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Analog and Q-ary pulse-position modulation in digital communication system

With the recent development of optical wireless communication (OWC), it has become the hot spot of next-generation communication technology. The demand for communication is increasing, the past RF system cannot satisfy the modern communication needs, so to find a higher bandwidth of communication, OWC becomes one of the RF system innovation complementary technologies. In OWC, pulse position modulation (PPM) technology is a more important modulation technology. Hence, this study focuses on Q-ary PPM technology. In this study, we utilize MATLAB for simulation, demonstrate the difference between digital PPM and analog PPM, and simulate the simplify digital communication system. The PPM signal will pass through the Additive White Gaussian Noise (AWGN) channel. We also discuss some demodulate theory, then analyze the effect of different signal-to-noise ratios on the signal, and finally Q-ary PPM bit error performance (BER) analysis has been given, which is based on soft decision and hard decision respectively. The study found that digital PPM is more applied than analog PPM nowadays, and different demodulation methods have different effects. Finally, with an increased Q value the BER becomes smaller.