Engineering Report

Co-existence Studies Between Wireless Microphones and Digital TV in the UHF Band

ENGINEERING REPORT SPP 05/2013

DECEMBER 2013

© Commonwealth of Australia 2013This work is copyright. Apart from any use as permitted under the Copyright Act 1968, no part may be reproduced by any process without prior written permission from the Commonwealth. Requests and inquiries concerning reproduction and rights should be addressed to the Manager, Communications and Publishing, Australian Communications and Media Authority, PO Box 13112 Law Courts, Melbourne Vic 8010.

Published by the Australian Communications and Media Authority

Contents1 Executive Summary 4

2 Background 52.1 Broadcasting Coverage Area 52.2 Wireless microphones interfering into Digital TV 62.3 Digital TV interfering into Wireless Microphones 92.4 Inter-modulation products 10

3 Methodology 113.1 Subjective failure point (SFP) measurement method 133.2 Modified SFP measurement method 133.3 Characterising reference receiver performance 14

4 Results 154.1 Co-channel operation 154.2 Adjacent channel interference studies 17

5 Discussion and additional considerations 205.1 Co-channel operation 205.2 Calculations using ITU-R Rec. P.1546-5 (draft) 205.3 Possible additional gains and losses 225.4 Received interference power from WMs into DTV 265.4.1 WM interfering into DTV – WM Indoor operation 265.4.2 WM interfering into DTV – WM Outdoor operation 275.5 Adjacent channel operation 305.6 Multiple WM in a single DTV channel scenarios 305.7 Interference from DTV into WMs 315.8 Coverage area definition 32

6 Recommendation 336.1 DTV Coverage definitions 336.2 Spectrum sharing 336.2.1 Co-channelling operation 336.2.2 Adjacent band operation 34

7 References 35

Appendix I: 37Spectrum characteristics of analog and digital wireless microphones under

various scenarios 37A.1 Analog FM microphones 37A.2 Digital Microphones 42

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1Executive SummaryThe main purpose of this report is to review the current spectrum sharing arrangements between wireless microphones (WMs) and Digital TV (DTV) which are reflected in the current Low Interference Potential Devices (LIPD) class licence document and to propose, where appropriate, revised conditions for this spectrum sharing. The main objectives of this review are:

Revised definition of the TV coverage area,

Scope to permit co-channel operation between WMs and DTV.

Revision of the 400 kHz guard band between WMs and DTV for adjacent channel operation.

This report consists of two parts. The first part is mainly a review of literature and spectrum sharing studies performed internationally with an overview of the solutions proposed in other jurisdictions. This part also briefly discusses the current Australian definitions for coverage areas in the broadcast UHF band. The second part of the report details engineering studies and results obtained by the ACMA. The following studies have been performed:

Co-channel spectrum sharing between WMs and DTV receivers.

Adjacent band spectrum sharing between WMs and DTV receivers.

While potential interference that may occur due to spectrum sharing is usually mutual, in this report the focus of the ACMA’s studies has been on potential interference into DTV receivers caused by the WM devices, i.e. testing the TV receivers in order to determine necessary protection ratios (PRs) and guard bands. The studies with no assumptions about signal losses have been performed first but appropriate correction factors have been provided to account for indoor and s

uburban/urban environments by assuming appropriate radio signal losses.

Based on the results of this review, the following changes to the LIPD have been recommended in this report:

1. New definitions of coverage areas have been proposed as per the following Table.

Minimum Field Strength [dBV/m]

UHF Blocks B and C(520-610 MHz)

UHF Blocks D and E (610-694 MHz)

50 54

2. Co-channelling operation between DTV and WMs should be allowed when WMs operate indoors. For outdoor operations the co-channelling should be avoided.

3. Guard band requirement between WM and DTV services (which is currently 400 kHz) should be removed, i.e. adjacent band arrangements are allowed without any restrictions).

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2BackgroundCurrently, a large number of wireless audio systems and devices operate on a secondary basis within the UHF frequency range 520-820 MHz. This frequency range is the same as that used by television broadcasting which has primary status. Wireless audio systems are low power and are allowed to operate under the Low Interference Potential Devices (LIPD) class licence [1] in the unused television channels on the basis of no interference and no protection from interference. Television services are currently in the process of changing over from analog to digital technology. This switchover and the subsequent digital TV channels restack will change the ranges of frequencies that television services use, and will therefore affect the spectrum available for wireless audio equipment.

On 9 July 2010, the Minister for Broadband, Communications and the Digital Economy announced that by switching from analog to digital television, 126 MHz of this UHF spectrum would be cleared in Australia of television and other services [2]. As a result, after the switchover from analog to digital television, and subsequent restack, only the range 520-694 MHz will still be available for use by UHF television broadcasting, while the 694-820 MHz range will be made available for other services.

The 126 MHz of digital dividend spectrum will be used for next generation mobile broadband services such as LTE and 4G. Consequently, the LIPD class licence has been updated to indicate that the band 694 MHz to 820 MHz will not be available for use after 1  January 2015. However, it is expected that the LIPD class licence will be further updated with revised parameters for the wireless audio devices.

This section provides a brief summary of current definitions for coverage area of broadcast digital TV services in Australia, as well as a review of interference studies between Wireless Microphones (WMs) and DTV, which have been conducted and published internationally. However, the first part of this section briefly reviews the current Australian definitions for coverage areas for UHF DTV Blocks B, C, D and E, and different environments. This is important because one of the objectives of the LIPD update is to also review the definitions for the coverage areas of the TV services which are currently based on the figures obtained for the analog TV services.

2.1 Broadcasting Coverage Area

The coverage area of a digital television service is that area delimited by the minimum field strength for the service. The minimum field strength will depend upon the technology in use, frequency band of operation, the radio noise environment and planned interference levels (if any). Detailed guidance is provided in the Broadcasting Services (Technical Planning) Guidelines 2007 (as amended) [3] and Digital Terrestrial Television Broadcasting Planning Handbook [4]. The legislative instrument and the policy document (respectively), together define the minimum field strengths planned for a service and for which protection is afforded against interference, as “modified’ in the Restack Planning Principles1. For UHF DTV the applicable values are shown in Table 2.1.1.

Minimum Field Strength

1 http://acma.gov.au/Industry/Spectrum/Digital-Dividend-700MHz-and-25Gz-Auction/Restack/issue-for-comment-072011-clearing-the-digital-dividend

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EnvironmentUHF Blocks B and C

(520-610 MHz)UHF Blocks D and E

(610-694 MHz)

Urban 71 74

Suburban 63 67

Rural 50 54

Table 2.1.1: Minimum field strengths for different UHF bands and radio noise environments

Note 1: The specified minimum field strength values are medians for 50% of locations and for 50% of the time, as measured at 10 metres above ground level. These figures include the location correction factor for 80%, 90% and 95% location availability for rural, suburban and urban environments, respectively.

Note 2: A higher minimum field strength may be specified for some broadcasting services in either a DCP or a TLAP. For example, an interference limited service, or a service intended to serve an area for which protection to the median field strength levels noted above is not required. An example of such a service could be a repeater that serves several suburbs with deficient coverage but whose coverage area is enclosed within that of a much higher powered transmitter that covers most of a much larger area. Services which are protected to a higher field strength can be identified through advisory notes included in the planning data accompanying TV Licence Area Plans (TLAPs)2.

Note 3: Only coverage within the licence area of a service is protected.

2.2 Wireless microphones interfering into Digital TV

1997 - Chester 1997 Multilateral Coordination Agreement [5]

In 1997, most member countries of the European Conference of Postal and Telecommunications Administrations signed "The Chester 1997 Multilateral Coordination Agreement relating to Technical Criteria, Coordination Principles and Procedures for the Introduction of Terrestrial Digital Video Broadcasting (DVB-T)". The agreement was abrogated at Constanta on 4 July 2007, but it does provide broadly accepted guidance on necessary protection ratios. Annex 5 of the agreement deals with "Methods and criteria for assessing compatibility between DVB-T and services other than broadcasting". The annex detailed the general principles to be applied in checking for compatibility between DVB-T services and services other than broadcasting, including formulae for necessary calculations.

The provided relevant table of protection ratios is as follows:

2 http://acma.gov.au/Industry/Broadcast/Spectrum-for-broadcasting/Broadcast-planning/final-television-licence-area-plans-spectrum-for-broadcasters-acma

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Frequency Offset Protection Ratio

0 MHz +4.0 dB

3.4 MHz +4.0 dB

3.94 MHz -27.0 dB

10.5 MHz -32.0 dB

Table 2.2.1: Necessary protection ratios for a single wireless microphone into DTV against frequency offset from 7 MHz channel centre

The values are stated to be for a wanted DVB-T signal in a 7 MHz channel interfered with by a companded radio microphone. Default ERP was -13 dBW and default transmitting antenna height was 1.5 m AGL. Companding is a commonly applied technique in radio microphone design to maximise signal to noise ratio in high radio noise environments. It effectively reduces the dynamic range of the transmitted signal, which upon reception is restored to its original value.

