On spectrally efficient multiplexing in cognitive radio systems

Recently, spectrum agile radios have been proposed for resolving the challenge of spectrum shortage in future wireless communications. These smart radios would monitor and sense their radio environment in order to identify spectral resources temporarily and/or spatially unused by their primary (licensed) users. This would enable opportunistic spectrum access for the secondary (unlicensed) users in case their transmissions cause no harmful interference to the primary systems. In this paper, the trade-off between the level of interference caused by secondary transmission to primary user and the spectral efficiency of secondary user is discussed in the context of cognitive radio. In particular, we analyze the influence of the choice of pulseshape used for the multicarrier modulation based overlay secondary transmission. It is shown that, with a proper choice of multicarrier scheme, spectrally efficient secondary multiplexing is possible while simultaneously minimizing the interference caused to the primary system.