unt the slow chan- nel variation. The MIMO mode is adapted slowly (e.g., only at the beginning of communication or every several 100 ms), in order to reduce the control signaling (including feedback) required to support the MIMO mode adaptation. For the con- trol channel, only a single stream using the multiple transmit antennas is supported. The function of the MIMO in the general downlink physical channels is shown in Figure 5.1. The baseband signal processing procedure is defined in terms of the fol- lowing steps [3]: scrambling coded bits in each of the code words to be transmitted on a physical channel; modulating scrambled bits to generate complex-valued modulation symbols; mapping the complex-valued modulation symbols onto one or several trans- mission layers; Code words Layers Antenna ports Modulation Resource Element OFDM Signal Scrambling Mapper Mapper Generation Layer Mapper Precoding Modulation Resource Element OFDM Signal Scrambling Mapper Mapper Generation Figure 5.1 Overview of physical channel processing with MIMO. © 2009 by Taylor & Francis Group, LLC MIMO OFDM Schemes for 3GPP LTE precoding the complex-valued modulation symbols on each layer for trans- mission on the antenna ports; mapping complex-valued modulation symbols for each antenna port to resource elements; and generating complex-valued time-domain OFDM signals for each antenna port. The baseline antenna configuration for MIMO is two transmit antennas at the cell site and two receive antennas at the UE. The higher-order downlink MIMO and antenna diversity (four transmit [Tx] and two or four receive [Rx] antennas) are also supported. The baseline antenna configuration for uplink single-user MIMO is two transmit antennas at the UE and two receive antennas at the cell site. If the UE has only a single power amplifier and two transmit antennas, the antenna switching/ selection is the only option that is supported for SU-MIMO. In addition, the fol- lowing techniques are supported [2]: codebook-based precoding with a single precoding feedback