RSCOM17-17 JRC Study on Alds.Pdf

EUROPEAN COMMISSION Directorate-General for Communications Networks, Content and Technology

Electronic Communications Networks and Services Radio Spectrum Policy

Brussels, 9 March 2017 DG CONNECT/B4

RSCOM17-17

PUBLIC DOCUMENT

RADIO SPECTRUM COMMITTEE

Working Document

Subject: Presentation of the study on Assistive Listening Devices (ALDs) in the 2.3-2.4 GHz band by the JRC

This is a Committee working document which does not necessarily reflect the official position of the Commission. No inferences should be drawn from this document as to the precise form or content of future measures to be submitted by the Commission. The Commission accepts no responsibility or liability whatsoever with regard to any information or data referred to in this document

European Commission, DG Communications Networks Content & Technology, 200 Rue de la Loi, B-1049 Bruxelles RSC Secretariat, Avenue de Beaulieu 33, B-1160 Brussels - Belgium - Office BU33 7/09 Telephone: direct line (+32-2)299.66.11 / 295.26.65 switchboard (+32-2)299.11.11. Fax: (+32-2) 296.83.95 E-mail : [email protected]

JRC Study on Coexistence between LTE and Wireless Hearing Aid Systems operating in the 2.4 GHz band

Final Report

09 March 2017

European Commission Joint Research Centre

Ispra (Italy)

Prepared by: Detlef Fuehrer, Jean‐Marc Chareau, Philippe Viaud, Tiziano Pinato, James Bishop

Contents Glossary ...... 5 1. Introduction ...... 7 2. Definitions ...... 8 3. Objectives of this study ...... 8 4. Summary of findings ...... 8 5. Hearing Aid Systems ‐ Background ...... 10 5.1 Hearing Aids ...... 10 5.2 Assistive Listening Devices (ALDs) ...... 11 6. LTE‐HAS Coexistence ...... 13 6.1 LTE characteristics ...... 13 6.1.1 TD‐LTE ...... 13 6.1.2 FDD‐LTE ...... 13 6.2 Previous studies on LTE‐HAS coexistence ...... 14 7. Assessment of the impact of LTE signals on HAS ...... 15 7.1 Tested devices ...... 15 7.2 Interference scenarios and use cases ...... 16 7.3 Test procedure ...... 16 7.4 Test signals and metrics ...... 16 7.4.1 Interfering signal characteristics ...... 18 7.5 Measurement setup ...... 19 7.6 Measurements and Observations ...... 22 7.6.1 Setup 1 ...... 22 7.6.2 Setup 2 ...... 25 7.6.3 Setup 3 ...... 27 7.6.4 Setup 4 ...... 31 7.6.5 Setup 5 ...... 34 7.6.6 Setup 6 ...... 35 7.6.7 Setup 7 ...... 36 7.6.8 Setup 8 ...... 37 7.7 Analysis ...... 38 7.7.1 Quality assessment methodology ...... 38 7.7.2 Results ...... 39 8. Summary and conclusions ...... 41 Appendix A – List of measurement equipment ...... 42 Appendix B – Audio recordings ...... 43 List of Tables ...... 44 List of Figures ...... 45 Bibliography ...... 46

Note: All trademarks and registered trademarks are the property of their respective owners.

Glossary

ALD Assistive Listening Device Bluetooth LE Bluetooth Low Energy BS Base Station BTE Behind‐The‐Ear CCTV Closed Circuit TV CEPT European Conference of Postal and Telecommunications Administrations CF Centre Frequency CIC Completely‐In‐Canal dB Decibel dBm Decibel milliwatt DL Downlink DUT Device Under Test EC European Commission ECC Electronic Communications Committee EHIMA European Hearing Instrument Manufacturers Association ETSI European Telecommunications Standards Institute EU European Union E‐UTRA Evolved UMTS Terrestrial Radio Access FDD‐LTE Frequency Division Duplex LTE FM Frequency Modulation HA Hearing Aid HAS Hearing Aid System IEC International Engineering Consortium IIC Invisible‐In‐Canal ISM Industrial, Scientific, Medical ISTS International Speech Test Signal ITC In‐The‐Canal ITE In‐The‐Ear ITU‐R International Telecommunication Union ‐ Radiocommunication Sector JRC Joint Research Centre LOS Line Of Sight LSA Licensed Shared Access LTE Long Term Evolution MOS Mean Opnion Score MUS Minimum Usable Signal NFMI Near‐Field Magnetic Induction Ofcom UK [UK] Office of Communications OOB Out‐Of‐Band PAR Peak‐to‐Average Ratio PDSCH Physical Downlink Shared Channel PEAQ Perceptual Evaluation of Audio Quality PMSE Program Making and Special Events RF Radio Frequency RIC Receiver‐In‐Canal RITE Receiver‐In‐The‐Ear 5

RSC Radio Spectrum Committee Rx Receive SRD Short Range Device SNR Signal‐to‐Noise Ratio TD‐LTE Time Divivsion Duplex LTE TV Television Tx Transmit UAS Unmanned Aircraft Systems UE User Equipment UL Uplink WBB Wireless Broadband WHO World Health Organisation Wi‐Fi Wireless Fidelity (IEEE 802.11)

1. Introduction

The band 2300‐2400 MHz is allocated to the Mobile Service on a co‐primary basis by ITU radio Regulations in all three ITU regions, and footnote 5.384A of the Radio Regulations identifies this frequency band for IMT. Existing use of the 2300‐2400 MHz frequency band in the European Union (EU) includes telemetry (terrestrial and aeronautical); fixed links, other governmental use including unmanned aircraft systems (UAS) and closed‐circuit television (CCTV), program making and special events (PMSE) ancillary video links as well as amateur radio as a secondary service. Following a positive opinion of the Radio Spectrum Committee (RSC), the European Commission (EC) submitted in April 2014 a Mandate to the European Conference of Postal and Telecommunications Administrations (CEPT) to develop harmonised technical conditions in the 2300‐2400MHz band for wireless broadband (WBB) electronic communication services in the EU. In response to the Commission Mandate and following a public consultation, the CEPT delivered in November 2014 its Report 55 on the technical conditions for wireless broadband usage of the 2300‐ 2400 MHz band. In light of the comments submitted by Member States, the on‐going trials of Licensed Shared Access (LSA) in some Member States, and concerns brought to the attention of the EC regarding possible interference of LTE equipment operating in the 2300‐2400 MHz band with other equipment operating in the 2400 MHz band, the Commission proposed and RSC decided at its July 2015 meeting to postpone the adoption of an Implementing Decision until after WRC‐15. Despite the variety of studies on coexistence between 2300 MHz TD‐LTE and systems operating in the 2400 MHz unlicensed band (further on referred to as “victims” or “victim systems”) that have been conducted so far no consensus among the stakeholders regarding the severity of interference from TD‐LTE could be reached. One of the perceived shortcomings of these studies was the limited number of potential victim devices that were tested. Therefore, the EC’s Joint Research Centre (JRC) was requested to conduct a comprehensive technical study on the potential impact of TD‐LTE on the population of deployed Wi‐Fi devices. The final results of this study were presented to the RSC at its October 2016 meeting. At the July 2016 meeting of the RSC it had been agreed that a subsequent study should assess the impact of LTE interference on Assistive Listening Devices (ALDs) operating in the 2.4 GHz band. Within the scope of this study a four‐day measurement event was held in November 2016 at the premises of the JRC in Ispra in which representatives of the European Hearing Instrument Manufacturers Association (EHIMA) and three major manufacturers of hearing aid systems participated. The results of this study are presented in the current document.

2. Definitions

A variety of terms and definitions exist for assistive listening devices and hearing aids, with often slightly different connotations. In this document we use the following terms and definitions:

Hearing aid (HA): Medical device comprising an electro‐acoustic amplifier including a microphone and a loudspeaker and having a frequency response and dynamic characteristics specific to each person's individual hearing loss. Some modern hearing aids feature integrated wireless receivers. Assistive Listening Device (ALD): Radiocommunication device used in addition to hearing aids to make more sounds accessible to people with hearing impairment. It usually comprises a transmitter, which can be handheld, on a table or around the neck of a hearing impaired person, and one or more receivers, where each receiver can have a wired or wireless (inductive) connection to a hearing aid or be an integral part of a hearing aid. Hearing Aid System (HAS): Comprises the hearing aid(s) plus accessories as well as any type of assistive listening device1.

3. Objectives of this study

A number of studies have been published that address coexistence between TD‐LTE and HAS and other types of wireless short‐range devices (SRD) that use Bluetooth, Bluetooth LE and similar technologies [1] [2] [3] [4]2. The objective of this study was to complement the findings from the aforementioned studies by assessing the additional impact on HAS performance from FDD‐LTE operating in the 2.5 GHz band and by more systematically analysing the effect of concurrent Wi‐Fi operation on different channels. As the group of test devices included a number of prototypes featuring the latest technology the results should also provide an indication of the progress made in terms of HAS performance and robustness against interference.

4. Summary of findings

In this study we examine the effects of adjacent‐band LTE signals on the quality of audio signals received by ALDs and hearing aids. For this purpose we conducted measurements with 21 devices from six major manufacturers in 23 different test configurations. Overall, 192 individual measurements were made. We focused on the effect of transmissions from LTE User Equipment (UE) operating in proximity of hearing aid systems.

When HAS were operating near the receiver sensitivity level, i.e. when their RF signals were highly attenuated, the presence of strong adjacent‐band LTE signals resulted in degradation of the audio signals in a number of cases. Adding in‐band Wi‐Fi signals generally worsened the situation.

