Hemispherical lens based imaging receiver for MIMO optical wireless communications

White lighting LED based systems are emerging as an important form of high data rate communications, especially for indoor applications. Two limitations of existing systems are the small field of view of typical receivers and the poor performance of optical wireless MIMO due to lack of spatial diversity. In this paper we describe a novel design which overcomes these problems by using a hemispherical lens in the receiver. We show that the new system has a wide field of view and also provides significant spatial diversity for typical MIMO visible light scenarios. Numerical results are provided for a range of LED transmitters with different half power semi-angles. Our analysis shows that systems can be designed with adequate channel gain for angles of incidence as large as 70 degrees. The optical power density is also calculated to show the received optical power distributions for the case of four LED transmitters. The results indicate that the images of the LEDs are clearly separated. This reduces the channel correlations between individual transmitters and receivers and thus promises a significant diversity order for MIMO optical wireless systems.