essentials of mimo james zik
TRANSCRIPT
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Essentials of MIMO
Testing for DASSystems
PCTEL RF Solutions
James Zik, Senior Product
Marketing Manager
Dale Bass, Engineering
Support Service Manager
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What is MIMO?
LTE MIMO Measurements MIMO O-DAS Case Study
Agenda
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Antenna Techniques
MIMO is a smart antenna
technoIogy that employsmultiple antennas at the
Tx and Rx ends
MIMO is NxM (i.e. 2x2,
4x2, 4x4, 8x8, etc.) whereN>1 and M>1
2x2 (deployed), 4x4 and
4x2 (emerging),
8x8 (LTE Advanced)
Radiated signals traveling
on different paths provide
the possibility of
performance
improvements
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Why MIMO?
-300
-200
-100
0
100
200
300
2011 2012 2013 2014
Spe
ctrumS
urplus(MHz)
FCC Licensed Spectrum Needs*
Need to get maximum throughput on available spectrum
*FCC, Mobile Broadband: The Benefits of Additional Spectrum (October 2010).
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Why MIMO? Medium cost method to improve transmission performance
(already built-in on many LTE base stations)
Increases physical layer capacity (w/ spatial multiplexing MIMO) Throughput gain dependent on number of Tx and Rx antennas
i.e. 2x2, 4x4, etc.
LTE Peak Spectral Efficiency per 3GPP
LTE Peak Throughput of 4x
LTE Peak Throughput of 2x
5
0
5
10
15
20
25
30
35
10 5 0 5 10 15 20 25 30
PeakPhysicalLayer
Spectral
Efficiency
(b/s/Hz)
SNR
(dB)
2x1
2x2
4x4
8x8
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How Does MIMO Work?
Spatial Multiplexing:Transmits multiple data
streams simultaneously in
the same frequency and
time, taking advantage of
different paths
Requires separate paths
Requires high SNR to
improve throughput
Transmission shown one way (eNB to UE) for simplicity
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Transmission Modes
3GPP Defined Transmission Modes
Currently deployed transmission modes
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What is MIMO?
LTE MIMO Measurements MIMO O-DAS Testing
Agenda
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Why Test MIMO?
What are we trying to accomplish by testing MIMO?
Optimize the RAN physical layer for Maximum Throughput Provide throughput gain of the physical layer for each
transmission mode (using standards number)
Characterize Link efficiency
Troubleshoot the RAN physical layer Isolate path issues
Test for channel independence
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What Parameters are
Necessary for MIMO Testing
Premise: Operators need to understand MIMO transmissioncharacteristics of the physical layer in RAN
Path measurements
Channel Quality Indicator (CQI as defined by 3GPP)
Throughput
Channel Condition Number (CN)
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RF Path Measurements Determines if there is a problem with base station port or
a particular antenna with regard to MIMO paths
Measurements are provided for each Tx/Rx antenna pair
4 paths for 2x2 MIMO
RSRP, RSRQ, RS CINR for each path
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CQI
Consistent indicator of theoreticaltransmission physical layer
efficiency User layer throughput reduced up
to 10X due to control overhead Handshaking
Synchronization
Retransmission
CQI measurement is an essentialtool for MIMO
With SISO, CINR translatesdirectly to CQI
With MIMO, CINR does NOTtranslate to CQI i.e. throughput
CQI Index ModulationCode Rate x
1024Efficiency(b/s/Hz)
0 out of range
1 QPSK 78 0.1523
2 QPSK 120 0.2344
3 QPSK 193 0.3770
4 QPSK 308 0.6016
5 QPSK 449 0.8770
6 QPSK 602 1.1758
7 16QAM 378 1.4766
8 16QAM 490 1.9141
9 16QAM 616 2.4063
10 64QAM 466 2.7305
11 64QAM 567 3.3223
12 64QAM 666 3.9023
13 64QAM 772 4.5234
14 64QAM 873 5.1152
15 64QAM 948 5.5547
TS 36.213 Table 7.2.3-1: 4-bit CQI
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Throughput
How and where is throughput measured?
Physical Layer Throughput(for RAN optimization)
Throughput measurement includes RAN, Backhaul,
Network Loading, Server, etc.
CQIThroughput (Mbps)
5 MHz 10 MHz 20 MHz
1 0.55 1.10 2.19
2 0.84 1.69 3.38
3 1.36 2.71 5.43
4 2.17 4.33 8.66
5 3.16 6.31 12.63
6 4.23 8.47 16.93
7 5.32 10.63 21.26
8 6.89 13.78 27.56
9 8.66 17.33 34.65
10 9.83 19.66 39.32
11 11.96 23.92 47.84
12 14.05 28.10 56.19
13 16.28 32.57 65.14
14 18.41 36.83 73.66
15 20.00 39.99 79.99
Physical Layer
Throughput
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Condition Number (CN) CN is a measure of the independence (or correlation) of the
channels (paths)
Measured from 0 to 50 dB; lower values are better indicating lowcorrelation
CN helps analyze potential causes for throughput issues but is not usedto calculate throughput
Studies show MIMO can still be effective with high CN if CINR is high
CN (dB) Indication
0 Two totally independent channels, an ideal condition that
can enable maximum throughput
~19* High correlation where MIMO generally would not induce a
condition that would increase throughput
*The CNs indicating the level of correlation are based on industry published approximations and can vary by several dB depending on conditions
Industry Norm
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Value of MIMO
Measurements Separate CN, ECQI and transmission mode
measurements allow operators to diagnose the causes of
low throughput Low CN and low CQI means there is an interference or a
power issue
High CN and low CQI means high channel correlation and
probable low SINR
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What is MIMO?