In combination, TD‐LTE and FDD‐LTE degraded victim signal quality slightly more than individually.

1 This definition essentially corresponds to that of “aids for hearing impaired” in ETSI TR 102 791 V1.2.1 (2013‐ 08) [1]. 2 A summary of the results of these studies is provided in section 6.2 of this document 8

For adjacent‐band LTE signals to cause degradation of a HAS audio signal a number of conditions must be fulfilled:

` The quality of the RF link between HAS transmitter and receiver is poor, i.e. the signal‐to‐ noise ratio (SNR) at the receiver is low. ` There is a nearby LTE UE transmitting continuously, e.g. during the upload of a large file to a remote base station. ` The LTE UE is located close to the HAS receiver. Depending on the model of LTE UE the distance at which the audio signal is impaired can be between a few centimetres to 1 metre for severe degradation, and up to 11 metres for minor degradation. These values were calculated for free‐space / line‐of‐sight conditions. ` LTE is operating at the band edges, i.e. 2390 MHz for TD‐LTE and 2505 MHz for FDD‐LTE3.

We also noted that the RF emissions from certain HAS models can severely degrade Wi‐Fi performance. Overall, our findings are fully in line with those of the various previous studies. The adaptive frequency‐hopping mechanism that has apparently been implemented in the devices we tested proved to be very effective for interference mitigation. We conclude that while HAS audio signal quality can be impaired by adjacent‐band TD‐LTE signals the combination of prerequisites for this to happen makes the overall risk appear low. Furthermore, we conclude that the additional presence of FDD‐LTE UE signals in the 2.5 GHz band does not significantly increase the degradation of HAS audio quality.

3 Due to time constraints the impact of LTE signals further removed from the 2.4 GHz band edges could not be assessed. While previous studies considered only TD‐LTE and frequencies up to 2390 MHz the conditions created in this study correspond to worst‐case scenarios. 9

5. Hearing Aid Systems ‐ Background

According to the World Health Organization (WHO) over 5% of the world’s population – 360 million people of which 32 million are children – suffer from disabling hearing impairment [5]. Although hearing loss mostly affects the elderly the number of children and young adults suffering from hearing loss is growing steadily. It is estimated that in the US around 5% in the age between 5 and 24 are affected [6]. Globally, some 1.1 billion teenagers and young adults are at risk of hearing loss due to the unsafe use of personal audio devices and exposure to damaging levels of sound at noisy entertainment venues, the WHO reports [7]. Hearing aid systems can enable these persons to participate in daily life. Currently, hearing aids are used by about 50 million people4.

5.1 Hearing Aids While their mechanical predecessors have been in use since at least the early 17th century electric hearings aids came into play at the beginning of the 20th century, with the advent of the carbon microphone. The first wearable hearing aid was developed in 1938 [8]. Until the late 1980s hearing aids were based on analogue technology when advances in semiconductor manufacturing and digital signal processing heralded the digital age, initially in hybrid analogue‐digital models in which digital circuits controlled an analogue compression amplifier. Fully digital models debuted in 1996, and programmable models, which allow for greater flexibility and fine‐tuning of the hearing aids according to the patient's needs, became available in 2000 [8]. In 2004, the first wireless hearing aid was introduced [9]. The majority of hearing aids fall under the “air conducted sound” category [10]. The two major groups are “In‐The‐Ear” (ITE), located in the ear canal and “Behind‐The‐Ear” (BTE) located behind the ear, but with parts of the aid located in the ear canal [11]. There are several kinds of canal‐style devices: “Completely‐In‐Canal” (CIC) and “Invisible‐In‐Canal” (IIC) devices fit the deepest within the canal; a tiny extension cord is used to place and remove the instrument. “In‐The‐Canal” (ITC) devices are slightly larger, so they extend farther out but remain hidden [12]. “Receiver‐In‐Canal” (RIC) and “Receiver‐In‐The‐Ear” (RITE) devices are similar in concept to BTE hearing aids, with the exception that the speaker has been detached from the case and fitted in the ear canal or ear and connected to the case of the hearing aid with a thin wire [13].

Various other types of hearing aids exist such as bone‐anchored aids and cochlear implants. These types have not been included in this study and are therefore not covered here. Detailed information on hearing impairments and the different types of hearing aids can be found in [10] and [14].

The global market volume for hearing aids (BTE, RIC, RITE, IIC) is estimated between 4.5B [15] and 6B USD [16]. In 2014, 12 million hearing aids were sold globally [6]. By 2019 this number is forecast to increase to 17 million, [17]. Europe accounts for 41% of units sold [18].

In the first‐half of 2016, about 9 of 10 (87.5%) hearing aids sold contained wireless technology [19]. While still negligible today, shipments of Bluetooth devices are expected to increase to 6 million units by 2019 [20] which corresponds to a market share of 35%.

The hearing aid market is dominated by six major suppliers which in 2014 held a combined market share of approximately 98% [6].

4 Estimate based on figures reported in [18] 10

Figure 1: Hearing aid manufacturers‘ global market shares (2014) [6]

5.2 Assistive Listening Devices (ALDs) ALDs are, in most cases, comprised of an audio source, an RF transmitter and a gateway. The gateway receives the audio signal from the RF transmitter and relays it to the hearing aid(s), typically via a neck loop using near‐field magnetic induction (NFMI). The transmitter coil inside the neck loop produces a magnetic field, typically in the 3 to 15‐MHz range which is picked up by an induction receiver coil in the hearing aid. The audio signal can originate from a smartphone, a wireless microphone, or from any other audio equipment such as a TV set (Figure 2). Hearing aids featuring integrated RF receivers do not require a gateway but can be connected to the ALD directly (Figure 3).

RF transmitter and receiver typically operate in the FM, 900 MHz, or 2400 MHz band. Recent ALDs and hearing aids increasingly use digital wireless technologies such as Bluetooth and Bluetooth Low‐ Energy. The use of digital technologies in the 2.4 GHz band is relatively new; first products were announced in 2011.

Bluetooth 4.0 was introduced as part of the main Bluetooth standard in 2010, incorporating Bluetooth Low Energy, which was later renamed Bluetooth Smart by the Bluetooth Special Interest Group. Bluetooth Smart was aimed at new low‐power and low‐latency applications for wirelesss devices within a range up to 50 m. Devices operating with this version consume a small fraction of the power of classic Bluetooth and they quickly became available in products within the healthcare, fitness, and home entertainment industries [4].

Figure 2: Wireless audio transmission to Gateway device

Figure 3: Direct wireless audio transmission to Hearing Aids

A particular challenge for this type of hybrid wireless transmission lies in the delay the audio signal undergoes on its way between source and the user’s eardrum. This delay results from audio data compression, coding and transcoding from the RF protocol to the NFMI signal. In the case of a TV signal, such delay may result in a lack of synchronicity between the video and the streamed audio signal. The International Telecommunication Union suggests that audio/video transmission delays should not exceed −40 milliseconds (audio delayed) and +20 milliseconds (audio advanced) [21].

Listeners’ tolerance for delay within an audio stream is even smaller when streamed and direct audio signals are combined. Small delays in streamed audio may result in a perceived echo which is particularly detrimental for users who enjoy listening to music through open‐canal hearing aids. In the case of well‐vented or open‐canal hearing aids, a delay of 5 milliseconds may degrade sound quality. Latencies higher than 5 ms will affect speech intelligibility but also other parameters such as the user’s ability to locate the origin of the sound [11].

6. LTE‐HAS Coexistence

In Europe the 2400‐2500 MHz band has been made available to unlicensed wireless systems which comprise a variety of technologies, such as Wi‐Fi and Bluetooth, and services such as wireless broadband, audio transmission, and motion detection. The bands above and below this unlicensed have been allocated to wireless broadband (Figure 4). FDD‐LTE in band 7 has already been deployed in a number of European countries; TD‐LTE in band 40 is so far only being deployed or in preparation to be deployed by operators in Lithuania and Russia [22]. On the band edges the frequency separation between LTE channels and the unlicensed band is very small so that there is a potential risk of interference between the systems deployed in adjacent bands. The hearing aid system community has therefore been concerned that the presence of high‐power LTE systems operating in the adjacent bands may lead to degradation of HAS performance.

Band 40 ISM and others Band 7 (up) Band 7 (down) TD‐LTE ALDs FDD‐LTE FDD‐LTE

2300 2400 2483.5 2500 2570 2620 2690

Figure 4: LTE and HAS frequency allocations between 2300 and 2690 MHz (Europe)

6.1 LTE characteristics

6.1.1 TD‐LTE CEPT Report 55 [23] proposes to make the 2300‐2400 MHz band (band no. 40) available for TD‐LTE. The frequency arrangement should be based on 20 blocks of 5 MHz (Figure 5).

TD‐LTE Band 40

MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz

2395 2390 2385 2380 2375 2370 2365 2360 2355 2350 2345 2340 2335 2330 2325 2320 2315 2310 2305 2300

5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5

Figure 5: Proposed TD‐LTE frequency arrangement in the 2300‐2400 MHz band [23]

LTE user equipment (UE) may transmit with a power of up to 23 ±2 dBm, measured as the sum of the maximum output power at each UE antenna connector [24].

