The scarcity of available radio spectrum presently limits the extension of modern multimedia systems. This paper presents a theoretical investigation into the possibility of using a frequency overlay of a narrowband Code Division Multiple Access (CDMA) System and a Time Division Multiple Access (TDMA) System to provide a greater spectral efficiency. This paper shows that under certain conditions the two systems can operate in the same frequency band and in the same area with a considerable improvement in the overall capacity of the whole system.