Coded OFDM and OFDM/OQAM for Intensity Modulated Optical Wireless Systems

Infrared optical wireless (OW) is a promising technology associating free-space propagation and infrared radiation for home networks. OW offers several advantages over radio technologies, making it an attractive solution for short range communications. However, OW technology is not as mature as for radio; further advanced studies regarding optical components and physical layer issues are still open. Coded orthogonal modulations such as Coded OFDM (COFDM) are currently used in many radio and fixed transmission systems. Among these modulations, COFDM/OQAM is an interesting alternative to classical COFDM modulation, as it does not require the use of a guard interval and it has an optimal spectral efficiency. In this paper, we present a comparative study of modified COFDM and modified COFDM/OQAM schemes adapted to intensity modulation and direct detection over a diffuse channel based on experimental measurements. If M-ary QAM modulation is used, the two schemes offer the possibility to increase the bit rate of OW communications. They also mitigate the effects of inter symbol interference (ISI). On the other hand, modified COFDM/OQAM could outperform modified COFDM schemes with a cyclic-prefix.