Integration of TETRA with Satellite Networks: A Contribution to the IMT-A Vision

Transcription

1 Wireless Pers Commun (2008) 45: DOI /s Integration of TETRA with Satellite Networks: A Contribution to the IMT-A Vision Emiliano Re Marina Ruggieri Giovanni Guidotti Published online: 22 February 2008 Springer Science+Business Media, LLC Abstract The paper addresses the integration architecture (I-concept) between a terrestrial technology TETRA (TErrestrial Trunked Radio) and satellite systems. This approach, that enhances and harmonises the features of both technologies, could provide an interesting contribution to the effectiveness of the International Mobile Telecommunications-Advanced (IMT-A) and, hence, to the 4G vision. TETRA can represent an interesting building block of an integrated network devoted to both civil and military scenarios; it meets the suitable technological capability requirement for integration, because it represents a consolidated terrestrial technology that can be trusted, hence focusing the integration effort on the definition, design and implementation of proper interfaces. System architectures are here proposed referring to short, medium term and long term scenarios. Keywords I-concept TETRA Satellite Interfaces 1 Introduction The integration of networks and services as well as the convergence of heterogeneous technologies represent a cornerstone for the effective deployment of 4G scenarios [1,2]. Intense research efforts have been devoted in the last years to the definition of the Integration Concept (I-Concept) and the identification of possible integration architectures for the provision of advanced services to both mobile and fixed users, including the convergence of communications and navigation (NavCom) services [1 8]. E. Re (B) M. Ruggieri Department of Electronics Engineering, University of Roma Tor Vergata, Roma, Italy emiliano.re82@gmail.com M. Ruggieri ruggieri@uniroma2.it G. Guidotti SELEX Communications, Via Mattei, 21, Chieti, Italy giovanni.guidotti@selex-comms.com

2 560 E. Re et al. The above is the ideal frame to define and test integrated architecture that can take benefit from the exploitation of different technologies. TETRA (TErrestrial Trunked Radio) can be an interesting building block of integrated networks devoted to both civil and military scenarios. TETRA allows the quick deployment of mobile networks: speed and mobility are two key-words particularly in an emergency environment. Moving from the above frame, the paper analyses possible integration scenarios between TETRA and satellite systems, aiming at the provision of an effective building block in the deployment of the 4G vision. The paper is organised as follows. In Sect. 2 an introduction of TETRA features is provided; in Sect. 3 some TETRA application scenarios are highlighted; in Sect. 4 possible integration scenarios between TETRA and satellite systems are depicted; in Sect. 5 conclusions are drawn and future perspectives of TETRA integration are provided. 2 TETRA The professional mobile radio market, which includes Private access Mobile Radio (PMR) and Public Access Mobile Radio (PAMR), has traditionally been scattered in many dimensions in terms of technologies, frequency allocations, etc. The first change towards international standardisation was the introduction of the analogue MPT1327 trunked radio standard. It was developed in 1988 by the British Department of Trade and Industry (DTI), and is primarily used in the United Kingdom, Europe, South Africa, and Australia [9]. Systems based on MPT 1327 generally consist of several radio channels: at least one of these channels is defined as the control channel and all other channels are traffic channels. Data messages between mobiles and the network are exchanged on the control channel at 1,200 bits per second. Each subscriber in an MPT-1327 trunked radio network has a unique call number. After it has been entered the call number will be converted in the mobile to a 20-bit address. For the duration of his call a subscriber is exclusively allocated a traffic channel from the available trunk. On an MPT-1327 network, various types of communications can take place: mobile mobile in different cells; mobile-line access unit via landline or radio; mobile-dispatcher station via landline or radio; mobile-pabx, Mobile-PSTN. Data Communications allow status messages on the control channel, short data messages on the control channel and transparent data transmission on the traffic channel (data communication). Point to point connections as well as group calls with/without talk entitlement are possible [9]. The introduction of the MPT 1327 trunked radio standard lead to a market success in most part of the world. TETRA is the first truly open standard for the digital mobile radio system, contributing to open the international market in the professional communications. The standard is defined by the European Telecommunications Standard Institute (ETSI), that joins network operators, national administrators, equipment manufacturers and users. ETSI publishes telecommunications standards that are mandatory for use in Europe, but also widely applicable outside Europe. TETRA standard does not specify a detailed network as in case of other standards; its aim is to define the air interface and the interface between the TETRA network and other networks like ISDN, PSTN, PDN, PABX and other TETRA systems. The network architecture is left to proprietary implementations in order to provide optimized solutions for various applications. TETRA is, hence, a powerful multi-function mobile radio standard that provides a comprehensive tool kit from which system planners may choose in order to

