- 1 - Rep. ITU-R BS.1203-1 REPORT ITU-R BS.1203-1* DIGITAL SOUND BROADCASTING TO VEHICULAR, PORTABLE AND FIXED RECEIVERS USING TERRESTRIAL TRANSMITTERS IN THE UHF/VHF BANDS (1990-1994) This Report contains background and descriptive material for Recommendation ITU-R BS.774 entitled "Digital sound broadcasting to vehicular, portable and fixed receivers using terrestrial transmitters in the UHF/VHF bands". 1. Introduction Digital techniques have been used in sound programme production and transmission by some broadcasters for many years now, and more recently have become cheap enough to be introduced into the domestic consumer market, leading to wider public appreciation of high-quality sound, albeit via non-broadcast digital media. At the same time, there is rapidly growing congestion in the VHF/FM radio bands in many countries; thus the FM broadcasting services, which can deliver unimpaired sound quality into the home, are under threat of erosion of the quality deliverable. Overcrowding will inevitably increase the levels of interference which must be tolerated, particularly for vehicular and portable receivers, which do not benefit from elevated, directional, receiving antennas, usually assumed in planning service coverage. Although VHF/FM services can still provide excellent service to properly-installed fixed receivers, the solution for the future development of sound broadcasting is to provide an entirely new digital sound broadcasting service, designed at the outset to meet all the reception requirements of the diverse listening audiences. Also, a complete digital sound programme chain can be established from studio to domestic receiver. In contrast to existing sound broadcasting systems, the new system has to provide unimpaired sound broadcast reception to fixed, portable and mobile receivers. The requirement for mobile reception necessitates entirely new transmission methods which have been defined and are described below. This Report describes the requirements for digital sound broadcasting to vehicular, portable and fixed receivers using terrestrial transmitters, the techniques employed in the digital sound broadcasting system, and considers relevant planning parameters and sharing considerations. The Report also makes reference to the terrestrial part and common system characteristics of the mixed satellite/terrestrial digital sound broadcasting service concept as well as the hybrid delivery concept. The mixed satellite/terrestrial service concept is based on the use of the same frequency band by both satellite and terrestrial broadcasting services to the same receiver. The hybrid delivery concept is based on the use of low power terrestrial "gap-filler" to improve the satellite coverage. Both concepts are made possible by the techniques employed in the digital sound broadcasting system and are described in more detail in Report ITU-R BO.955. * Radiocommunication Study Group 6 made editorial amendments to this Report in October 2010. - 2 - Rep. ITU-R BS.1203-1 Most of the information included in this Report is based on studies and tests undertaken in Canada, Germany, France, the Netherlands, United Kingdom, Sweden and by the EBU in association with the Eureka-147 Project using the system concept described in Annex 1-A. Recent efforts have been undertaken to explore other possible digital sound broadcasting systems (see Annex 2). 2. Service and system requirements In defining a digital sound broadcasting system, the following requirements shall be taken into account. The system shall be intended for fixed as well as portable and vehicular reception. The list of system requirements applies to terrestrial, cable, satellite as well as mixed/hybrid satellite/terrestrial delivery concepts. The requirements are: 2.1 Sound quality levels - High quality stereo sound of two or more channels with subjective quality indistinguishable from high quality consumer digital recorded media ("CD quality"). 2.2 Sound control signals - Transmission of control information on sound representation (loudness, dynamic range compression, matrixing, etc.). 2.3 Service configurations - High-quality channel stereophonic sound. - High-quality monophonic sound. - For special applications, the possibility of adding further sound channels to the basic system (for the universal multi-channel stereophonic sound system as defined in Recommendation ITU-R BS.775). - Value added services with different data capacities and delivery time (e.g. traffic message channel, business data, paging, still picture/graphics, 1.5 Mbit/s video/sound multiplex, future Integrated Services Digital Broadcasting (ISDB)). - Flexible allocation/reallocation of services, without affecting continuing services. 