Height Gain Study for Digital Television Broadcasting at UHF Bands in Two Regions of Mauritius

Transcription

1 Proceedings of the 2007 Computer Science and IT Education Conference Height Gain Study for Digital Television Broadcasting at UHF Bands in Two Regions of Mauritius V. Armoogum University of Technology - Mauritius, Pointe aux Sables, Mauritius K. M. S. Soyjaudah University of Mauritius, Reduit, Mauritius varmoogum@utm.intnet.mu N. Mohamudally University of Technology - Mauritius, Pointe aux Sables, Mauritius alimohamudally@utm.intnet.mu ssoyjaudah@uom.ac.mu T. Fogarty London South Bank University, London, England fogarttc@lsbu.ac.uk Abstract After the official launching in October 2005 of Digital Terrestrial Television (DTT), plans were made to carry out field measurements across the island. Field strength, Carrier-to-Noise Ratio and Bit-Error-Rate were measured for digital broadcasting at UHF Bands (470 to 862 MHz) at two antenna heights (4 m and 6 m) in the north and south of Mauritius. Measurements were also done at few locations at an antenna height of 8 m. Moreover, a small test was carried by increasing the transmitted power in the south. Firstly, height gains are calculated using these measurements and then compared between the two regions. In both regions the height gain varies from location to location for the same distance around the transmitter which implied that the topography of the island need to be considered before developing a novel digital model for Mauritius. The measurements show that at most locations in the north, the gain is better than in the south. This can be explained by the fact that the south is more affected by slow and fast fading effects as well as the irregularity of the land than the north due to very dense forests with hills, mountains and gorges. However, the results also show that in some regions in the north at a distance of 10 km from the base station, the height gain is less compare to the same distance in south. This can be explained by the fact that the signal received in these regions in the north may be affected by tall commercial buildings, residential Material published as part of this publication, either on-line or in print, is copyrighted by the Informing Science Institute. Permission to make digital or paper copy of part or all of these works for personal or classroom use is granted without fee provided that the copies are not made or distributed for profit or commercial advantage AND that copies 1) bear this notice in full and 2) give the full citation on the first page. It is permissible to abstract these works so long as credit is given. To copy in all other cases or to republish or to post on a server or to redistribute to lists requires specific permission and payment of a fee. Contact Publisher@InformingScience.org to request redistribution permission. houses and hotels. Secondly, observations show that more height gain can still be obtained when raising the antenna height to 8 m or more before reaching the saturation gain value of 0 db. This again proves that the signals received in the two regions are very affected by some factors such as slow and fast fading, terrain and climates. However, better height gains are observed in

2 Height Gain Study for Digital Television Broadcasting the north than in the south. Finally, there is an increase in height gain when increase the transmitted power from 200W to 250W. Key words: Bit Error Rate, Carrier to Noise ratio, Height Gain, DTT, DVB-T, Field Strength, Multipath, Multiplexing, Path Loss, Propagation, Transmission. Introduction Mauritius is a tropical island in the Indian Ocean, located in the Southern Hemisphere. Mauritius has two kinds of climate. Below the 400-meter level on most of the windward (southeastern) side of the island and below 450 meters on the leeward side, a humid, subtropical climate prevails. Above these altitudes, the climate is more temperate, but there is no sharp break, and variations in exposure, altitude, and distance from the sea produce a wide range of patterns. The island has two seasons. The hot and wet summer lasts from November through April. February is the warmest month with highest temperatures of 38 ºC in the lowlands and 34 ºC on the plateau. Winter is cool and dry, influenced by the steady southeasterly trade winds. July is the coolest month and has average temperatures of 22 ºC in the lowlands and 16 ºC in the plateau. Rainfall is abundant, ranging from 90 cm per year in the western lowlands to 500 cm in the tableland and an average of 200 cm per year overall. Humidity is frequently above 80 %. The whole terrain is irregular and with numerous mountains and hills and gorges. The area is about 1860 km 2. The central plateau, which is not really flat, gradually rises towards the south west where it reaches its highest point at 800 m with the Piton de la Rivière Noire peak. This plateau is surrounded with some craters in the form of a chain of mountains and some isolated peaks. Buildings, houses, sugar cane plantation and trees are scattered in the north part of Mauritius while the south is mainly covered by large areas of sugar cane field, dense forests and range of mountains and gorges. In this paper, we classify the north as suburban (76%) and the south as rural will apply the category of the terrain mentioned in the ITU-R Recommendations (International Telecommunication Union, 1997). Some works were carried out in Southern India using VHF/UHF bands (Prasad & Iqbal, 1997; Rao et al., 2000) and recently an intensive research works are done over Indian Subcontinent (Prasad, 2006) on field strength measurements and path loss analysis. However, the authors did not carry out any study to check the effects gain can obtained if the received antenna height is raised or if the transmitted power is increased. Recently, a similar work was done in Singapore on height gain measurements for digital television reception (Ong, Rao, Hong, & Shanmugam, 2004). The experiments are conducted in a region where buildings are clustered together having the same height of m. Measurements are carried in one of the buildings from 1st floor to the 15th floor. This paper is the continuation of a series of research works undergone by the authors of this paper (Armoogum, Soyjaudah, Fogarty, & Mohamudally, in press; Fogarty, Soyjaudah, Armoogum, & Mohamudally, 2006) on field strength measurements and path loss analysis in the north and the south of Mauritius. The aim of this paper is to measure the height gain for digital receptions in the two above mentioned regions in Mauritius and compare the results. Experimental Details and Methodology Adopted DVB-T (European Telecommunications Standards Institute [ETSI], 1997a, 1997b), the most sophisticated and flexible digital terrestrial transmission system, is used in Mauritius. This standard uses the Coded Orthogonal Frequency Division Multiplexing (COFDM). A power of 200 W is used to transmit the digital signal. A receiving antenna (Log periodic Aerial) LPV345HV UHF band from Fracarro is used to capture the signal. The measurements points, as shown in Figure 1, were taken by connecting a spectrum analyzer and an Advanced Field Strength Meter (AFSM) PROLINK-4C for TV signal analysers to measure the Bit Error 18

