The Feasibility of Introducing Digital ENGOB Video Links

7/29/2019 The Feasibility of Introducing Digital ENGOB Video Links

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The feasibility of introducing digital

ENG/OB video links

A study by The Smith Group

for the Radiocommunications Agency


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List of contents

2

List of abbreviations...................................................5

1 Introduction............................................................5

1 Introduction............................................................5

List of abbreviations...................................................6

1 Introduction.............................................................7

1.1 General................................................................................7

1.2 Background..........................................................................7

1 Introduction............................................................81.3 Study objectives and methodology......................................8

1.4 About this document............................................................9

2 User requirements..................................................10

2.1 Introduction........................................................................10

3 Products survey....................................................10

2.2 Qualitative issues ..............................................................10

3 Products survey....................................................10

2 User requirements.................................................122.3 Temporary point-to-point links...........................................13

2.4 Mobile video links..............................................................15

2.5 Radio cameras...................................................................16

3 000Products survey................................................17

3.1 Introduction........................................................................17

4 Modulation schemes..............................................17


3 Products survey....................................................18

3.2 Video coders......................................................................19

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3.3 Transmitters.......................................................................22

3.4 Receivers...........................................................................24

3.5 Digital fixed links...............................................................25

3.6 Conclusions........................................................................26

4 000Modulation schemes.........................................27

4.1 Introduction........................................................................27

6 Migration strategy.................................................27

4.2 Options for modulation scheme.........................................27



4.3 The radio environment and its implications on choice of

modulation scheme.....................................................30

4.4 Conclusions........................................................................32

5 000The band plan and sharing arrangements..........35

5.1 Introduction........................................................................35

A References............................................................35

5.2 Frequencies and channelisation.........................................35

A References............................................................35


5.3 Sharing arrangements and pressure on existing spectrum

.....................................................................................38

5.4 Other sharing options........................................................435.5 References for sharing properties and protection ratios....44

6 Migration strategy..................................................45

6.1 Introduction........................................................................45

6.2 Pressures for change..........................................................46

6.3 Making space for digital.....................................................48

6.4 Conclusion..........................................................................49

A References.............................................................50

A.1 Introduction ......................................................................50

A.2 Documents and articles.....................................................50

3


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A References............................................................51

A.3 Contacts.............................................................................51

4


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ASIC Application Specific Integrated Circuit

BBC British Broadcasting Corporation

BPSK Binary Phase Shift Keying

BSS Broadcast Satellite Service

BT British Telecom

(C)OFDM (Coded) Orthogonal Frequency Division Multiplex

DAB Digital Audio Broadcasting

DSP Digital Signal Processing

DVB Digital Video Broadcasting

FM Frequency Modulation

FSK Frequency Shift Keying

ENG Electronic News Gathering

FSS Fixed Satellite Service

GPS Global Positioning System

ITN Independent Television News

ITU International Telecommunications Union

List of abbreviations

1 Introduction1 Introduction


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JFMG JFMG Ltd

kbps kilo bits per second

Mbps Mega bits per second

MMDS Multi-point Microwave Distribution System

MPEG Moving Pictures Expert Group

Msps Mega symbols per second

MSS Mobile Satellite Service

MVDS Multi-point Video Distribution System

OB Outside Broadcast

PAL Phased Alternate Line

QAM Quadrature Amplitude Modulation

QPSK Quadrature Phase Shift Keying

RA Radiocommunications Agency

RF Radio Frequency

SAB Services Ancillary to Broadcasting

SNG Satellite News Gathering

UMTS Universal Mobile Telecommunications Service

WRC World Radio Conference

List of abbreviations


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7

1.1 General

1.1.1 This document has been prepared by The Smith Group Limited (Smith) for

the Radiocommunications Agency (RA), to investigate the technical

feasibility of the introduction of digital electronic news gathering (ENG) and

outside broadcast (OB) video links and to propose a migration plan for their

introduction.

1.1.2 This document represents the final report of the study.

1.2 Background

1.2.1 Analogue FM video links are currently used to transfer pictures from outside

broadcast locations back to television studios. Such links occupy significant

amounts of spectrum and, with the advent of digital techniques which can

reduce the bit rate required to transmit a video picture, the RA is seeking to

investigate the possibilities for the digitisation of these links.

1.2.2 With the explosion in the number of television channels that is taking place

through the introduction of digital television, there is an increasing demand

for ENG/OB spectrum to enable more programmes to be made and it would

therefore be of great benefit if digital techniques could be used to increase

the number of video links that share the available spectrum.

1.2.3 There are also pressures on the spectrum used for ENG/OB links from other

users and, within 4 years, the introduction of UMTS will, potentially, further

restrict the spectrum available.

1.2.4 Digital techniques which allow video signals to be transmitted at low bit

rates typically add delay into the transmission path and, in extreme cases,

can lead to deterioration the picture quality. Whilst the drive for lower

occupied bandwidths is important, it must be balanced against the need for

high quality pictures and, where important, low delay transmission paths.

7

1 Introduction


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1.2.5 In order to give ENG/OB link users the confidence to invest in new digital

technology, it will be necessary to ensure that spectrum can be made

available to them. Whilst it may be possible to share spectrum between

digital and analogue links, the creation of specifically designated digital link

bands would be more likely to increase the uptake of the new technology.

1.3 Study objectives and methodology

1.3.1 The study has set out to meet several objectives, namely:

0to determine users requirements for digital links and to determine any

parameters within users qualitative requirements which may place

limitations on the suitability of certain types of link;

1to determine the technical feasibility of a move to digital ENG/OB video

links;

2to examine the equipment available on the market to determine when

such a change is possible;

3to propose a revised band plan and a migration path from existing

analogue to digital links.

1.3.2 In order to meet these objectives, we have undertaken a

number of interviews with users and with manufacturers. Details of those

contacted can be found in Appendix A as can a list of documents and

articles relating to the topics examined in this report.

1.3.3 The issue of the technical feasibility of a move to digital

ENG/OB video links would at face value seem to revolve around the possible

modulation schemes and other technical implementation issues. However,

given the cost of equipment and the limited amount of such equipment

available on the market, the issues concerning implementation are more to

do with allowing a sufficient flexible approach to spectrum allocation and

bandplanning to encourage the uptake of digital systems.

1 Introduction


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1.4 About this document

1.4.1 In section 2 we present the results of our discussions with

users. Here we analyse what links are used for and what users require from

their links. This enables us to divide links into three categories and for each

category identify the important properties required of the links.

1.4.2 In section 3 we look at the equipment currently available on

the market for each of the components of a video link system, considering

its capabilities, cost, and size, and power consumption. This enables us to

assess the feasibility of using the different technologies in the different

applications.

1.4.3 In section 4 we take a closer look at the different modulation

schemes currently available, considering the bit rates which are possible

and their resistance to various forms of interference.

1.4.4 In section 5 we consider the bands used for ENG/OB

applications and possibilities for sharing within these bands.

1.4.5 In section 6 we propose a plan for the introduction of digital

links with a suggested band plan and migration path.

1.4.6 Appendix A contains a list of useful references and contacts.

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2.1 Introduction

2.1.1 This section sets out the applications to which radio based video links are

put and examines the physical and operational characteristics of the

equipment used and the technical and qualitative requirements placed on

the links.

2.1.2 There are three basic uses for radio based video links are put, each with its

own distinct characteristics. These three uses are:

4temporary point-to-point links;

5mobile (and portable) video links;

6radio-cameras.

2.1.3 Each of these applications is described in more detail later in

this section, but we begin with a consideration of the qualitative issues

concerning video links.

2.2 Qualitative issues

2.2.1 In discussion with the users of video links, it has become clear

that when comparing video links there are three main qualitative issues

which need to be addressed:

2 User requirements

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7Picture quality (resolution): Digital picture quality does not just depend

on the sampling resolution. Existing analogue links offer (in most

instances) sufficient bandwidth and signal to noise to faithfully reproduce

the 5.5 MHz bandwidth of a PAL television picture. In digital terms, such

a picture can be reproduced using a data stream requiring a bit rate of

270 Mbps. In order to reduce this to a realistic rate for transmission overradio links, various video compression (coding) techniques are used.

