Joint channel equalization and detection of Spectrally Efficient FDM signals

Abstract

This paper investigates the transmission in time dispersive channels of Spectrally Efficient Frequency Division Multiplexed (SEFDM) signals, where carrier orthogonality is intentionally violated in order to increase bandwidth efficiency. Sufficient statistics of the transmitted SEFDM signal can be obtained by projecting the received signal onto an orthonormal base generated at the receiver using an Iterative Modified Gram Schmidt (IMGS) procedure. In order to reduce the computational complexity resulting from Inter-Carrier Interference (ICI), detection has been implemented based on a Regularized Sphere Decoding (RSD) algorithm. The proposed scheme was previously tested in Additive White Gaussian Noise (AWGN) for various SEFDM signal parameters. In the present work, these results are extended to account for the effect of time dispersive channels. Randomly generated SEFDM symbols are used as pilots to provide estimates of the channel impulse response in systems with or without cyclic prefixes. A joint equalization-detection is subsequently performed in a RSD stage. We show that it is possible to detect optimally SEFDM signals of small dimensionality (e.g. N = 32), with up to 20% bandwidth gain with respect to OFDM systems of the same symbol-rate. This indicates that the wireless transmission of non orthogonal SEFDM signals is tangible.