Multi-Target Performance of LMMSE Filtering in Radar

Coded orthogonal frequency division multiplexing (OFDM), like several other coded waveforms, exhibits inherent high range sidelobes after matched filtering. Consequently special processing at the receiver is required that can serve for sidelobe suppression in order to avoid target masking. However unmasking is not the only concern. It is crucial to evaluate the filtering scheme both in terms of sidelobe suppression capability and in terms of output signal-to-noise ratio (SNR). This last criterion is essential when aiming at detecting weaker reflections also. The theoretical performance of the reiterated filtering technique based on the linear minimum mean square error (LMMSE), as implemented in the adaptive pulse compression (APC) scheme, is derived and compared with the matched filter (MF). The analysis of the performance is done for a multi-target scenario where targets are close enough for the sidelobes of a target to interfere with the mainlobe of another target. Consequently the unmasking capabilities are relevant, but also output power figures. Complex-valued filter output peaks are also evaluated and compared with the MF output peaks. Moreover the performance of the method is evaluated for OFDM communication-encoded radar waveforms and compared with linear frequency modulated waveforms aiming at simultaneous use of the radar signal for both communication and radar.