3 Armoogum, Soyjaudah, Mohamudally, & Fogarty Rate (BER), the carrier to Noise ratio (C/N), the field strength (E) and the Carrier to Signal Interference (CSI). Table 1 summarises the transmission parameters for the transmitter used. Figure 1: View of Part of the South of Mauritius CHARACTERISTICS Table 1: Transmission parameters for DTT broadcasting BUTTE AUX PAPAYES (NORTH) TRANSMITTER Antenna height above sea level (m) Transmitter power (W) Antenna gain (db) 8 12 Polarisation Horizontal Horizontal RF Channel (Transmit) UHF Ch MHz Antenna Height only (m) MALHERBES STATION (SOUTH) UHF Ch MHz Measurement locations were divided into three groups for each region, that is, three concentric circles CC1N, CC2N and CC3N for the north and CC1S, CC2S and CC3S for the south. The radius determines the horizontal distance between the measured point (receiver antenna) and the transmitter. The radii of CC1N/CC1S, CC2N/CC2S and CC3N/CC3S are 5 km, 10 and 15 km respectively. Approximate points were selected on the circles as shown in Figure 1 and determined the measuring sites. The exact measuring locations are determined when taking measurements physically on the sites. The measurements were conducted around the relay station and were repeated for two receiving antenna heights - 4 m and 6 m. 19

4 Height Gain Study for Digital Television Broadcasting Results and Discussions Comparative Study of Height Gain in Both Regions at Height Difference of 4 to 6 m Theoretically, the height gain at a constant distance from the station around it should be same. But this is not the case as depicted in the graphs in Figure 2.1, Figure 2.2, and Figure 2.3. This shows that the measuring locations are not in line of sight with the transmitters. Hence, in some locations, there are more obstacles which yield a very low height gain while in some regions there are very few obstacles, yielding a high height gain. In general, the mean height gain is higher in the north than in the south which is clearly shown in Table 2 for all three distances. This indicates that there are more factors affecting the signal strength and propagation in the south than in the north. The mean path loss is more in the south than in the north and mentioned that shadowing effect and fast fading are responsible for that problem (Armoogum, Soyjaudah, Fogarty, et al., in press; Armoogum, Soyjaudah, Mohamudally, et al., in press). In the present study, the height gain is less in the south reconfirms the presence of more these factors in the south. Another observation made here is that in some measuring sites in the north, the height gain is less than that in the south for the same distance (10 km) as depicted in Figure 2.2. These villages / towns are the measuring sites locations 2, 3, 4, 5 and 6 of CC2N. These locations (e.g. Grand Bay, Goodlands, Petit Rafray, Beau Sejour and Poudre D Or Hamlet) are tourist places and the busiest in the north. They are highly residential areas, scattered by hotels, bungalows, tall buildings as well as trees and mountains. In the region of Grand Bay, the angle of diffraction occurring at the edge of a building is greater when the antenna height is 4 m compare to height of 6 m. As a result, the power received from the 6 m antenna is greater than that from the 4 m antenna. More details about locations with best gains and weakest gains are shown in Table 2. Figure 2.1: Variation of Height Gain for North and South Regions at a Distance of 5 km from Transmitter 20