3 Integration of TETRA with Satellite Networks 561 satisfy their requirements. The TETRA suite of mobile radio specifications provides a radio capability encompassing trunked, non-trunked and direct mobile-to- mobile communication with a range of facilities including voice, circuit mode data, short data messages and packet mode data services. In addtion to these basic services, moreover, it supports a wide range of supplementary services such as call authorization by dispatcher, dynamic group assignment, priority calling and late entry to calls in progress. Many of these services exclusive to TETRA [10]. 3 Examples of TETRA Integration TETRA demonstrated in the past years to be a powerful technology for private mobile radio applications. Today, an intense work is ongoing to integrate TETRA networks with different technologies characterized by different maturity levels, also in the perspective of meeting the user growing demand for a wide range of multimedia applications [10]. A first step towards Heterogeneous Networks interoperability can be achieved by convergence over an IP core network: all voice, data and video signals can be exchanged through different networks using an IP core. The use of TCP/IP protocols over TETRA is suggested to assure a universal suitability of customer oriented applications. The IP protocol can be located in the Mobile Termination (MT) or in the Terminal Equipment (TE). In the latter case, the most important protocol is the Sub Network Dependent Convergence Protocol (SNDCP). The most important improvement enabled by the use of the IP protocol in TETRA networks is access to IP of networks and Internet. The drawback is the low data transmission rate allowed by TETRA. This issue is solved through the introduction by ETSI of TETRA release 2, where a high speed data transmission (HSD) is defined. The first step, the so called TETRA Advanced Packet Service (TAPS) based on adaptation of GPRS and EDGE systems, has been jumped by manufacturers, which are moving directly towards the final implementation named TEDS. The TETRA Enhanced Data Service is very flexible and allows variable data rates via channels with different bandwidths. Another interesting frame for TETRA is the integration with the IEEE x family. TETRA specifications are constantly being evolved by ETSI and new features are being introduced to fulfill the growing and ever demanding PSDR requirements. Mobile broadband technology could enhance TETRA networks to achieve the advanced services envisioned in the next generation of PSDR communication systems. Therefore, TETRA integration with IEEE x has been proposed more recently. Finally, the most advanced system providing integration of TETRA with other systems, and in particular with communication satellites, is the Nomadic Centre, that is being developed and tested by Telespazio and Elital (Fig. 1). The key feature of this system is its transportability, that makes it suitable in emergency scenarios. It has been conceived for the Civil Protection use. It is able to integrate wireless terrestrial technologies (WiFi, WiMax, TETRA, GSM, Radio - UHF/VHF, DTT) and to provide a wideband satellite link through SkyplexNet technology for backup purpose of such networks. 4 TETRA and Satellites There are two main reasons for integrating TETRA with satellites (Fig. 2). The satellite-based system(s) can provide to the TETRA-covered area data/information that can help TETRA users. The data/information exchanged among TETRA users could be rendered available

4 562 E. Re et al. Fig. 1 The nomadic centre Fig. 2 Example of TETRA and satellite communications integration to satellite-covered areas. The above points apply to many situations, but certainly become crucial when an emergency meant in a dual mode, i.e. in either a military or a civil environment is the reason for the deployment of the TETRA network. TETRA could be connected in principle with various satellite systems, characterized by different services and/or coverage and/or nature (civil, military). The crucial aspect becomes then the development of a proper interface (TSI, TETRA- Satellite Interface) that is able to manage the data exchange between the satellites and the

