co-existence_of_LTE_systems_in_790-862mhz_with_DTT.pdf

DotEcon Ltd

800MHz auction: Co-existence of LTE systems in 790-862 MHz with Digital Terrestrial Television

August 2011

Contents i

800MHz auction: Co-existence of LTE systems in 790-862 MHz with Digital Terrestrial Television - August 2011

Contents

1 Introduction 10

1.1 Structure of this document 13

2 Overview of approach and main assumptions 14

2.1 Approach taken 14

2.2 Main assumptions 15

2.3 DTT coverage and frequency plan 17

2.4 LTE network assumptions 27

3 Analysis of LTE networks operating at maximum power levels 30

3.1 Summary of results 30

3.2 Effect of interference on indoor coverage of DTT 35

3.3 Conclusions from the initial analysis 35

3.4 Observations on relevance of the initial analysis to real LTE deployments 37

4 Impact of interference assuming realistic LTE deployment assumptions 39

4.1 Determination of individual EIRP levels 39

4.2 Impact of realistic EIRP levels on potential for receiver overload 47

4.3 Composite overload effect from three networks 51

4.4 Impact of using realistic EIRP levels on the potential for ACI 52

4.5 Impact of realistic EIRP levels on ACI in DTT Channel 60 areas 61

4.6 Effect on indoor coverage 70

4.7 Effect of site sharing between the three networks 74

4.8 Near-field interference effects 74

4.9 Summary of results 75

5 Evaluation of possible mitigation measures 79

5.1 Use of DTT receiver filters 79

5.2 Mitigation via additional filtering on LTE base stations 82

5.3 Use of cross-polarisation between LTE and DTT 83

5.4 Improving the DTT signal level via on-channel repeaters 84

5.5 Mitigation via improving DTT receiver design 85

5.6 Platform change 87

5.7 Other forms of mitigation 88

6 Interference from LTE uplink emissions 89

7 Conclusions and recommendations 91

7.1 Summary of the main interference issues 91

7.2 Conclusions on the suitability of different mitigation techniques 92

ii Introduction

800MHz auction: Co-existence of LTE systems in 790-862 MHz with Digital Terrestrial Television August 2011

7.3 Recommendations 94

Annex A Blocking results by geo-type within Danish broadcast regions (initial analysis) 96

Annex B : DTT site characteristics for Channels 60, 59 and 58 in Denmark 98

Annex C : Maps showing areas of interference (initial analysis) 99

Annex D : LTE link budget 104

Annex E : Summary of modelling steps 106

Contents iii


Tables & Figures

Table 1 Channel plan for DTT multiplexes 1 to 6 [Source: NITA] .................. 20

Table 2 Regions in Denmark using upper DTT channels [Source: Analysys Mason] ........................................................................................................ 20

Table 3 DTT planning assumptions [Source: Analysys Mason] .................... 23

Table 4 DVB-T PRs in the presence of LTE interfering in a Gaussian channel environment [Source: ECC] ........................................................................ 24

Table 5 LTE-DTT channel offsets in MHz used in the ACI analysis [Source: Analysys Mason]......................................................................................... 24

Table 6 Correction factors applied to PR values [Source: Analysys Mason] . 25

Table 7 Interpolated PR values Gaussian channel [Source: Analysys Mason] ........................................................................................................ 25

Table 8 Interpolated ratios with correction factors Boxer DTT coverage [Source: Analysys Mason] .......................................................................... 26

Table 9 Interpolated ratios with correction factors Digi-TV DTT coverage [Source: Analysys Mason] .......................................................................... 26

Table 10 PR values plus correction factors, Boxer coverage fixed outdoor reception [Source: Analysys Mason] ........................................................... 27

Table 11 PR values plus correction factors, Digi-TV coverage fixed outdoor reception [Source: Analysys Mason] ........................................................... 27

Table 12 Cell radii for LTE model [Source: Analysys Mason] ......................... 29

Table 13 Summarised results of blocking calculation from LTE to DTT, initial analysis (59dBm EIRP, with 56dBm in Channel 60 areas) fixed outdoor reception [Source: Analysys Mason] ........................................................... 31

Table 14 Number of existing GSM900 sites of each operator in the area of analysis [Source: Analysys Mason] ......................... 32

Table 15 ACI to Channel 60 in Vordingborg, portable indoor reception [Source: Analysys Mason]......................................................................................... 35

Table 16 Calculated cell ranges for different EIRP levels [Source: Analysys Mason] ........................................................................................................ 41

Table 17 Theoretical site separation for different EIRP levels [Source: Analysys Mason]27 ..................................................................................................... 41

Table 18 Number of base stations within the North Copenhagen sample area [Source: Analysys Mason] .......................................................................... 42

Table 19 Number of sites per geo-type within the North Copenhagen sample area [Source: Analysys Mason] .................................................................. 44

Table 20 Receiver overload per network [Source: Analysys Mason] .............. 47

Table 21 Receiver overload using realistic LTE EIRP levels scaled nationally from the North Copenhagen sample area [Source: Analysys Mason] ......... 51

Table 22 Interference power sum of receiver overload from three networks for sample area [Source: Analysys Mason] ...................................................... 52

iv Contents


Table 23 ACI per network Network A in blocks FDD1/FDD2 [Source: Analysys Mason] ......................................................................................... 53

Table 24 ACI per network Network B in blocks FDD1/FDD2 [Source: Analysys Mason] ......................................................................................... 53

Table 25 ACI per network Network C in blocks FDD1/FDD2 [Source: Analysys Mason] ......................................................................................... 53

Table 26 ACI from LTE block FDD 1 to DTT Channel 59 using realistic LTE EIRP levels, scaled nationally [Source: Analysys Mason] ........................... 58

Table 27 Number of sites per geo-type within the Ringsted-Sor sample area [Source: Analysys Mason] .......................................................................... 63

Table 28 ACI per network Network A in blocks FDD1/FDD2 [Source: Analysys Mason] ......................................................................................... 66

Table 29 ACI per network Network B in blocks FDD1/FDD2 [Source: Analysys Mason] ......................................................................................... 66

Table 30 ACI per network Network C in blocks FDD1/FDD2 [Source: Analysys Mason] ......................................................................................... 66

Table 31 ACI from LTE block FDD 1 to DTT Channel 60 using realistic LTE EIRP levels, scaled nationally [Source: Analysys Mason] ........................... 70

Table 32 PR values plus correction factors, Channel 60 coverage, portable indoor reception [Source: Analysys Mason] ................................................ 70

Table 33 ACI per network for indoor coverage Network A in blocks FDD1/FDD2 [Source: Analysys Mason] ...................................................... 71

Table 34 ACI per network for indoor coverage Network B in blocks FDD1/FDD2 [Source: Analysys Mason] ...................................................... 71

Table 35 ACI per network for indoor coverage Network C in blocks FDD1/FDD2 [Source: Analysys Mason] ...................................................... 71

Table 36 ACI from LTE block FDD 1 to DTT Channel 60 using realistic LTE EIRP levels, scaled nationally, indoor coverage [Source: Analysys Mason] 73

Table 37 Site sharing in North Copenhagen sample area [Source: Analysys Mason] ........................................................................................................ 74

Table 38 The effect of using realistic LTE EIRP levels and increased site sharing on receiver overload [Source: Analysys Mason] ............................. 74

Table 39 Estimated reduction in the potential for blocking from use of DTT receiver filters using realistic EIRP analysis for selected Channel 59 area [Source: Analysys Mason] .......................................................................... 81

Table 40 Estimated reduction in the potential for ACI from use of DTT receiver filters using realistic EIRP analysis for selected Channel 59 area [Source: Analysys Mason] ......................................................................................... 81

Table 41 Estimated reduction in the potential for ACI from use of DTT receiver filters using realistic EIRP analysis for selected Ringsted-Sor area [Source: Analysys Mason] ......................................................................................... 82

Table 42 Impact of improving the blocking threshold modelled for one LTE network interfering with DTT, operating at maximum licensed EIRP [Source: Analysys Mason] ......................................................................................... 87

Contents v


Table A.1 Site data for DTT Channels 60, 59 and 58 [Source: NITA] ........... 98

Table D.1 LTE link budget for downlink [Source: Analysys Mason] ........... 104

Table D.2 LTE link budget for uplink [Source: Analysys Mason] ................ 105

