Two novel frequency rotation techniques that suppress multipath interference and increase the frequency diversity gain are proposed for uplink IFDMA systems. These benefits are especially important as the performance of traditional IFDMA falls significantly when the number of simultaneous accessing users becomes large. Frequency rotation was originally proposed to suppress the multipath interference and enlarge the frequency diversity gain of downlink access. Unfortunately, it cannot be applied to the uplink due to the loss of orthogonality among users in the frequency domain. In the proposed frequency rotation techniques, users do not share the multiple frequency orthogonal channels and thus orthogonality among users is maintained. The proposed technique is verified by computer simulations.