Physical Layer Considerations for Cognitive Radio: Modulation Techniques

Cognitive radio (CR) is one of the promising future possibilities for wireless broadcasting and communication. One of the key issues is the physical layer, where the modulation waveform best suitable for the CRs has to be chosen. In this paper we present the most promising modulation schemes with their advantages and disadvantages. Orthogonal frequency division multiplexing (OFDM) is the most favored modulation nowadays for high speed digital communications, but many other modulation techniques show advantages over it. Notably DFT-spread OFDM (DFTS-OFDM), Constant Envelope OFDM (CE-OFDM) and Filter Bank Multicarrier (FBMC).We give an overview of these schemes to see which is the most suitable with a given set of parameters or in a specific scenario. We compare these methods via spectral characteristics, signal metrics and system performance in the presence of non-linear distortions.