3: E-MBS Registration/De-Registration Procedure
2. E-MBS Session start/update/termination: The E-MBS server requests a BS to broadcast the session start
message before the start of a certain E-MBS flow using the EMBS_Session_Start( ) message. If needed, the
E-MBS server requests the BS to broadcast a session update message while the session is going on using the
EMBS_Session_Update( ) message. The E-MBS server requests a BS to broadcast the session termination
message at the end of the E-MBS flow using the EMBS_Session_Termination( ) message.
5
IEEE C802.16m-08/1045
MS
BS
EMBSServer
EMBS_Session_Start( )
EMBS_Session_Update( )
EMBS_Session_Termination( )
Figure 4: E-MBS Session Start / Update / Termination procedure
E-MBS Zone Management
E-MBS Zone configuration: Each E-MBS zone has a unique zone ID, and consists of at least one BS. All the
BSs in an E-MBS zone shall broadcast the same E-MBS zone ID. If a BS belongs to several E-MBS zones, it
shall broadcast all the zone IDs with which it is associated.
E-MBS Inter-Zone Mobility Management: Neighbor Zone information could be part of MOB_NEG_ADV( )
message, which is useful for inter-E-MBS-zone handover when the unicast MAC of an E-MBS MS is in active
mode. The other option is to broadcast neighbor zone information as part of E-MBS control signaling, which is
useful for inter-E-MBS-zone handover when the unicast MAC of an E-MBS MS is in idle mode.
6
IEEE C802.16m-08/1045
Normal Operation
(Active Mode, EMBS)
Cross Cell
Boundary?
No
Yes
Complete Inter-Cell Handover
Cross EMBS Zone
Boundary?
No
Yes
Complete Inter-EMBS-Zone
Handover
Figure 5: Inter-EMBS-Zone Handover (active mode)
1. For a MS with its unicast MAC in active mode, handover in unicast occurs when the MS crosses the cell
boundary. If the cell boundary is also the boundary for a new E-MBS zone, the MS shall do inter-EMBSzone handover as well. This procedure is illustrated in Figure 5.
2. For a MS with its unicast MAC in idle mode, location update in unicast occurs when crossing paging
area boundary as illustrated in Figure 6. The MS shall do inter-E-MBS-zone handover also if it is
crossing E-MBS-zone boundary also.
3. The MS could also cross E-MBS zone boundary without location update. In this case, the inter-E-MBSzone handover could be triggered by the following events.
a. Neighbor-Zone Indication: The E-MBS control signaling may indicate if the present cell is at
the edge of the present E-MBS zone. Having detected this information, as illustrated in Figure 7,
the MS shall prepare and execute inter-E-MBS-zone handover with or without going back to
active mode.
b. E-MBS Signal Indication: The MS could implicitly detect the zone edge if the E-MBS signal
degrades below a certain threshold, which triggers the MS to search for new E-MBS zone with or
without going back to active mode as illustrated in Figure 8. The MS shall return active mode
during inter-EMBS-zone handover if required by the EMBS configuration, and complete
functions such as the renewal of EMBS registration. However, the MS could execute the interEMBS-zone handover without returning active mode if allowed.
7
IEEE C802.16m-08/1045
Idle Mode Operation
(EMBS)
No
Cross Paging Area?
Yes
Complete Location Update
Cross EMBS Zone
Boundary?
No
Yes
Complete Inter-EMBS-Zone
Handover
Figure 6: Inter-E-MBS-Zone Handover during Location Update
8
IEEE C802.16m-08/1045
BS-1
(EMBS zone i)
MS
BS-2
(EMBS zone i)
BS-3
(EMBS zone j)
Idle Mode
EMBS Flow
EMBS Flow (Edge of Zone i)
Active Mode
Inter-EMBS-Zone Handover
Idle Mode
EMBS Flow
Figure 7: Inter-E-MBS-Zone Handover (Zone-Edge Triggered)
BS-1
(EMBS zone i)
MS
BS-2
(EMBS zone i)
BS-3
(EMBS zone j)
Idle Mode
EMBS Flow
EMBS Flow
EMBS Flow
EMBS Flow
Signal < Threshold
Inter-EMBS-Zone Handover
Idle Mode
EMBS Flow
Figure 8: Inter-E-MBS-Zone Handover (E-MBS Signal Level Triggered)
9
IEEE C802.16m-08/1045
E-MBS-Unicast Interactivity
While downlink only mode for MBS offers efficiency, it is not completely future proof. Increasing demands for
interactive multimedia applications require the E-MBS not only provide useful in-depth content to all users but
also be flexible enough to allow users to tailor the content to their taste. While the proposed MBS architecture
is efficient, a strong E-MBS-Unicast Interactivity module is not only necessary but also essential to offer
discriminating content to all users. Examples of the usage scenarios where such E-MBS – Unicast Interactivity
or the Unicast – E-MBS interactivity will be needed are as follows:
 DL E-MBS Paging: This particular scenario occurs when users interested in a particular content
are paged when the content becomes available in their local MBS zone as illustrated in Figure 9.
