Optimisation of Resilient Satellite Communications for Sustainable Digital Connectivity in Remote Rural Africa

Abstract

Digital connectivity using telecommunications network infrastructure has become indispensable for the socio-economic development of today’s modern society. This digital connectivity is being achieved using terrestrial, satellite or the integration of both to form a more realistic heterogeneous communications network characterise by wireless/wireline, long/short latency, and high/low bandwidth. Satellite and Integrated Satellite-Terrestrial Networks (ISTNs) exhibit unique characteristics such as large bandwidth/capacity and global coverage capabilities, which is being exploited to connect even the remotest and poorest communities in the world in an optimally cost-effective and efficient way.
This thesis investigated the optimum, cost-effective, efficient and sustainable way to help bridge the digital divide between the mainly terrestrially connected developed cities and unconnected remote rural villages, particularly in the isolated remote rural African communities. This was achieved by optimised data transmission using the most widely used (de facto) standard transport protocol over the Internet in a pure satellite or hybrid ISTN environment that is characterised by large Bandwidth Delay Product (BDP). Transmission Control Protocol (TCP) accounts for 80 − 90% Internet data traffic and applications over Internet Protocol (IP) nowadays, which makes it one of the most important protocols for data transmission over the Internet.
Experiments were carried out to measure the practical and simulated End-to-End (E2E) latencies of Satellite and ISTN environments from which a framework for E2E latency of ISTN environments was developed for quantifying practical E2E latency of pure satellite and ISTN environments. The practical E2E latency was measured by a passive measurement method using two testbeds of Geostationary satellite network providers that transmit and receive voice over IP signals while the active method was used by the simulation experiments, in which File Transfer Protocol (FTP) traffic over TCP enabled within the designed ISTN topology was created. The measured E2E latencies were used to investigate the impact of long Round-Trip Time (RTT) of Satellite and ISTN environments on large BDP and the standard TCP schemes.
Following the successful E2E measurements and framework development, this thesis also developed and propose an enhanced congestion control algorithm called TCP HYBIC for long RTT and high-speed networks such as ISTN and pure satellite environments. HYBIC is based on large BDP CUBIC and HYBLA TCP algorithms. HYBIC performance analysis and evaluation in comparison to these large BDP schemes were conducted using numerical and simulation methods. The performance analysis and evaluation of HYBIC in comparison to a standard, CUBIC, and HYBLA TCP schemes showed that HYBIC achieves performance in terms of packet delivery ratio of up to 99.96%, jitter of 34 μs, and efficient capacity utilisation of up to 67%. These have overcome the challenges of standard TCP over long RTT and large BDP paths, which form part of the realistic communications network nowadays and the future by improving the utilisation and packet delivery rate.
Finally, as part of future work, this thesis recommended exploring the effect of background traffic on fairness and the effect of more complex network topologies could also be interesting. Experiments with more queue management schemes such as Active Queue Management (AQM) where packets are dropped from the queue before the queue overflows could also be an interesting work for the future. Potential areas of applications such as Tele-medicine and Tele-agriculture could be tested with network topologies designed for resilient and sustainable Satellite and ISTN communications. These would be useful for Telecommunications services and application in remote rural areas, and for emergency/disaster management when terrestrial communications infrastructure failed in the event of a disaster.