German Commission for Electrical, Electronic & Information Technologies

of DIN and VDE

Working Group 731.0.8 “Professional Wireless Microphones”

Report on preparations for an LTE measurement in cooperation with Vodafone and Huawei

Düsseldorf, 15th December 2009

1. Objective of the Working Group's activity

To prepare measurements/ a measurement set up for LTE pilot trials

If possible

o Collect measured data for the LTE spectrum and

o Test the effect of interference on wireless microphone paths

2. Information on measurement methods and setup

Measurement setup for the free space measurement method

Measurements were not taken during the preparatory laboratory trial.

Test setup for the conducted measurement method

The test setup is comparable with that for the free field measurement method. The

free field path is replicated by the antenna coupler and the attenuator . The “RF

generator” emulates the wireless microphone transmitter:

DKE WG 731.0.8 “Professional Wireless Microphones”: LTE Measurement Preparations – February 2010

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Conducted test setup (Base station and Terminal)

The LTE terminal equipment and the LTE base station are connected by RF cable.

Attenuators in the cable connection emulate the antenna path. An additional RF

coupler decouples the interferer signal.

Principal measurement method

A measurement generator modulated with a 1 kHz tone simulates a wireless mi-

crophone transmitter and feeds an antenna (free field measurement) and a

branch of an antenna coupler (laboratory measurement), thus simulating a wire-

less microphone.

A microphone receiver, connected to an additional coupler antenna output, is op-

erated on the same frequency. The NF is routed to a SINAD measuring device.

The distance of the measurement antennas from each other is approx. 6m. In the

laboratory measurement, the free field is replicated by attenuators.

The measuring transmitter level is set as such that a SINAD of 20 dB is produced

without an interfering signal. Measurement generator level and frequency are to

be entered in the measurement log.

The interfering source is now switched on (direct radiation into the free field sig-

nal or the other antenna coupler port) and alternated with the measuring trans-

mitter and receiver frequency at the interfering frequency (pilot transmission).

This will adversely affect the SINAD and noticeably increase the unwanted noise.

A SINAD of 20 dB is again set by changing the measuring generator level. After

this, the measurement generator level and frequency are to be entered in the

measurement log.

This measurement is to be repeated at a number of frequencies below, at and

above the interfering frequency.

The graph of the generator level against the measurement frequency displays the

interference range and the effect on the microphone receiver.

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Installed LTE and microphone equipment

Base station:

The base station was a prototype, which could not be documented in more detail.

Terminal equipment:

The terminal equipment’s were Huawei laboratory models, which most likely did not

equate to the properties of later terminal equipment in terms of their overall behav-

iour.

Devices under test

(1) Sennheiser EW 100 G3 series microphone receiver

When in the presence of a large signal, this receiver behaves in approximately the

same manner as the reference receiver described in the SRDoc “Draft ETSI TR 102

546”.

DKE WG 731.0.8 “Professional Wireless Microphones”: LTE Measurement Preparations – February 2010

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(2) Sennheiser 3000 series EM 3732 microphone receiver

Compared with the “EW 100 G3” this represents a large signal improvement of ap-

proximately 10 to 15 dB.

Laboratory set up with LTE terminal

Microphone receiver (DUT) and a measurement generator replicating a microphone

Terminal equipment, wideband coupler and attenuators

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Measurement generator and RF splitter

Dummy antenna for the base station and replication of the antenna path using a variable attenuator

3. Measured results

LTE signal within the frequency range

LTE terminal spectrum measured with RMS and peak detectors

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LTE terminal spectrum measured with RMS and peak detectors

LTE terminal spectrum with differing data rates (2 and 30 Mbits/s)

LTE terminal spectrum (2 and 30 Mbits/s), integrated over 2 minutes

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LTE signal in time domain:

LTE terminal signal (30 Mbits/s) in time domain

The microphone reception effected by LTE

EW 100:

Frequency-dependent microphone receiver level for 20 [dB] SINAD in the presence of a 30 Mbits/s LTE signal

(A slight rise in the interference frequency to 865 MHz occurs with the EW100)

Generator level for 20 dB SINAD

DKE WG 731.0.8 “Professional Wireless Microphones”: LTE Measurement Preparations – February 2010

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EM 3732:

Frequency-dependent microphone receiver level for 20 [dB] SINAD in the presence of a 30 Mbits/s LTE signal

4. Analysis

LTE terminal signal in TV channels 65-69

Frequency-dependent terminal level at a 50Ω terminating resistor

Generator level for 20 dB SINAD

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Rough estimate of the terminal effect in the microphone link

With an adjacent channel level of -35 dBm /-40 dBm /-50 dBm, a safety distance of

approximately 270 m / 150 m / 50 m is required for safe operation of wireless micro-

phones at 840 MHz. At lower frequencies, the safety distance increases accordingly.

If there is no line of sight, then lower safety distances can be depicted.

Notes:

A rough calculation is obtained from a[dB]~22dB+20*log(D/λ)

[a = attenuation (dB), D = distance (m), λ = wavelength (m)]

Permitted interference level for microphone receivers ≤ -115 dBm (ETSI TR

102 546)

Because these are not the final LTE devices, these statements in the best case

are only a pointer. For subsequent measurements with improved LTE devices,

particular care should be paid to whether unwanted transmission into adjacent

channels, for example by using filters, has improved.

Estimate of the base station effect in the microphone link

The base station could not be examined. In principle it can be assumed from this

that these have, on the one hand, a significantly better output power and on the

other it can be assumed that better antenna filters are in use.

An assessment will only be possible as part of measurements that are still in the

planning stage only.

Summary

As part of a preparatory trial, it was possible to gather initial experiences regarding

the interaction of wireless microphones when in the presence of LTE signals.

However, it must be assumed from this that the signal spectrum emitted by LTE de-

vices still does not equate to the future situation. As such, all observations must be

considered provisional.

It was possible to confirm the recommended technical measurement rig in practice

and therefore this can be used for comparable activities.

The DKE Working Group is available to take further measurements with LTE data devices.