eedback mode Sub-band index for best-M Sub-band index for best-M Correlation matrix R for the transform Short-term PMI for closed-loop SU- codebook and long-term beamforming MIMO/MU-MIMO Wideband CQI Stream index for open-loop MU-MIMO Long-term PMI FIGURE 10-44 Summary of IEEE 802.1 16m downlink MIMO feedback 10.6 The IEEE 802. 16m uplink MIMO schemes The feedback schemes to support various MIMO modes are classified into three classes: (1) long-term; (2) short-term; and (3) event-driven. The elements of MIMO feedback in each category are summa- rized in Figure 10-44. Since multicast and broadcast services are typically a downlink-only type of transmission, only open-loop transmit diversity or spatial multiplexing schemes are used for E-MBS, and no closed-loop MIMO scheme is supported in E-MBS. 10.6 THE IEEE 802. 16M UPLINK MIMO SCHEMES The physical layer procedures in the uplink MIMO on the transmitter side are shown in Figure 10-45. The MIMO encoder block maps a single L = 1 layer into Ns > L streams, which are fed to precoder block. A layer is defined as a coding and modulation processing path that is the input to the MIMO encoder. A stream is defined as the output of the MIMO encoder which is the input to the precoder block. For SU-MIMO and collaborative spatial multiplexing, there is only one FEC block per allocated resource unit, i.e., vertical MIMO encoding is only supported in the uplink at the transmitter side. The precoder block maps the streams to antennas by generating the antenna-specific data symbols according to the selected MIMO mode. The MIMO encoder and precoder blocks do not exist when the MS has only one transmit antenna. The decisions corresponding to resource allocations in the uplink take into consideration the allocation type (use of distributed or localized allocation), single-user/ multi-user operation mode, MIMO mode (use of open-loop or closed-loop scheme), user grouping (which users are assigned to the same resource unit in MU-MIMO), rank (for the spatial multiplexing modes in SU-MIMO 