6.1.2 FDD‐LTE The frequency arrangement within the 2500‐2690 MHz band was defined in ECC/DEC/(05)05 [25].

In this frequency arrangement which is shown in Figure 6 any FDD uplink block (UL xx) is paired with its corresponding FDD downlink block (DL xx). The minimum block or channel width is 5 MHz5. In Europe, the most common channel widths are 10 MHz and 20 MHz. MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz MHz

2500 2670 2505 2675 2510 2680 2515 2685 2520 2690 2525 2530 2535 2540 2545 2550 2555 2560 2565 2570 2575 2580 2585 2590 2595 2600 2605 2610 2615 2620 2625 2630 2635 2640 2645 2650 2655 2660 2665 UL UL UL UL UL UL UL UL UL UL UL UL UL UL TDD DL DL DL DL DL DL DL DL DL DL DL DL DL DL 01 02 03 04 05 06 07 08 09 10 11 12 13 14 or 01 02 03 04 05 06 07 08 09 10 11 12 13 14 FDD Uplink BlocksFDD Downlink (External) FDD Downlink Blocks

Figure 6: Frequency arrangement within the 2500‐2690 MHz band

6.2 Previous studies on LTE‐HAS coexistence

Copsey Communications conducted a series of measurements with a number of ALDs and hearing aids using Bluetooth, Bluetooth LE, or proprietary protocols that were exposed to interference from adjacent‐band TD‐LTE signals [1]. Both 10 MHz signals, centred at 2385 MHz and 20 MHz signals, centred at 2380 MHz were used. During all measurements Wi‐Fi was present. Three types of equipment were tested, categorised as streamers, microphones, and smart devices/ experimental systems. The study found that, depending on the type of LTE signal and device under test (DUT), performance degradation/receiver blocking occurred within a distance of 0.15 to 4 metres from the TD‐LTE UE. In 2013 Mac Ltd. conducted a study for Ofcom UK on the effects TD‐LTE signals in the 2.3 GHz band have on Bluetooth equipment operating in the 2.4 GHz band [2]. Both quantitative and qualitative tests were made. In the first case, a Bluetooth tester was employed to generate a test signal and measure the bit error rate of the device under test. For the qualitative test, an audio signal was streamed from a mobile phone to a Bluetooth DUT in the presence of a TD‐LTE signal. With all three devices that were tested, distortion of the audio signal occurred only when the interfering signal level reached very high levels (15 dBm into the antenna at a few centimetres separation from the headset), and only in one case it was possible to break the Bluetooth link. The authors concluded that a) the most significant interference mechanism is Bluetooth receiver blocking and TD‐LTE OOB emissions would have little impact, and b) Bluetooth devices are robust in the presence of interference and users of Bluetooth devices are unlikely to notice any impact if TD‐LTE services were introduced in Band 40. Coexistence measurements conducted by Cambridge Silicon Radio (CSR) on Bluetooth devices showed that the tested devices “exceeded the expected performance, continuing to function in the presence of very strong LTE interference with a UE signal at ranges down to 0.05 m” [3]. The interferer was a TD‐LTE signal with a bandwidth of 20 MHz and a centre frequency of 2380 MHz. During all measurements Wi‐Fi was present. With only two devices tested, the authors cautioned that it could not be concluded that all devices in the field would operate as robustly. In a study published by the EHIMA the possible effects of LTE signals occupying the 2350‐2390 MHz band on Bluetooth LE‐based ALDs were examined, taking into account ALD receiver blocking, LTE out‐of‐band (OOB) emissions, and ALD receiver selectivity noise [4]. Simulations were made for indoor and outdoor LTE base stations, femtocells and user equipment as interference sources. The study found that for an LTE signal occupying the frequency range up to 2390 MHz minimum separation distances between LTE UE and ALD of 0.5 to 50 metres would be required to satisfy the Bluetooth LE bit error rate requirement of 10‐3.

5 As an exception, Annex A of EC Decision 2008/477/EC [26] allows a departure from the arrangement for TDD operation on a national basis. This would result in TDD operation starting in DL and UL blocks 14 and extending downwards the band in contiguous blocks as required. 14

7. Assessment of the impact of LTE signals on HAS

To assess the potential impact of adjacent‐band LTE signals on HAS performance the following approach was taken, in close collaboration with EHIMA and HAS manufacturers:

1. Selection of devices to be tested 2. Definition of usage and interference scenarios 3. Definition of signal parameters and test metrics/performance indicators 4. Development of measurement setups 5. Measurement of the impact of interfering signals on HAS performance 6. Analysis of measurement results 7. Conclusions

7.1 Tested devices Measurements were conducted with 22 different devices in 23 configurations6.

DUT Victim link DUT type Companion device type ID technology 1 Wireless receiver with inductive loop TV audio streamer Bluetooth 2 Remote microphone Wireless receiver with inductive loop Proprietary 3 Remote microphone Wireless receiver with inductive loop Proprietary 4 Remote microphone Wireless receiver with inductive loop Proprietary 5 TV audio streamer Wireless receiver with inductive loop Bluetooth 6 Hearing aid Smartphone Bluetooth LE 7 Wireless receiver with inductive loop Smartphone Bluetooth 8 TV audio receiver & control TV audio streamer Proprietary 9 Hearing aid Smartphone Bluetooth 10 Hearing aid Smartphone Bluetooth 11 Hearing aid Smartphone Bluetooth 12 Hearing aid Smartphone Bluetooth 13 Hearing aid Smartphone Bluetooth 14 Remote microphone Wireless receiver with inductive loop Bluetooth 15 Hearing aid Smartphone Proprietary 16 Hearing aid Remote microphone Proprietary 17 Hearing aid Remote microphone Proprietary 18 Wireless receiver with inductive loop Remote microphone Proprietary 19 Wireless in‐ear receiver Remote microphone Proprietary 20 Hearing aid Smartphone Proprietary 21 Hearing aid Smartphone Proprietary 22 Hearing aid TV audio streamer Proprietary 23 Wireless headphone Smartphone Bluetooth

Table 1: List of tested devices

6 DUT21 and DUT22 were identical but tested with different companion devices. 15

7.2 Interference scenarios and use cases In this study we focus on the impact of interference from LTE UE signals on HAS operation. The interferer (the UE) operates in proximity of the victim, and both are located indoors, for instance in a room or a vehicle. The LTE base station signal is assumed to be weak in comparison to the UE signal.

Three typical use cases, as proposed by the Hearing Aid industry, have been considered.

` Case A: Two persons are sitting in a bus next to each other. One person makes an LTE data link from their phone and uploads a big file or movie. The second person is streaming audio wirelessly (e.g. via Bluetooth LE) to their hearing aid devices. ` Case B: Two persons are sitting in a car close to each other. One person, sitting in the passenger front seat makes an LTE data link from their phone and uploads a big file or movie. The second person who sits in the back seat of the car is streaming audio wirelessly from an ALD placed in the front of the car to a gateway device which relays the audio signal to their hearing aid. ` Case C: A hearing aid user is watching TV using a 2.4 GHz ALD to listen to the TV audio. A second person in the same room makes an LTE data link from their phone and uploads a big file or movie.

Furthermore, we took into account the possibility of multiple interferers being active simultaneously. In Case A, for instance, there could be one another passenger sitting in the next row and uploading a file from his FDD‐LTE UE, or in Case C there could be a download ongoing via Wi‐Fi. In all of the above cases the distance between HAS components is small so that under LOS conditions the RF link between them would be strong. Under certain conditions, however, additional attenuation, for instance from a body blocking the RF signal, can amount up to 50 dB, as outlined in [4].

7.3 Test procedure The test procedure was relatively simple: An RF link was established between DUT and companion device. An audio signal (also referred to as ‘test signal’) was transmitted to the DUT from a companion device. In some cases the level of the wanted RF signal (also referred to as ‘victim signal’ or ‘victim link’) was set to the lowest level at which, in the absence of interference, no audible degradation of the test signal could be observed7.

At the beginning of each measurement cycle a recording of the audio signal was made without any interfering signal being present. This recording would constitute the reference that the other signals would be compared to. Then, the DUT was exposed to one or more interfering RF signals. The received audio signal was aurally monitored and simultaneously recorded for later analysis.

7.4 Test signals and metrics Owing to the volatile nature of the wireless channel audio signals streamed over wireless links may experience degradation of the perceived sound quality, particularly when highly compressed audio codecs are employed to reduce the required transmission rate. The amount of error correction that can be applied is limited due to the low‐latency requirements in case direct sounds are transmitted or synchronisation between audio and video signals needs to be maintained.

7 This level will further on be referred to as “Minimum Usable Signal” (MUS) level. 16

Typical degradation effects include bandwidth reduction, distortion artefacts, and signal drop‐outs. A selection of artefacts, as provided in [26] is shown in Table 2.

Artefact/Attribute Description Inherent noise Continuous hissing. Distortion Crackling, short bursts of hissing, buzzing, clipping. Spatial distortion Wobbling, sound image stability, loss of directionality. "Birdies" or tweets "Chirps" in mid to high frequencies. Temporal smearing Pre/post echo, "sound shadow", diffuse onset of the sound. Tone trembling Sounds like trembling tones, noticeable on longer notes. Sparkling. Thin sound Timbre artefact related to skewed frequency response, lack of bass. "Can" sound Timbre artefact related to boost and/or resonances in the mid‐range frequencies.

Table 2: Observed artefacts and attributes of streamed audio signals [26]

Radio interference from other wireless systems can add to the amount and impact of artefacts being generated.