Figure 1 Band plan for 470870MHz in Europe [Source: Analysys Mason] ... 11

Figure 2 FDD channelling arrangement for 790862MHz [Source: ECC] ...... 11

Figure 3 DTT directional receiving antenna [Source: ITU-R BT.419] ............. 18

Figure 4 Danish broadcast regions [Source: NITA]........................................ 19

Figure 5 Regions using Channel 60 [Source: NITA] ....................................... 21



Figure 8 Jaybeam antenna pattern [Source: Jaybeam, Analysys Mason] ...... 28

Figure 9 Areas of blocking from the three LTE networks [Source: Analysys Mason] ........................................................................................................ 32

Figure 10 Areas affected by ACI into DTT channel 60 from two LTE networks [Source: Analysys Mason] .......................................................................... 34

Figure 11 Illustration of areas of coverage overlap in one LTE800 network deployed on GSM900 sites [Source: Analysys Mason] ............................... 38

Figure 12 Selected area for analysis [Source: Analysys Mason] .................. 40

Figure 13 Approach to setting EIRP per base station site [Source: Analysys Mason] 40

Figure 14 EIRP required for different site separations [Source: Analysys Mason] 42

Figure 15 Site to geo-type matching Network A [Source: Analysys Mason]43

Figure 16 Site to geo-type matching Network B [Source: Analysys Mason]43

Figure 17 Site to geo-type matching Network C [Source: Analysys Mason]44

Figure 18 EIRP per site and coverage Network A [Source: Analysys Mason] 45

Figure 19 EIRP per site and coverage Network B [Source: Analysys Mason] 46

Figure 20 EIRP per site and coverage Network C [Source: Analysys Mason] 46

Figure 21 Areas affected by receiver overload Network A [Source: Analysys Mason] 48

Figure 22 Areas affected by receiver overload Network B [Source: Analysys Mason] 49

Figure 23 Areas affected by receiver overload Network C [Source: Analysys Mason] 50

Figure 24 Areas affected by ACI Network A in FDD1/FDD2 [Source: Analysys Mason]......................................................................................... 55

vi Contents


Figure 25 Areas affected by ACI Network B in FDD1/FDD2 [Source: Analysys Mason] ......................................................................................... 56

Figure 26 Areas affected by ACI Network C in FDD1/FDD2 [Source: Analysys Mason] ......................................................................................... 57

Figure 27 Areas affected by ACI only, compared to ACI and blocking Network A in FDD1/FDD2 [Source: Analysys Mason] ................................. 59

Figure 28 Areas affected by ACI only, compared to ACI and blocking Network B in FDD1/FDD2 [Source: Analysys Mason] ................................. 60

Figure 29 Areas affected by ACI only, compared to ACI and blocking Network C in FDD1/FDD2 [Source: Analysys Mason] ................................. 61

Figure 30 Selected Ringsted-Sor sample area for ACI Channel 60 analysis [Source: NITA] ............................................................................................ 62

Figure 31 Geo-types assigned to existing GSM900 sites in Ringsted- Sor [Source: Analysys Mason] .......................................................................... 63

Figure 32 EIRP per site and coverage Network A [Source: Analysys Mason] 64

Figure 33 EIRP per site and coverage Network B [Source: Analysys Mason] 64

Figure 34 EIRP per site and coverage Network C [Source: Analysys Mason] 65

Figure 35 Areas affected by ACI Network A in FDD1/FDD2 [Source: Analysys Mason] ......................................................................................... 67

Figure 36 Areas affected by ACI Network B in FDD1/FDD2 [Source: Analysys Mason] ......................................................................................... 67

Figure 37 Areas affected by ACI Network C in FDD1/FDD2 [Source: Analysys Mason] ......................................................................................... 68

Figure 38 Density of households near Ringsted city area [Source: Analysys Mason] 69

Figure 39 Areas affected by ACI (indoor reception) Network A in FDD1/FDD2 [Source: Analysys Mason] ...................................................... 72

Figure 40 Areas affected by ACI (indoor reception) Network B in FDD1/FDD2 [Source: Analysys Mason] ...................................................... 72

Figure 41 Areas affected by ACI (indoor reception) Network C in FDD1/FDD2 [Source: Analysys Mason] ...................................................... 73

Figure 42 Characteristics of UHF filter [Source: Braun Telecom] ................. 80

Executive Summary 7


Executive Summary

The National IT and Telecom Agency (NITA) is responsible for planning and preparing an auction of 800MHz spectrum for the final decision by the Minister of Science, Innovation and Technology (the Minister). In this regard, NITA has engaged DotEcon and Analysys Mason as advisers. Particularly, we have been tasked with: analysing the scope for use of this spectrum; assessing the risk of interference from the use of this band to digital terrestrial television (DTT) services; considering whether, and how, any coverage obligations may be imposed on the licences in pursuit of the governments overall broadband goal; and designing a suitable auction.

This report presents the results of theoretical modelling and analysis that DotEcon and Analysys Mason have conducted for NITA considering the potential interference to DTT from future mobile use of the 790862MHz band (the 800MHz band) in Denmark.

The results of our analysis suggest that between 9 000 and 10 000 households nationally might be at risk of some kind of interference from mobile use of the 800 MHz band.

Two modes of interference have been considered; receiver overload and adjacent channel interference (ACI).

More detailed results of our analysis suggest that:

Between 2 500 and 3 000 households nationally might be at risk of interference from receiver overload

Between 4 500 and 5 000 households might be at risk of interference from ACI in areas of Denmark receiving DTT services using Channel 60, and up to 2 000 households in areas using Channel 59

Our analysis was conducted in two parts. The purpose of the first high-level analysis was to establish whether interference from LTE to DTT could potentially be a problem. This first part of the analysis considered the potential interference mechanisms into DTT that might occur from one or several long-term evolution (LTE) network(s) operating at assumed maximum licensed power levels, and the extent of interference created.

The results of this initial analysis suggested that there is considerable scope for interference from LTE to DTT if it is assumed that all LTE base stations operate at their maximum licensed power level.

Having established from our initial analysis that there could be an interference problem from LTE to DTT, we then conducted more detailed analysis to model the effects of a series of realistic LTE network deployments. This further analysis took into account that in practice, only a proportion of LTE base stations will transmit at the maximum licensed power level, and the majority will use lower power levels for various practical reasons (e.g. due to planning restrictions, other site restrictions or management of internal interference).

We found that the number of DTT households affected by receiver overload from three LTE networks across Denmark was reduced to around 2 500 - 3 000 DTT households. The effect of ACI is also substantially reduced for areas of the country using DTT Channel 59, with an estimate of around 2 000 DTT households in total being affected.

8 Executive Summary


We found that around 4 500 5 000 DTT households might be affected by ACI in areas of the country using DTT channel 60, as a result of interference from one LTE network.

The third and final part of the analysis was to assess the feasibility of further reducing the impact of interference predicted from LTE to DTT, through the consideration of various possible interference mitigation techniques.

Considering the range of possible mitigation methods that can be used to reduce the impact of LTE interference to DTT and/or to restore the DTT service, we found that the use of filters at DTT receivers appears to be the most cost effective and practical mitigation technique. Our modelling suggests that use of filtering will substantially eliminate interference from both overload and ACI, leaving a small number of households for which filtering is not suitable. These are most likely to be households viewing DTT services using Channel 60 and receiving interference from LTE block FDD1.

Other suitable forms of mitigation, which can be applied on a case-by-case basis, include filtering of LTE base stations (which can be used in conjunction with DTT receive filters to further reduce the number of households affected), cross-polarisation between LTE and DTT antennas (i.e. using the opposite of DTT polarisation at LTE sites), and installation of DTT on-channel repeaters. The latter might be particularly considered in areas where television viewing households are located at the edge of DTT coverage.

A possible further means of mitigation against DTT receiver overload and ACI would be to improve the immunity of DTT receivers, by designing them with a higher interference threshold (called overload threshold, or Oth) and protection ratio (called PR). A higher Oth and PR limit could be specified within receiver standards for DTT services, to ensure that future receivers are designed with a higher threshold and protection ratio in mind. Recent measurements conducted by the European Communications Committee (ECC) suggest that some DTT receivers on the market today already exhibit a better Oth and PR than assumed within the modelling for this report. It is noted that Denmark would not be able to make this change to DTT standards itself. It is possible that a change to standards could be market driven; if regulatory action is required, this would potentially require EU-wide cooperation, since standards for DTT are pan-European.

