IEEE C802.16m-08/040
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
TDD Frame Structure for IEEE 802.16m
Date
Submitted
2008-1-16
Source(s)
Re:
Kevin Power, Sunil Vadgama and Chris
Williams, Fujitsu, London, UK
E-mail: kevin.power@uk.fujitsu.com
E-mail: sunil.vadgama@uk.fujitsu.com
E-mail: chris.williams@uk.fujitsu.com
Keiichi Nakatsugawa, Masato Okuda,
Fujitsu, Japan
Email: nakatsugawa@jp.fujitsu.com
Email: okuda@jp.fujitsu.com
Hua Zhou, Fujitsu, China
Email: zhouhua@cn.fujitsu.com
Yuefeng Zhou, NEC, London
Email: Yuefeng.Zhou@EU.NEC.COM
IEEE 802.16m-07/047 (“Call for contributions on Project 802.16m SDD”)
Target topic: “Proposed 802.16m Frame Structure with special attention to legacy support”
Abstract
This contribution proposes a TDD frame structure for the IEEE 802.16m system. The proposed
frame structure provides the required legacy support whilst allowing support for enhanced
feature MS. The frame structure is capable of evolving from a system supporting predominantly
legacy terminals to one which is supporting an ever increasing number of enhanced feature MSs.
The frame structure allows the BS to support a mix of IEEE 802.16m and legacy MSs when both
are operating on the same RF carrier, where the round-trip latency of the enhanced feature MSs
can be reduced whilst providing improved efficiency at high mobility due to the increased
frequency of CQI feedback.
Purpose
To be discussed and adopted by TGm for use in the IEEE 802.16m 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
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
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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>.
TDD Frame Structure for IEEE 802.16m
Kevin Power, Sunil Vadgama, Chris Williams,
1
IEEE C802.16m-08/040
Keiichi Nakatsugawa, Masato Okuda, Hua
Zhou, Fujitsu
Yuefeng Zhou, NEC
1.
Introduction
This contribution proposes a TDD frame structure that is flexible and therefore capable of adapting to a
system that is evolving from supporting predominantly legacy terminals to one which will be supporting an
increasing number of 16m terminals. The coexistence of both legacy and 16m terminals within the
proposed frame structure will have no impact on the performance of legacy MSs. Depending on the
required number of either legacy or 16m terminals that need be supported, the deployment will have the
ability to define a frame configuration where the number of subframes per frame is configured based on the
feature set of the operational subscriber stations and the mobility and latency requirements of enhanced
feature mobile stations (16m) such that the frame structure at all times retains sufficient features to support
the attachment of legacy stations that do not support the enhanced features of 16m.
The proposed frame structure meets the legacy support and latency requirements in sections 5.1 and 6.2 of
[1], respectively. Therefore, we would like this proposal to be considered for the TDD Frame Structure
section of the SDD.
2.
Design Considerations
Considering the legacy support requirements in Section 5.1 of [1] and in particular the requirement which
specifies that an IEEE 802.16m BS must support a mix of IEEE 802.16m and legacy MSs operating on the
same RF carrier, with the same channel bandwidth, then this can constrain the flexibility in the frame
structure design. In order for the 16m BS to support both 16m and 16e terminals then the necessary legacy
features must be present within the frame structure that will allow a legacy MS to access the network as if
served by a legacy BS. Therefore, it is critical that the legacy MSs can successfully proceed through the
Initialization, Access, Connected, and Idle states. For the Initialization state, the legacy preamble must be
transmitted every 5ms to allow the MS to perform scanning and DL synchronization. Following the legacy
preamble must be the FCH and DL-MAP to allow the MS to realize common control channel acquisition
followed by the detection of DCD/UCD which will provide information on the downlink and uplink
physical channels. For the Access state, an uplink Ranging region must be allocated for ranging and UL
synchronization which will allow for basic capability negotiation to begin, followed by MS authentication
etc, registration with serving BS and finally MAC CID establishment and IP address assignment.