Not all users, however, will be equally sensitive to the aforementioned artefacts which makes objective measures for and statements about sound quality difficult. Different methods for sound quality measurements exist. Some are based on physical measurements and perceptual models, such as PEAQ (Perceptual Evaluation of Audio Quality, ITU‐R BS.1387), others on structured listening tests. The latter method was proposed for this study by the HAS community. A reference audio signal commonly used in ALD/hearing aid test and measurement is the International Speech Test Signal (ISTS). ISTS was developed by EHIMA and adopted by the International Engineering Consortium (IEC) in hearing aid standard IEC 60118‐15 [27]. The ISTS consists of fragments of real speech recordings from six different languages, namely Arabic, English, French, German, Mandarin, and Spanish. The resulting signal has all major characteristics of speech, can be recognized by humans as being composed out of real speech, but is not intelligible. The signal bandwidth ranges from 100 Hz to 16 kHz so that hearing instruments with conventional bandwidths up to about 6000 Hz, as well as those with high‐frequency extended bandwidths can be measured. During the measurement campaign not all manufacturers of ALDs/hearing aids used the ISTS for detecting impairments of the audio signal. Several products were tested with a 1 KHz sine wave signal. For the aural assessment of the recorded signals the following metrics were chosen: Audible drop‐ outs, clicks, and glitches, as well as variations in volume or frequency response, and the occurrence of wobbling or trembling.

Furthermore, the Mean Opinion Score (MOS) for each of the recorded signals should be determined. The values obtained for recordings made in the presence of interference would then be compared to those of the reference signals. The MOS is frequently used to determine the perceived quality of received voice that has undergone processing for transmission over a digital link. On a scale from 1 to 5 the MOS indicates the expected level of user satisfaction in respect to voice quality (Table 3).

User Satisfaction Level MOS Very satisfied 4.3 ‐ 5.0 Satisfied 4.0 ‐ 4.3 Some users satisfied 3.6 ‐ 4.0 Many users dissatisfied 3.1 ‐ 3.6 Nearly all users dissatisfied 2.6 ‐ 3.1 Not recommended 1.0 ‐ 2.6

Table 3: Mean Opinion Score (MOS)

7.4.1 Interfering signal characteristics Table 4 lists the main characteristics of the interfering signals that were applied during the measurements. Due to time constraints only a limited number of waveforms could be evaluated. We therefore selected those TD‐LTE waveforms which in our previous study on TD‐LTE and Wi‐Fi coexistence [28] had been found to cause the highest amount of degradation of victim performance.

Interferer Centre frequency Channel Waveform [MHz] width [MHz]

2310.0 20 UE UL, Rome B2.3 2350.0 20 UE UL, Rome B2.3 TD‐LTE 2390.0 20 UE UL, Rome B2.3 2397.5 5 TM 1.1 2505.0 10 Ispra FDD UL FDD‐LTE 2486.0 10 Ispra FDD UL 2422 (Ch 1+5) 40 Wi‐Fi 2447 (Ch 6+10) 40 2452 (Ch 11+7) 40

Table 4: Interfering signal characteristics

The signal UE UL is a signal recorded close to a TD‐LTE UE during upload a large file to a remote base station. The measured transmit power levels (during transmission) were +19 dBm (maximum) and +16 dBm (mean), resp. The Peak‐to‐Average Ratio (PAR) for this signal is 14.6 dB.

Rome B2.3 is a signal recorded close to two TD‐LTE UEs which simultaneously uploaded large files to a remote base station. The PAR for this signal is 20 dB.

TM1.1 corresponds to test model E‐UTRA 1.1, as defined in [29]. E‐TM1.1 is employed to test various TD‐LTE base station parameters, including output power, unwanted emissions, and transmitter intermodulation. It is based on uplink/downlink configuration no. 3 and Special Subframe (SSF) configuration no. 8 defined in 3GPP TS36.211 [30]. It is a downlink‐heavy configuration with 6 downlink slots and 3 uplink slots per TD‐LTE frame. The Physical Downlink Shared Channel (PDSCH) is fully occupied by a single user, without power variation during transmission. The PAR for this signal is 12.4 dB.

Ispra FDD UL is a signal recorded close to an FDD‐LTE UE uploading a large file to a commercial base station located on the JRC Ispra site. The PAR for this signal is 6 dB. A few measurements were conducted with the centre frequency set to 2486 MHz to study the hypothetical case of a broadband signal being present at the edge of the 2.4 GHz band.

To study the impact of in‐band interference from Wi‐Fi three different IEEE802.11n‐compliant signals were selected which occupied either the lower, centre, or upper part of the victim band. To maximise spectrum occupation the channel width was set to 40 MHz.

7.5 Measurement setup The measurements were conducted in a fully shielded anechoic chamber of the JRC’s Radio Spectrum Lab in Ispra. The chamber which measures 7 m x 3.5 m x 3 m (D x W x H) has been calibrated for frequencies up to 18 GHz. To assess the impact of simultaneous interference from TD‐ LTE and FDD‐LTE on HAS operation two broadband horn antennas were installed which transmitted the interfering signals. The DUT was placed in line of sight of, and at the same height as the horn antennas. Initially, the distance between the horn antennas and the DUT was 3.7 metres. To model realistic conditions, particularly in terms of RF signal propagation a phantom head (Figure 7) was employed which is used for characterisation and optimisation of the RF link of hearing aids (COLHA). Depending on the type of test, either DUT or companion device were attached to the head. The LTE signals were generated by two arbitrary waveform generators. The waveforms had been recorded in the course of the previous JRC study on coexistence between TD‐LTE and Wi‐Fi. Furthermore, a Wi‐Fi router and client were installed in the chamber to be able to study the effects of additional in‐band interference from Wi‐Fi. The iperf3 tool was used to generate TCP traffic between router and client. In the initial setup the companion device was placed behind the horn antennas to minimise its exposure to the interfering signal(s). For certain measurements which required an adjustment of the wanted RF signal level the companion device was placed inside a shielded box. The RF port of Figure 7: COLHA head the box was connected to an omnidirectional antenna via a programmable attenuator. The auddio test signal was streamed from the companion device to the DUT. The audio output signal from the DUT was amplified, digitised, and recorded with a personal computer. Victim and interfering signals were monitored using a log‐periodic monitoring antenna and a spectrum analyser. The initial test setup inside the chamber is shown in Figure 8, the explanatory block diagram in Figure 9. A list of the measurement equipment is provided in Appendix A of this document.

Figure 8: Initial HAS measurement setup inside the JRC’s anechoic chamber

Fully‐shielded anechoic chamber

Monitoring Wi‐Fi antenna Router Tx antenna 1 RF (LTE)

Companion Victim link Audio DUT device RF (LTE)

Tx antenna 2 3.7 m

Wi‐Fi Client

Signal Signal USB Audio Audio PC generator 1 generator 2 ADC Pre‐amp

Spectrum analyser

Figure 9: Initial HAS measurement setup (Setup 1)

For the initial measurements the distance between Tx antennas and DUT had been chosen so that the DUT was located in the far field of the Tx antennas and interfering signal levels at the victim of up to ‐21 dBm could be reached. The objective was to assess the impact of LTE on HAS operation at LTE signal levels which had been observed in real‐life situations.

After no negative impact on HAS performance was observed for any of the evaluated scenarios the setup was modified on request of the HAS industry representatives. The objective was revised to determine the interfering signal levels at which HAS operation would be disrupted. The measurement distance was reduced to 1 m so that the maximum interfering signal levels at the DUT increased by up to 11 dB8.

Depending on the type of DUT and the usage scenario the companion devices were placed in various locations inside the anechoic chamber (Figure 10). For certain measurements which required an adjustment of the wanted RF signal, i.e. the victim link level the companion device was placed inside a shielded box. The RF port of the box was connected to an omnidirectional antenna via a programmable attenuator.

Overall, there were eight variations of this setup which differed in terms of the number of Tx antennas, the Tx antenna polarisation, and the location of the companion device.

Fully‐shielded anechoic chamber

Wi‐Fi Companion Router device

Tx antenna 1 RF (LTE)

Companion Companion DUT device device RF (LTE)

Tx antenna 2 1 metre Audio

Wi‐Fi Client

Signal Signal USB Audio Audio PC generator 1 generator 2 ADC Pre‐amp

Figure 10: Final HAS measurement setup (Setups 2‐8)

8 Taking into account near‐field antenna gain. 21

7.6 Measurements and Observations

7.6.1 Setup 1 In this setup which corresponds to the initial setup shown in Figure 9 a total of 43 measurements with six DUTs (DUT 1 to 6) were conducted. As audio test signal the ISTS was used.

DUT 1 The phantom head with receiver (the DUT) and HAs was placed on top of the support at a distance of 3.7 metres from the transmit antenna. The companion device was placed behind the transmit antennas, approximately 4 metres from the DUT.

Figure 11: DUT 1 (Setup 1)

For the first set of measurements the DUT was oriented in the horizontal position. • Interfering signal: TD‐LTE UE UL • Centre frequencies: 2310, 2350, and 2390 MHz • Transmit power9 range: ‐30 dBm to +5 dBm • Resulting LTE signal power at the DUT: ‐67 to ‐32 dBm (mean10), and ‐55 to ‐19 dBm (peak)

As no audible impartments to the test signal could be observed two additional measurements were conducted with signal TD‐LTE UE UL at a centre frequency of 2390 MHz and with transmit power levels of +10 dBm and +15 dBm. For this purpose the TD‐LTE signal was transmitted from the second signal generator. The resulting LTE signal power levels (mean/peak) at the DUT were ‐28/‐13 dBm and ‐23/‐8 dBm, resp.

9 “Transmit power” indicates the power setting of the signal generator which corresponds to the mean signal power measured over the entire duration of the signal 10 Mean power at the DUT indicates the mean signal power during the period of transmission 22

To take into account a possible polarisation mismatch between the Tx antennas and the integrated DUT antenna a second set of measurements was conducted with the DUT oriented in the vertical position. Centre frequencies and power levels were set to the maximum values to create worst‐case conditions.

