1. HARQ Timing Document Number: IEEE C802.16m-09/0287
Date Submitted:
Source: Yujian Zhang
Hujun Yin
Yuan Zhu
Intel Corporation
Re: IEEE m-08/053r1, “Call for Contributions on Project m Draft Amendment Content”. Target topic: “Channel coding and HARQ”
Venue: IEEE Session#59, San Diego
Base Contribution: C802.16m-09_0286.doc (or later versions)
Purpose: Discussion and Adoption by TGm
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2. Introduction
This contribution documents the design principles and provides examples for the HARQ timing amendment text in contribution C802.16m-09/0286.

3. Principles for HARQ Timing Design
For HARQ timing design in this document, following principles are applied:
For UL, start subframe position of retransmission is same as that of initial transmission.
Minimum processing time for receiver side is 3 subframes; minimum processing time for transmitter side is 2 subframes.

4. Processing Time
Processing time is the most important factor to consider
The larger the processing time, the smaller the impact on receiver implementation
The smaller the processing time, the less the latency.
Rx processing time
3 subframe delay is appropriate since the processing time is then 1.85 ms – RTT (1.85 = * 6 * 3), minimum value is 1.18 ms assuming 100 km cell radius (requirements as per section 7.4 of SRD).
Tx processing time
Tx processing time can be relaxed compared with Rx processing time. Considering the RTT, 2 subframe delay is appropriate.

5. Factors Related to HARQ Timing (1)
DL/UL Ratio
Number of subframes per frame
Generally, there are 8 subframes per frame.
In 7 MHz BW, there are only 6 subframes per frame.
Totally 34 OFDM symbols: 4 subframes with 6 OFDM symbols and 2 subframes with 5 OFDM symbols
In 8 MHz BW, there are 7 subframes per frame.
Totally 43 OFDM symbols: 6 subframes with 6 OFDM symbols and 1 subframe with 7 OFDM symbols.
Variable TTI
One TTI could contain multiple subframes. The processing time is defined with the reference to the end of the TTI instead of the start of the TTI. The rationale is that processing time should be reserved with respect to the end of data burst.

6. Factors Related to HARQ Timing (2)
Relay Zones
HARQ timing should be defined for BS/MS/RS when relay is used.
For MSs when relay is not used, the available DL/UL subframes might be different due to the introduction of relay.
Legacy 16e Zones
When mixed with legacy zones, the available DL/UL subframes for 16m transmissions are different.
Availability of ACKCH
DL: when n=2 is configured for USCCH, some subframes do not contain USCCH therefore DL ACKCH cannot be transmitted.

7. General Notations and Assumptions
Each subframe position is denoted with pair (m, n).
Frame index m.
Subframe index n: for each sub-frame, there is an associated sub-frame index n, with n=0 denoting the 1st sub-frame of the frame and n=7 denoting the last sub-frame of the frame (for 8-subframe-frame). Note that n is numbered continuously within the frame, irrespective DL/UL, legacy/16m/relay zones.
Starting subframe position for transmission is (m, n), ACKCH subframe position is (m’, n’), starting subframe position for retransmission is (m’’, n’’).
Total number of subframes per frame is Nsf, with possible values of 8, 7, and 6.
Number of subframes per TTI is NTTI.
Rx processing time is PRx=3 subframes, and Tx processing time is PTx=2 subframes.
nUSCCH=1 or 2 for USCCH.
Frame structure is constant for every frame.

8. FDD - Notations
There are possibly 2 idle regions with length of Ndg1, Ndg2 subframes for DL and length of Nug1, Nug2 subframes for UL. Each of Ndg1, Ndg2, Nug1, Nug2 could be 0.

9. FDD – Equations – DL HARQ
Timing relationship of USCCH and associated data.
When nUSCCH=1, start subframe of DL data transmission is same as corresponding USCCH.
When nUSCCH=2, 1 bit in USCCH indicate start subframe of DL data transmission is the same subframe or next subframe.
ACKCH timing

10. FDD – Equations – UL HARQ
Timing relationship of USCCH and associated data.
Explicit indication of the timing is needed.
ACKCH timing
Retransmission timing

11. FDD – Examples (1)
“Normal” case, nUSCCH=1, Nsf=8, NTTI=1,Ndg1= Ndg2= Nug1=Nug2=0.
DL HARQ
UL HARQ

12. FDD – Examples (2) nUSCCH=2, Nsf=8, NTTI=2,Ndg1= Ndg2= Nug1=Nug2=0.
UL HARQ

13. TDD - Notations
There are possibly 3 idle regions with length of Ng1, Ng2, Ng3 subframes respectively. Each of Ng1, Ng2, Ng3 could be 0.

14. TDD – Equations – DL HARQ
Timing relationship of USCCH and associated data.
When nUSCCH=1, start subframe of DL data transmission is same as corresponding USCCH.
When nUSCCH=2, 1 bit in USCCH indicate start subframe of DL data transmission is the same subframe or next subframe.
ACKCH timing

15. TDD – Equations – UL HARQ
Timing relationship of USCCH and associated data.
Explicit indication of the timing is needed.
ACKCH timing
Retransmission timing

16. TDD – Examples (1)
nUSCCH=1, D:U=5:3, with Nsf=8, NTTI=2,Ng1= Ng2= Ng3=0
DL HARQ
UL HARQ

17. TDD – Examples – nUSCCH=2 (2)
nUSCCH=2, D:U=3:2, with Nsf=8, NTTI=1,Ng1= Ng2= Ng3=1
UL HARQ

18. Benefits
Guarantee sufficient processing time for both transmitter side and receiver side.
Simple equations can handle various factors affecting HARQ timing.
Periodical retransmission timing. Retransmission can occur with the same subframe index, which allows periodical frame structure design for various patterns.