Tetra+factsheet[1]

Transcript

TETRA Factsheet Version Version 2.2: 1 November 2005 TETRA Factsheet 1 2/14 Introduction TETRA is a digital, cellular trunked radio system for voice and data communication. It is expected that in spite of its considerable complexity, TETRA will allow more economical solutions than to date due to its uniform technical basis and large unit quantities, in addition to offering a high degree of flexibility. Digital trunked radio systems are modern radio systems for private and public professional radio applications and for emergency radio applications (PMR/PAMR 1). Unlike earlier  conventional analogue fixed-channel systems (a specific radio channel was allocated to each service and each user for the whole time), in the case of trunked radio systems frequencies are allocated dynamically to individual users and services. It is therefore possible to fully utilise so-called trunk gain and to increase spectrum efficiency. In addition, the quality and security of radio systems could be considerably improved using digital technology.  As early as the first half of the 'eighties, initial attempts were being made to seek appropriate solutions for digital PMR systems. This step was essential in order to increase spectrum efficiency, improve technical reliability and facilitate encryption of the connection. It was at this time that the first proprietary digital PMR systems appeared, including ASTRO and iDEN (both by Motorola), EDACS (Ericsson), SR 440 (Bosch/Ascom) and Tetrapol (Matra Communication). However, the establishment of a uniform standard for digital PMR systems began only when manufacturers, administrations and user groups decided within ETSI in 1989 to draw up such a standard, designated TETRA. Since then, TETRA has become one of the most comprehensive standards ever developed by ETSI, comparable only to the successful GSM standard for mobile radio systems. Potential users of trunked radio systems include closed user groups such as transport services (taxis, Swiss Federal Railways, haulage companies, etc.), airports, energy companies and the emergency services (e.g. police, the fire brigade, ambulance services, the army, civil defence, the frontier police, etc.). All these user groups either have their own private trunked radio system or use the services of a trunked radio systems operator. Today, approximately 90% of professional radio systems are still based on analogue technology. Trunked radio systems differ from public mobile radio systems such as GSM or UMTS primarily in terms of their faster call set-up, group calls, priority calls, end-to-end encryption and the possibility of direct calls from mobile station to mobile station without a connection via a base station (this is known as direct mode). 2 Development in Europe The market for professional mobile radio systems world-wide is approximately 4.6 billion euros per year, or almost CHF 7 billion. Of this, about one third, or 1.5 billion euros, probably relates to Europe − with approx. 6 million users. The number of  potential users in Europe is estimated to be 10 million 2. A growth rate of 2% - 3% per year is being forecast from various sides. This growth is expected because market penetration of PMR systems in Europe amounts to only 2%. Compared with the USA this is low; there, penetration is already up to 1 The market for professional mobile radio is designated PMR (Private Mobile Radio) or PAMR (Public Access Mobile Radio). In the case of PMR the radio system is operated by the user himself; with PAMR the trunked radio services are obtained from an independent network operator. PAMR operators also generally offer access to the fixed network. 2 Funkschau 5/98, p. 80 ff. TETRA Factsheet 3/14 8%3. In addition, approximately 90% of the PMR systems in Europe today are still based on outmoded analogue technology, which will be replaced sooner or later by more modern digital systems. The market trend in PMR and in emergency radio applications in particular clearly points in the direction of large, jointly used networks. Traditional users of PMR systems such as public utility companies (electricity, gas and water supply) as well as the transport industry are outsourcing their radio activities more and more to specialist trunked radio operators. 4 Today (in 2001), more than 40 regional or national organisations and services in Europe are equipped with TETRA systems 5. Estimates indicate that by 2003 approximately 80% of the digital PMR market in Europe will be operating using TETRA technology. A total of 1.22 million participants are forecast in 2003 in the digital PMR market in Europe. Of these, around 80% will be using TETRA technology 6. 