IC1004 TD(13)07037 Ilmenau, Germany 2013/May/28-31

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1 EUROPEAN COOPERATION IN THE FIELD OF SCIENTIFIC AND TECHNICAL RESEARCH EURO-COST IC1004 TD(13)07037 Ilmenau, Germany 2013/May/28-31 SOURCE: Departement Elektrotechniek TELEMIC, Katholieke Universiteit Leuven, Belgium Analysis of a DVB-H system using an antenna placed on top of a wind turbine gondola. Emmanuel Van Lil, Jordi Bracke Manzanares, Jan-willem De Bleser ESAT / TELEMIC Kasteelpark Arenberg 10 BUS 2444 B-3001 Heverlee BELGIUM Phone: Fax: emmanuel.vanlil@esat.kuleuven.be

2 Analysis of a DVB-H system using an antenna placed on top of a wind turbine gondola. E. Van Lil, J. Bracke Manzanares, J.-w. De Bleser Div. ESAT-TELEMIC KU Leuven Kasteelpark Arenberg, 10; Bus 2444; B-3001 Heverlee, Belgium Emmanuel.VanLil@ESAT.KULeuven.Be Abstract The aim of this work is to study the feasibility of installing a DVB-H antenna on top of the gondola of a wind turbine. At the time the study was initiated, there was only information available on the influence of wind turbines on analog TV reception [1]. The rotating blades will generate reflected/diffracted rays with Doppler and delay. The electromagnetic rays arriving at the receiver antenna are computed with EPICS ray tracing software and analyzed using Matlab. The resultant data are introduced into a DVB-H link simulator to compute the BER, with as input relative amplitude, Doppler and delay of 2 rays. Conclusions will be drawn concerning the effect of these interferences on the DVB-H receiver. Only in few cases can significant effects be noticed. Index Terms DVB-H; wind turbine; antenna on gondola I. INTRODUCTION This paper studies the feasibility of installing a DVB-H antenna on the top of the gondola of a wind turbine. More specifically, the effects of the rotating blades on the reception of the signal are investigated. These installations have the advantage that no power lines are needed to power the transmitter and there is no need to build a tower to mount the antenna, thus reducing the installation costs. First the electromagnetic simulation will be detailed (section II), then the effects on the Doppler shifts and delays on the reception of a DVB-H signal will be investigated (section III). Conclusions will be drawn in section IV. II. ELECTROMAGNETIC SIMULATION A. Scenario A single windmill with an antenna installed on top of the gondola will be considered. Blades and gondola can rotate around their respective axes, but only the Doppler shift due to the rotation of the blades will be considered here. A receiver is placed at 1 km distance. B. Simulations The simulations are performed with KU Leuven ray tracing software EPICS [2]. Other authors use NEC to reduce the computational burden, but limits themselves to only Doppler analysis [3]. The simplified 3D model of Fig. 1 has been used to perform the simulations. The wind turbine has been simplified sufficiently so as to speed up the computations without losing significant accuracy. The simulations here are done with two nested loops: all the possible positions of the gondola and the blades are simulated in 10 degree steps. For every step of the gondola a complete revolution of the blades is simulated. The blades are rotating at maximal speed. Fig. 1: 3D model of the windmill with the antenna placed in the gondola. Fig. 2: 3D plot of the absolute Doppler frequency received. The Doppler shift, shown in Fig. 2, has its peak value when one of the blades is vertical and when the gondola is either 0 or 180 degrees. The received multipath ray power is shown in Fig. 3.

3 Fig. 3: plot of the multipath ray received power. A value of -140 db means that no multipath ray is received. The power has its peak value for positions of the gondola around 270 degrees and one of the blades vertical (Fig. 4). This corresponds with a situation where the ray is reflecting in the blade and sent back to the receiver antenna. Fig. 5: 3D plot of the direct to multipath power ratio. III. LINK SIMULATION A DVB-H link has been coded in Matlab in order to evaluate the receiving conditions. The link is basically an OFDM modulator (Fig. 6: DVB Modulator (from wikipedia).fig. 6) and a demodulator (Fig. 7) connected through a distorting module. Fig. 6: DVB Modulator (from wikipedia). Fig. 7: DVB Demodulator (from wikipedia). Fig. 4: Windmill with gondola turned 270 degrees. Blades are at the back of the receiver. This module adds a copy of the ray with Doppler, delay and attenuation as well as Gaussian noise. This study was done with only one dominant and one interfering ray to investigate the sensitivity to the interferer and to Doppler. The used filter turned out to have a significant effect. In this case a Butterworth filter has been used (Fig. 8). Fig. 8: Used filter (Butterworth).

4 Then, we can simulate constellations corresponding with different cases of C/I, delay and Doppler. Fig. 9 illustrates the case for a C/I ratio of 0.5 db,.and increasing delays by 0.4 µs. steps. One can see that problems only start to occur for delays larger or equal than 2 µs. Fig. 9: Constellation diagrams A BER of 0 is only achievable when the direct to multipath power ratio is at least than 1 db (Fig. 10, red curve to the right). This is not accomplished for any position of the blades and the gondola. When adding Doppler the performance decreases. Results can be seen in Fig. 11: the only way to decode the information with no errors is by having a C/I better than 1.5 db. The interference is, for instance, due to reflections or diffractions. We note that a minimum SNR in the 40 to 60 db range is needed to be able to recover the information. Generally the higher the C/I the higher the SNR needed to achieve the same level of BER. Fig. 10: BER against the SNR and the C/I ratio.

5 REFERENCES [1] ITU-R recimmendation 805 Assessment of Impairment caused to Television Reception by a Wind Turbine, International Telecommunication Union, Geneva, 3 pp., 1992 [2] Iris De Coster, E. Van Lil, Thomas Neubauer and T. Ergoth, Comparison of indoor penetration measurements with geometric and Physical Optics Predictions, Proc. Millennium Conference on Antennas and Propagation, Davos, Switzerland, 4 p., 9-14 April 2000 [3] A. Navqi, S. Yang and H. Ling, Investigation of Doppler Features From Wind Turbine Scattering. IEEE Antennas and Wireless Propagation Letters, Vol. 9, 2010, pp Fig. 11: BER against the SNR and the C/I ratio with a Doppler set to 100 Hz. When combining both results from the electromagnetic simulation and link simulation we get the results of Fig. 12. There are 6 lines where the BER is not good enough to recover the information successfully. Fig. 12: BER in function of the angle of the gondola and the blades. IV. CONCLUSION Reception of the signal will be error free in 25% of the cases. In other cases the received signal will have 3 glitches per revolution. Further studies have to be done to determine what the effects of these glitches are in the receiver. These problem cases are occurring mainly when the relation of power between the direct and the multipath ray is smaller than the minimum ratio of 1.5 db. Results may be improved by adding spatial diversity to transmitting antennas.