Generally these exploit spatial and temporal similarities in the signal,

and an understanding of what visual information cannot be seen by the

eye and therefore does not need to be transmitted. The result is a signal

which in principle contains less information than the video source. With

high levels of compression this loss of information can be visible to the

viewer (artefacts such as ringing and blockiness are typical): ie there is a

perceived (as well as actual) loss of picture quality. One other

mechanism for reducing the required bit rate is to reduce the resolution.

This is used in some of the higher compression ratio 1 digital coders, with

corresponding effects on the picture quality.

Because of the nature of what is being transmitted, the bit rate required

to achieve acceptable picture quality depends upon the application, with

sports events requiring the highest (because all forms of compression

exploit similarities between successive frames and so perform better

with static or slow-moving scenes than with fast action) and news

footage (especially that of a presenter stood talking against a stationary

background) the lowest. Satellite news gathering uses compressed video

at 8 Mbps and it is understood that, for outside broadcasts, digital links

at 34 Mbps are being used. The BBC also informed us that for very

remote locations they operated store and forward systems which codedvideo at 2 Mbps and were considering the use of video conferencing

systems which can operate at only 64 kbps.

1

The compression ratio is the ratio of the original bit rate to the encoded bit rate. Forexample, compressing a 270 Mbps video signal into 8 Mbps uses a compression ratio of

270:8 or, as is more usually written, 33:1.

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8Delay: A terrestrial analogue video link produces virtually no end-to-end

delay. A satellite link produces typically a 250 millisecond (ms) end-to-

end delay. Digital video coders can add an additional delay from

anywhere between 100 and 300 ms. Given the increasing move towards

satellite news gathering, broadcasters are getting to grips with ways of

circumventing the problem of delayed video, often using zero delay (ietelephone based) voice links to allow the studio based presenter to chat

with the remote presenter and thereby cutting out the bi-directional

delay on the conversation that would otherwise exist. Given that such

techniques are already being developed and that digital satellite links

having delays of over 350 ms are already being used, we can see no

reason why the delay imposed by a terrestrial digital video link would

cause additional problems for broadcasters.

9Link quality and signal degradation: The question here is whether the

digital link is robust enough to provide a signal in all situations where an

analogue link can get through. For some applications, notably fast-moving radio cameras, the quality of the link is far less important than

the existence of a picture of some sort. Analogue links have the property

that in many very far from ideal conditions a picture of some sort does

get through. Users are concerned that in situations where the radio path

is deteriorating, a digital link, though it might provide high quality

pictures for longer than an analogue link would, would go down

completely in situations where the analogue link would still be getting

through.

A related concern raised with respect to the use of digital video links was

the effect of signal degradation. Both producers and mobile cameraoperators like to be aware of the quality of pictures coming through the

link (for cameramen this is often provided using a return link to the

mobile camera). With an analogue link, if the signal begins to fade, this

becomes immediately visible in the recovered video and the producer

can make a decision as to whether to cut to another picture source. With

a digital link, the picture is likely to freeze (or disappear) without any

warning as the signal will either be there or not. This lack of warning of

an impending loss of signal was seen as a potential problem in the

production of live programming. With the provision of bit error rate

meters and signal strength meters, we do not believe this need be a

serious difficulty; however manufacturers should be aware of the need to

incorporate mechanisms for feedback of this kind.

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2.2.2 All these issues apply when considering digital links designed

to replace analogue links. However, most if not all of these problems can be

overcome in the digital environment and often more beneficially so than for

their analogue counterpart. There is no reason, therefore, to believe that a

move to digital would adversely affect the quality of video produced nor

impact the ability of programme makers to make decisions as to camerashots.

2.3 Temporary point-to-point links

2.3.1 Temporary point-to-point l inks are used to transmit video

pictures from a (typically live) event back to a studio facility for inclusion in

a programme. Such links fall into two categories, planned and unplanned.

Planned links take place for events which are known about in advance such

as a sports event or a concert. Unplanned links are required for short notice

applications, typically for news gathering.

2.3.2 From conversations with news organisations such as ITN and

BBC, the use of terrestrial links for unplanned events is diminishing and

being replaced with the use of satellite news gathering (SNG). This is for a

number of reasons, including:

10there is no necessity for a network of (expensive) ground based receivers

to be maintained;

11setting up a satellite link is simpler, faster and less labour intensive than

an equivalent terrestrial link;

12the cost of satellite space and uplink equipment is on a par with

terrestrial equivalents;

13a satellite uplink can be established almost anywhere and does not need

to be in range of ground based facilities.

2.3.3 These benefits are so great to news broadcasters that they

have already almost exclusively moved to SNG and have only a very small

number of terrestrial ENG vehicles left. A move to digital ENG is not likely to

affect this change away from satellite.

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2.3.4 For other applications, there are moves away from terrestrial

links as more and more venues are fitted with fibre-optic cable. BT estimate

that any venue which is used (for television broadcasts) more than 4 to 5

times per year is now so equipped and that it is only economical to provide

other types of terrestrial links to smaller, less frequently used venues.

2.3.5 The main exception to this general trend away from the use

of terrestrial video links is for planned events that are concentrated in an

area which can be covered using only a small number of receive sites, for

example central London and other dense urban areas. In these areas the

urban canyons created by tall buildings often obscure a line of sight path to

or from a given satellite and only a terrestrial link is possible.

2.3.6 Overall, we see a move away from the use of terrestrial

circuits for point-to-point video links, except in urban areas and for planned

events which occur infrequently in any given location. In this latter case, the

BBC told us that if more than a single microwave hop is required it quicklybecomes more economical to use satellites.

2.3.7 Qualitatively, these types of link can be used for a variety of

purposes including sports events and as they are typically inserted into live

programmes or are live broadcasts in their own right, quality is important.

The use of at least 8, if not 34 Mbps, would be suitable.

2.3.8 Users supplying footage from a particular event into several

different programmes would be interested in multiplexing more than one

video channel down a link if it were possible.

2.3.9 From a frequency point of view, almost any of the available

bands would be suitable with the possible exception of 24 and 48 GHz which

only offer a limited hop distance. Currently, bands used by major users

include 2.5 GHz, 5 GHz, 7 GHz and 12 GHz .

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2.4 Mobile video links

2.4.1 We have defined mobile video links to be those where a

camera is mounted on a moving (land or air based) vehicle. Where links

from land based mobile cameras are relayed to a ground based receive site

via an air based vehicle (eg a helicopter) we place both links into this

category.

2.4.2 These types of link are the most arduous from a radio

perspective. The use of microwave frequencies which require a strict line of

sight and where multi-path reflections can be severe entail careful antenna

placement and often require transmit and receive antennas to track each

other to ensure a good signal is received. Systems which rely on GPS

positioning information to automatically steer antennas are becoming more

commonplace in an attempt to overcome this latter difficulty. Resilience to

multi-path interference is of great significance in this area and certain users

may be willing to pay a large premium for digital links if they perform wellin this area.

2.4.3 There are no real alternatives to the use of radio for these

applications. The major advantage which the use of radio based links has

over and above other possible communication media is that of mobility. We

therefore see a continued demand for this type of radio based link and

possibly an increase as the demand for the type of programming which uses

them likewise increases.

2.4.4 The required quality of the video link depends critically on its

exact application but is typically lower than would be required for a point topoint link. Whilst 8 Mbps or possibly less would be sufficient for many

applications, in considering the options for the digitisation of these types of

links we need to allow for much greater bandwidths in certain

circumstances.

2.4.5 From a frequency point of view, there are distinct advantages

to operating in the lower of the available bands (2.5 and 3.5 GHz). Better

propagation characteristics across non line of sight paths and improved

performance in light of multi-path reflections are distinct benefits for these

types of application.

