800MHz Interference and Co-existence - Copy

ICT KTN Wireless Technology & Spectrum Working Group

800MHz Interference and co-existence challenges – August 2011

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ICT KNOWLEDGE TRANSFER NETWORK

800MHz Interference and co-existence challenges – Interim report

Wireless Technology and Spectrum working group publication



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About the ICT Knowledge Transfer Network (ICT KTN) The ICT KTN is an organisation established by an industry-led group of leading players, with funding from the Technology Strategy Board. We seek to bring competitive advantage to the UK by promoting collaboration and knowledge sharing between the users and providers of ICT, and helping to drive innovation in the sector. If you are involved in ICT, and have not yet registered as member of the ICT KTN and/or the Wireless Technology and Spectrum working group please visit our web page and register as a member. To join the working group you will have to first register as KTN member. KTN Membership, register for free: www.ictktn.org.uk For further information on the Wireless Technology and Spectrum working group please visit https://ktn.innovateuk.org/web/spectrum. If you would like to get actively involved in this community please join group, membership is free. ICT KTN, Russell Square House, 10–12 Russell Square, London WC1B 5EE Email: [email protected] Telephone: +44 (0) 20 7331 2056 Contact points for positioning paper: Stuart Revell, ICT KTN [email protected] David Barker, Quintel Solutions [email protected] Terry Wells, Virgin Media [email protected] Brian Copsey, Copsey Communications [email protected] John Burns, AEGIS

Andrew Lillywhite, Sennheiser [email protected]

Mark Waddell, BBC R&D [email protected] Steve Hope, Docobo [email protected] Clive Harding, Malvern Consulting [email protected]

[email protected] The opinions and views expressed within this positioning paper have been reviewed by the members of the ICT Knowledge Transfer Network Wireless Technology & Spectrum working group. The views and opinions do not necessarily reflect those of the individual members of the ICT KTN or the Working Group or the organisations that the members represent.

http://www.ictktn.org.uk/

https://ktn.innovateuk.org/web/spectrum

mailto:[email protected]












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1 Contents

1 Contents ................................................................................................................ 2 2 Abbreviations and definitions ................................................................................. 4 3 Introduction ............................................................................................................ 6 3.1 Purpose of this paper ............................................................................................ 7 4 Executive summary ............................................................................................... 8 5 Background (Spectrum)....................................................................................... 10 5.1 800MHz compatibility issues ............................................................................... 12 6 Digital Television services ................................................................................... 14 6.1 DTT Receiver Selectivity Characteristics............................................................. 15 6.2 LTE-800 Interference into Digital Television (DTT) ............................................. 17 6.2.1 LTE-800 BS Interference into DTT Ch60 – N+1 offset .................................. 17 6.2.2 LTE-800 UE Interference into DTT– N+9 offset ............................................ 17 6.2.3 Interference resulting from „out of band‟ emissions ....................................... 18 6.3 Interference Discussion – Possible solutions ................................................ 20 6.3.1 On-Channel Repeaters ................................................................................. 21 6.3.2 DTT & Cellular Cooperative Network Evolution Proposal ............................. 22 6.3.3 Shared DTT Broadcast and Cellular Topology.............................................. 23 6.4 Recommended DTT tests for trial test bed .......................................................... 25 7 Hybrid Fibre Cable (HFC) Networks .................................................................... 26 7.1 800MHz spectrum usage and impact to Cable & STB industry ........................... 26 7.2 LTE Interference into Cable and DVB-C/DOCSIS CPE....................................... 27 7.2.1 Set Top Box - LTE Interference testing ......................................................... 27 7.2.2 Cable Modem – LTE Interference Testing .................................................... 30 7.2.3 In- Home Cabling – LTE Interference Testing ............................................... 30 7.2.4 Summary of LTE Interference with Cable systems ....................................... 31 7.3 Cable Interference - Possible mitigation and solutions ........................................ 32 7.3.1 Restrict cable transmissions to below 790 MHz. ........................................... 32 7.3.2 Reduce QAM rates to make the system more robust: .................................. 32 7.3.3 Increase HFC signal level ............................................................................. 33 7.3.4 Increase immunity of CPE ............................................................................ 33 7.3.5 Home Cabling improvements ........................................................................ 33 7.3.6 Pilot Tone ...................................................................................................... 33 7.4 Cable Summary ................................................................................................... 33 7.5 Recommended Cable and DVB-C/DOCSIS CPE tests for trial test bed.............. 34 7.5.1 Interference scenarios .................................................................................. 34 7.5.2 Testing Procedure ......................................................................................... 34 8 Communal Antenna Systems .............................................................................. 35 8.1 Communal Antennas – Systems and Topologies ................................................ 35 8.2 Communal Antenna Interference Issues ............................................................. 37 8.3 Communal Antenna Customer base ................................................................... 37 8.4 Communal Antenna Interference Assessment .................................................... 38



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8.5 Innovation to solve the problems ......................................................................... 38 8.6 Recommended Communal Antenna tests for trial test bed ................................. 39 9 Applications above 862 MHz - Short Range Devices .......................................... 40 9.1 863MHz-865MHz testing (Copsey Communications) .......................................... 41 9.2 863MHz – 865MHz test set up and results .......................................................... 42 9.3 863MHz-865MHz test conclusions ...................................................................... 45 9.4 Recommended tests for trial test bed .................................................................. 45 10 PMSE 470-790MHz ............................................................................................. 47 10.1 PMSE Interference .............................................................................................. 47 10.2 Recommended PMSE tests for trial test bed ....................................................... 48 11 Conclusions and recommendations .................................................................... 48

Table of Figures

Figure 1: Evolution of Spectrum allocations up to 3GHz from 1970 to 2010 ................. 10 Figure 2 Cellular spectrum below 1 GHz in different ITU Regions (source: Aegis) ....... 11 Figure 3 Frequency plan for LTE-800 deployment ....................................................... 14 Figure 4 DTG C/I performance targets for DTT receivers and mean performance for 7 receivers ........................................................................................................................ 15 Figure 5 Performance variation for DTT CH60 for different LTE traffic conditions......... 16 Figure 6 LTE-800 Base station (BS) interference to DTT CH60 .................................... 17 Figure 7 LTE handset (UE) interference to DTT CH57-60 ............................................ 18 Figure 8 LTE base station OOB causing interference to DTT CH60 ............................. 19 Figure 9 Benefits of repeating DTT from Cellular Base Stations ................................... 22 Figure 10 British scenario set top box,representative system outlet and cabling .......... 27 Figure 11 LTE-radiated European scenarios, STBs 1 to 21 .......................................... 29 Figure 12 LTE-Radiated European Scenario, CM 1 - 9 ................................................. 30 Figure 13 Test 24, LTE-radiated 25m coaxial cables .................................................... 31 Figure 14 863MHz to 870MHz Spectrum usage ........................................................... 40 Figure 15 excerpt from presentation “MFCN base station emission limits for different 800 MHz licensees”, UK Ofcom. ................................................................................... 42 Figure 16 Test environment and arrangement of equipment ......................................... 43 Figure 17 Maximising wireless opportunities through Government & Industry collaboration .................................................................................................................. 49



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2 Abbreviations and definitions

Abbreviation Definition

3D TV Three Dimensional Television

3GPP 3rd

Generation Partnership Project

BS Base Station

C/I Carrier to Interference (Ratio)

CATV Cable Television

CAGR Compound Annual Growth Rate

CENELEC European Committee for Electrotechnical Standardisation

CEPT European Conference of Postal and Telecommunications Administrations

Ch Channel (Allocated frequency slot)

COFDM Coded Orthogonal Frequency Division Multiplexing

COGNEA Cognitive Networking Alliance

CPE Customer Premise Equipment

DAB Digital Audio Broadcast

DCKTN Digital Communications Knowledge Transfer Network

Dig Div (DD) Digital Dividend 800MHz Spectrum (790-860 MHz)

DOCSIS Data Over Cable Service Interface Specification

DSO Digital Switchover

DTG Digital Television Group

DTT Digital Terrestrial Television

DTV Digital Television

DVB-C Digital Video Broadcasting – Cable

DVB-T Digital Video Broadcasting - Terrestrial

DVB-T2 Digital Video Broadcasting – Terrestrial (2nd

generation)

DVD Digital Video Disc or Digital Versatile Disc

ECC Electronic Communications Committee

ECMA Standards body for Information and Communication Technology and Consumer Electronics

ECN Electronic Communication Networks

EDGE Enhanced Data rates for GSM Evolution

EIRP Effective Isotropic Radiated Power

ERP Effective Radiated Power or Equivalent Radiated Power

ETSI European Telecommunications Standards Institute

FCC Federal Communications Commission (US Regulator)

FM Frequency Modulation

FTTC Fibre To The Curb

GI Guard Interval

GMSK Gaussian Minimum Shift Keying

GPRS General packet radio service

GPS Global Positioning System

GSM Global System for Mobile communications

GSMA Global System for Mobile communications Association

HD High Definition



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HDTT High Definition Television

HDMI High-Definition Multimedia Interface

HFC Hybrid Fibre Cable

HSPDA High-Speed Downlink Packet Access

HSPA+ Evolved High-Speed Packet Access

ICT Information and Communication Technologies

IEM In Ear Monitor

IF Intermediate frequency

IMT International Mobile Telecommunications

IoT Internet of Things

IPTV Internet Protocol television

IRS Integrated Reception Systems

LBT Listen Before Talk

LNB Low Noise Block (converter)

LTE 3GPP Long Term Evolution

MATV Master Antennae Television

MFCN Mobile Fixed Communications Network

MBMS Multimedia Broadcast Multicast Service

MER Modulation Error Rate or Modulation Error Ratio

MIMO Multiple-input and multiple-output antenna configurations

NTP Network Termination Point

OFDM Orthogonal Frequency Division Multiplex

PCB Printed Circuit Board

PMSE Programme making and special events

QAM Quadrature Amplitude Modulation

QoS Quality of Service

R&D Research and Development

R&TTE Radio and Telecommunications Terminal Equipment Directive

RF Radio Frequency

RFID Radio Frequency Identification (RFID tag)

RS Reed Solomon

SAB Services Ancillary to Broadcast

SAP Services Ancillary to Programme making

SIM Subscriber Identity Module (SIM Card)

SMATV Satellite Master Antennae Television

SNR Signal to Noise Ratio

SRD Short Range Device

STB Set Top Box

TACS Total Access Communication System

TETRA TErrestrial Trunked RAdio

TETRA 2 TErrestrial Trunked RAdio (2nd

generation)

TRP Total Radiated Power

UE User equipment

UHF Ultra High Frequency

UMTS Universal Mobile Telecommunications System

UMTS r99 UMTS Release '99 higher speed data transmission in 3GPP networks

WSD White Space Device

xDSL Digital Subscriber Line



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3 Introduction Wireless technology has already reached a level where it is embedded in our daily work, social and leisure activities. The demand for services is now reaching beyond the traditional broadcast, mobile cellular applications and local area network connectivity. The ICT KTN Wireless Technology & Spectrum working group believes „Wireless Technology‟ is the key enabler for several markets and is seen as the critical element for future development of these segments. Wireless is becoming all pervasive and critical for future development in areas such as: • Future Mobile Internet

