We propose a technique that enhances the performance of Torrieri and Bakhru's maximin algorithm in the presence of frequency offsets and modulated interferences, a common scenario in multiple-access environments, where we observed that the Maximin algorithm suffers performance degradation in the aforesaid scenario. To combat modulated interferences and fading effects, we propose to update the step length during every smart antenna weight vector update. We found that our scheme improves the robustness of the maximin algorithm to a greater extent. Simulation results for a frequency-hopping system confirm the validity of the approach and demonstrate improvements in the performance of the maximin algorithm in the presence of frequency offsets and data modulated interferences in a fading channel environment.Index Terms-Frequency hopping, maximin, smart antenna, step length.

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A ground moving target's velocity estimation algorithm applicable for a SAR-GMTI system using 2 channel displaced phase center antenna(DPCA) is proposed. In this algorithm, we assume target's across-track velocity can be estimated by along-track interferometry (ATI) and present a method to estimate target's along-track velocity. To accomplish this method, we first transform a radar-target geometry in which a moving target has zero velocity via altering a radar velocity such that target's velocity is reflected into it and next manipulate the spectral centers of the subapertures within the synthetic aperture. The validity of the proposed algorithm is demonstrated through simulation results showing the performance of the target's velocity estimation and the enhancement of reconstructed target image quality in terms of resolution and SINR.

The Maximin algorithm, proposed by Torrieri and Bakhru, adaptively updates the weights of an antenna array to provide simultaneous interference suppression and beamforming in a frequency hopping (FH) communication system. The Maximin algorithm is named such because the desired signal is enhanced and the interference is suppressed simultaneously. And the Maximin shows good performance under a broadband tone interference environment, but poor performance under frequency offset and friendly interference, i.e., a data-modulated interference environment. This paper analytically derives how the frequency offset affects on the Maximin algorithm and verifies the analytical results with simulation results. In addition, this paper proposes to use the recently published MOSTLE algorithm because the MOSTLE is robust against frequency offset and friendly interference.

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