SPATIAL AVAILABILITY IN SATELLITE-TO-INDOOR BROADCASTING COMMUNICATIONS Nuan Song1, Giovanni Del Galdo1, Marko Milojevic´1, Martin Haardt1, Albert Heuberger2 1Communications Research Laboratory, Ilmenau University of Technology, P.O. Box 100565, 98684 Ilmenau, Germany, {nuan.song, giovanni.delgaldo, marko.milojevic, martin.haardt}@tu-ilmenau.de, 2Fraunhofer Institute Integrierte Schaltungen IIS, Am Wolfsmantel 33, 91058 Erlangen, Germany, [email protected] ABSTRACT polarization diversity. With high power broadcasting satellites becoming techni- To analyse the satellite-to-indoor channel, either empirical cally feasible, satellite-to-indoor propagation has drawn in- measurements can be performed or deterministic channel creasing interest. This contribution investigates the spatial modeling methods such as ray-tracing can be used. In order availability of satellite links inside rooms in particular in an to achieve a good reception quality, it is crucial to know office environment. The static satellite-to-indoor channels the propagation conditions inside a room. In the litera- are obtained by a 3D ray tracing engine and by a geometry- ture, only a few measurements are available dealing with based channel modeling tool. Different antenna configura- the performance of different receive antennas strategies, es- tions are considered at the receiver: single as well as multi- pecially with respect to polarization diversity. Measurement ple antennas with different polarimetric beam patterns. The results in [1] show that the received electromagnetic field is results show that the additional antennas placed at the re- strongly diffused in the interior of a building. Therefore the ceiver reduce the spatial variability of the channel, leading received power does not depend on either the gain or the to much lower transmit power that is required in order to polarization of different types of antennas. At frequencies obtain the same availability. If the power is kept the same, close to those assigned to the future Galileo navigation sys- the availability increases significantly. tem (1.1 GHz - 1.6 GHz), it was confirmed in [2] through both statistical and ray tracing channel modeling based on 1. INTRODUCTION the measurements that wall attenuation influences the in- door coverage the most. The MAESTRO project [3] car- In future mobile satellite communications, broadcasting, ried out the satellite-to-indoor measurements in Erlangen and navigation systems, the knowledge of the satellite-to- and Athens by using the Worldspace Afristar satellite (48 indoor propagation conditions is becoming more and more dBW) in the L-band. From the local Cumulative Distribu- important with the increasing needs for the delivery of tion Function (CDF) of the building penetration loss it was multimedia content such as audio or video to the termi- concluded that the percentage of positions where a satellite nal, for example, in Satellite Digital Multimedia Broadcast signal can be received lies in the range of 30 % up to 80 % (SDMB) systems. Satellite broadcast systems are of high with corresponding link margins of 10 dB to 16 dB. With interest for future mobile communications because of high the help of simulations based on a 3D ray tracing tool it is transmission power and large radio link margins. For in- shown in [4] that the polarization state of the propagation stance, the Effective Isotropic Radiated Power (EIRP) of the wave changed significantly inside the room. satellite planned for the future SDMB service will be rather Performing the measurements is very time-consuming and high, in the range of 72 dBW and higher, and existing newer expensive. Moreover, measurement data always represents satellites like the XM Radio satellites offer link margins of a specific scenario and its propagation conditions which up to 18 dB, which makes the reception from satellite to limit the flexibility of measurements-based channel mod- indoor possible. Moreover, since in mobile reception only eling. Therefore, in our work we apply deterministic chan- time diversity (using long interleavers) has been employed nel modeling based on the 3D ray-tracing WinProp simula- so far, there is still some room for improvement in stationary tion tool developed by AWE Communications [5] and the or portable reception (e.g., inside rooms) by using spatial or IlmProp, a flexible geometry-based MIMO channel model- ing tool developed at Ilmenau University of Technology [6], as well as other objects such as desks and cupboards can be which supports different receive antenna patterns. modeled with planar elements that have an arbitrary number This paper is organized as follows: First, we briefly de- of corners and individual material properties. Doors and scribe the features and functions of the WinProp followed windows can be created as subdivisions inside walls. The with the proposal of an office environment scenario and the proposed office scenario consists of a closed room (of size creation of the indoor database, i.e., its geometrical mod- 5.6m × 6.4m × 3m) with windows, doors, and