TErrestrial Trunked RAdio - TETRA

With 124 Figures and 22 Tables

123

Peter Stavroulakis

TErrestrial Trunked RAdio - TETRA

A Global Security Tool

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Prof. Peter Stavroulakis

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Dedication

This book is dedicated in memory of my sister Mary whose affection,support and guidance during the early years of my University studies affected my career in a fundamental way.

Acknowledgements

I feel indebted to the contributors of this book whose diligent work and

collaborator Anastasios M. Haddad who spent countless hours to put the material in the format required by the publisher.

unique contributions made this book possible. Special thanks are due to my

Preface

Following the development of wireless communications starting from satellites in the late 60’s to the wireless cellular in the 80’s and now the Private Mobile Radio (PMR) systems, it is obvious that each time every new technology achieved a good technical solution satisfying a special need at an acceptable price until another need would come up that needed special consideration. Of course the technology evolves at a different pace at different time periods through the centuries but one thing has to be true. Special needs always existed, but remained unsatisfied until technology could be used to offer an acceptable solution at a reasonable price.

The last, at least five years, the public safety issue, became of major importance. Many types of Public/Private Mobile systems have appeared as we show in chapters 2 and 3, which seemed to satisfy the need at that time. The European Telecommunications Standards Institute (ETSI), foresaw that Terrestrial Trunking Radio - TETRA systems are good candidates to satisfy this need even on an international level. With the encouragement and support of the TETRA MOU, standards were in a continuous evolution and TETRA has become the tool to design any type of public security system.

In this book we show the TETRA can be improved greatly and these improvements eventually will be part of future standards. The areas examined include channel assignment and multiple access techniques, video transmission, WLAN integration and the establishment of multiple wireless mesh networks. Since the requirements for these networks is security we show that innovative techniques such as those based on chaotic signals can be used to maximize security. It is believed that this book will become a reference point for many new researchers whose ambition is to find a general solution to the modern problems within the context of public safety.

List of Contributors

Peter Stavroulakis Technical University of Crete Crete, Greece

Stavros Kotsopoulos Wireless Telecommunication Laboratory Department of Electrical and Computer Engineering University of Patras, Patras, Greece Email: kotsop@ece.upatras.gr

Dr Konstantinos Ioannou Wireless Telecommunication Laboratory Department of Electrical and Computer Engineering University of Patras, Patras, Greece Email: ioannou@ece.upatras.gr

Dr John Panoutsopoulos, Michail Tsagkaropoulos Wireless Telecommunication Laboratory Department of Electrical and Computer Engineering University of Patras, Patras, Greece Email: gpanouts@ece.upatras.gr

mtsagaro@ece.upatras.gr

Ilias Politis Wireless Telecommunication Laboratory Department of Electrical and Computer Engineering University of Patras, Patras, Greece Email: ipolitis@ece.upatras.gr

Email: pete_tsi@yahoo.gr

Apostolis Salkitzis

Dimitris Axiotis Telecommunications Laboratory School of Electrical and Computer Engineering National Technical University of Athens E-mail: jaxiot@telecom.ntua.gr

Pau Plans, Carles Gomez, Josep Lluis Ferrer and Josep Paradells Technical University of Catalonia (UPC) Wireless Networks Group (WNG) E-mail: pplans@entel.upc.edu

List of Contributors

Motorola, 32 Kiffisias Ave., Athens, Greece 15125 E-mail: salki@motorola.com

X II

Table of Contents

1 Introduction .............................................................................................1 1.1 Why TETRA ..................................................................................1

References....................................................................................................4 2 Modern Security Requirements in Private Mobile

Communications Systems........................................................................5 2.1 Introduction ....................................................................................5 2.2 PMR Systems [1]............................................................................6

2.2.1 PMR Configurations .............................................................6 2.2.2 Comparison Between PMR and Cellular [2].......................11 2.2.3 PMR Standards [1] ..............................................................14

2.3 PMR Limitations [4] ....................................................................28 2.3.1 Edge of Coverage Voice Quality ........................................28 2.3.2 Requirements of PMR Services ..........................................33 2.3.3 Interoperability [6] ..............................................................37

References .............................................................................................42 3 TETRA Providing an Acceptable Security System Solution ................43

3.1 Introduction ..................................................................................43 3.2 Hierarchical analysis ....................................................................44

