Slide 1

802.16m HARQ

Document Number: C802.16m-08/340

Date Submitted: 2008-05-05

Source:Sean McBeath, Juejun Liu, Jianmin Lu Voice:Huawei Technologies E-mail: {smcbeath, juejunliu, lujianmin}@huawei.com

Fang Huiying fang.huiying@zte.com.cnZTE

Dong Xiaolu, Du Ying {dongxiaolu, duying}@mail.ritt.com.cn CATR*<http://standards.ieee.org/faqs/affiliationFAQ.html>

Venue: IEEE 802.16m-08/016r1: Call for Contributions on Project 802.16m System Description Document (SDD).Target topic: “Hybrid ARQ (protocol and timing)”.

Base Contribution: None

Purpose:Discussion and approval by TGm for the 802.16m SDD

Notice: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.

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<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 >.

Slide 2

Introduction• For HARQ, there are three main scheduling options: dynamic scheduling

(802.16e), semi-persistent scheduling (802.16 Rev. 2), and persistent

scheduling, all of which are illustrated on the next slide.

• In these slides, we focus on the following two issues

- Timing associated with transmission of acknowledgement information

• Applies to all three scheduling options

- HARQ timing for persistent scheduling

Slide 3

HARQ Scheduling OptionsDynamic Scheduling

Variable Variable Variable

Semi-Persistent Scheduling

time

Pre-Defined Resource Dynamic Resource

Persistent Scheduling (Synchronous HARQ)

HARQ RTT

1st HARQ Transmission of Packet 1

1st HARQ Transmission of Packet 2

Variable Variable

Slide 4

Minimum Processing Time

For DL traffic, the MS requires a minimum amount of time to decode a

burst before transmitting acknowledgement information. In these slides,

we use a value of 3 subframes.

Receive Packet

Transmit Acknowledgement

Information

Minimum Processing Time

Slide 5

Minimum Scheduling Time

For DL traffic, the BS requires a minimum amount of time to process

acknowledgement information before transmitting a subsequent packet or

a HARQ retransmission. In these slides, we use a value of 2 subframes.

Transmit Subsequent Packet or

HARQ Retransmission

Receive Acknowledgement

Information

Minimum Scheduling Time

Slide 6

Timing of Acknowledgement Information

Downlink Uplink Downlink Uplink

For each TDD ratio, for each subframe, the timing relationship between the reception of the packet and the transmission of acknowledgement information should be predefined. The example above represents the 5:3 TDD ratio. This relationship should exist for dynamic scheduling, semi-persistent scheduling, and persistent scheduling.

Slide 7

Overview of Synchronous HARQ• With asymmetric TDD, the period associated with synchronous HARQ cannot

be the same for all mobile stations or cannot be the same for all time

• In the following slides, we present two timing options for synchronous HARQ

Slide 8

Synchronous HARQ Option 1

5

5

5

5

10

10

Uplink Downlink Uplink

average HARQ latency

Downlink Uplink Downlink

Downlink Uplink Downlink

Uplink Downlink Uplink

A

B

C

D

E

F

A

B

C

D

E

F

Slide 9

Synchronous HARQ Option 2

A

B

C

D

E

F

A

B

C

D

E

F

6

6

6

6

6

6

average HARQ latency

Downlink Uplink Downlink Uplink Downlink Uplink

Downlink UplinkDownlink Uplink Downlink Uplink

Slide 10

VoIP Timing Diagram for Synchronous HARQ Option 1

VoIP Packet Arrival Rate (No Jitter) Transmission Opportunities

0 10 20 30 40 50 60 70 80 90 100-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

time(msec)

Slide 11

VoIP Timing Diagram for Synchronous HARQ Option 2

VoIP Packet Arrival Rate (No Jitter) Transmission Opportunities

0 10 20 30 40 50 60 70 80 90 100-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

time(msec)

Slide 12

Tradeoffs• Advantages of Option 1

- More straightforward scheduler implementation

- DRX cycles are periodic

- Lower minimum HARQ timing

• Disadvantages of Option 1

- HARQ timing is not consistent for all assignments

• Advantages of Option 2

- Lower average HARQ timing

- HARQ timing is consistent for all assignments

• Disadvantages for Option 2

- Less straightforward scheduler implementation

- DRX cycles are not periodic

- Small time difference between jitter free VoIP packet arrival rate and

transmission opportunity

Slide 13

Synchronous HARQ Option 1A

Downlink Uplink

In the example above, for a TDD ratio of 5:3, persistent scheduling can only be initiated in subframes 0-3. In sub-frame 4, persistent scheduling is prohibited, so dynamic scheduling or semi-persistent scheduling must be used.

To simplify operation, we could impose a restriction that persistent scheduling (synchronous HARQ) can only be used when the frame structure allows the time between retransmissions to be 5 msec. In other cases, dynamic scheduling or semi-persistent scheduling must be used.

Slide 14

Open Issues

• Comparing persistent scheduling (synchronous HARQ) to semi-persistent

scheduling, there are two open issues:

- In synchronous HARQ, we need to predefine the first HARQ

transmission or define a start of packet indication.

- In synchronous HARQ, holes in the time-frequency space are created

due to HARQ early termination. We need to define an efficient

mechanism to fill these holes.

• For example, some mobile stations are assigned fixed resources

for synchronous HARQ, while other mobile stations are assigned

dynamic resource for synchronous HARQ (resource adaptive

synchronous HARQ).

Slide 15

Proposed TextInsert the following text into the Medium Access Control Sub-Layer (i.e. Chapter 10 in IEEE 80216m-08_003r1.pdf):------------------------------- Text Start ---------------------------------------------------

10.1 Timing of Acknowledgement InformationFor each TDD ratio, for each subframe, the timing relationship between the reception of the packet and the transmission of acknowledgement information shall be pre-defined in the standard with a minimum value of 3 subframes (i.e. if the traffic occurs in sub-frame N, then acknowledgement information shall be transmitted no earlier than sub-frame N+4)..

10.2 Synchronous HARQFor synchronous HARQ, the period of the allocation shall be an integer number of radio frames.