some fur- eling. Then by introducing the IlmProp, we describe the niture such as tables, closets, and chairs. Table 1 describes satellite-to-indoor channel model considering polarization the structure and material parameters [7] of the room. An and receive antenna patterns. Finally, we compare the re- overview of the indoor scenario is shown in Figure 2. sulting power values at the receiver using different antenna Table 1. Material properties of indoor scenario configurations with respect to correlation and evaluate the Object Material Reflection Diffraction spatial availability of signals inside the room. (Thickness) Loss (dB) Loss (dB) Wall Brick (30cm) 9.52 22 Roof/Floor Concrete (30cm) 7.51 21 2. THE SATELLITE-TO-INDOOR CHANNEL Window Glass (5mm) 7.53 21 MODEL Windowsill Clinker (20cm) 9.94 22 Door Wood (15cm) 15.09 24 For satellite broadcast systems, the reception quality is of Table/Closet Wood (5cm) 11.43 22 Chair Wood (10cm) 15.09 24 prime interest especially in indoor scenarios. Investigations of the improvement in reception quality focus on signal availability and coverage given different antenna configura- 4 4 tions considering polarization issues. In our work the chan- 1 2 nel fading properties are assessed by using the WinProp [5] 2 to obtain the propagation paths, and the IlmProp [6] to re- 1 trieve the channels for different antennas. Figure 1 shows the satellite-to-indoor channel modeling framework and the 1 spatial availability analysis. 3 3 6 5 Fig. 2. Office layout (1-chair; 2-desk; 3-closet; 4-window; 5-door; 6-wall) Path Parameters 2.1.2. Satellite-to-Indoor Realization IPlm rop The calculations of the satellite-to-indoor scenario were car- ried out using 3D ray tracing in WinProp. For the propaga- tion paths, transmission, reflection, and diffraction are taken Channel Coefficients into account. In [8], [9], and [10], WinProphas already been validated with the help of measurements. The elevation of geostationary satellites in the area of Eu- rope lies in the range of 33 ◦ and 45 ◦. In this satellite-to- indoor scenario, the elevation is set to 40 ◦. A circular po- larized satellite signal (EIRP assumed to be 48 dBW from Fig. 1. Block diagram of our analysis the satellite) with carrier frequency 2.0 GHz is received by a stationary receiver through a window in a closed room. The signals undergo frequency flat fading. The described indoor scenario was used to evaluate the field 2.1. The Ray Tracing Engine strength coverage. The satellite antenna was simulated by 2.1.1. Indoor Scenario Definition a vertical omni-directional antenna set far enough from the room to obtain the approximately planar wavefronts. Fig- An indoor database was generated with WinProp [5]. It uses ure 3 shows the predicted receive power with resolution a full 3D vector data base to describe the scenario. Furniture 8 cm at a height of 1 meter and also ray paths. the multipath propagation. The signal in the area that is ReceivePower very close to the window includes a strong LOS compo- dBW -145 nent, which determines the total field strength as well as -150 the polarization state. However, the diffuse property of the -155 -160 Non Line Of Sight (NLOS) field may provide more room -165 for the improvements in reception quality by using low-cost -170 antennas and certain receive diversity schemes which will -175 -180 be discussed in the following section. -185 -190 3. SIMULATION RESULTS AND DISCUSSIONS The aim of the simulations is to assess the possible im- provements of the system coverage when different receive Fig. 3. Receive power prediction (1-meter height and 8-cm antenna configurations are used in satellite-to-indoor com- resolution) with ray paths simulated by WinProp munications. Of primary interest is the NLOS indoor region where exists high variance of the received power. In fact, in 2.2. Geometry-Based Channel Modeling LOS regions the received power is relatively constant and has much higher values than in the NLOS regions (typically The IlmProp [6] developed at TU Ilmenau is a flexible 10 dB higher). This implies that in LOS communications geometry-based propagation model for wireless communi- we cannot gain much from neither polarization nor spatial cations. After the satellite-to-indoor scenario is defined and diversity, and the coverage is determined merely by the av- modeled by the Winprop, the path strength and spatial infor- erage received power. In practical cases, if the availability mation about each path obtained from WinProp are further in NLOS regions is higher than 60 %, then in LOS region processed as scatterer-related parameters. Each path is char- the availability reaches values close to 100%. Therefore, acterized by the positions of the points of interaction and by we restrict our simualtions to investigate diversity in NLOS complex reflection coefficients which determine the attenu- regions. ation. All these parameters are then input into the IlmProp The simulation results presented here are obtained in the which gives us the flexibility to apply different receive an- following order.