2000 - ERC Report 88 [6]

In 2000, the European Radiocommunications Committee published a report "Compatibility and Sharing Analysis between DVB-T and Radio Microphones in Bands IV and V", ERC Report 88. The report was largely based upon two sets of measurements from the United Kingdom and a single set of measurements from Germany. The first United Kingdom measurements indicated co-channel protection ratios of -3 dB, -4 dB and -9 dB (0 MHz, 2 MHz and 3.8 MHz respectively). The second United Kingdom measurements indicated co-channel protection ratios of -3 dB, -4 dB and -10 dB (0 MHz, 2 MHz and 3.8 MHz respectively). The results are summarised in the Table 2.2.3.

Protection Ratio

Frequency Offset United Kingdom 1 United Kingdom 2 Germany

0 MHz -3 dB -3 dB -4 dB to -10 dB

2 MHz -4 dB -4 dB N/A

3.8 MHz -9 dB -10 dB N/A

4.5 MHz -37 dB -36 dB N/A

6.0 MHz -51 dB -45 dB N/A

7.0 MHz -52 dB -48 dB N/A

8.0 MHz -53 dB -52 dB N/A

Table 2.2.3: Necessary protection ratios for a single wireless microphone into DTV against frequency offset from 8 MHz channel centre

The DVB-T receiver under test in all instances was a professional grade monitoring receiver rather than a consumer grade unit. Some correction may be needed for this aspect, but this should be quite small excepting at the channel edges where consumer receiver selectivity may be variable.

The distinguishing feature between the two United Kingdom measurement sets was the wanted DVB-T RF level: being -46 dBm and -52 dBm respectively. DVB-T modulation type was 2k, 16QAM and 3/4 FEC code rate.

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The German measurement set utilised a wanted DVB-T RF level of -66 dBm and modulation schemes of 2k, QPSK / 16 QAM / 64 QAM with FECs of 1/2 or 2/3.

2008 – Sagentia [7]

In 2007 and 2008, Sagentia issued a report for Ofcom which was successively revised on at least 4 occasions. The final version was titled "PMSE Spectrum Usage Rights & Interference Analysis" and dated 13 June 2008. In common with most PMSE reviews of the era, the report largely accepts the ERC Report 88 value of -3dB for a single analogue wireless microphone into digital television. It does however provide brief details of a set of measurements intended to estimate co-channel protection ratios for between one and six wireless microphones into a digital television service. The provided results are tabulated in the following:

Number of Wireless Microphones

Protection Ratio for Wireless Microphones(per microphone)

Analogue WMs Digital WMs

1 +1 dB +1 dB

2 +4 dB +6 dB

3 +8 dB Not measured

4 +10 dB Not measured

5 +13 dB Not measured

6 +13 dB Not measured

Table 2.2.4: Necessary co-channel protection ratios (per microphone) for DTV signals in an 8 MHz channel in the presence of interference from multiple wireless microphones (DTV signal off-air, parameters not stated, likely 16QAM which was most common pre-switchover)

The report indicates that the investigations were quite limited and states that the results should be taken as qualitative. Only a single consumer grade digital television receiver was used. The digital television signal was sourced off air and was considered to be already somewhat degraded. The interfering "microphones" were simulated by signal generators. For the measurements with 5/6 analogue microphones and 2 digital microphones, the interference was simulated using a smaller number of wider bandwidth sources. It is also noted in the report that a very fast failure of the digital television signal was observed with increasing numbers of microphones.

2010 Cobham and Aegis [8]

In June 2010 Cobham and Aegis Spectrum Engineering published a final report entitled "Spectrum efficiency of wireless microphones" for Ofcom as part of their review of the Programme Making and Special Event (PMSE) service category which in turn was part of their overarching Digital Dividend Review. The report provides considerable new material in respect, amongst other things, of spectrum requirements for major special events, inter-modulation issues in spectrum dense environments and technical specifications for wireless microphone systems. But for co-channel and adjacent protection ratios for wireless microphones into digital television, it relies entirely upon the earlier work of ERC Report 88 in

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2000 and Sagentia in 2008. Accordingly, this report will not be further discussed in this section.

2011 Ofcom [9]On 16 May 2011, Ofcom published a statement "Future access to interleaved spectrum for programme making and special events" [9] as part of their consultation "Digital dividend: band manager award: second consultation on detailed award design" published22 June 2009. Ofcom had indicated in an earlier statement [10] that a number of locations in the United Kingdom could have a quantity of available interleaved spectrum which was lower than peak historic demand. The former statement revised that assessment by altering some key technical assumptions in light of actual licensing experience in areas which had already switched over. It released all 32 interleaved channels for indoor use post-switchover. A spectrum quality metric was also defined to enable wireless microphone users to readily assess levels of interference from DTV in a given area. Those changes also included a relaxation of the Chester 1997 [5] protection ratios, as follows:

Protection Ratio

Channel relationship Chester 1997 BBC / JFMG

Co-channel +4.0 dB +1.0 dB

Adjacent channel -27.0 dB -31.0 dB

Table 2.2.5: Necessary protection ratios for DTV interfered with by a single wireless microphone against channel relationship in Chester 97 and BBC / JFMG system

The BBC / JFMG3 figures are stated to have been taken from a BBC document "Parameters to be used in the production of the SAB overlays", which the ACMA have not been able to acquire.

An important aspect of this report is that, as a consequence of the relaxed spectrum sharing requirements, indoor operation of WMs is permitted across the entire DTV spectrum range. Outdoor WM operation, however, remains subject of further evaluations on the case-by-case basis. The results presented in this report are obtained for single WM operation but it is argued that even in the multiple WM scenarios, due to variations in power levels among WMs, there would normally be one dominant WM, which would be similar to the single WM scenario.

2.3 Digital TV interfering into Wireless Microphones

In the European Radiocommunications Committee's Report 88 [6], a protection ratio of 12 dB has been identified as necessary between a wanted analog wireless microphone signal and an interfering DTV signal. In addition, a minimum wanted field strength of 68 dBV/m has been used giving a maximum interfering field strength (from the DTV service) of 56 dBV/m in order to avoid interference into an analog wireless microphone. Using an extrapolation (for short distances) based upon the former ITU-R Rec. P.370 propagation model [11] it is determined that the minimum necessary spatial (distance) separation between an analog wireless microphone and a DTV transmitter site (ERP 200 W, 150 m effective height) is 11 km (outdoors) and 8 km (indoors). Indoor building penetration loss of 7 dB and clutter loss of 12 dB in urban areas have been assumed in the study. The later Sagentia report for Ofcom [7] 3 JFMG is the dedicated band manager for programme-making, entertainment, special events and other related broadcasting activities in the UK.

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applied the values of the ERC report without change. This aspect of the ERC Report is also summarised in the Aegis/Cobham report [8].

2.4 Inter-modulation products

A major issue with wireless microphones is inter-modulation products. These products occur when two strong signals pass through a non-linear device. Although such a device can generate a large number of unwanted signals of different frequencies, in practice, the most critical are third order components at frequencies 2xf1-f2 and/or 2xf2-f1. These products are particularly critical when they fall within the frequency band used by a wireless microphone device, and therefore cannot be filtered out.

Inter-modulation products are particularly important because they determine the number of microphones that can be accommodated within a single TV channel. Several studies have been conducted previously to determine the maximum number of wireless microphones that can be used within a single TV channel without significant degradation of the performance. While there is no general consensus in the literature about this issue, figures that frequently appear suggest somewhere between 8 and 17 wireless microphone channels per 8 MHz (European standard) TV channel [8]. However, as explained in [8], the actual figure often depends on the specific requirements and how much interference may be tolerated. In its Rules and Regulations, Part 15 "Radio Frequency Devices" (§15.713(h)(9) refers4), the FCC establishes a benchmark that in events which require the use of a large number of WMs, at least 6 to 8 WMs must be accommodated in each 6 MHz TV channel, and those applications which do not satisfy the benchmark will not be registered in the database.

