Very Large Scale Integrated-Circuit Architecture for Offset Quadrature Phase Shift Keying Modulation Using Offset Generator

Abstract

This work presents an architecture for Offset Quadrature Phase Shift Keying (OQPSK) using an Offset generator. The Offset generator generates symbol patterns such that there is a maximum phase shift of ±90° only between the symbols, unlike the Quadrature Phase Shift Keying (QPSK) modulator which has a maximum of ±180° phase shift. Here the effort of designing an Offset generator, which can be embedded onto QPSK modulator to generate OQPSK with minimum combinational logic, has been discussed. Whenever the input symbols to the Offset generator varies in phase with a ±180° in constellation, it generates an intermediate symbol which differs only in ±90° with the previous one. Then it continues to give out the original symbol to be transmitted. This follows the exact OQPSK technology while it doesn't follow the conventional generation method of OQPSK modulation which provides an offset between the even and odd bit patterns of the symbols to be transmitted. The architecture is modelled using Verilog HDL and the functionality is validated from the simulation result.