Analysis of TCP over visible light communication networks

The research and development of new technologies for the upcoming 5G networks is crucial in order to provide faster trustworthy data transmissions, with innovative materials and techniques, at a lower price. Within this scenario, visible light communications has become one of the most important fields of study towards new generation networks as they can provide non-interfering and faster transmissions by modulating the light signals of light emitting diodes. This type of technologies could take advantage of existent indoor and outdoor infrastructure such as ceiling lights or street lampposts, which reduces deploying expenses. Nevertheless, a lot of research has to be done to polish, standardize and promote visible light communications. The work presented in this document aims to analyse the performance of the TCP protocol when used in VLC networks. For this purpose it has been necessary to develop a model that could be used to simulate a VLC channel along with the transmission of data using TCP. This model was implemented with NS-3 which is one of the principal simulation tools used for research in the networking area. Using the developed model, parameters such as received optical power, signal-to-noise ratio, and error rate for several modulation schemes were analysed. Furthermore, the performance of TCP was studied employing two TCP variations, TCP New Reno and TCP Westwood. The effects of using several modulation techniques such as OOK and OFDM were also evaluated. In addition, simulation scenarios that include mobility of the receiver were used. The results gathered demonstrate that the visible light communications channel provides high signal-to-noise ratio values. This enables data transmission over large distances using the appropriate modulation technique. Moreover, TCP is totally feasible to operate over VLC networks as the error rate inside the coverage area of the light source is very low. However, the results show that when reaching the edges of the coverage area, there is a drastic fall in the TCP throughput. Finally when talking about mobility, TCP works adequately when the receiver is inside the coverage zone. The performance of TCP Westwood decreases at higher receiver's speed compared to New Reno. When the receiver continuously moves inside and outside the critical coverage area, TCP Westwood presents better performance indicators