LTE interference on analogue and digital PMSE devices · 15.10.2013 LTE interference on analogue and digital PMSE devices ... LTE interference on analogue and digital ... aspect of

Benjamin Lembke, IRT

15.10.2013 LTE interference on analogue and digital PMSE devices

Testing Report

____________________________________________________________________________

___________________________________________________________________________________ © 2013 Institut für Rundfunktechnik GmbH. All rights reserved. Page 1 of 22

Copyright Notice

This document and all its contents are protected by copyright law. IRT reserves all

its rights. You may not alter or remove any trademark, copyright, or other notice.

Institut für Rundfunktechnik has granted its client the right to distribute to

third parties and to publish (also electronically solely in non-editable and

non-copyable.pdf format) this complete and unchanged document.

Translation and modification of any parts of this document as well as the

distribution of excerpts requires the prior written permission of Institut für

Rundfunktechnik.

____________________________________________________________________________


Content

1 Abstract .............................................................................................................................................. 3

2 Introduction and Test Setup ............................................................................................................... 3

3 Results ................................................................................................................................................ 7

3.1 One UE transmitting in Band 13 (700 MHz) ............................................................................... 7

3.1.1 Analogue PMSE receiver .................................................................................................... 8

3.1.2 Digital PMSE receiver ......................................................................................................... 9

3.1.3 Effect on audio the signal ................................................................................................... 9

3.2 One UE transmitting in Band 3 (1800 MHz) ............................................................................. 10

3.2.1 Analogue PMSE receiver .................................................................................................. 11

3.3 Three UE transmitting in Band 20 (800 MHz)........................................................................... 12

4 Additional Information ..................................................................................................................... 13

4.1 Information about the Link budged calculation ....................................................................... 13

4.2 Sound and Video files ............................................................................................................... 14

5 Conclusion ........................................................................................................................................ 14

6 Acknowledgements .......................................................................................................................... 14

7 List of abbreviations ......................................................................................................................... 15

8 List of devices ................................................................................................................................... 15

9 Annex ................................................................................................................................................ 16

10 Reference Documents .................................................................................................................. 20

____________________________________________________________________________


LTE interference on analogue and digital PMSE devices

within the IMT duplex gap based on recent test at IRT in Munich

1 Abstract

Analogue and digital audio PMSE systems are meant to operate in areas like theatres, operas,

conference-rooms or other professional installations for TV productions and events. The mobile

network operators for smartphones in Germany have started their expansion of LTE base stations in

the UHF-frequency-band to provide the new technology to the consumers.

PMSE systems and LTE share the same frequency band. The most common way of transmission via LTE

is the FDD mode in which a duplex gap is present for the use of e.g. PMSE systems. However, this gap

can be occupied by disturbances of LTE devices. These disturbances are out-of-band emissions of the

LTE-UEs due to the change of resource block allocation in the scheduler. The outcome of the

measurements is that PMSE devices can be disturbed by LTE UEs under specific conditions.

2 Introduction and Test Setup

To prove if there are any out-of-band emissions of LTE UE devices some tests have already been done

in the past [1]. This new measurement campaign was focused on the E-UTRA-Band 13, which is

situated in the 700 MHz Band. In Germany the 700 MHz Band has not been allocated for LTE yet. So it

was assumed that a device acts similarly in the Band 13, Band 17 or wherever at 700 MHz, and the

interference is comparable to the 800 MHz Band.

Band 3 was also under examination. As well a point of interest was the interference of 3

simultaneously working devices (representing 3 different operators) close to each other while running

a PMSE device in the duplex gap. Therefor we had been provided with another LTE Base Station

Simulator CMW500 by Rohde and Schwarz to employ it in addition to our one.

It has to be mentioned that the LTE UE was always decoupled by 47 dB from the PMSE link. In the free-

space-loss situation this corresponds to a distance of 7 meters. No antenna gain, diversity or any other

aspect of a commonly used link budget is considered for this point of view. If an antenna of a cellular

phone is hand-held or held close to the body (which is the common case), the gain and the propagation

patterns will change significantly. There are many different scenarios so the 47 dB free-space-loss can

be assumed as a reference point.