Considering the case where a legacy MS is in connected state, then the frame must appear as if transmitted
from a legacy BS, therefore the 16m BS must emulate a 16e carrier and both 16m and 16e MS must coexist
within the same 5ms frame. Finally, for Idle state, the MS must maintain synchronization and be able to be
paged from a 16m BS. To summarize and complement the above, the following features must be present
within the 16m frame structure:

16e preamble (every 5ms)

FCH and DL-MAP following every 16e preamble

DCD/UCD transmitted every ith frame
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IEEE C802.16m-08/040

Uplink Ranging region allocated every jth frame

Allocated uplink ACK and CQICH regions (optional)
It is anticipated that the initial IEEE 802.16m network rollout will involve the deployment of IEEE 802.16m
BSs where a large percentage of terminals using these BSs will only support the legacy features specified in
the WiMAX forum profile (Release 1.0)[2]. However, it is also anticipated that over time this large
percentage will gradually decrease as most users will eventually switch from using legacy equipment to
using IEEE 802.16m terminals. It is therefore required that the IEEE 802.16m frame structure must be
capable of an almost seamless transition from a legacy-like system to an IEEE 802.16m system. The state
of this transition will solely depend on the percentage of legacy terminals wishing to access the network. As
the number of legacy users decrease then it would be expected that the performance of the IEEE 802.16m
MSs should improve and vice-versa. As the legacy and 16m MSs are to coexist within the same 5ms frame
and if the attachment of advanced feature MS’s increase, then one would expect the available resources for
these MSs to increase. Moreover, if the deployment is serving predominantly 16m terminals, then the
design of the TDD frame structure can be tailored to meet the latency and mobility requirements specified in
[1]. In this case, the 5ms frame consisting of a DL and UL subframe can be split into two DL and UL
subframes which can ultimately reduce round-trip latency and at the same time can improve support for
users travelling at high mobility as the CQI feedback frequency can be increased.
3.
TDD Frame Structure
As legacy support is currently confined to TDD mode only, then the following sections will define frame
structures for this mode only. It is important that the 16m frame structure can adapt and evolve over time
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IEEE C802.16m-08/040
and is simple, practical and efficient. The following sub-sections will provide example frame structures for
the evolution where the BSs will be supporting an ever increasing number of enhanced feature terminals.
3.1
Initial Frame Structure
As mentioned previously, the initial deployment will involve support for a higher number of legacy
terminals than of 16m, therefore the frame structure should be capable of supporting these terminals but
must also be capable of supporting advanced feature MSs. An example of such a frame structure is shown
in Figure 1, where both legacy and 16m terminals can coexist within the same 5ms frame.
5 ms
[18 symbols]
[29 symbols]
FCH
DL
UL
Ranging
DL Burst
UL Burst
Region
DL Burst
UL
MAP
UL Burst
As seen by
16m MS
P
R
E
A
M
B
L
E
DL Burst
P
R
E
A
M
B
L
E
DL Burst
UL Burst
DL
DL Burst
MAP
16m Zone
CQICH
16m Zone
Region
enhanced
features
enhanced features
DL Burst
UL Burst
DL Burst
DL Burst
UL Burst
UL
DL Burst
MAP
ACK
Region
16e and 16m
16m only
16e and 16m
UL Burst
16m only
RTG
FCH
TTG
[29 symbols]
[18 symbols]
DL
UL
Ranging
DL Burst
Region
DL Burst
UL Burst
UL
MAP
UL Burst
As seen by
16e MS
P
R
E
A
M
B
L
E
DL Burst
P
R
E
A
M
B
L
E
DL Burst
UL Burst
DL
DL
DL Burst
UL
MAP
CQICH
Region
DL Burst
GAP
GAP
UL Burst
DL Burst
DL Burst
UL Burst
UL
MAP
DL Burst
ACK
Region
16e and 16m
UL Burst
16e and 16m
16m only
TTG
16m only
RTG
Figure 1 – Initial Frame Structure
From Figure 1, it is clear that enhanced feature zones have been inserted into the DL and UL subframes
of the legacy frame. This will ensure that 16m MSs can utilise the enhanced features defined in the 16m
amendment of the IEEE 802.16 WirlessMAN-OFDMA specification. The access zone in the DL will be
transparent to legacy MSs and will be indicated by a STC_DL_ZONE_IE() with DIUC=13 in the DLMAP as this will ensure the legacy terminals will ignore the received signal within the zone. For the
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IEEE C802.16m-08/040
uplink, simply no allocations for legacy terminals shall be made within the enhanced feature access
zone. From a 16m perspective, the advanced feature zones in both DL and UL may be defined in the
DL and UL MAPs respectively by means of a new “pointer IE”. Note, it may be possible to increase or
decrease the size of the 16m only zone, depending on the number of enhanced feature terminals that
need be supported.
