1. Downlink Symbol Structure Requirements for Supporting Adaptive Frequency Reuse in IEEE 802.16m
Document Number:
IEEE C802.16m-08/403r3
Date Submitted:
Source:
Hongmei Sun, Clark Chen, Hua Yang {hongmei.sun, clark.chen, hua.yang, shilpa.talwar,
Shilpa Talwar, Hujun Yin, hujun.yin, vladimir.kravstov,
Vladimir Kravstov, Yuval Lomnitz
Intel Corporation
Re:
Call for Contributions on IEEE m-08/003r1 system Description Document (SDD)
- Comment for downlink PHY structure
Purpose:
Discussion and approval
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2. Outline Motivation AFR Requirements AFR Architecture Performance
Standards support
Symbol Structure
Signaling
Measurement and feedback
Conclusions and recommendations

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

4. 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

5. 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

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. 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. 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

9. 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

10. 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

11. 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

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

13. 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

14. 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

15. 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