TABLE OF CONTENTS A multilevel (M-ary) phase shift keying (PSK) signal shifts the phase angle of the carrier frequency to one of M discrete values during the symbol time T s for the representation of N= log 2 M binary logic signals for the transmission of information. The modulated sinusoidal carrier signal 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 3.60.
| (3.60) |  |
A convenient set of equally spaced phase angles k p m j( t) for 4-PSK, also known as quaternary (Q) PSK, is 45 and 135 for one symbol time T s. QPSK is the terminology often used for 4-PSK and the signal then is given by Equation 3.61.
| (3.61) |  |
The input information is straight-binary coded data ( b 2 i, b 2 i +1), but is Gray-coded (di-bit) so that if a symbol error is interpreted as an adjacent symbol it would now only produce one bit in error. The Gray code improves the BER performance of the M-ary digital communication system, as described in Chapter 2.
Using the trigonometric identity A cos( u + v) = A cos( u) cos( v) - A sin( u) sin( v), Equation 3.61 for QPSK can be described in terms of an in- phase (I, cosine)...
