The advent of the first mobile phones in the 1980s marked the beginning of mobile communications for commercial purposes. Now, thirty years later, wireless connectivity has become a fundamental part of our everyday lives and is increasingly being regarded as an essential commodity like electricity, gas and water. This unparalleled success means that we are today facing the imminent shortage of radio frequency (RF) spectrum: It is predicted that the amount of data sent through wireless networks will increase by a factor of 10 during the next five years. Moreover, data from Qualcomm demonstrates that the spectrum efficiency (number of bits transmitted per Hertz bandwidth) is saturating. Therefore, the US Federal Communications Commission has warned that a "spectrum crisis" is looming.
Using light has many key advantages as compared with RF. The available spectrum is vast, the visible light spectrum is 10,000 times larger than the RF spectrum; it is free as it is not subject to government regulations; it is more secure than the radio frequency spectrum the signals of which can be intercepted outside a premise; it can achieve three orders of magnitude higher data density per unit area. Compared to the infrared spectrum, the visible light spectrum has additional advantages. First, it is not power-limited due to eye-safety concerns. Second, it can serve two purposes at the same time: illumination and high speed data transmission, resulting in a better use of energy. However, while several hundred megabit per second (Mbps) have been demonstrated for a single link using an off-the-shelf white LED, 1 gigabit per second (Gbps) and room coverage is still an open issue. In addition, there is little research for multi-user networked OWC systems. Also, the effects of dimming on the achievable data rates are not well understood. In addition, there are environments and scenarios where the use of light is difficult or not possible such as when there is heavy blockage between transmitters and receivers, or when terminals move with high speeds. In those situations, it will still be more appropriate to use the RF spectrum. To sum up, there are potential large overall performance improvements when wireless systems can select their transmission medium autonomously and in a dynamic as well as self-organising fashion.
A second essential pillar of the proposed research is to overcome the RF spectrum efficiency saturation of current cellular systems while at the same time reducing the energy consumption. A key to solving this issue is to successfully tackle interference in wireless networks which occurs when multiple communication links in close vicinity use (or reuse) the same bandwidth or frequency. On the one hand frequency reuse is beneficial since the more often transmission resources are used per unit area, the higher the spectrum efficiency. On the other hand, intensive frequency reuse results in the aforementioned interference issues. Radically new approaches will be followed that include interference already in the design of a new wireless air-interface. In the past, wireless air-interfaces were optimised for single transmission links, and performance degradations due to interference in a system deployment were mended subsequently, but existing solutions are either impractical or sub-optimum. We will investigate a new air-interface that is based on the recent successful demonstrations of and world-wide research on the concept of spatial modulation which was originally proposed by the applicant.