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1 Maximizing LTE MIMO Throughput Using Drive Test Measurements PCTEL RF Solutions

Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

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Page 1: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

1

Maximizing LTE MIMO

Throughput Using

Drive Test

Measurements

PCTEL RF Solutions

Page 2: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

2

James Zik, Senior Product

Marketing Manager, PCTEL, Inc.

Bruce Hoefler, Vice President

Product Management, PCTEL, Inc.

Page 3: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

3

Mobile Bandwidth Need

18X growth from 2011 to 2016

Page 4: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

4

Spectrum Crunch

-300

-200

-100

0

100

200

300

2011 2012 2013 2014

Spectr

um

Surp

lus

(MH

z)

FCC Licensed Spectrum Needs*

Need to get maximum throughput on available spectrum

*FCC, “Mobile Broadband: The Benefits of Additional Spectrum” (October 2010).

Page 5: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

5

• Air Interface Bottleneck Solutions

How do we Get There?

More Spectrum • Limited licensed spectrum available

• Expensive

Migration to LTE

LTE MIMO

• Carrier grade WiFi and backhaul required

• 22% of mobile traffic by 2016 (Cisco VNI Mobile 2012) WiFi Offload

• Small Cells and DAS (expensive)

• Backhaul required to each cell/DAS

Increased Cell

Density

• Migration to LTE and LTE Advanced

• LTE MIMO

Spectrum

Efficiency

Must employ all of these solutions to solve the spectrum crunch

Page 6: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

6

Why MIMO?

• Low to 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

Peak Physical Layer Spectral Efficiency (b/s/Hz)

SNR (dB)

2x1

2x2

4x4

8x8

Page 7: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

7

What is MIMO?

• MIMO is a smart antenna

technoIogy that employs

multiple antennas at the

Tx and Rx ends

• MIMO is NxM (i.e. 2x2,

4x2, 4x4, 8x8, etc.) where

N>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

Page 8: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

8

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

Page 9: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

9

Transmission Modes

Single User MIMO Modes

Currently deployed

transmission modes

Page 10: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

10

Why Test MIMO?

What are we trying to accomplish by testing MIMO?

• Determine the air interface Maximum Throughput capacity

for different MIMO Modes (MIMO Gain)

– Provide throughput gain of the physical layer for each

transmission mode (using standards number)

• Optimize the RAN physical layer for Maximum Throughput

– Characterize Link efficiency

• Troubleshoot the RAN physical layer

– Isolate path issues

– Test for channel independence

Page 11: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

11

What Parameters are

Necessary for MIMO Testing

Premise: Operators need to understand MIMO transmission

characteristics of the physical layer in RAN

Path measurements

Channel Quality Indicator (CQI as defined by 3GPP)

Throughput (maximum air interface throughput capability)

Channel Condition Number (CN)

Page 12: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

12

RF Path Measurements • Determines if there is a problem with base station port or

a particular antenna with regard to MIMO paths

• Antenna, cabling or TX port issues

• Measurements are provided for each Tx/Rx antenna pair

– 4 paths for 2x2 MIMO

• RSRP, RSRQ, RS CINR for each path

Page 13: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

13

CQI

Consistent indicator of theoretical transmission physical layer efficiency

• CQI measurement is an essential tool for MIMO

– With SISO, CINR translates directly to CQI

– With MIMO, CINR does NOT translate to CQI i.e. throughput

CQI Index Modulation Code Rate x

1024

Efficiency

(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

Source: 3GPP TS 36.213 Ver. 10.7.0 (Sept. 2012)

Table 7.2.3-1: 4-bit CQI

Page 14: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

14

Throughput

How and where is throughput measured?

Physical Layer Throughput

(for RAN optimization)

Throughput measurement includes RAN, Backhaul,

Network Loading, Server, etc.

CQI

Index

Throughput (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

User layer throughput reduced up to 10X due to control overhead - Handshaking - Synchronization - Retransmission

Maximum Throughput

Capacity of the Air Interface

(Physical Layer)

Page 15: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

15

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 low correlation

– CN helps analyze potential causes for throughput issues but is not used to 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

~<13* Favorable condition that can enable much better throughput

than SISO/MISO based transmission systems

~13 to 19* Medium correlation that can provide marginal throughput

improvement

~>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

Page 16: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

16

Interpreting 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

Page 17: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

17

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

Page 18: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

18

• 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

MIMO oDAS Case Study

Antenna Locations

Page 19: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

19

How we Tested

• Simultaneous oDAS Testing with Scanner and UE Data Card

‒ PCTEL SeeGull® EX Scanner

‒ Test data card on another system

• Orientation Test

• Walk Test vs Drive Test

• MIMO Transmission Modes (on the scanner)

• RSRP, CN, CINR and Throughput

Page 20: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

20

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……..”

