Broadband interference excision for software-radio spread-spectrum communications using time-frequency distribution synthesis

A new method is introduced for interference excision in spread-spectrum com munications that is conducive to software-radio applications. Spare process ing capacity in the receiver permits the use of time-frequency techniques t o synthesize a nonstationary interference from the time-frequency domain us ing least squares methods. The synthesized signal is then subtracted from t he incoming data in the time domain, leading to jammer removal and increase d signal-to-interference-and-noise ratio at the input of the correlator, Th e paper focuses on jammers with constant modulus that are uniquely describe d by their instantaneous frequency characteristics. With this a priori know ledge, the jammer signal amplitude is restored by projecting each sample of the synthesized signal to a circle representing its constant modulus. With the phase matching provided by the least squares synthesis method and ampl itude matching underlying the projection operation, a significant improveme nt in receiver performance/bit-error rates is achieved over the case where no projection is performed. Software-radio aspects including computational complexity and processing modes are also discussed.