• Interfering signals: TD‐LTE UE UL, Rome B2.3, TM 1.1 • Centre frequencies: o UE UL: 2390 MHz o Rome B2.3: 2390 MHz o TM1.1: 2397.5 MHz • Transmit power levels: o UE UL: +15 dBm o Rome B2.3: +10 dBm o TM1.1: +17 dBm • Resulting LTE signal power at the DUT (mean/peak): o UE UL: ‐23/‐8.4 dBm o Rome B2.3: ‐26/‐8 dBm o TM1.1: ‐21/‐8.6 dBm

On one channel of the reference signal very faint artefacts were observed, originating most probably from a mobile phone coupling into the audio link in the control room. These artefacts were not present in any of the other recordings.

The last set of measurements was then repeated with DUT 1 oriented in the vertical position but rotated by 180 degrees.

In the next step the effect of two adjacent band LTE signals on victim performance was evaluated. • Interfering signals: o TD‐LTE: Rome B2.3 o FDD‐LTE: Ispra FDD UL • Centre frequencies: o Rome B2.3: 2390 MHz o Ispra FDD UL: 2505 MHz • Transmit power levels: o Rome B2.3: +10 dBm o Ispra FDD UL +14 dBm • Resulting LTE signal power at the DUT: o Rome B2.3:: ‐27 (mean), ‐9 dBm (peak) o Ispra FDD UL ‐28 (mean), ‐23 dBm (peak)

A final set of measurements was made with the companion device placed in a shielded box. The victim RF signal level was reduced to the minimum at which no audible degradation of the test signal could be observed. • Interfering signal: TD‐LTE Rome B2.3 • Centre frequency: 2390 MHz • Transmit power range: ‐10 dBm to +10 dBm • Resulting LTE signal power at the DUT: ‐51 to ‐31 dBm (mean), and ‐33 to ‐13 dBm (peak)

As no audible effects on the test signal could be observed in any of the above scenarios a few additional experiments were conducted during which the following observations were made:

` A TD‐LTE signal (Rome B2.3) was transmitted in the 2.4 GHz band (CF= 2442 MHz). The audio link could not be disrupted, even when operating at the MUS level. ` Two TD‐LTE signals (Rome B2.3 and UE UL) were transmitted simultaneously in the 2.4 GHz band (CF= 2432 MHz and 2462 MHz, resp.). The audio link could not be disrupted, even when operating at the MUS level. ` When the frequency of the TD‐LTE signal UE UL was changed to 2452 MHz there was a reduction of audio quality lasting several seconds but then the HAS recovered.

DUT 2 The DUT, a remote microphone) was placed on top of the support; the phantom head with receiver and HAs was placed on the floor next to the support to simulate a real usage scenario (Case A). • Interfering signal: TD‐LTE UE UL • Centre frequencies: 2390 MHz • Transmit power level: +15 dBm • Resulting LTE signal power at the DUT: ‐26 dBm (mean), ‐13 dBm (peak)

Observations: ` Very faint artefacts were present in all signals, even in the absence of interference. No further degradation was observed when interference was added. ` Even with two in‐band TD‐LTE signals present simultaneously (Rome B2.3 and UE UL, at various frequencies and with maximum transmit power) the audio link could not be disrupted.

DUTs 3‐5 Each DUT (remote microphones and audio streamer) was placed on top of the support; the phantom head with receiver and HAs was placed on the floor next to the support.

To save time we maintained the previous setup and conducted measurements with two in‐band interferers. Observations: ` The results were the same as for DUT 2: Even with two in‐band TD‐LTE signals present simultaneously (Rome B2.3 and UE UL, at various frequencies and with maximum transmit power) the audio link could not be disrupted.

DUT 6 DUT 6, a hearing aid, was attached to the phantom head and placed on top of the support. The companion device was placed at the opposite end of the chamber. In this case audio was streamed from companion device directly to the hearing aids. The link quality between DUT 6 and the companion device (smartphone) was so poor that a piece of absorbing material placed in front of the companion device disrupted the audio stream. Thus, it was inferred that the HAS operated at MUS level. DUT 6 was the only device identified as using Bluetooth LE. • Interfering signal: TD‐LTE UE UL • Centre frequency: 2390 MHz • Transmit power range: ‐30 dBm to +15 dBm

• Resulting LTE signal power at the DUT: ‐73 to ‐28 dBm (mean), and ‐58 to ‐13 dBm (peak) Observations: ` Even without interference being present some artefacts (glitches, wobbling) were present in the audio signal. ` No further degradation was observed when interference was added.

With this setup the DUTs were exposed to electrical fields of up to 1.6 V/m (mean) and 7 V/m (peak). No impact on the HAS audio signal quality could be observed.

7.6.2 Setup 2 In Setup 2 Tx antenna 2 was removed and the separation distance between Tx antenna 1 and the DUT was reduced to 1 metre. Only DUT 6 was measured with this setup. ISTS was used as the audio test signal. The DUT was placed on top of the support, with the phantom head reversed, i.e. with its back facing the Tx antenna. The companion device was placed on the opposite end of the chamber. This setup corresponds to Case B defined in Section 7.2.

Figure 12: DUT 6 (Setup 2)

The first set of measurements was made with TD‐LTE signal UE UL at 2390 MHz and a transmit power range from +4 dBm to +15 dBm (resulting LTE mean signal power at the DUT: ‐25 to ‐14 dBm) Observations: ` From +8 dBm on audio quality started deteriorating. At +8 dBm the audio signal from the left channel was lost after 45 seconds and did not recover until the end of the recording. A second recording was made during at the same power level; this time only minor artefacts were observed. The corresponding LTE signal power at the DUT was ‐21 dBm (mean) / ‐6 dBm (peak). ` Between +9 and +11 dBm some artefacts occurred (glitches, wobbling). At +12 dBm the audio signal from the left channel was lost after 25 seconds but returned 30 seconds later. ` Between +13 and +15 dBm a few artefacts could be observed (wobbling but no glitches) suggesting that the HAS may have adapted to the interference environment.

A further measurement was made with TD‐LTE signal Rome B2.3 at 2390 MHz and a transmit power of +10 dBm (LTE mean signal power at the DUT: ‐19 dBm). Observations: ` There was a slight degradation of the audio quality. Several glitches and instances of wobbling could be observed. The corresponding LTE signal power at the DUT was ‐17 dBm (mean) / ‐2 dBm (peak).

For the next set of measurements additional interference from Wi‐Fi was generated. • Distance from Wi‐Fi AP to DUT: 3.8 m • Distance from Wi‐Fi client to DUT: 2.9 m

The Wi‐Fi signal level at the DUT was approximately ‐47 dBm11.

1. Wi‐Fi channel 1+5 ` With only Wi‐Fi present a few artefacts were audible during the first 10 seconds. After that, no degradation of the audio signal could be observed.

Next, TD‐LTE signal Rome B2.3 was added (centre frequency: 2390 MHz, Tx power range: +5 dBm to +10 dBm). ` At a Tx power level of +5 dBm the audio signal from the left channel was lost after approximately 15 seconds but recovered 20 seconds later (Figure 13). The resulting LTE signal power at the DUT was ‐22 dBm (mean) / ‐4 dBm (peak); the electric field strength was 1.2 V/m (mean) and 12 V/m (peak).

Figure 13: Distortion of the DUT 6 audio signal in the presence of Wi‐Fi and TD‐LTE (setup 2)

` For Tx power levels from +6 dBm to +9 dBm no degradation of the audio signal could be observed.

11 Average power during transmission. 26

` At a Tx power level of +10 dBm the audio signal from the left channel was lost after 16 seconds but recovered 23 seconds later. The resulting LTE signal power at the DUT was ‐ 17 dBm (mean) / +1 dBm (peak).

2. Wi‐Fi channel 6+10 Measurements were made with Wi‐Fi only and with Wi‐Fi plus TD‐LTE signal Rome B2.3 (centre frequency: 2390 MHz, Tx power: +10 dBm). Observations: ` With only Wi‐Fi present a few artefacts were observed (two glitches and a few instances of wobbling). ` When both Wi‐Fi and TD‐LTE were present no degradation of the audio signal could be observed.

3. Wi‐Fi channel 11+7 Measurements were made with Wi‐Fi only and with Wi‐Fi plus TD‐LTE signal Rome B2.3 (centre frequency: 2390 MHz, Tx power: +10 dBm). Observations: ` When only Wi‐Fi was present the audio signal from the right channel showed disruptions during the first 12 seconds and then was lost permanently. ` When both Wi‐Fi and TD‐LTE were present severe degradation of the audio signal occurred.

7.6.3 Setup 3 For Setup 3 Tx antenna 2 was installed again. Four DUTs were measured, two hearing aids (DUTs 6 and 9), one Bluetooth receiver with inductive loop (DUT 7) and one TV audio receiver (DUT 8). For DUTs 6‐8 the ISTS was used as test signal, and for DUT 9 a 1 kHz sine tone.

DUT 6 The DUT was placed on top of the support; the companion device (audio streamer) was placed at the far end of the chamber. The phantom head remained in reverse position (back facing the antenna).

Figure 14: DUT 6 (Setup 3)

To assess the impact on HAS operation of a broadband signal at the upper edge of the 2.4 GHz band the FDD‐LTE frequency was set to 2486 MHz.

