Line-of-Sight method of simple code transmitting for outdoors
Sunlight in optics represents a large but slow moving dc signal. This is easily got rid of by high pass filtering the received optical signal. Providing the level or intensity of the sunlight doesn't "saturate" the receiving device, all you need to ensure is that the data transmitted is modulated at a "carrier" frequency of several kHz or more. Thisis usually how this problem is overcome. Modulating the data means it carries no slow or dc component that is vital for data transmission integrity.