It should also be noted that some recent studies have indicated that significantly better performance (in terms of inter-modulation products) could be achieved with digital technologies. However, it should also be observed that the digital technologies (digital wireless microphones) have appeared in the market only recently and it may take some time until they become well established. For instance, two of the major wireless microphone manufacturers Shure and Sennheiser did not offer digital wireless microphones in 2010 [8] and the new digital devices offered by these two manufacturers appeared only recently in the market. A major problem with the digital technologies appears to be latency, which due to delay inherent in the digital processing techniques is difficult to keep within the requirement of 2-3 ms for live performances. Another problem is that if overly complex digital signal processing techniques are applied (to allow better receiver performance in terms of noise+interference tolerance), power consumption is increased and device battery life is accordingly reduced.

4http://www.gpo.gov/fdsys/pkg/CFR-2012-title47-vol1/pdf/CFR-2012-title47-vol1-sec15-713.pdf

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3Methodology The main purpose of this study is to determine possible spectrum sharing arrangements between DTV and WMs. At the moment WMs use the UHF broadcast part of the spectrum (520 – 820 MHz) under class licence arrangements, meaning “no interference, no protection” conditions. In practice, wireless microphones use those broadcast frequencies (TV channels) which are not in use in their area of operation. The performed studies can be classified into two categories – co-channel spectrum sharing (protection ratios) and adjacent bands operation (guard bands and separation distances).

1. R&S SFU Broadcast Test System - 50 Ω N type RF output2. 50 Ω N type male - 50Ω coax - 50 Ω N type male3. 75 Ω IEC 169-2 male to 75 Ω F-connector female4. Power splitter, N-type ZFSC-2-2N+5. 50 Ω N type male to 75 Ω BNC female adaptor6. 75Ω BNC male - 75Ω coax –IEC 169-2 female7. R&S ETL TV analyser - 75 Ω RF input8. STB or digital television under test

Figure 3.1: Measuring set-up and equipment specifications for co-channel studies.

The system model used to perform co-channel studies is shown in Figure 3.1. For this scenario, an R&S SFU Broadcast Test System is used to generate wanted signal. A “Diver” video sequence supplied with the R&S SFU is used to test the effect of interference to the wanted signal. The “ARB” option has been used as the source of interfering signal waveforms and the interfering sequences (waveforms) were created externally using R&S WinIQSIM2 software5 for digital WM scenarios; and MATLAB and C programming language for analog FM WM waveforms. The output signal from the R&S SFU (which is a mixture of wanted DTV and interfering WM signals) is then fed via a splitter into R&S ETL TV analyser and an actual TV receiver which is either a standalone Digital TV receiver or a Set Top Box (STB).

5 http://www.rohde-schwarz.com/en/product/winiqsim2-productstartpage_63493-7614.html (retrieved 3 September 2013)

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8

1 2

6

3

7

Test

5 65

4

1. R&S SFU Broadcast Test System - 50 Ω N type RF output2. 50 Ω N type male - 50Ω coax - 50 Ω N type male3. 75 Ω IEC 169-2 female to 75 Ω F-connector female4. Power splitter, N-type ZFSC-2-2N+5. 50 Ω N type male to 75 Ω BNC female adaptor6. 75Ω BNC male - 75Ω coax – IEC 169-2 male7. R&S ETL TV analyser - 75 Ω RF input8. STB or digital television under test9. 75 Ω IEC 169-2 female to 75 Ω IEC 169-2 female10. VHF/UHF indoor antenna (“Rabbit ears”), 1.2 m cable, 75 Ω IEC 169-2 male connector.

Figure 3.2: Measuring set-up and equipment specifications for adjacent band studies.

The system model used to perform adjacent band studies is shown in Figure 3.2. For this scenario, the wanted Digital TV signal is an actual off air signal on channel 30 (543.5 MHz) received using an indoor antenna. Here, the R&S SFU Broadcast Test System is used to generate interfering signal only in identical manner as described for the co-channel studies. The output interfering signal from the R&S SFU is then mixed with the wanted signal from the antenna via a splitter and first fed into an actual TV receiver which is either a standalone Digital TV receiver or a Set Top Box (STB).

In order to measure levels of wanted and interfering signals, the R&S ETL TV analyser was used. When the interfering signal level was measured, the wanted input into the splitter (cable “6” in Figure 3.2) was disconnected and the centre frequency of the interfering signal was set to 543.5 MHz. Similarly, when the wanted Digital TV signal was measured, the interference source on the R&S SFU instruments was set to “None” (this is effectively equivalent to disconnecting cable denoted “2” in Figure 3.2). These signal level measurements were obtained before the actual adjacent band studies were performed.

It should be observed that the main reason behind such setup was that the for the adjacent band studies the peak power of the WM signal (in frequency domain) is significantly higher

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1 2Test

654

5

910

6

3

8

7

than the peak power of the Digital TV signal causing an issue with the R&S SFU which results with significant inter-modulation products. This issue has been noticed for cases where the interfering WM signal was about 15 dB or more higher than the wanted Digital TV signal. To avoid this issue, the R&S SFU was set to generate both Digital TV and interfering WM signal. However, the centre frequency of the Digital TV signal generated by the R&S SFU was set using the maximum frequency offset on the R&S SFU of 40 MHz, i.e. 583.5 MHz and the power level of the WM was set to be identical to the DTV signal. In practice, the SFU generated DTV signal was not used and the 40 MHz separation between two DTV signals is sufficient to prevent any interference between services.

3.1 SUBJECTIVE FAILURE POINT (SFP) MEASUREMENT METHOD

Early studies of the protection ratios for the DVB-T system were typically based on a target Bit Error Rate (BER) of 2 x 10–4 measured between the inner and outer coders, i.e. before Reed-Solomon decoding (refer Recommendation ITU-R BT.1368-10 [12]). For the case of a noise-like interferer, this has been taken to correspond to a quasi-error-free (QEF) picture quality with a BER 1 x10–11 at the input of the MPEG-2 demultiplexer. However, for domestic DVB-T receivers the point between the inner and outer coders is not physically accessible and consequently, it is not possible to measure the BER at this point. To address this issue, a subjective failure point (SFP) method for protection ratio measurements is described in Annex 7 of [12].

The SFP method corresponds to the picture quality where no more than one error is visible in the picture over an average observation time of 20 seconds. The adjustment of the wanted and unwanted signal levels for the SFP method should be carried out in 0.1 dB steps. The RF protection ratio for the wanted DVB-T signal is then a value of wanted-to-unwanted signal ratio at the receiver input, determined by the SFP method, and rounded to the next higher integer value. All protection ratio values for wanted digital TV signals should be measured with a receiver input power of 60 dBm. It is stated that for a “noise-like” interferer the difference in a value of wanted-to-unwanted signal ratio between the QEF method with a BER of 2 × 10–4 and the SFP method is less than 1 dB (but it should be noted that the text also specifies that protection ratio values should be rounded up to the nearest integer).

3.2 MODIFIED SFP MEASUREMENT METHOD

Co-channel protection ratio measurements in this report were conducted using a slightly modified SFP method. Average observation time was increased from 20 seconds to one run of the 24 second R&S “Diver” test sequence and the value of the power level adjustment step was increased from 0.1 dB to 1 dB. These modifications were made in order to achieve a more practical and less time consuming measurement procedure. It is considered that the changes will not have a significant effect on measurement results. The test was performed for DVB-T signal modulation scheme with 64QAM, 8k OFDM, and 1/16 guard interval. For co-channel studies FEC code rate 3/4 was used while for the adjacent channel studies the FEC code rate was 2/3 (which is the code rate of the actual signal received off air and which was used in the adjacent channel studies). For co-channel studies a receiver input level of -60 dBm was used and the measurements were performed using a wanted UHF DVB-T channel 50 (683.5 MHz) and unwanted wireless microphone signals as described in Appendix 1. Measurements were performed for a condition where no thermal noise was added. For the adjacent band studies, the actual parameters of the off-air DTV signal were measured and are discussed Section 4 of this report.

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3.3 CHARACTERISING REFERENCE RECEIVER PERFORMANCE

The main objective of performing these measurements was to obtain data to ensure an appropriate level of protection of digital television services sharing the same band. Given that measurements on samples of receivers will produce results that spread over a range of values, a question arises about what value(s) would best characterize a “reference receiver” that can be used in broadcast service planning. Superficially it might be thought that worst case values should be used. However this is unsatisfactory because it is unrealistically conservative (especially if a receiver in the sample is very poorly designed or is malfunctioning). Also, if a relatively small receiver sample is used it can be argued that the sample may not be large enough to have included the “worst” receiver. A more robust approach is to select an appropriate percentile level from within the range of the measured results. The 75th percentile value was selected since it will protect three-quarters of the receiver population, but does not unduly bias planning toward poorly performing receivers (this would lead to less efficient use of spectrum resources). Arguably, this approach also sends a signal that receiver manufacturers should improve the performance of receivers at the poorer end of the scale. The approach of using the 75th percentile results from measurements of receiver populations has been used previously by the former Department of Transport and Communications, Communications Laboratory during a measurement exercise involving RF performance measurements on large numbers of FM radio receivers in 1991 [13].

