Uplink Power Control in 802.16m IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number: IEEE C802.16m-08/675 Date Submitted: 2008-07-07 Source: Jeongho Park, Jaehee Cho, Suryong Jeong, Jaeweon Cho, Heewon Kang, Hokyu Choi, DS Park
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Samsung Electronics Co., Ltd 416 Maetan-3, Suwon 443-770, Korea Venue: IEEE 802.16m-08/024, “Call for Contributions on Project 802.16m System Description Document (SDD)”, on topic of ‘Power Control' Base Contribution: None Purpose: To be discussed and adopted by TGm for the 802.16m 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.
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Outline • Power Control in Legacy System – Uplink Power Control Algorithm in 802.16e – Gain of Power Control • LLS verification • SLS verification • Cell Edge Performance • Tx Power Consumption
• Function of Power Control – IoT Control in Interference Limit Environments – Effect of IoT variance
• Power Control in 802.16m System – Requirement of 802.16m Power Control
• Proposed Text
2
Power Control in Legacy System • Uplink Power Control (PC) Algorithm in 802.16e – Closed Loop Power Control • BS calculates the required Tx tone power of every MS –
based on the latest received packet and the packet which will be assigned to MS
• BS lets every MS know the amount of tone power correction –
via message or MAP IE
– Open Loop Power Control • Every MS determines its own Tx power – based on uplink noise and interference (NI) level that BS broadcasts – based on path-loss each MS estimates
Power Control in Legacy System • Gain of Power Control ; LLS Verification Fast fading compensation WITH channel estimation error
No fast fading compensation
Fast fading compensation WITHOUT channel estimation error
– Condition – Nep : 480 – Code rate : 1/2 Repetition : no – Number of Rx Antenna : 2, MRC – Center freq. : 2.3GHz – Sampling rate : 10MHz – Num. of UL symbol for data : 15 – Subchannelization : PUSC SR on – Delay btw estimation & Tx: 10ms* – Estimation error model : Normal(0,1.3)** – MS speed : 3km/h – Channel : Ped A
Æ Even with realistic channel estimation error, link performance can benefit from power control (2.7dB @ PER10%, 4.8dB @ PER 1%) * Refer to Appendix A for definition of delay between estimation & Tx ** Refer to Appendix B for estimation error modeling
Power Control in Legacy System • Gain of Power Control ; LLS Verification (cont’d)
Æ As generally known, low speed and short delay between estimation and UL transmission can bring large gain of power control
Power Control in Legacy System • Gain of Power Control ; SLS Verification* – OLPC (open loop PC) vs Max power transmission in 802.16e system 5%-tile User Throughput (Kbps) Sector Throughput (Mbps)
15.45 16.0
2.381 2.40
12.0
2.30 2.20 2.10 2.00
14.0
2.052 Max Power
Open Loop Power Control
10.0 8.0 6.0 4.0
1.90
2.0
1.80
0.0
– Noticeable enhancement can be achieved by PC • For both of sector throughput and cell edge * Refer to Appendix C for SLS conditions
10.58
Max Power
Open Loop Power Control
Power Control in Legacy System • Gain of Power Control ; SLS Verification* (cont’d) – OLPC (open loop PC) vs Max power transmission in 802.16e system • OLPC can have “Tx Power Consumption Reduction” • This is thanks to low mean value of IoT level. Averaged IoT of All Sector Distance-Tx power 25 T x P o w e r
25.00 20
20.00
16.1272
15
15.00 10
( d B m
21.2402
10.00 5
)
Cell Boundary
Max Power
Open Loop Power Control
5.00
0 0
50
100
150
200 250 Distance(m)
300
350
400
0.00
– MS also can benefit from power control in terms of power consumption
Function of Power Control • IoT Control in Interference Limited Environments – What value of IoT is most efficient in system viewpoint? – Theoretical throughput S ⎞ ⎛ C = BW log 2 ⎜1 + ⎟ ⎝ I+N⎠ = BW log 2 1 + γ 1 − IoT −1
(
(
))
• BW = effective bandwidth (10MHz*15/47*2/3)
•
γ = avg. S/I (fudge factor, 1.4 in this case)
Required additional IoT to achieve 10% throughput increase
– Simulation throughput • Power control with IoT control
Æ When IoT becomes too high (over 9dB in this case), throughput increase is very inefficient.
Function of Power Control • IoT Control in Interference Limited Environments – Relationship between IoT and cell edge performance
– There is the optimum IoT value to maximize cell edge performance
Æ Ability to control IoT level is desirable in interference limit situation
Function of Power Control • Effect of IoT Variance – Definition of IoT Var • Mean {Sector Var} where Sector Var is the variance of IoT along time IoT Var
Sector Tput
5%-tile User Tput
Case 1
1.2657
2.382
30.81
Case 2
1.8877
2.413
22.29
Case 3
1.9859
2.330
16.95
Case 4
3.4892
2.209
12.45
Case 5
6.1636
2.138
11.61
– As IoT Var increases, system/edge performance is degraded
Power Control in 802.16m System • Requirement of 16m Power Control – Estimation delay should be minimized • Reference signal used to estimate uplink channel should be prepared to support effective power control
– Ability to control IoT is desirable • BS should be able to operate network adaptively on its purpose • It is desirable to keep IoT variance low as much as possible
Proposed Text • Insert the following text into SDD Section 11 in IEEE 802.16m-08/003r3
11.X Power Control Uplink power control should be supported to compensate the pathloss, shadowing and fast fading. Uplink power control can be used to control inter-cell interference level. BS shall transmit signaling channel or message to MS required to support uplink power control. MS shall transmit signaling channel or message to BS required to support uplink power control. BS can transmit signaling message to BS required to support uplink power control through backbone network.
11.X.1 Closed Loop Power Control 11.X.2 Open Loop Power Control
Appendix A • Delay between Estimation and UL Transmission UL Channel Estimation
Delay
time
Channel amplitude
UL Transmission
– In addition to MS speed, delay between estimation and UL Tx impacts on the gain of power control – In FDD systems, UL channel estimation can be based on UL reference signal such as CQICH, control header and so on – In TDD systems, UL channel estimation can be based on DL reference signal such as preamble, common pilot and so on. (thanks to DL/UL reciprocity)
Appendix B • Channel Estimation Error Model – Reference signal for uplink channel estimation : 802.16e CQICH’s pilots – Assumption of CQICH operating SNR : 0dB
– Channel power estimation error can be modeled as Gaussian (0,1.3) in dB scale
Appendix C • SLS Simulation Conditions Basic Conditions Scenario Channel Mix
802.16m EMD
Traffic type
Best Effort
NGMN Configuration TDD and FDD in EMD
Queue size
Infinite
ITU (mandatory scenario in EMD)
Scheduling
Round Robin
Error Vector Magnitude
N/A
Channel Estimation
Ideal
Link to system
RBIR
Power control
Open Loop
Number of users per sector
20
Number of scheduled users
5
Bandwidth assignment Power margin Power outage handling UL CINR Estimation
Last Packet or BRTH
BRTH report period
3 frames
Outer Loop Rate Control NI broadcasting period NI averaging
in Linear scale
NI time domain windowing
Yes (10 frames)
Equal bandwidth 0 assign lowest MCS level No 1 frame