2.4 Service delivery Use of common signal processing in receivers for: a) local, sub-national and national terrestrial VHF/UHF networks; b) mixed use of terrestrial and national/supernational UHF satellite services; c) cable. It would be advantageous, in some countries, to design the system and plan the service in such a way that a common receiver could be used for all the above delivery concepts. - 3 - Rep. ITU-R BS.1203-1 2.5 Service information - Radio programme data related to each programme signal (programme labelling, programme delivery control, copyright control, conditional access, dynamic programme linking, services for the hearing-impaired). - Multiplex system information (simple programme or service identification, selection and linking). 2.6 Interface - Recording capability of sound signals (in bit-rate reduced form) and related data. This implies recording the complete programme signal including its programme-related data, and the ability to access small blocks of data in the encoded signal. - Data interface capability to information technology equipment (ITE) and communication networks. 2.7 Service availability - Vehicular, portable and fixed reception. - High-coverage availability in location and time. - Subjectively acceptable failure characteristics. - High immunity to multipath (long and short delay) and Doppler effect (for mobile receivers). - Trade off between extent of coverage for a given emission power, service quality and number of sound programmes and data services. 2.8 Spectrum efficiency - High spectrum utilization efficiency (better than FM, maximize frequency reuse and single frequency networking, minimize sharing constraints with other services) - Multiple programme service provision within a contiguous frequency band. 2.9 Complexity - Low-cost basic receiver configuration - Use simple, non-directional receiving antenna appropriate to vehicular and portable reception. 3. System design considerations 3.1 Channel characteristics The design of both a satellite and a terrestrial digital sound broadcasting system is strongly dependent on the factors affecting the propagation characteristics of the path to the vehicular receiver. The propagation path in the VHF/UHF frequencies is subject to attenuation by shadowing due to buildings and other obstacles, and to multipath fading due to diffuse scattering from the ground and nearby obstacles such as trees, etc. The shadowing and multipath effects depend on the operating frequency, the elevation angle to the transmitter and the type of environment in which the receiver is operating: whether it is an open, rural, wooded suburban or dense urban environment. A - 4 - Rep. ITU-R BS.1203-1 mathematical description of a vehicular broadcast channel with multipath propagation is given in Annex 1-C together with experimental results. Conventional digital modulation systems are particularly sensitive to multipath signals since these can create severe inter-symbol interference related to the differences in path delays. The inter- symbol interference cannot be overcome by an increase of the transmit power. In relation to the digital channel bandwidth necessary, the multipath propagation may be frequency selective and also time varying. For a conventional digital modulation scheme, the achievable error performance is then strongly limited by the frequency selectivity and the fast field-strength variations with mobile reception. Studies of the statistical distribution of the field-strength (see Report ITU-R BO.955) have shown that it follows a log-normal distribution over large areas, coupled with a Rayleigh (no line-of-sight path) or Rice distribution (consisting of the direct path and Rayleigh distribution) within small areas (usually of dimensions of the order of a few hundred wavelengths). Therefore, in most respects the Rayleigh channel within dense urban areas is the least favourable. Any new system must be designed to operate in this propagation environment. A certain amount of wideband propagation data is available [Cox et al., 1975]. Typically, at UHF, the 90% correlation bandwidth is of the order of 30 kHz with independence (<10% correlation) at frequency separations of the order of 3 MHz. Also the delay spread in urban areas is found to be of the order of 1-2 μs but exceeds 3 μs for about 1% of locations in any localized area. In mountainous and hilly terrain, delay spreads can be many tens of microseconds for large area coverage. For a fixed receiver, the time delay of each path will typically be fixed, but for a moving receiver, the time delay will vary proportionally to the speed of the receiver parallel to the direction of each received path. Thus, different Doppler shifts are associated with multiple paths arriving at the receiver from different angles. The Doppler effect is described in terms of