Data Forwarding for RS Group
IEEE 802.16 Presentation Submission Template (Rev. 9)
Document Number:
IEEE S802.16j-08/100r6
Date Submitted:
2008-09-16
Source:
Kanchei (Ken) Loa, Yi-Hsueh Tsai, Yung-Ting Lee, Hua-Chiang Yin,
Youn-Tai Lee, Chun-Yen Hsu
Institute for Information Industry (III)
Voice: +886-2-66000100
E-mail: loa@iii.org.tw
Gamini Senarath, Israfil Bahceci, Hang Zhang, Peiying Zhu,
Wen Tong, Derek Yu, Sun Sheng, Mark Naden
Nortel Networks
E-mail: gamini@nortel.com
Shiann-Tsong Sheu
National Central University (NCU)
E-mail: stsheu@ce.ncu.edu.tw
Yih-Guang Jan, Yang-Han Lee
Tamkang University (TKU)
*<http://standards.ieee.org/faqs/affiliationFAQ.html>
Venue:
IEEE-SA Sponsor Ballot: P802.16j/D6a
Base Contribution:
IEEE C802.16j-08/100r6
Purpose:
Text proposal for P802.16j/D6a Draft Document.
Notice:
E-mail: yihjan@mail.tku.edu.tw
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.
Release:
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.
Patent Policy:
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 >.
Data Forwarding Scheme in an RS
Group Defined in 16j/D6a
• When CID-based forwarding is used for
– Non-selective forwarding: all RSs members shall
transmit according to the MAPs received, without
using the per CID transmission
– Selective forwarding: using RS_Member_List_Update
message to update CID list at each RS, each RS
would look for the data bound to its subordinate
stations or data coming from the subordinate stations
in the uplink and forward in the assigned times
indicated in the MAP.
Issues of Non-selective CID-based
Forwarding in DL(1)
• MAC PDUs are concatenated into a burst by
MR-BS and then multicasted to all member RSs.
Each RS then partitions the burst into separate
PDUs by sequentially decoding each MAC PDU
header
– RS group members may decode different set of
“correct” PDUs when some PDUs are in error due to
interference on the relay links
– As a result, the RS group members will transmit
different burst “content” at the same allocation to an
MS Strong interference at MS
Issues of Non-selective CID-based
Forwarding in DL(2)
• Alternatively, the RS member which detects the
PDU errors stops its normal DL
forwarding/transmission operations related this
burst containing one or more error PDUs. But it
causes the following open questions
– Does the RS member need to send pilots with null
data?
• If yes, it would degrade the channel estimation performance
at the MS.
• If no, there would be no DL pilot when all RS members detect
at least one PDU error
Issues of Non-selective CID-based
Forwarding in UL
• As defined in 16j/D6a, there would be more than
one RS member designated to send UL data to
the MR-BS in the same allocations
• Two issues shall be resolved
– Similar to DL, RS members may send different PDUs
to the MR-BS when errors happen on the access link,
which will cause strong interference at the MR-BS
– How to perform ranging procedure, especially the UL
power control, when different RS member subgroups
are designated to transmit data to the MR-BS in the
same relay zone?
Issues on Selective CID-based
Forwarding
• In line 53 of page 66 of 16j/D6a, it defines
that the RSs receiving the
RS_Member_List_Update message may
respond with an MR_Generic_ACK or MR
Acknowledgement Header for confirmation
– ACK only since there is no way for the RS to
send NAK
Issues Raised by Using
RS_Member_List_Update Message (1)
• If the BS knows the processing latency
required by the RS, it can poll the RS for
the RS to send the ACK message or
header with minimum delay
– T1 >= (PHY + MAC) processing time
– Typically, T1 >= 3 frame (1 frame for Rx
message +1 frame for MAC processing + 1
frame for Tx ACK message)
MR-BS
RS_Member_List_Update
T1 >= 3 frame
MR_Generic_ACK, or
MR_Acknowledgement Header
RS
Frame Number Action
Issues Raised by Using
RS_Member_List_Update Message (2)
• The minimum Frame Number Action = T1
(PHY+MAC processing time) + T2 (Frame
Number Action cancellation)
• T2 >=3 frame (1 frame for BS MAC
processing + 1 frame for RS Rx message
+ 1 frame for RS MAC processing)
T1 >= 3 frame
T2 >= 3 frame
MR-BS
RS_Member_List_Update
X
Not Rx MR_Generic_ACK or RS_Member_List_Update
MR_Acknowledgement Header
RS(s)
Frame Number Action
Issues Raised by Using
RS_Member_List_Update Message (3)
RS2-MS connection gets very weak and
RS1-MS connection gets strong
MR-BS
RS1
Member_List_
Update
Assign MS to
RS1
-actiion time:
K1 frames
later
ACK
RS2
MS
served
by RS2
No ACK
Message
from any
RS
(data or
ack lost )
Member_List_Update
Assign MS to RS1
-action time: K2
frames later
ACK
Frame at which first
update message is
effective
ACK
Frame at which
retransmitted update MS
message is effective served
by RS1
MS
For 5 ms frame duration, 50 ms is 10 frames. Here delay can go
10-20 frames which is not desirable for delay sensitive services.
Why Self-contained Burst Transmission
is Necessary for RS Grouping (1)
• When an MS moves from one member RS
area to other RS coverage area, the
membership update message is sent to the
RS group. This message needs to be acked
by all the involved RSs in order to take this
change into effect.
• For this, there is an action time (say 5-10
frames). If an ack is not received from all
the involved RSs, the membership update
needs to be extended to another 5-10
frames.
Why Self-contained Burst Transmission
is Necessary for RS Grouping (2)
• During that time the services to MS in transition
is interrupted for their services. Current
handover transition interruption is 50 msec in the
profile.
• Ack failure may happen at MR-BS, and message
may be lost in the forward link by one of many
RSs.
• Therefore, we should define a forwarding
scheme which does not require the membership
list so that RSs can forward the data with zero
service disruption. The scheme is Burst-based
Forwarding Scheme.
Burst-based forwarding scheme
• In order to solve the data forwarding and
signaling overhead problem in relatively faster
varying environments as well as the inconsistent
data forwarding problem
• Including a DL_Transmit_Reference IE in the
MAP is to provide the selective forwarding
information to RSs.
• The overhead incurred based on this method
does not depend directly on the number of
connections, but rather depends on number of
bursts which can be minimized by proper
resource allocation methods.
Summary
• In RS_Member_List_Update without burst-based
forwarding scheme, the action time should be extended
to 11 frames in total if the RS_Member_List_Update or
ACK is lost at even one of the RSs. (5 frames for
detecting the lost and 6 frames for resetting the frame
number action time)
• The burst-based forwarding scheme optimizes the
control signaling overhead for resource allocation on the
R-link and enables efficient data forwarding from
transparent RSs and/or RS group members to their
subordinate MSs.
• RS_Member_List_Update with burst-based forwarding
scheme imposes 0 frame latency
• Adopt the contribution C802.16j-08/148