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4 Other Public Mobile Radio Systems 4.1 Airline Telephone Network for Public Air–Ground Communication In 1993 ETSI RES 5 submitted a standard for the Terrestrial Flight Tele- phone System (TFTS), specifying the radio interface and the interfaces to public telecommunications networks. At the same time the European Airlines Electronic Committee (EAEC) specified the airline equipment and interfaces to cabin facilities. Commercial operations began in 1994. In July 1994, after inviting international tenders, the Ministry of Post and Telecommunications granted a licence to DeTeMobil for the operation of TFTS. DeTeMobil was to supply radio coverage to all airspace up to an altitude of 4500 m. The service was available by 1996. Thirteen network operators in Europe have signed an MoU for the intro- duction of TFTS and an agreement on a cooperation with the major European airlines in order to resolve related commercial, organizational, technical and operational issues [1, 2]. 4.1.1 TFTS Cellular Network TFTS is a cellular system that uses direct radio links to ground stations (GS) that are connected to the fixed network to provide public communication services for air passengers (see Figure 4.1). There are three types of ground stations differentiated by area covered (cell) and related transmitter power: • En-route (ER) GS for altitudes from 13 to 4.5 km, with cell radii up to 240 km • Intermediate (I) GS for altitudes below 4.5 km, with cell radii up to 45 km • Airport (AP) GS, with cell radii of 5 km Handover between areas is part of the system. According to WARC’92, two 5 MHz wide bands have been specified for operation of the TFTS: • 1670–1675 MHz for uplink (ground-to-air) Mobile Radio Networks: Networking and Protocols. Bernhard H. Walke Copyright © 1999 John Wiley & Sons Ltd ISBNs: 0-471-97595-8 (Hardback); 0-470-84193-1 (Electronic) 302 4 Other Public Mobile Radio Systems h h ER, MAX INT, MAX 43000 ft (14 km) 15000 ft (4.6 km) EN-ROUTE GS INTERMEDIATE GS AIRPORT GS Figure 4.1: Coverage areas and ground stations 1/33 MHz 1/33 MHz Channel Channel #1 #1 #2 #2 #164 #164 Uplink Downlink 1670 1675 (MHz) 1800 1805 (MHz) Figure 4.2: TFTS channel map • 1800–1805 MHz for downlink The system offers automatic dialled connections to PSTN/ISDN without any limitation on target subscribers, with the same quality of service as cus- tomary in PLMNs. In addition to speech, data services such as facsimile, data transfer at 4.8 kbit/s and DTMF signalling are supported. Calls from the ground to an aircraft are only allowed to be made for operational purposes or for paging. The user is billed directly by (credit) card for services used. 4.1.2 Frequency and Time-Multiplexing Channels Each 5 MHz band is divided into 164 FDM channels (each 30.45 kHz wide); see Figure 4.2. Each FDM channel transmits at 44.2 kbit/s gross. On the uplink this capacity is divided into 17 time channels based on the TDM method, and on 4.1 Airline Telephone Network for Public Air–Ground Communication 303 Traffic Channel #1 #2 #3 #4 TDMA Frame (80 ms) 4.706 ms Traffic/Control/ Specific Data Sync Data Guard Guard 2.5 11 192 2.5 (bit) 208 bit (4.706 ms) Figure 4.3: Frames and time slots the downlink into 17 time channels based on the TDMA method. Each FDM channel carries four voice channels. According to Figure 4.3, 17 time slots are combined into a frame of 80 ms duration, and 20 frames form a superframe of the duration of 1.6 s. Each time slot contains 208 bits and has a duration of 4.706 ms. 4.1.3 Voice and Data Transmission Voice signals are digitally coded into blocks of 192 bits and transmitted at 9.6 kbit/s in time slots. A 9.6 kbit/s voice channel occupies 4 of the 17 time slots of an FDM channel; the 17th slot is used for network control. As soon as voice codecs are available for a 4.8 kbit/s transmission rate, the number of voice channels will be doubled. Data services at 4.8 kbit/s require 2 time slots per frame, therefore each FDM channel carries 8 data channels. 4.1.4 Functional Characteristics Each aircraft has transmitting and receiving facilities (transceiver), which can be tuned selectively to one of the different FDM channels. Four communica- tions can be carried out on the same FDM channel at the same time. Ground stations can transmit to different aircrafts simultaneously (on different time channels) on each one of their FDM channels. Signals are transmitted digitally with linear π/4-DQPSK (Differential Quadrature Phase Shift Keying) modulation, and require a simple non- coherent receiver. 