In conclusion, we have found that, whilst our initial analysis suggested that interference from LTE to DTT is a problem, in practice assuming that mobile operators will optimise the power and characteristics of individual base stations within their network (and not use maximum licensed power limits at all sites), the interference problem is substantially reduced. Application of the further mitigation methods discussed above could almost eliminate any issues, leaving only a very small number of affected DTT households possibly of the order of a few hundred in total across Denmark. For the remaining few households that continue to suffer receiver overload or ACI after all appropriate mitigation methods have been considered, the only option would to use an alternative television (TV) platform such as cable, satellite or IPTV.

Given that operators are likely to apply reduced power levels in many areas of their network, we do not think it is necessary for NITA to consider any specific licence conditions within the 800 MHz licences other than a maximum EIRP limit. However, it is possible that additional requirements could be considered in relation to managing interference from the lowermost LTE blocks (FDD1/FDD2)

Executive Summary 9


to DTT services in areas of Denmark using Channel 60, which our analysis has suggested could be particularly problematic in terms of potential for ACI. It might be necessary to consider a reduced EIRP limit for base stations using blocks FDD1 and FDD2 although it is noted that this limit should be considered carefully in view of its impact upon the ability of mobile operators to provide LTE coverage, particularly in suburban and rural areas.

10 Introduction


1 Introduction

The migration from analogue to digital terrestrial TV (DTT) transmission is now well underway in most European countries, and was completed in Denmark on 1 November 2009. In Denmark, all terrestrial TV services are now being delivered digitally using DVB-T technology. These digital services, like the superseded analogue services, use UHF spectrum for their transmission. The UHF spectrum used for broadcasting was originally 470862MHz, but the ITU World Radio Conference in 2007 (WRC-07) decided to allocate the upper part of this spectrum, from 790862MHz, for mobile services on a co-primary basis with broadcasting.

Following WRC-07, the European Commission (EC) recommended that Member States make the sub-band from 790862MHz (the 800MHz band) available for electronic communications services, via a decision published in 2010 (EC Decision 2010/267/EC). The EC also requested the European Communications Committee (ECC) to consider harmonised technical conditions, including a frequency plan. The Danish government has decided to award licences in the 800MHz band in line with the European harmonisation efforts: the underlying band plan will follow the European plan.

The harmonised European plan for the 800MHz band (as described in ECC Decision (09)03) divides the spectrum into two 30MHz blocks for FDD1 downlink and uplink respectively.2 There is an 11MHz duplex gap, which is intended for use by PMSE3 in Denmark.

According to the European Common Allocation Table (ERC Report 25), the band above 862MHz is designated for use by various short-range devices (SRDs), including RFID.4

There is a 1MHz guard band between 790 and 791MHz, which divides the top of the DTT spectrum and the first long-term evolution (LTE) channel.

The European band plan for 470870MHz is summarised in Figure 1 below.

1 Frequency Division Duplexing

2 The conclusion of CEPT Report 31 was that the preferred frequency arrangement for the

800MHz band was an FDD plan. The 230MHz FDD plan with an 11MHz duplex gap was 2 The conclusion of CEPT Report 31 was that the preferred frequency arrangement for the

800MHz band was an FDD plan. The 230MHz FDD plan with an 11MHz duplex gap was subsequently defined in ECC Decision (09)03.

3 Programme-Making and Special Events

4 Radio-frequency Identification: applications that exchange data between a reader and an

electronic tag attached to an object, for the purpose of identification and tracking.

Introduction 11


Figure 1 Band plan for 470870MHz in Europe [Source: Analysys Mason]

Assuming that the 800MHz band is divided into 5 MHz channels, this suggests six FDD channels can be accommodated within the band as illustrated in Figure 2 below (it is noted that the ECC also considered other frequency arrangements, including unpaired spectrum for time division duplexing (TDD) systems, but the recommended channelization is using paired channels).

FDD1 FDD2 FDD3 FDD4 FDD5 FDD6605958

DTT channels LTE FDD downlink

1 MHz

8 MHz 5 MHz

790 MHz 791 MHz821 MHz

11 MHz

Figure 2 FDD channelling arrangement for 790862MHz [Source: ECC]

Throughout our report we therefore refer to FDD1, FDD2, FDD3, etc., as being consecutive FDD downlink channels of 5MHz bandwidth, starting from the 791MHz band edge, in line with the channel plan illustrated above.

As a result of various compatibility studies conducted within the European Conference of Postal and Telecommunications Administrations (CEPT), the band plan shown above for mobile use of the 800MHz band employs a duplex direction that is reversed when compared to the normal European convention. Normally, mobile bands are planned with the uplink (base station receive/mobile transmit) in the lower band and the downlink (base station transmit/mobile receive) in the

upper band. However, due to concerns regarding interference from future mobile transmission to DTT below 790MHz, it was decided for the 800MHz band to reverse the duplex direction, so that the downlink is in the lower band.

For the purposes of the interference analysis presented in this document, we have assumed that:

future mobile use of the 790862MHz band will be based on LTE technology

LTE will use a 5MHz carrier width, which results in six channels (blocks) being available.5

5

In the remainder of this report we refer to these six blocks as FDD1 FDD6.

12 Introduction


Although a 1MHz guard band has been incorporated into the European plan, it was recognised during the compatibility studies conducted by CEPT that such a 1MHz guard band might not be sufficient to resolve potential interference from LTE base stations to DTT reception below 790MHz. Two modes of interference are possible:

Adjacent channel interference (ACI) interference caused by a transmitter operating in an adjacent channel.

Receiver overload (blocking) occurs when a strong in-block LTE signal overloads the DTT receiver front-end, making it unable to detect the DTT transmission (regardless of the level the DTT signal is at).

Overload is primarily dependent on the absolute level of the LTE signal within the

DTT operating band, and has only limited dependency on frequency.6 ACI is

frequency-dependent, however, and is dependent on the ratio between the DTT and the LTE signal levels. The channels closest to 790MHz (DTT Channels 60, 59 and 58) are therefore likely to be the channels that are most susceptible to ACI.

The ECs 800MHz Decision defines certain baseline technical requirements for use by electronic communications networks deployed within the 800MHz band, which are aimed at reducing the potential for interference, while recognising that they will not resolve all cases of interference and that further restrictions might be required. The conditions specified in the EC Decision are defined using block

edge masks (BEMs) based on technical work conducted within the CEPT.7 The BEMs consist of in-block and out-of-block components, which specify the permitted emission levels for frequencies within, and outside of, the 800MHz block respectively (with particular regard to protection of adjacent DTT services below 790MHz).

The in-block limits incorporated into EC Decision 2010/267/EC provide flexibility for national regulators to determine an in-block EIRP limit if required. The Decision suggests that, unless otherwise justified, limits would normally lie within the range 56dBm to 64dBm (in a 5MHz bandwidth).

For the purposes of this study, NITA has asked us to initially assume a maximum licensed EIRP value of 59dBm in each of the LTE channels, except for two areas (Sjlland and Lolland-Falster) where DTT Channel 60 is used: in these areas a maximum value of 56dBm is assumed for LTE Channels FDD1 and FDD2 only. In our initial analysis, we assume that all base stations transmit at these maximum limits. In our subsequent analysis, we apply different EIRP levels at individual base stations, in line with more realistic mobile deployments.

The DTT-to-LTE interference analysis that is being conducted as part of this study therefore uses these assumptions as inputs to evaluate the potential for interference from LTE to DTT caused by overload and ACI, and the various ways that this impact can be reduced. All of the analysis described in this report has

6

This is illustrated by Table 5b of ECC Report 148, which lists overload threshold (Oth) values for different frequency offsets.

7 CEPT Report 30: Identification of common and minimal (least restrictive) technical conditions for 790862MHz for the digital dividend in the European Union.

Introduction 13


been conducted using a radio planning tool to predict (area) coverage of interference caused by overload and ACI, and how this reduces when different mitigation techniques are applied either individually or collectively.

1.1 Structure of this document

The remainder of this document is structured as follows.

Section 2: Describes the approach and main assumptions used throughout the analysis.

Section 3: Assesses the impact of interference from one or several LTE network(s) operating at maximum power levels, summarising the main interference issues identified, and the various deployment scenarios and operational environments within which different issues are most likely to occur.