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4Results4.1 Co-channel operation

Scenarios with 1, 8, 9, 16 and 17 wireless microphones operating within a single 7 MHz channel and co-channelled with a DTV signal have been analysed. The reasoning behind the choice of numbers of WMs within a single DTV channel is to study the entire range of potential WM deployments. The scenarios with multiple WMs are designed to explore cases when different maximum numbers of WMs per a DTV channel are assumed (e.g. 8 and 16) as per [8]. In addition, cases with 9 and 17 WMs are also considered when an additional WM is added to operate at the central frequency of the DTV services and to check the effect of such co-channelling. Australian digital channel 50 (with central frequency 683.5 MHz) has been selected in this study. It should be observed that all measurements involving multiple WMs assume that the power levels of individual WMs are uniformly distributed i.e. equal power levels for all WMs. While such a scenario is somewhat unrealistic, it is assumed as a conservative starting point and future studies, if required, may include cases with unequal power levels for WMs.

Analog wireless microphones into DTV

The R&S WinIQSIM2 software cannot create analog FM signals, and therefore, the signals used to emulate the wireless analog FM microphones were created in MATLAB and then converted using C programming language into appropriate binary files that can be read by the R&S SFU instrument. It should be observed that the C program code is reproduced from the Help menu of the R&S SFU. The value for the FM modulation index has been appropriately selected to achieve the signal bandwidth of 200 kHz. A music sample has been used as the modulating signal. Figures in Appendix 1 show interfering FM signals under various scenarios as created in MATLAB and at the RF output of the R&S SFU (as seen on the R&S ETL TV Analyser screen).

Digital wireless microphones into DTV

For the purpose of the digital WM interference modelling, the signal generating software R&S WinIQSIM2 has been used. The signal is modulated using /4 differential QPSK modulation (as per [14], [15]). The signal bandwidth is set to 200 kHz and the cosine pulse shaping filter with the 0.35 roll-off factor has been used. The sequence length is set to 200,000 symbols. Figures in Appendix 1 show interfering digital signals under various scenarios as created in the WinIQSIM2 software and at the RF output of the R&S SFU (as seen on the R&S ETL TV Analyser screen).

Measurement results

Protection ratios for all described scenarios are shown in Tables 4.1.1-4.1.4. It should be noted that the protection ratios in Tables 4.1.1 and 4.1.3 are determined relative to the total interfering power, i.e. cumulative power from all WMs for the multiple WM scenarios. Since it is assumed that all WMs are received with identical power levels, the power of an individual WM can simply be calculated by subtracting the adjustment factor 10*log10(N) from the cumulative multiple WM power, where N is the number of WMs for particular scenarios. Tables 4.1.2 and 4.1.4 show adjusted values, i.e. the DTV power relative to an individual WM for various scenarios where the appropriate adjustment factor 10*log10(N) is added to the protection ratio relative to the multiple WMs case. These results are discussed in more detail in Section 5.

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Protection Ratio [dB]Number of WMs DTV-1 STB-1 STB-2 STB-3 75th percentile

value17 -5 -5 -9 0 -5

16 -5 -5 -9 2 -5

9 -6 -7 -8 3 -6

8 -3 -6 -10 0 -3

1 -1 0 2 -8 0

Table 4.1.1: Protection ratios (in dB) between the DTV service and the interfering analog wireless microphone power levels with QEF DTV reception.

Protection Ratio [dB]Number of WMs

Adjustment DTV-1 STB-1 STB-2 STB-3 75th percentile

value17 12 7 7 3 12 7

16 12 7 7 3 14 7

9 10 4 3 2 12 4

8 9 6 3 -1 9 6

1 0 -1 0 2 -8 0

Table 4.1.2: Protection ratios (in dB) between the DTV service and the interfering individual analog wireless microphone power level with QEF DTV reception.

Protection Ratio [dB]Number of WMs DTV-1 STB-1 STB-2 STB-3 75th percentile

value17 18 18 18 18 18

16 18 18 18 18 18

9 17 17 15 16 17

8 17 17 14 16 17

1 2 3 1 9 2

Table 4.1.3: Protection ratios (in dB) between the DTV service and the interfering digital wireless microphone power levels with QEF DTV reception.

Protection Ratio [dB]Number of WMs

Adjustment DTV-1 STB-1 STB-2 STB-3 75th percentile

value17 12 30 30 30 30 30

16 12 30 30 30 30 30

9 10 27 27 25 26 27

8 9 26 26 23 25 26

1 0 2 3 1 9 2

Table 4.1.4: Protection ratios (in dB) between the DTV service and the interfering individual digital wireless microphone power levels with QEF DTV reception.

4.2 Adjacent channel interference studies

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For the adjacent channel study, a single microphone interferer was simulated as shown in Figures 4.2.1 and 4.2.2 for analog and digital microphones, respectively. For the adjacent channel scenario, the measurements have been performed using the actual off air digital TV signal, which was then interfered by a WM signal. Channel 30 (543.5 MHz) was received off air, since this is the only UHF digital TV service in Canberra, where measurements took place. The measured received power using an indoor TV antenna was around -75.5 dBm. It should be observed that this value is just above the theoretical sensitivity threshold of -78.7 dBm for Block B UHF and 75 input resistance (or 30 dBV [4]). Two values for the interfering (wireless microphone) power level were selected, -47.2 dBm and -55.1 dBm, corresponding to the levels at 100 m and 250 m from a wireless microphone transmitter operating at an EIRP of 100 mW, assuming free-space propagation.

Figure 4.2.1: An example of an analog FM WM operating adjacent to a DTV service

Figure 4.2.2: An example of a digital WM operating adjacent to a DTV service

It should be observed that these values are about 28 dB and 20 dB higher than the received digital TV signal, for separations of 100 m and 250 m, respectively. The standard formula for the free space propagation loss has been used, i.e.

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Lfree-space [dB] = 92.45+20 log10d+20 log10 f , (1)

where d is distance in km and f is frequency in GHz. No additional gains/losses have been assumed at this stage (e.g. receiver antenna gain or feeder losses). The main purpose of this study was to determine the guard band between a wireless microphone and the DTV service, without causing any interference into the DTV service. The results are shown in Tables 4.2.1-4.2.3.

Frequency offset [MHz]Interference level/distance DTV-1 STB-1 STB-2 STB-3 75th percentile

value-47.2 dBm/ 100 m (free space) 3.9 3.56 4.3 4.1 4.1

-55.1 dBm/ 250 m (free space) 3.5 3.5 3.5 3.5 3.5

Table 4.2.1: Frequency offsets in MHz between centre frequencies of the DTV channel (543.5 MHz) and the interfering digital wireless microphone with QEF DTV reception.

Frequency offset [MHz]Interference level/distance DTV-1 STB-1 STB-2 STB-3 75th percentile

value-47.2 dBm/ 100 m (free space) 4.1 3.7 18 6 6

-55.1 dBm/ 250 m (free space) 3.8 3.55 10.8 3.7 3.8

Table 4.2.2: Frequency offsets in MHz between centre frequencies of the DTV channel (543.5 MHz) and the interfering analog wireless microphone with QEF DTV reception.

The measurements have been performed in the following manner. The centre frequency of the wireless microphone was initially set to correspond with the edge of the TV channel, i.e. with 3.5 MHz offset from the centre frequency of the DTV channel. If interference was observed (e.g. pixelation) on the TV screen, the frequency offset was gradually increased by 10 kHz steps until the picture on the TV screen became free of any observable interference. The procedure was then repeated with other TV receivers. As can be observed from the Table 4.2.1, for the interfering power level of -55.1 dBm (corresponding to 250 m distance from the transmitter), no interference has been observed when the digital interfering waveform was used. This implies that even when half of the wireless microphone bandwidth is within the TV channel, the DTV receivers were capable of tolerating this level of interference. However, the results were degraded for the interfering power level of -47.2 dBm (corresponding to 100 m distance from the transmitter), with the exception of the STB-1 where it was found that for QEF DTV reception a frequency offset of 3.56 MHz was required, i.e. the WM central frequency was only 60 kHz outside the DTV channel. This means that a part of the interfering power was still within the DTV channel without causing observable reception issues. However, the remaining DTV receivers required more frequency separation to achieve QEF reception.