5 Armoogum, Soyjaudah, Mohamudally, & Fogarty Figure 2.2: Variation of Height for North and South Regions at a Distance of 10 km from Transmitter Figure 2.3: Variation of Path Loss for North and South Regions at a Distance of 15 km from Transmitter 21

6 Height Gain Study for Digital Television Broadcasting DISTANCE CC1 CC2 CC3 REGION Table 2: Height Gain Comparison MEAN IN DB LOCATIONS WITH LOWEST GAIN LOCATIONS WITH HIGHEST GAIN North & 6 (+2 db) 3 & 5 (+10 db) South & 15 (0 db) 9 (+23 db) North , 2, 3, 4 & 5 (+2 db) 11 & 12 (+11 db) South (+1.3 db) 5 (+13.3 db) North & 15 (+1.7dB) 12 (+9.2 db) South & 15 (+0.4 db) 9 (+6.8 db) Comparative Study of Height Gain in Both Regions at Height Difference of 6 to 8 m Some measurements are carried out in some few measuring sites in both regions as shown in Table 3 and Table 4. This test is carried out to determine whether or not more gain can be increased if the antenna height is raised to 8 m. A comparison study is done between the height gain 4 to 6 m and the height gain 6 to 8 m. The results show there is a height gain which is slightly less than the gain obtained between 4 and 6 m. It also indicates that additional gain may be obtained when raising the antenna height above 8 m until the field strength remains constant. This will reach when the receiver antenna will be in line-of-sight with the transmitter and hence gain will be 0 db. Moreover it is observed that better height gains are obtained in the north than in the south. DISTANCE CC1 CC2 LOCATION Table 3: Height Gain in the South HEIGHT DIFFER- ENCE (M) HEIGHT GAIN IN DB (200W) HEIGHT GAIN IN DB (250W) 4 to to to to to to to to to to

7 Armoogum, Soyjaudah, Mohamudally, & Fogarty Table 4: Height Gain in the North DISTANCE LOCATION HEIGHT DIFFERENCE (M) CC1 CC HEIGHT GAIN IN DB (25W) 4 to to to to to to to to Effect on Height Gain When Raising the Transmitted Power from 200 W to 250 W A test was carried out in the south to measure the height gain when the transmitted power is increased to 250 W. The 200 W-transmitter (200 W) model DVB-T 200 W from Tekko Telecom was replaced by a 250 W-transmitter model DVB-T 250 W. Field measurements were carried out in few regions using the new 250 W transmitter to measure the new values of field strength so as to calculate the height gain as shown in Table 3. There is a rise in height gain which is obvious due to a rise in field strength. Conclusions Firstly, in both regions, the height gain varies from location to location for the same distance around the transmitters because some measuring points are in line-of-sight with the transmitters while others are not. This means that there are more obstacles which yield a very low height gain at some regions while in some regions there are very few obstacles, yielding a high height gain. Moreover, in general, a lower mean height gain is supposed to be obtained in a rural area compared to a sub-urban area. A rural area is usually one which does not consist of tall buildings and hence the effects of slow and fast fading are supposed to reduce considerably. However, it is noticed that a lower height gain is obtained for the south which implies that this terrain is more irregular in this region. It also concludes that the south is quite different from the ITU- R (International Telecommunication Union, 1997) definition of rural areas. More investigations need to be done here. Secondly, an increase in an antenna height from 6 m to 8 m yields an increase height gain which is slightly less than the gain obtained between 4 and 6 m. Thirdly, the transmitted power in the south is raised from 200 W to 250 W. There is a rise in height gain which is obvious due to a rise in field strength. However, better height gains are obtained in the north than in the south. Lastly, the height gain is increase when raising the transmitted power fro 200 W to 250 W. Hence, it can be concluded that the height gain in both regions are affected by terrain, diffraction, reflection, refraction, absorption, shadow, scattering as well as the radiation pattern of the transmitted antennas. 23