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2.5 Radio cameras

2.5.1 We have defined radio cameras to include those where the

camera is truly portable (ie is carried by an individual) and also situations

where short radio links (typically a couple of hundred metres) are used

instead of a wired connection, such as for rostrum cameras at race courses,

purely on the basis of cost and simplicity. In both instances, the distance of

the link is very small (compared to the other two instances).

2.5.2 Directional and, where necessary, tracking receive antennas

are used but directional transmit antennas are less common, especially

where a single operator carries both the camera and the transmitter. In

many instances of the use of radio cameras there are wired alternatives

available, though in some circumstances (for example in the pits at a

Formula 1 race) wires trailing across the ground could prove a safety

hazard.

2.5.3 We foresee a continued demand for the use of radio for these

types of applications unless a point is reached whereby alternative, wired or

otherwise (such as infra-red or using THz 2 technology), solutions become

more cost effective. Cost is an important factor in determining demand but

given the nature of these types of application, the size and power

consumption of the video link equipment is also important.

2.5.4 Again, the required quality of the link depends on the

application but typically sits somewhere in the range between that required

of a mobile link and that required of a point to point link. From a frequency

point of view, almost any of the available bands is suitable. For portablecameras, there may be limitations on the upper frequency, especially if the

link has to travel any great distance in a harsh multi-path environment. For

rostrum cameras, these limitations are less of a problem and, indeed, the

use of the higher frequencies (24 and 48 GHz) are distinct possibilities.

2 Radio technology using frequencies around 1500 to 2500 GHz (1.5 to 2.5 THz) is being

developed which has properties similar to that of visible light.

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3.1 Introduction

3.1.1 This section explores the equipment currently available on the market that

can support digital ENG/OB activities and looks ahead to what may become

available in the future.

3.1.2 The main areas with which we are concerned in examining available

equipment are video coding, error correction and modulation,

standardisation and any associated RF equipment such as frequency

converters.

C a m e r a A / D C o d e r M o d u l a t o r R a d i o

R F o u t

V i d e o D / A D e c o d e r D e m o dR a d i o

R e c e i v e r

R F i n

A B C D E

A ' B ' C ' D ' E '

Figure 0-1: Block diagram of a digital video link

3.1.3 The basic block structure of a digital ENG/OB system shown is in figure 3-1

above. As can be seen, there is a symmetrical structure to the two ends of

the link. The form taken by the signal as it moves between components is

shown in this table 3-1:

Stage Format

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A,A Analogue video and audio, 6 MHz bandwidth

B,B Raw digital video, 270 Mbps

C,C Coded digital video, 0.5-50 Mbps (typically 8

Mbps)

D,D IF (typically 70MHz) carrying modulated data

E,E Final RF output (470MHz 48GHz)

Table 0-1: Inputs/Outputs of a digital video link

3.1.4 The video output can be taken either after the digital-to-analogue converter

(point A) where the link is being used to replicate an analogue one or at

points B or C, where the source and sink are both digital. Where two links

are used back-to-back (ie up and down to a helicopter) the link betweentransmitter and receiver could be made a points D and D which would

purely relay the incoming RF signal or at points C and C after any error

correction to allow the link to attempt to regenerate any of the incoming

signal that has been corrupted.

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3.1.5 There are an increasing number of professional television cameras on the

market which have direct digital outputs. The DVBPro range from

manufacturers such as Sony have digital outputs at either 25 or 50 Mbps.

Using one of these cameras as a source, the digital transmission of the

picture is simplified as no coding would be required. Adding a digital

modulator (with in-built error correction) and transmitter to one of thesecameras would produce a very simple and effective digital transmission

system.

3.1.6 Editing and the transition to digital broadcasting create further problems,

since there is a serious loss of quality if a signal is passed through a video

coding stage more than once (known as tandem coding), as might be the

case if a signal was encoded to be transmitted from an OB to the studio,

decoded for editing, then re-encoded for digital transmission. This is

because the coding techniques remove from the picture, artefacts which are

not (or are only partially) visible to the human eye. Each time that this

process is repeated more gets taken away from the picture eventuallyreducing the remaining content to a point where the transmitted material is

badly corrupted. Tandem coding using different coding algorithms can make

matters worse or better depending upon the exact algorithm used. It is wise

to avoid tandem coding, especially at high compression ratios, as far as

possible. It is possible to edit the coded signal, but it is difficult and the

equipment is very expensive.

3.1.7 We now examine each of the building blocks required to make a digital

video link in turn in terms of the current availability and specification of

equipment, and the foreseeable trends in its development.

3.2 Video coders

3.2.1 Equipment covering a wide range of video coding compression techniques is

available on the market for both professional and domestic use. Even within

the professional environment, there is still a wide range of available

compression techniques and this presents the problem of compatibility.

Thankfully, link equipment does not seem to be shared a great deal

between broadcasters hence the problem of incompatibility of equipment is

less of a problem than may otherwise be the case. Also, it seems that only a

limited subset of the available standards are actually being used, thesebeing:

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14ETSI: Dating from 1992, the ETSI video coding standard was designed for

digital satellite news gathering applications of contribution quality. The

ETSI standard number is ETS 300 174. It is typically used to provide

encoded data at 8 Mbps; although the standard supports the range 7.5

Mbps to 45 Mbps. The BBC, ITN and many other organisations are

currently using this system (at 8 Mbps) for their SNG operations due toits low coding delay (typically 100 milliseconds). Currently only Thomson

manufacture coders to this standard. The ETSI compression algorithm, in

its Thomson implementation supports only 4:3 aspect ratio pictures.

15MPEG-1: The MPEG-1 standard (ISO/IEC 11172-1 to 11172-5) was

published between 1993 and 1994. It defines a low bit rate non-

interlaced encoding scheme, intended for CD-ROM applications. In

principle the maximum permitted bit rate is 1.86Mbps, though in

practice this restriction is often ignored, leading to a system which

performs adequately for non-interlaced media, in particular for film.

It should be noted that the two MPEG standards do not define a

coding algorithm, but merely the syntax of the coded data stream (and

consequently determine the effect of the decoding algorithm). This

leaves scope for proprietary innovation in the encoding algorithm, and

therefore two different MPEG systems running at the same bit rate may

well produce output of significantly different video quality.

16MPEG-2: The MPEG-2 standard (ISO/IEC 13818-1 to 13818-9) was

published in 1994 and 1995. It is designed for TV signals, both interlaced

and non-interlaced (progressive); it handles larger pictures at higher

resolution than MPEG-1. There is little improvement over MPEG-1 at thesame bit rate for certain non-interlaced applications, in particular film.

The primary application of MPEG-2 is all-digital transmission of broadcast

TV quality video at coded bit rates between 4 and 9 Mbps. There are

implementations down to 0.5 Mbps, and it has been found to be efficient

for higher bit rates and sample rates, eg for HDTV.

MPEG-2 was adopted by the DVB group. More specific guidelines

and restrictions on the use of the MPEG-2 standards were necessary, and

ETR 154 is the ETSI report containing guidelines on the use of MPEG-2

and restrictions on MPEG-2 parameters for use in DVB.

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We note here that MPEG coding can handle a variety of screen

formats, in particular the wide-screen 16:9 format which is becoming

more popular. Current analogue OB links cannot handle this format.

3.2.2 Other standards include:

17Motion-JPEG: is an adaptation of the JPEG code for compressing still

pictures. It codes each frame separately, which means it has much less

delay and is easy to edit, but it does not achieve a high enough

compression ratio.

18H.230, H.261 and H.263: these are videoconferencing formats

designed for small pictures and low bit rates. H.230 is designed to work

at up to 400 kbps; H.261 is designed to operate on ISDN lines at

multiples of 64 kbps; and H.263 at rates below 64 kbps. However has

turned out to be useful at higher speeds as well, and though it is

restricted to a few picture sizes and is not suitable for the presentapplication, techniques from H.263 are being incorporated into the

forthcoming MPEG-4 standard.