3.2.1 Air interface specifications..................................................44 3.2.2 GSM ASCI ..........................................................................45 3.2.3 Enhanced Multi-Level Precedence and Pre-emption

service (eMLPP)..................................................................45 3.2.4 Voice Group Call Service (VGCS) .....................................46 3.2.5 Voice Broadcast Service (VBS)..........................................47

3.3 TETRA .........................................................................................47 3.3.1 Comparison of specified features ........................................48 3.3.2 Technical analysis ...............................................................49

References .............................................................................................66 4 Channel Assignment and Multiple Access

in Trunking Radio Systems [1]..............................................................67 4.1 Channel Assignment Techniques [1]............................................67

4.1.1 Introduction .........................................................................67 4.1.2 Channel Allocation Schemes ..............................................68

4.2 Channel Assignment Optimization...............................................80 4.2.1 Introduction .........................................................................80 4.2.2 Model Formulation..............................................................80 4.2.3 One Layer Architecture using Erlang Model ......................82 4.2.4 Channel Assignment Scheme based on a Three Layer

Architecture.........................................................................84 4.2.5 Comparison of One layer with Three Layer

Architecture.........................................................................90 4.3 Multiple Access Techniques.......................................................102

4.3.1 CDMA Techniques in TETRA systems ..........................102 References ...........................................................................................126

5 Video Transmission over TETRA .......................................................133

5.1 Introduction ................................................................................133 5.2 Evolution of Public Safety Mobile Networks.............................134

5.2.1 Evolving Data services for public safety...........................135 5.2.2 The TETRA solution to PSDR

communication environment.............................................136 5.2.3 The Market Considerations ...............................................138 5.2.4 TETRA Enhanced Data Service-TEDS ............................139

5.3 Overview of DATA Transmission over TETRA .......................141 5.3.1 TETRA (V+D) Technical Characteristics.........................141 5.3.2 TETRA Network Services ................................................147 5.3.3 High Speed Data service provisioning ..............................149

5.4 Video Encoding Techniques.......................................................151 5.4.1 Background .......................................................................151 5.4.2 Compression standards overview......................................153 5.4.3 Encrypted Video over TETRA..........................................170

5.5 Performance Analysis of video broadcasting over TETRA .......174 5.5.1 Performance Evaluation ....................................................175 5.5.3 Video Quality Measurements............................................178

5.6 Vision for Future Public Safety Communication Systems .........181 5.6.1 Future Trends ....................................................................181 5.6.2 All-IP convergence............................................................182 5.6.3 TETRA – TEDS interoperability ......................................183 5.6.4 TETRA over IP .................................................................183 5.6.5 Integrated TETRA-WLAN system ...................................184

5.7 Conclusions ................................................................................186 References ...........................................................................................188

X IV Table of Contents

Table of Contents

6 TETRA as a Gateway to Other Wireless Systems..............................191 6.1 Introduction ................................................................................191 6.2 TETRA Air Interface: Logical and Physical Channels ..............192

6.2.1 Logical Channels...............................................................193 6.2.2 Physical channels ..............................................................194

6.3 TETRA Packet Data Transmission ............................................195 6.3.1 Packet Data transmission and reception procedures .........198 6.3.2 TETRA IP user authentication ..........................................202

6.4 SNDCP states and state transitions.............................................205 6.5 UDP versus TCP on top of TETRA IP layer..............................211 6.6 TETRA Packet Data modems ....................................................213

6.6.1 Types of Packet-data Mobile Stations...............................214 6.7 TETRA and WLAN Integration for Improving Packet-Data

Transmission Capabilities ..........................................................216 6.7.1 Integrated WLAN/TETRA System Overview ..................220

6.8 System Architecture ...................................................................223 6.8.1 Architecture Elements and Interfaces ...............................223 6.8.2 Protocol Architecture ........................................................225 6.8.3 Packet Structure ................................................................227 6.8.4 WLAN Association and TETRA Location

Update Procedure ..............................................................228 6.8.5 Group Call Initiation and Participation .............................230

6.9 Conclusions ................................................................................231 References ...........................................................................................233

7 TETRA as a Building block to WMNs................................................235

7.1 Introduction ................................................................................235 7.1.1 Requirements.....................................................................239 7.1.2 Discussion .........................................................................244

