The capacity achievable with a broadband CDMA microcell underlay to an existing cellular macrosystem

Broadband code division multiple access (B-CDMA) using direct sequence spread spectrum can be used as an overlay to an existing analog or narrowband digital cellular system to provide increased capacity and new data services. In order to achieve significant capacity, it has been shown that both transmit and receive notch filters should be used at the base station. This paper addresses whether the B-CDMA overlay concept can be applied to creating a CDMA microcell underlaying an existing analog macrocell. It is shown that indeed high capacity can be achieved in the microcell on both forward and reverse links, largely independently of the separation between microcell and macrocell bases. Furthermore, in the forward link the effect of neighboring base stations is shown to be negligible. In order to achieve maximum capacity, it is found that transmit and receive notch filters at the microcell base station are invaluable at small separations between micro and macrocells. It is also shown that key parameters which must be properly controlled are the powers of the CDMA base and mobile transmitters relative to their analog counterparts