Interference Analysis ebook

INTERFERENCE ANALYSIS

MODELLING RADIO SYSTEMS FOR SPECTRUM MANAGEMENT

This edition first published 2016© 2016 John Wiley & Sons, Ltd.

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Library of Congress Cataloging-in-Publication Data

Names: Pahl, John, author.Title: Interference analysis : modelling radio systems for spectrum management / John Pahl.Description: Chichester, UK ; Hoboken, NJ : John Wiley & Sons, 2016. | Includes bibliographical references and index.Identifiers: LCCN 2015044553 (print) | LCCN 2015049974 (ebook) | ISBN 9781119065289 (cloth) | ISBN 9781119065319 (ePDF) | ISBN 9781119065326 (ePub) | ISBN 9781119065296 (online) | ISBN 9781119065319 (Adobe PDF)Subjects: LCSH: Radio--Interference–Mathematical models. | Radio--Transmitters and transmission–Mathematical models. | Electromagnetic waves–Transmission–Mathematical models. | Radio frequencyallocation–Management.Classification: LCC TK6552 .P24 2016 (print) | LCC TK6552 (ebook) |DDC 621.382/24–dc23LC record available at http://lccn.loc.gov/2015044553

A catalogue record for this book is available from the British Library.

Cover image: fotographic1980/Getty

To my family

Acknowledgements

The radio spectrum management industry is full of bright and friendly people, and the best bit of advice I can give is to be prepared to ask questions and then listen to the suggestions from others. There are so many people I would like thank and these are just a few in alphabetical order: Tony Azzarelli, David Bacon, Malcolm Barbour, Joe Butler, Ken Craig, Ian Flood, Paul Hansell, Dominic Hayes, Chris Haslett, Philip Hodson, Whitney Lohmeyer, Karl Löw, Bill McDonald, Steve Munday, John Parker, Tony Reed, John Rogers, François Rancy, Kumar Singarajah and Alastair Taylor – in addition the team at Wiley in particular Victoria Taylor, Tiina Wigley, Sandra Grayson, Purushothaman Saravanan and Nivedhitha Elavarasan.

My thanks also go to:

ITU for permission to quote documents such as Radio Regulations and Recommendations

Ofcom for permission to quote documents such as Consultation Documents and Technical Frequency Assignment Criteria

Ofcom and Ordnance Survey for permission to use the Ofcom 50m terrain and land use database in the production of coverage prediction figures

Transfinite Systems for use of their simulation tools and time to write this book

General Dynamics for provision of the measured gain pattern data

Every attempt has been made to avoid typographic errors: if any should be spotted, the author would greatly appreciate notice via email at [email protected]

Additional Credits

Front cover screenshot credit: Visualyse Professional, overlay credit: NASA: Visible Earth Screenshots from Visualyse Professional, Visualyse GSO, Visualyse Coordinate, Visualyse PMR, Visualyse Spectrum Manager and Visualyse EPFD are credit: Transfinite Systems Ltd www.transfinite.com

Overlay from NASA: Visible Earth full credit: NASA Goddard Space Flight Center Image by Reto Stöckli (land surface, shallow water, clouds). Enhancements by Robert Simmon (ocean color, compositing, 3D globes, animation). Data and technical support: MODIS Land Group; MODIS Science Data Support Team; MODIS Atmosphere Group; MODIS Ocean Group Additional data: USGS EROS Data Center (topography); USGS Terrestrial Remote Sensing Flagstaff Field Center (Antarctica); Defense Meteorological Satellite Program (city lights).

Foreword

Radiocommunications is the generic term to describe the various uses of the radio-frequency spectrum that have gradually become an integral part of our daily life in the last 30 years.

Television and sound broadcasting, satellite communications, radionavigation systems (such as GPS), mobile telephones or smartphones, Wi-Fi or Bluetooth systems or garage door openers, radars, emergency or defence communications, aircraft or maritime communications, radio relays, meteorological radiosondes or satellites, scientific or Earth exploration satellites, radio astronomy and deep space missions are only a few examples of the ever-increasing number of systems and applications that rely on spectrum to exist.

The associated investments represent trillions of dollars and are increasing every day as gathering and exchange of data also increase. The task of ensuring a viable ecosystem for the coexistence of these investments in the short, medium and long terms is entrusted to the International Telecommunication Union (ITU), which celebrated its 150th anniversary on 17 May 2015.

