Block-based PAM with frequency domain equalization in visible light communications

In this paper, we analyze block-based pulse amplitude modulation with frequency domain equalization (block-based PAM-FDE) for visible light communications (VLC) in realistic application scenarios. Typical effects of the VLC-channel, such as different frequency responses of the LED together with the wireless optical propagation channel are included. We consider a measured LED response from our experimental system reaching a noticeable extended 3 dB cutoff frequency of 60 MHz. Further simulations are then based on a 60 MHz low-pass approximation. To consider multipath propagation, two common models for diffuse and non-directed line-of-sight (LOS) conditions are used. We illustrate the influence of the transmitter and propagation characteristics and observe in general significant gains by using a higher system bandwidth while the modulation order is increased only if the received power is very high. We show that in a mobile scenario with variable receiving power, depending on the availability and strength of the LOS-path, optimization of both the symbol rate and the modulation format will be the key parameters enabling efficient and reliable highspeed transmission using block-based PAM-FDE.