Mark ratio modulation over pulse position modulation

Abstract

• Mark ratio modulation over inverse PPM modulation is proposed for optical label switching. • Two signals are transmitted by one ASK modulation. • The mark ratio difference of PPM and inverse PPM is utilized to deliver an overlay signal. • The mark ratio modulation doesn’t degrade the PPM signal. Orthogonal modulation superimposes non-amplitude-modulated signals on Manchester coded or pulse position modulated amplitude shift keying (ASK) signals, allowing two traffic flows with different bit rates to be modulated on the same wavelength channel, and hence improving spectrum efficiency. Inspired by the orthogonal modulation, this paper proposes a novel modulation format, i.e., mark ratio modulation over pulse position modulation (PPM), which utilizes the mark ratio difference between the PPM symbols and the inverse PPM symbols to deliver an overlaid signal. Better than traditional orthogonal modulation, in the mark ratio modulation over PPM, both low-speed and high-speed traffic flows are modulated by ASK with no need to sacrifice the extinction ratio, while keeping the reception simple and easy. According to theoretical analysis and test, we found 4PPM is a good option, which can balance the trade-off between the PPM signal’s effective bit rate and the mark ratio modulated signal’s quality.