Section 4: Describes the results of our modelling of the impact of interference from multiple LTE networks operating at power levels consistent with actual power levels we believe might be used by mobile operators in practice, rather than all transmitting at the maximum licensed power level. In this analysis, we have selected a sample area to the north of Copenhagen, and evaluated the potential for receiver overload (blocking) and ACI to occur from LTE networks designed using base station locations based upon existing GSM900 networks, but with power levels at individual base stations individually determined based upon the location of the base station with respect to its nearest neighbour. In order to assess the potential for ACI to DTT Channel 60, we have also selected a further sample area Ringsted-Sor which uses this channel.

Section 5: Describes our assessment of possible mitigation approaches this describes the different approaches that could be used, and the deployment scenarios and operational environments in which they might apply. It also presents the analysis we have conducted into the suitability of different possible mitigation techniques, in terms of reducing the impact of predicted effects of overload and ACI from LTE to DTT.

Section 6: Describes potential interference effects from LTE uplinks (i.e. mobile devices) to DTT.

Section 7: Presents our conclusions and recommendations, including the conclusions on the use of practical EIRP limits below the maximum licensed limit, and the suitability of different interference mitigation techniques, along with various recommendations for NITA to consider in relation to finalising policy with regards to the conditions for award of 800MHz licences.

14 Overview of approach and main assumptions



2.1 Approach taken

The overall approach to modelling interference that we have adopted throughout our analysis uses a radio planning tool to predict coverage and interference. The tool used is the ATDI ICS Telecom radio planning tool (version 9.8.0). This has been used alongside a Microsoft Excel model and MapInfo software, to estimate coverage loss from interference and the associated impact in terms of the numbers of Danish households affected.

We have used the following data sets within our analysis:

Danish household data from The National Survey and Cadastre of Denmark (KMS)

digital terrain (height) data from Denmark with 50-metre resolution

clutter data with 50-metre resolution

site and frequency data for existing DTT sites from the ITU-R Geneva 06

(GE-06) agreement8 as modified through associated bilateral agreements for Denmark, provided by NITA the DTT channel plan taken into consideration in this study is therefore the modified version of the original GE-06 plan, taking account of DTT re-planning out of the 800 MHz sub-band

base station mast data for current 2G and 3G mobile deployments in Denmark, as provided by NITA (March 2011 version)

measured overload threshold (Oth) and protection ratio (PR) values from the ECC Report 148, with selected values consistent with protecting 90% of receivers

DTT wanted field strength maps produced in CRC-Predict and IRT2D, provided by the Danish terrestrial broadcasters (Boxer and Digi-TV).

The analysis conducted using the radio planning tool is based upon the potential for interference due to receiver overload or ACI from LTE base stations. The results from this analysis are presented in Sections 3 and 4.

We have also undertaken a literature review of a number of published reports, as agreed with NITA, which consider the potential for interference from the LTE uplink (i.e. mobile devices) to DTT receivers. It is noted that the ECC band plan provides a 42MHz frequency separation between the upper edge of DTT Channel 60 and the first uplink channel, which is expected to mitigate the majority of interference problems from the uplink channel. The documents we have reviewed, which are further described in Section 6 of this report, are as follows:

CEPT Report 30 identification of common (and least restrictive) technical conditions for 790862MHz for the digital dividend in the European Union

8 ITU-R: Final Acts of the Regional Radiocommunications Conference for planning of the digital

terrestrial broadcasting service in parts of Regions 1 and 3, in the frequency bands 174-230MHz and 470862MHz (RRC-06).

Overview of approach and main assumptions 15


material presented by the European Broadcast Union at various

workshops9

A study conducted in the UK by the government-sponsored Digital

Communications Knowledge Transfer Network10

A contribution from the UK to ECC Task Group 4, on UK measurements

of LTE into DVB-T conducted by Cobham Technical Services.11

2.2 Main assumptions

Our analysis makes various assumptions in relation to DTT and LTE deployment in Denmark, in the absence of any interference mitigation being applied. A summary of the main assumptions is as follows.

DVT-T transmission in Denmark uses two system variants: the multiplexes operated by Digi-TV use a 64-QAM 2/3 code rate, while the multiplexes operated by Boxer use a 64-QAM 3/4 code rate. This leads to differences in DTT planning levels for the two networks, and impacts receiver protection ratios (the minimum carrier-to-interference ratio necessary to avoid performance degradation to DTT viewing as a result of LTE interference, at a given frequency offset). In particular, for our analysis, the different code rates give rise to a 2dB difference in the required protection ratio for Boxers multiplexes compared to Digi-TV, which we have incorporated into our analysis.

We have assumed from our household dataset that there are a total of 2 359 106 households in Denmark. The number of households receiving DTT on one or more television set is assumed to be 20% of total households in Denmark (i.e. the remaining 80% receive television using alternative platforms). The source of this assumption is Gallup statistics (for end 2010). Results throughout this report for households that could potentially be affected by interference are presented as affected DTT

households, which is 20% of total households in Denmark

The DTT coverage criteria are assumed to be 95% of locations, with a

lognormal field strength standard deviation of 5.5dB.12

We have also assumed that interfering LTE signals are subject to lognormal fading with a standard deviation of 5.5dB, which has been

9 http://tech.ebu.ch/docs/events/ecs10/presentations/ebu_ecs10_workshop_sami.pdf

10 http://docbox.etsi.org/Etsi_Cenelec/PUBLIC%20FOLDER%20on% 20DD/UK%20DKTN%20DD/DCKTN%20Digital%20Dividend%20 Technologies%20Spectrum%2011Jun10%20v11%20(SR).pdf

11 ECC TG4(10)317, UK measurements of LTE into DTT, presented to the 15th meeting of ECC

TG4.

12 Location probability is the probability that within a given (small) area a field strength level is exceeded at a required percentage of points see ITU-R JTG 5/6 Methodology for sharing studies between the mobile and terrestrial broadcasting service in the band 790862 MHz, Section 3.1.1.1.



reflected in the link budgets used for the overload and ACI thresholds

within our planning tool.

We have modelled the actual antenna polarisation and patterns for DTT, which are taken from the GE-06 agreement and plan data for Denmark,

as modified by NITA to account for cross-border coordination agreements.

We have assumed fixed outdoor (rooftop) reception for DTT throughout the majority of our analysis, but have compared the effects of reception to portable coverage within a selected area of Denmark, as described in

Section 3.

We have assumed that LTE antennas will use slant polarisation (i.e. employing two sets of antennas slanted at 45 degrees to the horizontal plane), providing 3dB discrimination against horizontal/vertical polarised DTT signals. However, we have also separately considered the impact of using vertically polarised antennas for LTE as a means of comparison with the use of slant antennas, and as a possible means of improving

interference mitigation.

For field strength predictions, a height and clutter database with 50 metre resolution has been used. This is not always sufficient to detect very small

coverage gaps, which is noted as a limitation of our analysis.

For our initial analysis using maximum licensed EIRP limits, we first calculated theoretical LTE cell radii necessary to provide a downlink data rate of 8Mbit/s using a link budget (for details see Annex D). We then used these theoretical cell radii values to develop a theoretical LTE network providing coverage across Denmark, based upon using the base station locations of an existing GSM network in Denmark as the basis of the network, but adding additional cell sites where required to achieve the calculated cell radii for LTE. We then assumed that all sites would transmit at their maximum licensed power level of 59dBm EIRP (or 56dBm EIRP in areas where DTT Channel 60 is used), irrespective of the

actual power level required at the site from the link budget.

For our subsequent analysis using individually determined EIRP levels per base station, we used the same link budget to develop a theoretical relationship between the required EIRP of a site and the separation between the site and its nearest neighbour (assuming sites are located in line with the existing GSM900 networks currently operating in Denmark). We then applied these individual EIRP levels within the base stations of three networks, modelled on different GSM900 networks in Denmark, referred to as Network A, Network B and Network C. Each of the three networks modelled therefore exhibits different site densities and EIRP per site.

Protection ratios for DTT interfered with by mobile services are based upon interpolated values obtained from ECC Report 148.



2.3 DTT coverage and frequency plan

2.3.1 DTT coverage

Frequencies for DTT services have been planned within Europe and across ITU Region 1 via the GE-06 agreement and plan. The Final Acts of GE-06 contain DTT planning parameters assumed within the agreement, along with the detailed methodology for coordination of DTT networks between neighbouring countries. GE-06 describes three reception modes for DTT:

fixed reception where a rooftop-mounted directional receiving antenna is used

portable reception where a portable receiver with an attached or built-in antenna is used, either outdoors or indoors

mobile reception where reception is via a receiver in motion.