304 4 Other Public Mobile Radio Systems GS GS GS GS GSC GSC PSTN/ISDN/PSPDN OMC NMC AC Figure 4.4: Architecture of a complete TFTS network Handover can be initiated by the mobile or the ground station, and is controlled by signal quality, distance and flight state. The particular ground station selected as a target is the one towards which the mobile station is moving. The distance between mobile and ground stations is estimated on the basis of signal propagation delay time. This information also determines the net- work synchronization for the ground stations capable of receiving. Ground stations are linked to the fixed network through ground switching centres (GSC) (see Figure 4.4). The GSC has responsibility for all the ground stations linked to it, and its tasks include mobility management, connection establishment to mobile sub- scribers, handover control and dynamic frequency management. The TFTS fixed network additionally contains three management components, namely: • Operations and maintenance centre (OMC) • Network management centre (NMC) • Administration centre for billing (AC) The MoU group produced a coordinated introduction plan for the TFTS ground network to enable the system to be introduced throughout Europe. This effort required a cooperation between telecommunications network oper- ators and airlines. 4.2 The US Digital Cellular System (USDC) 305 1 7 10 11 2 3 4 5 8 9 12 13 14 15 16 19 20 21 22 17 18 24 25 26 27 28 29 30 31 32 33 34 35 36 42 40 6 Figure 4.5: Cellular coverage through en-route ground stations in Europe 4.1.5 Ground Stations and Frequency Plan En-route ground stations are spaced approximately 380 km apart according to a hexagonal grid, with a nominal range of approximately 240 km, which cannot be exceeded for signal propagation reasons (see Figure 4.5). Cochannel ground stations are planned at a distance of 760 km, and neigh- bouring channel cells at a distance of at least 600 km. Cell planning is more difficult compared with terrestrial cellular networks because of the need to incorporate flying altitudes. 4.2 The US Digital Cellular System (USDC) During the 1980s there was an impressive increase in the number of subscribers to the public cellular mobile radio network in the USA. Because approval for the installation of new base stations and antennas is expensive and difficult to obtain in larger cities, only a portion of this increased need for capacity could be accommodated through a reduction in cell sizes. A permanent solution turned out to be the development of a digital system capable of coping with increased capacity without the need for new base stations. In March 1988 the Telecommunication Industries Association (TIA) set up the TR-45.3 subcommittee to develop the standard for a cellular digital system. This digital system, the American Digital Cellular System (ADC), 306 4 Other Public Mobile Radio Systems Mobile Station MS Base Station BS E A Um Sm B D G Visitor Location AC PSTN ISDN H F Ai Di C Centre Authentication Public Switched Register VLR Visitor Location Register VLR Home Location HLR Register Equipment Identity Register EIR MSC Mobile Switching Centre Mobile Switching MSC Centre Telephone Network Figure 4.6: Functional architecture of the USDC system was to support and be compatible with the existing analogue mobile radio network, the American Mobile Phone System (AMPS); see [3]. The digital system operates in the frequency range of the analogue AMPS system at the same time, which allows individual channels to change over gradually to digital technology. A characteristic of this system is that terminal equipment can be used for analogue as well as for digital operation (dual-mode). In addition to increased capacity, the ADC standard enables the introduction of new services, such as authentication, a data service and a short-message service, which were not supported by AMPS. In 1990 the digital standard was accepted by industry as Interim Stan- dard 54 (IS-54). The North American digital system with the architecture illustrated in Figure 4.6 is now called US Digital Cellular (USDC). In ad- dition, a number of standards have been accepted by FCC for the Personal Communication System PCS 1900 market, e.g., IS-134. 4.2.1 Technical Data on the USDC System The USDC system uses the 824–849 MHz frequency band for transmission between mobile station and base station (uplink), and in the reverse direc- tion (downlink) the 869–894 MHz band. The duplex separation between the transmit and receive frequency is therefore 45 MHz. The frequency bands are divided into FDM channels with a 30 kHz bandwidth, thereby providing 832 frequency carriers. 4.3 CDMA Cellular Radio According to US-TIA/IS-95 307 Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 Slot 6 20 ms 6.7 ms Figure 4.7: Structure of a TDMA frame in the USDC system with half-rate chan- nels The modulation technique used is π/4-DQPSK (Differential Quadrature Phase Shift Keying), a four-level scheme that, although it produces higher spectral efficiency than GMSK, places a heavy demand on the linearity of the output amplifier. In addition, for optimal detection at the receiver in- put, filters with a transmission function capable of describing the root of the Nyquist transmission function are required, and this is something that in- expensive filters can only approximate. In contrast to GMSK, π/4-DQPSK contains different amplitude components. The eight different phase states in π/4-DQPSK modulation are all in one circle, but the four allowed phase tran- sitions from one phase to another do not run in the circle. This