The objective of the ITU in this regard is to ensure the rational, efficient, equitable and economical use of the natural resources of the radio-frequency spectrum and satellite orbits. This is done by the application and regular updating of the ITU Radio Regulations, the international treaty that regulates the use of these resources by all countries in the world. The overriding objective of these regulations is to ensure operation of the radiocommunication systems of all countries free of harmful interference, thereby protecting these systems and the associated investments and providing the assurance that existing and future investments will be protected in the future.

To this end, any change foreseen in spectrum use is duly scrutinized by a population of experts coming from all parts of the world to attend frequent and multiple meetings of the Study Groups and Working Parties of the ITU Radiocommunication Sector. These experts literally dedicate their lives to building the future of radiocommunication systems and applications. Mr John Pahl is one of them. Over the last 20 years, he has played a key role in pushing the state of the art in analysis of interference between complex systems and developing appropriate regulations and best practices for their use of spectrum.

His book benefits from his long experience in world-level discussions within the technical, operational and regulatory decision-making process of the ITU Radiocommunication Sector. It covers the various aspects that need to receive careful consideration in assessing the interference that may occur among radiocommunication systems, at the design or coordination stage of these systems.

With the increased use of spectrum required to satisfy the growing demand for orbit and spectrum resources, more efficient use of these resources will come with increased complexity in system design, regulations, frequency assignment and coordination. Mr John Pahl’s book will certainly be a gold mine for the current and future generations of spectrum managers, communication system designers and regulators in their day-to-day work to continue to deliver viable radiocommunication services and meet the growing expectations of the world’s population in this regard.

Preface

We were on the lookout for ice.

I was in a 32 foot sailing yacht with writer and explorer Tristan Gooley, undertaking a double-handed sail from Scotland through the Faroes up to 66° 33′ 45.7″ N and the midnight sun. Now sailing out of the Arctic Circle we were approaching Iceland from the north, heading for the Denmark Straits, where ice flowed south. The Admiralty Pilot warned of bergs but the ice charts we had sailed with were over a week old. We needed an update.

So I reached for the Iridium satellite phone and rang a number in Greenland. A polite voice reassured us that as long as we kept within 50 nm of Iceland we should be okay.

Though I’d never had need of a satellite phone before that call, it was a technology I’d been involved in for nearly 20 years. It was by working on one of the other non-GSO mobile-satellite systems that I learnt the techniques and engineering principles of interference analysis. It turned out that there was a lot to cover: dynamics, antennas, link budgets, service objectives, thresholds, methodologies, modulations, coverage and much, much more.

On that voyage we didn’t get to see any icebergs but the following year would make up for it when I sailed from Iceland over to Greenland and then down its east coast to Tasiilaq, passing close to the one in the photo on the previous page.

A berg like this drifted into the Atlantic in 1912 to sink the RMS Titanic, which radioed in distress for a rescue that was to come too late. Just a few months after this disaster, the International Radiotelegraph Conference in London was spurred to agree on common frequencies, and this led to what we now call the Radio Regulations.

I would have to learn about those too, first studying the ITU-R Regulations, Recommendations and Reports, then writing some of my own, getting them approved within the ITU-R, understanding the processes and, where necessary, chairing meetings.

Interference analysis involves engineering and regulation, and this book will by its nature cover both.

My hope is that it will assist those who want to learn about these topics and help others to avoid some of the potential icebergs.

1Introduction

All radio systems share the same electromagnetic spectrum. This means that each radio receiver is detecting not just its wanted signal but all other signals transmitted at the same time anywhere – not just on this planet, but anywhere, even in space. If there are aliens out there using radio technology, their signals will also be added to the mix.

But it is rare for us to experience interference into our communication devices – such as radios, televisions and mobile phones – on a day-to-day basis. This is not an accident but the result of years of hard work by radio engineers and regulators to ensure that the signals from one user of the radio spectrum do not degrade significantly another user or, as is more commonly described, cause interference into the receiver.

Interference analysis is the study of how one or more radio systems can degrade the operation of other users of the radio system. It includes techniques to predict the level of interference and whether that could be tolerated or would represent a serious degradation, otherwise known as harmful interference.