The different reception modes affect the height and gain of the receiver assumed when calculating the field strength for acceptable reception. For fixed reception, a 10 metre height (above ground level) is assumed, whereas for portable and mobile, a 1.5 metre height is assumed.

Standard radiation patterns for fixed receiving antennas are provided in

Recommendation ITU-R BT.419.13 For portable and mobile reception it is usually assumed that an omnidirectional antenna is used.

Within our analysis, we have assumed DTT fixed reception throughout the majority of our analysis, with antenna characteristics according to ITU-R BT.419, as illustrated below.

13 Recommendation ITU-R BT.419-3: Directivity and polarisation discrimination of antennas in

the reception of television broadcasting.



Figure 3 DTT directional receiving antenna [Source: ITU-R BT.419]

In the current Danish DTT coverage plan, coverage is defined to exist when 95% of locations within a 50x50 metre pixel receive field strength above a specified threshold. The minimum field strength is taken to be 47dBV/m for the 64-QAM,

2/3 coded mode of DTT in channel 60, in line with the GE-06 agreement. In accordance with the JTG 5/6 methodology, in order that an area can be considered as covered, the wanted field strength must exceed the minimum field strength at 95% of the locations within the area. An uplift of 9dB is therefore added to the minimum value, to correspond to the reception of an un-interfered DTT signal at 95% of locations, giving a minimum median field strength in the

pixel of 56dBV/m for 2/3 coded transmission, and 58dBV/m for 3/4 coded.14

Danish DTT networks are planned on the basis of 15 broadcast regions, and we have used these regions within our analysis to enable calculation of households covered with, and without, interference, per region. The 15 regions are illustrated in Figure 4 below.

14 Section 5.3.2.2 of the JTG methodology



Figure 4 Danish broadcast regions [Source: NITA]

2.3.2 Frequency plan

In line with many other European countries, the DTT deployment in Denmark uses a multi-frequency network, which means that many households do not use the upper DTT channels (i.e. 58, 59 and 60), which are particularly susceptible to ACI. It is noted that receiver blocking can occur irrespective of frequency offset, and so all households in Denmark could theoretically be affected by that.

The frequency plan for DTT in Denmark is based on five multiplexes, with a sixth reserved for mobile television (using DVB-H technology). DTT services are provided by two broadcast companies Digi-TV (DR and TV2) and Boxer. The frequency plan for multiplexes 16 is summarised below.



Area name MUX 1 MUX 2 MUX 3 MUX 4 MUX 5 MUX 6

Tolne-Nibe 29 57 50 37 35 39

Thisted 31 42 22 43 21 49

Videbaek 40 59 52 48 34 28

Viborg 40 59 52 56 21 45

Hadsten + Aarhus 26 44 24 56 55 36

Hedensted 30 44 33 46 55 36

Varde 30 54 33 46 53 28

Aabenraa 37 50 32 22 49 41

Tommerup + Svendborg 25 43 27 22 49 41

Vordingborg + Nakskov 58 34 42 38 60 48

Jyderup 58 51 42 31 60 23

Kbenhavn 53 51 54 31 59 23

R 59 56 51 39 31 32

Table 1 Channel plan for DTT multiplexes 1 to 6 [Source: NITA]

From the table above it can be identified that the following regions in Denmark use the upper DTT channels, which are the most susceptible to ACI.

DTT channel Regions affected

60 (782-790MHz) Vordingborg + Nakskov, Jyderup

59 (774-782MHz Kbenhavn, R, Videbk, Viborg

58 (766-774MHz) Vordingborg + Nakskov, Jyderup

Table 2 Regions in Denmark using upper DTT channels [Source: Analysys Mason]

The regions in Denmark that uses the upper DTT channels are shown in Figure 5 to Figure 7 below.



Legend

CH60 coverage region

Other regions

Figure 5 Regions using Channel 60 [Source: NITA]

Legend


Other regions




Legend


Other regions


Digi-TV operates services using Channels 58 and 59 in Vordingborg + Nakskov, Jyderup and R. Boxer operates services using Channels 59 and 60 in Kbenhavn, Vordingborg + Nakskov, and Jyderup. Since the Digi-TV and Boxer networks use different DTT configurations (3/4 coding and 2/3 coding respectively), we have modified our analysis of ACI for the affected channels to reflect the difference in planning and protection parameters (minimum received signal strength and PR) resulting from the different coding rates. Also, since the coverage areas of Channels 58 and 60 overlap, we have not conducted specific analysis within the study on Channel 58 areas.



2.3.3 Characteristics of DTT transmitters and receivers

A summary of other parameters used in our analysis is provided below.

Value Assumption and source

Modulation and coding 64-QAM, 2/3 coding (MUX 1 and 2) and 3/4 coding (MUX

3, 4 and 5) (Source: NITA)

DTT channel bandwidth 8MHz (Source: ITU-R GE-06)

Minimum field strength for fixed

outdoor reception (DTT Channel 60)

47dBV/m (Source: ITU-R Recommendation1368-8)

Location probability 95% (leading to an operating field strength of 56dBV/m,

including 9dB uplift to account for 95% location probability

as indicated by ITU-R15)

Receiving antenna gain 12dBd (Source: ITU-R GE-06), with antenna pattern as

illustrated in Figure 3.

Receiver feeder loss 5dB (Source: ITU-R GE-06)

Directivity discrimination 3dB (between slant polarised LTE antennas and

horizontal/vertical DTT source JTG5/6 methodology for

sharing studies between the mobile service and DTT,

section 4.2.2.4)

Wanted and unwanted signal

standard deviation

5.5dB giving a combined location correction factor of

12.8dB

Building penetration loss 8dB with a 5.5dB standard deviation

Table 3 DTT planning assumptions [Source: Analysys Mason]

2.3.4 DTT protection ratios and overload threshold

Two of the key parameters used within our analysis are the protection ratio (PR) between the DTT and the LTE signal, and the DTT overload threshold. We discuss each of these below.

DTT PR values fixed outdoor reception

Protection ratio refers to the ratio (in dB) of the power of the wanted signal to the total power of interfering signals, usually expressed at the receiver input. PRs for a DTT signal interfered with by another DTT signal are well understood, and are specified in various ITU-R recommendations, and also in the GE-06 Final Acts. For the purposes of this analysis, however, PRs for a DTT signal interfered with by an LTE signal are required. This has been the subject of recent study within the CEPT and the ITU-R, and studies within the CEPT have led to ECC Report 148 being published in 2010, detailing measurements on the performance of

15 For example, in ITU-R JTG 5/6: Methodology for sharing studies between the mobile service,

on the one hand, and the terrestrial broadcasting service, on the other hand, in the band 790862MHz.



DVB-T receivers in the presence of interference from the mobile service. The report provides the combined results of measurements conducted in a number of European countries, for a range of DTT receiver types and models. Table 5.1 of Report 148 provides the following PR values for a 64-QAM, 2/3 coded DTT

signal16, for the stated frequency offsets.

Channel edge separation DVB-T protection ratio (dB)

1 -33

9 -40

17 -44

25 -48

33 -49

41 -50

49 -50

57 -51

65 -45

Table 4 DVB-T PRs in the presence of LTE interfering in a Gaussian channel environment [Source: ECC]

The PRs quoted above are presented for a 64-QAM, 2/3 coded signal at the stated channel edge separation (e.g. from the edge of the 790862MHz band in 8MHz offsets). In order to obtain PRs suitable for our analysis, we have interpolated the values above to reflect the frequency offsets of interest to this study, which are detailed below. We have also applied a number of correction factors, as detailed in the ECC report and other sources, as shown in the following tables.

LTE/DTT

channel

DTT 58 DTT 59 DTT 60

FDD1 17 9 1

FDD2 22 14 6

FDD3 27 19 11

FDD4 32 24 16

FDD5 37 29 21

FDD6 42 34 26

Table 5 LTE-DTT channel offsets in MHz used in the ACI analysis [Source: Analysys Mason]

16 90 percentile values are quoted in Figure 3.4, and for silicon tuners, although ECC Report 148

also presents results for 10 and 50%, with the percentage referring to receivers measured, i.e. the 90 percentile values should be used to protect 90% of receivers measured, and also for can and silicon USB tuners.



