DSP implementation of sqrt(M)-Best rotated QAM soft-demapper

In the second generation terrestrial digital video broadcasting (DVB-T2) systems, one of the important features is the usage of rotated quadrature amplitude modulation (QAM) to exploit signal space diversity. However, the implementation of soft-demapper is very challenging and becomes more complex as the modulation order increases. Recently, a √(M)-best soft-demapper was proposed which can achieve the same performance as the full search scheme but with low complexity. In this paper, we implement the √(M)-best soft-demapper on a digital signal processer (DSP) with a coarse-grained reconfigurable array (CGRA) architecture. The best candidate selection algorithm is accordingly modified for friendly implementation. Our results show that the √(M)-best soft-demapper can be implemented with 82% less cycles than the full search based soft-demapper for the most complex 256-QAM case.