Suppression of FM interference in DSSS communication systems using projection techniques

This paper presents an orthogonal subspace based technique for nonstationary interference excision in direct sequence spread spectrum (DSSS) communications. The interference is an FM signal, which is uniquely characterized by its instantaneous frequency (IF). In the proposed technique, the received data over one symbol period is partitioned into blocks. The data in each block are projected on the subspace orthogonal to the respective interference subspace, which is provided using the IF estimate. The results of the projection are then combined and correlated with the PN sequence at the receiver. The paper shows the receiver performance as a function of the number of blocks and the noise variance. It compares the proposed projection approach with the previously introduced notch filtering techniques for nonstationary interference excisions in DSSS.