We present a concept for networked optical wireless communications, also denoted as LiFi, to meet the requirements of industrial wireless applications. These are primarily mobility support with moderate data rates per device, reliable real-time communication and integrated positioning. We describe a distributed multiuser multiple-input multiple-output architecture, serving mobile devices via an optical wireless infrastructure. The system consists of a central unit, being connected to a number of distributed optical frontends covering a larger area. Our main contribution is a medium access control protocol based on spacedivision multiple access. Evaluation results demonstrate the advantages of joint transmission from adjacent optical frontends and the dynamic switching between spatial diversity and multiplexing. The relevance of spatial multiplexing becomes obvious in channel measurements in an indoor scenario. Moreover, we highlight a low-power physical layer based on onoff-keying for battery-powered mobile devices. Our architecture can easily integrate positioning by simultaneously measuring the time-of-flight between multiple optical frontends and the mobile device. We highlight the use of plastic optical fiber as an analog fronthaul technology and discuss the integration with other networks. The main functions described in this paper will be supported by the upcoming IEEE Std. 802.15.13.
LiFi has been considered as a promising candidate for future wireless indoor networks. The IEEE P802.15.13 and P802.11bb standardization groups agreed upon channel models generated using the non-sequential ray tracing approach of OpticStudio. In this paper, in order to validate the channel modelling approach, at first 2 × 2 multiple-input multiple-output (MIMO) channel measurements are carried out over 200 MHz bandwidth using a channel sounder. The experimental scenario is also modeled in 3D by applying ray tracing. The obtained results indicate good agreement between simulations and measured channel impulse responses, from which parameters such as path loss and delay spread are derived. After validating the channel modeling approach, we investigate the singular values and the effect of user mobility onto the performance in a 4 × 4 distributed multi-user MIMO scenario.
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