7.2 Wireless Mesh Networks............................................................245 7.2.1 Definition and classification of WMNs ............................245 7.2.2 MANET routing protocols ................................................246 7.2.3 Influence of routing protocols on network performance...253 7.2.4 Multicast in WMNs ...........................................................259

7.3 TETRA DMO.............................................................................263 7.3.1 DMO overview..................................................................263

7.4 TETRA Release 2.......................................................................273

X V

7.5 TETRA extensions for building WMNs.....................................275 7.5.1 Routing capabilities...........................................................277 7.5.2 Wireless Interface..............................................................283 7.5.3 Overview of network performance figures .......................287

7.6 Conclusion..................................................................................293 References ...........................................................................................295

Appendix..................................................................................................299

X VI Table of Contents

1 Introduction

Peter Stavroulakis

1.1 Why TETRA

If someone has been following the recent (last five years) International events both in the sphere of technical developments but also in the Interna-tional politics, he would have noticed that there is a general outcry for the development of secure telecommunication systems covering all aspects of wireless communications. This situation has become much more serious and demanding because of the fact that wireless technology evolution is accelerating to satisfy the ever increasing market demands for more mo-bility to all kinds of telecommunications services whether they involve voice, IP, Video, WLANS, Ad-Hoc, Mesh, Peer- to-Peer and Sensor Net-works to name a few.

This newly created demand, a large part of which comes from the public and private safety sectors such as police, fire brigades, ambulances (tele-medicine) and the private sector such as the trucking transport businesses, airport safety authorities e.t.c, is being satisfied by the Public/Private Mo-bile Radio(PMR) systems. These systems have, on one hand, the general characteristics of cellular systems but, on the other hand possess such unique security characteristics such as end to end encryption, field control by a dispatcher type of capabilities as well as trunking(switching) capabil-ity and thus create autonomous telecommunications systems and distinct from cellular.

In this book, we are examining this evolution and we are showing that TETRA is the best candidate to satisfy all above requirements whether they are technological, security or service oriented. The reader who is not familiar with the fundamental aspects of PMR or TETRA is referred to [1 and 2]. Since TETRA was developed mainly for voice communications,

the European Telecommunications Standards Institute (ETSI) which is re-sponsible for developing its standards at least for Europe, is continuously updating its them in order to meet new requirements. See chapter 7. We, in this book, examine new ways and go one step further to prove that fur-ther improvements and innovative techniques, which we hope one day will become TETRA standards, can make TETRA the building block for fu-ture security networks for universal use. As a matter of fact we propose, in the Appendix, a general scheme which is based on the results presented in the chapters 2-7 and on references 2 and 3 that TETRA not only could become the building block for integrating WLANS and Ad-Hoc networks into unified networks for providing general wireless services but will also serve as a global security tool through the use of the proposed chaotic based encryption and/or modulation techniques.[3, 4].

We show in Chapter 2 the basic features of the class of systems to which TETRA belongs, their basic configurations, the different technologies used and the problems that present in their usage as security tools in the Private Mobile Radio (PMR) communications field. Actually, even though these systems have been designed as the security alternatives of their public equivalents such as the GSM, still they have limitations which are pointed out. As the best candidate to satisfy modern security requirements, we pre-sent TETRA. It is shown, by identifying the elements on which a com-parison of the requirements with its special features of the evolving stan-dards and the improvement that are possible for TETRA, that TETRA can play a major role in the next generations of PMR systems. This com-parison takes place in chapter 3 where the differences between TETRA and a GSM solution are analysed in three dimensions in the hope to exhibit the clear and perhaps unique advantages of TETRA for security applica-tions as will be shown in the subsequent chapters. The first dimension compares the applicable ETSI specifications and points out which func-tions are available according to the standards. Proprietary solutions will not be discussed on that level. The second dimension, a technical analysis, discusses how the end users and the operators perceive the differences be-tween the network-solutions. Since it is possible technically to provide TETRA capabilities using GSM, an economic analysis focusing on the cost of the two alternative solutions, including capital and operational costs for the network infrastructure and end-user terminals which constitutes the third dimension, will be touched upon only briefly because the applica-tions of secure systems do not depend as much on economic terms but on their technical feasibility and the existence of international standards and on their ability to satisfy certain predefined requirements. We go one step further, in chapter 4, to show that the TETRA system can be improved to become an unique tool for security. First area of enhancement is the

2 1 Introduction

channel assignment methodology. We first provide an overview of different channel assignment algorithms as they relate to TETRA Networks and compare them in terms of performance, flexibility, and complexity. We first start by giving an overview of the channel assignment problem in a cellular environment and we discuss the general idea behind major channel alloca-tion schemes. Then we proceed to discuss different channel allocation schemes within each category and we follow with the development of an op-timization technique in channel assignment. Finally we present multiple ac-cess techniques in section 4.3.

