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.