5 Integration of TETRA with Satellite Networks 563 TETRA network as well as to process bulky data so to transfer through TETRA only the volume compatible with the allowed data rates. The design and shaping of the TSI could be a key-step for the effective exploitation of TETRA in a satellite inclusive 4G scenario. The type of data flowing through the TSI can be different. In particular, data can belong to: Global Navigation Satellite Systems (GNSS), covering the area of interest for TETRA deployment. Global or Local Communications Satellite Systems (GCSS, LCSS) in either broadcasting or point-to-point/multipoint connection modes. Global Earth Observation Systems (GMES and in the System of Systems medium term vision GEOSS). Global Integrated Satellite Systems (GISS) where two or all three types of data (communications, navigation, Earth observation) are available (medium and long term vision). In the above frame, TETRA could be a flexible and quick means to deploy a local terrestrial connection area that, thanks to the TSI and, hence, to the satellite connections, can more easily perform its task event in disaster areas where the terrestrial networks have been damaged. The design of TSI should keep the following items into account: Flexibility: the interface performance should be mainly based on the software component, so that it can be reshaped to match different situations, rapidly variable with time and geographical area. Speed: the interface should be quickly deployed and if necessary reshaped. Security: the interface has to transform the security standard of the satellite-based data into the one required from the TETRA network. Two different TETRA-satellite intergration scenarios are envisioned: (i) a medium term scenario, where already available technologies and systems are employed; (ii) a long term scenario, where future trends are addressed, even envisioning a more complex contest where communications, navigation and Earth observation satellite systems are exploited jointly into a single powerful platform. TETRA is based on a precise network architecture, similar to that of GSM. This means that the main objective of TETRA technology is to provide a professional mobile communications service in given sites, and presently the use of TETRA can be limited by the availability of a proper core network infrastructure. Therefore, this powerful technology seems to show limitations whenever a fast deployable network architecture is needed. For instance, in a peace-keeping mission, an armed force could move to an hostile site where the presence of a network infrastructure for communication purpose is not guaranteed. In such an emergency scenario, the flexibility of a communication solution is the main point to make it successful or not. The answer to this user requirement could be met thanks to telecommunications satellites, providing backbone connectivity to a transportable satellite gateway, able to interface a local TETRA network to another one located in the satellite coverage, or to a mission control centre. In the short-medium term scenario, the envisioned system integrates a TETRA isolated cell, which is operating in DMO (Direct Mode Operation), with a satellite communication system. This integration is achieved through a transportable station, implementing the TSI.

6 564 E. Re et al. Fig. 3 A possible configuration in the short/medium term scenario It is commonly accepted that TETRA is more suitable in emergency scenarios than other commercial systems such as GSM/GPRS/UMTS, because its professional nature makes possible that in these situations the network does not become congested, and also a Base Station fall-back mode is available. Nonetheless, at present one of the main weakness of TETRA in emergency scenarios is the need for a terrestrial infrastructure that, even if designed with redundancies, could be no longer available when disasters occurs (fires, storms, Earthquakes etc.). At the same time, TETRA has a very powerful operation mode, the DMO, that allows to deploy an ad-hoc network without the need of any infrastructure. This is a typical example of a peace keeping mission, or a civil protection mission after a disaster, where a team need to keep in touch each other without needing any external facility. The drawback of such an ad-hoc network is its intrinsic isolation that does not permit to exchange information with the external world. This problem can be easily solved thanks to communication satellites, which can provide global coverage at any time without the need of terrestrial infrastructure. Figure 3 shows a system architecture, where a transportable station acts as a dedicated Gateway, interfacing TETRA terminals with a communication satellite. The gateway implements two DM functions, exploiting the same direct mode air interface: DM-GATE for TETRA terminals which want to access the remote network through the satellite extension. DM-REAPETER for TETRA terminals which want to connect locally, inside the coverage of the Transportable Station. The satellite forward the signal in downlink to a ground station (G/S), that finally sends data to an Emergency centre through a dedicated wired channel, or via a Virtual Private Network. In a second configuration (Fig.4), the ground station forwards data to the TETRA switched network (SwMI). In this configuration, the G/S has to implement the interface acting as a

