Analysis of random orientation and user mobility in LiFi networks

Mobile data traffic is anticipated to surpass 49 exabyte per month by 2021. Smartphones, as the main factor of generating this huge data traffic (86%), are expected to require average speed connection of 20 Mbps by 2021. Light-fidelity (LiFi) is a novel bidirectional, high-speed and fully networked optical wireless communication and it is a promising solution to undertake this huge data traffic. However, to support seamless connectivity in LiFi networks, real-time knowledge of channel state information (CSI) from each user is required at the LiFi access point (AP). The CSI availability enables us to achieve optimal resource allocation and throughput maximization but it requires feedback transmitted through the uplink channel. Furthermore, the important aspects of the indoor LiFi channel such as the random orientation of user device, user mobility and link blockage need to be carefully analysed and effective solutions should be developed. In contrast to radio frequency (RF) channels, the LiFi channel is relatively less random. This feature of LiFi channel enables a potential reduction in the amount of feedback required to achieve high throughputs in a dynamic LiFi network. Based on this feature, two techniques for reducing the amount of feedback in LiFi cellular networks are proposed: 1) limited-content feedback scheme based on reducing the content of feedback information and 2) limited-frequency feedback scheme based on the update interval. It is shown that these limited-feedback schemes can provide almost the same downlink performance as full feedback scheme. Furthermore, an optimum update interval which provides maximum bidirectional user equipment (UE) throughput, has been derived. Device orientation and its statistics is an important determinant factor that can affect the users throughput remarkably in LiFi networks. However, device orientation has been ignored in many previous performance studies of LiFi networks due to the lack of a proper statistical model. In this thesis, a novel model for the orientation of user device are proposed based on experimental measurements. The statistics of the device orientation for both sitting and walking activities are presented. Moreover, the statistics of the line-of-sight (LOS) channel gain are calculated. The influence of random device orientation on the received signal-to-noise-ratio (SNR) and bit-error ratio (BER) performance of LiFi systems has been also evaluated. To support the seamless connectivity of future LiFi-enabled devices in the presence of random device orientation, mobility and blockage, efficient handover between APs are required. In this thesis, an orientation-based random waypoint (ORWP) mobility model is proposed to analyze the performance of mobile users considering the effect of random device orientation. Based on this model, an analysis of handover due to random orientation and user mobility is presented. Finally, in order to improve seamless connectivity, a multi-directional receiver (MDR) configuration is proposed. The MDR configuration shows a robust performance in the presence of user mobility, random device orientation and blockage.