3.2.3 Encoders currently on the market are relatively large,

certainly if their use in mobile or portable applications is considered. The

smallest take up around 2-3U3 of a 19 rack and older models are larger

than this. The typical cost of a modern MPEG-2 coder is around 20,000. At

the moment, the video encoding process is the preserve of broadcasters

and content providers, however at some point, home digital video cameras

and video recorders will become available and these will require in-built

video coders of some kind. It seems likely, therefore, given the use ofMPEG-2 for broadcasting purposes, that small, low cost MPEG-2 coders will

become available over time. Given the rate of progress in this market,

current estimates suggest that affordable, portable coders will be available

in 5 to 7 years time.

3.2.4 MPEG-2 encoding introduces a delay of around 100ms into the

signal path. As mentioned earlier, we do not anticipate this being a major

problem for broadcasters.

3 1U = 1 inches or 44.5 mm.

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3.2.5 Decoders, on the other hand, are based on technology

designed to be mass-produced for the consumer digital television market

and so are already much cheaper and smaller. Single chip implementations

of MPEG-2 decoders are now available at a reasonable price. Decoders,

therefore, are much smaller (professional ones can be incorporated into a

1U rack-mount box).

3.2.6 Coders with a 34 Mbps output are already in use by

broadcasters and program makers as part of high-bandwidth digital links,

used over terrestrial, satellite and optical fibre transmission media.

3.3 Transmitters

3.3.1 Modulation schemes themselves are covered in detail in

section 4. Here we examine the range, size and cost of the various

modulators that will are required in order to enable the various potentialmodulation schemes. In addition, we look at frequency converters for the

up-conversion of the transmitted signal and the down-conversion of the

received signal.

3.3.2 A transmitter basically comprises three stages:

19A modulator: This converts the incoming (analogue or digital) base-

band signal into an RF signal.

20A frequency converter: This changes the frequency produced by the

modulator (which is normally constant and much lower than thetransmission frequency, 70 MHz is common) to the frequency of

transmission.

21Amplifiers: To raise the power of the up-converted signal to the required

level (typically a few Watts).

3.3.3 A suitable antenna is also required, but its requirements will

not change regardless of the type of modulation employed and will not be

considered further at this stage.

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3.3.4 Current analogue video links use FM which produces a

constant carrier level and hence does not require linear amplifiers in the

transmitter stages. Frequency Shift Keying (FSK) is a simple digital

modulation scheme, based on the use of a number of discrete frequencies

to represent each symbol of data. Like analogue FM, it has a constant

carrier level. The use of an FSK transmission protocol can be accommodatedusing existing video link equipment by simply altering the modulation signal

from the analogue video to an appropriate digital stream.

3.3.5 A variant of FSK is Phase Shift Keying (PSK). This can also be

made to have a constant carrier level and hence could use the same

amplifiers. The modulation stage, is, however, fundamentally different and

hence new equipment would be required.

3.3.6 Many high level digital modulation schemes, such as 16QAM

do not produce a constant carrier and therefore require both a new

modulator and new, linear, amplifiers.

3.3.7 The more complex the modulation scheme, the more complex

the modulator and this is reflected in the size and cost of the equipment.

The transmission frequency also has some bearing on the equipment with

higher frequencies being more difficult and hence more costly to produce. A

basic FM transmitter operating at 2.5 GHz can be fitted in a space not much

larger than a mobile phone (note that mobile phones can operate on

frequencies near 2 GHz and are significantly more complex than an FM

video transmitter) and cost 1,000. An OFDM modulator takes up around 2U

in a 19 rack and costs in the order of 12,000.

3.3.8 Basic digital links, of many types (including PSK and QAM

modulation schemes) are in wide use for fixed point-to-point links for the

likes of telecommunications operators. Thousands of such links operate in

the UK alone and equipment costs are relatively low (a fully installed, bi-

directional, 7 GHz, 34 Mbps link costs around 20,000 including antennas).

We have explored the potential for the use of such equipment in section

3.5.

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3.3.9 The power consumption of a constant carrier transmitter is

less than that required for a linear one as the amplifiers can operate in a

non-linear (and hence more efficient) mode. A basic 2.5 GHz FM link

typically consumes around 3 times the output transmitter power, hence a 1

Watt transmitter need only consume around 3 Watts of electricity. Fixed

point-to-point links are designed to be installed in equipment rooms wherepower is not a consideration and hence consume many more times this

amount. A 1 Watt transmitter may consume 50 Watts or more. OFDM

equipment is very power hungry due to the large amount of digital signal

processing (DSP) required to generate the signal. The modulators alone

consume upwards of 150 Watts. Should a manufacturer design a custom

ASIC (application specific integrated circuit) to perform the OFDM

modulation, this could be very significantly reduced.

3.3.10 As such, a digital transmitter could take up to 6U of rack

space and consume more than 200 Watts. Such a system could easily be

installed in an OB truck and possibly in a helicopter but is most definitelynot suitable for radio camera applications. Within 5 years, however, the

situation may have changed significantly and it is feasible that in this

timescale a truly portable digital transmitter, even using OFDM, may be

available.

3.4 Receivers

3.4.1 Digital receivers for any of the modulation schemes

considered are widely available, indeed more so than transmitters. Due to

the proliferation of digital broadcasting services, including satellite,terrestrial and cable services, demodulators and video decoders for MPEG-2

based DVB services are widespread and relatively inexpensive (a set top

box capable of decoding an OFDM signal retails, without subsidy, for around

400).

3.4.2 Such DVB compliant receivers will decode OFDM (for

terrestrial services, DVB-T), QPSK (for satellite services, DVB-S) and

256QAM (for cable services, DVB-C). The size, weight and power

consumption of such units are all significantly less than for their transmitter

counterparts.

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3.4.3 For other digital modulation schemes, off-the-shelf equipment

can be purchased in the form of that used for fixed links. Given the analogy

between fixed point-to-point digital telecommunication links and point-to-

point digital video links, we have considered the implications of the use of

fixed link equipment separately.

3.5 Digital fixed links

3.5.1 Digital point-to-point fixed links are used by

telecommunications companies to provide the long-haul back-bone of their

fixed networks in places where it is uneconomical to run fibres or other

cables. The equipment used for such links has been available for many

years and there are several manufacturers producing equipment.

Competition has driven down costs and increased innovation and quality.

Links using most digital modulation schemes from BPSK to 64QAM (and

higher level schemes) are available in off-the-shelf packages and often offerbi-directional digital connectivity.

3.5.2 A complete end-to-end link capable of carrying 34 Mbps of

data, including the necessary dishes and installation, is now under 20,000.

Equipment capable of being installed on an ad hoc basis may be slightly

more expensive than this to allow for the ruggedisation necessary to allow

operation in the harsher portable environment.

3.5.3 Such links would not offer any form of video compression

hence a suitable video coder would be required in order to complete the

link, as would suitable decompression equipment for the receive end.However, as the coder is not usually an integral part of a link, this is much

less of a problem.

3.5.4 The spectrum allocated to fixed links includes frequencies

adjacent to those used for ENG/OB links and it is not expected that the

modification of equipment to cover the frequencies used for ENG/OB links

would add a premium to the cost of the equipment. Indeed, in some

countries, the frequencies used for ENG/OB links in the UK are used for fixed

links hence such equipment may not be bespoke and may be off-the-shelf.

Existing fixed link equipment is available for frequencies in excess of 50

GHz and those below 2.5 GHz hence there should be no problem in adaptingthe available equipment for any of the current ENG/OB bands.

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3.5.5 The one current problem with fixed link equipment is that it

operates on a 3.5 MHz raster, that is to say that the channel bandwidths

supported are in multiples of 3.5 MHz (3.5, 7, 14, 21, 28 etc). Currently,

analogue FM links occupy (and more crucially are assigned) 20 MHz

channels hence if a move to fixed link equipment were envisaged, some

reorganisation of the existing channel raster may be required.

