Joint Optimization of Signal Waveforms and Filters for Long-Range MIMO Radars

Abstract

This paper describes a cyclic algorithm for minimization of signal sidelobes and crosstalk in multiple-input multiple-output (MIMO) radar. The algorithm, called SWAP by the authors, is suitable mainly for long-range radars, such as ground-based surveillance, approach, or weather radar. The minimization of energy, minimization of side lobes, and crosstalk were used as the optimization criteria. Although the optimized signals do not maintain a strictly constant envelope, the peak-to-average power ratio (PAR) can be maintained below 1.7. This value is acceptable, especially for radars with modern transmitters based on GaN HEMTs. The algorithm allows for any arbitrary choice of elements weights, enabling the optimization of calculations for a wide range of applications. The effect of the Doppler shift can also be included in the optimization. This article also presents the results of algorithm testing under various conditions. The designed algorithm makes it possible to suppress the side lobes and crosstalk by up to 20 dB more than the matched filters. These results were achieved at the cost of a slight deterioration in signal-to-noise ratio (SNR) loss (less than 1 dB) and an increase in PAR (up to 2). The resolution of weak close targets is also slightly deteriorated. The algorithm converged quickly, and already after ten or 20 iterations, the results changed only minimally.

Simultaneous Optimization of Mismatched Filters and Controlled Amplitude Signals for Long-Range MIMO Radars

“…For the PSL criterion, it reaches a minimum at a = 0.2, and then increases sharply to values of approximately 6 dB. This is in contrast with our previous findings [9]. With the SWAP algorithm the PAR for the ISL criterion deteriorates significantly, and on the other hand, the losses stay below 2 dB in all cases.…”

“…The calculation of filters in step 2 based on the ISL or PSL criteria is described in [9]. The gradient algorithm in Step 4 is a standard algorithm that searches for optimal signals for the given filters using an iterative method.…”

“…Some publications also deal with mismatched filters (e.g., [6]- [8]), which, at the cost of a small increase in loss, allows improvements in side-lobe suppression and crosstalk over the entire time lag. If the constant envelope requirements are partially relaxed, it is possible to further improve the suppression of the side lobes and crosstalk over the entire lag by up to 20 dB (e.g., [9]). The speed of the computation (optimization) of signals or filters is another aspect of the evaluation of design methods.…”

“…For these radars, efforts should be made to suppress all the side lobes and crosstalk. This paper follows [9], where an SWAP algorithm is presented that splits the entire process into the optimization of individual filters and signals. Thus, the algorithm is relatively simple and computationally efficient, making it faster than variants of the WeCAN algorithm.…”

Optimization of Mismatched Filters With Asymmetric Side-Lobe Shape for Short-Range MIMO Radars

“…In other words, they allow for better utilization of the maximum power of the amplifier during transmitting. However, even a relatively small relaxation of this requirement allows for significant improvement of side lobe suppression [12], [13]. Under certain conditions, the side lobes can also be suppressed significantly (up to 150 dB), but only over a limited range of lags to the main lobe [14].…”