7 Integration of TETRA with Satellite Networks 565 Fig. 4 A further configuration in the short/medium term scenario gateway on the side of the TETRA SwMI. Considering the transportable station, the satellite and the G/S as a joint entity, it corresponds to a DM-GATEWAY, connecting the user to the TETRA SwMI. Some comments apply to both configurations. The presence of the satellite is seamless to the user, that does not require any upgrading on his terminal. The most critical issues to be deeply understood are the following: Quality of Service (QoS) parameters, in particular: Service availability Connection set-up time, especially due to the satellite bandwidth demand; Queuing strategy in the Transportable Station; Delay time; Delay variations. End-to-end Security: Encryption; Authentication. In the long term scenario, the terrestrial TETRA network is fully integrated with the Global Integrated Satellite Systems (GISS) where two or all three types of data (communications, navigation, Earth observation) are available (Fig. 5). In this scenario, the architecture includes: User Segment, including the Mobile Terminals; Space Segment, including: Communications (Com) Satellites; Data Relay Satellite (DRS); Navigation (Nav) Satellites; Earth Observation (EO) Satellites.

8 566 E. Re et al. Fig. 5 Long term scenario Ground Segment, including: Satellites (Nav, Com, DRS, EO) G/S; Satellites (Nav, Comm, DRS, EO) Control Centres ; P/Ls Control Centres ; Emergency Control Centre; Transportable Station; IP Networks; Dedicated wired links. In this architecture, there are two core system elements from the proposed service point of view: Transportable Station Emergency Control Centre. The first one is in charge of providing the service access to the remote on-the-field users. It implements the above mentioned TETRA-Satellite Interface, and thus it must manage the user authentication and the authorizations to access the external world. Moreover, we can suppose that this station is fixed once it has reached the emergency location. Therefore, it can act as an augmentation element of the GNSS, sending the augmentation signal (the differential errors calculated inverting the navigation equations once it has precisely determined it own position) in order to allows the user terminal to improve the accuracy of its navigation receiver (if available). Concerning the latter element, the Emergency Control Centre is the real brain of the system. In fact it is in charge of process all the information coming from the EO satellites and from the emergency area, and to decide which information must be forwarded, and to whom it must be delivered.

9 Integration of TETRA with Satellite Networks Conclusions In this paper, moving for the 4G vision where integration of systems and convergence of technologies are keys for success, a system architecture for the integration of different terrestrial (TETRA) and Space (Nav, Comms, EO) technologies has been presented. This integrated platform is suitable for managing dual use scenarios, like peace-keeping missions and emergencies. Therefore, here a high level solution is proposed. Nevertheless, several technical elements needs to be evaluated in further works, in order to investigate the impact of satellite features mainly on QoS parameters. References 1. Cianca, E., De Sanctis, M., & Ruggieri, M. (2005). Convergence towards 4G: A Novel View of Integration. Kluwer Wireless Personal Communications, Special Issue on Wire-(d)/-(less) Convergence towards 4G. 2. Prasad, R., & Ruggieri, M. (2003). Technology trends in wireless communications. Boston. Artech House. 3. Maral, G., Ohmori, S., & Ruggieri, M. (2003). Editorial Broadband Mobile Terrestrial-Satellite Integrated Systems. Kluwer Wireless Personal Communications, 24(2), Cianca, E., & Ruggieri, M. (2003). SHINES: A research program for the efficient integration of satellites and HAPs in future Mobile/Multimedia systems. In Proceedings of WPMC, Japan, October 2003, pp Prasad, R., & Ruggieri, M. (2005). Applied satellite navigation using GPS, GALILEO, and augmentation systems. Boston: Artech House. 6. Prasad, R., & Ruggieri, M. (2008). Convergence of networks: An aerospace-friendly strategic vision. InM.Ruggieri&E.DelRe(Eds.), Satellite communications and navigation systems (pp ) Springer. 7. Ruggieri, M. (2006). Next Generation of Wired and Wireless Networks: the NavCom Integration. Springer Wireless Personal Communications, Special Issue on Future Convergence of Wired and Wireless Networks (Selected Topics from the Strategic Workshop 2005), Vol. 38, No. 1, June 2006, pp Ruggieri, M. (2006). Satellite navigation and communications: An integrated vision. Invited paper in Wireless Personal Communications (Springer), Special Issue dedicated to the 60th birthday of Ramjee Prasad, Vol. 37, Nos. 3 4, May 2006, pp Re, E., Ruggieri, M., & Guidotti, G. (2008). Intergration of TETRA with Satellites. To appear on Proceedings of IEEE Aerospace Conference, March 2008, USA. Author Biographies Emiliano Re received his University Degree in 2006 in Telecommunication Engineering from the University of Rome Tor Vergata. Currently he is a Ph.D. student in the Department of Telecommunications and Microelectronic Engineering at the same university. His main fields of research are EHF Satellite Communications and the exploitation of millimetre wave in Deep Space Communications and Radar Systems. Since February 2007 he has been working on the WAVE phase A2 project funded by the Italian Space Agency, aiming at developing four W-band experimental payloads for aerospace applications. He has been working on the ASI vision for moon exploration, focusing on a W-band payload suitable for rover on the Moon or Mars surface, for navigation and communication purposes.