3.6 Conclusions

3.6.1 The equipment proposed for DVB based digital links is

currently big, heavy, expensive and power-hungry. Typically, to reproduce

PAL equivalent quality, a link of over 6 and typically 8 Mbps is required. The

encoder for any compression scheme achieving PAL quality in 6Mbps or less

is large and expensive; also modulation equipment for OFDM (which, as we

shall see in the next section, is the only modulation scheme able to cope

with multi-path environments) is large and expensive.

3.6.2 Off-the-shelf equipment for fixed links (not using OFDM) is

cheap but the channel raster is not fully compatible with the existing

licensing regime and unless the large and heavy video coders are used,

large bandwidths are needed.

3.6.3 In the short-term future (one to two years), size and power

consumption of the above mentioned items of equipment will come down

considerably. However costs may not follow for some time unless custom

ASICs are built.

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4.1 Introduction

4.1.1 This section sets out the options for modulation schemes which could be

used to support digital ENG/OB activities and draws conclusions as to which

are suited to the various radio based video links applications.

4.2 Options for modulation scheme

4.2.1 There are a wide variety of digital modulation schemes, many of which may

be suited for use in digital ENG/OB applications. In considering the

possibilities, however, we have first examined the modulation schemes

proposed by the Digital Video Broadcasting (DVB) group. This is for a

number of reasons but is mainly because modulators and receivers for

these schemes are already available and they are an open standard which

would allow new manufacturers to produced products which can interwork

with existing ones.

4.2.2 The DVB series of specifications details three different modulation schemes

and the applications for which they are intended. Table 4-1 shows how the

modulation schemes relate to each of the specifications.

DVB specification Modulation scheme

DVB-T (terrestrial) OFDM (7 or 8 MHz channel)

DVB-C (cable) 256QAM (8 MHz channel)

DVB-S (satellite) QPSK (27 MHz channel)

DVB-M (microwave) 256QAM (below 10 GHz)

QPSK (above 10 GHz)

Table 0-1: Modulation schemes proposed by DVB

4 000Modulation schemes

6 Migration strategy6 Migration strategy


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4.2.3 The nearest counterpart to ENG/OB activities is the DVB-M specification

which relates to the transmission of digital video using microwave links (for

example for MMDS or MVDS applications). MMDS systems typically operate

at 2.5 GHz and tests have been carried out in Ireland to evaluate the

suitability of 256QAM as a terrestrial microwave distribution medium. It was

found that almost any multi-path reflections cause significant degradationto the received signal. Given the scale of the problem of multi-path for all

but the best point-to-point links, this suggests that 256QAM would not make

a suitable modulation scheme for digital ENG/OB activities.

4.2.4 QPSK is a well understood modulation scheme and is known to outperform

analogue FM in good line of sight paths. For satellite use, in a 27 MHz RF

bandwidth, QPSK requires a received carrier to noise level of only 10 dB

whereas an analogue FM signal required a carrier to noise of 15 dB to

produce similar quality reception. This implies that signals 5 dB lower than

comparable analogue FM signals need to be received to give the same

picture quality. In a 20 MHz bandwidth, this effect is likely to be somewhatless as the wider the RF bandwidth of an FM signal, relative to the base-

band bandwidth, the lower the signal required to give the same

demodulated picture quality. The ratio of the RF bandwidth (B w) to the base-

band video bandwidth (Bv) is called the modulation index (m) and is given in

equation 4-1 below.

12B

Bm

v

w= [4-1]

4.2.5 In a 27 MHz RF bandwidth and assuming a 6 MHz video bandwidth, m is1.25; in a 20 MHz bandwidth m is only 0.67, hence the performance in a 20

MHz bandwidth will be of order half (ie 3dB) worse than in a 27 MHz

bandwidth. Generally, however, improvements over and above FM are

expected from a QPSK signal.

4 Modulation schemes


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4.2.6 Tests have also been carried out in the US, Ireland and Thailand on the

effectiveness of OFDM at 2.5 GHz in relatively line of sight and in harsh

multi-path environments. These tests have shown, quite categorically, that

the performance of OFDM in these environments is significantly better than

the equivalent analogue FM signals even with transmitter powers 6 dB

lower. Note that OFDM itself is not a full definition of a modulation scheme.The term OFDM relates to the way in which the carriers containing the

digital information are spaced in frequency next to each other. OFDM can

operate in several modes such that each individual carrier can be either

QPSK, 16QAM or 64QAM.

4.2.7 In addition to those options presented by the DVB standards, a wide variety

of modulation schemes are in use for fixed links from BPSK to 64 QAM. In

terms of equivalent performance to existing analogue FM signals, an 8 state

modulation scheme (such as 8PSK) requires approximately 3 dB more

receive power for a given error rate than the QPSK system described above

and hence would offer similar performance to an FM system. Note that bythe addition of more error correction into the digital scheme, its

performance can be further improved.

4.2.8 The table below illustrates the channel bandwidths that are required in

order to transmit an 8 and a 34 Mbps digital signal including a 50%

overhead for error correction (representing a 2/3 rate 4 Reed-Solomon error

correction code), giving transmitted data rates of 12 and 51 Mbps

respectively.

4 The rate of an error code represents the input to output ratio of the data. A 2/3 rate code

therefore produces 3 bits our for every 2 bits in, a 50% increase in bit rate.



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Modulation scheme Channel width for 8

Mbps

Channel width for 34

Mbps

QPSK 7.2 MHz 30.7 MHz

16QAM 3.6 MHz 15.4 MHz

256QAM 1.8 MHz 7.7 MHz

OFDM5 (QPSK) 7 or 8 MHz Not possible

OFDM (16QAM) 7 or 8 MHz Not possible

OFDM (64QAM) 7 or 8 MHz Not possible

Table 0-2: Bandwidths required by various modulation schemes

4.2.9 Note that existing OFDM modulators do not, even with the minimum of error

correction and using 64QAM, support a bit rate of more than 31 Mbps of

input data. Note also that existing OFDM modulators allow channel widths of

7 or 8 MHz only though in principle the modulation scheme itself canoperate in any bandwidth (OFDM is used for DAB in a channel bandwidth of

1.5 MHz to support up to 12 audio channels giving a payload of around 1.5

Mbps).

4.2.10 It is also worth pointing out that off-the-shelf digital link equipment work in

channel width multiples of 3.5 MHz and not in the bespoke intervals

suggested in table 4-2. Using off-the-shelf digital link equipment has the

advantage of cost as such equipment is relatively mass produced and

competition between suppliers has led to lower costs.

4.3 The radio environment and its implications on choice of modulation

scheme

4.3.1 Each of the three categories of video link that we have identified operate in

different radio environments. In most cases, the actual signal level will be

sufficiently above any background noise that the main concern is the

problems caused by multi-path reflections. The different categories of link

operate in the following environments:

5 A guard interval of 1/8 has been used.



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22Temporary point-to-point links: These links have the least harsh

environment in which to operate, indeed a correctly set-up link will have

characteristics not dissimilar to a well-engineered fixed point-to-point

link. Multi-path reflections will be generally small, though links across

cities such as those used for news gathering can be, due to the

occasionally marginal paths employed, subject to some reflections.

In the case of this type of link, therefore, almost any of the potential

modulation schemes would be suited to use for a digital video link with

the possible exception of higher order schemes such as 256QAM which

are sensitive even to small amounts of multi-path reflection.

23Mobile links: Due to the fact that the path of a link of this type is

continually changing, there is significant fading and multi-path

reflections.

Only two schemes perform better than FM generally and hence given theharsh environment are worth consideration. These are QPSK and OFDM.

