1. 1 Adaptive Frequency Reuse in IEEE 802.16m Document Number: S80216m-08/702r3 Date Submitted: 2008-07-17 Source: Clark Chen, Hongmei Sun, Hua Yang Email: {clark.chen, hongmei.sun, hua.yang, shilpa.talwar, Shilpa Talwar, Vladimir Krasvtov, vladimir.kravstov, yuval.lomnitz, himayat.nageen, Yuval Lomnitz, Hujun Yin hujun.yin} @intel.com Intel Corporation Kwanhee Roh, Jaehee Cho, Jeongho Park, E-mail:kwanhee.roh@samsung.com Sooryong Jung Samsung Electronics Venue: IEEE 802.16m-08/024, Call for Comments and Contributions on Project 802.16m System Description Document (SDD), Interference Mitigation Base Contribution: C80216m-08/702r3 Purpose: For discussion in TGm and adoption of proposed SDD text into the IEEE 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: 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 S80216m-08_702r3

2. 2 Outline Motivation AFR Requirements AFR Architecture AFR Algorithm Standard Support Conclusions and recommendations

3. 3 IEEE 16m SRD Requirements Meet 802.16m downlink Data requirement

4. 4 Interference is serious problem with Reuse 1 Geometric SINR distribution in hexagon cell structureGeometric 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

5. 5 Adaptive Frequency Reuse Concepts PHY MAC RRM Tx Beamforming Interference Randomization Uplink Power Control Rx Interference Mitigation Interference- aware Scheduling FFR (semi-static) FFR (dynamic) Interference-aware BS Coordination AFR

6. 6 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

7. 7 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

8. 8 AFR Architecture N = [K]Reuse partition: N = [K] partitions (to support reuse 1, N, M) [W, P, C]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 system-wideCostOptimal resource allocation achieved by setting system-wide Cost for each partition

9. 9 Various deployments with AFR Architecture Supported reuse factorNumber of partition groups /(corresponding size vector) Single reuse factor system Reuse 11 / Reuse 3/23 / Reuse 33 / AFR syste m 2 mixed reuse partitions Reuse 1 and reuse 3/24 / Reuse 1 and reuse 34 / 3 mixed reuse partitions Reuse 1, reuse 3/2, reuse 3 7 / Example: Reuse 1 and soft reuse 3 AFR system Power level of Sector 1 Power level of Sector 2 Power level of Sector 3 Example: Reuse 1 and soft reuse 3/2 AFR system Power level of Sector 1 Power level of Sector 2 Power level of Sector 3 Hard Reuse Soft Reuse

10. 10 AFR Algorithm Details Problem definition and theory introduction Cost and BW partition adaptation Performance Summary

11. 11 Problem and Definition Optimal resource allocation problem: –How power loading level and AFR partition size is adapted? –What measurements are needed? –What information is fed back from SS? –How SS’s are scheduled on different resource types? Definitions –Radio Resource Type: FFR partition with different average S/I –Cost: a real value that is a measurement of system resources used by a particular resource type –Normalized SE: a value represents the normalized efficiency achievable on particular resource type in terms of system resource. –User Distribution: position and corresponding S/I distribution of users (SS) in the system –Fairness Constrain: a pre-defined percentage curve that specifies the throughput CDF of all SS * Complete mathematic proof in a separated document

12. 12 Optimal Resource Allocation Theory Solution Assumptions –The user distribution and corresponding average signal/interference level doesn’t change during the optimization time. –A user’s average spectrum efficiency is a rising function of their average SINR at different radio resource types. Theory Solution –Given a user distribution  and a fairness constraint , for every power loading factor , there is a optimal resource allocation solution achievable, that yields the highest average SE, with a unique (, ), where the system partition is proportional to SS’s relative bandwidth request on different resource types, and all SS are allocated resources that yield maximum normalized SE amongst all resource types. Reference: –Problem of optimal radio resource allocation, by Vladimir Kravstov, Intel (unpublished doc)

13. 13 AFR Scheme Details – Theory Solution Exemplary Intuitive example: AFR system with Hard Reuse 3 –Cost of reuse-3 is 3 while cost of reuse-1 is 1 Each resource block in Reuse 3 occupies 3 times system resource compared with resource block in Reuse 1 –SS should be allocated with FFR partition that yields highest nSE Only SS that can get more than 3 times SE gain should use Reuse 3 –The optimal Reuse partition would be decide by all SS’ choice of reuse partition and their corresponding bandwidth required (fairness constrain) Key learning –Cost of different reuse partition is different Must find optimal cost vector online –Reuse Partition should be proportional to SS’ relative bandwidth request Must adapt online * Complete mathematic proof in a separated document

14. 14 AFR Implementation and Procedure Given SS distribution and S/I, find the optimal {P, W, C} Power loading –predefined according to engineering experience or network planning Initial Partition –Enable SS measurement on different AFR partition Initial Cost –Can start from any real value or choose on engineering experience Two steps adaptation –cost adaptation and channel partition adaptation. –the cost adaptation is a necessary step for partition adaptation. * Complete mathematic proof in a separated document

15. 15 AFR Scheme Details – Cost adaptation ‘Market Price Iteration’ algorithm to find the ‘optimal’ C incrementally Decreases the cost values if there are too many/few bandwidth requests from SS for the corresponding channel partitions Target is to achieve balanced bandwidth request on three reuse- 3 partitions Theory proves the convergence and unique of cost vector BS autonomous decision process in cost adaptation, and deals good with un-balanced SS distribution among BS

