Sidelobe suppression for OFDM based cognitive radio systems using genetic algorithm for subcarrier weighting

摘要

Orthogonal frequency division multiplexing (OFDM), because of its different advantages, has been proposed as the enabling modulation technology for cognitive radios. However, the high sidelobes of the subcarriers are a major disadvantage that result in out-of-band radiation (OOB) causing interference to adjacent licensed users. Subcarrier weighting is an efficient technique for suppressing these sidelobes. This paper proposes the genetic algorithm to solve the subcarrier weighting technique's optimization problem that gives the optimum weight vector for sidelobe suppression. The genetic algorithm calculates the weights of the OFDM subcarriers in an optimized way such that the sidelobes of these subcarriers interfere destructively with each other, resulting in a smooth signal in the optimization range thus the sidelobes are suppressed and minimal interference is offered to adjacent users.