Factor Value/source

Correction for fixed reception conditions

(Ricean channel) relative to Gaussian channel

(for 2/3 coding)

1.1 dB

Correction for fixed reception conditions

(Ricean channel) relative to Gaussian channel

(for 3/4 coding)

2.8 dB

Location correction factor 12.8dB

Table 6 Correction factors applied to PR values [Source: Analysys Mason]

Interpolation of the PR values given in Table 4 above provides the PRs calculated for LTE Channels FDD1, 2 and 3, with respect to DTT Channels 58, 59 and 60, as follows.

DTT/LTE channel FDD1 FDD2 FDD3

60 -33 -37 -41

59 -40 -43 -45

58 -44 -47 -48

Table 7 Interpolated PR values Gaussian channel [Source: Analysys Mason]

Within our planning tool, we have then applied the various correction factors described in Table 6 to the PR values above, to account for alternative DTT coding, reception conditions and locations margin. This gives the following input values to our planning tool (see Table 8 and Table 9 below), using the PR values above in combination with the various correction factors. There are two different sets of inputs to reflect analysis for the Digi-TV and Boxer DTT coverage areas, respectively.



Frequency offset Interpolated PR from

ECC Report 148

Plus location

correction factor

Plus 2.8 dB correction for 3/4

coding and fixed reception (Ricean

channel)

1 -33 -20 -17

6 -37 -25 -21

9 -40 -27 -24

11 -41 -28 -25

14 -43 -30 -27

16 -44 -31 -28

17 -44 -31 -28

19 -45 -32 -29

21 -46 -33 -30

24 -48 -35 -31

25 -48 -35 -32

27 -48 -35 -32

29 -49 -36 -33

Table 8 Interpolated ratios with correction factors Boxer DTT coverage [Source: Analysys Mason]

Frequency

offset

Interpolated PR from

ECC Report 148

Plus location correction

factor

Plus 1.1 dB correction for

fixed reception (Ricean

channel)

1 -33 -20 -19

6 -37 -24 -23

9 -40 -27 -26

11 -41 -28 -27

14 -43 -30 -29

16 -44 -31 -30

17 -44 -31 -30

19 -45 -32 -31

21 -46 -33 -32

24 -48 -34 -33

25 -48 -35 -34

27 -48 -35 -34

29 -49 -36 -35

Table 9 Interpolated ratios with correction factors Digi-TV DTT coverage [Source: Analysys Mason]

This gives the following PR inputs to our planning tool for the various frequency offsets of interest to the study (incorporating correction factors).




60 -17 -21 -25

59 -24 -27 -29

58 -28 -30 -32

Table 10 PR values plus correction factors, Boxer coverage fixed outdoor reception [Source: Analysys Mason]


60 -19 -23 -27

59 -26 -29 -31

58 -30 -33 -34

Table 11 PR values plus correction factors, Digi-TV coverage fixed outdoor reception [Source: Analysys Mason]

This means that, in our planning tool, the median field strength predicted from LTE FDD1 must be a maximum of 17dB above the median wanted (DTT) signal in Channel 60 for the Boxer coverage, to avoid interference.

DTT overload threshold

Receiver blocking or overload refers to the effect of a strong out-of-band interfering signal on the receivers ability to detect a low-level wanted signal. The DTT overload threshold (Oth) is defined in ECC Report 148 as the interfering signal level expressed in dBm, above which the receiver begins to lose its ability to discriminate against interfering signals at frequencies differing from that of the wanted signal, i.e. the onset of non-linear behaviour.

ECC Report 148 describes the measured Oth for various DTT receivers, suggesting that overload typically occurs at a level of LTE interference of between -15dBm and -5dBm.17 For our analysis, we have selected a value at the lower end of this scale, and we have used an overload threshold of -15dBm throughout our modelling. This therefore represents a conservative assumption, and it should be noted that most TV receivers and set top boxes will perform

better than this18. Our analysis can therefore be considered to represent a worst case in terms of possible TV receiver performance.

2.4 LTE network assumptions

To simulate an LTE network in our analysis, we have needed to make assumptions on the number and location of base stations within a typical LTE network.

17 This is the typical range the full range of measurements described in ECC Report 148 range

from 03dBm to -26dBm.

18 According to ECC Report 148 the -15dBm value corresponds to the value at which the 10% worst performing receivers overload.



The following parameters have been assumed:

LTE base stations transmit in the 791-821 MHz band

Channel bandwidth is 5 MHz

Location probability is 75% at the cell edge

Receiver height is 1.5 metres

Base station maximum licensed in-band EIRP is 59 dBm/5MHz (reduced to 56dBm/5 MHz for the lower most LTE BS channel on islands of

Sjaelland and Lolland-Falster, where DTT Channel 60 is used)

Base station antenna gain is 15dBi

Tri-sectored cells are assumed

Propagation model used for predicting LTE coverage is ITU-R P.1812

It is noted that mobile networks can deploy a hierarchy of macro, micro and pico-cells, with micro and pico cell base stations typically operating at reduced power and height. We have not incorporated micro and pico-cells into our analysis but have instead focussed on macro cells.

Throughout our analysis we have assumed an antenna height of 30 metres being applicable to macro-cell base stations, and have assumed a Jaybeam B800A085 antenna, as illustrated in Figure 8 below.

Figure 8 Jaybeam antenna pattern [Source: Jaybeam, Analysys Mason]

To calculate the theoretical cell radii of LTE base stations within a typical network, we have used a link budget (see 0). The link budget has been derived to achieve an 8Mbit/s downlink service in different outdoor coverage environments (urban, suburban and rural). We have assumed a 75% cell edge probability when deriving the cell radii for LTE, which is consistent with typical assumptions made



by the cellular industry when developing link budgets.19 The resulting cell radii calculated from the link budget and used in our model are listed below.

Geo-type Cell radius (km)

Urban 2.1

Suburban 3.6

Rural 5.8

Table 12 Cell radii for LTE model [Source: Analysys Mason]

These cell radii have been calculated as being representative of cell radii needed to achieve an LTE 800MHz coverage layer. In practice, it is assumed that operators will also deploy LTE at 1800MHz, 2100MHz and/or 2600MHz to meet capacity requirements. Therefore, the above cell radii do not take into account the level of traffic to be delivered within a network, but are designed primarily to achieve coverage.

In our initial analysis using maximum licensed EIRP levels, we have modelled an LTE network using base station locations based upon an existing GSM900 network in Denmark, but have added additional sites, where required, to provide a network of the required dimensions to achieve the cell radius above, consistent with requirements for a network achieving around 98% population coverage at a downlink data speed of 8 Mbit/s. In this initial analysis, the actual power level required at each base station site relative to neighbouring sites has not been accounted for.

In our subsequent analysis, we modified our approach to individually vary the EIRP of base stations as necessary, relative to neighbouring sites. In this case, we have again used the existing base station locations of GSM900 networks in Denmark as the basis of LTE site locations, but have modified the EIRP per site based upon its geo-type (urban, suburban or rural) and distance with respect to its nearest neighbouring site. This subsequent analysis has focussed on one area of Denmark in particular, to the north of Copenhagen; this area uses DTT Channel 59.

19 For example, see WCDMA for UMTS: HSPA Evolution and LTE, Holma and Toskala, 2010

30 Analysis of LTE networks operating at maximum power levels



The first part of the analysis considered the potential interference mechanisms into DTT that might occur from LTE networks operating at maximum licensed power levels, and the extent of interference potentially created under that assumption. The purpose of this first high-level analysis was to establish the extent to which interference from LTE to DTT could be a problem, and to assess the main characteristics of both LTE and DTT networks that influence the extent of interference.

In practice we expect that the majority of LTE base stations, particularly those in urban areas, will use a lower power level than the maximum allowed limit, for various practical reasons. In the section, we consider the impact of this in more detail, by predicting interference effects caused by receiver overload and ACI under the assumption that individual power levels at LTE base stations might be varied depending on the location of the base station and its proximity to neighbouring sites. In this section, interference is modelled assuming that all base stations transmit at their maximum licenced transmit power (EIRP) level.

3.1 Summary of results

Our initial modelling using maximum licensed EIRP levels per base station site has considered two interference mechanisms from LTE to DTT, namely blocking and ACI. Overall, our analysis suggests that the dominant interference issue affecting DTT households in this case could be blocking, rather than ACI. A summary of our results is provided below.

