CDMA transmitter filtering for cellular overlay systems

i%eoverlay of a CDMA system in a frequency band which is already servicing narrowband users has the potential for significant gains in user capacity [1]. For the single-cell case, it was shown in [2] that interference caused to the narrowband system by CDMA users is significant, even when the CDMA system is very lightly-loaded. The use of notch filtering at the CDMA transmitter to avoid active narrowband users was shown to greatly alleviate the effects of the CDAL4 inte~erence on the narrowband system. It was also demonstrated that the iWMSE receiver can perform well in receiving these jiltered CDA4Asignals. In this papec overlay will be applied to the cellular case, in which the narrowband users in each cell only utilize a fraction of the system bandwidth even when the system is filly loaded. As in the single-cell case, it will be seen that overlay causes significant degradation to the narrowband system, which can again be alleviated greatly through the use of transmitter notch-filtering. It will be demonstrated that overlay is very promising for cellular systems.