IEEE C802.16m-08/984
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
Control Structure for Multicarrier Support
Date
Submitted
2008-9-5
Source(s)
Youngsoo Yuk, Inuk Jung, Ronny
Yongho Kim and Kiseon Ryu
Voice: +82-31-450-7808
E-mail: sixs@lge.com
LG Electronic Inc.
Re:
PHY: Multi-Carrier Operation; in response to the TGm Call for Contributions and Comments
802.16m-08/033 for Session 57
Abstract
This contribution covers the considerations about the control structure for supporting the
multicarrier system.
Purpose
To be discussed and adopted by TGm for use in the IEEE 802.16m SDD
Notice
Release
Patent
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Control Structure for Multicarrier-support
Youngsoo Yuk, Inuk Jung, Ronny Yong-ho Kim and Kiseon Ryu
LG Electronics
1. Introduction
In this contribution, we discuss various considerations on the control structure for supporting multicarrier. The
protocol architecture and the location of the control channels are mainly discussed.
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IEEE C802.16m-08/984
2. Protocol Architecture
In the current SDD text [1], the protocol architecture for multicarrier system is described as follows:
“A common MAC entity may control a PHY spanning over multiple frequency channels.”
The current description contains several potential meanings about detailed MAC structure. In our view, the main
consideration point is to separate multi-carrier data. Three possibilities can be considered; separation after ARQ
(a), after HARQ (b) and after channel coding (bit-level operation) (c). Figure 1 shows the description of the 3
different structures.
ARQ
ARQ
MAC
MAC
PHY
HARQ
HARQ
HARQ
HARQ
Carrier 1
Carrier 2
Carrier 3
PHY
(a) Dividing after ARQ function
Carrier 1
Carrier 2
Carrier 3
(b) Dividing after HARQ function
ARQ
MAC
HARQ
Channel Coding
Multiplexing
PHY
Carrier 1
Carrier 2
Carrier 3
(c) Dividing after Bit-level processing function
Figure 1. Three possible protocol architectures for multicarrier support
Table 1 shows pros and cons for each scheme.
Basically, as HARQ being related to the PHY structure, it is natural for transmitter to have one HARQ entity per
carrier (a). In addition, by using many HARQ processes, the flexibility of scheduling is improved. On the other
hand, it requires large buffer at the receiver ARQ entity.
For case (b), the MAC operation can be performed with little consideration of PHY conditions. In addition, we
can have opportunities to save the bandwidth by reducing the control signal common to all carriers (single
ACK/NACK, HARQ related parameters in the USCCH etc). However, it requires a new design of USCCH and
control channel structures to obtain the gain of bandwidth saving. Moreover, the retransmission loss is relatively
larger than case (a), because the size of the retransmission block may be larger than that of case (a).
The case (c) is similar to case (b) in terms of MAC issues. In addition, we can get more flexibility for using
various IR versions and various link adaptation techniques. However, it is difficult to apply different MCS for
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different carriers.
Even case (b) requires more design efforts of control channels, the optimization of the transmission of the
control channels may improve the performance of the multicarrier system. More discussion will help us to select
more efficient scheme among these candidates.
Dividing Position
(Transmitter Aspect)
After ARQ (a)
Advantages
Drawbacks
- Simple extension from single carrier to
multi-carrier
- Easy to extend the number of HARQ
processes
- Minimize retransmission loss
(retransmission is performed per
carrier)
After HARQ (b)
- Relative small ARQ window size and
buffer at the receiver
- Can reduce the size of the control
signal (ACK/NACK, HARQ related
parameters etc)
- Simple MAC operation without
considering PHY structure
- Similar to (b)
- More optimization for control
signaling is possible.
- Multi-carrier diversity and various IR
version
- Multiple HARQ process/soft buffer
- Large ARQ window size and buffer at the
receiver ARQ entity
- All control signaling should be performed
at every carriers (ACK/NACK, HARQ
parameters)
- MAC PDU generation is affected by PHY
structure
- Retransmission loss for large HARQ block
- Hard to increase the number of HARQ
process (constraint of time)
- New design of control channel is required
After Bit-level
Operation (c)
- Similar to (b)
- Hard to apply different MCS for different
carriers
3. Control Channel Structure
The most important consideration about the multicarrier control structure is the location of each control channel.
In this section, we discuss the several options for the downlink control channels. We consider the case where
one primary carrier and multiple secondary carriers are allocated to an MS.
A. BCH
The BCH is not dedicated to the MS supporting multicarrier. On the other hand, it should be received by all
MSs in the cell whether multicarrier is supported or not. Thus all the fully configured carriers should transmit
their BCH. However, the BS can transmit BS’s capability information about the support of the multicarrier via
BCH, and system information of the secondary carriers can be transmitted on the primary carrier for efficient
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IEEE C802.16m-08/984
multicarrier support.