3.1.1 DTT receiver overload

Our initial modelling suggests that around 54 000 of DTT households could be affected by receiver overload in Denmark from a single LTE network, assuming an LTE base station EIRP of 59dBm in most areas (and 56dBm in Channel 60 areas). The network modelled consisted of a total of 1445 macro base stations, distributed between urban, suburban and rural areas. The number of households predicted to be affected by receiver overload corresponds to around 2.3% of the total households in Denmark, and 3.4% of the total country area could be affected.

Our results suggest receiver overload could potentially affect a proportion of households in almost all urban areas of Denmark. This is due to the higher density of base stations in urban compared to suburban or rural areas and the fact that in areas where there are mixed geo-types, the highest number of affected households are in urban areas. For example, within the Kbenhavn broadcast region, 72% of affected households are in geo-types we have defined

in our model as urban20.

20 The geotypes in our initial analysis are defined based on municipal areas in Denmark and

population density.

Analysis of LTE networks operating at maximum power levels 31


A full breakdown of results is presented in Table 13 below. A map showing the areas of interference is included in Annex C.

Broadcast region Total area

(km2)

Total

households in

area

Affected area

(km2)

Affected DTT

households

Anholt 21 588 1.1 0

Laeso 117 3526 8 37

Tolne-Nibe 6140 266 939 166 5 777

Viborg 2599 85 044 68 1 348

Thisted 1529 44 170 28 977

Videbaek 5094 150 321 106 2 573

Hadsten + Aarhus 4507 279 245 195 7 490

Hedensted 3060 163 648 102 3 462

Varde 2684 99 804 70 1 930

Aabenraa 3810 124 076 96 1 911

Tommerup + Svendborg 3473 231 985 148 4 797

Kbenhavn 2844 551 716 233 16 549

Vordingborg + Nakskov 3339 151699 180 3 178

Re 585 27 820 32 892

Jyderup 2956 178 525 99 3 125

Table 13 Summarised results of blocking calculation from LTE to DTT, initial analysis (59dBm EIRP, with 56dBm in Channel 60 areas) fixed outdoor reception [Source: Analysys Mason]

We have repeated this analysis for one area of Denmark assuming three LTE networks operate in the same area, to illustrate the increase in blocking compared to a single network. We have chosen to model three networks since it is likely that there will be three 800MHz licence winners in Denmark, as has been the case in other European countries where 800MHz frequencies have been auctioned. The area selected is to the north of Copenhagen; it was chosen because it contains predominately urban areas. The number of base station sites within each of the three networks within the area of our analysis is shown below. As before, we assume that each base station operates at its maximum licensed EIRP of 59dBm (or 56dBm where Channel 60 is used).

We have assumed that three LTE networks operate within the selected area, which we refer to in our analysis as Networks A, B and C. Base station locations within each network are based upon existing 900MHz base station locations in

Denmark21.

21 We have manually modified coverage in some areas to reflect a target coverage of 98% population within the area.



Operator Number of sites

Network A 74

Network B 128

Network C 129

Table 14 Number of existing GSM900 sites of each operator in the area of analysis [Source: Analysys Mason]

In terms of the impact of three networks operating in the same area, we have found that the number of households potentially affected by receiver overload could increase from around 5 900 for one network, to 16 000 DTT households if three networks are operating in the same area. This equates to just over half (52%) of all households within the area at risk of blocking from at least one of the LTE networks.

It can be seen that many of the areas affected by blocking from the three separate networks overlap, as shown in Figure 9 below.

Figure 9 Areas of blocking from the three LTE networks [Source: Analysys Mason]

Of the households affected, we have found that the majority (88%) of these in the area considered are located in urban areas. This is in line with expectations that the risk of blocking is likely to be higher in areas where there is a high concentration of LTE sites, which normally occurs in highly populated areas.

The results demonstrate the following.

Having three LTE networks within the area increases blocking by almost three (2.8) times the amount caused by a single network. Given our initial result that one network operating at maximum licensed power levels could



cause receiver overload to around 54 000 households nationally, this could scale to around 150 000 DTT households if three national networks operating at maximum licensed power levels were deployed in the 800MHz band.

The majority of blocking is predicted to occur in areas where there is a high concentration of LTE base stations typically in urban areas. This suggests the highest risk of blocking to DTT services will be in urban areas, which concurs with the results for a single LTE network.

The high incidence of receiver overload is due to the assumption that all base stations will transmit at their maximum licensed EIRP level, whereas in practice it is likely that operators will choose to use lower EIRP at some base stations depending on the environment (urban, suburban or rural) and density of base stations deployed. Our subsequent analysis, described in the section 4, therefore explores this effect in more detail.

3.1.2 Adjacent Channel Interference (ACI)

Our initial analysis suggests that ACI is predicted to affect less households than receiver overload (when assuming that LTE network operate at maximum licensed power levels). Households affected are limited to those located in areas where DTT services using Channels 60, 59 and 58 are operating. We found that around 5 600 DTT households in Channel 60 areas could potentially experience interference from LTE services using the closest channel (FDD1). This number reduces to around 4 800 DTT households affected by ACI from FDD2, and around 1 400 DTT households from FDD3. FDD2 and FDD3 produce less interference because of the increased frequency separation between FDD2 and FDD3 and the DTT channel(s), compared to FDD1.

We also found that around 4 800 households might be affected by ACI from the closest channel (FDD1) within channel 59 areas.

Areas of interference from ACI from one LTE network using Channel FDD1 are illustrated in Annex C.

We have also considered the cumulative effect of ACI from multiple LTE networks using different channels within the 800MHz band, to DTT areas using Channels 60, 59 and 58. This shows that the lowermost LTE block (FDD1) contributes the most significant cumulative ACI into adjacent DTT channels. Blocks FDD2 and FDD3 interfere with a sub-set of households affected by ACI from FDD1. Channel 60, which is only used by Boxer in Denmark, is most affected by ACI.

Whereas our analysis suggests that around 5 600 DTT households could be affected by ACI from a single LTE network within Channel 60 areas, the analysis also suggests that the cumulative number of households affected by ACI from two LTE networks (one using Channels FDD1 and FDD2, and the second using



Channels FDD3 and FDD4) could be up to 7 800 DTT households. We estimate that around 1 000 of these might receive interference from both networks22.

This is illustrated in Figure 3.2, where the blue areas represent ACI caused by the network using FDD1/FDD2 and the yellow areas represent ACI caused by the network using FDD3/FDD4.

Figure 10 Areas affected by ACI into DTT channel 60 from two LTE networks [Source: Analysys Mason]

It is noted that a large proportion of households suffering ACI will also suffer from receiver overload, since the areas affected by ACI overlap with the areas affected by receiver overload, as described above. Our analysis suggests that, of the 5 600 DTT households in Channel 60 areas who are affected by ACI from LTE block FDD1, around 3 800 might also suffer receiver overload.

Overload is also potentially the more severe of the two modes of interference because, in the presence of receiver overload, reception of all DTT services is lost, whereas with ACI the interference affects reception of services using particular DTT MUXs (in particular, those broadcast using Channel 60 and Channel 59).

22

The sum of the households affected by ACI from FDD1/FDD2 and FDD3/FDD4 is 42 905, compared to the cumulative number of households of 37 947, equating to a difference of 4958.



3.2 Effect of interference on indoor coverage of DTT

To illustrate the effect of LTE interference on indoor DTT reception23, we have repeated our ACI analysis for the Vordingborg area only. For this, we have applied the height-gain correction factor of 18dB, as provided in ITU-R GE-06. We have also assumed an omnidirectional antenna with a gain of 0dBi. For portable reception indoors, a building penetration loss is also required we have used a value of 8dB, with a standard deviation of 5.5dB. No feeder loss has been included.

Within the Vordingborg area, DTT coverage is provided using Channel 60. The total area is around 1000km2, and the total number of households in the area is 45 600.

The results of our analysis into the effects of ACI on indoor reception are summarised below (these number represent the potential maximum total households in the area rather than the proportion of households receiving television using DTT).