• Digital Media & Content

• Energy & Environment

• Public Safety & Emergency Services

• Health

• Assisted Living

• Smart Grids / Metering

• Intelligent Transport

• Automation

• M2M and IoT applications

• Future of the internet

• eCommerce, Payment technologies and Banking

The terrestrial broadcast spectrum released by the switch from analogue to digital TV transmission is known as the digital dividend (DD) and will become available for new applications from 2012. This spectrum includes cleared and interleaved space between 470 MHz and 862 MHz. The band has many desirable propagation characteristics which can enable enhanced broadband communications services to a wider population. The broadcast spectrum has traditionally been used solely for TV broadcast and low power radio microphones for programme making and special events (PMSE). New applications targeting the spectrum include LTE, which requires dedicated, cleared spectrum. Reallocation of broadcast spectrum to provide these new services requires careful coordination with existing users to prevent interference. Potential issues need to be identified at an early stage, as fixing these problems retrospectively will become increasingly expensive as the new services are deployed. The existing applications for the UHF broadcast band are given below:



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Existing services:

1) Broadcast Television – Digital TV (470-862MHz)

2) Communal Antenna Systems (distribution of terrestrial broadcast to multiple

dwellings)

3) Cable Television and home media consumer platforms 15-862MHz

4) Short Range Devices (Adjacent band 863-870MHz, e.g. social alarms)

5) PMSE applications (e.g. wireless microphones, in-ear monitors)

The challenges and opportunities this represents, provides the UK with some significant opportunities for our R&D community to address locally and benefit through global exploitation.

3.1 Purpose of this paper The purpose of this paper is to provide the basis for discussion amongst all interested stakeholders as to how a deeper collaboration regarding the 800MHz spectrum interference and co-existence challenges, identified in this paper, can be solved through further R&D activity / investment, therefore providing the UK eco-system an excellent opportunity to lead in development and deployment of world leading wireless technology and services. The document and associated presentations shall be used at appropriate Knowledge Transfer events to inform the wider industry, ICT KTN members and as vehicle to stimulate discussion with industry, academia and government bodies.



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4 Executive summary

The Ofcom consultation on 800MHz interference and co-existences challenges has created a big debate on the actual levels that could be experienced and who solves this, when interference occurs. The technical assumptions used, have predominately been derived from simulation and modelling and a minor adjustment of a variable can make a large impact to the population or households that could be impacted. Getting agreement across multiple stakeholders of what the real model variables should be is very difficult to do, this document will look at each of the potential issues and suggest some solutions and areas for further exploration and/or analysis between existing digital television services in the 470 to 790MHz band (including communal and conventional antenna systems), Short Range Devices (SRD) in the 863 to 870MHz band, Cable services served over Hybrid Fibre Coax using frequencies from 15 to 862MHz, PMSE services in the bands below 790MHz and new applications for LTE based cellular services targeted at the cleared Analogue TV bands from 791MHz to 862MHz. The potential DTT problems are particularly acute in the UK where a successful broadcast industry makes extensive use of the services, with Ofcom statistics showing that DTT is used in between 80 and 90% of the 27.2 million households either for the primary set or on a secondary set. It must also be noted that 5 to 6 million households are flats and potentially served through communal antenna systems. It is strongly recommended that an appropriate test bed be made available for such innovation to thrive and for the industry to further understand, replicate and manage such interference issues. The executive summary is intended to provide an overall summary with the supporting sections providing more detailed information for the reader to use if required. It is vitally important that the information is known and publicly available before the auction of the new 800MHz spectrum proceeds, detailing what mitigations strategies and plans need to be prepared and declared ahead of the event. The general public is unlikely to understand how or why interference is occurring or what to do about it when it does but they could be seriously inconvenienced. Table 2, section 5.1 provides a good overview of how potential issues interact with different services and users of the spectrum. Table 1 below is a summary of the issues detailed in this document. The vertical axis represents the users or service being provided and the horizontal axis represents the potential interferers. Each box summarises the potential solutions or action required.



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Table 1: Positioning paper recommendations

New Entrants (Potential interferers)

Mobile (791-862MHz)

Exis

tin

g U

sers

Ca

ble

(15

-86

2M

Hz)

Challenge: High probability LTE in close proximity will interfere.

Short term solutions / actions:

R&D opportunities exist to solve these issues, industry challenge.

Encourage industry and Ofcom to conduct further analysis and testing to ascertain design challenge parameters.

Encourage Cable and Mobile industries to conduct further collaborative engineering trials. Collaborative R&D opportunity.

Long term solutions: Implement equipment design recommendations for Cable receivers, possible collaborative operation modes in the home to avoid on channel radio interference.

Dig

ita

l T

V

(47

0-7

90

MH

z)

Co

nv

en

tio

na

l a

nd

Co

mm

un

al

An

ten

na

Sys

tem

s

Challenge: Adjacent channel ch60 and image channels +9, possible interference up to 100MHz away from mobile transmission. Communal antenna and amplifiers systems vulnerable to interference (approx 5-6 million homes served).

Short term solutions / actions:

R&D opportunities exist to solve these issues, industry challenge. Solutions: Base Station filters, DTT home filters and On Channel Repeating (OCR).


Encourage Broadcast TV and Mobile industries to conduct further collaborative engineering trials.

Long term solution: Equipment design recommendations for DTT receiver conformance parameters.

Sh

ort

Ra

ng

e

De

vic

es

863

-

870

MH

z

Challenge: High probability LTE in close proximity will interfere.

Short / long term solution:

R&D opportunities exist to solve these issues, industry challenge. Radio design changes required.


PM

SE

470

-

790

Mh

z Same interference issues exist as DTT and solutions are also applicable.

Further complexity of the management of available PMSE assignments will result in less spectrum availability and the only longer term solution is to find additional spectrum and/or tighter spectrum management and control.



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5 Background (Spectrum) The UHF spectrum from 300MHz to 3GHz is particularly attractive for mobile and portable applications. Above 3GHz, high building penetration losses prevents use indoors and below 300MHz, the antenna size become impractically large for portable devices. The development of mobile services has relied on spectrum vacated by established services with most of the current cellular spectrum formerly used either by the military or for fixed links which have since migrated to higher bands or alternative technologies such as fibre. The figure below shows how the spectrum available for mobile has grown in the last 40 years, especially in the higher frequency bands. Further growth in cellular applications, especially for broadband wireless data, is resulting in increasing demands for new spectrum to be released.

Military Aeronautical Broadcasting Cellular

1970

1990

2010500MHz 750MHz 1GHz 1.25GHz 1.5GHz 1.75GHz 2GHz 2.25GHz 2.5GHz 2.75GHz

Fixed Links Other (e.g. GPS, WiFi)



Figure 1: Evolution of Spectrum allocations up to 3GHz from 1970 to 2010

Note figure above, „Cellular‟ = Mobile applications. Digital TV broadcasting provides greater efficiency allowing an increased number of TV services to be delivered in less bandwidth compared to analogue delivery. This has enabled the top end of the TV spectrum to be cleared for use by the cellular industry. Different regions of the world are reallocating different parts of the TV spectrum for mobile as shown below:



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Figure 2 Regional reallocation of TV spectrum for mobile use

The following diagram compares the amount of spectrum that will be available below 1GHz in each of the three ITU regions following re-allocation of the digital dividend spectrum. Note that the amount available in Europe is substantially less than in Region 3, prompting interest in possible extension of the current digital dividend band.

698 MHz 790 8 62 880 960

Digital TV

ITU Region 1 (Europe / CEPT) : 2 x 65 MHz total

Digital Dividend2 x 30 MHz

900 MHz band2 x 35 MHz

698 MHz 746 787 824 894 960

ITU Region 2 (USA): 2 x 54 MHz total


Lower 700 MHz2 x 18 MHz

Upper 700 MHz2 x 11 MHz

698 MHz 806 824 890 894 960

ITU Region 2 / 3 (South America & Asia Pacific): 2 x 87 MHz total



Digital Dividend2 x 45 MHz

Mobile transmit Base station transmit

Figure 2 Cellular spectrum below 1 GHz in different ITU Regions (source: Aegis)



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5.1 800MHz compatibility issues The new 800MHz spectrum for mobile use is providing many new challenges for the wireless industry to address. The combination of interested parties is unique due to the attractiveness of the spectrum. New licensed-exempt devices and mobile cellular services using paired and unpaired spectrum assignments are vying to operate alongside traditional broadcast applications. The potential problems are particularly acute in the UK where a successful broadcast industry makes extensive use of the services, with Ofcom statistics showing that DTT is used in between 80 and 90% of households either for the primary set or on a secondary set. Traditionally the wireless industries have always differentiated licensed-exempt and licensed spectrum by assigning different bands. The cable industry has been using the entire UHF TV band and additional spectrum at lower frequencies. Typical systems operate between 15-862MHz within wired hybrid fibre optic and coaxial cables (HFC) and provide high quality TV and high speed (up to 100 Mbps) broadband connections to the consumer. The deployment of mobile cellular between 790-862MHz can inject interfering signals into the in-home set top box and cabling, due to imperfect screening; this can disrupt the quality of the video and broadband cable services. Radio interference between different types of service is usually controlled by guard bands which are used to separate the different assignments or by ensuring sufficient spatial separation. For new mobile cellular deployments planned in the upper cleared band (790-862MHz), the guard band has been reduced to just 1MHz. The close proximity of cellular and digital TV assignments will result in interference to digital TV services in some areas, particularly near the edge of coverage. This will require co-ordination between the broadcasters and the mobile operators to manage the problem. This document will look at each of these potential issues and suggest some areas for further exploration and/or analysis. The table below shows a matrix of the potential interactions between the different technologies:



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Table 2: Interaction of Digital Dividend potential users

Spectrum users

Potential Interferers

Cable (15-

862MHz)

Cellular (791-862MHz)

Digital TV (470-

790MHz)

Short Range Devices

(863-870MHz)

PMSE (470-

790MHz)

Serv

ices im

pa

cte

d

Cable (15-862MHz)

Yes – potential co-channel and on

channel breakthrough into

CPE

Close proximity to broadcast

transmitter / repeaters

No interference

No interference

Cellular (791-862MHz)

No interference

Yes – responsibility of Cellular to

solve

Yes – potential adjacent channel

interference and blocking

Yes, low probability –

potential adjacent channel

interference and blocking

Digital TV (470-

790MHz) Conventional

Systems

No interference

Yes – Adjacent channel ch60 and image channels

+9. Potential interference up to

100MHz away from Tx channel.

No

interference

No – prevented

through band / power

management

Digital TV (470-

790MHz) Communal Antennas

No interference

Yes – same as conventional with potential increase

dues to higher amplification stages and

antenna gain / height.

