Two-stage code reference beamformer for the reception of frequency hopping modulated signals

Abstract

This paper presents a beamforming technique for the reception of frequency hopping (FH) modulated signals, which takes advantage of their inherent frequency diversity. This technique, based on a code reference beamformer, requires neither temporal nor spatial a priori reference and allows continuous self-calibration of the array. The proposed framework is composed of two different stages. The first stage employs the inverse of the noise plus interference covariance matrix obtained by an anticipative processor. The second stage makes use of the steering vector of the signal of interest which is adaptively obtained by maximizing the output signal to interference plus noise ratio (SINR). Using this information, the first stage is in turn readjusted and, as a result, the scheme is able to track non-stationary scenarios following the channel variations with no previous references other than knowledge of the frequency hopping sequence. The two-stage code reference beamformer provides the convergence rate necessary to avoid the SINR reduction associated with frequency hops in existing methods.