This is especially useful when the users set this request using unicast feedback channels or
higher layer signaling and goes into idle mode.
 UL User Interaction: This interaction is useful in tailoring a particular broadcast to users or when
users react to certain broadcast applications. A few examples follow:
o If users request more information on a particular content, then the content can be unicast
from the BS to the MS using unicast channels without affecting the MBS data flow as
shown in Figure 10
o When users participate in real-time polling or commentary for a particular program,
unicast uplink channels must be used to forward their data to the MBS server for further
processing as illustrated in Figure 11.
 Idle Mode Unicast Paging: This scenario uses the complement interactivity – the unicast – EMBS interactivity to pass unicast idle mode messages using E-MBS. IEEE 802.16m supports EMBS deployed on a dedicated carrier. An idle mode MS subscribing to an E-MBS service has to
switch between difference carriers to check idle mode notification message, which will lead to
unnecessary switching overhead and the periodic interruption of E-MBS streaming services. To
solve this problem, we propose that the idle mode notification should be managed as one of the
E-MBS multicast services.
1
0
IEEE C802.16m-08/1045
MS
EMBSServer
BS
MS requests to be informed if program K is broadcast
Program K to be
broadcasted
Request to page MS
EMBS Page
Registration for program K
EMBS Broadcast (program K)
Figure 9: EMBS Paging
MS
EMBSServer
BS
EMBS Broadcast (program K)
Request more details about program K
More on program K
More on program K
Figure 10: EMBS Content Tailored to a subscriber
1
1
IEEE C802.16m-08/1045
MS
BS
EMBSServer
EMBS Broadcast (program K)
Comment (***)
EMBS Broadcast (program K)
Comment (****)
EMBS Broadcast (program K)
Comment (*****)
Figure 11: EMBS Real-Time Feedback
E-MBS MAP Signaling
E-MBS MAP contains the control, scheduling and mapping information for the broadcast content. The E-MBS
MAP is a pointer to the information content in the upcoming frames and contains necessary information for the
successful processing of the E-MBS data PDUs in the PHY and the MAC layers. The frequency of the E-MBS
MAP transmission along with details of its construction needs to be specified. The E-MBS MAP broadcasts the
frequency, location and details of the E-MBS flow as well as logical-to-physical channel mapping information.
The details for the E-MBS MAP construction and its contents are TBD. Given this information, a MS could
receive the E-MBS flow of its interest in a power efficient manner. Some of the control signaling could be sent
in cell-specific manner, where the other signaling is sent as part of the E-MBS flow among the whole E-MBS
zone. In the SFN mode, the E-MBS MAP construction and transmission is synchronized across all BSs in the
E-MBS Zone.
References
[1] IEEE 802.16m-07/002r4, “IEEE 802.16m system requirements”
[2] IEEE 802.16m-08/003r4, The Draft IEEE 802.16m System Description Document, July 08
[3] IEEE P802.16Rev2/D4, “Part 16: Air Interface for Broadband Wireless Access System”, April 08
[4] IEEE 802.16m-08/361, “Improvements in System Performance due to simultaneous transmission of EMBS and Unicast”, Samsung Telecommunications America
[5] IEEE 802.16m-08/644, “Multiple CPs for 16m downlink OFDM frame structure”, Samsung
1
2
IEEE C802.16m-08/1045
Proposed Text for the System Description Document
8.x The IEEE 802.16m Enhanced Multicast Broadcast Service (E-MBS) Protocol Structure
The protocol structure for IEEE 802.16m E-MBS is described in Figure x. The functional blocks describe both
the data plane and control plane of the E-MBS capable BS. The E-MBS protocol structure is a logical structure
that describes MAC operations for E-MBS and complements the IEEE 802.16m protocol structure for unicast
transmission in Figure 9. In fact, the functional blocks on the left size of Figure x represent the control plane of
the protocol structure in Figure 9.
The data plane for E-MBS is similar to the data-plane of unicast service except there is no ARQ functional
block in E-MBS. In the control plane, E-MBS MAC operates in parallel with the unicast MAC. Unicast MAC
could operate independently from E-MBS MAC. E-MBS MAC may operate differently depending on whether
unicast MAC is in active mode or idle mode, especially during inter-EMBS-zone handover.
Figure x The IEEE 802.16m E-MBS Protocol Structure
The E-MBS MAC consists of the following functional blocks:
1
3
IEEE C802.16m-08/1045
E-MBS Zone Management: This block manages the configuration of E-MBS zones. A BS could belong to
multiple E-MBS zones. All the BS of the same E-MBS zone should operate in the single frequency network
(SFN) mode.
E-MBS Operation Configuration: This block decides the best way to deliver E-MBS flow to a MS in its cell.
The BS could transmit the E-MBS flow using unicast channel if there is a few numbers of MS interested in that
E-MBS flow. The BS could transmit the same content to multiple MSs in the single –BS broadcast mode.
Otherwise, the BS shall operate in SFN mode.
E-MBS Service Management: This block manages E-MBS service registration / de-registration and session start
/ update / termination, and the BS is responsible for forwarding the data for registration/termination from and to
the E-MBS server.