3.2
Low Latency Evolved Frame Structure
Although the frame structure in Figure 1 can support a mix of both legacy and 16m terminals, it may not
provide efficient support for high mobility cases as the CQI feedback frequency is limited to a minimum
of 5ms. Moreover, the effective data latency may be reduced due to H-ARQ retransmissions and as a
result, may not meet the requirements specified in section 6.2 of [1]. For these reasons, we are
proposing a low latency frame structure in which the legacy frame (5ms) is divided into two DL and UL
subframes as opposed to one DL and UL subframe. Figure 2 shows a high level overview of the
proposed frame structure where four legacy frames are concatenated together to form one 16m
“superframe” and where a legacy frame comprises of two 16m frames which contain one DL and UL
subframe each. Note, the concatenation of four legacy frames to form one 16m superframe is for
illustration purposes only and this issue is FFS. The adoption of a superframe concept will allow for a
signalling hierarchy to be introduced where the control signalling can be decomposed (i.e., some for the
superframe, some for the frames and some for the sub-frames) with the intention of reducing overhead.
16m Superframe n-1
16m Superframe n
16m Superframe n+1
Time
Legacy frame i-1
Legacy frame i
16m Frame j
TTG_1
Legacy frame i+1
Legacy frame i+2
16m Frame j+1
RTG_1
TTG_2
RTG_2
DL
UL
DL
UL
Subframe
Subframe
Subframe
Subframe
Legacy and 16m
16m only
16m only
Legacy and
16m
Figure 2 – Overview of Low Latency Frame Structure
It is clear from Figure 2 that legacy allocations must only be made in the DL subframe of 16m Frame j
and in the UL subframe of 16m Frame j+1. Note, the UL and DL subframes of 16m Frame j and j+1
respectively, shall only be used for 16m allocations and shall be transparent to legacy terminals.
Figure 3 takes a closer look at how the legacy frame may be broken into two DL and UL subframes,
where the new enhanced feature MSs will experience reduced round-trip latency and increased
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IEEE C802.16m-08/040
efficiency within the higher mobility classes when compared to legacy terminals. This can be achieved
by allocating 16m resources within the first DL subframe and then 16m uplink allocations in the first UL
subframe which will reduce the minimum CQI feedback to ~ 2.5ms.