“The MIMO OTA throughput is measured at the top of

physical layer of HSPA and LTE system”

• Scanner use omni-directional antennas

• Scanners measure throughput at the physical layer

• Scanners provide throughput for multiple MIMO transmission

modes

• UEs only provide throughput for the MIMO mode the UE is

locked onto

Page 21: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

21

0

2

4

6

8

10

12

14

16

18

Fre

qu

en

cy

Position: 0°

01020304050607080

Fre

qu

en

cy

Position: 90°

Position A Average: 2.820 Mbps

Position C Average: 1.232 Mbps

Orientation Analysis UE Data Card

2.3X difference depending on

orientation due to directionality

of UE antennas

(stationary test)

kb/s

kb/s

MIMO antennas in UEs

are typically very

directional

Page 22: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

22

0

5

10

15

20

25

30

35

40

45

# o

f D

ata

Po

ints

Speed Analysis

UE Drive Test (~20 mph) UE Walk Test

UE Throughput drops by 2X w/ drive test, scanner is not affected by speed

Throughput (kb/s)

((

4

2

)

4

)

(42)

0

10

20

30

40

50

60

70

80

1 500 1000 1500 2000 2500 3000 3500 4000 4500 5000

# o

f D

ata

Po

ints

(24)

Throughput (kb/s)

Page 23: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

23

UE Data

Scanner Data

Drive Test Data (Throughput)

0

200

400

600

100 1000 2500 5000 10000 More

# o

f D

ata

Po

ints

UE

0

1000

2000

3000

4000

5000# o

f D

ata

Po

ints

Scanner

UE Data

Tput (kb/s)

Lost Connection

Significant differences

between scanner & UE

Note: Throughput is very low.

Scanner show higher throughput

since it’s measuring at the physical

layer

Tput (kb/s)

Page 24: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

24

Scanner Transmission

Modes (MIMO Gain)

0

200

400

600

800

1000

1200

100 1000 2500 5000 10000 20000 30000 More

# o

f D

ata

Po

ints

Open Loop Transmit Diversity (mode 2)

0

200

400

600

800

1000

100 1000 2500 5000 10000 20000 30000 More

Fre

qu

en

cy

Closed Loop Spatial Multiplexing (mode 4)

No throughput gain from multiple data streams

Tput (kb/s) Tput (kb/s)

Page 25: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

25

RSRP

Test results show marginal RSRP

RSRP

dBm

# o

f D

ata

Po

ints

Page 26: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

26

CINR for MIMO

CINR

Test results show very LOW CINR

dB

# o

f D

ata

Po

ints

Page 27: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

27

CN for MIMO

MIMO requires high CINR and prefers low CN to maximize throughput

Condition Number (CN)

Test results show low CN

dB

# o

f D

ata

Po

ints

Page 28: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

28

oDAS Case Study

Conclusions

MIMO is ineffective in this network

• Network has a severe interference and/or noise problem – Marginal RSRP and very poor CINR

Conditions favorable for MIMO to improve throughput

• Low CN

UE Measurements for MIMO must be carefully examined since they are 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

Page 29: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

29

MIMO Macro Cell

Case Study (Oct 2011) PCI-Best Server by RSRP (Baltimore: Urban Environment)

Focus on Best

Server Region

for PCI (best

server)

(PCI, # of data pts)

Page 30: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

30

LTE RSRP (Best Server)

Excellent RSRP

Page 31: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

31

MIMO Drive Test Transmit Diversity and MIMO Throughput

Best Server Region

for PCI of interest

Transmit Diversity MIMO (mode 4)

Mbps

Page 32: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

32

MIMO Drive Test Delta (MIMO-Transmit Diversity)

Throughput

Mbps

Why is (MIMO – Transmit Diversity)

negative at the cell edge (pink)?

For extremely low CINR, transmit diversity

is more efficient. The UE will switch to

transmit diversity in this region.

Large MIMO gain for much

of the center region of the cell

Page 33: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

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MIMO Drive Test Condition Number and CINR

High CN with high

MIMO Gain

Condition Number CINR

dB

dB

Very High CINR

Significant MIMO gain exists for LOS condition

if CINR is high even with high CN

Page 34: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

34

Summary • MIMO was very effective for maximizing throughput in the Baltimore

Macro cell case study

• MIMO may not be effective in sub-optimal designs, deployments or terrains as shown in the oDAS case study

• Testing Benefits with a Scanner – 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

Page 35: Maximizing LTE MIMO Throughput Using Drive - PCTELrfsolutions.pctel.com/artifacts/MIMOThroughputDriveTestWebinar.pdf · Maximizing LTE MIMO Throughput Using Drive Test Measurements

35

Questions?

Thank you

http://rfsolutions.pctel.com/content.cgi?id_num=36

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