A low complexity demodulator for coordinate interleaved modulation schemes

This paper discusses techniques to reduce the demodulation complexity at the receiver of systems that use coordinate interleaving (CI) with N²-QAM constellations. CI is a method used to increase the diversity order of any modulation scheme on fading channels, but has a high demodulation complexity. The techniques described reduce the complexity required to calculate the maximum likelihood and log likelihood ratio metrics for such systems from O(N²) and O(N²logN) respectively to O(NlogN), without any loss in performance.