On the application of sphere decoding algorithm in overload MIMO systems

As a kind of computationally efficient maximum likelihood detection (MLD) algorithm, sphere decoding algorithm (SDA) has been widely studied in Multiple Input Multiple Output (MIMO) systems. The traditional SDA only applies to the MIMO systems that the number of the transmit antennas is equal to or less than the number of the receive antennas. This paper proposed an improved SDA, which can be applied to the overload MIMO systems that the number of the transmit antennas is greater than the number of the receive antennas when the input signal uses constant amplitude phase modulation. Numerical results demonstrate that the improved SDA has much lower complexity and could provide the same performance as ML in the overload MIMO systems.