Spatial Diversity, Low PAPR and Fast Decoding for OFDM using L2-Orthogonal CPM ST-Codes

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) schemes provide high data rates and good robustness against frequency selective fading for communication systems. Space-Time Block Coding (STBC) is an efficient way to introduce space-time diversity in Multiple-Input Multiple-Output (MIMO) systems. Using non-linear modulations such as Continuous Phase Modulation (CPM) with its constant envelope property may be a way to construct MIMO OFDM systems that alleviates the typical Peak to Average Power Ratio (PAPR) issue of OFDM. However, CPM based systems are usually plagued by decoding complexity issues. In this paper, we introduce space-time-frequency diversity techniques based on L2-orthogonal multi-h CPM Space-Time codes designed for OFDM transmission. We benchmark these codes under frequency selective Rayleigh channels and show how they achieve full spatial diversity at full rate for any number of antennas, good spectral compactness, low PAPR and robustness to frequency fading. Furthermore, L2-orthogonality allows fast decoding with complexity growing only linearly in the number of Tx antennas.