3 Licences in Switzerland In the international environment within the mobile radio applications sector, in addition to the increasing penetration of GSM, the possible introduction of digital trunked radio applications for special communications purposes has emerged. ComCom reacted to this trend as early as 1999 by commissioning OFCOM to undertake a clarification of demand in the 870 876 MHz / 915 - 921 MHz band and to organise an invitation to tender in the 410 - 430 MHz band. The results of this work showed that there was no great interest in the upper frequency range. In the lower frequency range the available channels were not sufficient to set up a viable trunked radio network, despite the restitution of the Modacom company's frequencies.  At that time, this frequency band was still heavily occupied by the Swisscom analogue trunked radio network (Speedcom) and by individual professional radio applications. The introduction of a digital trunked radio network was excluded, since the essential continuous frequency ranges were not available. In the year 2000 Swisscom officially announced that it would be withdrawing from the Speedcom business as of 30 September 2000. This decision led ComCom to reassess the situation. In spring 2000 OFCOM was again asked to undertake a study of demand (in the 410 - 430 MHz frequency range). The results of the study showed that the number of  interested parties had grown fundamentally and that today a viable network could be set up with the additional frequencies. ComCom commissioned OFCOM to organise an invitation to tender with regard to auctioning a national licence. When the deadline for submissions expired on 22.12.2000, however, no candidature dossiers for a national licence had been received. At the same time interest was shown in regional networks. The licensing of regional networks is now being examined. 4 Services Thus far, it is mainly the characteristics of the radio channel and the structure of TETRA channels at the physical level of the air interface which have been considered. For the user, however, it is much more important to know what services can be provided by TETRA. 3 Tetrapol PAS Conversion by ETSI, E xplanatory report, Part 1. 4 See also: ERC Report 52, "Methodology for Assessment of PMR Systems in terms of Spectrum Efficiency, Operation and Implementation". 5 6 TETRA Swiss News, Issue 5, 1 August 2000. Intex Management Services Ltd; 6 Dencora Business Park; Booth Drive; Wellingborough, NN8 6GR; England; Tel: +44 (0)1933 40 22 55; Fax: +44 (0)1933 40 22 66; Email : [email protected] 4/14 TETRA Factsheet In simple terms it can be said that TETRA can provide almost everything which has been possible to date with conventional PMR systems, plus a wide range of possibilities on the ever more important data communications side. Estimates indicate that by 2004 more than 50% of all radio communications will consists of packet data traffic, including IP telephony. In addition, however, TETRA's flexible system and interface structure offers even more opportunities. To illustrate this, we have sub-divided the services into different groups: teleservices, carrier services (or data services) and supplementary services. Many of these services are not yet available in the public mobile radio systems. The list below is not exhaustive and contains merely a small selection of services which can be provided by TETRA. Teleservices:        Individual Call: This service corresponds to a call in a public mobile radio system (GSM, UMTS). One user calls another individual user and is connected with the latter. Group Call: One user calls a predefined group. Each member of the group can hear  everything and can speak. The group call can be set up so that the individual members have to acknowledge or not. A group can be modified dynamically, i.e. members can be added or removed. Direct Mode: In direct mode, two or more mobile stations communicate with each other, without involving a base station (walkie-talkie). Broadcast Call: This is a unidirectional point-to-multipoint call within a specified area. The area and the users are defined in advance. The individual users do not acknowledge the call and therefore the caller is unable to verify who has and who has not received the call. Emergency Call: An emergency call button sets up a high-priority call to a dispatcher  or a predefined group of users. Include Call: During a call, this type of call makes it possible to ring one or more additional users and include them in the call. Open Channel:  A group of users can converse with each other on a specific channel for a specific period. Within the group, all participants can hear each other and can speak at any time. In TETRA this service is not explicitly standardised. However, it can be installed with the aid of a broad range of extra services (e.g. Pre-emptive Priority Call and Call Retention) (see ETR 120). Carrier services (data services):    Status Transmission: very short, predefined messages can be transferred from the dispatcher to the mobile stations and vice versa or between mobile stations. Short Data Service: predefined messages can be sent to individual subscribers or to a group. Circuit-swit ched data services: non-protected data transmission: protected data transmission: - - highly protected data transmission: n x 7.2 kbit/s n x 4.8 kbit/s (n = 1, 2, 3 or 4) (n = 1, 2, 3 or 4) n x 2.4 kbit/s (n = 1, 2, 3 or 4) TETRA Factsheet 5/14 (n = number of time slots which are used on a carrier frequency).  