Abstract-Rotated and cyclic Q-delayed (RCQD) M -QAM (Quadrature Amplitude Modulation) provides signal space diversity and thus improves system performance over fading channels. However, previously published RCQD solutions were designed without fully considering the high demodulation complexity which prohibits wider applications. In this paper, a complete solution is proposed to reduce complexity for both the modulator and the demodulator. This solution uses a series of rotation angles α =arctan(1/ √ M ) which bring many interesting properties to the RCQD signals. A simplified sphere demapping algorithm is derived for fading channels with and without erasure events. In contrast to the sphere-decoder used for MIMO detection, the radius of the proposed sphere-demapper involves an exact amount of constellation points, thereby ensuring to perform the soft demapping operation successfully. Moreover, when either the in-phase (I) or the quadrature component (Q) is erased, the proposed demapping algorithm performs as well as the fullcomplexity Max-Log algorithm, with a reduced complexity. Compared to the solution currently used in DVB-T2, the proposed method reduces tremendously the computational complexity while still achieving similar performance over fading channels and even better performance over fading erasure channels.

This letter deals with a Peak-to-Average Power Ratio (PAPR) reduction scheme for Orthogonal Frequency Division Multiplexing (OFDM) systems with Signal Space Diversity. An original algorithm for the selection of two Rotated and Cyclically Q-Delayed (RCQD) QAM constellations is proposed to jointly optimize the Bit Error Rate (BER) and the blind detection performance of a SeLected Mapping (SLM) technique. Simulation results show that the proposed method achieves a large PAPR reduction with no spectral spoilage, and also enhances the BER performance in the case of DVB-T2 over different channels.

We investigate an optimized blind SeLected Mapping (SLM) algorithm to reduce the Peak-to-Average Power Ratio (PAPR) for Orthogonal Frequency Division Multiplexing (OFDM) systems with Signal Space Diversity (SSD). Several phase sequences based on two Rotated and Cyclically Q-Delayed (RCQD) constellations are used at the transmitter to considerably reduce the PAPR. The pair of RCQD constellations is selected so as to achieve the highest average mutual information for both the Coded Modulation (CM) and the Bit-Interleaved Coded Modulation (BICM) schemes. These constellations also allow, along with Hadamarad sequences, good blind detection performances with no spectral spoilage. Simulations totally confirm our theoretical results.

This paper presents a fully adaptive Minimum Mean Square Error (MMSE) iterative equalization with a joint phase estimation, using various adaptive step-sizes scheme. To meet the requirement of fast convergence and low MSE over time-varying channels, we propose an original self-optimized algorithm whose step-sizes are updated adaptively and assisted by soft-information provided by the channel decoder in an iterative manner. Simulation results show that our proposal achieves better performance over various multipath time-varying channels, compared to the conventional equalizer using a fixed step-size.