16m enhanced feature Zone (transparent to legacy terminals)
5 ms
2.5 ms
2.5 ms
[14 symbols]
[9 symbols]
[14 symbols]
UL
DL
FCH
DL
[9 symbols]
UL
Ranging
DL
Burst
Region
UL
Burst
UL
MAP
UL
As seen by
16m MS
P
R
E
A
M
B
L
E
P
R
E
A
M
B
L
E
Burst
DL
Burst
UL
DL
Burst
16m
Zone
MAP
DL Burst
enhanced
features
16m Zone
16m Zone
enhanced features
enhanced features
16m
Zone
CQICH
Region
UL
enhanced
features
Burst
DL Burst
UL
Burst
UL
MAP
DL Burst
ACK
UL
Region
Burst
16e/16m
16e/16m
16m only
16m only
16m only
RTG_1
½ symbol
TTG_1
½ symbol
RTG_2
Legacy RTG
Same as
Legacy TTG
*****************************
Offset must be an integer number of
symbols from beginning of legacy UL
*****************************
Start of legacy UL
(depends on DL/UL ratio)
29sym+TTG
FCH
16m only
TTG_2
[29 symbols]
[18 symbols]
DL
UL
Ranging
DL
Burst
Region
UL
Burst
UL
MAP
UL
As seen by
16e MS
P
R
E
A
M
B
L
E
Burst
DL
P
R
E
A
M
B
L
E
Burst
UL
DL
Burst
DL GAP
MAP
UL
UL
CQICH
Region
DL Burst
Transparent to all legacy terminals
GAP
UL
GAP
Burst
DL Burst
UL
Burst
UL
MAP
DL Burst
ACK
Region
UL
Burst
16e/16m
16e/16m
TTG
RTG
Figure 3 – Evolved Low Latency Frame Structure
From Figure 3, it is clear that the 5ms legacy frame has been dissected into two DL and UL subframes
which are separated by TTGs and RTGs. The first consecutive DL and UL subframes (16m Frame j) that
will be available for 16m allocations will span 24 OFDMA symbols (including ½ symbol for TTG_1
and RTG_1). The second DL and UL subframes available for 16m will also span approximately 24
symbols, however in this case TTG_2 will be equivalent to the legacy TTG (105.87µs) as this will
ensure that legacy allocations begin on an integer number of symbols from the beginning of the legacy
uplink (i.e., NsymbolsDL+TTG). RTG_2 that precedes the preamble will also be equivalent to the legacy
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IEEE C802.16m-08/040
RTG (60µs) as this will ensure that the duration of two 16m Frames is exactly 5ms. Information
regarding the TTGs and RTGs is only required by enhanced feature terminals therefore it may be
transmitted as an extension of the legacy DCD/UCD.
Information regarding the start time of the 16m DL and UL subframes may be encapsulated within an
enhanced 16m DL and UL- MAP which may be present in the first 16m DL Zone and will be pointed to
by a pointer IE that may reside within the legacy DL-MAP. It shall be possible to increase or decrease
the size the 16m zones in the first DL subframe or the last UL subframe depending overall 16m terminal
load. It is important to note that the DL/UL ratio within a 16m Frame may be configurable and that the
fixed DL/UL ratio in Figure 3 is only for illustration purposes. From a 16e MS perspective, an
STC_DL_ZONE_IE() with DIUC=13 in the DL-MAP will indicate a gap in the legacy DL subframe
and for the uplink, simply no legacy allocations will be present within the specified enhanced feature
zones.
Figure 4 highlights the frame structures’ capability of adapting to a system that is evolving from
supporting predominantly legacy terminals to one which will be supporting an increasing number of
16m terminals.
5 ms
FCH
DL
DL Burst
UL
UL Burst
DL Burst
UL
MAP
P
R DL
E
A MAP
M
B
L
E
UL Burst
DL
DL Burst
Burst
UL Burst
16m
Zone
DL Burst
DL Burst
16m
Zone
UL Burst
DL Burst
DL Burst
UL Burst
UL
DL Burst
MAP
UL Burst
16e and 16m
16m only
16e and 16m
16m only
TTG
2.5 ms
DL
UL
FCH
RTG
2.5 ms
DL
UL
UL Burst
DL Burst
UL
MAP
P
R DL
E
A MAP
M
B
L
E
UL Burst
DL
Burst
DL
Bur
UL Burst
16m Zone
16m Zone
st
DL Burst
UL Burst
DL Burst
UL Burst
UL
DL Burst
MAP
UL Burst
16e and 16m
16m only
16m only
TTG_2
RTG_1
TTG_1
DL
16e and 16m
UL
DL
16m Zone
16m Zone
RTG_2
Evolution
UL
FCH
DL
Bur
st
UL
DL
Bur
MAP
P
R
DL
E
MAP
A
M
B
L
E
UL
MAP
st
DL Burst
16m
Zone
16m
Zone
DL Burst
DL Burst
16e/16m
TTG_1
RTG_1
16m only
TTG_2
UL
DL
16m Zone
16m Zone
RTG_2
UL
FCH
DL
16e/16m
16m only
16m only
16m only
P
R
DL
E
MAP
A
M
B
L
E
16m Zone
16m
Zone
UL
MAP
16e/16m
16m only
16m only
16m only
TTG_1
RTG_1
16e/16m
TTG_2
16m only
RTG_2
Figure 4 – Evolving Frame Structure
4.