B. USCCH
The main issue of the USCCH for multicarrier support is the location of USCCH. We can consider two
alternatives: (a) distributed or (b) centralized transmission.
In the distributed transmission scheme, the data burst and the corresponding USCCHs are transmitted through
the same carrier. On the other hand, the USCCHs for multiple carriers are transmitted only through the primary
carrier in the centralized transmission.
Table 2 shows the advantages and drawbacks for each case. Since the separately coded USCCH may be applied,
we assume that the blind detection is applied for detecting USCCHs.
Table 2. Comparison between the different schemes of the USCCH transmission.
Advantages
Drawbacks
Distributed
- Simple extension from single carrier to multi- Large searching space for blind
carrier (Reuse of same USCCH of singleUSCCH decoding
carrier)
- Limited ID resource
- Efficient with multiple HARQ entity
- Easy load balancing with partially configured
secondary carriers
Centralized
- Small searching space for blind USCCH
- New USCCH design for multidecoding
carrier support
- One Station ID is enough for multi-carrier MS
- Additional indication is required to
- Easy to adopt power saving for secondary
map between USCCHs and multicarrier
carriers
- Efficient with single HARQ entity
- Possible to reduce the USCCH overhead
C. ACK/NACK for UL Burst
The transmission of ACK/NACK bit for UL burst is deeply related to the protocol architecture. With case (a) in
figure 1, the same method as the single-carrier system can be applied for ACK/NACK.
However, with case (b) and (c), we can consider multiple options.
 Option 1: One single ACK/NACK at the primary carrier
 Option 2 : Multiple ACK/NACK for each carrier (Different ACK/NACK values for each carrier)
 Multiple CRC per carrier
 Possible to apply the selective retransmission
 Option 3 : Multiple ACK/NACK for each carrier (same ACK/NACK values)
 Single CRC
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 Same ACK/NACK values for diversity
D. UL Control Channels
For the uplink control channels, we can discuss about similar issues of the downlink control channels.
The location of feedback channel is a problem that needs to be addressed. In addition, in the SDD, since
asymmetric carrier allocation is possible, the transmission through the primary carrier seems to be efficient.
However, some channels, such as sounding channel, should be transmitted at every carrier.
E. MAC Management Messages
Two types of MAC management messages can be considered. The first is the unicast control messages. The
unicast control messages for an MS are transmitted through the primary carrier for efficient control.
However, in some case for supporting handover, secondary carrier can be used for receiving the unicast control
messages from the target BS [2].
The second is the additional broadcast information transmitted via data burst.
These messages should broadcast to all MSs without considering of multicarrier support. Thus basically, they
should be transmitted at every fully configured carrier. However, for paging related channels, it should be
transmitted at the primary carrier.
4. Conclusion
In this contribution, we discussed various considerations for the design of the control structures for
multicarrier support. From the comparisons, we propose to use the following options.
 Single HARQ entity through multiple carriers (Case (b))
 Most control channels are transmitted via the primary carrier
 One Station ID is used for identifying MS in a cell even for multicarrier support.
 To design special control channels for supporting multicarrier transmission
References
[1] IEEE 802.16m-08/003r4, The Draft IEEE 802.16m System Description Document, 2008-07-29
[2] IEEE 802.16m-08/995, Multi-Carrier Supported Handover Procedure, 2008-09-05
Text Proposal for the IEEE802.16m SDD
============================== Start of Proposed Text =================================
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IEEE C802.16m-08/984
11.7.4 Multi-carrier Control Structure
11.7.4.1 Downlink Control Strucuture
Each fully configured carrier has its own PBCH and SBCH. The capability of the BS, for supporting
multicarrier, is transmitted on the SBCH. A part of the information of the BCH of other carriers is transmitted
via SBCH or MAC management messages.
All USCCHs and the unicast control messages from the upper-layer (e.g. Handover, paging etc) for an MS
supporting multi-carrier are transmitted through the primary carrier of the corresponding MS.
11.7.4.2 Uplink Control Structure
Uplink feedback channels for multicarrier support are transmitted via the primary carrier.
For supporting multicarrier operation, the information about the preferred carriers can be included as a feedback
information.
To utilize the sounding channel, symmetric allocation of multicarriers should be supported. The sounding
channel is transmitted at every active carrier.
19.x Multicarrier Support Protocol Structure
MS has one Station ID even for communicating with multiple carriers.
There exists only one HARQ entity between the serving BS and the MS for multicarrier transmission.
============================== End of Proposed Text =================================
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