If illumination is not desired in the uplink, infrared (IR) LEDs or indeed RF would be viable solutions. In VLC, the information is carried by the intensity (power) of the light.
As a result, the information-carrying signal has to be real valued and strictly positive. Traditional digital modulation schemes for RF communication use complex valued and bipolar signals. Modifications are therefore necessary, and there is a rich body of knowledge on modified multi-carrier modulation techniques such as OFDM for intensity modulation (IM) and direct detection (DD).
Data rates of 3.5 Gb/s have been reported from a single LED.
It has to be noted that VLC is not subject to fast fading effects as the wavelength is significantly smaller than the detector area.
While the link-level demonstrations are important steps to prove that VLC is aviable technique to help mitigate spectrum bottlenecks in RF communications, it is essential to show that full-fledged optical wireless networks can be developed by using existing lighting infrastructures.