essentials of mimo james zik

7/23/2019 Essentials of MIMO James Zik

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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

essentials of mimo james zik

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