means that not only the phase but also the amplitude is covered in the specifications for modulation. Like the GSM system, the USDC system operates in time-division multi- plexing (TDM) and multiple access (TDMA) mode, albeit with three voice channels being transmitted over one carrier. The length of the TDMA frame is 20 ms and is divided into three time slots each of 6.7 ms duration. The modulation data rate per FDM channel (3 time slots, 30 kHz) is 48.6 kbit/s. After the development and introduction of a half-rate codec, a TDMA frame will contain six time slots (see Figure 4.7) [5]. The USDC system uses a VSELP speech codec (Vector Sum Excited Linear Prediction) which, compared with GSM, results in lower source rates. With a full-rate codec, voice coding together with error-protection coding produces an overall transmission rate of 13 kbit/s, whereas the total rate on the SACCH is 0.6 kbit/s. 4.3 CDMA Cellular Radio According to US-TIA/IS-95 TIA Interim Standard 95 was developed by QUALCOMM. Unlike IS-54, which guarantees compatibility of a digital system with analogue, the IS-95 standard defines a CDMA transmission system. It includes the lowest three levels of the OSI reference model. The transmission system of the LEO sys- tem Globalstar will be based on the IS-95 standard with modifications (see Section 14.3.3). The physical layer is described below. However, only the 308 4 Other Public Mobile Radio Systems modulators have been standardized but not the demodulators; these can be specified by the manufacturer. 4.3.1 Forward-Link Forward-link uses coherent QPSK modulation in which transmitter and re- ceiver must be phase-synchronized for demodulation. Walsh sequences are used for channel separation (see Section 2.6.4). A short PN sequence is used for each in-phase and quadrature-phase for the spreading. A long PN sequence individually assigned to the user is used for the traffic channel. Demodulation is carried out through a pilot tone that is also transmitted. 4.3.1.1 Modulator Figure 4.8 shows the modulator for the forward link. A number of physical channels are available for establishing a connection. The first thing that must be carried out when a mobile station is switched on is synchronization. Phase synchronization and frame synchronization are achieved through the trans- mission of a pilot tone. The network synchronization is then carried out over the synchronization channel. This involves transmitting the paging channel data rate and power control information. Data for channel allocation is sent over the paging channel. Information is transmitted over the traffic channel. Pilot channel The all-one Walsh sequence W 0 is combined with a short code and transmitted to the modulator. With a value set of (0, 1) the two codes are added modulo 2, or with a bipolar (−1, 1) approach they are multiplied. The Walsh sequences are the lines of the Hadamard matrix, and are formed according to the following recursion: H 1 = 0 and H 2N =  H N H N H N ¯ H N  (4.1) in which N must be a power of two and ¯ H N is the negation of H N . The next two matrices are formed in the same way: H 2 =  0 0 0 1  and H 4 =    0 0 0 0 0 1 0 1 0 0 1 1 0 1 1 0    (4.2) All Walsh sequences of the same matrix are orthogonal to each other. The IS-95 standard uses 2 6 = 64 Walsh sequences. The Globalstar system will probably use 2 7 = 128 sequences. In IS-95 the short code is formed with two irreducible polynomials (the polynomials 121 641 and 117 071 are primitive. Note that because code se- quences can be produced with a polynomial and its reciprocal polynomial, 4.3 CDMA Cellular Radio According to US-TIA/IS-95 309 Block Interleaver Block Interleaver Block Interleaver =1/2 R =2 k =1/2 R =2 k =1/2 R =2 k Paging channel 1200 bit/s Synchronization channel (0,0 .,0) Walsh Pilot channel 4.800 symb/s 19.2 ksymb/s 19.2 kbit/s 9600 bit/s 4800 bit/s 1200 bit/s Paging code Power control 19.2 ksymb/s Traffic channel 9600 bit/s 4800 bit/s 2400 bit/s 1.200 bit/s 19.2 kbit/s Multiplexer f Wv c Convolutional coder Convolutional coder Subscriber code Convolutional coder Long code Long code Q I PN sequences W 0 32 W W f Figure 4.8: Modulator for forward-link 310 4 Other Public Mobile Radio Systems Xor Xor Xor Xor Xor Xor Access-Channel Information Paging-Channel Mask 0 0 41 110001111 Traffic-Channel Mask Permuted Serial Number 41 110001100 1 2 3 6 42 Modulo 2 Addition 4 5 Long Code Mask Long Code Figure 4.9: Long code generator only one polynomial is given in the tables [7]). In IS-95 the grade is n = 15; in the Globalstar system the grade will probably be n = 17. The polynomials for the in-phase components and the quadrature-phase components in IS-95 are P I = x 15 + x 13 + x 9 + x 8 + x 7 + x 5 + 1 (4.3) P Q = x 15 + x 12 + x 11 + x 10 + x 6 + x 5 + x 4 + x 3 + 1 (4.4) The short code is the same for the whole system. In Globalstar a code mis- alignment (different misalignment in the shift register) is used to provide unique identification of the gateway, the satellite and the beam. The Walsh sequence is spread with the short code at a 1.23 MHz clock-pulse rate over the entire bandwidth and QPSK-modulated. Synchronization channel The synchronization channel produces data flow at a rate of 1200 bit/s. The data is channel-coded with a (R = 1/2, K = 9) convolutional coder, then interleaved and combined with the Walsh sequence W 32 . The signal is then spread with the short code and QPSK-modulated. Paging channel Data is channel-coded with a (R = 1/2, K = 9) convolu- tional coder, then interleaved and spread with a long code. For the channel separation the signal is combined with the W p Walsh sequence allocated to the paging channel. The signal is then spread with the short code and QPSK- modulated. Figure 4.9 shows the structure of a long-code generator. [...]