No

interference

No – prevented


management

Short Range Devices (863-

870MHz)

No interference

Yes - Potential adjacent channel interference and

blocking

No interference

No

interference

PMSE (470-

790MHz)

No interference

Yes - Potential adjacent channel interference and

blocking

No – prevented


management

No interference



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The following sections will look into all of these technologies in more detail

6 Digital Television services

The 790-862MHz spectrum band is a harmonised band for additional broadband mobile cellular applications (typically LTE-800) across Europe and other parts of the world as a benefit of digital switch over (DSO). This spectrum band is proximate and adjacent to DTT broadcasts which will continue to occupy spectrum up to 790MHz. The transmitter powers, sites, network delivery infrastructure, antennas and network topologies are quite different for broadcast DTT and mobile cellular networks and as a result of these differences and the very small guard band, a number of interference scenarios are emerging. These need to be considered, understood and ultimately resolved to ensure compatibility between cellular and broadcast technologies. The LTE-800 mobile band has been designed to support 2x30MHz paired LTE FDD deployment in either 5MHz or 10MHz bandwidth modes. The proposed channel plan was developed within CEPT SE42 and is shown in Figure 3 below for the 5MHz LTE mode. For 10MHz LTE modes, the 5MHz carriers would be aggregated in pairs. The plan includes a 1MHz guard band between the edge of the broadcast channel 60 and the first LTE base station downlink. A reverse duplex scheme was chosen, with the base station in a lower frequency band to the mobile uplink, as this was felt to reduce some of the interference effects between handsets and the broadcast service.

Figure 3 Frequency plan for LTE-800 deployment

The close proximity of the LTE base stations (BS) to the broadcast channels and the finite selectivity and image rejection performance of DTT receivers results in a number of interference mechanisms.



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6.1 DTT Receiver Selectivity Characteristics The selectivity performance of domestic DTT receivers is specified in the UK by the DTG, who define minimum performance targets in a publication known as the D-book1. The selectivity performance is specified in terms of a protection ratio which is the minimum carrier to interference ratio required for the onset of picture failure quality at a given frequency offset. Performance targets for LTE are currently being introduced by the DTG, but since DVB-T and LTE base stations both use COFDM technology, the C/I characteristics for LTE into DTT were expected to be similar to the DVB-T into DVB-T targets currently specified. Figure 4 shows the C/I targets specified by the DTG, and a graph of typical performance for the average of 7 receivers using traditional discrete-component, Tin-Can tuners:

Figure 4 DTG C/I performance targets for DTT receivers and mean performance for 7

receivers

Using this data, it should be possible to predict the LTE signal levels that will provoke the onset of picture failure. The data above applies to the UK DVB-T mode selected for switchover (64-QAM, rate 2/3 FEC, 1/32 guard interval, 8k FFT). Slightly reduced performance would be expected for the Freeview HD service, which uses a DVB-T2 mode.

1 DTG D Book http://www.dtg.org.uk/publications/books.html

http://www.dtg.org.uk/publications/books.html



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Unfortunately, the LTE mobile signal is quite different in character to a TV signal, and tests have shown that approximately 5% of TV receiver designs, particularly some modern designs with silicon tuners, are especially vulnerable to interference. For some devices, the performance with LTE interferers is up to 30dB worse than for steady state broadcast signals. This effect is illustrated in Figure 5 below which shows how performance varies with traffic condition and interference level. For a given level of interference (I), the graph shows the level of wanted signal (C) to restore reception for 3 receiver designs and 2 LTE traffic conditions. The two traffic conditions considered in the figure are the 100% loaded base station, corresponding to full loading of all LTE resource blocks and the idle condition where the base station carries only synchronisation symbols and network signalling. Receiver 1 (RX1) shows the anomalous behaviour typical of 5% of designs where the idle signal interacts badly with the tuner AGC giving rise to a 20-30dB loss in protection performance. This behaviour does not affect all receivers, indeed receiver 2 (Rx2) has improved performance on idle signals, which are 9dB lower in average power than the 100% loaded BS signal.

Figure 5 Performance variation for DTT CH60 for different LTE traffic conditions

Notice that the protection performance is non linear. At higher interferer levels, the performance degrades and the curves steepen as the overload condition is approached.



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6.2 LTE-800 Interference into Digital Television (DTT) The following sections provide information regarding the main interference mechanisms.

6.2.1 LTE-800 BS Interference into DTT Ch60 – N+1 offset

Given the 1MHz offset between the broadcast service in UHF channel 60 and the first LTE downlink in channel 61, interference can be expected when the adjacent channel protection ratio target is exceeded. This will typically occur when the LTE signal level is 27dB greater than the DTT signal and is shown in Figure 4. Given a received DTT signal level of -72dBm at the coverage edge, the maximum level of LTE signal that can be tolerated will be -45dBm. The proposed base station power levels are expected to be up to 64dBm, suggesting a minimum isolation requirement of 109dB. This corresponds to a separation of 24km between the base station and the victim DTT receiving antenna for the worst case where line of sight propagation from the base station and a 7dBi TV antenna gain applies. For a more-cluttered environment, where the Hata sub-urban propagation model applies, interference problems would be predicted where the victim DTT antenna is within 900m of the base station. For receivers that are susceptible to the time domain variation of the base station signal, estimated to affect 5% of chassis designs, an additional 20dB of isolation would be required, typically increasing the interference radius of the base station by up to a factor of 10.

Figure 6 LTE-800 Base station (BS) interference to DTT CH60

6.2.2 LTE-800 UE Interference into DTT– N+9 offset

The DTT receiver characteristics shown in Figure 4 show a steadily improving performance as the offset between the interferer and wanted signal increases. This is to be expected given the characteristics of the receiver‟s IF and RF filters. There is however a noticeable reduction in performance for interferers at N+9 offset (72MHz) for traditional CAN tuners due to the finite image rejection performance of designs with a first IF of 36MHz. This gives rise to an interference mechanism whereby a handset at



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72MHz offset from the wanted DTT channel can produce picture break up. This scenario is illustrated in below:

Figure 7 LTE handset (UE) interference to DTT CH57-60

For a typical handset EIRP of 25dBm, and a received DTT signal of -72dBm at the coverage edge, the maximum permitted level of handset signal for the onset of failure would be -41dBm, suggesting a required isolation of 66dB between DTT antenna and LTE UE. This corresponds to a minimum separation of 50m between handset and DTT antenna. In practice, the interference may be worse still, as tests on LTE handsets suggest the time domain characteristic of the signal results in degraded receiver protection ratio performance causing picture break-up at lower interferer levels. Additional interference mechanisms involving handsets are expected to affect households using set top antennas for secondary sets in bed rooms. Due to the very short coupling distances, such installations are expected to be particularly vulnerable to overload. To some extent, this can be controlled by not using smart phones in the vicinity of set top antennas; however this is not always possible to control, particularly in flats and terraced properties. Handset interference can also couple into standard domestic installations through the downlead, antenna plate and fly lead causing overload or adjacent channel interference. Newer installations using double screened cable (e.g. CT100) and screened outlet plates are less vulnerable, but many households still use single screened cable and unscreened outlet plates.

6.2.3 Interference resulting from ‘out of band’ emissions

Problems resulting from the finite selectivity of the receiver are only a part of the story. In practice, a mobile base station will radiate significant energy into the broadcast band, and this will result in interference, even if additional filtering is used at the receiver in an



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attempt to reject the base station signals. This interference cannot be addressed at the receiver. This effect is shown in Figure 8 below and interference levels up to 0dBm co-channel with TV channel 60 are permitted by the recommendations made by CEPT SE42. The permitted levels of out of band would result in a 20dB degradation in receiver sensitivity at 500m from the cellular base station, and could dramatically reduce broadcast coverage.

Figure 8 LTE base station OOB causing interference to DTT CH60

The minimum requirements for Out of Block (OOB) characteristics of the base station defined by CEPT SE42 have been harmonized across Europe in EC 2010/367/EU2. Given a typical ACS performance for the DTT receiver for the first adjacent channel of 55dB, the SE42 studies showed that improving the BS ACLR beyond 59dB made no further improvement to the interference problem, as the adjacent channel interference would be dominated by the receiver ACS performance. The ACLR requirements in EC 2010/387/EU actually permit 0dBm OOB radiation into every TV channel from CH21 to CH60 (470-790MHz). This high level of OOB permitted by this decision unfortunately limits the mitigating effects of receiver filters as the ACLR component of the interference will dominate, even if ACS is improved through use of receiver filters.

2 COMMISSION DECISION of 6 May 2010 on harmonised technical conditions of use in the 790-862 MHz frequency band for terrestrial systems capable of providing electronic communications services in the European (2010/267/EU) http://www.erodocdb.dk/Docs/doc98/official/pdf/2010267EU.PDF

http://www.erodocdb.dk/Docs/doc98/official/pdf/2010267EU.PDF



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6.3 Interference Discussion – Possible solutions

The interference mechanisms described so far are an inevitable consequence of the non-ideal behaviour of receivers and transmitters and the FDD band plan with the narrow guard band chosen by the CEPT. Although the RF transmissions are designed to occupy their intended bandwidth, RF energy leaks into adjacent spectrum due to finite implementations of the transmitter devices, and the selectivity performance of the receiver (i.e. receivers will also pick up energy outside of their intended receive bandwidth). Interference problems will be a particular issue towards the edge of DTT coverage and TV channel 60 appears to be particularly vulnerable. A number of solutions are emerging: (1) Use fast roll-off filtering at the LTE800 base station to provide additional protection. To realise the benefits, DTT receiver filters must also be used. (2) Restrict the EIRP of the base stations, in locations where CH60 us used for DTT. Restricting the 5MHz license from 791 to 796MHz is particularly beneficial. (3) Restrict the antenna polarization to that opposite to DTT in CH60/59 areas. This unfortunately prevents MIMO deployment, reducing the mobile network performance, but gives up to 16dB of additional isolation between BS and DTT victim. (4) Re-point DTT antennas to alternative transmitters where broadcast coverage overlaps allow. This may also be possible if additional DTT relay transmitters are deployed using interleaved spectrum. (5) Consider alternative band plans. The TDD approach favoured by Asian countries would permit a greater separation between the mobile and broadcast services. This would allow for the design of filters that could be retrofitted and later included in the DTT designs to allow the DTT and mobile bands to be decoupled. (6) Repair the damage by transmitting the DTT signal from the cellular base station site, thus ensuring that the link budget differential between DTT and LTE800 at the DTT receiver falls within the limits defined by the protection ratios. See section 6.3.1 The following sections discuss how collaboration between the cellular and broadcast industries might further address these problems to ensure and guarantee harmonisation and minimize pathological interference scenarios. Furthermore, such collaboration may result in additional opportunities creating value to customers through working together at the infrastructure, technology and business levels.



