Infrared uplink space and time multiple access supported by angle diversity and successive interference cancellation

Handling multiple access represents a key challenge of indoor optical wireless communications, even though rarely addressed in the uplink case. Typical solutions in the literature rely on orthogonal access schemes, providing interference-free links to users but suffering from low performance when the number of access requests grows. An alternative is represented by non-orthogonal multiple access, even though its feasibility and effectiveness are generally assessed only for simple scenarios with few users. In this paper, we introduce a space-time division multiple access framework where access points equipped with an angle diversity receiver allow the channel resources to be managed in both space and time domain. Moreover, by resorting to successive interference cancellation, it is possible to serve users in a non-orthogonal fashion. Herein, we propose two novel resource allocation algorithms aimed to maximize the users access rate. Performance results demonstrate the capability of the proposed solution to serve up to 9 users, outperforming the other benchmark orthogonal and non-orthogonal strategies. Additionally, we introduced two mechanisms that, combined with successive interference cancellation, guarantee a reliable detection of superposing signals, with bit error rate below 10-3. Summarizing, the presented multiple access scheme allows users to transmit simultaneously and reliably, thus realizing channel resources saving as well.