Downlink Symbol Structure Requirements for Supporting Adaptive Frequency Reuse in IEEE 802.16m Document Number: IEEE C802.16m-08/403r3 Date Submitted: 2008-05-08 Source: Hongmei Sun, Clark Chen, Hua Yang Email: {hongmei.sun, clark.chen, hua.yang, shilpa.talwar, Shilpa Talwar, Hujun Yin, hujun.yin, vladimir.kravstov, yuval.lomnitz}@intel.com Vladimir Kravstov, Yuval Lomnitz Intel Corporation Re: Call for Contributions on IEEE 802.16m-08/003r1 system Description Document (SDD) - Comment for downlink PHY structure Purpose: Discussion and approval 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 located at <http://standards.ieee.org/board/pat/pat-material.html> and <http://standards.ieee.org/board/pat >.

Outline Motivation AFR Requirements AFR Architecture Performance Standards support Symbol Structure Signaling Measurement and feedback Conclusions and recommendations

IEEE 16m SRD Requirements Meet 802.16m downlink Data requirement

Interference is serious problem with Reuse 1 Geometric SINR distribution in hexagon cell structure Geometric SINR under different reuse factors More than 30% of subscribers have average SINR below 0dB Worst SINR conditions seen at cell-edges Higher reuse helps improve SINR, but lowers cell capacity Solution: mixed reuse to tradeoff cell-edge performance with cell-capacity

Adaptive Frequency Reuse Concepts AFR RRM Interference-aware BS Coordination FFR (semi-static) FFR (dynamic) MAC Interference-aware Scheduling Uplink Power Control Interference Randomization PHY Rx Interference Mitigation Tx Beamforming

AFR Components Fractional frequency reuse (reuse partitioning): Restrict usage of certain frequencies or power level of these frequencies in a sector to minimize interference. Ex. allocate fraction of frequency sub-channels to reuse 3 for cell-edge users Interference aware scheduling: Scheduler allocates resources to users based on FFR partition and interference aware CQI metrics Interference-aware BS co-ordination: Base stations dynamically adjust FFR partition by exchanging information across the network backbone, to adapt to time-varying user traffic loads & distributions a) Static - no information exchange b) Semi-static - on order of 100msec to seconds c) Dynamic - on order of frame duration

AFR Design Requirements Support multiple reuse settings: 1, 3, 3/2 Support diversity & contiguous permutation modes Support hard reuse (AFR-H) and soft reuse (AFR-S) Flexibility with non-uniform user distributions Adaptation to time-varying traffic conditions Exploit channel aware scheduling gains Robustness to mobile environments Low system complexity

AFR Architecture Reuse partition: Up to 7 partitions (to support reuse 1, 3/2, 3) Attributes of partition: A triplet of N-dim vectors: [W, P, C] Bandwidth partition W: Power level P: System cost C: Soft reuse achieved by setting power level of each partition group Optimal resource allocation achieved by setting system-wide Cost for each partition

Typical deployments with AFR Architecture Supported reuse factor Number of partition groups /(corresponding size vector) Single reuse system Reuse 1 1 / Reuse 3/2 3 / Reuse 3 AFR system 2 mixed reuse partitions Reuse 1 and reuse 3/2 4 / Reuse 1 and reuse 3 3 mixed reuse partitions Reuse 1, reuse 3/2, reuse 3 7 / Flexible Reuse partition Example: Reuse 1 and soft reuse 3 AFR system Power level of Sector 1 Power level of Sector 2 Power level of Sector 3 Reuse 1 and soft reuse 3/2 AFR system Soft Reuse Hard reuse can be achieved by setting PLow to 0

Performance of AFR with Distributed Resources 5% CDF throughput: 450kbps, 2x over 16e reference: should we check with Tolis the baseline? (16e PUSC) Hard reuse: 5% throughput = 492kbps (+72%); Gross SE = 3.47bps/Hz (+1%) Soft reuse: 5% throughput = 499kbps (+74%); Gross SE = 3.80bps/Hz (+10%) AFR provides 1.7x cell-edge throughput gain Note: results of FFR over reuse 1 with PUSC-like resource block (48x6) under PedB-3kmph

Performance of AFR with Localized Resources 5% CDF throughput: 450kbps, 2x over 16e reference: should we check with Tolis the baseline? (16e PUSC) Hard reuse: 5% throughput = 724kbps (+16%); Gross SE = 5.30bps/Hz (-9%) Soft reuse: 5% throughput = 805kbps (+29%); Gross SE = 5.26bps/Hz (-10%) AFR-S with AMC permutation provides 805 kbps at cell-edge; close to 16m requirement of 900 kbps Note: results of FFR over reuse 1 with AMC-like resource block (48x6) under PedB-3kmph

Standards support 1) FFR partition needs to be inherent in Symbol Structure Symbol structure with localized and distributed resources per FFR partition

Standards support 2) Downlink Signaling 3) CQI Indication: AFR system configuration needs be broadcast in BCH/SFH or DL MAP AFR information includes Bandwidth Partition, Power Level, and System Cost of each partition May also include SS grouping information, such as cell-edge versus cell-center, to reduce CQI feedback from SS Needed for each SS in initial entry process and measurement 3) CQI Indication: CQI feedback is needed to support frequency selective scheduling For example, best-M CQI feedback scheme CQI is interference-aware, ex. post-processing SINR after LMMSE

Standards support 4) Measurements: Long-term measurements: Geometric SINR on different reuse partitions is needed to select best partition for each SS Can be computed from AFR-friendly preamble Short-term measurements: Instantaneous SINR (localized or distributed) on different partitions is needed to support frequency selective scheduling Can be measured from dedicated pilots in symbol structure design Symbol structure should support boosted pilots proportional to data for soft reuse

Conclusions and Recommendations Adaptive Frequency Reuse (AFR) can effectively improve cell edge performance Symbol structure, Signaling design, and Measurement and feedback support are needed to implement AFR We would like to recommend the following to be incorporated in SDD to support AFR Support Adaptive Frequency Reuse partition framework Support Symbol structure design that accommodates AFR framework Support Downlink Signaling necessary for AFR Support Measurements necessary for AFR, including preamble and dedicated pilots Support CQI feedback for AFR