Nonstationary interference excision in spread spectrum communications using projection filtering methods

A new nonstationary interference excision technique in direct sequence spread spectrum (DSSS) communication is introduced. This technique is based on the notion that both the additive noise and the DSSS signal cover the entire time-frequency (t-f) domain, whereas the jammer occupies a small t-f region. A projection filter is constructed using the jammer underlying t-f signature or its expected occupancy region in the t-f domain. The filter output is either directly despreaded or first subtracted from the input data and then despreaded by the PN sequence, depending on whether the filter passes or removes the jammer signal. We derive the SNR of the DSSS receiver implementing the projection filters and discuss its relation to existing excision methods based on instantaneous frequency information.