QPSK is a constant amplitude M-ary digital modulation scheme. Since QPSK provides high performance on bandwidth efficiency and bit error rate, it is considered as the most widely used modulation technique in the digital communication system. Using QPSK, we can have a processing rate twice as that of a normal mode.
QPSK (Quadrature Phase Shift Keying) modulation in its idea is similar to the previously discussed BPSK modulation. The difference is using four possible phase shifts instead of two. Four offsets numbered in a binary system require two bits. Therefore, two bits are encoded in one carrier period. Thus, with the same carrier frequency, QPSK modulation allows for twice as fast data transmission than BPSK. In a typical case, when the probabilities of occurrence of each of the two bits (00, 01, 10, 11) are equal, phase shifts are arranged symmetrically. These can be, for example, 45 °, 135 °, 225 °, and 315 ° angles.
Here we have used LABVIEW (Laboratory Virtual Instrumentation Engineering Workbench) as the simulation platform. This programming environment being graphical gives a good visualization of the results.