LTE signal characteristics: • Waveforms o TD‐LTE: Rome B2.3 o FDD‐LTE: Ispra FDD UL • Centre frequencies o Rome B2.3: 2390 MHz o Ispra FDD UL: 2486 MHz • Transmit power levels o Rome B2.3: +10 dBm o Ispra FDD UL +14 dBm • Resulting LTE signal power at the DUT o Rome B2.3:: ‐17 (mean), +1 dBm (peak) o Ispra FDD UL ‐18 (mean), ‐13 dBm (peak)

The first measurement was made with a TD‐LTE signal and an FDD‐LTE signal present at the same time. ` During the first 35 seconds there were only minor artefacts audible. After that the audio signal quality was severely degraded.

For the next measurement a Wi‐Fi signal on channels 6+10 was added. LTE frequencies and signal levels were left unchanged. ` Audio signal quality was severely degraded from the beginning with multiple glitches occurring on both channels.

The Wi‐Fi channel was then changed to 11+7. ` The audio from the right channel was lost permanently after 4 seconds. The audio signal from the left channel remained stable with only minor degradation.

Finally, a measurement was made with only FDD‐LTE present. ` There was a very noticeable impact on the audio signal in the form of wobbling on both channels and multiple glitches on the right channel.

DUT 7 The phantom head was reversed again so that it faced the LTE Tx antennas (Figure 15). The DUT was placed on top of the support, and the companion device was placed at the far end of the chamber.

Figure 15: DUTs 7 and 8 (Setup 3)

With DUT 7 two measurements were made, with Wi‐Fi only (Channel 6+10), and with Wi‐Fi, TD‐LTE, and FDD‐LTE present at the same time.

LTE signal characteristics: • Waveforms o TD‐LTE: Rome B2.3 o FDD‐LTE: Ispra FDD UL • Centre frequencies: o Rome B2.3: 2390 MHz o Ispra FDD UL: 2505 MHz • Transmit power levels: o Rome B2.3: +10 dBm o Ispra FDD UL +14 dBm • Resulting LTE signal power at the DUT: o Rome B2.3:: ‐17 (mean), +1 dBm (peak) o Ispra FDD UL ‐18 (mean), ‐13 dBm (peak)

` No degradation of the audio signal quality was observed.

DUT 8 For DUT 8 the previous setup was maintained. During all measurements Wi‐Fi was present on channels 6+10.

The first measurement was made with only Wi‐Fi present. ` No degradation of the audio signal quality was observed.

For the second measurement an FDD‐LTE signal was added. 29

• Centre frequency: 2505 MHz • Transmit power level: +14 dBm • Resulting LTE power at DUT: ‐18 dBm (mean) / ‐13 dBm (peak)

` A number of short drop‐outs in the audio signal occurred.

For the third measurement the FDD‐LTE signal was replaced with a TD‐LTE signal. • Signal: Rome B2.3 • Centre frequency: 2390 MHz • Transmit power level: +10 dBm • Resulting LTE power at the DUT: ‐17 dBm (mean) / +1 dBm (peak)

` When the TD‐LTE signal was switched on the audio signal was lost immediately. When the transmit power was reduced to +5 dBm the audio signal was received but suffered from dropouts.

Further measurements were conducted with various combinations of TD‐LTE and FDD‐LTE signals and signal levels. ` When a strong FDD‐LTE signal was present (Tx power: +14 dBm, power at the DUT: ‐18 dBm) a relatively weak TD‐LTE signal (Tx power: ‐26 dBm, power at the DUT: ‐53 dBm) was sufficient to cause dropouts in the audio signal. ` An increase of the TD‐LTE transmit power to +5 dBm (power at the DUT: ‐22 dBm) resulted in the immediate and permanent loss of the audio signal.

DUT 9 The phantom head was reversed again so that the back was facing the antenna. The DUT was placed on top of the support; the companion device was placed at a distance of approximately 2 metres and in line of sight (LOS).

For DUT 9 a 1 KHz sine wave was used as audio test signal. It was noticed that this signal displayed a periodic pitch shift which occurred approximately every 2 seconds.

Figure 16: DUT 9 (Setup 3)

Three measurements were made with this configuration. During all measurements Wi‐Fi was present on channels 6+10.

The first measurement was made with only Wi‐Fi present. There were several occurrences of short bursts of low‐level noise, approximately 0.3 s in length.

For the second measurement an FDD‐LTE signal was added. • Centre frequency: 2505 MHz • Transmit power level: +14 dBm • Resulting signal power at the DUT: ‐18 dBm (mean) / ‐13 dBm (peak) Again, there were several occurrences of short bursts of low‐level noise.

For the third measurement a TD‐LTE signal was added so that all three interferers were active. • Signal: Rome B2.3 • Centre frequency: 2390 MHz • Transmit power level: +10 dBm • Resulting signal power at the DUT: ‐17 dBm (mean) / +1 dBm (peak)

As in the previous two measurements several short bursts of low‐level noise were observed.

7.6.4 Setup 4 A total of five DUTs, all hearing aids, were measured with this setup (DUTs 9 – 13). For these DUTs a 1 KHz sine wave was used as audio test signal. In each case the DUT was placed on top of the support; the companion device was placed in shielded box at a distance of approximately 1 metre from the DUT (Figure 17). For each DUT the wanted signal level was adjusted to the minimum level at which no degradation of the audio signal quality could be observed (MUS). The LTE Tx antennas were rotated by 90 degrees into the horizontal polarisation plane, as the DUTs would be more susceptible to horizontally polarised interfering signals.

Figure 17: DUTs 9‐13 (Setup 4)

For all DUTs measurements were made for various combinations of interference from Wi‐Fi, TD‐LTE, and FDD‐LTE. 31

• Interfering signals: o Wi‐Fi: Channel 6+10 o TD‐LTE: Rome B2.3 o FDD‐LTE: Ispra FDD UL • Centre frequencies: o Rome B2.3 2390 MHz o Ispra FDD UL: 2505 MHz

Transmit power levels were varied between ‐10 dBm and +10 dBm for the TD‐LTE signal, and between ‐10 dBm and +14 dBm for the FDD‐LTE signal. Several additional measurements were made with an FDD‐LTE signal centred at 2486 MHz.

DUT 9 Even in the absence of interference there was noticeable background noise indicating that the system was working at MUS level. Four measurements were conducted with different configurations in which all active interferers transmitted at maximum power level. ` When only Wi‐Fi was present the audio signal was lost after 33 seconds but recovered 3 seconds later. ` With only TD‐LTE present the background noise level increased noticeably and short dropouts occurred frequently. ` When TD‐LTE and Wi‐Fi were active the audio signal was lost temporarily. ` When TD‐LTE, FDD‐LTE, and Wi‐Fi were active the audio signal was lost permanently.

Further measurements were conducted with different combinations of interferers and transmit power levels. ` At a TD‐LTE transmit power level of ‐10dBm there was no impairment of the audio signal, even with FD‐LTE operating at maximum power and Wi‐Fi active at the same time. ` The audio signal started being disrupted when the TD‐LTE transmit power reached ‐8 dBm which corresponds to a signal level at the DUT of ‐35 dBm (mean) / ‐17 dBm (peak).

DUT 10 Even in the absence of interference there was noticeable background noise indicating that the system was working at MUS level. ` When only Wi‐Fi was present there was a strong increase in background noise, accompanied by frequent pitch shifts and dropouts. ` When only FDD‐LTE was present audio quality started deteriorating at a transmit power level of ‐3 dBm. At maximum transmit power (signal level at the DUT: ‐18 dBm) the audio signal was lost immediately. ` When both TD‐LTE and FDD‐LTE were present the audio link could only be maintained when the FDD‐LTE signal level at the DUT was lower than ‐40 dBm. ` When TD‐LTE and Wi‐Fi were present the audio link broke down after a few seconds. It could only be maintained when the TD‐LTE power at the DUT was lower than ‐32 dBm. Additional measurements were conducted with an FDD‐LTE signal at 2486 MHz and a maximum power level at the DUT of ‐34 dBm. No degradation of the audio signal quality was observed.

DUT 11 Even in the absence of interference there was noticeable background noise indicating that the system was working at MUS level. ` When only Wi‐Fi was present the audio signal was lost twice, for durations of 5 and 6 seconds. ` When only TD‐LTE was present (Tx power = +10 dBm) the audio link was lost almost immediately. ` When both TD‐LTE and FDD‐LTE were present the audio link could only be maintained when the FDD‐LTE signal level at the DUT was lower than ‐41 dBm and the TD‐LTE signal level was lower than ‐42 dBm. ` When TD‐LTE, FDD‐LTE, and Wi‐Fi were present the audio link could only be maintained when the FDD‐LTE level was lower than ‐43 dBm and the TD‐LTE level was lower than ‐42 dBm.

Additional measurements were conducted with an FDD‐LTE signal at 2486 MHz. ` The audio signal was lost immediately when the FDD‐LTE signal was switched on (signal level at the DUT: ‐18 dBm). ` Audio quality started deteriorating at an FDD‐LTE signal level at the DUT of ‐38 dBm. Although Wi‐Fi signals alone caused disruptions to the audio signal the addition of FDD‐LTE at 2486 MHz (signal level at the DUT below ‐38 dBm) appeared to improve the situation. No degradation of the audio signal could be observed, probably because the Wi‐Fi system adapted or the HAS completely avoided the upper part of the 2400 MHz band.

