Sphere Decoding for MIMO Systems with Newton Iterative Matrix Inversion

This work considers the application of Newton´s iterative method of matrix inversion for reducing the complexity of calculating the unconstrained solution in Sphere Decoding (SD) for Multiple-Input Multiple-Output (MIMO) wireless communication systems. This paper also proposes a simpler initialization procedure for Newton´s method. It is shown that as the size of the MIMO system increases, it becomes more tolerant to errors in the unconstrained solution for SD, and hence it requires a smaller number of Newton iterations. For a 16 × 16 MIMO system with QPSK or 16-QAM we show that 7 iterations are sufficient to ensure lossless SD performance. With only 4 iterations, a QPSK 32 × 32 MIMO system exhibits less than 0.1 dB performance loss relatively to SD employing the exact unconstrained solution.