This subject builds upon other specialist topics, such as antenna design and propagation, and often involves analysis of scenarios that includes different types of radio system. Therefore when undertaking interference analysis, it is necessary to become familiar with a wide range of other topics plus mathematical modelling techniques, statistics and geometry.

The objective of this book is to be useful to anyone involved in interference analysis – to help understand the various techniques and methodologies that could be used in studies. The approach in this book is to give an integrated view of interference analysis, describing all the key issues necessary to generate results. It will consider different types of interference and metrics to determine whether the interference could be accepted or would be considered harmful.

1.1 Motivations and Target Audience

There are different motivations for undertaking interference analysis, in particular:

System design: to optimise a radio system to allow the maximum service while reducing interference, whether within the system, to other systems or from other systems

Regulatory: to identify what radio services can share with other radio services and hence allow them to be included in the tables of allocation used by spectrum managers

Frequency assignment: to determine if a regulator can issue a new licence (e.g. to a taxi company) without it causing or suffering harmful interference

Coordination: during discussions between two radio system operators (or countries) to identify ways to protect each other’s receivers from the other’s transmissions.

This book is aimed at anyone with an interest in interference between radio systems, in particular those operating with frequency above about 30 MHz. This could include:

A member of a national spectrum management regulator is meeting with representatives from a neighbouring country to make a bilateral agreement that can be used to protect each country from interference. What would be a suitable interference threshold level to agree and how would it be checked/calculated?

A mobile operator’s spectrum management team wants to open up new bands for next generation broadband. They need to argue at an international level, in particular at the International Telecommunication Union, that such an introduction would be the most effective use of the scarce radio spectrum.

A satellite operator is meeting with another satellite operator to ensure that neither causes harmful interference into the other. At the coordination meeting they will agree the signal levels that can be transmitted on each satellite beam: what should they propose and how can they check the suggestions from the other company?

A consultant is working for the aeronautical community to help identify bands that can be used to provide broadband services to commercial aircraft. They must undertake sharing scenarios and convince regional bodies, such as Europe and North America, that these will be safe.

The national spectrum management regulator receives a request for a new licence to provide a service (e.g. land mobile or fixed link). How can they check it would not cause or suffer interference to/from existing licensees?

Students studying electrical engineering, communication systems or simulation techniques, who wish to learn more about interference analysis and modelling radio systems, together with academics undertaking research on these topics.

1.2 Book Structure

The book is structured as follows:

Chapter 2. Motivations

: considering the reasons why people undertake interference analysis, including the regulatory framework, international organisations and working methods.

Chapter 3. Fundamental Concepts

: covers the basics of radio engineering, including modulations, access methods, antennas, noise calculations, the underlying geometry and dynamics, link budgets and their attributes.

Chapter 4. Propagation Models

: the model of how radio waves propagate between transmitter and receiver (whether wanted or interfering) can make a huge difference to the results, so it is important to understand the various propagation models that are available and when they should be used.

Chapter 5. The Interference Calculation

: how to use the concepts above to calculate interference, including aggregation effects, polarisation adjustment, co-frequency vs. non-co-frequency, thresholds, interference apportionment and possible mitigation techniques.

Chapter 6. Interference Analysis Methodologies

: the complexity of the analysis can vary from static analysis, where the answer is a single number, to dynamic, Monte Carlo and area analysis, each with strengths and weaknesses. To help explain each of the different approaches, worked examples will show how they can be used to analyse sharing between:

A deployment of base stations of a Long Term Evolution (LTE) network into satellite Earth stations in parts of C-band

A non-GSO mobile-satellite service (MSS) system and point-to-point fixed links.

Chapter 7. Specific Algorithms and Services

: some services and sharing scenarios have well-defined publically available algorithms to calculate performance including interference analysis. Examples would be broadcasting, private mobile radio, white space and satellite coordination.

1.3 Chapter Structure and Additional Resources

Each chapter is structured starting with a summary of its contents and ending with pointers for further reading. Within each chapter are examples of the calculations involved to, as far as possible, allow the reader to reproduce the analysis undertaken. There are also available additional resources to increase understanding of the topics being analysed. These include:

Spreadsheets to support standard calculations, such as link budgets and geometry conversions

Example simulation files configured for the scenario under discussion.

