Complexity reduced colored noise cancellation in overloaded MIMO spatial multiplexing with non-linear precoding

This paper proposes complexity reduced overloaded MIMO spatial multiplexing with colored noise cancellation, which can be applied for uplinks in wireless systems with massive MIMO where the number of the transmit antennas is less than that of receive antennas. This paper analyzes the characteristics of the colored noise cancellation. The analysis proves that the proposed colored noise cancellation can shrink the search space for the brute force search needed in the log-likelihood ratio (LLR) estimation, which reduces the complexity of the colored noise cancellation. Because the complexity of the colored noise cancellation dominates that of the proposed spatial multiplexing, the proposed spatial multiplexing is made less complex than the conventional spatial multiplexing by reducing the complexity of the colored noise cancellation. Computer simulation reveals that the receiver with the colored noise cancellation can be implemented with about 80 % less computational complexity than that with full search space, even though the transmission performance is less than 1 dB degraded at the BER of 10⁻⁴ in a 2 × 6 MIMO channels, where 6 streams are spatially multiplexed.