16. 16 AFR Scheme Details – BW Partition adaptation Require the cost converged in each BS individually BS report all SS preference of different reuse partition to RRM RRM take system wide fairness rule in addition to the relative bandwidth request RRM (function) unit takes charge of BW partition changes for all neighboring BS in a system Partition adaptation is relatively slow, from tens of minutes or hours, on carrier’s choice, depending on system dynamic Cost/Partition adaptation approaches optimal system operation point

17. 17 AFR Scheme Details – Soft Reuse with AFR Architecture AFR-S: AFR with reuse 1 and soft reuse 3

18. 18 AFR Scheme Details – AFR Performance With standard proportional fair scheduling, AFR soft reuse provides –limited gain on both cell edge and cell capacity in localized (AMC-like) resources –89% gain on cell edge with +23% gain on cell capacity in distributed resources * Initial data and due to change according to updates SchemeChannel ModelGross SE (bps/Hz/cell) Gain on SECell edge user throughput Gain on cell edge user throughput Note AMC baselinePedB-3kmph5.84667kstandard PF AMC AFR-S5.931.6%689k3.3%standard PF Dist-baselinePedB-3kmph3.68315kstandard PF Dist AFR-S4.5222.8%595k88.9%standard PF

19. 19 AFR Scheme Details – AFR Performance (continued) SchemeChannel ModelSE (bps/Hz/Cell) gain on SEcell edge user Throughput (kbps) gain on cell edge user throughput Note baselinePedB-3kmph5.84667standard PF AFR-S5.931.6%6893.3%standard PF AFR-S5.71-2.2%77215.7%Weighted PF AFR-S5.29-9.4%81922.8%Weighted PF AFR-S5.18-11.2%84326.4%Weighted PF AFR can further improve cell edge user throughput at the expense of cell capacity loss by changing scheduling policy

20. 20 AFR Summary Theory indicates the optimal (power loading, partition, cost) combination that AFR system achievable AFR architecture approaches the optimal solution point with self- learning process AFR architecture well deal with the dynamic facts in real system with un-predictable SS distribution and changing propagation environment AFR architecture is simple, scalable, and has light overhead

21. 21 Standard Support Symbol Structure Signaling Support Measurement and feedback Inter-BS Co-ordination

22. 22 AFR Implementation Details 1) FFR partition needs to be inherent in Symbol Structure Symbol structure with localized and distributed resources per FFR partition

23. 23 AFR Implementation Details 2) Downlink Signaling –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 –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

24. 24 AFR Implementation Details 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

25. 25 AFR Implementation Details 5) Inter-BS Co-ordination –BS ex-change information for system BW adaptation by: Bandwidth partition: W, Power level: P Cost vector: C Load on different FFR partition, etc –A RRM (function) unit should decide whether the BW partition should be adapted according to fairness constrain and performance metric (system SE and/or edge throughput) –The adaptation of system wide AFR configuration can be dynamic, semi-static or static

26. 26 Conclusions and Recommendations Conclusions –Adaptive Frequency Reuse (AFR) can effectively improve cell edge performance while keep or gain in SE –Adaptive Frequency Reuse (AFR) provides very flexible solution to dynamic deployment environments which approaches the optimal resource allocation in system –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 and feedback necessary for AFR, including preamble and dedicated pilots

27. 27 Proposed Text 11.x Inter-cell interference mitigation 11.x.1 Flexible Frequency Reuse Flexible Frequency Reuse can be used to help users suffering from severe inter-cell interference. With FFR enabled, subcarriers across the whole frequency band are grouped into [K] frequency partitions. Associated with partitions are the parameters of power and cost. The usage of frequency partitions is limited in each BS such that parts of frequency partitions can be unused or have lower/higher transmission power. There is a system cost associated with partitions which is a measurement of the system resource used by the partitions due to its different transmission power, in terms of interference caused to other cells. For example, the cost of a partition is high if this partition is restricted in other sectors to create higher reuse pattern (3, 3/2), or if the partition uses higher transmission power and causes interference to neighbor cells. To control system-wide interference, the BS can adjust partition and power in coordination with other BSs.

28. 28 Proposed Text (Cont’d) The following diagram shows an example of frequency partition and power control to mitigate the interference in DL. The system may have [K] frequency partitions in mixture of reuse-1, reuse-M, reuse-N according to deployment needs. Figure x: Example of Flexible Frequency Reuse

29. 29 Proposed Text (Cont’d) 11.x.2 Control signaling for inter-cell interference mitigation BS can transmit necessary information through signaling channel or message to MS to support Flexible Frequency Reuse. The necessary information includes frequency partition and additional partition information such as power and cost. MS can transmit measurements through signaling channel or message to BS to support Flexible Frequency Reuse. The necessary information includes CINR measurements (long-term and instantaneous) or their representatives. The feedback from MS across the frequency partitions should be minimized. BS can coordinate and exchange information with neighbor BSs to support Flexible Frequency Reuse through the backbone network. The necessary information includes frequency partition, cost and interference level.

30. 30 Q & A

31. 31 Backup - System Simulation Assumptions Number of cells19 cells, with 3 sector per cell (with wrapping around) Number of sectors per cell3 Site-to-site distance1.5km Carrier Frequency2.5GHz User Number10 users/sector Permutation modeAMC, PUSC MIMO2x2 with rank adaptation (STBC/SM) with MMSE aware receiver RepetitionON Target PER0.1 Strong interference number14 Channel modelPedB 3kmph CQI feedbackFull feedback with 5ms, 10ms, 15ms delay HARQChase-combing with 4 retransmission with 4 frames of retransmission delay RB size48 sub-carriers x 6 symbols Frame length5 ms SchedulerPF