Low-complexity iterative demapping for rotated QAM constellations in DVB-T2 system

Bit-Interleaved Coded Modulation (BICM) with rotated constellation is utilized to increase the signal space diversity in the second generation digital video broadcasting system, i.e., DVB-T2. However, at the receiver side, the complexity increases with product of the number of constellation points and the modulation order. In this paper, we propose a low-complexity iterative demapping algorithm which uses the hard decision results as the feedback input. Comprehensive simulation is conducted with different channel models, modulation orders and channel coding rates. Results show that the proposed algorithm performs well for both Ricean and Rayleigh fading channels. It can achieve performance gains for all 4-,16-,64- and 256-QAM modulation types and different LDPC coding rates. At least 4dB gain on required Signal to Noise Ratio (SNR) can be achieved after 5 iteration in DVBT-P Rayleigh fading channels for each modulation type.