A Novel Quadrature Carrier Multiplexing Scheme

Abstract

This paper presents a multiplexing scheme that uses a periodic sine like pulse and its orthogonal versions to multiplex analog low pass signals. The sine like pulse is derived by multiplying a few cosine waves whose frequencies are harmonically related. The highest frequency of the cosine wave is decided based on the time instant at which the first zero crossing of the periodic sine like pulse is expected. The lowest frequency of the cosine wave decides the period of the sine like pulse. The number of available phase quadrature versions or orthogonal versions for the periodic sine like pulse is given by 2n where ‘n’ is the number of cosine waves that are multiplied to generate the periodic sine like pulse. The multiplexed signal is generated by adding the double sideband suppressed carrier (DSBSC) modulated signals generated by multiplying message signals and quadrature versions of the periodic sine like pulse. At the receiver, the message signals are detected using coherent detection. The proposed system requires a bandwidth of 2(1.875W) per signal where W is the highest frequency of the message signals. The bandwidth required per signal in the proposed scheme is more than conventional QCM scheme. However, the proposed scheme allows multiplexing eight signals using three cosine carriers. In QCM, only six message signals can be multiplexed with three cosine carriers and their quadrature versions.