1. Uplink Power Control Recommendations for IEEE 802.16m Document Number: IEEE C802.16m-08/666 Date Submitted: 07-07-2008 Source: Ali Taha Koc, Shilpa Talwar, Apostolos Papathanassiou, ali.t.koc@intel.com, shilpa.talwar@intel.comali.t.koc@intel.com Rongzhen Yang, Nageen Himayat, Hujun Yin Venue: IEEE 802.16m-08/016r1 Call for System Description Document (SDD) Comments and Contributions, on theIEEE 802.16m-08/016r1 topic of “Uplink power control”. Base Contribution: None Purpose: Discussion and approval of the proposal 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

2. Uplink Power Control IEEE 802.16m system requirements from SRD [1] Average User Throughput Cell edge Throughput Our view, IEEE 802.16m requirements on uplink power control can be improved by Open Loop Power Control (OLPC) –Slow power control –Provide balance between cell edge and sector throughput –Limit the level of IoT Closed Loop Power Control (CLPC) –Fast power control –Limit the MAC overhead of the signaling –Effective estimation of uplink interference Coupling of CLPC and OLPC –Provides high efficiency with reduced signaling overhead

3. Open Loop Power Control Path loss and shadowing variation can be compensated –Received signal level from different users does not have very large dynamic range Average IoT (Interference over Thermal) levels can be controlled Using an Open Loop Power control saves on continuous signaling of power control commands Using fractional open loop power control provides flexibility to balance the cell edge vs. sector throughput

4. Closed Loop Power Control In a full frequency reuse system, inter-cell interference dominates the system performance –Controls the power of interference sources individually at the expense of signaling overhead –Requires estimating uplink interference per user –Requires measurement of uplink received signal strength (for example, HARQ ACK/NACK can be used) Track and compensate the effect of user’s fast fading channel

5. OLPC and CLPC Comparison Open Loop Power Control Closed Loop Power Control Signaling OverheadLow Only broadcast algorithm initial parameters No signaling for power control commands High Broadcast algorithm initial parameters Signaling power control commands Power Control Accuracy Low Algorithm depends on the estimated path loss value that is based on reciprocity Limited information on MS make it difficult to achieve better adaptation High Accurate uplink signal measurement and interference estimation. Better control of interference by BS information exchanging

6. Common Open Loop Schemes Full Power –Bad for the cell edge users –High SINR variation SNR based –Each user transmits enough power to meet receive SNR target at BS –BS broadcasts the SNR target –Tradeoff Low SNR target: bad for the center edge user (low spectral efficiency) High SNR target: bad for the cell edge users (high interference)

7. Proposed Open Loop Scheme Takes interference into account –Set the SNR target depending on the DL SIR estimate Base station broadcasts gamma and beta values Automatic ‘Soft reuse’ –Assign high SNR target for cell-interior users –Assign low SNR target for cell- edge users

8. Justification of Proposed Method in a interference limited system By changing gamma, the scheme can control the IoT level By changing beta, the balance of cell edge versus sector throughput can be adjusted We can write SNR as We set SNR target as function of SIR (dB)

9. IoT Curves for Different Gamma

10. Open Loop and Closed Loop Coupling Open Loop is going to be the default scheme –Open Loop Power Control coarsely adjust uplink transmit power with low signaling overhead When there is data packets, Closed loop will the main power control scheme –Closed Loop Power Control signals can be piggyback to the data traffic for the fast control (for example, only a few bits combined with resource allocation IE (DL/UL MAP IE) for refined power adjustment)

11. Minimize CLPC Signaling Overhead by Piggyback Example for using existing loop – DL HARQ for CLPC Proposed CL scheme

12. Text Proposal to IEEE 802.16m SDD Insert the following text into Physical Layer clause (Chapter xx in [IEEE 802.16m-08/003r1]) ------------------------------- Text Start ------------------------------- 11.x.x.x Uplink Power Control A power control algorithm is supported for in the uplink channels with both initial calibration and periodic adjustment procedure. The parameters of power control algorithm are optimized on system-wide basis by the BS, and broadcast periodically. 11.x.x.x.1 Open Loop Power Control Uplink open loop power control compensates all or a fraction of the pathloss and shadowing. Uplink open loop power control uses channel and interference knowledge to operate at optimum power control settings. Mobile stations can derive their initial transmission power according to the path loss, interference measurements obtained from the downlink preambles and pilots. 11.x.x.x.2 Closed Loop Power Control Closed loop power control compensates for fast variations in channel and interference on a per subscriber basis, while minimizing MAC signaling overhead. Closed loop power control couples with open loop power control for efficient operations. Closed loop power control is active with data transmission. Close loop power control measures uplink power using uplink data and/or control channel transmissions and sends control command in unicast service control channel (USCCH). ------------------------------- Text End -------------------------------

13. References [1] IEEE 802.16m-07/002r4, “TGm System Requirements Document (SRD)” [2] IEEE 802.16m-08/004r1, “Project 802.16m Evaluation Methodology Document (EMD)”

14. Backup

15. Uplink Power Control in Legacy System Open Loop –Maintain same transmitted power density unless the maximum power reached –Normalized CNR values are determined in the standard –Full path loss compensation Closed Loop –In the initial ranging phase, the mobile users derives its initial transmission power according to the path loss measurement from the downlink pilot channel. –After that the mobile users adjusts its transmission power according closed-loop power control messages signalled by the base station. –Signalling overhead is too much for the 802.16e system. –BS -> MS: Send Offset information FPC (Fast Power Control) Message Power Control IE RNG-RSP for periodic ranging

16. Common assumptions for IoT = 7dB SNR Target = 8dB provides IoT target Changing SNR target has shifting affect on IoT values IoT Curves

17. SINR Curves

18. Increasing Gamma has minimal affect on SINR –Increasing gamma increase signal strength and interference at same time After finding the optimum gamma, alpha is important to have cell edge and center cell balance SINR Curves