Somewhat different results were obtained with the analog FM microphone as an interferer. For the WM power level of -55.1 dBm, the STB-1 receivers showed similar performance to the digital WM scenario, i.e. no interference has been observed when the frequency offset was 3.55 MHz. However, DTV-1 and STB-3 required larger offsets (i.e. 3.8 and 3.7 MHz,

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respectively) to achieve QEF reception. However, the STB-2 failed to achieve interference free performance for offsets significantly higher than 3.5 MHz and the exact cause of such behaviour has not been determined. For the WM power level of -47.2 dBm, corresponding to the 100 m separation, the performances of the DTV-1 and STB-1 were still similar to the digital WM scenario. However, STB-2 and STB-3 showed significantly worse performance compared to other scenarios.

Finally, since the results for the analog WM case were not conclusive, an additional set of measurements were taken to identify the interfering WM power levels for which DTV receivers achieve QEF performance when the frequency separation was 3.6 MHz, i.e. no guard band between the DTV and WM, but no part of the 200 kHz WM spectrum is (theoretically) within the DTV channel. These results, together with the corresponding protection ratios, are shown in Table 4.2.3. It can be observed that, again, STB-1 outperformed other receivers, while the 75th percentile value for the interference level of the analog WM was about -64 dBm, corresponding to the spatial separation of about 450 m (as per equation (1)). For digital WM case, this additional set of measurement was not performed since it was clear from the performed measurement that spatial separation for which no guard band is required is below 250 m.

DTV-1 STB-1 STB-2 STB-3 75th percentile value

Interference level for 3.6 MHz separation (dBm)

-59.2 -53.1 -65.7 -63.9 -63.9

Protection ratio for 3.6 MHz separation (dB) -16.3 -22.4 -9.8 -11.6 -11.6

Table 4.2.3: Interference levels and protection ratios from analog WMs, when frequency offsets is 3.6 MHz between centre frequencies of the DTV channel (543.5 MHz) and the interfering analog wireless microphone, with QEF DTV reception.

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5Discussion and additional considerations

5.1 Co-channel operation

For the co-channel scenario, it can be observed that significantly different results are obtained depending on whether digital or analog WMs have been used, and that greater level of interference can be expected for digital WMs. This could possibly be explained by the fact that the spectrum characteristic of a digital WM is “wider” compared to an FM analog WM, as it can be observed from Figures A.1.2 and A2.2. This observation is consistent with [16] where the spectral mask of an analog WM is modelled to be more “narrow” compared to the corresponding mask of a digital WM. Therefore, it could be inferred that a digital WM potentially affects/interferes with more sub-carriers of the OFDM DTV signal than an analog WM.

It can also be observed that as the total number of WMs decreases there is a trend of decreasing protection ratio, although that decrease is rather marginal for scenarios between 8 and 17 WMs. However, when a single WM is used the protection ratio is significantly lower compared to multiple WM scenarios. It should be noted though that the protection ratios are measured relative to the total interfering power, i.e. relative to the total cumulative power from all WMs. Therefore, the power level of a single WM can be calculated by dividing the total interfering power by the number of WMs for a particular scenario. For instance, for the 8 WM scenario, the power of a single WM would be one eight of, or about 9 dB lower compared to the total interference power. These adjustments are shown in Tables 4.1.2 and 4.1.4.

It is also worthwhile noting that similar protection ratios are obtained for DTV employing either 16 QAM or 64 QAM and the single WM scenario (note: 16 QAM DTV results are not included in this report but have been performed). A possible explanation is that a single WM destroys a number of DTV OFDM subcarriers, and this number of subcarriers is fixed regardless of the modulation scheme (e.g. whether 16 QAM or 64 QAM has been used). Therefore, the relative number (i.e. the percentage) of destroyed QAM symbols (and subsequently information bits) is fixed regardless of the modulation schemes and the FEC decoder needs to correct sequences with similar (in theory identical) pre-Viterbi Bit Error Rates (BERs). This observation is also consistent with results discussed in [6].

5.2 Calculations using ITU-R Rec. P.1546-5 (draft)

Although use of the Free Space propagation model for short distances (less than 1km) may seem appropriate, it arguably over-predicts signal levels and therefore produces results which are overly conservative. Therefore, additional analysis has been performed here using the ITU-R Recommendation 1546-5 (draft revision), which will be referred to as draft ITU 1546-5 model in this report. One of the additional features of the draft ITU 1546-5 model (which does not exist in earlier revisions) is field strength prediction calculation for short distances, i.e. less than 1 km. For more details on these calculations the reader is referred to Annex 3 and Section 15 of Annex 5 of the draft ITU 1546-5 model document. In addition, Sections 4 and 14 of Annex 5 of the draft ITU 1546-5 model have also been used to account for the cases when the transmitter (WM) antenna height is less than 10 m and the different heights of transmitter (WM) and receiver (DTV) antennas. In all calculations the default receiver (DTV) antenna height of 10 m and frequency of 600 MHz have been used, while the transmitter (WM) antenna height is set to 1.5 m [5]. The numerical values for the field strengths relating to 50% of time availability have been used since at the short distances there are no significant differences between various time availability percentages, as it can be observed in Annex 3 of the ITU 1546-5 document.

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Figure 5.2.1: Calculated WM field strength using Free-space and ITU 1546-5 model

Figure 5.2.2: Calculated WM received power using Free-space and ITU 1546-5 model

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No terrain data has been used and the appropriate adjustment has been applied to account for the WM EIRP of 100 mW. Figures 5.2.1 and 5.2.2 show how the WM field strength and received power levels (respectively) depend on distance dWM between WM and TV receiver antenna. The curves in each Figure are obtained using free-space and ITU 1546-5 propagation models. The curves are generated without using any additional gains or losses (e.g. antenna gains, body attenuation, or wall penetration loss). The figures show significant differences between the corresponding values depending on which propagation model is used. For instance, the ITU 1546-5 model predicts that the WM signal will fall to -60 dBm 6 after only 170 m, while according to the Free-space model the required distance where the WM signal falls to -60 dBm is 400 m. It should also be noted in Figure 5.2.2 that the sensitivity threshold for Band V UHF -77.7 dBm and is 1 dB higher than previously used (in Section 4 of this report) threshold of -78.7 dBm for Band IV UHF.

5.3 Possible additional gains and losses

This subsection discusses potential additional gains and losses that may affect the levels of potentially interfering signal from WMs.

Gains

First it should be observed that all previous discussions and studies assume no TV receiver antenna gain, which is according to [4] nominally set to 12 dB in Band V UHF. However, the nominal feeder losses are set to 5 dB, giving overall receiving TV antenna system gain of 7 dB.

Losses

When considering losses, it should be observed that in many instances WMs operate indoors in which case building penetration loss needs to be taken into account. This loss can be regarded as extra interference protection in both directions. A standard figure which has been used in the ERC Report 88 [6], and reports afterwards (e.g. [8], [9]) is 7 dB. However, in the ETSI Technical Report [15] a range of possible values for the penetration loss has been provided and they are shown in Table 5.3.1. It is understood that Thermo Plane figure is absorption due to insulation and therefore should be added to selected figure, where appropriate. Therefore, the range for penetration loss could potentially vary between 7 dB (for Lightweight concrete 11.5 cm only with no insulation) to 26 dB (Lime sandstone 24 cm + Thermo Plane). Additional potential losses have been identified in [6] and [8] for the WM signal such as fading loss estimated to about 20 dB to 30 dB [15], attenuation by body for hand held and body worn transmitters has been estimated to 6 dB and 14 dB, respectively.

Loss mechanism Estimated loss at 650 MHz [dB]

Lime sandstone 24 cm 21Lime sandstone 17 cm 16Ytong 36.5 cm 21High hole brick 24 cm 9Reinforced concrete 16 cm 11Lightweight concrete 11.5 cm 7Thermo Plane 5

Table 5.3.1: Absorption in walls [15]

6 Reference received power of -60 dBm, which was used for protection ratio measurements in Section 4 of this report.

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Figure 5.3.1: Interference attenuation due to TV receiver antenna discrimination

In some cases, depending on the position and polarisation of TV receiver antennas, directivity or polarisation discrimination of the TV receiver antennas could also be taken into account. This additional attenuation of the interfering signal can, depending on the receiver antenna configuration, range between 0 and 20 dB [17]. It should be noted though that, for planning purposes, only one of these two losses should be used, i.e. either directivity or polarisation, but not both. It should be noted that in this report, the directivity discrimination is used only since the no information is generally available about the polarisation o fthe WM signal. In addition, polarisation of a broadcast station also may differ in different areas and therefore it would be difficult to make any assumption about the polarisation discrimination between WM and DTV services. Figure 5.3.1 shows how much attenuation of the interfering signal could be expected depending on the pointing direction of the TV receiver antenna relative to the WM interferer. The graph in this Figure is derived from the TV receiver antenna pattern in [17]. It can be observed from the graph that within an area where TV reception is potentially affected by the WM, two thirds of the area will benefit from the maximum 16 dB TV receiver antenna discrimination while additional approximately 22% of the area (between green and red lines) will still benefit from some discrimination, which, depending on the pointing direction of the TV receiver antenna, will vary between 0 and 16 dB. Consequently, in only about 11% of the area (between red lines) the TV receiver antennas will fully receive the interfering WM signal without any loss due to TV receiver antenna discrimination.

