Offset Generator for Offset Quadrature Phase Shift Keying Modulation

Abstract

The key concept of this paper is development of an Offset generator architecture for Offset Quadrature Phase Shift Keying (OQPSK). Offset generator designed is embedded into QPSK and generates OQPSK modulation. The symbol pattern which the offset generator generates is such that there is only a maximum phase shift of ±90° between the consecutive symbols, unlike the QPSK which have ±180° maximum phase shift between the transmissions of symbol. The offset generator is designed so that it has a minimal combinational logic. The major focus of this paper is regarding the design and working of the offset generator, and OQPSK modulation. The offset generator which takes the symbol to be transmitted as input will generate an intermediate symbol when the phase of the consecutive symbols varies ±180° in constellation. The intermediate symbol differs only in ±90° with the previous symbol. After the generation of the intermediate symbol, offset generator gives out the next 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.