Power-efficient transmission for high-speed wireless infrared local area networks

While use of power efficient signaling schemes appears to be effective in compensating for the inherent high pathloss associated with pure diffuse infrared links, it begins to lose its effectiveness as data rate is increased. At very high data rates, intersymbol interference (ISI) can result in a very high and sometimes irreducible power penalty, preventing the system to operate at a low bit-error probability. In this paper, we introduce a new link design employing a multi-beam transmitter in conjunction with a narrow field-of-view (FOV) direction diversity receiver. The design goal is to eliminate the effect of ISI so that power efficient signaling schemes such as pulse-position modulation (PPM) can be employed at very high data rates. We also use high-rate Reed-Solomon codes to further increase the power efficiency of PPM signals. It is shown that a bit-error rate (BER) not exceeding 10 ^-9 can be achieved within the link coverage area with 99% probability at bit rates up to a few hundreds of megabits per second, using transmitted power levels well below one Watt.