Fig. 1. 4PPM－QPSK signal. (a) Schematic diagram; (b) constellation diagram

Fig. 2. Flow of the digital signal processing algorithm. (a) CMA; (b) two modulus equalization algorithm

Fig. 3. Probability density of Rayleigh distribution when σ＝1

Fig. 4. Schematic of the experimental setup

Fig. 5. Module distribution of MPPM－QPSK signal. (a) m＝2; (b) m＝4; (c) m＝8; (d) m＝16

Fig. 6. Optimal δ of two modulus equalization algorithm. (a) m＝2; (b) m＝4; (c) m＝8; (d) m＝16

Fig. 7. Optimal number of taps and step size of two modulus equalization algorithm. (a) m＝2; (b) m＝4；(c) m＝8; (d) m＝16

Fig. 8. Optical parameters corresponding to different ROP. (a) δ；(b) number of taps

Fig. 9. BER for MPPM－QPSK with different equalizer. (a) m＝2; (b) m＝4; (c) m＝8; (d) m＝16

Fig. 10. BER for Nyquist－MPPM－QPSK with different equalizer. (a) m＝2; (b) m＝4