ransmission capability. More specifically, the first version of LTE will support only two types of multiantenna schemes: closed-loop transmit antenna switching and multiuser MIMO (MU-MIMO). In the antenna switching solution, the eNode B can decide on a subframe level which of the two transmit antennas the UE should use for the next transmission. However, the gains with such an antenna switching solution are questionable. In the MU-MIMO case, multiple UEs, which have quasi-orthogonal channels, are scheduled on the same © 2009 by Taylor & Francis Group, LLC Architecture and Protocol Support for RRM resource block, which realizes a way of spatial multiplexing in the uplink. Such a MU-MIMO setup can be seen as a case when the transmit antennas of the MIMO system are at separate UEs and the receive antennas are at the eNode B. The location of the receive antennas at the same node (at the eNode B) facilitates the processing of the multiple UE streams, and this is exactly what enables the use of MU-MIMO in the uplink. In the downlink, MU-MIMO would be more problematic due to the receiver processing being in separate nodes (i.e., in separate UEs). For the operation of the downlink multiantenna schemes, various feedback report- ing mechanisms are required from the UE. Recall that the UE sends CQI reports, which is one form of an SINR measure, to assist the channel-dependent scheduling in the eNode B. For supporting the multiantenna transmission, the UE sends, in addition to the CQI reports, channel rank and precoding matrix selection reports with a periodicity in the order of subframe length (1 ms). The UE performs a prediction of the expected throughput assuming different precoder matrices and transmission rank values and reports the recommended transmission rank and precoder matrix back to the eNode B that yields the highest expected throughput. The eNode B may or may not follow the recommendations of the UE. The precoder matrix that has been selected by the eNode B for the transmission is indicated as part of the trans