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No interference attenuation

Interference attenuation0 dB < Atten. <16

dBInterference attenuation

0 dB < Atten. <16 dB

Max. Interference attenuation 16 dB

Figure 5.3.2: Three different scenarios of interference attenuation due to TV receiver antenna directivity discrimination

It should be observed though, that this analysis is valid only when the distance between the receiver TV antenna and the Broadcast Station (BS), dBS, is much larger than the distance between the TV receiver antenna and the WM interferer, dWM, which is almost always true near the edge of the BS coverage. Additional calculations, which are not presented in this

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WM

Broadcast Station

Viewer 1

Viewer 2

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report, show that when the ratio dBS/dWM=25 (or 0.04), the discrepancy between the exact and approximated value does not exceed 0.8 dB. When this ratio is dBS/dWM=10 (or 0.1), which is a rather conservative approach, the maximum discrepancy is still rather low and does not exceed 2.1 dB. For cases where this assumption is not valid (i.e. similar distance dBS and dWM), it is reasonable to expect that the DTV signal level would be significantly higher than the WM interfering signal, and therefore no interference into DTV services is expected to occur.

Figure 5.3.2 shows three different scenarios and how the TV receiver antenna discrimination affects different users depending on their pointing direction relative to a WM interferer. In the first case (Viewer 1), the bearing between the TV receiver antenna pointing direction and the WM is about 90 degrees and therefore, the maximum 16 dB attenuation of the interfering signal may be expected. In the second case (Viewer 2), the bearing is less than 20 degrees and therefore no interfering signal attenuation should be expected. Finally, for Viewer 3, the bearing is around 50 degrees and attenuation of about 8 dB of the interfering WM signal may be expected. It should be noted that the distances are not up to scale and that the distance between the BS and viewers is assumed to be significantly larger than between the viewers and the WM.

Finally, clutter loss is another factor which could potentially introduce additional attenuation of the interfering signal. This loss is particularly expected to occur in areas with a significant number of tall buildings, which is usually typical for metro areas where the heaviest usage of the professional WM systems is expected. In [8] this additional loss is estimated to be around 12 dB. As it could be observed, there are a number of signal attenuation mechanisms that should be considered should spatial separation between WM transmitters and TV receiver antennas (and vice versa) need to be determined. Some of these mechanisms have been considered in [9] leading to the decision to allow co-channelling between DTV and WMs, subject to indoor WM use. Table 5.3.2 provides a summary of these potential additional losses.

Loss mechanism Estimated loss [dB]Building penetration 7-26Fading 20-30Body – hand held 6Body – worn 14Antenna directivity 0-16Antenna polarisation 15-207

Clutter 12

Table 5.3.2: Summary of possible additional losses

7 No polarisation discrimination has been used in this report and it is provided for informational purposes only.

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5.4 Received interference power from WMs into DTV

In order to determine more realistic potential for interference of the WMs, the previously discussed propagation mechanisms need to be taken into consideration. Here, from the perspective of the DTV reception, two WM scenarios are considered – indoor and outdoor. In addition, the received signal levels of the WM signal as a wanted signal have also been briefly analysed and the results of this analysis are used in the following subsection.

It should be noted that when a range of possible values for a particular loss mechanism exists, a single figure for that loss mechanism has been derived as a mean value and then rounded down to the nearest integer. For instance, the building penetration loss has been found as

(21 + 16 + 21 + 9 + 11 + 7) / 6 = 14.17, which is then rounded down to 14 dB8.

Similarly, body loss has been determined as an average for ‘hand held’ and ‘worn’ cases, i.e. (7+14)/2=10.5, rounded down to 10 dB.

This single figure approach has been adopted for consistency reasons, i.e. to avoid using different figures for wanted and interfering scenarios, in which case conservative (or the worst case) calculations would require using different figures under different scenarios.

5.4.1 WM interfering into DTV – WM Indoor operation

Assumed gains:

- DTV receiver antenna system gain 7 dB

Total gain = 7 dB

Assumed losses:

- Building penetration loss 14 dB

- Body loss 10 dB

- Clutter loss 12 dB

- Fading loss 25 dB

Total loss = 61 dB

Total = 7 dB - 61 dB = -54 dB

The analysis produces an estimated loss of 54 dB. Plugging this figure into the previous distance dependent calculation of signal levels (Figure 5.2.2), Figure 5.4.1 is obtained. As it can be observed, outside the venue within which the WM is operating, the signal level is significantly below the sensitivity threshold of DTV receivers and therefore, no interference should be expected. It should be observed that even at 40 m distance the buffer between the DTV sensitivity threshold and the WM signal is about 17 dB while at a 100 m distance this buffer is about 30 dB. This implies that even if some of the losses are overestimated, the DTV services are not likely to suffer any interference when the WM operates indoors. This analysis assumes a 0 dB protection ratio between an individual WM and DTV service, as per the analog WM results obtained in previous section. It should be observed that according to the same studies, digital WMs require extra 2 dB protection ratio. However, this is not expected to cause any significant difference in analysis between analog and digital WMs.

8 Thermo plane loss has been omitted here.

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Figure 5.4.1: Estimated received interference power levels for indoor WM operation

5.4.2 WM interfering into DTV – WM Outdoor operation

Assumed gains:

- DTV receiver antenna system gain 7 dB

Total gain = 7 dB

Assumed losses:

- Body loss 10 dB

- Clutter loss 12 dB

Total loss = 22 dB

Total = -15 dB

The analysis produces an estimated loss of 15 dB. Plugging this figure into the previous distance dependent calculation of signal levels (i.e. Figure 5.2.2), Figure 5.4.2 is obtained. As it can be observed, and in contrast to indoor WM operation, in the area immediately surrounding the WM, the interfering signal level is above the sensitivity threshold of DTV receivers and therefore, some interference could occur even for those DTV viewers whose received signal level is equivalent to the reference level of -60 dBm if they are located within about 60 m from the WM. Viewers near the edge of the rural coverage area (or whose received signals is around the sensitivity threshold) may be affected if they are located within about 200 m from the WM. However, if the TV receiver antenna directivity discrimination is added to the total losses, this distance reduces to about 65 m, while viewers receiving the reference signal level should virtually be unaffected. Using the same assumption as previously (i.e. that the distance from the BS antenna is significantly larger than from the

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WM), for those viewers who receive their DTV signal exactly at the edge of rural coverage, i.e. the sensitivity level, the impacted area where the area potentially impacted by interference from the WM is shown in Figure 5.4.3 (the red contour).

Figure 5.4.2: Estimated received interference power levels for outdoor WM operation

The green contour with the radius of slightly above 200 m shows the area which would potentially be affected by interference from the WM if the TV receiver antenna direction selectivity is not taken into account. As it can be observed the directional selectivity significantly reduces the area of potential interference. However, it should also be observed that when the distance to the WM is becoming shorter the clutter loss might become less significant which could potentially increase the area of possible interference. The predictions are obtained using ITU 1546-5 model and 0 dB protection ratio as for individual analog WMs.

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Figure 5.4.3: The impact of the TV receiver antenna directional selectivity on the area of potential interference from the WM (red contour) near the edge of rural DTV coverage. The green contour shows the area of potential interference without taking into account the directional selectivity.

5.5 Adjacent channel operation

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Broadcast Station

WM

Radial axis – dWM [m]

The required minimum guard band between the DTV service and an individual WM (both analog and digital WMs considered) has been studied. The examples of these scenarios are shown in Figures 4.2.1 and 4.2.2. Studies have been performed for cases with wanted signal levels of -75.5 dBm, which is significantly lower than -60 dBm reference value. As it was observed in the previous section, virtually no guard band is required between the DTV and digital WM channels as long as no part of the WM 200 kHz channel is overlapping with the 7 MHz DTV channel. It should be noted that these results are obtained for the given scenarios where the interfering power level is about 20 dB higher than the wanted DTV signal (for the 250 m separation). For the analog WM scenario the results suggested that the DTV services could be more prone to interference due to WM adjacent band operation. However, these results should be subject to similar additional analysis as the co-channel scenario, i.e. the additional losses should be taken into account for indoor and outdoor scenarios.