In chapter 5 we present the scheme by which we can transmit securely VIDEO through TETRA. Within the context of this chapter, we monitor the QoS regarding MPEG-4 video streaming traffic delivery, in terms of both packet loss and perceived image quality, over TEDS networks.

The rest of the chapter is organized as follows. In Section 5.2, we at-tempt to follow the evolution in public safety mobile networks and the role of TETRA networks. The need for more complex context in the informa-tion exchange, guaranteed quality of service and secure, flexible and scal-able infrastructures led to the standardization of TETRA and TEDS sys-tems. Section 5.3, includes an extensive overview of data transmission over TETRA, followed by an insight on the evolutions incorporated in TEDS standard that allowed video and high data rates support. A detailed analysis of the current video encoding techniques and error concealment methods are contained in Section 5.4. Particular interest is given to MPEG-4 encoding standard as it enables higher video compression rates, thus making it an ideal solution for video traffic over TETRA and TEDS net-works. The main two techniques of video encryption are described in this section as well. In the following Section 5.5, we provide a performance analysis of video transmission over TEDS network.

In this chapter 6, we present an overview of packet data transmission over Terrestrial Trunked Radio (TETRA) release 1 networks as well as a solution for integrating TETRA with WLANs as a way to improve the packet data transmission capabilities. We first give a brief overview of the TETRA air interface and the available logical and physical channels. We then present various aspects of packet data transmission over TETRA, where we conclude that TETRA release 1 cannot provide the means to support demanding IP-based applications, mainly due to bandwidth and QoS constrains. Motivated from this conclusion, we then present a solution for integrating TETRA with Wireless Local Area Networks (WLANs) and thus realizing hybrid broadband networks suitable to support the next gen-eration of public safety communication systems. The specified solution al-lows TETRA terminals to interface to the TETRA Switching and Management Infrastructure (SwMI) over a broadband WLAN radio access

3 1.1 Why TETRA

network, instead of the conventional narrowband TETRA radio network. These terminals are fully interoperable with conventional TETRA termi-nals and can employ all TETRA services, including group calls, short data messaging, packet data, etc.

Possible extensions of the TErrestrial Trunked RAdio (TETRA) system with the purpose of building a mesh network are analyzed in chapter 7. The main objective is to provide the services, already offered by PMR sys-tems, everywhere and at any moment, taking then profit of the natural ad-vantages that a mesh network presents. We evaluate extensions which make use of already available functionality of TETRA, such as client, re-lay and gateway functions, in order to minimize the changes that should be made to the standard and make the adaptation as simple as possible. Fi-nally in the Appendix we show that TETRA can be used as a building block for universal super-secure systems using chaotic techniques.

References

1. J. Dunlop et.al, Digital Mobile Communications and the TETRA System, John

Wiley 1999. 2. Doug Gray, TETRA : The Advocate’s Handbook, Pryntya, 2003 3. Peter Stavroulakis, Chaos Applications in Telecommunications, Taylor and

Francis 2006 4. Peter Stavroulakis, Secure Telecommunication Systems based on Chaotic and

Interference Reduction Techniques, Pending International Patent PCT/GR000038

4 1 Introduction

2 Modern Security Requirements in Private Mobile Communications Systems

Peter Stavroulakis, Kostas Ioannou

2.1 Introduction

Having discussed the main objectives of the book in the previous chapter, we shall now embark on showing the basic features of the class of systems to which TETRA belongs, their basic configurations, the different tech-nologies used and the problems that present in their usage as security tools in the Private Mobile Radio (PMR) communications field. Actually, even though these systems have been designed as the security alternatives of their public equivalents such as the GSM, still they have limitations which are pointed out. As the best candidate to satisfy modern security require-ments, we present TETRA. It is shown, by identifying the elements on which a comparison of the requirements with its special features of the evolving standards and the improvement that are possible for TETRA, that TETRA can play a major role in the next generations of PMR systems. An area which requires special attention is the interoperability functional re-quirements based on both technical and operational issues The superiority of TETRA is then proven in chapter 3 comparing TETRA with its closest competitor which is GSM. This superiority becomes then the basis for us-ing TETRA as the building block in many applications that involve im-plementations of secure integrated designs.

