Transcript Slides S802.16m-08/1139r1

SDD detail about power loading for downlink MIMO transmission
IEEE 802.16 Presentation Submission Template (Rev. 9)
Document Number:
S802.16m-08/1139r1
Date Submitted:
2008-09-16
Source:
Keying Wu, Hongwei Yang
Alcatel Shanghai Bell Co., Ltd.
Pei-Kai Liao, Chih-Yuan Lin, Paul Cheng
Voice:
+86-21-58541240 Ext. 7796
Email: [email protected]
[email protected]; [email protected];
MediaTek Inc.
[email protected], [email protected]
Ren-Jr Chen, Chung-Liean Ho, Richard Li
ITRI
Venue:
IEEE 802.16m-08/016: Call for Contributions on Project 802.16m System Description Document (SDD): DL-MIMO
Base Contribution:
C802.16m-08/1139r1
Purpose:
Adopt proposed text into SDD.
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Background
• The power loading technique has been included in 16m SDD (in section
11.8.2.1.2.2 of 802.16m-08/003r4), to improve the performance of
downlink MIMO.
• In this contribution, we discuss some details of the power loading technique
by revisiting its motivation, power level calculation and simulation results.
Motivation of power loading
•
•
•
In a 22 downlink SM system with single codeword, the two streams go through
different channels, and they are likely to have unequal reliability after MIMO
detection if equal power allocation is used.
Such unequal reliability leads to a suboptimum decoding performance for most
channel decoders, including the turbo decoder.
Channel state information can be used to adjust the transmit power levels of the two
streams to improve performances
ps1
Demodulator
(s2, s1)
ŝ1
P/S
Decoder
( sˆ1 ,sˆ2 )
Modulator
S/P
Channel
encoder
ŝ 2
MIMO
detector
Un-balanced
reliability for the two
streams
ps2
Power level calculation
•
The two power levels p1 and p2 can be controlled by adjusting their ratio r = p1/p2.
•
The ratio r is calculated by the receiver based on the channel estimation result, and fed
back to the transmitter.
•
The ratio r is calculated as follows (for MMSE-SIC detector)
2
b

p1  /( ab  c),
r  
p 2 (ab  c)/ a 2 ,

if a  b
if a  b
2
2
2
*
*
where a  h11  h21 , b  h12 2  h22 2 , and c  h12h11  h22h21 , with hm,n the fading
coefficient between the mth receive antenna and the nth transmit antenna.
Simulation results
•
•
•
•
Link-level simulation compatible with 16m.
Channel is modeled as pedestrian A.
Rate-1/2 turbo code, QPSK and 16QAM modulation.
User data is mapped to 4 consecutive PRUs, each consisting of 18
consecutive subcarriers and 6 OFDM symbols.
• The power ratio is calculated based on the average CSI over 4 PRUs,
and quantized into 32 levels.
QPSK+ 1/ 2
16QAM+ 1/ 2
1.E+ 00
1.E+ 00
PER
1.E-01
1.E-01
1.E-02
BER/ PER
BER/ PER
PER
BER
SM w/ o PC w/ o PL
SM w PC w/ o PL
SM w/ o PC w PL
1.E-03
BER
1.E-02
SM w/ o PC w/ o PL
SM w PC w/ o PL
SM w/ o PC w PL
1.E-03
1.E-04
1.E-04
0
5
10
SNR (dB)
15
20
0
10
20
SNR (dB)
30
Text proposal
11.8.2.1.2.2 Power Loading Technique
For two-stream spatial multiplexing, power loading (PL) should be
considered. Since the best power ratio of the two streams depends on the
instantaneous channel condition and types of the receiver, it should be
calculated at MS and sent back to BS. As a result, the system should
provide a specific feedback channel from MS to BS for the power ratio
and the functionality of power allocation at BS to support power loading
technique.