 response to an estimated DL channel response. The transmitter and receiver hardware of the BS may be calibrated to assist the channel response mapping. The precoding matrix in this case is the same for all sub-carriers within a physical resource unit. A SU-MIMO open-loop technique that provides diversity gain is used for the broadcast control channel. The 2-stream SFBC with two transmit antennas is used for P-SFH and S-SFH transmission. 10.5 IEEE 802. 16m downlink MIMO schemes 4-bit DFT Codebook 6-bit Legacy Codebook 6.5-bit Transformed Codebook 3.5-bit Transformed Codebook SNR (dB) FIGURE 10-42 A comparison of the performance of closed-loop SU-MIMO rate-1 codebooks in low-correlated channels (4 N and angle spread 3°) For a more than two transmit-antenna configuration, P-SFH and S-SFH are transmitted by a 2-stream SFBC with precoding, which is decoded by the MS without any information on the precoding and antenna configuration. The 2-stream SFBC is used for the Downlink Unicast Control Channel. In summary, the IEEE 802.16m supports the following MIMO schemes in the downlink: Single-BS and multi-BS MIMO operation; Single-user MIMO and multi-user MIMO schemes: Vertical encoding for SU-MIMO; Horizontal encoding for MU-MIMO; Adaptive-precoding (closed-loop) and non-adaptive (open-loop) precoding; Codebook and sounding-based precoding: Short and long-term adaptive precoding; Dedicated (precoded) pilot sub-carriers for MIMO operation; Enhanced codebook design; Enhanced base codebook; Transform codebook; Differential codebook. CHAPTER 10 The IEEE 802. 16m Physical Layer (Part II) 95% CDF of User Throughput 3-bit Transformed Codebook 4-bit DFT Codebook 6-bit Legacy Base Codebook 10000 12000 User Throughput (kbps) FIGURE 10-43 A comparison of CDF of user throughput for highly-correlated channel (MU-MIMO with zero-forcing precoding, four transmit antennas at BS and two receive antennas at MS) Long-Term MIMO Feedback Short-Term MIMO Feedback Event-Driven MIMO Feedback Spatial rate Narrowband CQI for best-M Preferred MIMO f