PMI Feedback Mechanism IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number: C802.16m-09/0154 Date Submitted: 2009-1-05 Source: Yang SONG, Liyu Cai, Hongwei YANG Voice: + 86-21-50554550-7796 E-mail: hongwei.yang@alcatel-sbell.com.cn *<http://standards.ieee.org/faqs/affiliationFAQ.html> Re: IEEE 802.16m-08/052 Call for Comments on Project 802.16m System Description Document (SDD) – Section 11.8.2.1.3 Purpose: For 802.16m SDD discussion and adoption 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 >.

Current PMI feedback status in SDD Due to the fact that channel variation is slow in time and/or frequency domain for slow mobility mobile station, and the sequence of the channel codewords is highly correlated, differential precoding matrix codebook is proposed to reduce the feedback overhead. Instead of full PMI, three different feedback modes for the PMI shall be supported for differential codebook: The standard mode: The PMI feedback from a mobile station shall represent an entry of the base codebook. It shall be sufficient for the base station to determine a new precoder. The adaptive mode: The PMI feedback from a mobile station shall represent an entry of the transformed base codebook according to long term channel information. (The transform method utilizes the channel correlation information to enhance the performance of the standard codebook especially in the highly correlated channel.) The differential mode: the feedback from a mobile station provides a differential knowledge of the short-term channel information. This feedback represents information that is used along with other feedback information known at the base station for determining a new precoder. To prevent error propagation, the standard mode feedback will be sent periodically.

Problem to solve Once the codebook is designed, it is hard for current differential feedback to alter the precoding precision to track the channel variation speed since the channel may vary very fast or slow time to time. What we need is a feedback mechanism that is of: Reduced feedback overhead Flexible to match the channel variation speed with different resolution levels More resolution levels may be desired Benefit: reduced PMI feedback overhead Challenges on feedback: Fast and flexible switching between codebook resolution level and/or branch coarse resolution level PMI for fast changing channels fine resolution level PMI for slow changing channels

Two types of PMI feedback Solution Two types of PMI feedback Absolute and relative PMI index feedback Control signaling feedback (via a physical layer control channel or via a higher layer signaling message) Indicate PMI resolution level moving up or down the resolution maintaining a certain resolution level Indicate same PMI used by transmitter in the next few feedback intervals so that no redundant PMI feedback is transmitted, also indicate quick recovery from the silent feedback state Etc.

Proposed comment to SDD Add to section 11.8.2.1.3 (line 35 on page 102, SDD IEEE 802.16m-08/003r6) ‘Besides absolute or relative PMI feedback, control signaling feedback can be used to indicate the PMI level changing, PMI holding on/off, etc.’