QPSK, however, will suffer from multi-path reflections if the delay spread 6

of the multi-path reflections begins to approach the transmitted symbol

period (which for QPSK is twice the transmitted bit period as there are

two bits per symbol). Transmitting an 8 Mbps signal with a 2/3 rate error

correction code gives a symbol rate of 6 Msps, a 34 Mbps signal gives a

rate of 25.5 Msps giving symbol periods of 167 and 39 nanoseconds

respectively. The delay spread of signals in an outdoor environment is

between 10 and 3,000 nanoseconds hence there is no clear answer to

whether QPSK would be better. Much will depend on the quality of the

link and in particular whether there are any long delay reflections withsufficient strength to cause errors in reception.

OFDM on the other hand, is specifically designed to cope with multi-path

reflections. In the system used for DVB-T, each individual carrier has a

symbol rate of either 224 or 896 microseconds for a 2,000 or 8,000

carrier system respectively (allowing payloads between 5 and 31 Mbps).

This is significantly above the typical outdoor delay spread and hence

will overcome most, if not all, multi-path reflections.

6 The delay spread is the spread of the time taken for multi-path reflections to reach the

receiver after the direct signal has been received.



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24Radio cameras: Somewhere between the two above circumstances,

radio cameras can have changing paths but these are usually either:

very short such that the direct signal is sufficiently above the level of

any reflection which is therefore not a significant problem; or the path is

never badly obscured such that the reflections present less of a problem

than in the mobile case.

Again either QPSK or OFDM could be used for the link, however given the

slightly less harsh environment, QPSK has a better chance of succeeding

than in the truly mobile application.

4.4 Conclusions

4.4.1 For mobile links, OFDM offers advantages, not just in terms of

a reduction in the required spectrum but in performance terms too. QPSK

also offers spectral efficiencies and for most links can be expected toperform as well as, if not better than, existing analogue FM links.

4.4.2 For point-to-point links, the quality of the path (in terms of the

Fresnel clearance and thereby the likely multi-path reflections) determines

how suitable each of the possible modulation schemes becomes. For poor

links, QPSK is likely to offer improvements on existing links. For better links,

16QAM, 64QAM or even 256QAM are possibilities offering reduced

bandwidths and/or increased throughputs.

4.4.3 For radio cameras, the limiting factor is the size and weight of

the equipment. However, if the output of the camera is already digital(DVBPro cameras for example) and a small, low power, QPSK modulator can

be designed, this may offer benefits.

4.4.4 We can see, therefore, that dependent upon the application,

the appropriate modulation scheme is different. There is no single scheme

that can be used for all applications to the exclusion of all others. To allow

for the introduction of digital ENG/OB links, provision must therefore be

made for the user to select the appropriate modulation scheme.



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4.4.5 The following table summarises our findings, giving suggested

modulation schemes and typical bitrates for each application, with

corresponding bandwidths. We have selected bitrates of 8Mbps, as might be

obtained from an MPEG-2 or ETSI coder, 25 Mbps, as might be obtained

from a DVBPro camera, and the already popular bitrate of 34 Mbps. Where 8

Mbps is suggested, this is not meant to suggest that we disapprove of usersoperating links at lower bitrates and achieving corresponding savings in

bandwidth or multiplexing more than one channel together. We also include

50 Mbps (DVBPro) and 270 Mbps (raw digitised video) for comparison.



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Application Modulation

scheme

Comments Bitrate Bandwidth

Temporary point-

to-point links

QPSK Improvements over

analogue for poor links

8 Mbps 7.2 MHz

8PSK Lower bandwidth 8 Mbps 4.8 MHz16QAM or higher throughput 8 Mbps 3.6 MHz

64QAM For high quality links 8 Mbps 2.4 MHz

25 Mbps 7.5 MHz

256QAM For very high quality

links

8 Mbps 1.8 MHz

25 Mbps 5.6 MHz

34 Mbps 7.7 MHz

270 Mbps 61.1 MHz

Mobile links OFDM (QPSK) Very high multi-path

resistance

Up to 10 Mbps 7 or 8 MHz

OFDM (16QAM) Up to 21 Mbps 7 or 8 MHz

OFDM (64QAM) Up to 31 Mbps 7 or 8 MHz

QPSK Smaller, cheaper

equipment than OFDM;

benefits over analogue

8 Mbps 7.2 MHz

Radio cameras QPSK May offer benefits for

digital cameras

8 Mbps 7.2 MHz

25 Mbps 22.6 MHz

34 Mbps 30.7 MHz

50 Mbps 45.2 MHz

Table 0-3: Modulation schemes, possible bitrates and corresponding bandwidths, by

application



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5.1 Introduction

5.1.1 This section describes the current channel allocations and the associated

channel plans. We also examine the pressures on the spectrum allocated for

use by ENG/OB and the impact that this will have on existing, analogue

channelisation. We then go on to investigate the options for the introduction

of digital video links. Finally we consider other options for the introduction

of digital video links.

5.2 Frequencies and channelisation

5.2.1 Nine different frequency bands are available for use by ENG/OB in the UK.

These bands together with the frequency limits and the current applications

that make use of the bands are listed in table 5-1 below.

Band Frequency range Current availability

2.5 GHz 2390 2690 MHz Temporary point-to-point links

Mobile links

Radio cameras


Mobile linksRadio cameras


Mobile links

Radio cameras

7 GHz 7110 7424 MHz Temporary point-to-point links



Mobile links

Radio cameras

5 000The band plan and sharing arrangements

A ReferencesA References


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Mobile links

Radio cameras

24 GHz 24250 24500 MHz Radio cameras

48 GHz 48000 48400 MHz Radio cameras

Table 0-1: Current video link bands

5.2.2 Each video link is usually assigned a 20 MHz channel within one of these

bands. Where possible, the adjacent channels are left free in any given

geographical area to provide a degree of adjacent channel protection from

interference. In some circumstances, typically when a large number of video

links are required in a given area (a royal wedding for example) different

channel spacings are used and less adjacent channel protection is affordedin order to try and maximise the use of the available spectrum.

5.2.3 Users can request a channel in any of these frequency bands from JFMG

who are responsible for the management of these frequencies. Some

channels are dedicated to a specific organisation in a specific geographical

area (for example, a large operator has two permanent channels at 2.5 GHz

for use inside the M25 and another for use anywhere in the South of

England), others are available on a first come, first served basis. A standard

video channel takes 20 MHz but spectrum can be requested at these

frequencies in multiples of 5 MHz.

5.2.4 In total there is 1088 MHz of spectrum below 10 GHz available and 1450

MHz above 10 GHz, however some bands are only used by a limited number

of users. This is mostly historical frequency allocation and equipment

purchases. For example, one user uses only the 5.5 GHz band on a regular

basisthis is because that user originally had dedicated frequencies in this

band and hence purchased equipment for it. Now that it can use any band it

stays in the 5.5 GHz band as this means that no new equipment needs to be

bought.

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5.2.5 Some bands, and in particular the 2.5 GHz band, are heavily used by a wide

variety of users, others, for example 48 GHz are newly introduced and

hence under utilised.

5.2.6 In discussing the applications to which radio based video links are put in

section 2, we suggested that certain bands were more suitable for certain

applications than others. Generally speaking, the appropriateness of a given

band for a given application can be determined by two factors:

25Link distance: the shorter the link, the higher the frequency which can

be used.

26Link path (in particular multi-path reflections): where multi-path

reflections are a significant problem, lower frequencies offer advantages

as the size of objects required to cause reflections are smaller than at

higher frequencies.

5.2.7 Taking the three applications we identified, and applying

these simple rules (irrespective of modulation scheme) we can give an

approximation as to the most appropriate band for a given application.

Table 5-2 overleaf illustrates this principle.

Application Link distance Link path Appropriate bands

Temporary point-to-point

links

Medium to long Good to fair Medium frequencies

(5.5 to 12 GHz)

Mobile links Short to medium Fair to poor Lowest frequencies

(2.5 to 5.5 GHz)

Radio cameras Short Fair Medium to high frequencies

(10 to 48 GHz)

Table 0-2: Appropriate bands for each application

5.2.8 Comparing this table with table 5-1 we note that to a large extent, the

bands used by a given application are not dissimilar to those indicated by

this simple comparison. However, some differences do present themselves,

namely:

27Radio cameras are being used in the 2.5 to 5.5 GHz bands;



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28Mobile links are available in the 10 and 12 GHz bands (in fact although

these bands are available for mobile links, there is currently little or no

take-up of this service);

29Temporary point-to-point links are being established in every band from

2.5 to 12 GHz.

