TABLE OF CONTENTS Differential quaternary phase shift keying (DQPSK) is a noncoherent 4-level PSK digital communication system that is similar to DPSK. A coherent quaternary PSK (QPSK) digital communication system can be decomposed into an in-phase (I) and quadrature (Q) binary PSK signal, as given by Equation 3.62. The DQPSK signal can be analyzed in a manner analogous to both DPSK and QPSK. DQPSK transmits information as the difference between the carrier phase ? i transmitted for the current di- bit b 2 ib 2 i +1 and the carrier phase ? i -1 transmitted for the previous di- bit b 2 i -2 b 2 i -1as given by Equation 3.79.
| (3.79) |  |
DQPSK requires a two bit initialization time at the beginning of each data transmission. The DQPSK signal shifts the phase angle ? i of the carrier during the symbol time T s, as given by Equation 3.79. The modulated sinusoidal carrier has an amplitude of A V, a carrier frequency of f c Hz and a 0 reference phase angle, as given by the analytical expression in Equation 3.80.
| (3.80) |  |
From Equation 3.79, the current phase angle ? i is given by Equation 3.81.
| (3.81) |  |
The di-bit b 2 ib 2 i +1 is the symbol d i in Equation 3.81. Using the trigonometric identity A cos( u + v) = A cos( u) cos(
