Interference Constraint Power Control Document Number: IEEE C 80216 m-08/630 Date Submitted: 2008 -07 -07 Source: Xiaoyi Wang, Chunye Wang, Peter Skov Nokia Siemens Networks Heping Li Dongjie, No. 11 Beijing, China IEEE C 80216 m-08/630 Voice: +8613511021252 E-mail: xiaoyi. wang@nsn. com Venue: IEEE 802. 16 m-08/024: Call for Contributions on Project 802. 16 m System Description Document (SDD). Target topic: “Power control”. Base Contribution: N/A Purpose: Discussion and approval by TGm for the 802. 16 m SDD 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/sect 6 -7. html#6> and <http: //standards. ieee. org/guides/opman/sect 6. html#6. 3>. Further information is located at <http: //standards. ieee. org/board/pat-material. html> and <http: //standards. ieee. org/board/pat >. 1
IEEE C 80216 m-08/630 Motivations • UL data transmission is constraint by interference level. Power control is the most important way to reduce interference. • 16 m has to introduce efficient power control method to satisfy SRD (IEEE 802. 16 m-08/002 r 4) 2
IEEE C 80216 m-08/630 Classic uplink power control • • The overall target of uplink power control is to optimize MS transmit power according to the following criteria: Maximize throughput Limit interference (increase throughput for other MS’s) Maximize battery lifetime it is important to study the interaction of different MS’s power controls. The classical solution is to focus on the MS’s own throughput as optimization criteria. In this case the MS should transmit with maximum power except when its SINR is beyond the required SINR for the max MCS (no need to waste power when it can not buy any throughput). As the SINR depends on the interference level and path loss to serving base station these will be the two variables determining the MS transmit power. P = SINR_Target + L + N + Io. T Where P is MS transmit power in d. Bm per sub-carrier, L is path loss to serving sectorin d. B, N is thermal noise in d. Bm and Io. T interference rise over thermal noise in d. B. 3
IEEE C 80216 m-08/630 Fractional path loss compensation power control In network scenarios with high site density, the uplink sector throughput will be limited by the rise of interference not by the MS transmit power. To limit MS transmit power it was suggested to only compensate for a fraction of the path loss (fractional power control in LTE). Adding this feature a number of MS’s with intermediate path loss will not get sufficient transmit power. This will reduce the interference and extend the battery life. And as shown else where it can even improve throughput for MS’s on the cell edge. Tx. Power [d. Bm] Full path loss compensation Maximum transmit power Another way of viewing this algorithm is classic pc with path loss dependent SINR target. (MS with large pathgain has lower target SINR) Fractional path loss compensation P = SINR_Target + αL + N + Io. T SINR target + N +Io. T Minimum path loss Path loss [d. B] 4
IEEE C 80216 m-08/630 Interference constraint power control (ICPC) • In previous slides we showed that power control should target interference level rather than SINR. (adjusting interference to other sector rather than own throughput) The following formula should then be used: • P = NRT + N - g • Where P is the new transmit power in d. Bm, g is the equivalent path gain to all other BSs in d. B, N thermal noise and NRT the noise raise target in d. B. • Equivalent path gain (g) = received power – received signal power. – Received power includes radio power from all sectors, while received signal power only includes power from serving sector. • To enable adjustment of the user throughput distribution in a cell, the noise rise target could be varied for different bit rates. In that way users with low bit rate would be allowed to target for a higher interference. 5
IEEE C 80216 m-08/630 Basic Simulation Assumptions • • Layout: 7 sites – 3 sectors/site – wrap-around Simulation time: 5 run – 10 s per run – 2 s warm-up Users per sector: 10 Scheduling: Round Robin Link Adaptation: Open Loop Link Adaptation Traffic Model: Full Buffer with balanced load BLER Target at 1 st Tx: 20% PC range - period 40 d. B – 100 ms 6
IEEE C 80216 m-08/630 Simulation results UE mean MAC goodputs, one sample per UE 1 0. 9 0. 8 0. 7 CDF 0. 6 0. 5 Full, average = 10. 47 FPC, average = 9. 856 0. 7 CDF noise raise 1 ICPC average = 8. 194 0. 5 0. 4 0. 3 0. 2 Full, mean = 694. 4 FPC, mean = 765. 5 0. 1 ICPC, mean = 934. 5 0. 1 0 0 0 • • 500 1000 1500 goodputs(in kbps) 2000 2500 0 5 10 15 noise raise(d. B) 20 25 30 Full means Full compensation. FPC means Fractional Power control. ICPC shows more accuracy noise raise volume control than fractional power control Cell edge user throughput doesn’t have obvious gain over FPC. Intermediate users’ performance have gain in ICPC. 7
IEEE C 80216 m-08/630 Proposed Text to be included in SDD Insert the following text into section 11. • 11. x Open Loop Power Control – BS should indicates every MS how much interference it is allowed to generate to other sectors. (NRT) – MS shall estimate an equivalent pathgain to all other sectors. – MS should adjust its Tx power according to NRT and equivalent pathloss. • P = NRT + N – g + BSoffset – Where NRT is interference level indicated by BS, N is the noise power, g is the equivalent pathgain, BS offset is indicated by BS for some special reason for power adjusting. 8
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