IEEE C802.16m-08/207
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
A DL Control Structure in IEEE 802.16m
Date
Submitted
2008-03-10
Source(s)
Sungcheol Chang, Kwangjae Lim, Jaesun
Cha, Sungkyung Kim, Seokheon Cho,
Sunggeun Jin, Hyun Lee, Chulsik Yoon
ETRI
Voice: +82-42-860-5456
E-mail: scchang@etri.re.kr
kjlim@etri.re.kr
csyoon@etri.re.kr
ngkim@kyonggi.ac.kr
Namgi Kim
*<http://standards.ieee.org/faqs/affiliationFAQ.html>
Kyonggi University
Re:
IEEE 802.16m-08/005: Call for Contributions on Project 802.16m System Description
Document (SDD) - Downlink Control Structures
Abstract
This contribution provides a DL control structure based on super-frame structure.
Purpose
To discuss and adopt the proposed text in the next revision of the 802.16m SDD
Notice
Release
Patent
Policy
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A DL Control Structure in IEEE 802.16m
Sungcheol Chang, Kwangjae Lim, Jaesun Cha, Sungkyung Kim, Seokheon Cho, Sunggeun Jin,
Hyun Lee, Chulsik Yoon
ETRI
Namgi Kim
Kyonggi University
Introduction
In last meeting most of contributions about frame structure are based on super-frame concept. 802.16m Frame
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IEEE C802.16m-08/207
Rapporteur Group participants have discussed the 16m frame structure on the 16m reflector after the last
meeting and the Rapporteur Group chairs have provided an initial text which is based on the harmonized superframe structure.
The BS in the cellular system maintains and broadcasts radio configurations. This contribution shows signaling
structures of broadcast information and resource allocations in downlink. Several issues in the DL control
structures are mentioned in the followings while the system requirements of IEEE 802.16m are considered. Our
approaches in this contribution are based on the super-frame structure and maintaining the commonalities to
legacy system. The main items discussed in this contribution are in the followings:
-
Fixed-format BCH;
-
Broadcast information partitioning with two parts of fast period and relatively long period;
-
Supporting legacy broadcast management messages (UCD, DCD, NBR-ADV);
-
Broadcast message notification and scheduling
-
Paging message and its notification.
-
Downlink control signaling with heading and multiple MAPs (hybrid of joint/per-user coding).
-
Reducing resources required for allocating MAPs: subslot and blind decoding.
Broadcast Information Hierarchy
For broadcast of system information, we consider a hybrid of channel and message instead of a single type
message. In case a single type message is used, broadcast information does not have a hierarchical structure.
Therefore, an MS should receive the whole message although the MS does not need to acquire some parameters
included in the message and all the parameters included in the message should have the same broadcast period.
However, if a hybrid of a channel and message is used to broadcast system information, system parameters can
be distributed hierarchically into channels and messages based on required acquisition time of each system
parameter.
When we consider a hierarchy of broadcast information in 16m system, the enhancement points are as the
followings: 1) to avoid frequent MAP decoding of non-active users, 2) to avoid the FCH every frame, 3) to
obtain broadcast information for DL decoding quickly, 4) to broadcast variable information with a long period.
The BCH is introduced for BS to broadcast semi-static information for MAP decoding at relatively long period
without decoding DL MAPs in the sub-frames.
In this contribution a hybrid of two broadcast formats is proposed; BCH (Basic Control cHannel) and broadcast
messages, which are shown in Figure 1. BCH is fixed in size and includes static information such as frame
configuration, DL information for MAP decoding, etc. Because BCH is transmitted at the fixed position before
any DL-MAP every super-frame, MS can acquire the radio configurations from the BCH without decoding the
DL-MAP.
