1. Advanced ARQ for Relays Document Number: IEEE S802.16m-10/0002r1 Date Submitted: 2010-01-04 Source: Gauri Joshi E-mail : karandi@ieee.org Nirbhay Rane B. Srinadh Abhay Karandikar Prateek Kapadia (TICET, IIT Bombay) Shantidev Mohanty Muthaiah Venkatachalam (Intel Corp.) Re:IEEE 802.16m-09/0058r4: Letter Ballot Recirc #30b, Target Topic: IEEE P802.16m/D3: Section 16.6.2.8 Purpose: Supporting analysis for contribution C802.16m-10/0002 : Advanced ARQ for Relays 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: and.http://standards.ieee.org/guides/bylaws/sect6-7.html#6http://standards.ieee.org/guides/opman/sect6.html#6.3 Further information is located at and.http://standards.ieee.org/board/pat/pat-material.htmlhttp://standards.ieee.org/board/pat

2. Analysis of Advanced ARQ for 16m Relays

3. Hop-by-hop ARQ (as in D3) ABS clears packets ACKed by ARS, before they are received at AMS Thus, when an ARS-ABS or inter-ARS handover takes place, the packets queued at ARS are lost

4. Proposed A-ARQ protocol ABS maintains 2 ARQ pointers for relay and access links. Clears packets only after A-ACK No packet loss during handover

5. Motivation Hop-by-hop ARQ ▫Least packet delay and signaling overhead ▫But there is packet loss during handover Advanced ARQ ▫Signaling overhead due to additional ACK ▫2 ARQ pointers help avert packet loss during handover Through analysis we show that: ▫A significant packet loss is avoided by A-ARQ ▫Overhead of additional feedback is very small

6. Outline ARQ queue analysis ▫Theoretical derivation and simulations are performed to determine queue at ARS at the time of handover. ▫In the existing protocol these packets are lost during handover. Loss is averted by use of A-ARQ. Packet delay analysis ▫ The overhead due to the ACK over the existing protocol is insignificant

7. Handover Model Assume that a relay to relay handover takes place when there are N consecutive bad states

8. Parameter analyzed ▫Average queue length at relay at the time of handover ▫Handover probability ▫Percentage packet loss due to handover Theoretical derivation ▫Markov chain steady state analysis System level simulations ▫Go-Back-N ARQ protocol (Window size=4) ▫Handover model as described earlier Analysis of handover

9. Average Queue Length vs P 1 Relay buffer size = 50 No. of consecutive bad states to trigger handover = 5 Prob. of relay channel being bad = 0.2 Queue length shoots up around p1 =0.2 because for p1>0.2 the access link is worse than relay link. The queue length decreases later because the AMS hands over before the queue can build up

10. Packet Delay Analysis A-ARQ causes only a slight increase in packet delay over hop- by-hop % overhead <=k/(1+k) where k=T ACK /T PKT

11. Implementation In 16m, the ARS needs to convey the ARQ pointer of the AMS to the ABS The additional feedback can be sent to ABS in following possible ways: 1. After each packet is received by AMS. This will also help in flow control. 2. Only when handover of the AMS is triggered Compatible with both L2 and L3 relays (for e.g in L3, A_ACK will be sent on R8)

12. State transition diagram of A-ARQ

13. Conclusion Queue at relay at the time of handover. ▫ In the existing hop-by-hop protocol these packets are lost or highly delayed ▫ In proposed protocol there is seamless handover due to the 2 ARQ pointers at the ABS. Packet delay analysis ▫ The overhead due to the ACK over the existing protocol is insignificant