6 2 Modern Security Requirements

2.2 PMR Systems [1]

2.2.1 PMR Configurations

The simplest PMR configuration is point-to-point direct terminal commu-nication. Such a system has no infrastructure, and in most cases all termi-nals within range receive messages as shown in figure 2.1. It is possible, however, to conduct private conversations through the use of signaling tones or messages which mute terminals which the message is not intended for so that it is not heard. Either a single common frequency is used, or dif-ferent frequencies can be used for different call groups. Communication is only possible between terminals when they are in range of each other, and given the power limitations on battery operated portable devices, this may be a significant restriction.

Fig. 2.1. Simple direct mode PMR configuration

One of the most common PMR configurations is the dispatch operation. At least two channels are used, one for uplink communications between terminals and the base station, and one for the downlink to the terminals. Messages from the dispatcher on the downlink can be received by all ter-minals (although again individual addressing is possible), whereas mes-sages from the terminals can only be received by the dispatcher. Mobile to mobile communication is possible via the dispatcher. Links with the public switched telephone or data networks are possible, again via the dispatcher as shown in figure 2.2.

2.2 PMR Systems[1] 7

Fig. 2.2. Dispatch mode PMR configuration

A number of refinements to this basic system are possible. If extended

coverage is required, but central dispatch or PSTN network access is not necessary, the base station can be connected as a repeater. This is called “talkthrough” mode where any uplink messages are retransmitted on the downlink, effectively extending the range of mobiles to that of the base station. In Figure 2.3, the transmission from mobile 1 is received by mo-biles 2 and 3, even though they would not have been in range if the mes-sage had been transmitted directly.

8

Fig. 2.3. Talkthrough repeater operation

Different organizations can share repeaters (so-called “community base stations” or “community repeaters”) if the different users have signalling to identify their messages. The signalling is retransmitted by the base sta-tion, so that users in other groups are muted and privacy maintained. Since users in groups do not hear all the messages it is necessary to keep usage low to ensure access. Such systems therefore include time outs to ensure that users do not hog a channel.

A better option, although one which requires more complexity, is trunked operation. In this case, several channels are available, pooled be-tween different PMR operators. This allows trunking efficiency and makes it more likely that a free channel will be available.

In many cases, a single base station will not be able to cover the entire service area. If the uncovered area is limited to relatively small areas, such as in the shadow of a building, a remote radio port can be provided to il-luminate this area.

Since hand-held terminals usually have lower power than mobile termi-nals mounted in vehicles (due to battery and safety restrictions), mobiles can receive signals at greater ranges than hand-held. Portable vehicle-mounted repeaters can therefore be used to provide hand-held coverage to users working near to their vehicles. This mode of operation is commonly used by the emergency services.

2 Modern Security Requirements

9

Fig. 2.4. Using a radio port to fill a coverage black spot

Fig. 2.5.

If larger areas have to be covered, several base stations must be used as

shown in figure 2.6. If only a relatively low capacity is required, these can all transmit the same signal in a system known as simulating, and the sys-tem acts in the same way as one large cell. In analogue systems the fre-quencies used in the different cells vary by a few hertz which reduces problems in the overlap regions that receive signals from two or more cells. In digital systems, this is not possible, and systems have to be care-fully designed to ensure that terminals can receive an adequate signal in the overlap region.

2.2 PMR Systems[1]

10

Fig. 2.6. Wide area coverage using several base sites

Larger capacity systems would require the use of multiple cellular re-use. Such systems are considerably more complex than other configura-tions, requiring switching between the base stations and handover of mo-biles between cells as shown in figure 2.7. However, large PMR operators, and PAMR operators, need to use cellular configurations to give them suf-ficient capacity. Even large PMR or PAMR systems do not have as much traffic as public cellular systems, and so will have a relatively flat architec-ture compared to the complex hierarchical network architecture of GSM. The next section compares PMR and cellular operation more generally. A more detailed comparison will be given when TETRA will be compared technically with GSM in chapter 3.

