et of the base codebook for uplink SU-MIMO. The uplink MIMO features of the IEEE 802.16m can be summarized as follows: Support of single-user MIMO and collaborative spatial multiplexing; Vertical encoding for SU-MIMO and collaborative spatial multiplexing; Open-loop and closed-loop MIMO operation; Codebook-based and vendor-specific precoding: Short-term and long-term precoding; MS-specific precoded (dedicated) pilots for MIMO operation; Enhanced codebook design: Enhanced base codebook for both correlated and uncorrelated channels; Antenna selection codewords to reduce MS power consumption. 10.7 MULTI-BS MIMO Multi-BS MIMO techniques are used for improving sector throughput and cell-edge throughput through multi-cell collaborative precoding, network coordinated beamforming, or inter-cell interfer- ence nulling. Both open-loop and closed-loop multi-BS MIMO techniques are supported in the IEEE CHAPTER 10 The IEEE 802. 16m Physical Layer (Part II) 802.16m standard. For closed-loop multi-BS MIMO, CSI feedback via codebook-based feedback or sounding channel is used. The feedback information may be shared by neighboring base stations via a core network interface. Mode adaptation between single-BS MIMO and multi-BS MIMO can also be utilized. The multi-BS MIMO principle can be described as follows. When a mobile station is at the cell edge, it may be able to receive signals from multiple cell sites, and the mobile station's transmission may also be received at multiple cell sites (see Figure 10-46). If the data transmission and signaling from multiple cell sites can be coordinated, the downlink performance can be significantly improved. This coordination can be similar to the interference avoidance techniques or the case where the same data is transmitted from multiple cell sites. In the uplink, since the signal can be received by multiple cell sites, the system can take advantage of coordinated multiple reception to significantly improve the link performance. The Coordinated MultiPoint (CoMP) transmission used in both th