These can be found by following the link on the Wiley web site page for this book.

Wherever possible the international system of units are used for all calculations.

1.4 Case Study: How to Observe Interference

It is generally hard to accidentally create interference between different types of consumer radio systems. It should be noted that deliberately causing interference into another’s radio system is considered a criminal offence in most legal systems and so should not be attempted. But you could try observe the impact of interference into one of your own radio receivers in a licence exempt band and see if you can detect any change in behaviour.

A good frequency band to experiment with is the one used by Wi-Fi at around 2.4 GHz as this has a range of different uses including microwave ovens. These are shielded to reduce emissions outside the device but there is usually some leakage that can be used as a source of interference into communications equipment. In particular, this can lead to issues for sensitive services such as radio astronomy. In 2015 the Parkes Radio Telescope in Australia investigated unusual signals it classed as ‘perytons’ and the source was discovered to be an on-site microwave oven emitting pulses at 1.4 and 2.4 GHz (Petroff et al., 2015).

For example, consider the two set-ups in Figure 1.1 where a smartphone was configured with an application to test the speed of the broadband link accessed via a Wi-Fi connection. Initially in case A the smartphone was positioned 0.5 m from a microwave oven and about 5 m from the access point. The Wi-Fi access point was configured to use the 2.4 GHz band rather than other frequencies (e.g. those around 5 GHz).

Figure 1.1 Domestic test set-up for detecting interference

The throughput was tested twice for each of the cases when the oven is on or off with results as in Table 1.1.

Table 1.1 Results of tests for case A: Smartphone by microwave oven

Microwave oven

Off

On

Test 1

9.38 Mbps

0.72 Mbps

Test 2

9.40 Mbps

—

a

a The smartphone did not complete the speed test reporting ‘Network Communication Issues’.

In case B the smartphone was moved to be located 0.5 m from the access point and about 5 m from the microwave oven. The corresponding results are shown in Table 1.2.

Table 1.2 Results of tests for case B: Smartphone by Wi-Fi access point

Microwave oven

Off

On

Test 1

9.40 Mbps

7.24 Mbps

Test 2

9.38 Mbps

6.43 Mbps

From these tests the following results can be deduced:

The microwave oven can degrade the performance of the smartphone’s communication link

The degree of degradation varies depending upon the distances from the smartphone to the Wi-Fi access point and microwave oven.

You could try this yourself at home, though you are likely to get different numbers depending upon equipment types and broadband link. Note that no electronic device should be placed inside a microwave oven.

Note that while there was a degradation of the communication service from around 9.4 to 6–7 Mbps, this data rate could still be considered usable. One of the key questions about interference analysis is what counts as an acceptable level and what would be ‘harmful interference’.

This is an example of using measurement to detect how interference can degrade a communication service: the objective of this book is to describe tools and methodologies that can predict whether interference would or would not occur.

Important Note

All the systems and their parameters used in this book are for illustration purposes only. Any study based upon ideas in this book should check references, in particular for more recent developments.

2Motivations

This chapter considers the question of the motivations for interference analysis. It puts the subject in its context and describes the framework within which interference analysis is often undertaken, in particular the work of the International Telecommunication Union (ITU).

It begins by considering why we analyse interference, the drivers that lead to requirements for interference analysis and the different types of interference analysis and then looks at the international and regional regulatory organisations. Given the importance of these institutions, there is a description of the working methods involved and how the results of studies documented in input papers are handled.

2.1 Why Undertake Interference Analysis?

In the 1920s, in the United States, there was a boom in commercial radio stations so that by 1926 there were 536 stations transmitting but only 89 channels available. With such congestion, each would turn their power up to maximum to drown out their competitors. The result was chaos, with radio becoming ‘a tower of Babel’, and according to the New York Times, all you could hear was something like ‘the whistle of a peanut stand’ (Goodman, n.d.).

It was a classic example of the tragedy of the commons (Wikipedia, 2014c), a concept developed by the economist Garrett Hardin in which if a resource that has value is freely available, it will be over-utilised to the point at which it becomes unusable. In this case, the radio spectrum had value, as it permitted the radio broadcasters to operate: indeed their business model would fail without it. The problem was that uncontrolled use led to interference between radio systems, which meant that the operators were unable to achieve their required quality of service (QoS).