____________________________________________________________________________


The Downlink was set to a low level of about -60 dBm full cell bandwidth. Due to the directivity of the

coupler used in the test-bed, the downlink-signal attenuation was high enough to say that the base

station was decoupled and did not affect the results. The resource block allocation used during the

measurement campaign is shown in Figure 1. It was formerly considered to choose a more theoretical

scenario for the resource block allocation, e.g. 1 ms 50 resource blocks and 9 ms no resource block, but

the randomised scenario finally seems to be more realistic.

Figure 1: Resource Block Allocation

To be able to compare the results to former ones the criterion of an acceptable SINAD was set to 30 dB

[2]. But this method is only possible in analogue systems, digital systems just mute at the point where

no error-free transmission is possible. So the quality criterion for digital systems was set to the muting

point.

Figure 2 shows the usual measurement setup during the whole campaign. The CMW500 was working

as a LTE-Base-Station and was connected to the antenna ports of the UE. Only the uplink signal was

coupled out and the 40 dB decoupling was set via the variable attenuator. The SMU 200A Signal

Generator simulated a PMSE transmitter by producing a 1 kHz sine signal which was frequency

____________________________________________________________________________


modulated with a deviation of 3 kHz. This corresponds to a soft audio signal level (Pianissimo1) in the

PMSE transmitter.

To make sure that the UE was still connected to the base station during the measurements the FSW

Spectrum Analyser with a small antenna was acting like a watchdog. At the beginning of every

measurement the path had always been calibrated using the spectrum analyser with a short cable.

FSW Spectum Analyzer

PMSE Device

SMU 200AFM Signal

LaptopSINAD

Measurement

CMW500

Uplink

Antenna

α dB

(Variable)Attenuator

3 dBDivider

UE3 dB

Divider

2 Antenna

Ports

Directional Coupler

Figure 2: Setup of the Main Measurement with 1 UE

In Figure 3 one can see the setup for the simulation of 3 UEs operating in different frequency bands.

The 3 different paths had been combined to illustrate the sum effect. Every path needed to be

calibrated again.

To be non-committed at all the results do not include any name of manufacturers of the devices, which

had been used during the measurements.

1 Get further information: http://en.wikipedia.org/wiki/Dynamics_(music)

http://en.wikipedia.org/wiki/Dynamics_(music)

____________________________________________________________________________


CMW500

FSW Spectum Analyzer

UE3 dB

Divider

Uplink

2 Antenna

Ports

Uplink

CMW500

Uplink

Directional Coupler

UE3 dB

Divider

2 Antenna

Ports

Directional Coupler

3 dBDivider

3 dBDivider

3 dBDivider

Termination

UE3 dB

Divider

2 Antenna

Ports

Directional Coupler

Figure 3: Setup of the Measurement of 3 UEs

____________________________________________________________________________


3 Results First of all the UEs were set to their maximum output power and then switched to an alternating mode.

Spectrum figures always show 2 signals in max hold mode, one captured with RMS detector and one

captured with peak detector. A sweep time of 2 s and an approximate waiting time of about 1-2 min

made sure that every momentary frequency component was captured. If red vertical lines occur in the

figure, they mark the duplex gap in which the PMSE devices had been used. Only important results will

be shown, additional plots are added to the Annex. To be sure that the receiver was not overloaded of

the LTE uplink or downlink signal itself and that disturbances only occurred because of the spurious

emissions, a filter was put in the path to the PMSE device to decrease the power level of out-of-band

signals. But it was not necessary to use this filter because the results did not change with or without

the filter. That is why the filter is not shown in the setup.