5.2.9 Undoubtedly, some of these anomalies are caused by a

misclassification of the application. For example, the difference between a

radio camera and a mobile camera is small. Also, there will be occasions for

point-to-point links where the link path is not ideal and a lower frequency

may be necessary. Finally, equipment for the higher frequencies (24 and 48

GHz) is relatively scarce, and the 24 GHz band has only recently been

introduced.

5.2.10 In the main, however, it is likely that where applications are in

bands which are not necessarily the optimum, this is due to the use oflegacy systems. Many users bought equipment for a specific band some

time ago and are forced into the use of a given band due to the limited

capability of their equipment. Over time, as this equipment is replaced, a

move to the breakdown shown in table 5-2 would maximise the availability

of suitable spectrum for the appropriate application and we would

recommend that such appropriate use is encouraged.

5.3 Sharing arrangements and pressure on existing spectrum

5.3.1 Sharing of spectrum between different services and differentusers is an effective way to maximise the availability and use of spectrum,

which is a limited resource. Sharing can take the form of geographical

separation (ie users in Southampton and Edinburgh could use the same

spectrum without causing mutual interference) or can be by diversity of

service (fixed point-to-point links and satellite uplinks often share spectrum

as they are use highly directional transmit and receive antennas which

thereby minimise the potential for interference).



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5.3.2 Much of the spectrum available for video link use is shared

with other services. Table 5-3 below highlights the services with which the

available spectrum is shared. Where only part a band is shared with a

service, the particular part shared is shown in brackets. It can be clearly

seen that none of the spectrum assigned for ENG/OB activities is exclusively

used for that purpose.



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Band Frequency range Sharing parties

2.5 GHz 2390 2690 MHz Radio Amateurs (2390 2450 MHz)

ISM7and low power data links (2400 2500 MHz)

Trans-horizon links (2450 2690 MHz)

Radiolocation (2500 2600 MHz)

3.5 GHz 3500 3600 MHz Radiolocation

Space to Earth links

5.5 GHz 5481 5815 MHz Maritime radionavigation

Radiolocation

Radio Amateurs (5650 5815 MHz)

7 GHz 7110 7424 MHz Earth to Space links (7145 7235 MHz)

Space to Earth links (7250 7424 MHz)

8.5 GHz 8460 8500 MHz Radiolocation

Space research (Space to Earth)

10 GHz 10300 10360 MHz Radio Amateurs

12 GHz 11740 12480 MHz Broadcast satelli te downlinks

24 GHz 24250 24500 MHz Fixed links and short range devices

48 GHz 48000 48400 MHz Earth to Space links

Stratospheric communication systems

Table 0-3: Sharing arrangements

5.3.3 In many cases, sharing with other services is done on the basis of

geographic separation. For example, a band which is shared with satellite

uplinks can be used anywhere which is far enough away from all uplink

sites.

5.3.4 In most cases, video links co-exist with other services with little or no

interference. However from time to time, the International

Telecommunication Union (ITU), who are responsible worldwide for

spectrum allocation issues, allocates spectrum to new services which by

their nature will require exclusive use of spectrum. Recent decisions taken

by the ITU will affect the spectrum available at 2.5 GHz and this, together

with potential pressure at 12 GHz are discussed below.

7 Industrial, Scientific and Medical equipment.



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Changes in the 2.5 GHz band

5.3.5 The ITU has allocated spectrum for the use of another service in the 2.5 GHz

band to the Mobile Satellite Service (MSS). The spectrum affected is:

302483.5 to 2520 MHz;

312670 to 2690 MHz.

5.3.6 The spectrum allocated to MSS is not officially to be made

available for MSS until 2005, however several MSS operators (such as

Iridium, Globalstar and Odyssey) are due to begin service at various times

from the end of 1998 to 2000 using the spectrum between 2483.5 and 2500

MHz. Sharing studies have shown that the MSS services will require almost

exclusive use of the spectrum which they have been allocated and that, in

particular, sharing with terrestrial video links will not be possible. Note that

these studies have concerned themselves with sharing between MSS andanalogue FM video links. Using OFDM lower link powers can be used and

this, together with the different spectral density produced by an FM signal

may increase the opportunities for sharing. We do not expect, however,

given that the shared spectrum is that used by the downlink of the MSS

satellites, that such a sharing arrangement would be feasible as

interference would still be caused to subscribers in the neighbourhood of

the ENG/OB transmitter.

5.3.7 One of the key elements in determining the sharing potential

is the potential interaction between the video transmissions and the other

services with which the spectrum is shared. The spectral density of thetransmitted signal has a significant impact on the likelihood of interference.

The spectral density of a transmission indicates the amount of power

contained within a given bandwidth and can vary across the total bandwidth

of the transmission. Figure 5-1 below shows the relative spectral density of

an FM and an OFDM signal. Note that the FM signals spectral density varies

across its total bandwidth whereas the OFDM is more or less constant. A few

of the OFDM carriers do have increased power (6 dB more) to act as pilot

signals when tuning hence changing the flatness of the signal.



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FM OFDM

Figure 0-1: Spectral densities of different modulation schemes

5.3.8 Note that the spectral density of a QPSK signal is less flat than

either an FM or an OFDM signal having a large peak at the centre frequency

and falling off gradually as the extremities of the channel are reached.

5.3.9 However, the fundamental problem is one of mutual

interference. It seems unlikely that there are any workable solutions to this

problem as the affected spectrum at 2.5 GHz represents the downlink of the

MSS systems. As such, any users in an area where the signal strength of the

video link was sufficient to interrupt reception of the satellite signal would

be unable to receive a service. Had it been the uplink which used these

frequencies, using directional antennas would have much reduced the

potential for interference and may have allowed increased sharing.

5.3.10 This means that it is prudent to clear the spectrum required

by MSS as soon as possible. Certainly the section between 2483.5 and 2500

MHz will need to be cleared by the end of 1999. This will leave the 2.5 GHz

band somewhat reduced in size and somewhat fragmented. The remainingspectrum will be:

322390 to 2483.5 MHz;

332520 to 2670 MHz.

5.3.11 Neither of these two pieces of spectrum divides up evenly into

20 MHz channels. In the first instance 4 channels can be made between

2390 and 2470 MHz with a 13.5 MHz channel remaining between 2470 and

2483.5 MHz. In the latter case, 7 channels can be made between 2520 and

2660 MHz with 10 MHz remaining.



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5.3.12 The 2.5 GHz band is under further pressure from MSS

operators (including European proponents of satellite-UMTS) who see the

remainder of the band between 2.52 and 2.67 GHz as a potential candidate

for the expansion of their services. Currently this is on the agenda for the

year 2000 World Radio Conference (WRC) and given that changes are

usually notified at least 10 years in advance, this would suggest that theremaining spectrum will be available until at least 2010. From current

experience, however, if WRC rules in favour of the MSS operators, the

majority of the band could be lost from 2005 or earlier with only the

spectrum below 2483.5 MHz remaining.

Possible changes in the 12 GHz band

5.3.13 Links in the 12 GHz band are shared with the downlinks of the

broadcast satellite service (BSS). The BSS band is one of three bands

currently used to deliver direct-to-home satellite television. The majority of

services currently being received in the UK use spectrum below 11.7 GHz infrequencies assigned to the fixed satellite service (FSS). The British Satellite

Broadcasting service introduced at the end of the 1980s and using the now

infamous squarials operated in the BSS spectrum, however this service has

now terminated and there are no services aimed at the UK which currently

use the BSS spectrum. If, in future, a service in the BSS spectrum directed

at the UK were to be instigated, there may be pressure for ENG/OB links to

be removed from the band.