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IEEE C802.16m-08/207
Legacy System
16m System
Functionalities
16e Preamble
16m Preamble
Synchronization
DL-MAP
UL-MAP
Frame
Configuration
System
Information (DL)
16m BCH
Fast Information
Block
Basic Information
Block
Frame Control, Configuration
and Scheduling Information
Frame Configuration
16m Broadcast
Messages
Static Information
UCD
DCD
NBR-ADV
Sector
Information
(UCD/DCD)
System
Information
Neighbor BS
Information
DL/UL Detail Channel
Information
Neighbor BS Information and
their Broadcast Information
Figure 1. Functionalities of Broadcast Information in 16m
BCH consists of two information blocks: FIB (Fast Information Block) and BIB (Basic Information Block). The
broadcast period of FIB is a single super-frame but the broadcast period of BIB may be more than one superframe. By decoding of FIB and BIB, the MS acquires downlink radio frame configurations required to
synchronize with the radio frame, to decode the control signaling of resource allocation, and to receive bursts of
broadcast messages in downlink. Also broadcast messages include network entry and neighbor BS information.
For example, if an MS is turned on, the initial network entry is followed by the below procedures:
 PHY synchronization;
 Acquisition of DL frame configuration and scheduling from BCH;
 Acquisition of UL frame configuration.
Super-frame Header
Super-frame header is in first sub-frame in a super-frame and consists of preamble and BCH in order. Preamble
uses one symbol and its bandwidth in frequency is 5 MHz which is smallest one in the supported bandwidth
range at IEEE 802.16m SRD. New preamble is required for 16m system.
The some symbols except one symbol are fixed to the BCH. Because of its fixed size, there are two types of
broadcast information blocks: fast information block (FIB) and basic information block (BIB). The FIB is
repeated every super-frame. The BIB consists of a few tens of segments which are spread over several superframes. Figure 2 shows the BIB decoding after concatenation of “n” BIB segments. The number and size of BIB
segments are recommended to be fixed in the specification.
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IEEE C802.16m-08/207
Super-Frame
SFH
BCH
SFH
SFH
BIB (n/n)
FIB
Preamble
BIB (2/n)
FIB
Preamble
BIB (1/n)
FIB
Preamble
BIB (n/n)
BIB (2/n)
BIB (1/n)
FIB : Fast Information Block
BIB : Basic Information Block
SFH: Super-Frame Header
BCH: Broadcast Channel
BIB
Figure 2. BCH and Preamble in Super-Frame Header
The FIB may contain the followings:
-
Super-frame number LSBs;
-
Fast frame controls (load control, random access control);
-
Broadcast message versions (BIB counter, DCD counter, UCD counter, NBR-ADV counter);
-
Broadcast message change indicators (BIB change indicator, DCD change indicator, UCD change
indicator, NBR-ADV change indicator);
-
Super-frame offsets to indicate broadcast message bursts;
-
Paging message indicator;
-
Reserved field;
-
CRC.
The BIB may include the followings:
-
BIB counter;
-
Super-frame number MSBs;
-
Tx configuration;
-
Frame and DL Sub-frame configuration;
-
[the maximum number of MAPs, and MAPs’ MCS definition] these may be fixed in the
specification;
-
Multicarrier(wideband) information;
-
Reserved field;
-
CRC.
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IEEE C802.16m-08/207
Broadcast Messages and Notifications
Legacy DCD, UCD, and NBR-ADV management messages are reused mainly and refined with consistency of
the Broadcast Information Hierarchy in 16m system. Their details are out of the contribution. The FIB includes
broadcast message versions which consist of several counters about broadcast messages. The super-frame is
configured by broadcast messages of these broadcast message versions. The super-frame offset is transmitted to
notify MS of the duration from current super-frame to next super-frame of a burst of broadcast messages, shown
in Figure 3. If the MS gets the super-frame offset, decoding DL bursts for broadcast messages is not required
during the super-frame offset. Also the MS is informed of existence of new broadcast messages, which is
indicated by broadcast message change indicators. If a change indicator is set and the MS has not received a new
and correspondent broadcast message, the MS decodes DL sub-frames in the super-frame to receive it.