Fig. 2.7. Cellular PMR Configuration

2 Modern Security Requirements

11

2.2.2 Comparison Between PMR and Cellular [2]

PMR systems are in many ways similar to the public cellular systems. However, there are some significant differences between the two types of system which means that their design requirements are very different. The differences contribute to the security advantages of PMR over the cellular public systems as we shall see in chapter 3. The main differences between PMR requirements and the requirements of cellular systems are as follows.

Group calls.

Cellular users have a much lower requirement for group calls than PMR users, and such requirements can usually be covered by having some sort of conferencing facility to link calls. PMR systems, on the other hand, must have flexible group call facilities, including allowing parties to enter and leave groups, and the ability to contact all users in a particular area.

Dispatcher operation

Many PMR systems have a centralized dispatcher controlling and monitor-ing the system. This facility is not required in a cellular system.

Decentralized operation

PMR systems are often required to work in a direct mode, where mobiles contact each other directly rather than via fixed base stations and network infrastructure. This allows operation outside the coverage of the fixed in-frastructure and also in an emergency. Cellular systems must route all communications through the fixed infrastructure to allow for control and billing.

Fast call set-up

Cellular users dial a number, and wait for their call to be connected. This may take tens of seconds depending on the call’s destination and call han-dling issues such as billing. In contrast, PMR users with a push-to-talk expect to do exactly that -press and talk- without delay.

Supplementary services

Supplementary services are additional call services over and above the basic communication service. Examples include call forwarding for a voice call. PMR users are more likely to want supplementary services

2.2 PMR Systems[1]

12

tailored to their particular needs, such as variable priorities for different users, the ability to break into or monitor conversations, and so on. Cellu-lar operators, on the other hand, have a much broader user community and will wish to offer a fixed range of simpler services which they can be con-fident will be commercially viable.

Traffic patterns

With a PMR system which operates without dialing (i.e. a push-to-talk to contact the dispatcher or other users), calls are very short, consisting of a sentence or two. Usage regulations request a limit on shared PMR chan-nels of 15-20 seconds, and the system may include a time out limiting the length of activity periods to 30 seconds or one minute so that one user is not able to hog a channel. In contrast, cellular calls will consist of a con-versation, and so be longer. The average length of cellular calls is just un-der two minutes. Another difference between PMR and cellular is the des-tination of calls. Most cellular calls originate or terminate outside the mobile network, with only a small proportion of mobile to mobile calls within the operator’s network. On the other hand, PMR calls are usually intended for other users on that network, and the facility to route calls to other networks may even be absent as shown in figure 2.8.

Fig. 2.8. Sources and destinations of calls in PMR and cellular networks

2 Modern Security Requirements

13

Capacity

Cellular operators have a fixed allocation of frequency and they wish to maximize the number of users on the system to maximize their revenue. Their user base is large compared with their spectrum allocation and there is therefore an incentive to provide a large number of base stations, small cells, high re-use and efficient air-interface techniques to increase the number of simultaneous users supported. A PMR system is likely to have a much lower user base and the traffic is lower due to shorter calls, so capac-ity for the PMR operator is not likely to be an issue. PMR operators with their lower capacity requirements will want to minimize infrastructure costs, and so will have much larger cells, in the order of tens of kilometers. Cellular operators usually have cells limited to a few kilometers in radius at most. Capacity does affect PMR operators in another way when it comes to obtaining licenses. In many urban areas there are so many PMR opera-tors that there are no spare frequencies and channels have to be shared. A PAMR system allows trunking of calls and results in a more efficient use of the spectrum.

Frequency planning

In a cellular system, frequencies are planned throughout the whole system. This is not the case in PMR, where frequencies will be allocated to users for specific areas and there may be no co-ordination between users in a particular area. This means that a PMR system must obey strict interfer-ence limits with regard to neighboring earners, whereas cellular systems can tolerate adjacent carrier interference because neighboring cells can be planned with this in mind.

Control, billing and authentication

In a cellular system the user is authenticated and billed for each call. This is in contrast to a PMR system where permitted users may use the system at will. The PMR operator has to pay for the infrastructure but this is effec-tively a standing charge and there is no per call charge.

Relationship between the service provider and the user

In a PMR system the users are providing their own service, or will employ someone to provide the service on their behalf. The quality of the service is therefore directly within the control of the user. A cellular system

2.2 PMR Systems[1]

14

provides a standard service, though perhaps with some amendments. The user therefore has much less control. A PAMR system falls some-where between these two extremes.

