 to the UE as part of the downlink control information on the PDCCH. In order for MIMO schemes to work properly, each UE has to report information about the channel to the base station. Several measurement and reporting schemes are available which are selected according to MIMO mode of operation and network choice. The reporting may include wideband or narrowband CQI, which is an indication of the downlink radio channel quality as experienced by this UE, PMI which is an indication of the optimum precoding matrix to be used in the base station for a given radio condition, and Rank Indication (RI) which is the number of useful transmission layers when spatial multiplexing is used [30,107]. In the case of transmit diversity mode, only one codeword can be transmitted. Each antenna transmits the same information stream, but with different coding. The LTE employs space frequency block coding as a transmit diversity scheme. A special precoding matrix is applied at the transmitter side in the precoding stage in Figure 10-49. Cyclic delay diversity is an additional type of diversity which can be used in conjunction with spatial multiplexing in LTE. An antenna-specific delay is applied to the signals transmitted from each antenna port. This effectively introduces an artificial multipath to the signal as seen by the receiver. As a special method of delay diversity, cyclic delay diversity applies a cyclic shift to the signals transmitted from each antenna port [30,97]. For the 3GPP LTE uplink, multi-user MIMO can be used. Multiple user terminals may transmit simultaneously on the same resource block. The scheme requires only one transmit antenna at the UE side. The UEs sharing the same resource block have to apply mutually orthogonal pilot patterns. To take advantage of two or more transmit antennas, transmit antenna selection can be used. In this case, the UE has two transmit antennas but only one transmission chain. A switch will then choose the antenna that provides the best channel to the eNB [30,99,107]. To support MU-M