For the digital WM interfering scenario, by plugging the corresponding previously discussed losses, it is clear that no interference should occur regardless of whether the WM operates indoor or outdoor. Furthermore, the results of the studies suggest that digital WMs do not require any guard band and that they do not cause interference into DTV even when half of the digital WM spectrum is within the DTV channel.

For analog WM interferer, the results based on the spatial separation distance only (assuming free space probation) were less conclusive and therefore additional studies were performed to determine the interference levels and corresponding protection ratios when the frequency offset between centre frequencies of WM and DTV service has been fixed to 3.6 MHz, implying no guard band between WM and DTV but with no part of the WM spectrum (in theory) being inside the DTV channel. By including the additional losses, as discussed before, it can be concluded that the analog WMs can also operate indoors adjacent to the DTV services with no guard band requirement. In outdoor environments, the analog WMs have a very small potential to cause interference into area immediately surrounding them (up to about 90 m), provided that the DTV viewers are located near the edge of rural DTV coverage. However, for viewers receiving the reference level of -60 dBm, the interfering signal in the adjacent band level is about 7 dB below the level that could potentially cause interference into DTV services.

5.6 Multiple WM in a single DTV channel scenarios

The previous analysis presented in this section refers to the cases when individual WMs, analog or digital, are subject of spectrum sharing with DTV services. For multiple WM scenarios, i.e. cases when several WMs are accommodated within a single DTV channel, appropriate adjustments may be required. As shown in Tables 4.1.2 and 4.1.4 in the previous Section, these adjustments may be up to 30 dB for digital and up to 7 dB for analog WM cases.

For adjacent channel operations, these adjustments are not expected to have significant impact on the results because it is expected that only the WM with the smallest frequency separation from DTV would have the highest impact on the DTV services.

For co-channel operation, however, this impact is expected to be more significant. For the co-channel indoor case and an individual analog WM there is a significant buffer of about 20 to 30 dB (at 50 m and 100 m distances from the WM), and extra 7 dB of interference due to additional analog WMs is not considered to be significant. For the multiple digital WMs the additional 30 dB of interference would consume most of the buffer and could potentially cause some interference in the areas immediately surrounding the WMs. However, this interference, if any, is not expected to be significant due to TV receiver antenna discrimination (as per Figure 5.3.1).

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For outdoor scenario, an increase of number of digital WMs is expected to add significant interference compared to the individual digital WM case, and therefore, co-channelling should be avoided. For multiple WM scenario additional protection ratio of up to 30 dB (Table 4.1.4) should be added between DTV and WM interference (relative to the power of an individual WM), which when plugged to Figure 5.5.2 will increase the radius of potential interference to about 1.65 km (assuming near coverage edge DTV reception). Furthermore, even if the reference power of -60 dBm for the DTV is applied, the radius of the potential interference zone is still increased compared to the single digital WM case, and is about 500 m.

Nevertheless, it should also be noted that a scenario where all WMs are received with identical power levels is highly unlikely and therefore overly conservative. In practice, it may be expected that only a small number of WMs will be dominant interferers, while the contribution to interference from the remaining WMs would be insignificant and excluded from consideration. This observation is similar to the observation in [9] where it was assumed that even when there are multiple interferers, only one WM will be a dominant interferer and contributions from the remaining WMs could be disregarded.

5.7 Interference from DTV into WMs

Although not the main subject of this report, the interference into WMs for DTV should also be considered in a sense that, due to significantly disproportional EIRPs of WMs and DTV services, in most instances the WMs are significantly more prone to interference from DTV than vice versa. This is important to note because this implies that the co-channelling operation between WM and DTV services is somewhat self-regulatory in a sense that if a WM does not suffer interference from a DTV service then it is unlikely that the WM would cause any interference into the DTV service. Similarly, if a WM causes interference into a DTV service, than it is very likely that the WM would also receive significant interference from the DTV service and therefore would not be able to operate at that particular frequency occupied by the DTV service.

For instance, it has been already discussed in Section 2 of this report that WMs require at least 12 dB protection ratio in order to tolerate interference from DTV services. Therefore, the field strength DTV limit of 56 dBV/m has been derived in [8], [6] under which WMs would potentially tolerate interfering DTV signals. This implies that if a WM is located in an area with DTV reception more than 2 dB above the rural coverage (for Band V UHF), it is likely to suffer interference from the DTV service. Furthermore, if the WM is located in an area with suburban level DTV coverage (67 dBV/m for Band V UHF) it will receive rather severe interference from the DTV service. It should be noted that this brief analysis corresponds to an outdoor scenario where no losses apart from the propagation loss are taken into account (i.e. no clutter or body loss).

However, in practice, some of the loss mechanisms discussed earlier in this Section could be applied here as well. Two of these loss mechanisms have been considered here. First, for indoor WM operation, the building penetration loss would, to a certain extent, protect the WM receiver from the unwanted DTV signal. In addition, clutter loss could also be considered as another loss mechanism that equally affects the DTV interfering levels. Other loss mechanisms have not been considered because either they are not applicable to this analysis (e.g. body attenuation) or not sufficient information is available to characterise their impact on the WM operation (e.g. antenna discrimination).

Again, two scenarios could be considered here as well – indoor and outdoor WM operation. For the indoor scenario, the total loss that can be applied to the interfering signal is the sum of clutter and building penetration losses and as per the previous figures it is estimated to be 22 dB. For the outdoor scenario, only clutter loss should potentially be applied, which is 12 dB. By plugging these additional losses Table 5.7.1 is obtained witch summarises new estimates for the maximum DTV signal levels for various scenarios.

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No losses Indoor scenario Outdoor scenario

Maximum DTV level at WM receiver E [dBV/m] 56 78 68

Table 5.7.1: Summary of estimates of the maximum tolerable DTV signal levels for various scenarios

5.8 Coverage area definition

As it could be observed from Table 2.1.1, different levels of the minimum field strengths have been defined depending on the type of the propagation environment of a DTV services. However, in order to simplify the definition of the coverage area and to make it standard for all broadcast sites (i.e. non-site specific), it is suggested here that the minimum field strength relating to the rural level coverage should be adopted in the LIPD Class Licence document. However, it is not expected that this simplified definition would have significant practical implications since in reality WMs would be more impacted by interference from higher DTV field strengths if higher field strengths were adopted for some sites (as explained in the previous subsection 5.7).

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6Recommendation

As a result of both the ACMA’s studies and review of studies conducted and published internationally, and with the focus on the main objectives of this report, following changes to the LIPD are recommended:

6.1 DTV Coverage definitions

The coverage area of a digital TV services should be defined in the LIPD as per Table 6.1.1, i.e.

UHF Blocks B and C(520-610 MHz)

UHF Blocks D and E(610-694 MHz)

50 dBV/m 54 dBV/m

Table 6.1.1: Minimum field strengths for different UHF Blocks

Note: Consideration should also be given to bring the conditions relating to VHF WM and the coverage area DTV services into line with that for UHF WMs.

6.2 Spectrum sharing

Spectrum sharing recommendations for four different options are shown in Table 6.2.1 and further elaborated in the remainder of this subsection.

Co-channel allowed Adjacent band allowed(separation 0 kHz)

Indoor YES YES

Outdoor NO YES

Table 6.2.1: Summary of spectrum sharing recommendations within DTV service coverage area

6.2.1 Co-channelling operation

a) Indoor WM operation:

For the case of indoor WM operation, co-channel operation of WMs and DTV should be allowed since there is sufficient evidence suggesting that an individual WM is not likely to cause significant interference into DTV services (if any) due to various loss mechanisms that affect the level of the interfering WM signal. It is anticipated that even in an unlikely event if interference occurs, it would be confined to a very limited area immediately surrounding the WM. This recommendation is also consistent with a similar recommendation currently in place in the UK [9].

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b) Outdoor WM operation:

For the case of outdoor WM operation, there might be some potential interference near the edge of rural DTV coverage within a radius of about 200 m from the WM transmitter. The impact of interference is greatly reduced if the TV receiver antenna directivity is taken into account. However, studies in this report indicate that even some DTV viewers receiving a reference signal level of -60 dBm might be affected by the interference, provided that their TV antennas are within close proximity of the WMs. In addition, it is anticipated that the WMs would be significantly more prone to interference from the DTV services than vice versa, if co-channelled. Therefore, at this stage it is recommended that co-channelling operation between WMs and DTV services must be avoided for the outdoor scenario and within the coverage area of the DTV services.

