patial multiplexing is a virtual MIMO technique where users transmit over the same time-frequency resource unit in the uplink. This type of spatial multiplexing improves the sector throughput without requiring multiple transmit antennas at the mobile station. The received signals from the simultaneous uplink transmission of the users are processed in the BS using maximum likelihood detection techniques. The base station's scheduler groups the users with similar channel conditions and assigns their uplink transmissions to the same time-frequency region. The operation of a collaborative spatial multiplexing scheme is conceptually similar to the regular spatial multiplexing scheme using transmit antennas that are located at different locations (user terminals are geographi- cally apart). The throughput of collaborative spatial multiplexing theoretically increases by the number of users which are scheduled to transmit simultaneously over the same physical resource units. The Collaborative MIMO (Co-MIMO) is an extension of conventional single-BS based MIMO techniques. It allows multiple base stations to serve one or multiple mobile stations simultaneously over the same radio resource through coordination among the participating base stations. The Co-MIMO is characterized by the following three features: 1. In Co-MIMO, each MS is jointly served by multiple base stations, which is different from conventional MIMO techniques where each MS is only served by a single BS. Through BS coordination, the inter-cell interference among these coordinated base stations can be significantly reduced when using low frequency reuse factors. CHAPTER 10 The IEEE 802. 16m Physical Layer (Part II) 2. In Co-MIMO, each BS can also simultaneously serve multiple mobile stations using the same radio resource in order to increase the system throughput. The co-channel interference among these mobile stations can be minimized by use of spatial division multiple access techniques such as beamforming or multi-user MIMO schemes. 3. In Co-MIMO, SDMA p