ted to each MS. Single-BS MIMO Modes Closed-loop Closed-loop Open-loop Open-loop Closed-loop Closed-loop Open-loop SU-MIMO MU-MIMO SU-MIMO MU-MIMO SU-MIMO MU-MIMO SU-MIMO Localized Resource Allocations Distributed Resource Allocations Multi-BS MIMO Modes Closed-loop PMI Restriction PMI Recommendation Collaborative MIMO Macro Diversity Single-BS with PMI Coordination Multi-BS Precoding with Coordination FIGURE 10-37 Downlink MIMO mode classification 10.5 IEEE 802. 16m downlink MIMO schemes A layer is defined as an encoding and modulation input path to the MIMO encoder. A stream is defined as the output of the MIMO encoder that is further processed through the beamforming or the precoder block. For spatial multiplexing, the rank is defined as the number of streams to be used for the user. Each of various SU-MIMO or MU-MIMO open-loop or closed-loop schemes is defined as a MIMO mode. The MIMO encoder block maps L > 1 layers into Ns > L streams, which are fed to the precoder block. The physical layer procedures in the downlink MIMO on the transmitter side are shown in Figure 10-38. The encoder block contains the channel encoder, interleaving, rate-matching, and modulation blocks per layer. The resource mapping block maps the complex-valued modulation symbols to the corresponding time-frequency resources. The MIMO encoder block maps the layers onto the streams, which are further processed through the beamforming or the precoder block. The beamforming/pre- coding block maps the streams to antennas by generating the antenna-specific data symbols according to the selected MIMO mode. The sub-carrier mapping function is responsible for mapping the logical sub-carriers to physical sub-carriers before applying OFDM modulation. The OFDM modulation block maps antenna-specific data to the OFDM symbols. The feedback block contains feedback information, such as CQI or channel state information from the MS. The scheduler block schedules users to resource units and decides their MCS level, MIMO mode, MIMO rank, etc. This block is re