Super-Frame
Super-Frame
Super-Frame
SFH
BCH
FIB
0
FIB
FIB
1
Broadcast
messages
FIB
2
xx
Super-Frame
xx
Broadcast Message Super-frame Offset
Figure 3. Super-frame Offsets to a Burst of Broadcast Messages
Paging Message and Notification
Paging event occurrence is dynamic and unpredictable. Legacy PAG-ADV management message is reused to
keep consistency, and adopt its dynamics. Paging message indicator in the FIB notifies the MSs of existence of
PAG-ADV management message in the super-frame, shown in Figure 4. Only when the paging message
indicator is set, the MS decodes the DL sub-frames in the super-frame and get PAG-ADV management message
in a listening interval every paging cycle. If the BCH has a room enough to add paging information, the paging
indicator can be extended into n-bit indication of hash values with MS ID.
Super-Frame
Super-Frame
Super-Frame
SFH
BCH
0/1
FIB
FIB
1
PAG-ADV
message
FIB
0
0
Paging Message Indicator
Figure 4. Paging Message and its Indicator
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IEEE C802.16m-08/207
Heading and MAPs
Control signaling of resource allocation in downlink is updated and consists of Heading and MAPs. The
Heading is in fixed format and has the transmission format and length of each MAP. BS sends a Heading on first
logical slot(s) every DL sub-frame. Based on information indicated by the Heading, the MAPs transmitted in the
current DL frame shall be decoded by the MS.
Figure 5 illustrates the MAP pointing by the Heading. One or more MAPs are allocated consecutively after the
Heading. The first MAP block immediately follows the Heading. The following MAP blocks are transmitted in
the same way, in the order appearing in the Heading. The MAPs shall be ordered in the increasing order of
spectral efficiency of the MAP MCS and in the decreasing order of transmit power in case of the same spectral
efficiency.
MAP Heading
For 1 to NMAP
[MAP MCS]
MAP length
[MAP MCS]
MAP length
Power-controlled
MAP with MCS 0
and multiple IEs
(joint coding)
MAP #1 {
MAP IE
MAP IE
...
}
[MAP MCS]
MAP length
[MAP MCS]
MAP length
[MAP MCS]
MAP length
MAP Heading with a
fixed format
MAP MCS could be
omitted when blind
decoding
MAP #2 {
MAP IE
}
Power-controlled
MAP with MCS 0
and single IE
(per-user coding)
MAP #3 {
MAP IE
}
AMC-controlled
MAP with MCS 1
and single IE
(per-user coding)
MAP #4 {
MAP IE
MAP IE
}
AMC-controlled
MAP with MCS 2
and multiple IEs
(joint coding)
Figure 5. Heading and MAPs
To reduce radio resource required for multiple MAP transmissions, resources for MAPs are allocated in unit of
subslot. Contents in a MAP are variable and their granularity is small compared to normal slot, which is a basic
resource unit for traffic. The subslot is a basic resource unit for allocating MAPs. A MAP length in the Heading
is the number of subslots. Figure 6 illustrates that MAPs are pointed by their subslot length and the small size of
subslot increases resource utilization.
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IEEE C802.16m-08/207
Logical index for
normal slots
Slot 0
MAP Heading
Slot 1
Slot 2
1st MAP
2nd MAP
Slot 3
3rd MAP 4th MAP
Slot 4
Data burst
Slot 5
...
Logical index 0 1 2 3 4 5 6 …
for sub slots
MAP Heading {
MAP MCS 0
MAP subslot length = 14
MAP MCS 0
MAP subslot length = 8
14 subslots
8 subslots
7
7
subslots subslots
MAP MCS 1
MAP subslot length = 7
MAP MCS 2
MAP subslot length = 7
}
Figure 6. Heading, MAPs, and Subslots
To reduce the size of Heading as many as possible, the blind decoding of MAPs may be introduced. The
Heading contains only lengths of MAPs in subslots without MCS information of them. Firstly, a set of MCS
values applicable for MAPs broadcasts. The MS shall iterate decoding of a MAP burst with the MCS values and
if the MCS values between BS and MS match, the MS may receive the MAP successfully.
