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An Optimized Transmitter Precoding Technique with Power Constraint for TDD / DS-CDMA in Fading Multipath Channels

The desire to reduce complexity at the mobile units, in current code division multiple access (CDMA) mobile systems, has led research pursuing to transfer the signal processing from the mobile unit to the base station. The aim of this paper is to investigate a new bitwise scheme for transmitter precoding subject to a power constrained transformation at the transmitter output. The receivers are constrained to matched filter detection without channel state information (CSI). We investigate precoding for the forward link of time division duplex (TDD) CDMA systems. Finally, it is shown that the proposed approach leads to a simple precoding scheme that offers a reasonable alternative to receiver based multiuser detectors at only moderate additional complexity at the base station. Keywords— Transmitter Precoding, CDMA Systems, Frequency Selective Fading Channels.