Packet-switched data services: call-oriented packet data services: transmission of X.25 packets from a source node to a destination node. A logical or virtual circuit is established between the two nodes. - - non-call packet data services: a single data packet is transferred from a source node to a destination mode (or multiple destination nodes). No virtual circuit is established. TCP/IP Access: this data service allows the mobile stations to access the Internet or servers which support the TCP/IP protocol. WAP is also now offered in TETRA networks. Supplementary s ervices:     5 5.1 Discreet Listening: an authorised person can monitor radio communications without the subscribers concerned being aware of this.  Am bi enc e Li st eni ng : This supplementary service allows the dispatcher to listen in unnoticed to a vehicle in unclear and dangerous situations. This service is important above all for the police or other security services. Priority Call: This supplementary service allows a user to allocate a priority to the call. The call is then processed before all other calls which have a lower priority. If no more network resources are available (e.g. all channels are busy), the necessary resources can be released by means of the so-called Pre-emptive Priority Call. The calls with the lowest priority are consequently aborted in this case. Late Entry: This supplementary service allows a user to connect at a later time to a group call, for example if he was engaged at the time of the call or if he had not yet switched his equipment on. Environmental provi sions Protection fr om non -ionising radiation Both the base station transmitter antennas and the TETRA mobile sets will emit additional non-ionising radiation into the environment. With regard to the intensity of the radiation from mobile stations, the same requirements as in the EU are applicable for Switzerland: The recommendations of ICNIRP (International Commission on Non-Ionizing Radiation Protection) have to be implemented in the context of  the applicable technical norms. The radiation from the base stations, on the other hand, is limited by the Decree on NonIonising Radiation (Verordnung über den Schutz vor nichtionisierender Strahlung - NISV). On the one hand the decree contains requirements for individual items of equipment, and on the other hand it limits total high-frequency radiation and therefore, indirectly, the use of the frequency spectrum as a whole. For an individual mobile radio transmitter installation, the decree states that its radiation in locations subject to sensitive use may not exceed the limit value for the equipment. Such 6/14 TETRA Factsheet locations include rooms in buildings in which people regularly spend prolonged periods of  time, children's playgrounds as designated by planning law, and non-built-up construction areas. The equipment limit value is laid down for the electrical field intensity and is generally 3 V/m for TETRA equipment, which works in the frequency range between 400 and 500 MHz. The equipment includes all contiguous transmitter antennas for mobile radio and wireless subscriber connections. Compliance with the equipment limit value is checked by the competent planning authority of the community or canton. To this end, for each transmission installation which the licensee wishes to construct, lay or modify, the licensee completes a site data sheet which must contain technical information on the equipment and a prognosis of the radiation intensity in adjacent areas where people may be present. This site data sheet is a component of the planning application and may be made accessible to the public by the planning authority. In order that the equipment limit value can be complied with, a certain separation is essential between the transmitter equipment and locations subject to sensitive use. The size of this separation depends very greatly on the transmitter power and direction of radiation of the equipment, and on topographical conditions. For the total high-frequency radiation, including that of broadcasting, professional radio and amateur radio equipment, the decree imposes a limit at all locations where people may be present – even for a short time. The relevant limits – termed the immission limits – are seldom achieved or exceeded, and then mostly in the immediate vicinity of a transmitter  installation. In the case of mobile radio equipment, such potentially critical situations occur  almost exclusively on accessible flat roofs on which a transmitter installation is mounted. In the site data sheet, the licensee provides proof that the immission limits will not be exceeded by the radiation additionally generated by the planned installation. Details for the implementation of the NISV can be taken from the recommendations of  BUWAL under: www.umwelt-schweiz.ch/buwal/de/fachgebiete/fg_nis/index.html 5.2 Consideration of environmental