Proposed Text
[Add new sections after 11.6]
11.7 Synchronization
New preamble for synchronization is located at the first sub-frame in super-frame header. It uses one symbol
and its bandwidth in frequency is 5 MHz which is smallest one in the supported bandwidth range at IEEE
802.16m SRD.
11.8 Broadcast Information
BSs broadcast radio configurations in two formats: BCH and broadcast message. BCH has a fixed format and its
contents are static while broadcast messages are flexible to change contents. Without decoding the control
signaling of resource allocation, MSs acquire the radio configurations in the BCH. BCH is located at superframe header and appears every super-frame.
Information in the BCH consists of two parts: the fast and the basic. BSs broadcast fast information and basic
information every super-frame and a few tens of super-frames in periods, respectively. If an MS receives fast
information and basic information, the MS gets downlink radio frame configurations required for synchronizing
the radio frame, decoding the control signaling of resource allocation, and receiving bursts of broadcast
messages in downlink. For example, if an MS is turned on, the initial network entry is followed by the below
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IEEE C802.16m-08/207
procedures: 1) PHY synchronization, 2) acquisition of DL frame configuration and scheduling from BCH, and
3) acquisition of UL frame configuration.
Most of legacy DCD, UCD, and NBR-ADV management messages can be utilized and their current versions
and change indicators in BCH fast information are notified BCH Fast information includes broadcast message
versions which consist of several counters about broadcast messages. The super-frame is configured by
broadcast messages of these broadcast message versions in BCH fast information. The super-frame offset is
transmitted to notify MSs of the duration from current super-frame to next super-frame of a burst of broadcast
messages. Also the MSs is informed of receiving new broadcast message, which are indicated by broadcast
message change indicators. If a change indicator is set and the MSs do not have received a new and
correspondent broadcast message, the MSs shall decode DL sub-frames in the super-frame to receive it.
A legacy PAG-ADV management message is adopted to keep consistency, and accommodate the dynamics of
paging events. Paging message indicator in BCH fast information notifies MSs of existence of PAG-ADV
management message in asuper-frame
11.9 DL Control Signaling using Heading and MAPs
DL control signaling consists of Heading and MAPs. The Heading is in fixed format including the transmission
format and length of each MAP. A BS sends a Heading block on the first logical slots every DL sub-frame. One
or more MAPs are allocated consecutively after the Heading. The MAPs shall be ordered in increasing order of
spectral efficiency of the MAP MCS and in decreasing order of transmit power in case of the same spectral
efficiency.
In order to reduce MAP signaling overhead, resources for MAPs are allocated in unit of subslot, is a basic
resource unit for the allocations. . A MAP length in the Heading indicatesthe number of subslots.. Figure 7
illustrates that subslot length point MAPs in the Heading.
Logical index for
normal slots
Slot 0
MAP Heading
Slot 1
Slot 2
1st MAP
2nd MAP
Slot 3
3rd MAP 4th MAP
Slot 4
Data burst
Slot 5
...
Logical index 0 1 2 3 4 5 6 …
for sub slots
MAP Heading {
MAP MCS 0
MAP subslot length = 14
MAP MCS 0
MAP subslot length = 8
14 subslots
8 subslots
7
7
subslots subslots
MAP MCS 1
MAP subslot length = 7
MAP MCS 2
MAP subslot length = 7
}
Figure 7. An Example of Subslots and MAPs
Additionally, the blind decoding of MAPs is considered. The Heading contains only lengths of MAPs in
subslots without MCS information of MAPs. First, a set of MCS values applicable for MAPs are broadcast.
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IEEE C802.16m-08/207
MSs shall iterate decoding of a MAP burst with all the possible MCS values. If the MCS values between BS and
MS match the MS can receive the MAP successfully.
9