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6.3.1 On-Channel Repeaters

One of the proposed mitigation techniques to address LTE800 adjacent channel interference into Channel 60 DTT receivers is the use of On-Channel Repeaters (OCR‟s) to re-radiate a low-power quasi-synchronous transmission of the damaged DTT signals from a subset of LTE800 cellular sites under the footprint of the main DTT broadcast antenna. Initial recent field trial studies have been carried out by Ofcom using OCR‟s to understand their benefit as an LTE800 to DTT Adjacent Channel interference mitigation technique3. OCR results indicate that the solution can work but relies upon sites being able to provide very good isolation between DTT donor and DTT repeater antennas, which may not be achievable at all cellular base station sites. An adjacent channel on-air repeater could also be contemplated to address the above isolation requirement, where for example a DTT Channel 60 service is received via a donor antenna but re-transmitted at low power on another DTT channel. Such arrangements are known as “TV relays” or “rebroadcast links” (RBLs).This would require DTT receivers to be re-tuned, but this is already the case for DSO phases. However, initial feelings from broadcast radio network planners suggest that this may not be possible due to the already tight spectrum re-use topology that would be in place. Nevertheless, this may be something which would warrant a more comprehensive study to allow partial clearance of CH60. Alternatively, a fibre/cable/microwave backhaul connection to the LTE800 cellular base station site could be exploited which carries the DVB-T signals to be re-broadcast from the base station. This either requires sharing of backhaul bandwidth between mobile operator and broadcaster, or the need for separate physical backhaul circuits. For some DTT multiplexes, the required data could be made available via satellite. As for the adjacent channel on-air repeater solution above, the feasibility of backhaul based delivery of low-power re-broadcast of DTT services from cellular base station sites has not been studied comprehensively as an LTE800 to Channel 60 DTT interference mitigation technique, and would warrant further investigation. The backhaul requirements are typically 24Mb/s for DVB-T or 40Mb/s for DVB-T2. The network topology for DTT re-broadcast delivery is one where a main broadcast transmitter is at the centre and the broadcast transmission is re-transmitted (as a repeater) from a network of cellular base stations where the time difference between main broadcast antenna and repeated signal is within the Guard Interval (GI) of the DVB-T signal. Furthermore, re-transmission from the cellular network sites wouldn‟t have to be at all cellular sites, and needs only to be from one sector (sometimes two sectors), in order that the domestic TV rooftop antennas do not have to be re-pointed.

3 The co-existence of LTE and DTT services at UHF: a field trial: http://www.ofcom.org.uk/static/research/co-existenceLTEDTTservicesatUHF.pdf

http://www.ofcom.org.uk/static/research/co-existenceLTEDTTservicesatUHF.pdf



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Figure 9 Benefits of repeating DTT from Cellular Base Stations The image above depicts a full shared cellular/re-broadcast topology across a 40km radius area. The left image depicts the coverage to rooftop antennas for DTT service; the image on the right depicts the coverage when delivered (repeated) via a grid of cellular sites. Beyond a certain distance (20km), the cellular sites will always provide better service coverage.

6.3.2 DTT & Cellular Cooperative Network Evolution Proposal

The terrestrial TV broadcast industry has evolved at a somewhat slower pace to the cellular industry particularly in terms of its network topology. Unlike the cellular industry domestic TV installations are deemed expensive to upgrade (e.g. the fixed rooftop antenna, cabling and feeds for multiple TV sets). DTT network planning has many constraints due to domestic antenna frequency groupings, the directive properties of the antennas and the need to coordinate with international neighbours. As a result, DTT still uses high-power/high-tower network topologies designed using frequency planning and co-ordination rules dating back to the 1961 Stockholm Agreement. Terrestrial DTT is also seeing slowly growing competition from alternative delivery means such as Satellite (Sky, FreeSat), Cable (VirginMedia), and even broadband IP (IPTV delivery), but nevertheless remains the dominant platform in the UK. It is often the most cost effective platform and Cable and Satellite subscribers often chose DTT for secondary sets as additional subscriptions are expensive. Given this, one can understand the need to protect DTT reception and sympathise with the fact the terrestrial broadcast industry is losing spectrum as part of the digital dividend. Competing platforms are able to offer HDTV and many more channels, but Ofcom have decided to restrict the DTT platform and prevent digital dividend spectrum from being used for further HD services using the DVB-T2 technology beyond the 5 services that can be offered on a single HD DTT multiplex. IPTV and cable enable interactivity, which are becoming increasingly important to consumers and these



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techniques are being included in new hybrid platforms like “YouView” that will combine on demand technology for catch up services like iPlayer with broadcast DTT technology for traditional linear consumption. Many countries across the world have terrestrial TV delivery platforms. This includes UK, France, Spain, Italy, India, and China as examples. Cable and/or Satellite TV delivery platforms are more popular in other countries such as US, Canada, Germany and Japan, although these still having a significant terrestrial TV component, particularly important for portable and mobile services. Cellular networks have evolved at a more rapid pace as terminal equipment changes can be subsidised by the mobile subscription fee. Over 25 years, cellular operators have acquired 3 spectrum bands and this is expected to increase to 5 bands soon with the introduction of 800 and 2.6GHz services. The networks have gone through many generations of technology for the radio interface (TACS, GSM, GPRS, EDGE, UMTS, HSPA, HSPA+ and soon LTE and LTE-Advanced), and have adopted network spectral efficiency techniques such as cell-splitting, variable tilting antennas, frequency hopping (GSM), and now adaptive antenna Beamforming resulting in an evolved heterogeneous topology of Macro, Micro, Pico and soon Femto cell layers. This has been possible as consumers are prepared to replace their terminal equipment, almost on a yearly basis, which is certainly not the case for broadcast TV receivers. Terrestrial DTT and Digital Dividend Cellular share the prime UHF radio spectrum for delivery of content and information. Given this, the solution of re-broadcasting DTT from a cellular site to mitigate cellular interference to a DTT receiver has been proposed in the previous section to permit co-existence of the two networks and mitigate against adjacent channel interference. A remaining question is why the natural evolution can‟t be to arrive at a fully shared network topology and infrastructure. The next section explores what could be achieved if this infrastructure sharing could be carried out.

6.3.3 Shared DTT Broadcast and Cellular Topology

The proposed thinking brings together Broadcast and Cellular networks to essentially share base station sites and thus share the same topology. This proposes using low-power/lo-tower for broadcast services rather than the current hi-power/hi-tower model. Working together at the network topology level could bring the following benefits: a) Solves the near-far adjacent spectrum interference conditions discussed earlier for

all DTT-Cellular cases, and thus permits much tighter spectrum boundary or guard bands to be used between cellular and DTT services, for example, for the current LTE800 to Channel 60 DTT issue and for any potential future digital dividend releases. Moreover, broadcast moving to a cellular type topology would potentially allow better spectrum re-use for white space bandwidth and other users of interleaved DTT spectrum, such as wireless microphones, etc.



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b) Enhances DTT coverage penetration significantly, allows realistic Mobile DTT

services, and/or could even remove the need for rooftop antennas (which could in turn permit faster evolution of the DTT industry), allows significant power reduction from the main broadcast transmitter which in turns offers significant spectral efficiency in spectrum re-use, thus permitting more channels/content and/or HD content, and even a further dividend spectrum.

c) Assuming we keep the rooftop TV antenna in b) above then the domestic rooftop UHF Yagi antenna could also be connected to an LTE800 modem in the home. The fact the Yagi antenna is at 10m height, outdoors, above the rooftops/clutter, and has UHF directivity/gain can equate to something like a 10-15dB gain in received signal quality strength for LTE (over an indoor handheld device). This allows the mobile operators operating say an LTE800 network to offer “fixed” broadband delivery and thus competing against fixed broadband operators using xDSL, or Cable, and if the LTE800 signal is on-air repeated (assuming good isolation between rooftop and living room for example) in the house then this even may offer an alternative approach for the domestic femtocell.

DTT broadcast services transitioning to a low-power/low-tower topology would however require a significant investment in terms of infrastructure, and radical change from the traditional broadcast model, and raises the question how such investment would be funded. In the USA, the FCC are considering incentive based spectrum auctions where further prime UHF broadcast spectrum is auctioned, but a significant proportion of the auction proceeds go to the broadcast network operator to re-invest in DTT infrastructure. Perhaps such an incentive model may be a useful mechanism to discover or reveal the real economic value of UHF spectrum. Furthermore, if mobile operators allow broadcaster operators access to cellular sites then this naturally speeds up and facilitates any transition. Additionally, base station equipment vendors can now support multi-protocol transmissions, and hence raises the question could LTE800 and DVB-T/T2 be transmitted from the same physical hardware, thus potentially reducing costs, but would require changes to how networks are managed, operated, and maintained. The FCC national broadband plan4 also proposes the use of the broadcasters “transitioning to a cellular architecture” to solve many of the interference issues and broadcast/cellular co-existence; and hence a useful reference for collaborative thinking.

4 FCC National Broadband Plan, Connecting America. http://www.broadband.gov/download-plan/

http://www.broadband.gov/download-plan/



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6.4 Recommended DTT tests for trial test bed

Ofcom recently completed a detailed field trial of LTE800 co-existence with DTT services, with emphasis on testing various LTE800 adjacent channel interference into Channel 60 and below mitigation techniques. This field trial complemented Ofcom‟s theoretical analysis of the interference. Two dominant interference mechanisms were concluded:

Front end DTT receiver overload. This is when a strong LTE800 signal is in the presence of a weak DVB-T (regardless of channel frequency) signal causing the receiver to go into non-linear mode.

Adjacent Channel interference, in particular into Channel 60 but also into channels 59, 58 as discussed earlier.

Ofcom demonstrated and made conclusions that simple in-line passive Low-pass RF filters could be used to mitigate front end overload situations, and the majority of Adjacent channel interference issues for channels 58 and 59, providing the base station also has good Adjacent Channel Leakage Ratio (ACLR) filtering. However, the channel 60 interference issue remains without a silver bullet mitigation technique. In such cases, the use of OCR, or moving subscribers to Satellite or Cable TV services5 would be expected. The number of households that would be affected is a subject of current debate. Initial estimates, assuming a BS EIRP of 59dBm and additional roll off to OOB specification in EC2010/387/EU, suggest 750 thousand households could lose DTT reception if 9000 co-sited LTE base stations were deployed. Recent proposals by Ofcom to increase the BS EIRP to 64dBm, not to restrict the number of base station sites and not to specify the OOB roll off in the technical license conditions can be expected to further increase the number of households affected. Ofcom also has discussed, studied and trialled polarisation discrimination techniques such as LTE800 using vertically polarised transmission and DTV using Horizontal polarised reception. This showed some improvements but also concluded that cross polar discrimination varies widely depending upon domestic aerial types and quality of installation. Ofcom stated that this may not be a useful mitigation technique, especially as mobile operators would prefer to exploit slanted dual cross polar transmission for LTE for base station antennas to enable 2x2 MIMO techniques. However, there are a number of other channel 60 interference mitigation techniques which Ofcom hasn‟t tested. It is understood that suppliers are innovating with the view and desire to test/trial such mitigation concepts and with which the DTV, Cellular operators and other stakeholders should be keen to understand. As such, it is recommended that an appropriate test bed be made available for such innovation to thrive and for the industry to further understand and manage such interference issues.