Coverage

A cellular operator will provide coverage where it is economic to do so, which is where people who want to make mobile phone calls are. Cellular operators normally quote coverage in terms of the percentage of the popu-lation rather than the land mass, as complete coverage of the land mass of a country would be extremely expensive, and unless external factors such as government support are involved, may not be undertaken. On the other hand while cellular users may be able to operate their system at capacity in some areas, judging that the extra infrastructure costs would not be recov-ered by the additional traffic served. PMR operators may not have the op-tion of dropping or queuing high priority calls, and will therefore have to provide additional capacity to meet worst-case, rather than average, traffic load.

PMR operators usually require coverage over predefined areas of opera-tion. Cellular users must be able to use their phones over as wide an area as possible, including internationally. PMR users may not be interested in use outside their specific location, although in the case of police services or truck drivers this might still be a considerable area requiring roaming between mobile networks. It is then obvious that there is need for the fol-lowing peer standards.

2.2.3 PMR Standards [1]

The Need for and Development of Standards With the move towards digital PMR systems, there has been a trend away from proprietary systems toward a public standard with which equipment must conform, thus allowing equipment from different manufacturers to be used together. Moves towards public standards have come from manufac-turers and operators, as in the case of TETRA, or the user community, as in the case of APCO25. The attitudes of governments to the standardiza-tion process are quite varied. A hand off approach has been taken in the United States of America, where it has been decided not to insist on the APCO25 system but to allow the market to dictate which system is used. In contrast, in Europe, the European Commission is far more proactive in setting standards and even defining them at a technological level through

2 Modern Security Requirements

15

ETSI. This insistence that for certain government contracts systems conforming to ETSI proposals must be used is one of the reasons cited for the opening of the Matra PMR system resulting in the TETRAPOL standard.

Public standards have a number of advantages, as was shown by the success of GSM in the mobile radio sector. Public standards enlarge the market, allowing an economy of scale as well as opening the market for niche players in more specialized areas. All the various standards include defined interface points allowing users to source different parts of the sys-tem from different suppliers. As well as forcing more competition between providers, it means that suppliers are no longer required to produce all the components of the system, although turnkey .solutions are still certain to be required by some users.

Public standards also allow users more freedom to move equipment be-tween networks. This is less of an advantage than it would be in the case of public cellular systems, where some users want a high degree of mobility and roaming between networks. However, it can still be seen to be an ad-vantage to many PMR users, especially those, such as the emergency ser-vices, who co-ordinate with each other.

Analogue PMR

Early PMR systems were analogue and proprietary. However, a wish to share infrastructure costs and a need to share spectrum led to the develop-ment of trunked radio systems, and with this development came the need for standards so that equipment could be sourced from different suppliers. The earliest such system, which is still available from a number of differ-ent suppliers, is LTR (logic trunked radio) developed by E F Johnson. A number of these systems are in operation worldwide.

Another major analogue PMR standard is MPT1327 (Ministry of Post and Telecommunications), which developed in the UK in the late 1980s, but has been adopted by manufacturers and implemented worldwide. It is the most widely used PMR standard, common everywhere except the United States of America, where proprietary systems by Motorola, and to a lesser extent Ericsson, dominate. Although MPT1327 is more complex and expensive than some simpler analogue systems, it is relatively efficient in terms of spectrum use (digital systems are still better by a factor of two), and offers some data capabilities as well as the normal PMR voice call fea-tures such as group calls, fast call set-up, and priorities.

PMR networks are expensive, and decisions to replace or upgrade are not taken lightly. Analogue systems arc likely to remain until capacity, maintenance or required features force a replacement. At the time of writ-ing in 1999, manufacturers of LTR and MPT1327 equipment were still

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promoting their analogue systems, in particular for use in countries or ar-eas without spectrum capacity constraints.

Digital PMR [4]

Digital systems offer a large number of advantages over analogue systems. A major advantage is the ability to recover the signal completely as long as the noise level is below particular threshold. This compares with the ana-logue case, where noise is always and degrades the quality of the signal. There is a disadvantage in that when level approaches the threshold of a digital system, the system performance falls off very rapidly, whereas in an analogue system the quality falls off steadily, giving clear of the system’s limits as shown in figure 2.9.