DUT 12 Even in the absence of interference there was noticeable background noise indicating that the system was working at MUS level. ` When only Wi‐Fi was present short disruptions and glitches were observed. ` When only FDD‐LTE was present audio quality started deteriorating at a transmit power level of ‐3 dBm. At maximum transmit power (+14 dBm) the audio signal was lost immediately. ` When both TD‐LTE (signal level at the DUT: ‐17 dBm) and FDD‐LTE were present the audio link could only be maintained when the FDD‐LTE level at the DUT was lower than ‐41 dBm. ` When both TD‐LTE (signal level at the DUT: ‐17 dBm) and Wi‐Fi were present the audio link broke down immediately. The audio link could only be maintained when the TD‐LTE level was lower than ‐36 dBm. ` When both FDD‐LTE and Wi‐Fi were present the audio link could only be maintained when the FDD‐LTE level was lower than ‐36 dBm.

DUT 13 Due to time constraints no audio recordings were made for DUT 13. ` When only Wi‐Fi or FDD‐LTE (signal level at the DUT: ‐18 dBm) were present no degradation of the audio signal was observed. ` When only TD ‐LTE (signal level at the DUT: ‐17 dBm) was present minor glitches were observed. ` When any two of the interferers were present and transmitting at maximum power the audio signal was lost within 4 seconds. 33

` When both TD‐LTE and FDD‐LTE were present the audio link could only be maintained when the FDD‐LTE signal level at the DUT was lower than ‐33 dBm and the TD‐LTE less than‐35 dBm. ` When TD‐LTE, FDD‐LTE, and Wi‐Fi were present the audio link could only be maintained when the FDD‐LTE level was lower than ‐36 dBm and the TD‐LTE level was less than ‐35 dBm.

7.6.5 Setup 5 This setuup was used to measure DUT 14, a remote microphone. The DUT was placed on top of the support, audio was supplied from a smartphone via cable, and the companion device, a wireless receiver, was placed at the opposite end of the chamber (Figure 18). ISTS was used as the audio test signal.

Figure 18: DUT 14 (Setup 5)

Two measurements were conducted, one with only Wi‐Fi present, and one with all three interferers active. • Interfering signals: o Wi‐Fi: Channel 6+10 o TD‐LTE: Rome B2.3 o FDD‐LTE: Ispra FDD UL • Centre frequencies: o Rome B2.3: 2390 MHz o Ispra FDD UL: 2505 MHz • Transmit power levels o Rome B2.3: +10 dBm o Ispra FDD UL: +14 dBm • Resulting signal power at the DUT: o Rome B2.3: ‐17 dBm (mean) / +1 dBm (peak) o Ispra FDD UL: ‐18 dBm (mean) / ‐13 dBm (peak)

` No audible degradation of the audio signal could be observed.

7.6.6 Setup 6 This setup was used to measure DUT 15, a hearing aid. The DUT was placed on top of the support, the companion device, a smartphone, was placed at a distance of approximately 1 metre from the DUT (Figure 19). ISTS was used as the audio test signal.

Figure 19: DUT 15 (Setup 6)

Four measurements were conducted with this setup: 1. Wi‐Fi‐only 2. Wi‐Fi + TD‐LTE 3. Wi‐Fi + FDD‐LTE 4. Wi‐Fi + TD‐LTE + FDD‐LTE

• Interfering signals: o Wi‐Fi: Channel 6+10 o TD‐LTE: Rome B2.3 o FDD‐LTE: Ispra FDD UL • Centre frequencies: o Rome B2.3: 2390 MHz o Ispra FDD UL: 2505 MHz • Transmit power levels o Rome B2.3: +10 dBm o Ispra FDD UL: +14 dBm • Resulting signal power at the DUT: o Rome B2.3: ‐17 dBm (mean) / +1 dBm (peak) o Ispra FDD UL: ‐18 dBm (mean) / ‐13 dBm (peak)

` No degradation of the audio signal could be observed.

7.6.7 Setup 7 Five DUTs were measured with this setup, DUTs 16‐18 (hearing aids) and DUTs 19 and 22 (RF receivers). In each case the DUT was placed on top of the support; the companion device was placed at the opposite end of the chamber (Figure 20). ISTS was used as the audio test signal.

Figure 20: DUTs 16‐19, 22 (Setup 7)

For each DUT four measurements were conducted: 1. Wi‐Fi‐only 2. Wi‐Fi + TD‐LTE 3. Wi‐Fi + FDD‐LTE 4. Wi‐Fi + TD‐LTE + FDD‐LTE

Interfering signals: o Wi‐Fi: Channel 6+10 o TD‐LTE: Rome B2.3 o FDD‐LTE: Ispra FDD UL Centre frequencies: o Rome B2.3: 2390 MHz o Ispra FDD UL: 2505 MHz Transmit power levels o Rome B2.3: +10 dBm o Ispra FDD UL: +14 dBm Resulting signal power at the DUT: o Rome B2.3: ‐17 dBm (mean) / +1 dBm (peak) o Ispra FDD UL: ‐18 dBm (mean) / ‐13 dBm (peak) Field strength at the DUT: 2.1 V/M (mean) / 21 V/m (peak)

` No degradation of the audio signal could be observed during any of these measurements.

An additional experiment was conducted with DUT 20. To test the robustness of the RF link the two LTE signals were moved inband, TD‐LTE to 2422 MHz and FDD‐LTE to 2475 MHz, with Wi‐Fi still being present.

` Audio quality deteriorateed slightly. ` Wi‐Fi throughput was reduced from 55 Mbits/s to to 2 Mbits/s. ` When DUT 22 was tested with only Wi‐Fi present the Wi‐Fi link broke down completely. On the monitoring spectrum analyser it could be observed that the ALD system’s frequency hopping signal did not avoid the band occupied by Wi‐Fi. When the companion device was moved by about 50 cm, Wi‐Fi started working again but at a reduced rate of approximately 10 Mbits/s. ` When TD‐LTE was added, Wi‐Fi throughput deteriorated further, to less than 1 Mbit/s.

7.6.8 Setup 8 Three DUTs were measured with this setup, DUTs 20 and 21 (hearings aids), and DUT 23 (headphone). In each case the DUT was placed on top of the support; the companion device (smartphone) was placed at a distance of approximately 1 metre from the DUT (Figure 21).

Figure 21: DUTs 20, 21, and 23 (Setup 8)

For each DUT four measurements were conducted: 1. Wi‐Fi‐only 2. Wi‐Fi + TD‐LTE 3. Wi‐Fi + FDD‐LTE 4. Wi‐Fi + TD‐LTE + FDD‐LTE

Resulting signal power at the DUT: o Rome B2.3: ‐17 dBm (mean) / +1 dBm (peak) o Ispra FDD UL: ‐18 dBm (mean) / ‐13 dBm (peak) Field strength at the DUT: 2.1 V/M (mean) / 21 V/m (peak)

No degradation of the audio signal could be observed during any of these measurements.

7.7 Analysis

The objective of this study is to assess the impact of adjacent band TD‐LTE and FDD‐LTE signals on the performance of HAS equipment operating in the 2.4 GHz band. For this purpose any degradation of the quality of the received audio signal should be identified that might have been caused by LTE and/or Wi‐Fi signals.

During the measurements the audio signals were recorded and monitored, in real time, for flaws such as glitches and dropouts. Subsequently, the recordings where aurally examined to identify more subtle degradations such as wobbling and trembling. It should be mentioned that audio quality varied considerably between DUTs, particularly in terms of background noise and frequency response. Further information on this subject is provided in Appendix B of this document.

We also tried to make a quantitative assessment of the degradation of signal quality caused by different levels of interference. For this purpose we analysed the ISTS recordings by means of an audio quality analyser software tool, namely AQuA [31]. AQuA is a tool for end‐to‐end During the process, however, we encountered a number of voice and audio quality testing. problems which have prevented us from obtaining conclusive results as of now. It determines the Mean Opinion Score (MOS) and relative Audio files may contain drop‐outs or show other signs of degradation of an audio signal by degradation at random locations. If the total duration of comparing a reference or source these impairments is short compared to the overall file and a (degraded) received file. duration of the audio file they may not be considered critical for overall file quality by the audio analyser. As a consequence, the calculated MOS score for the degraded file may be not much lower than that of the original file although audio quality was severely degraded. In order to reflect the severity of such impairment more accurately it was proposed to split reference and test audio into short segments (e.g. of 10 seconds duration) and compare those separately.

AQuA features a large number of variable parameters to adapt its signal processing algorithms to the audio material and the test environment. In the time available for conducting this study it has not been not possible to fully understand and verify how variations of these parameters affect the results of the signal quality calculations. We therefore restricted our analysis to the qualitative method described below.

7.7.1 Quality assessment methodology Depending on the level of audio quality degradation we defined three impact categories: “Zero”, “Minor” and “Severe”.

` Zero: No audible degradation ` Minor: Up to two glitches or short dropouts, light wobbling or trembling, minor increase of background noise.

` Severe: Temporary or permanent loss of signal, more than two glitches or short dropouts, strong wobbling or other distortions reducing speech intelligibility, strong increase in background noise.

For each category we determined the interferer signal levels at the location of the DUT. We then calculated the corresponding separation distances between DUT and interferer by applying the free‐ space propagation model according to Friis.

For calculating the separation distances we had to take certain assumptions on the power transmitted by LTE User Equipment. In [28] we had characterised four different types of TD‐LTE UE and measured transmit power levels12 between ‐9 dBm and +20 dBm (median: +17 dBm). These measurements had been conducted during a file upload from the UE to the network when the UE was located deep indoors so that the base station signal was highly attenuated and the UE had to increase its transmit power to maintain the connection. In the calculations both cases were taken into accounts.

We further categorised the victim links as “Strong” or “Weak”. As the actual level of the wanted signal at the DUT was not measured the categories were defined as follows:

─ A link was considered “strong” when the signal was not artificially attenuated by placing the companion device in the shielded box. ─ Conversely, a link was considered “weak” when the companion device was placed in the shielded box.