5 Since DTT services are free to air in the UK and do not carry a subscription charge, the proposal to move affected households to subscription platforms is potentially unpopular.



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Alternative band plans might also be beneficial. In Asia, TDD modes of LE are popular that would allow increased separation and more effective filtering of LTE from DTT. Alternatively, it may be necessary to restrict deployment of LTE licence A (791-801MHz) in certain geographical areas where DTT CH60 cannot be cleared. Partial deployment of licence A using a 5MHz mode occupying 796-801MHz would be a third option.

7 Hybrid Fibre Cable (HFC) Networks Some thirteen million homes have access to the HFC networks within the UK to receive a wide range of services which include Digital TV, Video On Demand, Interactive and Time Shifted video services (available in Standard Definition, High Definition and 3D), in addition to High Speed Broadband services. HFC networks support the Government plans for wide scale high speed broadband with current speeds of between 50 and 100Mbits/s, and the ability of DOCSIS 3 to bond up to at least 32 channels mean that the final speeds to be achieved will be well in excess of the current offerings. HFC Head ends are fed with incoming signals via a national fibre optic network and are also capable of receiving and retransmitting off air signals as well as being able to stream locally stored media. A single Head end is capable of serving in excess of one million customers. A Head end distributes its signals using DVB-C and DOCSIS modulation schemes via a hybrid fibre optic and coaxial cable distribution system terminating at the customers premises‟ at an isolated outlet. Cabling from this unit to the various devices inside the premises is of high quality dual, triple or quad screened coaxial cable which is terminated using high quality “F” type connectors. Telephone services are also carried alongside the fibre/coaxial network and terminate in a conventional copper pair at the customer premises. Handbook providing in depth information is available on the ICT KTN website at: www.ktn.innovateuk.org/web/spectrum/document-library

7.1 800MHz spectrum usage and impact to Cable & STB industry

The cable industry was not aware of the changes in spectrum use until early 2009, since then it has taken part in a range of activities including; European Commission, ECC and Standards Bodies along with Ofcom UK. The challenge for Cable Networks is that of being able to operate co-channel with the LTE transmissions, and just not an adjacent channel issue. Hence protection can only be achieved by increased immunity; there is little opportunity in the way of filtering or other simple “add-ons” which will dramatically improve the situation for Cable Networks in the UK. The following sections will investigate the interference scenarios that have been established.

http://www.ktn.innovateuk.org/web/spectrum/document-library



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7.2 LTE Interference into Cable and DVB-C/DOCSIS CPE

A testing program carried out by Cable Europe Labs (the trade association of the Cable industry) and supported by Virgin Media has carried out an investigation into the interference mechanisms which can be expected from the new Electronic Communication Networks (ECN) and other use of cleared spectrum, copies of this work can be found at: www.ktn.innovateuk.org/web/spectrum/document-library The cable networks are operated within the frequency range 15 - 862 MHz, which is split between upstream and downstream as follows: • upstream from approximately 15 – 65 MHz, this is the return path from the

subscriber to the Headend

• downstream from 85 - 862 MHz providing the delivery of services from the Head End to the subscriber.

Each head end, which is capable of serving in excess of 1 million customers, may have different frequency plans dependent on local requirements. The testing program concluded that the HFC network itself was a robust structure and that the vast majority of interference would be experienced within the home. Where an ECN terminal device (or any other transmitter within the frequency reception range of the CPE) was in proximity to the customer premises equipment (Set Top Box, Personal Video Recorder, Cable Modem etc) at ranges of up to 3-4 metres. An interference range of some 3-4 metres is for a terminal unit operating at the maximum power quoted in ECC Decision of some 316 mW. These conclusions are similar to those found during other testing carried out by the Dutch Administration and within Germany. The various tests suggest that interfering signals generated in one premises will affect equipment in adjacent locations. No testing has been carried out using the fixed mobile units proposed for some locations using higher powers which will increase the interference to CPE, nor the higher base station powers now being proposed by Ofcom.

7.2.1 Set Top Box - LTE Interference testing

The UK components were assembled on a board as shown in the Figure 10. The scenario in use here is entitled „Scenario 1‟ as provided by Virgin Media, and makes use of a Tratec isolator, a two-way splitter with equal 3.6dB output attenuations, a 2m tri-shield cable for the STB, and an HDMI cable as provided with the STB or long SCART cable. Where an HDMI port was present on the STB, it was used in preference over a SCART port. Where no option existed, a 15m SCART cable connected the STB port to a television in the control room. Where coaxial ports remain unused on

Figure 10 British scenario with a set top box,

representative system outlet

and cabling

http://www.ktn.innovateuk.org/web/spectrum/document-library



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victim equipment, they have been left un-terminated, whilst all unused ports or cables attached to the cable network are terminated. Specific configuration data is contained in the following tables.

Table 3: Accessible signal level control point configuration

Point Affect on signal level

Tratec Ecoline 3-way splitter 7dB attenuation

Tratec tap 25dB attenuation

Prior to drop cable 3dB pad

Tratec isolator 0.4dB attenuation

Tratec Ecoline 2-way splitter 3.6dB attenuation

Table 4: Cables used in installation

Cable Length From To

Times Fiber RG6 siamese 70m Trunk network CPE installation

White tri-shield RG59 cable 9m System outlet Set top box

HDMI cable provided with STB 2m System outlet HDMI-fibre optic converter

Scart cable 15m STB output TV in control room

Table 5: Wanted signal characteristics

Signal standard

Modulation Symbol rate Input level (to the STB)

Frequency range

DVB-C 256QAM 6.875 Ms/s -10dBmV 675-859MHz

Signal levels present at the input port of the STB are approximately -10dBmV and provide a Modulation Error Ratio (MER) of approximately 30dB on each STB. Such an MER caused approximately one pre-Reed Solomon (RS) error per second; the RS filter is able to correct these errors such that there were zero post-RS errors. This level is considered „worst case‟ because a minor variation to any of the factors affecting MER could result in a post-RS error, and a visual manifestation of the problem, most likely in the form of macro blocking. Graph of results below.



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DVB-C STB tests: Maximum LTE level permitting stable audio and video on 256QAM

channels from 675-859MHz. STBs in representative networks, -10dBmV DVB-C input level

(LTE centre frequency 795 MHz, calculated separation distance 0.5m)

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

35

675 683 691 699 707 715 723 731 739 747 755 763 771 779 787 795 803 811 819 827 835 843 851 859

256QAM channel centre frequency (MHz)

LT

E t

ran

sm

it E

RP

(d

Bm

)

STB 1

STB 2

STB 3

STB 4

STB 5

STB 6

STB 7

STB 8

STB 9

STB 10

STB 11

STB 12

STB 13

STB 14

STB 15

STB 16

STB 17

STB 18

STB 19

STB 20

STB 21

LTE (10MHz BW)

at 316mW ERP

The red 316mW line is the nominal pow er (CEPT) of the terminal unit.

On-

chan

nel

Figure 11 LTE-radiated European scenarios, STBs 1 to 21



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7.2.2 Cable Modem – LTE Interference Testing

A similar test configuration to that shown in 0 was used for cable modems.

Table 6: Wanted signal characteristics

Signal standard Modulation Input level (to the STB) Frequency range

DOCSIS 256QAM -10dBmV 795MHz

Signal levels present at the input port of the cable modem are approximately -10dBmV and provide an MER of approximately 30dB.

Maximum LTE level permitting stable data on a 256QAM channel at 795MHz.

CM in representative networks, -10dBmV DOCSIS (Annex B) input level from cable

(LTE centre frequency 675-859MHz, calculated separation distance 0.5m)

-40

-30

-20

-10

0

10

20

30

40

675 691 707 723 739 755 771 787 803 819 835 851

256QAM channel centre frequency (MHz)

LT

E E

RP

(d

Bm

)

CM 1

CM 2

CM 3

CM 4

CM 5

CM 6

CM 7

CM 8

CM 9

LTE (10M Hz BW)

at 316mW ERPThe red 316mW line is the nominal power (CEPT) of the terminal unit.

On-c

hannel

Figure 12 LTE-Radiated European Scenario, CM 1 - 9 Points below the red line were affected by maximum power levels proposed for LTE terminal units. Graph demonstrates the effect these power levels will have at a distance of 0.5m and shows that the receivers display significant problems on-channel, on both adjacent channels, and on a number of off-channel frequencies.

7.2.3 In- Home Cabling – LTE Interference Testing

The UK cable operator uses high quality dual, triple or quad screened internal cables (light blue on graph Figure 13) when they install however the customer is not legally obliged to use the operator when extending or changing their installations.



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A number of tests were carried out on various qualities of domestic cables as the Dutch and other reports give in-home cabling as a major cause of ingress in their countries the indicative results of the Cable Europe testing show:

Test 24: Maximum LTE level permitting stable audio and video

on a DVB-T channel (centre frequencies 786, 818 and 850MHz). -60dBm input level

to outside receiver; 25m cables. Calculated separation distance 0.5m.

-20

-10

0

10

20

30

40

786 818 850

LTE transmit and DVB-T receive centre frequency (MHz)

LT

E E

RP

(d

Bm

)

Pro quad-shield

(black)

Good domestic

(black)

Standard domestic

(brow n)

Low -end RG59/u

(black)

LTE (10MHz BW) at

316mW ERP

The red 316mW line is the nominal pow er (CEPT) of the terminal unit.

On-c

hannel

On-c

hannel

On-c

hannel

Figure 13 Test 24, LTE-radiated 25m coaxial cables

7.2.4 Summary of LTE Interference with Cable systems

Testing demonstrates that the tested combinations of modulation and power levels with a STB or cable modem in an in-home installation are susceptible to on-channel (where the STB uses the same radio channel as the interfering signal) LTE interference at or below the 25dBm Total Radiated Power (TRP) level proposed for LTE terminal units in this band. Seven out of eight tests revealed susceptibility on adjacent channels, where the receive frequency is one 8MHz Ultra-High Frequency (UHF) channel offset from the interferer‟s transmit in addition to various image/IF channel interference.



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7.3 Cable Interference - Possible mitigation and solutions

A number of mitigation techniques have been suggested:

7.3.1 Restrict cable transmissions to below 790 MHz.

Whilst this would seem to provide an instant answer, unfortunately it has a range of practical drawbacks:

- The cable networks already use spectrum above 790 MHz; - Requirements for higher speed broadband will need up to 32 bonded 8 MHz

channels; - Transmission of High Definition, 3D and Interactive TV is spectrum hungry; - This will not provide an answer for the interference expected in the next stage of

Digital Dividend clearance to 600MHz or the use of white space devices (and indeed could compound the issues);

Costs of reconfiguring the networks to below 790MHz would be prohibitive, and the loss of existing and future revenue to enable competing technologies and delivery mechanisms to operate appears to be anti-competitive.

