Tri-State HARQ Feedback for Aggressive HARQ Transmission IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number: IEEE C802.16m-09/1465r1 Date Submitted: 2009-7-15 Source: Zheng Yan-Xiu, Yu-Chuan Fang, Chang-Lan Tsai, Chung-Lien Ho E-mail: zhengyanxiu@itri.org.tw. ITRI Venue: IEEE 802.16m-09/0028r1, Call for contributions on 16m AWD content “Comments on AWD 15.3.6.5.2.8 HARQ Feedback A-MAP IE” Base Contribution: IEEE C802.16m-09/0894r4 Purpose: To be discussed and approval by IEEE 802.16m TG 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. 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 >.

Motivation Question 1: 1~5USD cost reduction can be achieved for each AMS device? Question 2: 10 times throughput can be provided for an AMS given a HARQ soft buffer constraint? Question 3: Reliable wireless link can be achieved when 10 times throughput is operated? This three questions can be answered by YES. This contribution provides the solution.

Aggressive HARQ Transmission Tri-state HARQ mechanism If decoded data is correct, MS feedbacks ACK If decoded data is incorrect and the redundancy version can be completely stored in the HARQ buffer, MS feedbacks NACK If decoded data is incorrect and redundancy version can not be completely stored in the HARQ buffer, MS feedbacks DROP BS will retransmit the dropped packet when DROP is received, otherwise, BS will follow existing HARQ mechanism

Tri-State HARQ feedback Aggressive HARQ transmission operates the HARQ mechanism beyond HARQ soft buffer capacity. 1~5 USD might be saved by reducing at least 100K~300K soft bits (5~30% ASIC size) on AMS side Unreliable wireless transmission occurs due to lost of packet if 10 times transmission rate operates We can not enjoy 10 times transmission rate and 1~5 USD cost reduction due to unreliable wireless transmission Solution: Tri-State HARQ feedback maintains reliable wireless link The feedback facilitates HARQ buffer management by three states ACK/NACK/DROP

Tri-State HARQ and HARQ Error Handling MAC Complexity Verification HARQ Error Handling, AWD Draft 10r2, Page 47, Line 31-34 “In the absence (NULL detection) of an ACK or a NACK in the HARQ feedback channel assigned in the DL/UL Individual Persistent A-MAP IE, the ABS shall assume that the AMS has not received the DL/UL Individual Persistent A-MAP IE and the same DL/UL Persistent A-MAP IE can be transmitted again.” No significant changes imposed to HARQ procedure and product => This can be the same as the procedure when the DROP received on transmitter side

Simulation Environments Three mechanisms are compared Tri-State HARQ feedback Two-State HARQ feedback with buffer constraint Two-State HARQ feedback without buffer constraint Simulation Environments Each HARQ burst has 4800 bits Maximum 8 HARQ processes Maximum 4 successful transmissions HARQ buffer ranges from 10K to 80K soft bits Round trip delay=20ms Peak rate= 1.92Mbps No feedback error PB 3km/hr, VA 30km/hr and 120km/hr Aggregated buffer is applied

IR-HARQ with PB 3km/hr No CQI Report Error Transmission rate increases by 2~10 times for tri-state HARQ mechanism and two-state HARQ mechanism without buffer constraint No transmission occurs if HARQ soft buffer is insufficient Only half of transmission rate occurs when 80K HARQ soft bits are on AMS side Two-state HARQ mechanism introduces larger HARQ failure rate when HARQ buffer is insufficient

IR-HARQ with VA 30km/hr No CQI Report Error Transmission rate increases by 2~10 times for tri-state HARQ mechanism and two-state HARQ mechanism without buffer constraint No transmission occurs if HARQ soft buffer is insufficient Only half of transmission rate occurs when 80K HARQ soft bits are on AMS side Two-state HARQ mechanism introduces extremely larger HARQ failure rate when HARQ soft buffer is insufficient Two-state HARQ mechanism introduces large HARQ failure rate when HARQ buffer is below than 1/3 of HARQ soft buffer (60K soft bits)

IR-HARQ with VA 120km/hr No CQI Report Error Transmission rate increases by 2~10 times for tri-state HARQ mechanism and two-state HARQ mechanism without buffer constraint Tri-state further provides throughput gain by 30% when there is only10K HARQ soft buffer Two-state HARQ mechanism introduces large HARQ failure rate when HARQ buffer is below than 1/3 of HARQ soft buffer (60K soft bits)

Summary of Observations Tri-state HARQ feedback sustains highest throughput for all range of HARQ soft buffer without degraded wireless transmission Two-state HARQ feedback without buffer constraint renders high throughput but Lose link reliability when only 1/3 HARQ soft buffer exists Lose by 30% transmission rate to tri-state HARQ feedback when no sufficient HARQ buffer exists at high mobility scenario

Conclusion Three objectives are accomplished by tri-state HARQ feedback 2~10 times throughput enhancement 1~5 USD per AMS chip cost reduction Reliable wireless transmission is guaranteed It highly increases the system utilization and throughput when scarce AMSs are located within a cell No significant complexity imposed to MAC procedure

Text Proposal [Add the following subclause after 15.3.6.4.2.7] Aggressive HARQ Feedback A-MAP IE includes two bits and corresponding value for HARQ ACK/NACK/DROP information is shown in Table XXX. If AHF-A-MAP IE has the 0b00, 0b01 or 0b10, it shall be interpreted as ACK information, NACK information and DROP information, respectively, where DROP indicates that HARQ soft buffer is insufficient to store the current transmission... Table XXX—AHF-A-MAP-IE Syntax Size (bit) Notes AHF-A-MAP IE format { AHF-A-MAP IE value 2 0b00 : ACK feedback info. 0b01 : NACK feedback info. 0b10: DROP feedback info. 0b11: Reserved }

