IEEE 802.16m DL Interference Mitigation Document Number: IEEE C802.16m-08/626 Date Submitted: 2008-06-07 Source: Shirish Nagaraj, Phil Fleming, Fan Wang E-mail: shirish.nagaraj@motorola.com Motorola *<http://standards.ieee.org/faqs/affiliationFAQ.html> Venue: TGm – Call for contributions on Project 802.16m System Description Document – IEEE 802.16m-08/024 (interference mitigation) Base Contribution: Abstract: Proposal for 16m downlink interference mitigation. Purpose: Adoption of proposed text/content for 802.16m System Description Document 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 >.

DL Interference Mitigation Background & Problem Latency-sensitive traffic (VoIP, video etc) capacity is determined by the air-interface delay outage. Coverage improvements even for other classes of traffic are highly desirable, especially to allow dynamic fractional frequency reuse Loading conditions in real deployments not known a-priori Objective is to improve coverage and reduce outage with minimal impact to system capacity: Interference Overload Feedback: feedback from MS to interfering cells to indicate interference overload Enables slow but dynamic adaptation of Fractional Frequency Reuse (FFR) patterns using feedback from all users Adapts to actual cell and traffic distributions as opposed to static power/bandwidth partitioning

Adaptive Interference Mitigation Interference mitigation by fractional frequency reuse (FFR) Partition total bandwidth into sub-bands Reduce power spectral density (PSD) on specific sub-bands to achieve interference relief to users in other cells Allocate different cells a priority ordering of sub-band usage – high priority indicates that the PSD will not be reduced, and low priority indicated PSD can be reduced on that sub-band A cell will schedule its bad geometry users to a high priority (Priority I) sub-band, and good users on the lowest priority (low PSD) sub-band Power distribution on sub-bands is not fixed a-priori Users have a periodic (slow) signaling opportunity to indicate interference overload on their sub-band Signal is sent over the air through the UL Interference Overload Feedback information Cells respond to the composite Interference Overload Feedback signal and reduce their PSD on specific sub-bands according to received power of received signal Achieves adaptation in FFR patterns autonomously, without having to fix power distributions

Adaptive FFR using Interference Overload Feedback Users in Priority I sub-band in all cells transmit Interference Overload Feedback indicating sub-band used In response to received Interference Overload Feedback indicating sub-band 2, Cell A will reduce PSD by a larger value compared to Cell C Default power configuration is equal PSD for all sub-bands Cells re-adjust their PSD levels after the reception of every Interference Overload Feedback signaling interval

Interference Relief using Interference Overload Feedback Slow adaptation of fractional frequency reuse patterns Depending on an aggregate metric of Interference Overload Feedback signal, a BS can decide how much power to reduce on a given sub-band to allow for “soft FFR” Signaling is fed back at a slow basis, and allows FFR to adapt to network-specific loading conditions Other cells know the sub-band request by the position/modulation of the Interference Overload Feedback Users will automatically reach their dominant interfering cells (immediate neighbors) Requires a pool of common resources allocated for Interference Overload Feedback signaling Users can send the Interference Overload Feedback in a CDM or FDM fashion All the Interference Overload Feedback signals corresponding to the same sub-band request will incoherently combine at each base-station receiver Cells will mute or reduce transmit PSD on those requested sub-channels for the a duration following the request till the next Interference Overload Feedback opportunity How much power to reduce depends on the total power of the received (composite) Interference Overload Feedback signal, and the sub-band priority for that cell Power of Interference Overload Feedback signal can be boosted to reach strongest interfering cell

Standards Support Required for Adaptive Interference Mitigation Ability for MS to transmit an Interference Overload Feedback signal on UL Can use a system-wide common pool of bandwidth for such signaling (UL common control channel) Signaling opportunities in time also defined system-wide, with a given periodicity Same Interference Overload Feedback signal is transmitted by all users corresponding to a given sub-band given incoherent combining gains at the cell site Signaling can be a CDM waveform modulated with on-off keying, with a specific signature sequence for each sub-band Users not experiencing outage (or lower than expected data rates), will not transmit any energy on Interference Overload Feedback signal Sub-bands defined can be logical (no need to be physically contiguous) See C80216m-08_275 on UL Interference Overload Feedback