r plus noise received at the MS. The MS may accordingly request the preferred multi-BS MIMO scheme. The single-BS precoding with multi-BS coordination scheme is performed by combining two PMIs in order to mitigate the inter- cell interference when closed-loop MIMO precoding is used in the serving and the neighboring cells. One of the PMIs maximizes the transmission power of the serving cell, while the others minimize the interference to the neighboring cell. The PMI combination procedure is performed as follows. The PMI combination may be triggered by the BS in an unsolicited manner. Using uplink sounding, the serving and the neighbor base stations can measure the channel conditions of the mobile stations. Following the channel measurements, the serving and neighbor base stations can determine the PMI which maximizes the transmission power and the PMImin which minimizes the interference. The neighboring base stations may inform the serving BS of PMImi through the backhaul. The above PMIs are calculated based on the following criteria [2]: arg max (10-54) where HS and Hi denote the channel matrices from the MS to its serving and the neighboring base stations, respectively, and Vi is the ith codeword of the base codebook. The serving BS informs the MS of the PMI, PMImin, and PMI Combination Ratio r through UL Basic Assignment A-MAP IE, UL Sub-band Assignment A-MAP-IE, UL CSM Beamforming A-MAP IE, or AAI_UL_MultiB- S_MIMO_SBP MAC management messages. The transmitted precoder W is generated by combining the two precoders (WPMImin) WPMI) according to the following equation [2]: (10-55) 10.8 Interference mitigation The IEEE 802. 16m further supports uplink multi-BS MIMO to allow joint reception by multiple base stations, e.g., macro-diversity combining and cooperative beamforming. The collaborative zone initialization is defined as a common radio resource that is allocated as a collaborative zone among the participating base stations in the uplink multi-BS MIMO operation. The uplink sounding signals are assigned orthog