LTE channel Number of DTT

households

affected

Percentage of

households

affected

Area affected

(km2)

Percentage of

area affected

FDD1 253 2.8% 6 0.6%

FDD2 120 1.3% 3 0.3%

FDD3 55 0.6% 1 0.1%

Table 15 ACI to Channel 60 in Vordingborg, portable indoor reception [Source: Analysys Mason]

Our initial analysis suggests that, for fixed rooftop reception 4.0% of households using Channel 60 are potentially interfered from LTE Channel FDD1 within the Vordingborg sample area, with the affected area being 0.9% of the total area modelled. For portable indoor reception the potentially interfered households reduces to 2.8% of DTT households, with the affected area being 0.6%. This difference is potentially due to the lower height of the receiving antenna for portable receivers compared to fixed reception, and the fact that penetration of signals within buildings provides some mitigation from interference.

3.3 Conclusions from the initial analysis

Our initial analysis, assuming that each base station within an LTE network transmits at its maximum licensed power, concludes that

Blocking could affect 11.5% of DTT viewing households, equating to a total of around 54 000 DTT households, based on an assumed LTE EIRP of 59dBm (or 56dBm in Channel 60 areas). This mainly affects

23 i.e. where DTT services are not received via a fixed outdoor antenna but use a portable antenna located inside the building



households in urban areas for example, within the Kbenhavn broadcast region, 72% of affected households are in geotypes we have

defined as urban.24

The effect of having three LTE networks operating within the area increases blocking by almost three (2.8) times the amount caused by a single network. This could scale to around 150 000 DTT households nationally, if three national networks operating at maximum licensed power levels were deployed in the 800MHz band.

ACI from a single LTE network using Channel FDD1 could affect up to around 5 600 DTT households in Channel 60 viewing areas. For two LTE networks (one using Channels FDD1 and FDD2, and the second using FDD3 and FDD4) the cumulative number of households affected by ACI within Channel 60 areas rises to 7 600 DTT households. Some 1 000 DTT households could receive interference from both networks.

We have also considered the impact of ACI on indoor reception in the Vordingborg city area, for households covered using Channel 60. Our analysis suggests that 4% of households using fixed rooftop reception could experience ACI from LTE Channel FDD1. The affected area is 0.9% of the total area modelled. For portable indoor reception, the proportion of affected households reduces to 2.8% (affected area 0.6% of the total). This may be due to the lower height of the receiving antenna for portable receivers compared to fixed reception, and the fact that penetration of signals within buildings provides mitigation from interference.

Blocking is predicted to be the more significant of the two interference modes using our initial assumptions on LTE base station EIRP. ACI has a more localised effect, occurring only in areas where Channel 60 and Channel 59 are used, and where the DTT field strength is also low. Typically, DTT field strength is low where households are located at the edge of DTT coverage and so receive a weak TV signal compared to households with a better signal path to the DTT transmitter.

A large proportion of households suffering ACI will also suffer blocking, since the areas affected by ACI overlap with those affected by blocking. Of the 5 600 DTT households in Channel 60 areas who are affected by ACI from LTE block FDD1, around 3 800 might also be subject to receiver overload. Overload is potentially the more severe of the two modes of interference because it leads to the loss of reception of all DTT services, whereas with ACI affects reception of services using particular DTT MUXs (in particular, those using Channels 60 and 59).

The potential for blocking to occur is not frequency dependent25 (i.e. it could occur from any FDD block to any DTT channel, regardless of

24 The geotypes are defined based on municipal areas in Denmark and population density.



frequency), and is sensitive to the distance between the LTE base station and the household, primarily as a result of the design of DTT receivers and their overload threshold.

3.4 Observations on relevance of the initial analysis to real LTE deployments

Of particular relevance to the initial analysis is the assumption that a uniform EIRP, equivalent to the maximum licensed EIRP level, is deployed across the entire LTE network: that is, all sites transmit at the same power and with a similar height of antenna with the exception of base stations in Channel 60 areas, where we have assumed a slightly lower EIRP.

As described earlier in this section, our assumption has been that LTE800 will be deployed by mobile operators using existing 900 MHz sites where practical. It is noted that the density of 900 MHz sites deployed in some areas of Denmark will lead to significant overlapping coverage between neighbouring sites if all sites are assumed to transmit at the maximum licensed power level of 59 dBm.

As an illustration of this, the figure below illustrates the substantial coverage overlap that could occur if it is assumed that LTE800 is deployed on all GSM900 sites within a 2G network in Denmark with an EIRP of 59 dBm at all sites.

25 Although blocking is generally not frequency dependent, measurements of overload threshold (Oth) of different DTT receivers presented in ECC Report 148 indicate some dependency between the measured Oth and the frequency offset between the LTE and the DTT signal. Specifically, measurements suggest a variation in the Oth when the TV receiver is tuned to a channel at a frequency offset of 33MHz or less (which corresponds to the offset between LTE block FDD1 and DTT channels 56-60), compared to the Oth when the receiver is tuned to a lower channel (i.e. 21 to 55).



Areas covered by

more than 1 site

All sites with EiRP of 59dBm

Figure 11 Illustration of areas of coverage overlap in one LTE800 network deployed on GSM900 sites [Source: Analysys Mason]

In practice, we expect that operators will deploy base stations with a lower EIRP than 59 dBm in different parts of their network. This will be done in order to avoid significant coverage overlap between to sites (which would lead to increased interference within the network) as well as to comply with specific planning restrictions in some areas, which can affect the installation of base stations (e.g. due to height or antenna size restrictions), leading to lower EIRP levels being radiated. In particular, site availability and planning differences between urban, suburban and rural areas will mean that EIRP levels will vary in different parts of the network, with significantly lower EIRP levels typically being used in urban areas compared to the most rural sites, for example.

Since the assumption in our initial analysis that all LTE sites will transmit at maximum licensed levels is unlikely to reflect how LTE networks will be deployed in practice, the next section of this report considers the impact of assuming more realistic EIRP levels being used within an LTE network, and how this affects interference to DTT.

We have conducted this subsequent analysis focussed on two sample areas of Denmark (one to the north of Copenhagen and one in the Ringsted-Sor area), where we have varied the EIRP per individual base station site in line with a more practical network deployment.

Our approach and results to this analysis are described in the section 4.

Impact of interference assuming realistic LTE deployment assumptions 39


4 Impact of interference assuming realistic LTE deployment assumptions

Our first high-level analysis as described in the previous section assumed a uniform EIRP level is used across all sites in an LTE network, and also assumed that the maximum licensed EIRP level would be used at all sites. In practice, since mobile operators will use different EIRPs levels at different sites to manage interference within their networks, and in response to site planning restrictions in some areas, the initial analysis does not reflect how a real LTE network might be deployed in practice

This section therefore describes further analysis to consider the effects of more realistic assumptions being taken on LTE base station transmitted power levels.

The effect of altering EIRP at selected sites is discussed in more detail in this section, and the corresponding impact on the potential for receiver overload and ACI to DTT assessed.

4.1 Determination of individual EIRP levels

Mobile operators use a number of techniques to optimise the field strength transmitted from individual base stations, including varying the output power from the base station, use of antenna down-tilt, use of sectored antennas and, for LTE, use of MIMO (Multiple In, Multiple Out) antennas. Also, in WCDMA and in LTE networks, power control is used to optimise the power of individual links between the network and a device. The combination of these factors leads to variation in the transmitted power from individual base stations within a network, depending on the base station location, its distance from the nearest neighbouring site, and the characteristics of the traffic load.

For this analysis, we firstly selected a sample to the north of Copenhagen, which we have divided into urban, suburban and rural geo-types based upon the clutter

data used within our planning tool, as illustrated below26.

26 The morphology (clutter) data set for our planning tool includes urban, suburban and rural areas, shown as red, yellow and white in the diagram, as well as forest, shown as green. For our analysis we have incorporated forest areas into our rural geo-type. Our morphology data set also includes water and sea categories, which we did not use in our analysis.

40 Impact of interference assuming realistic LTE deployment assumptions


Figure 12 Selected area for analysis [Source: Analysys Mason]

Figure 13 below illustrates the methodology we have used to determine the EIRP at individual base station sites within several LTE networks operating in the same area.

Derive required

site separation

from cell range

Calculate cell

range for different

EIRP

Modify EIRP curves

based on planning

tool

Verify EIRP-site

separation curves

using planning tool

Assign sites in

LTE networks to

geo-types

Produce final

coverage plot per

network

Assign EIRP per

site based on

site separation

Re-run overload

and ACI effects

Figure 13 Approach to setting EIRP per base station

co-existence_of_LTE_systems_in_790-862mhz_with_DTT.pdf

Documents

Transcript of co-existence_of_LTE_systems_in_790-862mhz_with_DTT.pdf