7.3.2 Reduce QAM rates to make the system more robust:

Testing demonstrates that the combinations of modulation and power levels with a STB in an in-home installation are susceptible to on-channel (where the wanted channel operates on the same channel as the interfering signal) LTE interference at or below the 25dBm Total Radiated Power (TRP) level proposed for LTE terminal units in this band. Seven out of eight tests revealed susceptibility on adjacent channels (where receive frequency is one 8MHz Ultra-High Frequency (UHF) channel offset from the interferer‟s transmit frequency), and six out of eight revealed wider susceptibility to in-band interference. Amendments to the configuration revealed the following:

A regression to a more robust form of modulation – 64QAM – from 256QAM provides a marginal (between approximately 0 and 5.4dB) improvement in immunity.

Such a regression reduces data throughput by a factor of around 30%.

As DOCSIS 3 services are expanded, up to some 32 bonded channels may be required in order to obtain maximum data rates, causing the overall spectrum requirement to increase to maintain existing DTV and Broadband services.



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7.3.3 Increase HFC signal level

HFC Networks in the UK are designed to operate with input levels to the CPE as close as possible to the mid-point of their specified input level operating window. Increasing signal levels on the HFC Network would require considerable re-engineering at great expense. This would also increase the risk of signal levels at the system outlet and at the input to the CPE which are currently operating within specification being raised above maximum specified level as defined in EN60728-1 System Performance of Forward Paths.

7.3.4 Increase immunity of CPE

A long term solution, work is underway in the ETSI/CENELEC EMC Joint Working Group on these issues and with individual CPE and components manufacturers. However the short time scales before the introduction of ECNs suggest that new designs will not be commercially available in time in the quantities required. This does not of course address the issue of the millions of pieces of legacy CPE which are deployed across the UK HFC Networks.

7.3.5 Home Cabling improvements

Where interference occurs and existing in-home cables are dual-shield only, these can be upgraded to triple or quad-shield types. Subscribers must be actively discouraged from using inferior cables to modify or extend their own in-home cabling.

7.3.6 Pilot Tone

A tracking low level pilot tone transmitter attached to each piece of CPE would serve a number of purposes

- Cause the ECN terminal unit to avoid that frequency when communicating

- Provide sufficient level of RF power to be detected by white space devices

7.4 Cable Summary

Testing has shown that there is little in the way of filtering or other simple “add-on‟s” which will dramatically improve the situation in the UK as the issue is largely a co-channel one. Time is required for new CPE to be developed, the prime point by a range of agencies for use of ECN‟s is to provide rural broadband, roll out of ECN‟s in rural areas first would achieve Government objectives and allow time for the cable industry to both develop and fit new CPE.



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7.5 Recommended Cable and DVB-C/DOCSIS CPE tests for trial test bed.

7.5.1 Interference scenarios

There are 2 types of Cable CPE which need to be tested, and the impact of LTE interference is different for both the end user and the network. Firstly for Cable Modems, total loss of data is not always immediately apparent to the end user, depending on what operation they are carrying out at the time the interference occurs. If they are for instance streaming video and/or audio, this is obvious as the stream will stop. However if data is being downloaded, for example a large document, the end user may not notice as any undelivered packets are re-sent. This will potentially have a dramatic impact on the network as continually having to re-send dropped packets does impact on payload/data carrying capacity. For Cable Set Top Boxes, total loss of data is immediately apparent as the video and audio stream stops. These signals are not buffered or re-sent as they are received in real time, so any totally corrupted data is lost forever. It is also important

7.5.2 Testing Procedure

Each device under test (DUT) should be radiated by a real LTE carrier with a bandwidth of 10MHz, the interfering carrier should have 100% & 50% modulation applied and should also be operated in idle mode (0%). This constitutes 3 sets of tests For each Cable Modem tested, 2 conditions shall be recorded, the channel power of the interferer at the point when error correction commences and the channel power of the interferer at the point when data is lost. For each Cable Set Top Box tested, 2 conditions shall be recorded, the channel power of the interferer at the point when error correction commences and the channel power of the interferer at the point when the picture is lost. The DUT should be tuned to a target 256QAM, 8MHz wide channel with an input signal set to 0dBmV and the interferer varied in power and modulation until interference is seen or the limits of the terminal power reached (25 dBm, 316 mW). The input signal should then be set to -10dBmV and the process repeated.



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Hence for each device tested, up to 12 test procedures need to be completed.

8 Communal Antenna Systems Communal antenna systems are used to deliver television and radio signals received at a single location to a number of users. Typically, they are found in large houses, blocks of flats, anything from about four flats upwards, tower blocks with over 100 flats or housing estates with 1,000 homes, student halls of residence, prisons, hotels, etc. The systems often carry additional locally introduced signals ranging from hotel front of house systems to student education and information channels. The source of the Communal Antenna Systems section of this document has been supplied by the Confederation of Aerial Industries Ltd and has been used by permission granted via Copsey Communications.

8.1 Communal Antennas – Systems and Topologies

Communal antenna systems can be partitioned into three categories:

MATV (Master Antenna Television) systems, which deliver analogue and digital terrestrial television signals

IRS (Integrated Reception Systems), which deliver satellite services as well as terrestrial television

SMATV (Satellite Master Antenna Television), similar to MATV with the addition of locally modulated signals, commonly satellite programmes.

An IRS can be regarded as an MATV system with additional components to deal with satellite signals.

MATV systems have two principal parts:

The head end, in which there is at least one antenna to receive signals off-air and often more than one to receive radio, and a launch amplifier to overcome the loss of signal power in the distribution network

The distribution network, which is an arrangement of cables and splitters designed to carry signals from the launch amplifier to outlets in each dwelling.

MATV head ends can themselves also be partitioned into two categories:

Wideband, in which the head-end passes all signals from the frequency band used for terrestrial television

Processed, in which frequency selective components are used, so that the system does not pass all terrestrial television frequencies. These components include equalisers and channel amplifiers, designed to apply different amounts of gain to



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different channels, and channel changers, designed to move a signal from one channel to another. As a rule, small MATV systems tend to have wideband head-ends, and large systems will have processed head-ends, although this varies somewhat geographically and with the age of the system

The antenna array receives “off-air” terrestrial broadcast signals from both the main (i.e. local) television transmission station and, in many cases, transmission stations from an adjacent area. Signals range from the FM broadcast band through DAB to analogue and digital television signals. Many systems also have a satellite reception capability, receiving either Freesat channels or, depending on license arrangements a combination of Freesat and subscription channels. In addition to the signals mentioned above, some systems will also have the introduction of on-site and locally produced programmes including security cameras modulated into free channels in bands 4 and 5. The addition of satellite to the system comprises of a dish complete with LNB. The LNB has four outputs being low and high band with two polarities for each being horizontal and vertical. Each of the cables carries an IF range of signals between 950 and 2150 MHz. The head end amplifiers enable these four sets of signals to be distributed around the system as well as the terrestrial. Each distribution point has a satellite switch and connects via a single cable with an outlet plate in the flat where commands from the satellite decoder cause the switch to deliver the required polarity. A system such as this with one satellite being distributed is known as a 5 cable system. The addition of a further satellite would result in a system with 9 cables or 3 satellites, 13 cables and 4 satellites, 17 cables. The back bone of the system run between the head end and each switch and repeater amplifier is therefore that number of cables. Distribution components are readily available for up to 17 cable back bones. Systems delivering services such as Sky plus and HD would have a minimum of two cables feeding into the flat. In the case of retro fitting to provide the extra feed for Sky plus etc., a converter called a stacker may be used. A stacker will up convert one satellite output from the switch and add this to another output. In the flat, a down converter will separate out the two sets of signals. Stackers result in the distributed bandwidth increasing locally to the flat to between 88 and 3500 MHz. The interference immunity of the head-end varies widely dependant on age and installation design. The best systems will have channelized filtering to prevent interference from other transmissions. Other systems will have the terrestrial antenna connected directly to a broadband amplifier which may have a bandwidth as wide as 30-862MHz, with gains of up to 40dB or more.



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Distribution may be achieved through a variety of methods, the most common being star distribution and cascade. The selection of distribution will depend on the geography and size of the site concerned. Distribution of the signal throughout the building or buildings will be achieved by wide-band repeater amplifiers, normally without any filtering. The gain of these amplifiers will vary by up to 40dB, dependant on the cable losses incurred up to that point. Termination in customer premises will normally consist of an unfiltered plate which may have two or more sockets diplexing FM radio, DAB and UHF television. Cabling of these systems will vary widely from multi-screened cables to single screen. Wall sockets will also vary, the older systems having unscreened outlet and modern systems complying with EMC requirements. The link cables (fly lead) between the wall socket and customer equipment are normally provided by the customer.

8.2 Communal Antenna Interference Issues Many communal antenna systems located in major conurbations will be on high tower blocks where the head end may well be co-located with other radio services including GSM, 3G and in the future LTE systems. With the physical co-location of LTE base stations and communal antenna systems, the amplifiers used in a communal antenna system are likely to receive direct breakthrough from the LTE signal into the wideband amplifiers. Once in the system, the LTE signal may well overload the amplifier or, at minimum, cause interference to any co-located channels or adjacent channels. The interference effect will depend on the bandwidth of the interfering signal and the amount of out-of-band energy produced by the base station. In addition the terminal units will interfere with both the distribution amplifiers and domestic CPE. These conclusions have been borne out by both industry and Ofcom testing

8.3 Communal Antenna Customer base It is difficult to determine exact numbers of viewers as there is no single authority; communal antenna systems may be provided by the building owner, local council or a local company. However for the UK the following figures are the best estimate from the Confederation of Aerial Industries (CAI): There are in the order of 750,000 MATV / SMATV / IRS systems serving 5-6 million homes (Source: Mr D Hodges of the Confederation of Aerial Industries Ltd).



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8.4 Communal Antenna Interference Assessment From initial research, it is reasonable to state that interference will occur and is due to the physical proximity of the base station to the head-end equipment and to the wideband nature of amplifiers used for distribution of the signal within a building. Once the signal has entered the distribution chain it is unlikely that conventional RF filtering will resolve the interference issues. Cabling of communal antenna systems is unlikely to be generally accessible as, in some cases, it may have been put into conduit or, more likely, built into the fabric during the construction of the building and therefore replacement with better screened cables is unlikely to be economically viable. For the future, greater consideration of the cabling needs to be made. In addition to the base station interference, terminal units will cause interference within the distribution amplifiers and domestic CPE. This will be worse in hotel systems where the migrant population would be expected to use a higher percentage of terminal units for longer periods. Communal antenna systems and viewers will also be vulnerable to any other changes in the environment brought about by additional services being introduced in the television bands. These may include:

White space devices either due to non-local television signals being distributed throughout the system or for breakthrough into local wideband distribution amplifiers

New mobile or similar services introduced in the second phase of clearance above 600MHz

The proposed increases in terrestrial television transmission powers may also have an effect on these systems as a minimum rebalancing of the network would probably be required.