E-MBS Mobility Management: This block manages the handover when a MS crosses the E-MBS zone
boundary. The handover could be triggered irrespective of when the MS is in active or idle mode in unicast
MAC.
E-MBS-Unicast Interactivity: While E-MBS happens only in downlink, this specification also includes methods
allowing the MS to interact with the BS regarding E-MBS flow. These interactions are strictly unicast.
E-MBS Control Signaling: This block broadcasts the E-MBS scheduling and logical-to-physical channel
mapping to facilitate E-MBS receiving and power saving. This also helps when E-MBS may have its own frame
structure in cases where dedicated carriers are used for E-MBS.
10 Medium Access Control Sub-Layer
10.x. E-MBS MAC Support
10.x.1 E-MBS Zone Configuration
Each E-MBS zone has a unique zone ID, and consists of at least one BS. All the BSs in an E-MBS zone shall
broadcast the same E-MBS zone ID. If a BS belongs to several E-MBS zones, it shall broadcast all the zone IDs
with which it is associated.
10.x.2 E-MBS Inter-Zone Mobility Management
For a MS with its unicast MAC in active mode, handover in unicast occurs when the MS crosses the cell
boundary. If the cell boundary is also the boundary for a new E-MBS zone, the MS shall do inter-EMBS-zone
handover as well. This procedure is illustrated in Figure 5y.
For a MS with its unicast MAC in idle mode, location update in unicast occurs when crossing paging area
boundary as illustrated in Figure z. The MS shall do inter-E-MBS-zone handover also if it is crossing E-MBSzone boundary also.
The MS could also cross E-MBS zone boundary without location update. In this case, the inter-E-MBS-zone
handover could be triggered by the following events.
1
4
IEEE C802.16m-08/1045
a. Neighbor-Zone Indication: The E-MBS control signaling may indicate if the present cell is at
the edge of the present E-MBS zone. Having detected this information, as illustrated in Figure
xx, the MS shall prepare and execute inter-E-MBS-zone handover with or without going back to
active mode.
b. E-MBS Signal Indication: The MS could implicitly detect the zone edge if the E-MBS signal
degrades below a certain threshold, which triggers the MS to search for new E-MBS zone with or
without going back to active mode as illustrated in Figure yy. The MS shall return active mode
during inter-EMBS-zone handover if required by the EMBS configuration, and complete
functions such as the renewal of EMBS registration. However, the MS could execute the interEMBS-zone handover without returning active mode if allowed.
Normal Operation
(Active Mode, EMBS)
Cross Cell
Boundary?
No
Yes
Complete Inter-Cell Handover
Cross EMBS Zone
Boundary?
No
Yes
Complete Inter-EMBS-Zone
Handover
Figure y: Inter-EMBS-Zone Handover (active mode)
1
5
IEEE C802.16m-08/1045
Idle Mode Operation
(EMBS)
No
Cross Paging Area?
Yes
Complete Location Update
Cross EMBS Zone
Boundary?
No
Yes
Complete Inter-EMBS-Zone
Handover
Figure z: Inter-E-MBS-Zone Handover during Location Update
BS-1
(EMBS zone i)
MS
BS-2
(EMBS zone i)
BS-3
(EMBS zone j)
Idle Mode
EMBS Flow
EMBS Flow (Edge of Zone i)
Active Mode
Inter-EMBS-Zone Handover
Idle Mode
EMBS Flow
Figure xx: Inter-E-MBS-Zone Handover (Zone-Edge Triggered)
1
6
IEEE C802.16m-08/1045
BS-1
(EMBS zone i)
MS
BS-2
(EMBS zone i)
BS-3
(EMBS zone j)
Idle Mode
EMBS Flow
EMBS Flow
EMBS Flow
EMBS Flow
Signal < Threshold
Inter-EMBS-Zone Handover
Idle Mode
EMBS Flow
Figure yy: Inter-E-MBS-Zone Handover (E-MBS Signal Level Triggered)
15 Support for Enhanced Multicast Broadcast Services
15.1 General Concepts
15.1.1 E-MBS Zone
The E-MBS content is transmitted over an area identified as a zone. An E-MBS zone is a collection of BSs
transmitting the same content. The contents are identified by the same identifiers (IDs). Each BS capable of EMBS service can belong to one or more MBS zones. Each MBS Zone is identified by a unique MBS_Zone ID.
15.1.2 E-MBS Operation Mode
15.2 E-MBS Procedures
E-MBS Service Registration/ De-registration: The signaling for this procedure shall be transparent to the BS
because the registration and de-registration happens between the MS and E-MBS flow server The following
options for the subscriber to register for E-MBS service are FFS:
I.
The registration could happen on a different interface not related to E-MBS MAC. The subscriber
could use unicast signaling for registration / de-registration of E-MBS service or a different interface
such as R-2 for registration.
II.
If using unicast channels for registration, the messages that the MS uses to register/maintain the E-MBS
service should be specified if the registration goes through the BS.
1
7
IEEE C802.16m-08/1045
1
8