An SVD pre/post-RAKE for TDD CDMA systems

Since reciprocal channels can be found in time division duplex (TDD) systems, TDD code division multiple access (CDMA) systems are capable of implementing a pre-RAKE structure as a pre-distortion technique. We propose a singular value decomposition (SVD) pre/post-RAKE in which the RAKE combiner is utilized at both the transmitter and receiver. If the combining weights of the pre-RAKE and post-RAKE are determined by the singular value decomposition, then parallel sub-channels can be established in the eigen-space. We obtain the optimal information capacity by applying the water-filling solution to the SVD pre/post-RAKE. The SVD pre/post-RAKE provides remarkable capacity improvement without increasing the average transmit power or frequency bandwidth, since multiple data symbols can be reliably transmitted through the parallel sub-channels.