LTE MIMO Measurements MIMO O-DAS Case Study
Agenda
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FDD-LTE 2x2 MIMO outdoor DAS
When: April 2012
Outdoor DAS deployed due to cell tower restrictions
Area characterized by high foliage and low antenna height
What we Tested
Antenna Locations
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How we Tested Simultaneous O-DAS Testing with Scanner and UE Data Card
PCTEL SeeGull EX Scanner
LG test data card on another system
Why use a Scanner?
3GPP TR 37.976: 3GPP already defined conducted tests for
MIMO and multiple antenna receivers . but it is clear that
the ability to duplicate these gains in the field is highly
dependent on the performance of the receive-antenna
system..
Scanners use omni-directional antennas
3GPP TR 37.976: The MIMO OTA throughput is measured at
the top of physical layer of HSPA and LTE system
Scanners provide a neutral baseline
Orientation Test
Walk Test vs Drive Test
MIMO Transmission Modes (on the scanner)
RSRP, CN, CINR and Throughput
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0
2
4
68
10
12
14
16
18
Freq
uency
Position: 0
01020304050
607080
Frequency
Position: 90
Position A Average: 2.820 Mbps
Position C Average: 1.232 Mbps
Orientation AnalysisUE Data Card
2.3X difference depending on
orientation due to directionalityof UE antennas
(stationary test)
kb/s
kb/s
MIMO antennas in UEs
are typically very
directional
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0
5
10
15
20
25
30
35
40
45
#ofDat
aPoints
Speed AnalysisUE Drive Test (~20 mph)UE Walk Test
Throughput drops by approx. 2X with drive test
Throughput (kb/s)
kb/s
((
4
2
)
4
)
(42)
0
10
20
3040
50
60
70
80
1 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
#ofDataPoints
(24)
Throughput (kb/s)
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UE Data
Scanner Data
Drive Test Data
0
200
400
600
100 1000 2500 5000 10000 More
#ofDataPoints
UE
0
1000
2000
3000
4000
5000
#ofDataPoints
Scanner
UE Data
Tput (kb/s)
Lost Connection
Significant differences
between scanner & UE
Note: Scanner data rate much higher
since its measuring at the physical layer
Tput (kb/s)
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Scanner Data
Drive Test Data
0
1000
2000
3000
4000
5000
#ofDataPoint
Scanner
Overall throughput is low; expect physical layer scanner
throughput to be 30 to 80 Mb/s for effective MIMO gain
Tput (kb/s)
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Scanner Transmission
Modes
0
200
400
600
8001000
1200
100 1000 2500 5000 10000 20000 30000 More
#ofDataPoint
s
Open Loop Transmit Diversity(mode 2)
0
200
400
600
8001000
100 1000 2500 5000 10000 20000 30000 More
Frequency
Closed Loop SpatialMultiplexing (mode 4)
No throughput gain from multiple data streams
Tput (kb/s) Tput (kb/s)
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RSRP
Test results show acceptable RSRP
RSRP
dBm
#ofDataPoints
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CN and CINR for MIMO
CINR
Test results show very LOW CINR
dB
#ofDataPoints
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CN and CINR for MIMO
MIMO requires high CINR and prefers low CN to maximize throughput
Condition Number (CN)
Test results show low CN
dB
#
ofDataPoints
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Conclusions
MIMO is ineffective in this network
Network has a severe interference and/or noise problem Acceptable RSRP but very poor CINR
Conditions favorable for MIMO to improve throughput
Low CN number
UE Measurements for MIMO must be carefully examined since theyare affected by:
UE Orientation
Speed of movement during the test Drive test vs walk test for outdoor systems.
MIMO Transmission mode the UE is operating in Another UE may operate in a different transmission mode
A scanner is very effective in characterizing a MIMO network
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MIMO Testing Benefits
Characterize RF propagation for MIMO Consistent, repeatable RF data independent of the backhaul, network layer overhead &
server loading
Higher dynamic range to determine noise floor and potential interference effects
High data density to locate fading issues and reduced MIMO throughput
Determine channel independence Analyze network problems related to multipath conditions with condition number
Understand how antenna tilt or relocation can affect throughput
Provides result for various transmission modes Understand how different transmission modes affect RAN performance
Troubleshoot antenna/cabling issues and base station Tx port issues Path measurements
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Questions?
Thank you