An exception to this rule is DUT 6. As detailed in Section 7.6.1 the link between this device and its companion was found to be “weak” even under line‐of‐sight conditions.

7.7.2 Results Overall, 188 measurements were conducted. In 136 cases no degradation of the HAS audio signal was observed. 92 measurements were conducted with “strong” victim links. In eight cases (related to DUTs 8 and 9) degradation of the audio signal quality was observed. 96 measurements were conducted with “weak” victim links. In 44 cases degradation of the audio signal quality was observed. Severe degradations occurred only when audio signals were transmitted over “weak” victim links. There was one exception, DUT 8 which reacted considerably more sensitive to the presence of interference than other DUTs. It is therefore quite possible that the system operated at minimum sensitivity and the link actually was “weak”. A similar observation was made for minor degradations. These, too, occurred only when audio signals were transmitted over “weak” victim links. Again, there was one exception, in this case DUT 9, where audio signals recorded in the presence of interference showed several noise bursts. Although barely perceptible, these were taken into account as minor degradations. The calculated separation distances (line‐of‐sight) for different combinations of interfering signals and LTE UE transmit power levels which resulted in degradation of the audio signal are provided in Table 5 and Table 613.

12 Mean power during transmission. 13 The centre frequencies are 2390 MHz for TD‐LTE and 2505 MHz for FDD‐LTE. The channel widths are 20 MHz for TD‐LTE and 10 MHz for FDD‐LTE. 39

If an LTE UE transmits at low output power (‐ 9 dBm in this case) a minor degradation of the HAS audio quality can occur if the UE is located within a short distance from the HAS (Table 5). When more than one interferer is active separation distances increase slightly but not in all cases. For LTE UE transmitting at high output power (+20 dBm) a minor degradation of the HAS audio quality can occur if the UE is located within several metres from the HAS (Table 5). When more than one interferer is active separation distances increase in some but not all cases.

Audio degradation Minor UE transmit power Minimum Maximum Equivalent separation distance [m] Equivalent separation distance [m] TD‐LTE UE FDD‐LTE UE TD‐LTE UE FDD‐LTE UE

Interferer Range Median Range Median Range Median Range Median TD‐LTE only 0.02 ‐ 0.03 0.03 0.6 ‐ 0.9 0.71 TD‐LTE + Wi‐Fi 0.22 ‐ 0.45 0.33 6.3 ‐ 12.6 9.43 FDD‐LTE only 0.03 ‐ 0.29 0.2 5.7 5.7 FDD‐LTE + Wi‐Fi 0.03 ‐ 0.23 0.13 0.8 ‐ 6.4 3.62 TD‐LTE + FDD‐LTE 0.03 ‐ 0.45 0.11 0.16 ‐ 0.41 0.38 0.7 ‐ 12.6 3.16 4.6 ‐ 11.4 10.83 TD‐LTE + FDD‐LTE + Wi‐Fi 0.03 ‐ 0.45 0.20 0.03 ‐ 0.51 0.23 0.7 ‐ 12.6 5.61 0.8 ‐ 14.4 6.44

Table 5: Equivalent separation distances for different levels of LTE UE Tx power and minor audio quality degradation

For severe degradation of audio signal quality to occur LTE UE transmitting at low output power (‐ 9 dBm) have to be located within a very short distance from the HAS (Table 6). When more than one interferer is active separation distances increase insignificantly. For LTE UE transmitting at high output power (+20 dBm) severe degradation of the HAS audio quality can occur if the UE is located within approximately one metre from the HAS (Table 6). When more than one interferer is active separation distances can increase to a few metres.

Audio degradation Severe UE transmit power Minimum Maximum Equivalent separation distance [m] Equivalent separation distance [m] TD‐LTE UE FDD‐LTE UE TD‐LTE UE FDD‐LTE UE

Interferer Range Median Range Median Range Median Range Median TD‐LTE only 0.03 0.03 0.71 0.71 TD‐LTE + Wi‐Fi 0.03 ‐ 0.04 0.03 0.71 ‐ 1.26 0.71 FDD‐LTE only 0.03 0.03 0.81 0.81 FDD‐LTE + Wi‐Fi 0.03 0.03 0.81 0.81 TD‐LTE + FDD‐LTE 0.03 0.03 0.71 0.03 0.03 0.71 0.81 0.81 TD‐LTE + FDD‐LTE + Wi‐Fi 0.03 ‐ 1.58 0.12 0.03 0.03 0.71 ‐ 44.6 3.43 0.81 0.81

Table 6: Equivalent separation distances for different levels of LTE UE Tx power and severe audio quality degradation

The Friis Free space equation is valid only in the far field region of the transmitting antenna. The very small separation distances calculated above should therefore be considered qualitative indications.

8. Summary and conclusions In this study we examine the effects of adjacent‐band LTE signals on the quality of audio signals received by ALDs and hearing aids. For this purpose we conducted measurements with 21 devices from six major manufacturers in 23 different test configurations. Overall, 192 individual measurements were made. We focused on the effect of transmissions from LTE User Equipment (UE) operating in proximity of hearing aid systems.

We observed that when HAS receiver and transmitter were operating at a distance from each other that is representative of typical operating conditions almost all systems proved to be very robust against interference. Even in the presence of multiple high‐power in‐band interferers the HAS which all appeared to employ adaptive frequency hopping managed to maintain stable connections and provide distortion‐free audio. It could actually be observed how the (relatively) narrow‐band HAS signals moved to less‐interfered or unoccupied parts of the 2.4 GHz spectrum after an interfering signal had been activated. As the bit rate of digital hearing aids typically is around 64 kbits/s a few carriers appear to be sufficient to maintain a sufficient quality of service.

In combination, TD‐LTE and FDD‐LTE degraded victim signal quality slightly more than individually. For adjacent‐band LTE signals to cause degradation of a HAS audio signal a number of conditions must be fulfilled:

We also noted that the RF emissions from certain HAS models can severely degrade Wi‐Fi performance. Overall, our findings are perfectly in line with those of the various previous studies. We conclude that while HAS audio signal quality can be impaired by adjacent‐band TD‐LTE signals the combination of prerequisites for this to happen makes the overall risk appear low. Furthermore, we conclude that the additional presence of FDD‐LTE UE signals in the 2.5 GHz band does not significantly increase the degradation of HAS audio quality.

14 Due to time constraints the impact of LTE signals further removed from the 2.4 GHz band edges could not be assessed. While previous studies considered only TD‐LTE and frequencies up to 2390 MHz the conditions created in this study correspond to worst‐case scenarios. 41

Appendix A – List of measurement equipment

Schwarzbeck BBHA 9120E Tx antenna 1 Gain at 2.4 GHz: 15 dBi / 13 dBi (4 m / 1 m) Schwarzbeck BBHA 9120D Tx antenna 2 Gain at 2.5 GHz: 10 dBi /10 dBi (4 m / 1 m) Schwarzbeck ESLP 9145 Monitoring antenna Gain at 2.4 ‐2.5 GHz: 7.2 dBi Rohde & Schwarz SMU200A Signal generator 1 Max. output power: +20 dBm Rohde & Schwarz SMBV100A Signal generator 2 Max. output power: +30 dBm Spectrum analyser Rohde & Schwarz FSV

Audio DAC FocusRite Scarlett 2i2

Appendix B – Audio recordings

The graphs below depict the significant differences in frequency response between some of the tested ALDs and hearing aids.

List of Tables

Table 1: List of tested devices ...... 15 Table 2: Observed artefacts and attributes of streamed audio signals [26] ...... 17 Table 3: Mean Opinion Score (MOS) ...... 18 Table 4: Interfering signal characteristics ...... 18 Table 5: Equivalent separation distances for different levels of LTE UE Tx power and minor audio quality degradation ...... 40 Table 6: Equivalent separation distances for different levels of LTE UE Tx power and severe audio quality degradation ...... 40

List of Figures

Figure 1: Hearing aid manufacturers‘ global market shares (2014) [6] ...... 11 Figure 2: Wireless audio transmission to Gateway device ...... 12 Figure 3: Direct wireless audio transmission to Hearing Aids ...... 12 Figure 4: LTE and HAS frequency allocations between 2300 and 2690 MHz (Europe) ...... 13 Figure 5: Proposed TD‐LTE frequency arrangement in the 2300‐2400 MHz band [23] ...... 13 Figure 6: Frequency arrangement within the 2500‐2690 MHz band ...... 14 Figure 7: COLHA head ...... 19 Figure 8: Initial HAS measurement setup inside the JRC’s anechoic chamber ...... 20 Figure 9: Initial HAS measurement setup (Setup 1) ...... 20 Figure 10: Final HAS measurement setup (Setups 2‐8) ...... 21 Figure 11: DUT 1 (Setup 1) ...... 22 Figure 12: DUT 6 (Setup 2) ...... 25 Figure 13: Distortion of the DUT 6 audio signal in the presence of Wi‐Fi and TD‐LTE (setup 2) ...... 26 Figure 14: DUT 6 (Setup 3) ...... 28 Figure 15: DUTs 7 and 8 (Setup 3)...... 29 Figure 16: DUT 9 (Setup 3) ...... 30 Figure 17: DUTs 9‐13 (Setup 4) ...... 31 Figure 18: DUT 14 (Setup 5) ...... 34 Figure 19: DUT 15 (Setup 6) ...... 35 Figure 20: DUTs 16‐19, 22 (Setup 7) ...... 36 Figure 21: DUTs 20, 21, and 23 (Setup 8) ...... 37

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