concerns The construction of new telecommunications networks necessarily leads to the erection of  new infrastructures such as antenna installations. In order to balance the interests of the construction of telecommunications networks and the associated offering of  telecommunication services against the interests of environmental protection and area planning in practice, a working group of the Confederation and the cantons (UVEK/BPUK), with the co-operation of radio network operators, has been considering questions of coordinating the planning and approval procedures for radio infrastructures. The recommendations have been published on OFCOM's homepage ( www.bakom.ch). In addition, as part of the granting of the operators' licences, obligations are stipulated according to which antenna sites outside construction zones are to be used jointly, if  possible. In the case of construction of new sites, the legal provisions concerning area planning, protection of nature and the national heritage and the provisions of the decree on protection from non-ionising radiation must be complied with. On 30.10.1998, the Federal Office for the Environment, Forests and the Landscape (BUWAL, Landscape Department) published a notice concerning the requirements for the protection of nature and the landscape and for forest conservation with regard to the construction of mobile radio antennas. 7/14 TETRA Factsheet 6 Technology The channel access procedure used for TETRA is the TDMA (Time Division Multiple Access) method. TETRA provides four independent communication channels within one 25 kHz radio channel. One individual channel is occupied only for one quarter of the time for the duration of a time slot. During the remaining period, the radio channel can be used by other users. On a call, the transmitter is therefore switched on and off approximately 18 times per second. If  necessary for high transmission capacity, however, one individual user can also occupy multiple time slots (up to four). Both voice and data can be transmitted simultaneously by a single user. The principle of the procedure is shown in figure 1. 1 TDMA frame (56,67 ms) Transmitter sampling for  channel 1 1 time slot (14,167 ms) Channel 1 Channel 2 Channel 3 Channel 4 Channel 1 Figure 1: TETRA's TDMA channel access procedure  As for GSM, in the TETRA system the control channel is also transmitted on a specific carrier  in the first slot in each frame. This control channel is used to transfer the network's system data to the handsets and to allow synchronisation between handsets and the base station. The transmitting power of the mobile equipment is continuously regulated by commands from the base station to the respective minimum which the base station needs to detect the data from the mobile equipment (power control). By means of this power control, on the one hand interference can be minimised and on the other hand the battery life of the mobile equipment can be maximised. The transmitting power of the base station, on the other hand, is not regulated in TETRA. The modulation method used is π/4-DQPSK (Differential Quaternary Phase Shift Keying). Though this linear modulation method is extremely spectrum-efficient, it requires very linear  and therefore expensive transmitter final stages in order to generate low out-of-band transmissions which are undesirable. TETRA's maximum data rate is up to 28.8 kbit/s (non-protected) for a 25 kHz channel bandwidth. This relatively high data rate makes TETRA especially suitable for use in mobile data transmission. In principle, TETRA can be used on all frequencies below 1 GHz. In practice, however, only the typical frequencies authorised for PMR in the 160, 400 and 870 MHz band are used (see chapter 0). The TETRA specifications cover three quite different areas of application, namely:  Voice plus Data (V+D);  Packet Data Optimised (PDO);  Direct Mode. TETRA Factsheet 8/14 Different standards have been developed for these three applications. However, these are based on the same physical radio platform (modulation, RF channel spacing, frequencies, etc.). Equipment complying with the V+D specification offers a wide range of carrier services, teleservices and supplementary services for hybrid voice and data transmission. Equipment complying with the PDO specification supports only packet-switched data services. Although packet-based data services can also be transmitted from V+D equipment, the air interface of PDO is more suitable for the transmission of packet-based data. This is of  particular interest in that in the near future data services − especially packet-switched data services (e.g. Internet access) − will become more and more significant. Direct mode allows a direct link from mobile station to mobile station without involving a base station. This mode is used when users are outside the coverage area.  