3.1 One UE transmitting in Band 13 (700 MHz) The results shown in this chapter had been measured in the 700 MHz Band, especially Band 13. The

uplink is defined to work from 777-787 MHz, while the Downlink operates at 746-756 MHz. This yields

the operating range of 756-777 MHz for the duplex gap.

In Europe the operating bands from 694-790 MHz and the sharing criteria with PMSE in the duplex gap

have not been defined yet. Maybe there will be a guard band of about 1 MHz or similar to the duplex

gap in the future. That is why the measurements had started from 776 MHz instead of 777 MHz. The

LTE UE uplink bandwidth is set to 10 MHz.

Figure 4 illustrates an active UE transmitting at 782 MHz Uplink while the red lines show the area of the

supposed duplex gap. The traces had been recorded in max hold mode with either a peak detector or a

RMS detector.

Figure 4: UE transmitting in Band 13 near the duplex gap

____________________________________________________________________________


3.1.1 Analogue PMSE receiver

Analogue PMSE receivers are currently the most commonly used PMSE devices. If disturbances occur

they are audible. To be able to measure analogue PMSE links the SINAD was determined. It was

assumed that a link needs a minimum SINAD of 30 dB to work properly. For the highest quality link a

SINAD of 80 dB is required for example in TV or DVD production.

Figure 5: Analogue PMSE receiver affected by LTE UE

The results in Figure 5 show the necessary power level at the receiver input to reach a SINAD of 30 dB.

Different PMSE devices had been used and their results are very similar at all.

The LTE Interference begins at about 769 MHz and at the end of the duplex gap a 50 dB higher PMSE

signal level is required to keep a SINAD of 30 dB. This dramatically reduces the operating range of a

PMSE device.

On the left end of the duplex gap you can also see that the level needed for the PMSE device to

operate properly is rising for one particular device. This comes due to the fact that the PMSE receiver

design of this device produces structural conditioned crosstalk in the first IF-Filter.

____________________________________________________________________________


3.1.2 Digital PMSE receiver

Figure 6: Digital PMSE receiver affected by LTE UE

Digital PMSE receivers show similar interference behaviour. They drop out at 770 MHz and also need a

nearly 40-50 dB higher signal level (signal-to-interference ratio) at the upper end of the duplex gab. On

the left side the green line shows again interference, which comes from the down mixed LTE signal.

3.1.3 Effect on audio the signal

3.1.3.1 Clean single tone audio signal

The following figure shows a clean continuous sine wave signal (Figure 7) and the distortion made by

the LTE interferer, once on the analogue PMSE (Figure 8) system and the digital one (Figure 9).

The audio evaluation was carried out using “Audacity”.

Figure 7: Clean CW audio signal

____________________________________________________________________________


3.1.3.2 Effect on analogue PMSE links

Figure 8: The LTE UE noise transients superimposing the sound transmission

3.1.3.3 Effect on digital PMSE links

Figure 9: The LTE UE noise transients interrupting the sound transmission

3.2 One UE transmitting in Band 3 (1800 MHz)

The 1800 MHz Band has an advantage because the LTE bandwidth can be doubled to 20 MHz. However

the test-scenario should not be changed to compare the results to each other. That is why an Uplink of

10 MHz bandwidth was used again. To achieve the most disturbing condition the signal was set nearest

to the duplex gap. In figure 10 one can see the spectrum of the LTE UE where vertical lines again

represent the gap limits.

____________________________________________________________________________


Figure 10: LTE UE transmitting in Band 3

3.2.1 Analogue PMSE receiver

In Band 3, only analogue PMSE receivers are available yet and only one device was chosen to be tested.

As Figure 11 illustrates, the disturbing interferer had also appeared in Band 3. It has to be taken into

account that the used scenario of resource-blocks had been configured to work for a duplex gap on the

left side of the LTE UE spectrum. So the results show that the device is slightly less disturbing.