APPENDIX

Overhead Clarification

Overhead issue Tri-state feedback channel is only applied for aggressive HARQ transmission mode, e.g. long burst service Less resource shared by other users More concurrent HARQ feedback channels Bi-state feedback channel is applied for normal HARQ transmission mode, e.g. VoIP Configuration example: 4 LRUs is configured for UL feedback channels Tri-State HARQ feedback : 24 tri-state HARQ feedbacks (2 LRU)+36 1-bit HARQ feedbacks (2LRU) Transmitting large packet (≧50Kbits) with limited overhead is reasonable Nice-State two channel HARQ feedbacks: 36 tri-state HARQ feedbacks (2LRU)+36 1-bit HARQ feedbacks (2LRU) Transmitting more HARQ processes to increase throughput is reasonable

An Example of Overhead Calculation 96 LRU per subframe @ 20MHz 100Mbps @ Downlink 500Kbps per 5ms frame 16 concurrent HARQ processes per 5ms 31250 bps per HARQ process 16 HARQ feedbacks per 5ms 16 Tri-State feedback occupies 4/3 LRU => 2LRU = 2.08% per UL subframe Transmission (bits)/HARQ overhead (LRU) > 250K bits/LRU (high efficiency) 8 concurrent HARQ processes per 5ms 62500 bps per HARQ process 8 HARQ feedbacks per 5ms 8 Tri-State feedback occupies 2/3 LRU => 1LRU = 1.04% per UL subframe Transmission (bits)/HARQ overhead (LRU) > 500K bits/ LRU (high efficiency) VoIP: 26Kbps per user and 18 concurrent users 520bits per 20ms frame 18 concurrent users share one LRU for HARQ feedback (Intel, Samsung, LGe,…etc) Transmission (bits)/HARQ overhead (LRU)= 9.36K bits/LRU (Low efficiency) Feedback overhead is very minor for high throughput transmission

AGGRESSIVE IR-HARQ TRANSMISSION WITH 3DB CQI REPORT ERROR

IR-HARQ with PB 3km/hr 3dB CQI Report Error Transmission rate increases by 2~8 times for tri-state HARQ mechanism and two-state HARQ mechanism without buffer constraint At high SNR, aggressive HARQ mechanism provides more transmission rate Tri-state HARQ mechanism further provides throughput gain when buffer is insufficient Two-state HARQ mechanism introduces large HARQ failure rate when Buffer is insufficient

IR-HARQ with VA 30km/hr 3dB CQI Report Error Transmission rate increases by 2~8 times for tri-state HARQ mechanism Aggressive HARQ mechanism increases more throughput when SNR is high Two-state HARQ mechanism introduces large HARQ failure rate when HARQ buffer is below than 60K soft bits or SNR is below than 16dB Two-state HARQ mechanism introduces less transmission rate due to high HARQ failure rate

IR-HARQ with VA 120km/hr 3dB CQI Report Error Transmission rate increases by 2~8 times for tri-state HARQ mechanism Aggressive HARQ mechanism increases more throughput when SNR is high Two-state HARQ mechanism introduces large HARQ failure rate when HARQ buffer is below than 60K soft bits or SNR is below than 16dB Two-state HARQ mechanism introduces less transmission rate due to high HARQ failure rate

AGGRESSIVE CC-HARQ TRANSMISSION WITH NO CQI REPORT ERROR

CC-HARQ with PB 3km/hr No CQI Report Error Transmission rate increases by 2~8 times for tri-state HARQ mechanism Two-state HARQ mechanism introduces large HARQ failure rate when HARQ buffer is below than 60K soft bits Link reliability significantly decreases due to highly correlated channel condition

CC-HARQ with VA 30km/hr No CQI Report Error Transmission rate increases by 2~8 times for tri-state HARQ mechanism Two-state HARQ mechanism introduces large HARQ failure rate when HARQ buffer is below than 60K soft bits Tri-State HARQ mechanism provides better link quality

CC-HARQ with VA 120km/hr No CQI Report Error Transmission rate increases by 2~8 times for tri-state HARQ mechanism Two-state HARQ mechanism introduces large HARQ failure rate when HARQ buffer is below than 60K soft bits Tri-State HARQ mechanism provides better link quality

AGGRESSIVE IR-HARQ TRANSMISSION WITH 3DB CQI REPORT ERROR

CC-HARQ with PB 3km/hr 3dB CQI Report Error Transmission rate increases by 2~8 times for tri-state HARQ mechanism Two-state HARQ mechanism introduces large HARQ failure rate when HARQ buffer is below than 60K soft bits Link reliability significantly decreases due to highly correlated channel condition

CC-HARQ with VA 30km/hr 3dB CQI Report Error Transmission rate increases by 2~8 times for tri-state HARQ mechanism Two-state HARQ mechanism introduces large HARQ failure rate when HARQ buffer is below than 60K soft bits Tri-State HARQ mechanism provides better link quality

CC-HARQ with VA 120km/hr 3dB CQI Report Error Transmission rate increases by 2~8 times for tri-state HARQ mechanism Two-state HARQ mechanism introduces large HARQ failure rate when HARQ buffer is below than 60K soft bits Tri-State HARQ mechanism provides better link quality