As with most radio systems, TETRA also uses the frequency duplex method (apart from Direct Mode, see below). The uplink and downlink are handled on two different frequencies, which are separated from each other by so-called duplex separation. The size of this duplex separation depends on the frequency band in which the system is operated. TETRA terminals (like those of most PMR systems) generally work in half-duplex mode, i.e. it is not possible to send and receive simultaneously. Full-duplex operation corresponds to the mode with which we are familiar - public mobile systems and fixed telephony - and would be easy to implement in TETRA, however this mode is not used very frequently in TETRA systems. In the case of direct mode, only simplex operation is possible. The mobile stations involved in a call work on the same frequency. In the case of direct mode, up to two independent simplex calls can be maintained simultaneously on one carrier. Tetrapol and TETRA are the most well-known digital trunked radio systems in Europe. A brief  comparison of these two systems is therefore appropriate and is shown in Table 1 (a separate factsheet is available for Tetrapol). 9/14 TETRA Factsheet Table 1: Advant ages and disadvant ages of TETRA comp ared wit h Tetrapol  Ad vant ages of TETRA compared with Tetrapol         TETRA's data rates are clearly higher than those of  Tetrapol (up to a factor of 4 depending on trunking). Disadvantages of TETRA compared with Tetrapol  Voice and data can be transferred simultaneously with TETRA. Duplex mode is possible with TETRA without an antenna splitter thanks to the TDMA channel access method and is therefore simple to implement. TETRA's spectrum efficiency is greater than that of  Tetrapol (by a factor of 1.16 to 2.0 depending on the environment). TETRA is an acknowledged European standard, whereas Tetrapol has not yet been accepted as an ETSI standard.    The maximum cell radii of TETRA are approximately 30% smaller than those of Tetrapol (assuming the same peak transmission powers). TETRA therefore needs about twice as many base stations as Tetrapol to cover a specific area. With TETRA, out-of-band emissions are greater than with Tetrapol. Frequency allocation is more difficult. If  possible, whole frequency blocks must be allocated. With TETRA, common-frequency transmissions are more difficult to implement and require terminals with a powerful equaliser (MS Class E). Devices with TDMA channel access tend to have greater  peak transmission powers and may induce audible lowfrequency interference in electro-acoustic equipment. TETRA is an extremely flexible system and can be used for all PMR applications as well as for emergency radio and conventional PMR/PAMR. A less expensive antenna network is required in the base station, since TDMA (time-division multiple access) means that 4 channels are available for each carrier  frequency. With TETRA the transmitting output of the mobile station is regulated by the base station and adapted to current conditions. As a result, the battery life of the mobile station is increased and interference in the network is reduced. Table 2 below summarises the most important radio parameters of TETRA. 10/14 TETRA Factsheet Table 2: Major radi o parameters of TETRA Parameter Value Channel spacing 25 kHz Transmission power of base station per carrier frequency (typical) 25 W ERP Transmission power of mobile equipment 1 W, 3 W, 10 W Receiver sensitivity, static (BER = 1.2%; 4.8 kbit/s; N = 4) MS: -113 dBm BTS: -115 dBm Receiver sensitivity, dynamic (TU50; BER = 1.2%; 4.8 kbit/s; N = 4) a) MS: -104 dBm BTS: -106 dBm Mode Semi-duplex, duplex Channel access method TDMA Modulation π/4-DQPSK Channel bit rate 36 kbit/s Maximum data rate, non-protected (gross bit rate) 28.8 kbit/s Net data rate Non-protected: n x 7.2 kbit/s Low-protected: n x 4.8 kbit/s High-protected: n x 2.4 kbit/s (n = 1, 2, 3 or 4) Speech coding A-CELP; 4.567 kbit/s Spectrum efficiency in interference-limited environment (high traffic, many cells) 50 bit/(s*kHz*cell) Spectrum efficiency in noise-limited environment (an isolated cell) 384 bit/(s*kHz) Range b) ETSI standard Rural: Suburban: ca. 14 km ca. 4.5 km TETRA V+D: TETRA PDO: TETRA DMO: Testing: ETS 300 392 ETS 300 393 ETS 300 396 ETS 300 394 Notes: a) Class A equipment (optimised for hilly or mountainous terrain). b) Dynamic; f = 400 MHz; PMS = 3 W (peak power); interference margin = 1 dB; σS (shadowing) = 6 dB; reliability of  coverage at edge of cell = 90%; antenna height BTS = 30 m; antenna height MS = 1.5 m; propagation model SE21; antenna gains and feed losses = 0 dB. 7 Frequencies Basically, the following frequency ranges are available in Europe for digital trunked radio (ERC/DEC(96)04):  410 - 430 MHz;  870 - 876 MHz paired with 915 - 921 MHz;  450 - 470 MHz;  385 - 390 MHz paired with 395 – 399.9 MHz. In Switzerland, at present only the 410 - 430 MHz range can be considered for the introduction of larger regional or national TETRA systems, since all other ranges are either  heavily occupied by other applications (450 - 470 MHz), or no equipment is currently available (870 - 876 MHz paired with 915 - 921 MHz). The 385 - 390 MHz frequency range paired with 395 – 399.9 MHz cannot be used for civilian applications in Switzerland. In Switzerland it is envisaged to make available a total of 1.5 MHz of spectrum (in three subranges) from the 410 – 430 MHz range for several fairly large regional or one national digital 11/14 TETRA Factsheet trunked radio network (see chapter 3). There is also a possibility of making available a limited number of frequencies in the 450 - 470 MHz range for local TETRA networks (e.g. at airports), if necessary. 