Raised Cosine Pulse Shaping for Pre-equalized Optical Wireless Links

Their programmability means that digital preequalization techniques are more flexible than analog circuit equalizers. However, their performance depends on the number of samples per data symbol needed to accurately represent the pre-equalized time domain pulse. This requirement limits the maximum data rate that can be generated by a digital-to-analog converter (DAC). Another challenge when pre-equalizing the signal applied to a transmitter is the need to restrict the maximum voltage applied to the transmitter. Given these challenges, this paper demonstrates the benefits of constructing digitally pre-equalized On-Off Keying (OOK) symbols with raised cosine pulses. In addition, results are presented which show that each symbol can be represented with as few as 5 samples per bit. The performance of the proposed equalization method is investigated using an off-the-shelf LED-based optical wireless communication (OWC) link. Using equalization, the bandwidth of the link is increased by a factor of 10 to 100 MHz. Consequently, the data rate achievable with a 2 GSa/s DAC is 400 Mb/s.