
236 Optical Fiber Communication Systems with MATLAB
®
and Simulink
®
Models
shown
in Figure 6.16a. Without the pulse carver and sinusoidal RF signal, the output pulse
sequence follows NRZ–DPSK format, that is, the pulse occupies 100% of the pulse period
and there is no transition between the consecutive “1s.”
6.5.2.2 Differential Quadrature Phase-Shift Keying (DQPSK)
This
differential coding is similar to DPSK except that each symbol consists of two bits
that are represented by the two orthogonal axial discrete phases at (0, π) and (−π/2, +π/2)
as shown in Figure 6.17 or two additional orthogonal phase positions are located on the
imaginary ax