8 Height Gain Study for Digital Television Broadcasting Acknowledgment This research is a joint collaboration between the national broadcasting television carrier, the Multi Carrier Mauritius Ltd (MCML) and the University of Technology, Mauritius (UTM). The authors would like to thank all the engineers and staff of MCML for their tremendous help in terms of equipment and resources. A special thank goes to UTM for the financial help. References Armoogum, V., Soyjaudah, K. M. S., Fogarty, T., & Mohamudally, N. (in press). Path loss analysis between the north and the south of Mauritius with some existing models for digital television broadcasting for summer season at UHF bands. Proceedings of the 8 th IEEE AFRICON Armoogum, V. Soyjaudah, K. M. S., Mohamudally, N., & Fogarty, T. (in press). Comparative study of path loss with some existing models for digital television broadcasting for summer season in the north of Mauritius at UHF band. Proceedings of the 3 rd IEEE Advanced International Conference on Telecommunications. European Te1ecommunications Standards Institute. (1997a). Digital Video Broadcasting (DVB). Framing structure, channel coding and modulation for Digital Terrestrial Television (DVB-T), ETS European Te1ecommunications Standards Institute. (1997b). Digital Video Broadcasting (DVB), Implementation guidelines for DVB services. Transmission aspects, ETS Fogarty, T., Soyjaudah, K. M. S., Armoogum, V., T., & Mohamudally, N. (2006). Signal strength variation measurements of digital television broadcasting for summer season in the north of Mauritius at UHF bands. Proceedings of the 3 rd International Conference on Computers and Device for Communication. International Telecommunication Union, (1997). ITU-R recommendation P.529-2, Prediction methods for the terrestrial land mobile service in VHF and UHF bands. Ong, J. T., Rao, S. V. B., Hong, Y., & Shanmugam, G. (2004). Height gain measurements for DTV reception in Singapore. IEEE Transactions on Broadcasting, 50(4), Prasad, M. V. S. N. (2006). Path loss deduced from VHF and UHF measurements over Indian subcontinent and model comparison. IEEE Transactions on Broadcasting, 52(3), Prasad, M. V. S. N., & Iqbal, A. (1997). Comparison of some path loss prediction methods with VHF&UHF measurements. IEEE Transactions on Broadcasting, 43(4), Rao, T. R., Rao, S. V. B., Prasad, M. V. S. N., Sain, M., Iqbal, A., & Lakshmi, D.R. (2000). Mobile radio propagation path loss studies at VHF/UHF bands in Southern India. IEEE Transactions on Broadcasting, 46(2), Biography V. Armoogum is currently a Lecturer at the University of Technology, Mauritius (UTM). He completed a BSc in Computer Engineering (St Petersburg) in 1995 and an MSc in System Engineering (St Petersburg) in He worked as Research Officer (2000), then as Lecturer in the areas of Computing, Communication and Telecommunications at Swami Dayanand Institute of Management (Ex-Polytechnic), Mauritius ( ). He is also Member of the Board of Governors of UTM. Mr Armoogum is currently doing his Ph.D. study and undergoing research in the area of broadcasting, antenna and propagation. He was a member in the programme committee for the 2nd International Conference on Business Process Outsourcing & Modeling (BPOM 2006), Mauritius and reviewer for IEEE International Conference for Portable Information Devices (Portable07). 24

9 Armoogum, Soyjaudah, Mohamudally, & Fogarty Sunjiv Soyjaudah received his BSc (Hons) degree in Physics from Queen Mary College, University of London in 1982, his MSc degree in Digital Electronics from King s college, University of London in 1991, and his PhD degree in Digital Communications from University of Mauritius in He is presently Professor of Communications Engineering in the Electrical and Electronic Engineering Department at the University of Mauritius. His current interest includes source and channel coding, modulation, cryptography, voice and video through IP, broadcasting, as well as mobile communication. Prof. Soyjaudah is member of the IEEE. He is a Director in the Board of Directors of Multicarrier Mauritius Limited. Dr. Nawaz Mohamudaly is graduated from the University of Science and Technology of Lille I (France) in the field telecommunications. He is presently the Ag. Head of the School of Business Informatics and Software Engineering at the University of Technology, Mauritius. His topics of research interests comprise Business Process Outsourcing with emphasis on Global IT Management, mobile computing, web and educational technologies. Dr Mohamudally is currently working on a pilot project aiming at making software development a viable economic activity in the African continent. Terence Fogarty has completed a BA (Hons) in Mathematics and Computing and a PhD in Adaptive Rule-Based Control. He was a Professor of Computing at London South Bank University (LSBU) until He is also a member of the Institute for Computing Research at LSBU. Prof. Terence Fogarty is currently the Vice-Chancellor of Umutara Polytechnic University, Rwanda, Africa. For more information, please see his CV at 25