Novel hybrid soft-hard demodulation schemes for RQD constellation

Rotated constellation with Q-delay (RQD) is a new modulation scheme adopted by some wireless standards including the second generation of the digital video broadcasting for terrestrial (DVB-T2) system. This scheme offers significant improvement over unrotated modulation in terms of bit error rate (BER) performance due to its signal space diversity. In this paper, we present four novel computationally efficient demodulation schemes with hybrid soft-hard outputs used in hard demapping of data. The main idea is to take advantage of the unique projections the rotated cells have in the RQD system. The proposed schemes reduce the number of log likelihood ratio (LLR) computations. One proposed scheme gives the same BER performance as traditional LLR while reducing the computational complexity by 34% at SNR = 20 dB. Another scheme reduces the computations by 25% independent of the SNR level. The other two schemes offer a tradeoff between computational complexity and power efficiency.