MISO Concepts for frequency-selective channels

In order to limit interference and increase system capacity in CDMA systems, transmitted power required to achieve a certain performance should be as low as possible. Usually, receivers are designed to overcome the problems caused by the frequency-selective wireless channel. However, if the channel impulse response (CIR) is a priori known at the transmitter, the signal we want to transmit can be preprocessed. The CIR for the downlink can be estimated in the uplink in time-division duplex (TDD) systems or conveyed in a feedback channel from the receiver to the transmitter. By using multiple transmit antennas in multiple-input singleoutput(MISO) systems, performance improvement potentials are created. In this paper, several MISO concepts using FIR filters both in the transmitter and receiver are compared, their decision variables are given and the SNRs at the receivers are calculated analytically. The MISO generalized selection Eigenprecoder is derived which offers the possibility to trade off performance and complexity. Keywords—CDMA, space-time signal processing, MISO, transmit diversity, Pre-RAKE, Eigenprecoder