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The ongoing development of third generation systems sets the path for evolution of the existing second generation systems. Important issues are the need for compatibility and the establishment of a path of migration from the current operative mobile systems. This paper considers the feasibility of supporting CDMA capabilities within the GSM air interface in order to provide UMTS services. It produces performance estimates for two specific examples: Joint Detection CDMA channels, and Multicarrier DS-CDMA channels. It is shown that a number of advantages can be obtained by using a hybrid CDMA scheme.