6.2.2 Adjacent band operation

a) Indoor WM operation:

For the case of indoor WM operation, adjacent band operation of WMs and DTV should be allowed. It is clear that under this scenario potential for interference into DTV is significantly smaller compared to previously discussed indoor co-channel scenario. This recommendation is also consistent with a similar recommendation currently in place in the UK [9].

b) Outdoor WM operation:

The ACMA’s studies reveal that for digital WMs there is no need for any guard band between WMs and DTV services. However, analog WMs have more potential to cause interference to DTV services than digital WMs, when operating in a band adjacent to the DTV. The ACMA’s studies suggest that the analog WMs may cause interference to DTV reception to distances up to 90 m, in the areas near the edge of rural coverage. If no interference is to be tolerated this would suggest a necessary guard band of at least 200 kHz between WMs and DTV. However, when the TV receiver antenna discrimination is taken into account (similar to Figure 5.5.3), it is anticipated that only a very small number of DTV viewers might suffer interference from analog WMs. In addition, those viewers whose DTV reception is around the reference level of -60 dBm are not predicted to receive any interference from the analog WMs. On balance, it is concluded that a guard band requirement between WMs (both analog and digital) should be removed. It should be observed that currently in the UK [9] it is suggested that a 500 kHz guard band between WMs and DTV services may be applied solely based on the ERC Report 88 [6]. However, it has been noted that the purpose of this requirement is to protect WMs from interference caused by the DTV and not vice versa.

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7References

[1] Australian Communications and Media Authority, Radiocommunications (Low Interference Potential Devices) Class Licence 2000http://www.comlaw.gov.au/Series/F2005B00339 Retrieved 28 August 2013

[2] Stephen Conroy, Minister for Broadband, Communications and the Digital Economy, Australian Communications and Media Authority (Realising the Digital Dividend) Direction 2010http://www.comlaw.gov.au/Series/F2010L01990 Retrieved 28 August 2013

[3] Australian Communications and Media Authority, Broadcasting Services (Technical Planning) Guidelines 2007 (as amended)http://www.comlaw.gov.au/Series/F2007L02469/CompilationsRetrieved 18 August 2013

[4] Australian Broadcasting Authority, Digital Terrestrial Television Broadcasting Planning Handbook, http://www.acma.gov.au/~/media/Radiocommunications%20Licensing%20and%20Telecommunications%20Deployment/Publication/pdf/Digital%20Terrestrial%20Television%20Broadcasting%20Planning%20Handbook%20including%20technical%20and%20general%20assumptions.pdf Retrieved 28 August 2013

[5] European Conference of Postal and Telecommunications Administrations, The Chester 1997 Multilateral Coordination Agreement relating to Technical Criteria, Coordination Principles and Procedures for the introduction of Terrestrial Digital Video Broadcasting (DVB-T)http://www.archive.ero.dk/132D67A4-8815-48CB-B482-903844887DE3?frames=no&Retrieved 28 August 2013

[6] European Radiocommunications Committee, Compatibility and sharing analysis between DVB-T and Radio Microphones in Bands IV and V, ERC Report 88http://www.ecodocdb.dk/doks/filedownload.aspx?fileid=1978&fileurl=http://www.erodocdb.dk/Docs/doc98/official/pdf/REP088.PDF Retrieved 28 August 2013

[7] Mike Reynolds et al, Sagentia, PMSE Spectrum Usage Rights & Interference Analysis, revised report for Ofcom dated 13 June 2008 as part of their consultation Digital dividend review: 550-630MHz and 790-854MHz published 6 June 2008http://stakeholders.ofcom.org.uk/binaries/consultations/clearedaward/pmsesur.pdfRetrieved 28 August 2013

[8] Cobham and Aegis Spectrum Engineering, Spectrum efficiency of wireless microphones, Report 2202/DWM/R/2/2.0 for Ofcomhttp://stakeholders.ofcom.org.uk/market-data-research/other/technology-research/research/spectrum-efficiency/spectrum-efficiency-of-wireless/Retrieved 28 August 2013

[9] Ofcom, Future access to interleaved spectrum for programme making and special events, statement published 16 May 2011 as part of their consultation Digital dividend: band manager award: second consultation on detailed award design published22 June 2009http://stakeholders.ofcom.org.uk/binaries/consultations/bandmanager09/statement/pmse-future-access.pdf Retrieved 28 August 2013

[10] Ofcom, Access to interleaved spectrum for programme-making and special events after digital switchover, statement published 16 January 2008 as part of their consultation Digital dividend review published 19 December 2006http://stakeholders.ofcom.org.uk/binaries/consultations/ddr/statement/statement1.pdfRetrieved 28 August 2013

[11] ITU-R, VHF and UHF Propagation Curves for the Frequency Range from 30 MHz to 1,000 MHz, Recommendation ITU-R P.370-7 (withdrawn 2001)http://www.itu.int/rec/R-REC-P.370-7-199510-W/en Retrieved 28 August 2013

[12] ITU-R, Planning criteria, including protection ratios, for digital terrestrial television services in the VHF/UHF bands, Recommendation ITU-R BT.1368-10http://www.itu.int/rec/R-REC-BT.1368-10-201301-I/en Retrieved 28 August 2013

[13] Ian Anderson, Communications Laboratory, Department of Transport and Communications, Performance of FM Broadcast Receivers, Laboratory Report 91/9

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[14] Sony, Digital Wireless Microphone System DWT-B01 DWR-S01D DWA-01Dhttp://www.pro.sony.eu/res/attachment/file/68/1237485309868.pdf Retrieved 28 August 2013

[15] European Telecommunications Standards Institute, Electromagnetic compatibility and Radio spectrum Matters (ERM); Technical characteristics for Professional Wireless Microphone Systems (PWMS); System Reference Document, ETSI European Standard ETSI TR 102 546-1 V1.1.1 (2007-02)http://www.etsi.org/deliver/etsi_tr/102500_102599/102546/01.01.01_60/tr_102546v010101p.pdf, Retrieved 02 October 2013

[16] European Telecommunications Standards Institute, Electromagnetic compatibility and Radio spectrum Matters (ERM); Wireless microphones in the 25 MHz to 3 GHz frequency range; Part 1: Technical characteristics and methods of measurement, ETSI European Standard ETSI EN 300 422-1 V1.4.2 (2011-08)http://pda.etsi.org/pda/queryform.asp Retrieved 28 August 2013

[17] Australian Communications Authority, Braodcast planning instructions:Antenna directivity and cross polar discrimination, Document SP 4/2000http://www.acma.gov.au/webwr/radcomm/frequency_planning/spps/0004spp.pdfRetrieved 10 October 2013

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Appendix I: Spectrum characteristics of analog and digital wireless microphones under various scenarios

A.1 Analog FM microphones

Figure A.1.1: Modelled spectrum characteristic of a single analog FM WM as using MATLAB.

Figure A.1.2: Spectrum characteristic of a single analog FM WM observed on the R&S ETL.

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Figure A.1.3: Modelled spectrum characteristic of 8 analog FM WM as using MATLAB.

Figure A.1.4: Spectrum characteristic of 8 analog WMs observed on the R&S ETL.

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Figure A.1.5: Modelled spectrum characteristic of 9 analog FM WMs as using MATLAB.

Figure A.1.6: Spectrum characteristic of 9 analog FM WMs observed on the R&S ETL.

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Figure A.1.7: Modelled spectrum characteristic of 16 analog FM WMs as using MATLAB.

Figure A.1.8: Spectrum characteristic of 16 analog FM WMs observed on the R&S ETL.

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Figure A.1.9: Modelled spectrum characteristic of 17 analog FM WM as using MATLAB.

Figure A.1.10: Spectrum characteristic of 17 analog FM WMs observed on the R&S ETL.

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A.2 Digital Microphones

Figures (A.2.1 – A.2.10) show assumed spectrum characteristics for various digital WM scenarios as modelled in the R&S WinIQSIM2 waveform generating software and their corresponding actual characteristics as observed on the R&S ETL.

Figure A.2.1: Modelled spectrum characteristic of a single digital WM using R&S WinIQSIM2 software.

Figure A.2.3: Spectrum characteristic of a single digital WM observed on the R&S ETL.

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Figure A.2.3: Modelled spectrum characteristic of 8 digital WMs using R&S WinIQSIM2 software.

Figure A.2.4: Spectrum characteristic of 8 digital WMs observed on the R&S ETL.

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Figure A.2.5: Modelled spectrum characteristic of 9 digital WMs using R&S WinIQSIM2 software.

Figure A.2.6: Spectrum characteristic of 9 digital WMs observed on the R&S ETL.

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Figure A.2.7: Modelled spectrum characteristic of 16 digital WMs using R&S WinIQSIM2 software.

Figure A.2.8: Spectrum characteristic of 16 digital WMs observed on the R&S ETL.

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Figure A.2.9: Modelled spectrum characteristic of 17 digital WMs using R&S WinIQSIM2 software.

Figure A.2.10: Spectrum characteristic of 17 digital WMs observed on the R&S ETL.

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