A Rhombic-DCM Constellation for MB-OFDM UWB Systems

In Multi-Band Orthogonal Frequency Division Multiplexing Ultra WideBand (MB-OFDM UWB) systems, the used modulation schemes generate circular complex signals. A complex random variable is called circular if its probability distribution is invariant under rotation. Recently, it has been shown that non-circular signals provide significant performance gains. In this paper, we propose a modified Dual Carrier Modulation (DCM) scheme, namely rhombic-DCM, generating non-circular complex signals for MB-OFDM UWB systems. However, the particular nature of the generated signals requires Widely Linear (WL) processing to take advantage of all the available second-order statistics. For this reason, we derive a novel channel estimator based on WL processing technique. Via an illustrative example, we demonstrate the non-circularity of the proposed modulation scheme. We prove also that, under the rhombic deformation, the WL channel estimator achieves significant performance gains.