Model analysis for the radio channel of DVB-T indoor reception in a Single Frequency Network

Transcription

1 Model analysis for the radio channel of DVB-T indoor reception in a Single Frequency Network Chi-Fang Huang 1, Yi-Min Tsai 2, Feng-Ting Wen 2, Ming-Fu Wei 2 and Chia-Fu Yang 2 1 Graduate Institute of Communication Engineering, Tatung University Taipei, TAIWAN, ras@ttu.edu.tw 2 Engineering Department, Taiwan Public Television Service Foundation Taipei, TAIWAN Abstract Under a SFN (Single Frequency Network) operation with three distant DVB-T transmitters in northern Taiwan simultaneously, the radio channel of a DVB-T indoor reception has been analyzed. Detailed field strength indoor were fully measured, then the statistical model is validated for such a test. Employing SFN operation and 6MHz channel bandwidth are the different situation from the previous study in literature doing this kind of validation. Keywords DTV, DVB-T COFDM, Single Frequency Network, adio Channel, Lognormal 1. Introduction Since the introduction of European Digital TV transmission standard DVB-T COFDM [1], the indoor reception of DTV has become a new promising broadcasting service. It means, the viewer does not need a traditional directional antenna, for example, a Yagi-Uda antenna [2], which is usually installed on the roof of a house, instead, the viewer may only need a compact antenna [3] used in a room for receiving the broadcasting wave of digital TV. Enhancing the DVB-T s ability of managing multi-path signals in environment, OFDM techniques are able to offer the viewers inside a room stable TV programs. Such a kind of digital TV service has been widely deployed in many countries, for example, UK, German, Singapore and Taiwan [4], etc. When the broadcasting waves come into a room, it results a very complex electromagnetic environment, because the reflection, diffraction and interference do happen naturally and there is no LOS (Line-Of-Sight) reception at all. This room is to be fulfilled with multi-path

2 signals. Because of the characteristics of OFDM modulation plus the Guard Interval (GI) technique [1], it is suggested to use omni-directional instead of directional antennas for DVB-T reception inside a room [3]. As for the reception prediction in terms of field strength, analytical approach is quite impossible to be derived. Usually, this radio channel is supposed to be very statistical. Just like the other wireless communication in a build-up area, statistical model of radio channel is sometimes necessary for engineering analysis, for instance, network deployment [5] [6], receiver or receiving antenna design. The technology of Single Frequency Network [7] provided in DVB-T is a method to fulfill a large area with sufficient field strength for reception. Several transmitting stations at different distant locations broadcast the same TV program simultaneously with the same carrier frequency. Since an OFDM receiver is able to manage multi-path F signals, SFN can therefore enhance its receiving gain. SFN is able to establish a large area coverage in which a mobile receiver can appreciate the TV service when it is moving around. The work carried out by this project was tried to establish a statistical model for the indoor reception under a DVB-T SFN operation. Three transmitting stations were working simultaneously, while the reception of digital TV signals in a room was analyzed statistically. The analysis method in the work [8] is referred, yet SFN operation, 6MHz bandwidth and Taiwan s local terrestrial situation are alternatively considered in this evaluation project. The SFN system is shown to own better reception by statistical data. There are five digital TV broadcasters in Taiwan now, and their individual SFN has been deployed island wide. 2. Field measurement The measurement was carried out by the PTS (Public Television Service Foundation), who is one of five terrestrial broadcasters in Taiwan. eferring to the Fig. 1 and Fig. 2, from PTS HQ, the TV program is sent by a microwave link (DS3) to three DVB-T transmitter stations Chu-Tsu-Shan (13.92km far, 5KW), Wun-Lee (6.35km far, 3KW) and Deng-Tsu-Hu (47.9km far, 3KW), which form a SFN by employing proper individual antenna radiation pattern and the synchronization of GPS. These three stations are located at the northern part of Taiwan, including the Taipei metropolis, and serve about one third of Island in terms of area. The program is broadcasted in the UHF Ch26 channel (545MHz) with a 6MHz bandwidth. At the receiving end, the &S EFA test receiver was used for signal analysis, being accompanied with an omni-directional antenna of horizontal polarization [4]. eferring to the Fig. 3, the testing room is inside a 12-floor building near the PTS HQ. The layout is also illustrated with the coming directions of F signal of three transmitter stations. The measurement was carried out on the third and fifth floor. A measurement line with 12.5m long was set up, and the measuring step was 5cm (~ wavelengths).

3 Fig. 1 - PTS SFN formed by three DVB-T transmitters in Northern Taiwan Fig. 2 - elated positions of three transmitter stations located at the Northern Taiwan Fig. 3 - The testing room

4 Fig. 4 - Measured field strength along the measurement line indoor Table 1 floor Mean value Standard deviation 3rd dbμ v 4.60 dbμ v 5th dbμ v 3.95 dbμ v Fig. 4 shows the curves of measured field strength along the measurement line for 3 rd and 5 th floor. Moreover, the statistical parameters of measured data are listed in Table 1. By ec.itu- P.1546 document [8][9], the standard deviation is regulated as 5.5 db, and the present measured ones show the better case caused by the SFN for indoor reception. As expected in normal situation, the 5 th floor has higher mean values than that on 3 rd floor. 3. Model analysis As for the statistical model for the radio channel of indoor reception, the lognormal is usually referred [8]. The expression for lognormal model is, P( ) = 1 2πσ exp 1 2 M σ 2 (1) in which, M and σ are its mean value and standard deviation, respectively. The fitting curve of raw measured data is compared with this theoretical model in Fig. 5, in which, its fitted CDF (Cumulative Distribution Function) curve indeed follows the lognormal line [8]

5 Fig. 5 - CDF fitting of Lognormal 4. Conclusion This paper has presented the results of DVB-T indoor reception under a SFN operation with three distant transmitter stations in northern Taiwan. Statistical results are also derived and statistical model of such a radio channel is also analyzed. Lognormal model is validated to be matched with this kind of reception environment. Deployment of SFN is proved to be effective for indoor reception. 5. eferences [1] Massel, Mark (2000), Digital Television DVB-T COFDM and ATSC 8-VSB, [2] Burberry,. A. (1992), VHF and UHF Antennas, Peter Peregrinus Ltd., London. [3] Huang, Chi-Fang and Chen, Li (2002), A Compact Omni-directional UHF Antenna for DTV Broadcasting eception, XXVIIth General Assembly USI 2002, Maastricht, The Netherlands. [4] Huang, Chi-Fang, Chang, The Nan and Hsu, Chau-Yun, (2003), Field evaluations in Taiwan of the DVB-T COFDM and ATSC 8-VSB digital TV systems, EBU Technical eview. [5] Belloul, B. and Saunders, S. (2004), Accurate Coverage Prediction and Optimization for Digital Broadcasting, EBU TECHNICAL EVIEW, April. [6] Parsons, J. D. (2000), The Mobile adio Propagation Channel, John Wiley & Sons Ltd. [7] Ligeti, A. and Zander, J. (1999), Minimal Cost Coverage Planning for Single Frequency Networks, IEEE Trans. on Broadcasting, pp.78-87, Vol. 45, No. 1, Mar.

6 [8] Ong, J. T., Yan, H., ao, S. V. B., and Shanmugam, G. (2004), Indoor DTV eception: Measurement Techniques, IEEE Trans. on Broadcasting, pp , Vol. 50, No. 2, June [9] ITU- recommendations P.370.