10 568 E. Re et al. Marina Ruggieri graduated in Electronics Engineering in 1984 at the University of Roma. She was: with FACE-ITT and GTC-ITT (Roanoke, VA) in the High Frequency Division ( ); Research and Teaching Assistant at the University of Roma Tor Vergata (RTV) ( ); Associate Professor in Telecommunications at Univ. of L Aquila ( ) and at the University of RTV ( ). Since November 2000 she is Full Professor in Telecommunications at the RTV (Faculty of Engineering). Since 2003 she directs a Master in Advanced Satellite Communications and Navigation Systems at RTV. Her research mainly concerns space communications and navigation systems (in particular satellites) as well as mobile and multimedia networks. Since 1999 she has been appointed member of the Board of Governors of the IEEE AES Society; since 2005, Director for AESS operations in Italy&Western Europe; starting from 2008 she will be Executive Vice President of AESS. Since 2004 she has been member of Technical-Scientific Committee of the Italian Space Agency (ASI). Since 2007 she is Vice President of the ASI Technical-Scientific Committee. She is Director of CTIF_Italy, the Italian branch of the Center or Teleinfrastruktur (CTIF) in Aalborg (Danimarca), opened in 2006 at RTV premises. She is the PI of ASI satellite communications programs, national research programs co-funded by MIUR, Internalization Program funded by MIUR, Ariadna Program on novel constellation concepts and applications funded by ESA. She co-ordinates RTV Unit in various European Projects: EU FP6 IP MAGNET (My personal Adaptive Global NET); EU ASIA LINK EAGER-NetWIC; EU Network NEXWAY; GALILEO Joint Undertaking VERT and in the ASI program TRANSPONDERS. She is Editor of the IEEE Transactions on AES for Space Systems, Chair of the IEEE AES Space Systems Panel. Since 2002, she is co-chair of Track 2 Space Missions, Systems, and Architecture of the AES Conference. She participates in the organisation of many international events. She was awarded the 1990 Piero Fanti International Prize and she had a nomination for the Harry M.Mimmo Award in 1996 and the Cristoforo Colombo Award in She is author of about 230 papers, on international journals/transactions and proceedings of international conferences, book chapters and books. She is an IEEE Senior Member (S 84-M 85-SM 94) and member of AFCEA, IIN and AICA. Giovanni Guidotti graduated with Laude in Electrical Engineering at the University of Bologna in 1979, and started his activities in the field of digital communications for defense applications. In 1987 he spent a 6 months period at the University of California as Research Visitor, and in the following years he also acted as government expert in NATO and EUROCOM technical groups. Between 1995 and 2000 he has been R&D manager and Technical Director in two large companies operating in the civil market, extending his experience to Radio Relays, Cellular Networks, DVB, SDH. In Selex Communications he has initially been responsible for Technologies and Solutions, and now is VP for Market Analysis. He has published tens of technical papers and holds 9 patents, and in the last three years he has also been teaching Project Management at the University of L Aquila.