8 Networks Digital trunked radio systems for PMR − compared with public mobile radio systems such as GSM or UMTS − generally have small numbers of users with short call durations. Consequently traffic is low and in general large cells can be built. The radiated transmission power per base station carrier frequency is of the order of 25 W ERP. In TETRA, 4 to 5 carriers, i.e. 16 to 20 logical channels, are typically installed in one cell. The different PMR systems differ very greatly in terms of the number of users, the coverage area, volume of traffic and services provided. Some systems are noise-limited (system limits are determined by the receiver noise) or interference-limited (high common-channel interference from adjacent channels is present). The spectrum efficiency is heavily dependent on these parameters (see Table 2). The TETRA standard may be considered as a "tool kit" and offers system designers many opportunities to adapt the network optimally to users' needs. No special type of network implementation for building a network is laid down in the standard. The specifications merely define the interfaces which are essential so that interoperability, interworking and network management can be guaranteed between the individual network elements. The air interface, for example, i.e. the interface between the infrastructure (SwMI) and the mobile equipment, is one of these interfaces (see Figure 2). I6 (DMO) I1 SwMI MS MS Transit network BTS LSC Gateways PSTN ISDN MSC TETRA 1 I3 (connects two TETRA networks) TETRA 2 I3 I2 LS BTS DMO ISDN LSC LS MS MSC PSTN SwMI Base Transceiver Station Direct Mode Operation Integrated Services Digital Network L oc al Swit chin g Cent re Line Station Mobilstation Main Switching Centre Public Switched Telecommunication Network Switching and Management Infrastructure Major Interfaces: I1 Air Interface I2 Line Station Interface I3 Inter-system Interface (ISI) I6 Di re ct Mo de R adi o Air Int er fac e Figure 2: Network co nfiguration wit h the most important TETRA interfaces Connection of a TETRA network to other telecommunications networks such as PSTN or  ISDN is guaranteed via standardised gateways. If traffic is low and coverage is ample, TETRA can also make use of common-channel technology (co-channel radio, simulcast). In this case, all base stations transmit on exactly the same frequency. Both the high-frequency signal and the temporal position of the TETRA Factsheet 12/14 modulation signal are sent synchronously from the base stations. The network can be considered as a single giant macrocell, which is fed by multiple base stations. With this procedure, it is possible to achieve excellent coverage of a large but low-traffic location, with simultaneous high frequency economy. Because of TETRA's high bit rate, the terminals must be equipped with a special filter (an equaliser) so that they can be used for co-channel technology. 13/14 TETRA Factsheet  Abbreviations  A-CELP Algebraic - Code Excited Linear Predictive OFCOM Federal Office of Communications BER Bit Error Rate BPUK Swiss Conference of Directors of Planning and Environmental Protection BT Relative filter bandwidth BTS Base Transceiver Station (base station) BUWAL Federal Office for the Environment, Forest and the Landscape DMO Direct Mode Operation DQPSK Differential Quaternary Phase Shift Keying ERC European Radiocommunications Committee ERP Effective Radiated Power  ETR ETSI Technical Report ETS European Telecommunication Standard ETSI European Telecommunications Standards Institute FDMA Frequency Division Multiple Access GSM Global System for Mobile communications ISDN Integrated Services Digital Network ITU-R International Telecommunications Union, Radiocommunication Sector  MS Mobile station NISV Decree on protection from non-ionising radiation PAMR Public Access Mobile Radio PAS Publicly Available Specifications PDO TETRA PDO System (Packet Data Optimised) PMR Private Mobile Radio (or Business Private Radio) PSTN Public Switched Telephone Network PUEM Probability of Undetected Erroneous Message SBB Schweizerische Bundesbahnen (Swiss Federal Railways) SE21 ERC Working Group Spectrum Engineering, Project Team 21 SwMI Switching and Management Infrastructure TDMA Time Division Multiple Access TETRA Trans-European Trunked Radio TU50 Typical Urban, 50 kph UMTS Universal Mobile Telecommunications System UVEK Federal Department Communications V+D TETRA V+D system (Voice plus Data) WAP Wireless Application Protocol for the Environment, Transport, Energy and TETRA Factsheet 14/14