Satellite communication technology has played a significant role in bridging the digital divide between the undeveloped and developed countries of the world. As a cost-effective mode of communication covering a broad area, satellite technology has facilitated service provision especially in remote areas of Africa. According to recent research findings, integrating satellite technology with 4G and 5G terrestrial networks will not only expand their range but also enhance their services. This requires a comprehensive understanding of the application of multi-input-multi-output (MIMO) technology developed for terrestrial networks in their satellite variants.
In the latest research, two MIMO-based techniques: Space-time block code (STBC) and Uncoded space-time labelling diversity (USTLD) have been considered for improving the performance of mobile satellite communication systems. When constellations with two different binary mappings are used in USTLD, a significant improvement in error performance is observed as compared to single binary mapping in STBC. Traditionally, M-ary Quadrature Amplitude Modulation (MQAM) is the popular modulation scheme for general wireless communications systems. However, circular constellations are deemed more suitable for satellite links as compared to square and rectangular modulation schemes owing to their reduced number of amplitude levels and lower peak-to-average power ratio. As a result, circular constellations, such as Amplitude Phase-Shift Keying (APSK) and M-ary Phase-Shift Keying (MPSK) form the basis of the latest broadcasting standards for nonlinear satellite links.
In recent research, Dr. Tahmid Quazi and Dr. Sulaiman Saleem Patel from the University of KwaZulu-Natal, School of Engineering, proposed a new USTLD system designed specifically for mobile satellite communications. The system uses the circular M-ary Amplitude Phase-Shift Keying (MAPSK) constellations used in the standard Digital Video Broadcasting standard for nonlinear satellite links. The innovative aspect of this system is comprised of the new design of secondary mappers to achieve labeling diversity. As the authors state in their paper, this is the most critical aspect of developing a USLTD system. The proposed mapper designs exploits the similarity in structure between square MQAM and certain M-ary Amplitude Phase-Shift Keying (MAPSK), and adapts the heuristic-based algorithms used in the MQAM to produce secondary mappers for the appropriate MAPSK constellations from the DVB-S2X standard. Their work is currently published in the journal, Transactions on Emerging Telecommunications Technologies.
Bit error rate performance of the proposed system showed gains of 4dB and 5dB for 16 APSK and 64 APSK respectively when compared to the existing STBC system. Furthermore, these results were used in a study for investigating the most suitable metrics for quantitatively comparing USTLD mapper designs. The investigation showed that none of the metrics are individually suitable. As such, a two-stage approach for comparing the minimum product Euclidean distance of the mapper designs was put forward. When the metrics are found to be equal in the first step, the second stage is used in ranking based on the minimum summed product Euclidean distance. Interestingly, the approach was used correctly to rank the MQAM and MAPSK-USTLD mapper designs considered in the paper.
In summary, the scholars presented a new two-step methodology for an accurate comparison of the Uncoded Space-Time Labelling Diversity mapper designs. The feasibility of this method was successfully validated in the first design of the Amplitude Phase-Shift Keying-based USTLD satellite system. The results of this research have formed the basis for other research articles which are currently under review with leading international journals. Dr. Tahmid Quazi has also been invited to present the results of this study at the 2020 edition of the International Conference on Advances in Satellite and Space Missions.Based on the results, Dr. Quazi in a statement to Advances in Engineering noted that the proposed analytical comparison method is a promising solution for advancing the development of the latest diversity techniques for mobile satellite communication systems.
Quazi, T., & Patel, S. (2019). USTLD mapper design for APSK constellations over satellite links. Transactions on Emerging Telecommunications Technologies, 30(7).