DVB-SH Radio Network Planning Tool (Release 4.2) by AWE Communications GmbH. All rights reserved 1
1 Introduction 1.1 Overview Digital Video Broadcasting Satellite to Handheld (DVB-SH) aims to provide multimedia services to the mobile user on a cost-effective way by the inter-working of satellite systems with terrestrial networks. The DVB-SH system is based on the concept of a hybrid satellite/terrestrial architecture and relies on the OFDM radio interface defined for broadcasting networks to achieve a coherent combination of terrestrial and satellite signals. In such a single frequency radio network configuration, the satellite might be seen as a complementary signal source serving users in rural and suburban areas, while terrestrial repeaters operating at the same frequency as the satellite are used to amplify the signal in urban areas and to enhance indoor penetration, i.e. in those areas where the satellite signal is subject to shadowing. In order to assess the DVB-SH radio coverage in different environments the off-the-shelf radio network planning tool WinProp has been adapted to consider satellite transmitters and further extended according to the current specification of the DVB-SH system. This DVB- SH radio planning tool allows the investigation of the DVB-SH performance in terms of coverage, SNIR and system margin for different satellite and terrestrial repeater configurations within various environments. Such investigations will be used to trade the open radio parameters of the DVB-SH system architecture and to gain knowledge concerning the required density of the terrestrial repeaters for the network roll-out (in order to provide sufficient coverage in urban and indoor environments). Figure 1: Basic structure of the DVB-SH radio network planning tool by AWE Communications GmbH. All rights reserved 2
1.2 Concept The planning tool allows the user to define a specific DVB-SH network configuration comprising the satellite segment, an arbitrary number of terrestrial repeaters and the user equipment. Based on the accurate prediction of the satellite and repeater radio channels in terms of path loss delay profiles by using e.g. a deterministic ray-optical wave propagation model the defined DVB-SH network is evaluated. The calculation of the different path loss delay profiles forms the basis of the DVB-SH system simulation. The DVB-SH system simulator superposes the radio channels of the corresponding satellite and repeater links by taking into account the predicted path loss delay profiles and considers the various parameters (link budget, time delay) of the defined satellite and repeater infrastructure. For the evaluation of the coverage the OFDM receiver included in the user equipment is modeled in a detailed manner. The impinging contributions are analyzed according to their delay. Consideration of the guard interval determines the DVB-SH radio coverage for a specific location (inside an urban area of interest) and a given service. According to this concept there are two basic parts of the DVB-SH radio network planning tool as described in Figure 1: Wave propagation modeling of the radio channels (for satellite and repeaters) DVB-SH system simulation (superposition of signals, modeling of user terminal) Both parts have been integrated into the DVB-SH radio network planning tool which has been extended by a graphical user interface in order to allow the convenient definition of the DVB-SH infrastructure including all relevant parameters. Table 1: Principles of the DVB-SH radio network planning tool Principles Configurations OFDM air interface (SFN with guard interval) Downlink operation Satellite, terrestrial or hybrid infrastructure Superposition of satellite and repeater signals OFDM receiver in user terminal Service channels (allocated power, data rates) Signalling channels (allocated power) SNIR targets as coverage thresholds Intra- and intersystem interference Satellite diversity by AWE Communications GmbH. All rights reserved 3
2 Wave Propagation Modeling Wave propagation models are mandatory for radio network planning in order to determine the coverage situation and multi-path effects. Radio transmission in urban environments is subject to strong multi-path propagation (see Figure 2). Dominant characteristics are the reflection at walls, diffraction around corners, shadowing due to buildings and the wave guiding in street canyons (for terrestrial transmitters). Penetration is important if additionally the indoor scenarios should be taken into account. To consider these effects and as the DVB-SH system utilizes a guard interval incl. in the OFDM air interface the usage of a wave propagation model which is capable of predicting the impulse response (path loss delay profile) is required. Table 2: Scenarios and wave propagation models in the DVB-SH planning tool Scenarios Urban/Indoor based on 3D vector data of buildings pixel data of topography (optional) 3D vector data of vegetation (optional) Wave Propagation Models Ray Tracing (rigorous 3D) Ray Tracing (2x2D) Ray Tracing in horizontal plane plus knife-edge diffraction model Wide area based on clutter data in pixel format LMS channel model according to DLR for the satellite channel pixel data of topography (optional) Hata-Okumura plus ITU Vehicular A/B and Pedestrian A/B for the terrestrial channel 2.1 Ray tracing for urban and indoor scenarios The ray-optical model allows a site-specific prediction of the radio channel for terrestrial repeaters as well as for satellites in urban and indoor environments. For accuracy reasons a three dimensional description of the environment including building shapes and building heights has to be incorporated, i.e. each building is described as a polygonal cylinder with uniform height (see Figure 2). Valid rays between transmitter and receiver are determined according to a ray tracing technique using the principles of geometrical optics (incl. reflections and diffractions). To calculate the path loss of each ray the free space loss is superposed to the loss due to reflection, diffraction or penetration. The model takes into account up to six reflections and two diffractions including as well combinations of reflections and diffractions. Such a three dimensional ray optical approach requires an higher computational effort than simplified empirical models. However, the computation time is reduced significantly by a preprocessing of the building database, so that predictions are available within a few minutes. by AWE Communications GmbH. All rights reserved 4