Fig. 2.9. Comparison of analogue and digital speech quality ith differing signal to noise level

Additional advantages relate to the sending of data, which can be sent directly in a digital system the requirement for a modem, and for trunking, as a digital signal can be manipulated more easily than an analogue one. While digital modulation is more easily than analogue systems, the trans-formation of a speech signal into digital form use of very efficient com-pression techniques so that the spectrum required for a speech signal is lower with digital modulation and good speech coder than with an modula-tion scheme.

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Digital systems are more complex, and therefore more expensive. How-ever, the increased flexibility, availability of services, and efficiency, in combination with the increased quality of service, means that the PMR market is now moving towards digital in the same way as the cellular mar-ket five years ago. A short description of the ones which made an impact are summarized in the following.

1. EDACS

EDACS (Enhanced Digital Access Communications System) is a proprie-tary digital PMR system from Ericsson. The first systems were installed in the late 1980s, and the system has found application in the military field, as well as its principle use in public safety. When the system was launched, a major selling point was its data services, which were unusual for a mobile radio system of that time, and the system has achieved con-siderable success, particularly in the USA.

2. Geotek-FHMA

Geotek-FHMA is a digital system which uses slow frequency hopping on an FDMA structure. The technology employed is novel for the civil mobile radio environment, being more common for secure military communica-tions. As well as developing the system through its Israeli subsidiary, Geo-tek operated a limited number of digital networks itself in the USA, but the system suffered from limited take-up. A link up with IBM in 1997 failed to raise fortunes, and Geotek withdrew from digital network provision in 1998. The system itself, which has been installed in about half a dozen countries, is promoted as the PowerNet system for public safety applica-tions along with Rafael, the Israeli defense firm which was a partner in its development. National Band 3, a UK PAMR operator owned by Geotek, was going to adopt Geotek-FHMA, but this network is now owned by Telesystem International Wireless of Canada, which through its Dolphin Telecom subsidiary is using TETRA for new digital PAMR operations in the UK and France

3. APCO25

APCO25 was an initiative by the Association of Public-safety Communi-cations Officials - International, Inc. (APCO) to try to create a standard PMR system for public safety applications. While the emphasis in Europe has been to create a cross-border standard for such systems, the United States has a more market-orientated culture and different countries

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may have incompatible systems from different suppliers. The idea of a federally required standard has since been watered down, but the system has continued to be developed with Motorola, which owns lights to much of the key technology, licensing this to other manufacturers. Motorola’s Astra system was the first APCO25 system, launched in 1996.

Recently APCO25 and TETRA agreed to cooperate on future develop-ments. In its current form, APCO25 is an FDMA system with 12.5 kHz carrier spacing, which is compatible with existing analogue channel spac-ing. However, future plans foresee halving the bandwidth requirements for speech channels to make more efficient use of spectrum. A narrow-band FDMA approach with 6.25 kHz carrier spacing has been proposed to allow this, but this is being reconsidered in the light of TETRA developments which may see a TDMA approach being employed for this development has had a presence in the market for a couple of years before the roll out of TETRA systems, and has been adopted by users in 15 countries, mainly in the public safety area.

4. TETRAPOL

Tetrapol faces a problem in terms of take-up in the EU, since although it is recognized by the ITU, it is not a formal standard approved by ETSI, and moves to convert the TETRAPOL PAS (Publicly Available Specifica-tion) to an ETSI standard have recently stopped. Most European Union countries are planning to use TETRA, although TETRAPOL has been rec-ognized by Schengen Group along with TETRA, and it is in use by secu-rity forces in France, Spain and Austria, as well as other European coun-tries such as Romania, Slovakia and the Czech Republic.

5. TETRA

The main focus of this book is the TETRA standard as used in security ap-plications. More technical details are given in chapter 3 in the forum of a comparison between TETRA and GSM. the appendix we summarizing the technical characteristics of TETRA. TETRA was developed from the start as an open harmonized digital PMR standard within ETSI. As an ETSI ap-proved system, it has a significant commercial advantage within Europe, both from the point of view of manufacturer and operator support, and from the point of view of governments, which in Europe will specify ETSI approved systems for their contracts. The wide user and producer base should provide significant economies of scale. However, the PMR market has a number of existing 2nt generation digital systems in operation al-ready, and with 3ld generation cellular systems only a few years away it

2 Modern Security Requirements