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In the down link of a TDD/CDMA (time division duplex/code division multiplex access) system, the signal's multipath propagation causes severe ISI (intersymbol interference) and MAI (multiple access interference). It is well-known that these interference may create a near-far effect in which the standard techniques such as conventional modulation, power control and RAKE receivers provide a poor performance. This paper presents a joint modulation approach, which will process signals in pre-distortion based on the estimated channel parameters in up-link. Due to the pre-distortion process, the MAI and ISI will be reduced or suppressed when signals arrive at the mobiles. Some numerical results are given, which show a great improvement using this joint modulation instead of conventional modulation.