5.4 Other sharing options

5.4.1 From inspection of the RAs plans and those in discussion by

the European Radiocommunications Office, there does not appear to be

pressure on any of the other bands currently in use for ENG/OB services

from other services (other than the 2.5 and 12 GHz bands as described

above). Additional spectrum from 3400 to 3420 MHz is shown as being

considered by the RA for ENG/OB use.



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5.4.2 In addition to those bands allocated for video links, services

ancillary to broadcasting (SAB) is allocated spectrum over a wide range of

frequencies. Given that using OFDM or, in certain circumstances, QPSK can

result in a digital signal occupying 8 MHz of spectrum or less, it may

become possible to use alternative spectrum for ENG/OB links. In particular,

the whole of the UHF television band from 470 to 854 MHz is available forSAB and could provide a home for any type of radio link. The characteristics

of the UHF spectrum make it ideally suited to mobile video links and given

the pressure at 2.5 GHz, this could provide a new home for the services.

Tests using a mobile UHF OFDM transmitter in an adjacent channel to a high

power PAL broadcast have been carried out in Dublin, Ireland and proved

that even with the OFDM transmitter outside a domestic receive installation,

no perceptible interference was caused.

5.5 References for sharing properties and protection ratios

5.5.1 For band planning and channel assignment, JFMG need access

to data on the sharing properties of the new technologies and, in particular,

protection ratios for each possible combination of emission classes, given as

a function of the frequency separation between the emissions.

5.5.2 The following documents are relevant to OFDM sharing issues:

34OFDM sharing with OFDM: Chester 97, CEPT co-ordination agreement for

DVB-T;

35OFDM sharing with analogue AM TV transmissions: Chester 97, as above;

36OFDM sharing with analogue FM transmission: RA3/PMSE Projects 387

and 436, DVB-T/radiomicrophone interference studies.

5.5.3 Other reports which may be of interest in this area are:

37ITU Recommendation ITU-R SM 669, which includes protection ratios for

NICAM (which is modulated using QPSK) with NICAM and various

analogue TV and radio emissions;

38ITU Recommendation ITU-R BT 655, protection ratios for AM TV with AMTV, T-DAB, and full-field data signals in AM TV emissions;



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39ERC Report 40 (Rome 1996) which gives detailed parameters for fixed

service systems using a wide range of modulation schemes, intended for

use as input parameters into sharing studies.

5.5.4 Bibliographic details of each report are given in annex .

6.1 Introduction

6.1.1 The Radiocommunications Agency is keen to facilitate the introduction of

digital ENG/OB links and there is some evidence that users of video links are

also beginning to consider the possibilities. However, in many cases, the

cost of the upgrade from existing analogue equipment to new digital

equipment would force users to reconsider their options, and indeed for the

BBC and ITN, the prospect of having to re-equip has led to a transfer from

terrestrial to satellite news gathering.

6.1.2 Nevertheless with the loss of some of the 2.5 GHz band to MSS and possible

future threats to the 2.5 GHz band from satellite-UMTS; threats to 12 GHz;

increased pressure across the board for additional spectrum for new

services and the introduction of spectrum pricing for broadcasting and

related services, the spectral efficiency improvements offered by a move to

digital would improve the availability of channels for video links.

6.1.3 In section 2 we considered users qualitative requirements and determinedthat a move to digital would not compromise the standards demanded from

broadcasters, even for news and sporting events. In section 3 we

considered the equipment available to enable digital video links and

concluded that, though expensive, such equipment was currently available

and that cost would decline over the coming years.

6.1.4 In section 4 we considered the possible modulation schemes that could

support digital video links and determined that QPSK and OFDM could offer

spectral, and in some cases, quality improvements over existing analogue

links. We also concluded that given the wide variety of applications and

possible link qualities, no single modulation scheme offered a universalsolution but that a variety of schemes would offer flexibility.




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6.1.5 In section 5 we considered the pressures on spectrum and the options for

sharing brought about by the introduction of digital and concluded that as

well as offering the potential to squeeze more links into less spectrum,

sharing of other frequencies such as the UHF TV band became a distinct

possibility. We also suggested that users should be encouraged to use

certain bands for particular applications based on the suitability of thosebands to the three categories of video link which we have identified.

6.1.6 In this section we look at the wider pressures for a change to digital and

ways in which spectrum could be made available to encourage the

introduction of digital links. We believe that the introduction of digital links

should be based around a migration strategy which allows joint

analogue/digital use of spectrum that is flexible and may not require distinct

and exclusive digital allocations to be made.

6.2 Pressures for change

6.2.1 Here we analyse the different issues which might lead to pressure for

change from analogue to digital.

6.2.2 There is always increasing pressure on the radio spectrum, and an ongoing

desire to use spectrum most efficiently and for the UK to lead in the

development and application of modern spectrally efficient technologies.

Digital ENG/OB technology is spectrally more efficient than the present

analogue systems, by a factor of around 2.5.

6.2.3 With many users increasingly switching to SNG and fibre, there is littlepressure on the ENG/OB spectrum from within the ENG/OB users, and so

little internal pressure for increased spectral efficiency of ENG/OB

applications.

6.2.4 There is pressure on certain ENG/OB bands from other uses, notably at 2.5

GHz and also at 12 GHz, for MSS, BSS and eventually UMTS uses. The RA

will be aware of the constant need to ensure all spectrum is used in the

most efficient manner, and thus there is a significant pressure for change,

driven by the RA and other radio use sectors (notably satellite and UMTS

operators) but not by ENG/OB users.



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6.2.5 The introduction of spectrum pricing may change the attitude of the users in

this respect. Users are already complaining about paying the largest

licensing fees of any country in the world, and the present fees have been

implicated in the general switch to satellite that we have observed, even

though satellite uplink fees are significant as well. If pricing is brought in so

that licensing fees more closely reflect the market value of the spectrumused then users will react by looking for savings. However it seems that the

effect of this will mainly be to cause more users to switch to satellite rather

than to increase pressure for a switch to digital terrestrial links.

6.2.6 Relative cost of equipment is likely to be a major factor in determining

demand for digital ENG/OB links. We note that OFDM link equipment

remains extremely expensive, as does MPEG-2 encoding equipment. Even

taking realistic future differences in spectrum pricing into account there

does not appear to be any immediate possibility of digital terrestrial

ENG/OB systems being able to compete with analogue systems, or even

satellite systems, even for users who are re-equipping. When we considerthat much of the vast amounts of analogue equipment currently owned by

users has many years of life left, it seems even less likely that price factors

will generate any pressure at all for a switch to digital.

6.2.7 In terms of user requirements, most users are happy with their analogue

systems (but would be delighted if they could transmit 270Mbps digital

signals over terrestrial links). However digital links do confer some benefits

which cannot be obtained through an analogue system, for example

multiplexing several channels into one link and widescreen operation. A few

users are experimenting with digital links at realistic bit rates and for

applications which cannot be served by satellite they might well want tointroduce digital in a small way.

6.2.8 In conclusion we consider that in order to promote innovation and flexibility,

a small amount of provision should be made for users who wish to convert

some of their links to digital. However there is no significant desire on the

part of the users to make the switch, and it should not be imposed. Any

degree of compulsion, entered into in the interests of using ENG/OB

spectrum more efficiently, is likely to lead to increased migration to satellite

rather than significant take-up of digital. Moreover any such move would

have a serious financial consequence on the users of ENG/OB links.



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6.2.9 There is presently sufficient spectrum for a small digital allocation to work

alongside analogue allocations without causing serious congestion. Any

congestion in ENG/OB bands in the short to medium term future will be local

to particular congested bands, caused by the loss of parts of certain bands

and users having equipment restricted to particular bands. There will not be

an overall shortage of ENG/OB spectrum.

6.3 Making space for digital

6.3.1 It is clear that, currently, the pressure to move to digital comes more from

regulatory aspirations and pressure on spectrum (whether from other

services or b

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