Figure 11: Analogue PMSE receiver affected by LTE UE

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

1.7

85

.00

0

1.7

87

.00

0

1.7

89

.00

0

1.7

91

.00

0

1.7

93

.00

0

1.7

95

.00

0

1.7

97

.00

0

1.7

99

.00

0

1.8

01

.00

0

1.8

03

.00

0

1.8

05

.00

0

Rec

eive

r le

vel

to 3

0 d

B S

INA

D [

dB

m]

Analogue PMSE receiver affected by LTE UEs @ 3m distance

1G8 PMSE RX

____________________________________________________________________________


3.3 Three UE transmitting in Band 20 (800 MHz)

Usually the closest band to the duplex gap has the most disturbing influence. To see how the other

channels affect the disturbances, three channels in the Band 20 had been simulated at the same time.

This means 3 UE devices were operating at a centre frequency of 837, 847 and 857 MHz, each set to 10

MHz bandwidth. Then the different operator signals had been switched on and off to determine the

difference in how the duplex gap is affected.

Figure 12: Close LTE channel with and without an additional adjacent LTE channel

Figure 12 on the left illustrates a LTE uplink channel close to the duplex gap with a second activated

channel on its right side. The right side of Figure shows only the LTE channel next to the gap. The UEs,

respectively the Base Stations, always had been set to the same configuration except for the used

centre frequency. Like for the measurements before, this plot had been done in max hold mode using a

RMS and a peak detector with a sweep-time of a few seconds. The interference levels are similar in

both scenarios.

Figure 13: Further distant LTE channel with and without an additional adjacent LTE channel

The next plot in Figure 3 shows again an almost similar case. The difference is that now not the nearest

channel to the gap is considered, but the next one. Disturbances had been dramatically reduced due to

____________________________________________________________________________


the fact that now the main disturber is shifted about 10 MHz away from the duplex gap. Again, another

channel added to the right did not greatly affect the sum of the interferer signal.

Finally the Figure 14 shows three LTE UE operated in parallel:

Figure 14: three LTE UE operated in parallel

4 Additional Information

4.1 Information about the Link budged calculation

During this measurement campaign the minimum needed power level of a PMSE link to reach a SINAD

of 30 dB has been measured2. The maximum radiated output power of a PMSE device is fixed to 50

mW. To reach the minimum needed power level, the usable range of the audio device was decreasing.

The decoupling by 47 dB of the interfering signal to the wanted signal corresponds to a free-space-loss

of 7 meters, but this consideration does not include any link-budget e.g. antenna gain of either the LTE

UE or the PMSE receiver.

2 In absence of interference this is a PMSE reception level of about -85 dBm [3]

____________________________________________________________________________


4.2 Sound and Video files

The following sound files demonstrate the audible interference on the PMSE link by LTE. They were

recorded during the measurements directly from the PMSE receivers under test.

Links to sound files:

LTE UE effect on adjacent analogue PMSE [946 KB]

LTE UE effect on adjacent digital PMSE [948 KB]

The following video file shows a real time spectrum recording of the duplex gap of the 800 MHz band.

You can see there the recurring spurious emissions. The Markers are indicating the duplex gap

Link to video files:

IRT LTE Spectrum Record [63.955 KB]

LTE UE at 837 MHz [28.983 KB]

LTE UE at 847 MHz [47.941 KB]

5 Conclusion

It has been shown that LTE UE devices can disturb PMSE links. The out of band emissions of the UEs

can be very high due to the dynamic resource block allocation in the Uplink. The devices used during

the measurements had been forced to transmit at their maximum level. In a real scenario they also

tend to transmit at very high levels.

Even if is the transmitted power is not 23 dBm all the time, measurements have shown that the

average is around 10 dBm or more, depending on the distance to the base station. Due to this fact the

measurement campaign can be considered as a worst case scenario. But even if a production team is

working at a place where a disturbance appears only once a minute, this may not be acceptable.

