Spectrum Shaping for Interference Management in Cognitive Radio Networks

Most dynamic spectrum access research centers on determining the set of frequencies being used by spectrum license holders, taking its converse, and from what remains selecting the optimal subset of spectrum. This, however, assumes unlicensed transmissions have a square power spectrum By shaping our unlicensed power spectra, we can do much more. This paper investigates applications of spectrum shaping, and how they can be implemented using OFDM and DSSS. The first application involves creating notched power spectra that can take advantage of noncontiguous spectrum segments, increasing our signal bandwidth. The second is to create spectra inversely shaped to the current interference environment, allowing us to take advantage of gaps in the noise floor. By modulating the power in each sub-carrier, OFDM can be easily shaped. For DSSS, spreading codes with particular spectral characteristics can be devised that give the desired shape.