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Title: A resilient Ka-band satellite video broadcast system incorporating time diversity and maximal ratio combining
Author: Uggalla, L. C.
ISNI:       0000 0004 6057 3652
Awarding Body: University of South Wales
Current Institution: University of South Wales
Date of Award: 2015
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Steadily-increasing user demand for a wide range of high-quality video services delivered via satellite has driven broadcasters to move into the Ka-band and higher frequency spectrum in order to accommodate the necessary data rates. However, a major issue at these frequencies is the effect of severe rain-induced fading on link reliability, which requires that the system must be designed to implement mitigation techniques in order to achieve an acceptable quality-of-service. These techniques generally involve the use of adaptive modulation and data rates, together with various forms of diversity, switching or combining. In this thesis, we analyse and quantify the benefits of adding Time Diversity (TD) and Maximal Ratio Combining (MRC) to the widely-used DVB-S2 standard. Our results, which are based on i) 3 years of satellite beacon propagation measurements from 2 UK sites; ii) high-fidelity computer simulations; and iii) our new TD / MRC technology, indicate that substantial improvements in data throughput and significant reductions in outage time are readily achievable. Accurate knowledge of the statistical distribution of rain attenuation is necessary for the proper design of a Fade Mitigation Technique (FMT) to operate with the required level of service availability. Therefore, since July 2010, the University of South Wales and the Science and Technology Facilities Council have undertaken a programme of simultaneous satellite beacon measurements at the University campus in Pontypridd, Wales, and at the STFC Chilbolton Observatory, in Southern England, respectively. Transmissions from the Eutelsat Hotbird l3A (previously Hotbird 6) satellite at 19.7 GHz were recorded, together with meteorological measurements, at both sites. These data enabled reliable estimation of the instantaneous propagation conditions and carrier-to-noise ratio on the Ku-band beacon downlinks. Using standard ITU-R recommendations, the resulting data-set of measured 19.7 GHz attenuations was also frequency- scaled to yield a predicted data-set of 29.5 GHz attenuations. Thereby, the performance of an operationally-representative, hypothetical DVB-S2 communications link, with uplink at 30 GHz (from Chilbolton to the satellite), and downlink at 20 GHz (from the satellite to Pontypridd), was analysed based on l-year's data. The DVB-S2 transmission and reception signal processing architecture has been faithfully implemented in the MATLAB simulation environment with reference to the appropriate technical standards documents. Extensive testing has been conducted to verify that the bit error rate performance of the MATLAB simulation closely matches that defined in the DVB-S2 standard for all combinations of modulation schemes and coding rates. Inputs to the simulator comprise a test data stream (which can be a real HDTV signal), together with the uplink and downlink attenuation time- series data for the fading event being studied. Outputs consist of the bit error rate statistics and modulation scheme / coding rate configuration as a function of time, the total data throughput over the event duration, and the demodulated baseband signal. A novel feature of this work is the extension of the existing DVB-S2 standard to include TD and MRC. During periods of fading, TD is enabled, such that the transmitted data is duplicated into 2 parallel streams with a suitably-chosen time offset between them. In the receiver, MRC is employed in order to obtain a greater SNR improvement than could be achieved by the more traditional switched-combining method. We have designated this extended version of the DVB-S2 standard, incorporating the twin techniques of TO and MRC, as DVB-S2-TD. It provides the potential to continue delivering services at SNRs significantly below the currently acceptable threshold for DVB-S2, such as would be experienced under the propagation impairments associated with severe weather conditions. In this thesis, we describe the experimental systems used to collect the satellite beacon and meteorological measurements. The implementation of the MATLAB simulator for DVB-S2 is then discussed, together with the enhancements for TD and MRC. Finally, we compare the performance of DVB-S2 and DVB-S2-TD, so as to demonstrate the operational benefits of our new techniques.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available