IMPROVEMENTS IN OR RELATING TO RADIO COMMUNICATION SYSTEMS

摘要

CDMA (Code Division Multiple Access) can be used in cellular mobile radio systems to provide good spectral efficiency through averaging the interference wherever the number of users per carrier is large (several tens). This is readily practicable for voice users whose data rate requirements are modest but requies large spreading factors for ISDN data service users. This invention proposes an approach in which a multiplicity of CDMA carriers each with relatively low bandwidth are used for the voice services and overlayed with wide bandwidth CDMA carriers whose 'bandwidth occupies the whole (or most) of the band occupied by all of the narrowband CDMA carriers in order to service the data users. This allows the same RF band to service a relatively small number of data service users with wideband (and therefore higher cost) terminals without affecting the cost of terminals for the majority of voice users.