AbstractSatellite communication systems have proven to be at the centre of delivering the much-desired high capacity, high-speed and reliable broadband and multimedia communication applications and services. With the emergence of the fifth generation (5G) system and the demand of seamless connectivity, real-time and on-the-go services have become prominent. The advantages offered include coverage of areas inaccessible to terrestrial telecommunication infrastructure, enormous capacity, and flexibility.
In this context, the digital video broadcasting via satellite (DVB-S) is the cornerstone technology that enables the reliable transmission of signals for a variety of users and use-cases. Over time, the technology standard has evolved and at present, the extension of its second-generation (DVB-S2X) is the order of the day. This technology offers several features and advantages including higher modulation and coding (MODCOD) schemes, which, in addition to offering higher spectral efficiency and capacity, adaptively switches between the MODCODs depending on the transmission condition. For the classic fixed satellite services (FSS), the DVB-S2X has been optimised for robust performance. This is because the earth-space slant path propagation phenomena have been well identified and modelled. In addition to the propagation conditions affecting the FSS path, signal transmission for a mobile earth-station terminal experiences further impairments which exacerbate the demand on system resources required to contain the link effects of user mobility. Prominent among these impairments are shadowing and signal blockage in the intervening medium. This work focused on creating a more realistic mobile channel based on real terrain data.
In this thesis, the land mobile satellite (LMS) channel characterisation was carried out using the statistical Rician model to simulate the DVB-S2 and DVB-S2X systems, with results used to quantify the impact of user terminal mobility on system performance. Higher order MODCODs, namely 16APSK, 32APSK, 64APSK, 128APSK, and 256 APSK, were implemented to complement the existing 8PSK scheme in MATLAB® and SIMULINK®. To further investigate the impact of mobility on a realistic LMS channel, a novel LMS channel was developed using geo-spatial terrain data for Cardiff city obtained from the databases of Digimap and LiDAR. These datasets were processed in System Tool Kit (STK®) and integrated into MATLAB®. The mobile channel characteristics were thus determined, having three states, namely line-of-sight (LOS), shadowing and blockage. This characterisation was employed to implement a Markov-based multi-state LMS channel which is a better representation of a realistic channel. The novel channel was used to simulate the DVB-S2 and DVB-S2X systems and the results were compared with the Rician-based channel. The findings show that the Rician K approximation of the mobile channel needs more power than the new channel to achieve the same bit-error-rate (BER). For instance, the theoretical AWGN threshold of 32APSK (9/10) is 16.2 dB at BER of 10-7, but for K = 7, which represents a shadowed channel, the BER curve flattened at 10-3; whereas the new channel’s BER curve flattened at 10-4.
The DVB-S2X standard offers additional flexibility and advantages, which include sharper filtering roll-off factor and interference mitigation capabilities. It also presents an optional superframe deployment which offers additional system versatility in very-low signal-to-noise (VL-SNR) situations and mobile systems. The superframe adds a variety of pilots depending on the format selected and helps to improve system performance. In this regard, the superframe format two (2) was implemented to test its performance on the novel LMS channel developed and results show that the superframe configuration has the potential to enhance the mobile system’s BER performance. As a novel approach, in this work the number of bundled Physical Layer (PL) frames contained in the superframe was made variable and the results show that increasing the number of PL frames per superframe further improves system performance depending on the channel condition and MODCOD. For instance, for a lightly shadowed channel, superframe implementation for the 64APSK (7/9) presents a 1 dB gain for 9 bundled PL frames and increasing the number of bundled PL frames to 12 offered an additional 0.7 dB gain. Thus, adaptive MODCOD may be combined with a variable-frame superframe implementation to improve the performance of a mobile satellite communication system and achieve a more efficient trade-off between power and spectral efficiencies than is possible with adaptive MODCOD alone.
|Date of Award||2023|
|Supervisor||Ifiok Otung (Supervisor), Guoping Liu (Supervisor) & Nicholas Avlonitis (Supervisor)|