... develop a digital mobile radio standard Compared with existing analogue systems, this digital mobile radio system was to be more cost-eective and oer a higher level of capacity and security, as well as new services The new system, formerly called Japanese Digital Cellular (JDC) but now referred to as the Personal Digital Cellular (PDC) system, was specied by the Research & Development Center for Radio Systems... error-protection coding) amounts to a total of 11.2 kbit/s The signalling data is transmitted over the SACCH at a rate of 0.75 kbit/s 4.5 Comparison of some Second-Generation Cellular Systems Table 4.3 provides a comparison of the technical parameters for the radio interfaces of the digital public mobile radio systems (GSM, USDC and PDC) 318 4 Other Public Mobile Radio Systems Studies show that the... Indicator Tail ăÊ  ăĂƠÊĂ ÔÔâĂâĐƯÔ 172, 80, 40, 16 Bits/frame 312 Other Public Mobile Radio Systems 4.3 CDMA Cellular Radio According to US-TIA/IS-95 313 20 ms 172 9600 bit/s 12 8 Information Bits F T 80 8 8 Information Bits F T 4800 bit/s 8 40 2400 bit/s Information Bits T 16 8 Information Bits T 1200 bit/s F: Frame Quality Indicator T: Encoder Tail Bits Figure 4.11: Frame structure for dierent... open standardization and early availability of the system References [1] E Berrutto, et al Terrestrial ight telephone system for aeronautical public correspondence: Overview and handover performance In Digital Mobile Radio Conference DMR IV, pp 221228, Nice, France, Nov 1991 [2] G DAria, et al Terrestrial ight telephone system: Integration issues for a pan-European network In Digital Mobile Radio Conference... 1991 [6] R W Lorenz Digitaler Mobilfunk (Systemvergleich) Der Fernmeldeingenieur, Nr 1/2, 1993 [7] W W Peterson, E J Weldon Jr Error Control Coding, Vol 1 MIT Press, Cambridge, Massachusetts, 2nd edition, 1972 References 319 [8] TIA TIA/EIA IS-95 INTERIM Standard, July 1993 [9] S Titch Blind Faith Telephony, pp 2450, Sep 1997 [10] K Tsujimura Digital cellular in Japan In Mobile Radio Conference (MRC91),... two systems Comparisons of the spectral eciency of mobile radio systems are not appropriate, mainly because the systems are designed for dierent qualities of service yet this parameter is usually ignored in any comparative analysis Unlike the GSM system, the PDC system only uses antenna diversity and no equalizers In multipath propagation antenna diversity can be more advantageous than an equalizer, which...4.3 CDMA Cellular Radio According to US-TIA/IS-95 311 This involves setting up a shift register with 42 delay elements, with the outputs linked by a 42-bit long mask The outputs are added modulo 2 and generate the long code Trac channel The vocoder (standardized in accordance with IS-96), which is capable of producing dierent data rates as required, delivers the data... investigations in the number of base stations deployed to serve the same area by dierent systems (and operators) have resulted in the statistics shown in Table 4.2 [9] One reason for this result is that radio engineering for a given trac load is much more dicult with CDMA systems compared with FD/TDMA/FH 4.4 The Personal Digital Cellular System (PDC) of Japan 315 Table 4.2: Number of base stations in... Control Centers (MCC) are divided into Gate-MCC, VisitMCC and Home-MCC, with only the G-MCCs being connected to the xed network to save on the cost of infrastructure [4] 4.4.1 Technical Data on the PDC System The technical parameters of the PDC standard are similar to those of the American USDC system, albeit with some important dierences In Japan the digital system does not directly replace the existing... controlled analogously, corresponding to the receive power The power gradation is in the area of 85 dB However, only the mean value of the transmitted power can be computed Despite the speedy reaction to power changes, it is not possible to compensate for Rayleigh fading with open loop The reason is that forward-link and return-link are in dierent frequency bands, and Rayleigh fading occurrences of the two . parameters for the radio interfaces of the digital public mobile radio systems (GSM, USDC and PDC). 318 4 Other Public Mobile Radio Systems Studies show that. in April 1989 to develop a digital mobile radio standard. Compared with existing ana- logue systems, this digital mobile radio system was to be more cost-effective