Rx Tx Figure 2: Propagation scenario in a typical urban environment (Paris) 2.2 LMS and Hata-Okumura models for wide areas For the assessment of the DVB-SH coverage on large scale, i.e. on a significant part of a beam region (corresponding to thousands of km 2 ) wave propagation modeling results for such wide areas are required. Using the ray-optical wave propagation model for such wide scale simulations is rather difficult due to the computational demand and the lack of corresponding databases. So the alternative is to use an empirical (statistical) channel model as the DVB-SH tool has the possibility to use path loss delay profiles calculated by both deterministic and empirical channel models. Figure 3: Clutter database for wide area (80x80km 2 ) around Paris by AWE Communications GmbH. All rights reserved 5
For the evaluation of the satellite coverage in wide areas an empirical channel model has been included in the DVB-SH planning tool which allows to reproduce typical impulse responses of the land mobile satellite (LMS) channel based on different parameters (e.g. user environment, satellite elevation angle). The model is based on the usage of clutter databases as presented in Figure 3. Figure 4: Prediction of the satellite coverage around Paris (LMS model) In order to simulate the hybrid satellite/repeater infrastructure over such wide areas an empirical (statistical) model for the terrestrial channel has been implemented. For this purpose the ITU channel models vehicular A/B and pedestrian A/B have been selected (see Table 3). While the vehicular model is valid for macro-cells the pedestrian model represents the contributions from the repeater for a micro-cellular deployment. The path loss offset for the repeater channel is calculated by using the model according to the well known Hata- Okumura model (an empirical model widely applied for the path loss prediction in urban, suburban and rural areas). The Hata-Okumura model evaluates clutter as well as topographical databases for the path loss prediction. Table 3: Channel profile according to ITU vehicular A channel ITU-R vehicular A Reference model in vehicular and mobile environment with large cells and high power Tap # Relative delay [ns] Relative power [db] 1 0 0 2 310-1 3 710-9 4 1090-10 5 1730-15 6 2510-20 by AWE Communications GmbH. All rights reserved 6
3 DVB-SH System Simulation 3.1 OFDM air interface The DVB-SH system simulator superposes the radio channels of the corresponding satellite and repeater links by taking into account the predicted path loss delay profiles and considers the various parameters (link budget, time delay) of the defined satellite and repeater infrastructure. For the evaluation of the coverage the OFDM guard interval included in the air interface is modeled in a detailed manner. The impinging contributions are analyzed according to their delay (see Figure 5). Based on that the DVB-SH radio coverage for a specific location (inside an urban area of interest) and a given service is determined. Satellite 1st Repeater 2nd Repeater power [dbm] t in µs Start of Rake window End of Rake window Dedicated data channel Signalling channels (common channels) Other data channels Figure 5: Detailed modeling of the guard interval Based on this flexible realization of the DVB-SH planning tool it is possible to investigate various DVB-SH architectures and to trade the open parameters of the satellite segment, the terrestrial repeater segment and the user terminal segment. 3.2 Wave propagation results Based on the evaluation of the computed rays different results can be computed for satellites as well as terrestrial repeaters. Figure 6 shows the predicted received power for a satellite link in the urban area of Milan, Italy. by AWE Communications GmbH. All rights reserved 7
Figure 6: Satellite coverage in Milan for GEO satellite By adding the powers of the different rays the received power (and path loss) for a specific transmitter can be calculated. Figure 7 describes the prediction of the received power for a sectorised terrestrial repeater operating at 2197.5 MHz installed on top of one of the tallest buildings at 60m in the city center of Munich, Germany. The wave guiding effects in the street canyons as well as the shadowing behind buildings are clearly visible. Figure 7: Prediction of received power for sectorised repeater in Munich by AWE Communications GmbH. All rights reserved 8
3.3 Results indicating DVB-SH coverage for urban scenarios The coverage in urban environments can be analyzed based on the vector building data and the ray-optical wave propagation model. The simulations in general can be distinguished in two cases. The pure satellite case and the case with additional deployment of terrestrial repeaters in order to investigate the coverage improvements introduced by the repeaters. Figure 8: Coverage in Munich for pure satellite (left) and hybrid network (right) The coverage results computed by the DVB-SH RNPT for the urban scenario of Munich are presented in Figure 8 for the pure satellite case on the left and for the hybrid satellite plus IMR network on the right (green indicates coverage). Figure 9 shows the distribution of the SNIR coverage over the urban city center of Milan for the deployment of 3 repeater sites with three sectors each. Figure 9: SNIR coverage in Milan for given repeater deployment by AWE Communications GmbH. All rights reserved 9
3.4 Results indicating DVB-SH coverage for wide areas By using the empirical channel models for the satellite (and the terrestrial repeaters) coverage predictions for wide areas based on clutter (and topographical databases) are possible. The SNIR coverage in case of a hybrid satellite and terrestrial repeater (with hexagonal deployment) network is presented in Figure 10. Figure 10: Hybrid coverage depending on Tx power and environment Similar results can be generated for wide areas in case of satellite only infrastructure, i.e. without terrestrial repeater deployment. For the repeaters different network topologies (omni and sectorised repeaters) can be compared to an given SNIR target (depending on service parameters as data rate, fading margin). The DVB-SH radio planning tool can consider arbitrary sites where each sector can be individually configured concerning Tx power and antenna pattern as well as antenna orientation. The hybrid network has to be designed with care in order to ensure on one hand the sufficient coverage in urban and suburban areas but on the other hand to limit the degradation of the satellite signal in the surrounding of the city (due to the limited size of the guard interval the satellite and repeater signals will interfere from a certain distance on). by AWE Communications GmbH. All rights reserved 10