Raised Cosine Pulse Shaping for Pre-equalized Optical Wireless Links

Their programmability means that digital pre-equalization 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.