8.5 Innovation to solve the problems Several Interference resolution techniques could be deployed for installations to reduce interference, some of which will be shared with domestic TV and cable. To follow some suggested solutions.

8.5.1 Fibre Optic Systems Deploy fibre optic systems for use throughout new systems and as an add on where possible for existing systems.

8.5.2 Head end design



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Solutions that could be deployed to follow; develop and install new:

compact filters for both the antenna and amplifiers, preferably channelized with steep sides

housings for both existing and new equipment which will provide maximum shielding from interference

innovative antenna designs which minimise any but the wanted direction and channels

cable designs to maximise immunity

8.5.3 Distribution amplifiers Solutions that could be deployed to follow; develop and install new:

multiple compact filters with tuneable pass bands

housings for both existing and new equipment which will provide maximum shielding from interference

Interference proof connectors, possibly using fibre optics

8.5.4 Domestic Premises and CPE

Solutions that could be deployed to follow; develop and install new:

develop much better immunity both for the overall equipment casing and receiver performance

fibre connections for all CPE (interconnecting various devices such as recorders and hard disk units), perhaps as an add on for existing equipment

immune cable or fibre optic (perhaps with plastic fibre)

Pilot Tone - A tracking low level pilot tone transmitter attached to each piece of CPE would serve a number of purposes - Cause the ECN terminal unit to avoid that frequency when communicating - Provide sufficient level of RF power to be detected by white space devices

8.6 Recommended Communal Antenna tests for trial test bed

To follow is the recommended tests where equipment and cabling can be tested against radiated and conducted interference from 800MHz LTE systems:

a) Evaluate real base station LTE signal using the proposed licence conditions and plot the actual out of band and any other spurious energy

b) Same as a), but for terminal units c) Same as a), but fixed mobile units d) Use the results from a) to c) to generate radiated signals at 3m to identify:

- actual radiated immunity / interference to existing coax cables - actual radiated immunity / interference to all components of a

communal antenna system including the satellite sections - Actual efficiency/performance / interference to mitigation filtering



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9 Applications above 862 MHz - Short Range Devices The 863 – 870 MHz band is allocated on a harmonised basis throughout Europe for use by licensed-exempt Short Range Devices (SRDs). As this band lies just above the mobile transmit sub-band part of the 800 MHz digital dividend spectrum, there will be potential for interference to arise from mobile terminals into SRDs in the adjacent band. The SRD band is sub-divided into three application-specific sub-bands, which are illustrated below. The entire band may also be used by generic SRDs which may include conventional narrow band systems or wideband systems using spread spectrum technology.

Figure 14 863MHz to 870MHz Spectrum usage

Although licensed-exempt SRDs are expected to operate in a non-protected interference environment and many devices incorporate interference mitigation techniques such as very short duty cycles or “listen before transmit” protocols, existing standards reflect the current relatively benign adjacent band interference environment, with high power TV transmitters at fixed locations and a limited number of PMSE deployments. Operation of mobile terminals in close proximity to SRD receivers may lead to interference or blocking in some scenarios, particularly at the lower end of the SRD band. Common SRD uses include:

Wireless headphones for consumer markets. These will commonly be plugged into the headphone outlet of televisions, radios, Hi-Fi systems, games consoles and similar devices;

Consumer radio microphones, used with karaoke systems, camcorders and similar devices;

Radio microphones for semi-professional markets;

Radio microphones for professional markets;

Portable wireless microphone and receiver for professional markets;

Butt transmitters, these are plug-on units for existing audio microphones;

In Ear Monitoring systems (IEM) enable performers to hear the combined audio output of other musicians or singers;

Tour guide systems. These systems allow a tour guide to provide a commentary on the subject of the tour. In some cases there will be more than one frequency in use to allow additional languages to be used; A voice quality 7 kHz audio bandwidth is common in these devices;

Baby Alarms consisting of a sensitive microphone in the vicinity of a baby with the receiver adjacent to parents or other adults.



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These devices may use FM or digital modulation with an output power below 10mW. The receivers are capable of receiving signals in the 863-865MHz band. Ofcom has commissioned two studies to ascertain the extent of SRD deployment in the 863 – 870 MHz band in the UK and to assess the immunity of SRDs to interference from mobile terminals below 862 MHz. On the basis of these studies Ofcom has concluded that in general SRDs in this band are unlikely to suffer any significant increase in interference as a result of the deployment of mobile services in the 790-862 MHz band. In the specific case of social alarms, given the safety critical nature of these devices, Ofcom has commissioned further work to ascertain whether specific mitigation measures may be required. A separate study is also investigating the potential impact of mobile terminals on systems operated by the emergency services in the 862 – 863 MHz band. The potential for interference to licensed PMSE operations in channels below 790 MHz also requires investigation.

9.1 863MHz-865MHz testing (Copsey Communications) A variety of six professional, semi-professional and consumer devices operating in the license-exempt frequency band 863-865MHz conforming to the harmonised standards EN 301 357 or EN 300 422 were tested by Copsey Communications for susceptibility to a 10MHz bandwidth LTE signal transmitting from 700MHz to 862MHz emulating both the base station and terminal unit:

50% of devices were adversely affected by a 10MHz wide signal at 857MHz (this is the highest centre frequency for a 10MHz wide terminal unit);

A third of devices were susceptible to LTE transmissions below 830MHz;

One device out of six was susceptible to LTE transmissions below 779MHz.

Terminal units can use up to 316mW (ECC Decision (09)03 and draft EC Decision). Those devices susceptible to interference on the highest planned LTE terminal unit channel, centred at 857MHz, will start to show interference at powers above 0.15mW ERP (LTE signal transmitted from a 3m distance). This is a conservative figure with the cordless audio transmitter and receiver within 1.5m of each other, whereas normal operating conditions for the cordless audio equipment would probably be in the range 3-5m. One unit also showed interference from the base station transmit frequencies, which could well affect a large percentage of existing cordless headphone users.



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In addition whilst the base station out-of-band emissions are stringent at -49.5dBm EIRP, there is the possibility of interference from base stations under some circumstances, especially with the older cordless audio and baby alarm systems. The figure below reproduced by kind permission of Ofcom and Copsey Communications provides a graphic view of the energy dispersion over the band; this is obtained from the block edge mask contained in CEPT Report 30.

Figure 15 excerpt from presentation “MFCN base station emission limits for different

800 MHz licensees”, UK Ofcom.

The objective was to determine if Mobile Networks operating in the reallocated band 790-862MHz using LTE modulation will cause interference to incumbent devices transmitting and receiving in the 863-865MHz band. LTE modulation schemes are likely to include data dongles which may well be in close proximity to domestic equipment. As the cordless audio devices consists of two parts (a transmitter that broadcasts to a receiver or receivers in the vicinity), it was necessary for both components to be operating normally in the presence of an interfering signal in the 790-862MHz band to determine if there is potential for interference to the transmitter and/or the receiver. Various tests have been carried out within Europe and LTE terminal units have been shown to cause interference up to 4m away, this means that terminal units in adjacent flats or rooms may well generate interference into domestic setups. As these devices migrate into „Mobile phones‟ the possibility of these being in close proximity to radio microphones or even on the user of the cordless audio device will increase.

9.2 863MHz – 865MHz test set up and results The cordless audio devices were set up in an anechoic chamber at a 3m separation distance from the interferer antenna. Initially the cordless audio transmitter was located centrally and held stationary whilst the output of the receive unit was monitored as it was being moved around in proximity to the cordless audio transmitter. The locations



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were exchanged, and testing repeated. Moving the cordless audio units enables the impact of any nulls or peaks in the transmit power of both the LTE and cordless audio signals to be overcome. The devices were either mains-powered or powered by fully-charged or new batteries. A 1kHz audio tone was supplied to the transmit device, and the output of the receive device monitored on headphones in every case. The interferer was a 316mW ERP LTE signal transmitted in a 10MHz bandwidth, using a Frequency Division Duplex scheme. The characteristics of the signal are contained in Table below.

Table 7- LTE modulation parameters

Radio format

Bandwidth Standard rev Access

technique Modulation Waveform name

FDD Uplink 10MHz 2008-09 SC-FDMA Full-filled QPSK LTE_FDD_UL_10

Signal generator

RF amplifier

3 metres

1.5 metres

Bilog antenna

Cable

3

Cable 6

Control room Chamber

Receive

Transmit

Test support

Movement of receive unit

Figure 16 Test environment and arrangement of equipment



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The following results, were obtained from 4th-12th May 2010.

Table 8 - Cordless Audio devices (863-865 MHz). Susceptibility to LTE operating from 700 – 857MHz.

LTE generator centre frequency (1MHz steps) F

M W

ire

les

s h

ead

ph

on

es

Se

mi-

pro

fes

sio

na

l ra

dio

mic

rop

ho

ne

Pro

fes

sio

na

l ra

dio

mic

rop

ho

ne

sys

tem

1

Pro

fes

sio

na

l ra

dio

mic

rop

ho

ne

sys

tem

2

Pro

fes

sio

na

l p

ort

ab

le w

ire

less

mic

rop

ho

ne a

nd

rec

eiv

er

To

ur

gu

ide

sy

ste

m

700-769

770-779 *

780-789 **

790-799 **

800-809 **

810-819 *

820-829 * *

830-839 ** **

840-849 ** *

850-856 ** **

857 - highest potential 10MHz LTE Centre

Frequency ** ** ***

Key:

* Mild LTE noise present ** Moderate LTE noise present

*** Strong LTE noise present



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Three of the six devices tested where susceptible to signals radiated within the proposed 790-862MHz band. ECC Decision 09/03 provides for a terminal unit power of 23dBm +/- 2dB. For the purposes of testing a 25dBm signal has been used and stepped down where interference was observed, in an attempt to discern the power boundary where interference ceases. Table below shows the signal levels where interference to the cordless audio equipment starts to be observed.

Table 9 - maximum 10MHz bandwidth LTE signal power

Radiated power

(ERP, dBm) Radiated power

(ERP, mW)

FM Wireless headphones 13.96 24.88

Semi-professional radio microphone 15.3 33.88 Professional radio microphone system 1 -8.14 0.15

9.3 863MHz-865MHz test conclusions System susceptibility varied dependant on the physical location of the receiver relative to both the interfering transmission antenna and the cordless audio transmitter: nulls and peaks were detected during lateral movement around the 3m separation point, which in most cases had a reasonable or dramatic effect on the scale of the interference. Where the operating frequency could be selected, 861.3MHz was set as the frequency of transmission/reception for the cordless audio unit. Where selection could not be made, transmission was within the 863-865MHz band. A 10MHz bandwidth LTE signal with a centre frequency of 857MHz will occupy the range 852-862MHz. When listening to audio over a system any noise or interference is unacceptable. Where a radio microphone is in use, any interference will ruin a production or cause the audio amplification to overload with possible harm to the audience.