6 Acknowledgements We would like to thank:

AKG (Austria)

APWPT

Bayerischer Rundfunk (Germany)

DKE WG 731.0.8 at DIN/VDE (Germany)

EC Joint Research Centre – JRC (Italy)

Media Broadcast (Germany)

O2-Telefonica (Germany)

Sennheiser electronic (Germany)

http://www.apwpt.org/downloads/irt120713700mhzltevsanalog.wav

http://www.apwpt.org/downloads/irt120713700mhzltevsdigital.wav

http://www.apwpt.org/downloads/irt061113_lterealtimespectrum.m4v

http://www.apwpt.org/downloads/837mhz_pc.mp4

http://www.apwpt.org/downloads/847mhz_pc.mp4

____________________________________________________________________________


Shure Incorporated (USA)

Shure Europe (Germany)

Südwest Rundfunk - SWR (Germany)

University of Brunswick (Germany)

360communications (Germany)

7 List of abbreviations

LTE Long Term Evolution UE User Equipment PMSE Programme Making and Special Events SINAD Signal to Noise And Distortion Ratio IF Intermediate Frequency RF FDD

Radio Frequency Frequency Division Duplex

8 List of devices

Rohde & Schwarz FSW Spectrum Analyser Rohde & Schwarz FSQ8 Spectrum Analyser Rohde & Schwarz CMW500 Tektronix RSA 6114A Rohde & Schwarz RTO 1544

LTE Base Station Emulator Real-Time Spectrum Analyser GHz Real Time Oscilloscope

____________________________________________________________________________


9 Annex

Additional plots are shown in this chapter.

Figure 15: LTE UE 1 operating in band 17


____________________________________________________________________________




____________________________________________________________________________




____________________________________________________________________________


dB

0

-2.5

-5

-7.5

-10

-12.5

-15

-17.5

-20

-22.5

-25

800 MHz Duplex Gap Filter

S21

Duple

x g

ap

filt

er

loss [d

B]

Centre: 825.0000 MHz Span: 50.0000 MHz

Mkr Trace X-Axis Value Notes

1

1 S21 827.0000 MHz -0.68 dB Duplex gap centre

2

2 S21 822.0000 MHz -0.80 dB Duplex lgap ower edge

3

3 S21 832.0000 MHz -0.91 dB Dupex gap upper edge, LTE UE lower edge

4

4 S21 837.0000 MHz -4.23 dB LTE UE centre

5

5 S21 842.0000 MHz -11.88 dB LTE UE upper edge

Figure21: Filter which was used to determine if overloading occurred

____________________________________________________________________________


10 Reference Documents

[1] APWPT and the DKE WG 731.0.8 (DIN/VDE), “A study of LTE interference potential with regard to

PMSE operation”, June 2012, http://www.apwpt.org/downloads/lte-interference-potential-to-

micros30062012.pdf

[2] Joint ITU-R Study Group JTG 4-5-6-7, Document R12 JTG 4-5-6-7 C 0127 Annex 01, “SAB/SAP

PARAMETERS FOR SHARING STUDIES UNDER WRC-15 AGENDA ITEM 1.2”, www.itu.int

[3] European Telecommunications Standards Institute (ETSI) System Reference Document TR 102 546,

Attachment 2 “Applicable Receiver Parameter for PWMS below 1 GHz”, 2006,

not-binding copy: http://www.apwpt.org/downloads/tr102546v111202completecompressed.pdf

http://www.apwpt.org/downloads/lte-interference-potential-to-micros30062012.pdf

http://www.apwpt.org/downloads/lte-interference-potential-to-micros30062012.pdf

http://www.itu.int/

http://www.apwpt.org/downloads/tr102546v111202completecompressed.pdf

____________________________________________________________________________

© 2013 Institut für Rundfunktechnik GmbH. All rights reserved. Page 22

Institut für Rundfunktechnik GmbH

Floriansmuehlstraße 60

80939 Munich

Germany

www.irt.de

Phone +49 (0) 89 | 323 99 - 300

Fax +49 (0) 89 | 323 99 - 620

[email protected]

Register Court Munich HRB 5191