Overloaded MIMO Spatial Multiplexing Independent of Antenna Setups

This paper proposes overloaded MIMO spatial multiplexing that can increase the number of spatially multiplexed signal streams despite of the number of antennas on a terminal and that on a receiver. We propose extension of the channel matrix for the spatial multiplexing to achieve the superb multiplexing performance. Precoding based on the extended channel matrix plays a crucial role in carrying out such spatial multiplexing. We consider three types of QR-decomposition techniques for the proposed spatial multiplexing to improve the transmission performance. The transmission performance of the proposed spatial multiplexing is evaluated by computer simulation. The simulation reveals that the proposed overloaded MIMO spatial multiplexing can implement 6 stream-spatial multiplexing in a $2\times 2$ MIMO system, i.e., the overloading ratio of 3.0. The superior transmission performance is achieved by the proposed overloaded MIMO spatial multiplexing with one of the QR-decomposition techniques.