9.4 Recommended tests for trial test bed The tests detailed above clearly show that there is significant potential for interference between LTE in the 800MHz band and SRD‟s. Tests need to be conducted in real life scenarios to accurately replicate the possible interference modes. No attempt has yet



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been made to model the situation where more than one UE is present in the vicinity of the SRD, as they may well be in the domestic environment.

For example, in practice cordless headphones are mostly, but not exclusively, used by the elderly or hearing impaired whilst watching television. Usually this is to allow one or more persons to listen at a higher sound volume than the other viewers in the room who are listening via the loudspeakers. A realistic scenario therefore is that there may be one or more LTE UE devices within as little as 0.5m of the wireless headphone receiver that is on the users head since it is quite reasonable to expect that the user of the headphones may themselves have a mobile phone as well as every other person in the room. The transmitter for the cordless headphones will normally be located adjacent to the TV, usually some 2 or 3 metres from the viewers. The LTE UE devices will be indoors and quite possibly close to the body, in pockets, where signal strength will be degraded by building penetration and also potentially by body absorption. Body absorption alone at 800MHz frequencies can easily account for 20dB of signal loss. Hence the LTE devices could be operating at or near maximum power.

The assumptions regarding the likely EIRP of LTE 800 UE equipment in the domestic environment need to be further investigated since the assumption that UE devices will not be operating at or near their maximum EIRP seems to be key to the Ofcom conclusion that in general SRDs in this band are unlikely to suffer any significant increase in interference as a result of the deployment of mobile services in the 790-862 MHz band. The various protection distances for SRD‟s referred to in the Aegis /ERA report are large (e.g. 49.7m or 24.4m6) in comparison to the average domestic living room and normal TV viewing distances, so even with the LTE UE operating at lower powers the risk of interference would seem to be very real at normal domestic environment distances. In multiple occupancy premises such as flats, care homes, halls of residence, hospitals, etc. the interfering UE devices may be in an adjacent room or even property yet very close physically to the SRD. In this situation the victim has no control over the interference source and is in no position to take evasive action such as re-locating the offending device even if they are aware of the cause of the interference.

Tests are required to determine what possibilities exist, if any, for interference mitigation in existing SRD‟s in real world conditions. These tests should include simultaneous use of multiple LTE 800 devices at real world proximity to the SRDs and with the LTE 800 devices operating at various base station field strengths to replicate the effect of higher and lower mobile and base transmit powers. It is necessary to establish the safe LTE

6 Ofcom commissioned studies on potential SRD interference

Ofcom study 1 ERA Technology http://stakeholders.ofcom.org.uk/binaries/consultations/tlc/annexes/SRD-Study.pdf

Ofcom study 2 Aegis Spectrum Engineering http://stakeholders.ofcom.org.uk/binaries/consultations/tlc/annexes/Final_report.pdf

http://stakeholders.ofcom.org.uk/binaries/consultations/tlc/annexes/SRD-Study.pdf

http://stakeholders.ofcom.org.uk/binaries/consultations/tlc/annexes/Final_report.pdf



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800MHz mobile transmit power level in the domestic environment, where various types of SRDs are in use. To follow is the recommended tests where equipment and cabling can be tested against radiated and conducted interference from 800MHz LTE systems:

a) Evaluate real LTE terminal CPE signal using the proposed licence conditions and plot the actual out of band and any other spurious energy

b) Same as a), but for terminal units c) Same as a), but fixed mobile units d) Use the results from a) to c) to generate radiated signals at 3m to identify:

- actual radiated immunity / interference to Wireless Audio devices - actual radiated immunity / interference to RFID devices - actual radiated immunity / interference to Social alarms

10 PMSE 470-790MHz Programme Making and Special Events (PMSE) use the 470MHz to 790MHz band where professional PMSE users share with Analogue and Digital TV on a secondary basis. Use of the UHF spectrum by PMSE is not confined to the UK and similar activity can be found in most parts of the world, though the levels of formality and regulation vary widely. Hence there is a global market for many forms of PMSE wireless. In international spectrum regulatory circles the terms Services Ancillary to Broadcasting (SAB) and Services Ancillary to Production (SAP) are more commonly used to refer to the types of radio services in question. In the UK this use has been managed and licensed by various means over the last three decades. Instances of interference to UHF TV reception, analogue or digital, from PMSE, although a theoretical possibility, are unheard of. Since 1997 a contracted agent, JFMG Ltd.7, who receive licence fees and issue licences to individuals and organisations on behalf of Ofcom, has managed the PMSE sectors use of the radio spectrum in the UK. The technology used by the PMSE industry is almost entirely low powered (10 – 50mW ERP) wide band FM. Equipment development has historically focused mainly on improving performance and reliability as well as on reducing the size, weight and power consumption of portable devices.

10.1 PMSE Interference PMSE receivers do not automatically suffer the N+9 problem as there are many and various receiver architectures with different IF's, but otherwise the interference scenarios described in Section 6 which apply to DTT being the potential victim of interference from 800MHz LTE also apply to PMSE operating in the bands up to

7 JFMG Ltd, http://www.jfmg.co.uk/pages/about/about.htm

http://www.jfmg.co.uk/pages/about/about.htm



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790MHz. The effects of interference to PMSE can of course be far wider reaching than interference to an individual TV or even communal aerial system since it potentially affects the whole audience, which could be worldwide.

10.2 Recommended PMSE tests for trial test bed

PMSE in 470MHz to 790MHz needs a set of tests similar to those for DTT and SRD devices described in sections 6.4 and 8.6. To follow is the recommended tests where equipment and cabling can be tested against radiated and conducted interference from 800MHz LTE systems:

a) Evaluate real base station LTE signal using the proposed licence conditions and plot the actual out of band and any other spurious energy.

b) Use the results from a) to generate radiated signals at a defined distance to identify potential area around a base station site where PMSE devices could suffer interference.

11 Conclusions and recommendations A combination of the techniques discussed in this paper are likely to be essential for optimising LTE 800MHz mobile coverage and capacity whilst not interfering with existing services such as Cable, PMSE, DTT and SRD‟s It must also be noted that poor RF performance in the end user equipment increases the demand for spectrum and radio network density. Recent studies have shown a large variation in radio performance for user equipment and in recognition of this challenge the ICT KTN Wireless Technology and Spectrum group voted this as a 2011 priority to address the longer term R&D challenges to improve radio front end technology. The working group is working closely with a newly formed Cambridge Wireless Radio Technology SIG8 to address this challenge and will be hosting a series of events and workshops to address this topic. The Ofcom consultation on 800MHz interference and co-existences challenge has created a big debate on the actual levels that could be experienced and who solves this, when interference occurs. The technical assumptions used, have predominately been derived from simulation and modelling and a minor adjustment of a variable can make a large impact to the population or households that could be impacted. Getting agreement across multiple stakeholders of what the real model variables should be is very difficult to do and therefore it is strongly recommended that an appropriate test bed be made available for such innovation to thrive, understand the real interference and for industry to further develop techniques to manage such interference issues.

8 Cambridge Wireless Radio Technology SIG http://cambridgewireless.co.uk/sigs/radiotechnology/

http://cambridgewireless.co.uk/sigs/radiotechnology/



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Wireless technology development is a major opportunity for the UK to lead the way globally in deployment, technology innovation, policy and regulation. The key to unlocking this potential is collaboration at all levels. If this can be achieved we will be able to realise significant societal benefits whilst enabling our industry to benefit across the whole of the value chain. The concepts provided in this document can significantly help the deployment wireless services and increased capacity in high density areas within the UK and also help UK companies to trial and test concepts to enable global exploitation. The ICT KTN Wireless Technology and Spectrum working group believe we can act as the catalyst for this collaboration and is keen to take this to the next phase. The diagram below demonstrates how the UK eco-system could provide a more holistic joined up strategy to maximise the benefit for the UK.

Driving Innovation

Funding R&D to solve the major challenges

Feasibility R&D to ensure

technology can meet market, spectrum and

economic challenges

Policy and Regulation

Flexibility to implement R&D

trials

Innovation, collaboration

and knowledge transfer

Identifying & prioritising challenges

INDUSTRY

Wireless

Technology &

Spectrum

working group

Spectrum,

policy &

regulation

Global

exploitation

Figure 17 Maximising wireless opportunities through Government & Industry collaboration



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Wireless technology development, within the Digital Dividend Spectrum, is a major opportunity for the UK to lead the way globally in deployment, technology innovation, policy and regulation. The key to unlocking this potential is collaboration at all levels. If this can be achieved we will be able to realise significant societal benefits whilst enabling our industry to benefit across the whole of the value chain. The ICT KTN Wireless Technology and Spectrum working group believe we can act the catalyst for this collaboration and is keen to take this to the next phase. This document has highlighted some major opportunities for industry to address by solving the issues through technological innovation. To further enhance this eco-system we believe a more holistic UK approach is required involving not only industry but also Ofcom, DCMS, BIS and the Technology Strategy Board. To help focus the request to OFCOM, DCMS, BIS and the Technology Strategy Board a table of key priorities is listed below. The output of the ICT KTN working group is biased towards innovation and technology challenges and therefore this should be read as opportunities for innovation and best use of spectrum from a technical perspective.

Table 10 - Ofcom, DCMS, BIS & TSB recommendations

Ofcom BIS / DCMS Technology Strategy Board

Interaction issues require further investigation. DTT, Cable, PMSE, Mobile and SRDs. Public safety spectrum to be included if decision is made to use this spectrum. Support collaborative R&D Trials

Receiver conformance / design – how to ensure future compliance of receiver air interface requirements. R&TTE and EMC directives - need to be reviewed: Box level, Transmission over the air and through cables. Enable regulatory environment for RFI immunity. Public safety spectrum: regulatory framework for infrastructure sharing? Flexible regulatory environment to enable trials

Advanced Filter and RF switching technologies. Practical Cognitive radio techniques. Co-existence and interference challenges / network topologies Radio planning tools and dynamic radio management Antenna technologies Disruptive RF Front End Technologies

Cost considerations are taken into account relating to design, equipment and a technology perspective. The working group is not working on economic and service values, relating to wireless and spectrum. The objective of the working group is to focus on technology and innovation for other interested parties to use the information.



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The information provided in this document has been worked on by the ICT KTN Wireless Technology and Spectrum working group to prioritise the areas we wish to work in collaboration with Industry, Academia Technology Strategy Board, DCMS, BIS and Ofcom. Figure 17, Collaboration enabling UK Wireless Innovation, is critical to achieving the maximum benefit for the UK and the ICT KTN would welcome hosting meetings to see how this could be achieved with Ofcom, DCMS, BIS and Technology Strategy Board. We would also welcome new members to the working group who could strengthen this eco-system and potentially address some of the innovation challenges described in this paper.

Documents

800MHz Interference and Co-existence - Copy