Conclusion
It is clear from the previous figures that the proposed frame structure can allow:
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IEEE C802.16m-08/040



Systems based on IEEE 802.16m and the WirelessMAN-OFDMA Reference System to be able
to operate on the same RF carrier with the same channel bandwidth.
IEEE 802.16m BSs to support a mix of IEEE 802.16m and legacy MSs when both are
operating on the same RF carrier and the system performance with such a mix should improve
with the fraction of IEEE 802.16m MSs attached to the BS. (See Figure 4)
IEEE 802.16m BS to be able to support a legacy MS whilst also supporting IEEE 802.16m
MSs on the same RF carrier, at a level of performance equivalent to that a legacy BS provides
to a legacy MS.
It is also evident from Figures 2 and 3, that the 16m terminals will experience a significantly reduced
round-trip latency when compared to legacy terminals. This reduction in latency will facilitate in
faster CQI feedback by MS, which in turn will allow for improved efficiency for users travelling in the
higher mobility classes.
5.
Proposed Text
[Insert the following into Section 11 of [3].]
11.x Low Latency Frame Structure
An example frame structure is shown in Figure xxx.
A 16m “superframe” is created by the concatenation of four legacy TDD frames. The legacy frame is
divided into two DL and UL subframes where one 16m Frame comprises of a DL and UL subframe,
thus allowing two 16m Frames to reside within a legacy frame (16m Frame j and 16m Frame j+1).
The DL subframe of 16m Frame j begins with a legacy preamble followed by a legacy FCH, DL-MAP,
and possibly UL-MAP. The legacy DCD/UCD shall be broadcast periodically. This subframe may be
used for legacy and 16m allocations but may also contain a zone for 16m allocations only. The UL of
16m Frame j shall be used for 16m only as will the DL subframe in 16m Frame j+1. From a legacy
perspective, the 16m only zones shall be transparent and will be indicated by a STC_DL_ZONE_IE()
in the DL-MAP. The UL subframe in 16m Frame j+1 shall contain a zone for legacy and 16m
allocations where a legacy ranging region must be present. This UL subframe may also contain a 16m
only zone. As the 16m Frame structure consists of a DL sub-frame period and a UL sub-frame period
then in each frame, the TTG shall be inserted between the DL sub-frame and the UL sub-frame. The
RTG shall be inserted at the end of each 16m Frame.
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IEEE C802.16m-08/040
16m Superframe n-1
16m Superframe n
16m Superframe n+1
Time
Legacy frame i-1
Legacy frame i
16m Frame j
Legacy frame i+1
Legacy frame i+2
16m Frame j+1
FCH
2.5 ms
2.5 ms
Ranging
Region
DL
Burst
UL
MAP
UL Burst
DL
P
R DL
E
A MAP
M
B
L
E
Burst
UL Burst
16m
Zone
DL Burst
enhanced
features
16m Zone
16m Zone
enhanced features
enhanced features
16m
Zone
enhanced
features
UL Burst
DL Burst
UL Burst
UL
MAP
DL Burst
UL Burst
16e/16m
DL
16m only
TTG_1
½ symbol
16m only
16m only
UL
DL
RTG_1
½ symbol
16e/16m
TTG_2
Legacy TTG
16m only
UL
RTG_2
Legacy RTG
Figure XXX – Example of IEEE 802.16m OFDMA frame in TDD mode
6.
References
[1]
IEEE 802.16m-07/002r4, “IEEE 802.16m System Requirements”
[2]
WiMAX Forum™ Mobile System Profile, Release 1.0 Approved Specification
(Revision 1.4.0:19 2007-05-02)
[3]
IEEE C802.16m-07/320r1, “Draft Table of Content for the IEEE 802.16m System Description
Document”
9