The use of radar technology in the field of human activity recognition (HAR) has garnered considerable interest due to its notable benefits in terms of accuracy, resilience, and safeguarding of privacy. As the back-scattered radar returns are composed of multiple components & nonstationary in behavior, the time-frequency analysis like Wigner-Ville distribution (WVD) can play a significant role, but the presence of cross-terms limits the suitability of WVD. This study introduces a time segmentation and frequency windowing-based novel strategy for cross-terms free WVD of multicomponent nonstationary signals. The effectiveness of the proposed method is validated on synthetic signals which outperforms the existing related methods for different performancemeasures. The proposed time-frequency representation (TFR) is also applied for HAR from the received signals of frequency-modulated continuous-wave (FMCW) radar. A novel analysis of extracting slow-time signatures from the received signal captured by FMCW radar is developed and the proposed technique is utilized to generate cross-term free TFRs from these signatures for each activity. Threshold-based time windowing followed by 2-D segmented features extraction is performed on the TFRs for activity recognition system development. The optimization of ensemble classifier yields an impressive classification accuracy rate of 99.51%, surpassing the performances achieved by previous methodologies on the same data set.

A stretch processed radar system is presented in this paper. The radar system operates at S-band and employs stretch processing. Stretch processing helps a radar system to process wideband signals to increase its resolution, while relaxing its analog-to-digital converter's sampling rate requirement. The reported radar system exhibits a high dynamic range which enables it to be used in variety of applications such as surveillance systems. Furthermore, the radar system architecture comprises of multiple receiver channels which enable the radar to detect objects of interests at certain angular locations and reject jammers. The digital radar testbed was built using microwave components. Moreover, the radar system is integrated on a single die chip using IBM 180 nm CMOS process with a low power consumption, small form factor, and high performance.

Efficient utilization of resources is an important issue in the operation of modern radar systems. This paper develops a generalized framework for the radar task scheduling problem as an optimization model. In the proposed method, all radar task parameters are treated as variables, thereby allowing greater scheduling flexibility and the ability to handle more targets using a single radar. An efficient heuristic scheduling method is also proposed and computational results are presented to asses the performance of the proposed method. Note to Practitioners - This paper deals with scheduling a sequence of tasks for a radar system in a limited time-window. Previous work in the literature has addressed this problem by modeling each task as having a fixed duration. In an earlier paper of one of the authors, the task duration was modeled as a variable, which allowed for some flexibility in the task duration, enabling enhanced utilization of the radar timeline. However, a simplified radar task model was used that did not account for the internal structure of a radar task. This work adds a practical dimension by further extending the radar task model to allow for some flexibility in the task duration and also explicitly account for the internal structure of the task. It is shown that utilization of the radar timeline can be thus enhanced through monitoring the interplay of adjusting the dwell times of the internal components of a task.

A framework and method is presented for developing a cyclic task schedule in a multifunction radar. Rather than assuming the task dwell time to be a fixed value when building the schedule, the task dwell time is modeled as a fuzzy set to allow for increased radar schedule flexibility. An optimization model is developed for the scheduling problem and a heuristic method for its solution is proposed. The heuristic method exploits the fuzzy set model in order to intelligently adjust the task dwell times. This adjustment allows for accommodation of more tasks on the radar timeline, thereby resulting in fewer dropped tasks. Computational results are presented to assess the behavior of the proposed scheduling method.

This paper considers adaptive jammer rejection algorithms applicable to wideband stretch-processed systems. Specifically, sub-banding algorithms in which the received data is first pre-processed into narrow frequency bins are studied. In conventional sub-band STAP, the received signal is divided into narrowband frequency bins, following which the interference is adaptively rejected in each bin. This usually requires that a different weight vector be computed for each sub-band. Alternatively, the received data can be pre-processed so that every sub-band is shifted to a common central sub-band. This enables computation of a single weight vector that can be applied to all of the shifted sub-bands. Simulation results are presented to assess the behavior and performance of these algorithms.

Direction finding (DF) performance is assessed for an array of airborne vector sensors whose manifold is perturbed. A calibration algorithm explicitly accounting for the polarization diverse nature of the vector sensor is developed. DF performance improvements are demonstrated with use of the proposed calibration algorithm

The direction finding (DF) performance of an array of vector sensor antennas on a small aircraft is assessed. DF performance in the presence of additive noise, array manifold perturbations, and uncertainty of polarization parameters is examined with simulated data and compared to the Cramer-Rao lower bound. DF performance improvements are demonstrated with a least-squares type calibration technique with and without the use of synthetic antenna elements.

Two recently published external array self-calibration algorithms are applied to experimental data obtained using a surveyed 12-element large sparse aperture array operating at 980 MHz. Though the algorithms are similar in that they use iterative methods to attempt to estimate the angle-of-arrival (AOA) of incoming signals with an imperfectly calibrated array, they are formulated quite differently. The performance of these algorithms is evaluated through their ability to reduce spurious peaks in direction finding (DF) spectra and accurately estimate the AOA of an incoming signal.

Transmitter/receiver optimization for a generic narrowband overlay communication scenario is addressed. The overlay and existing legacy systems are assumed to occupy the same frequency bands for spectral efficiency, thus introducing cochannel interference; however, the new and legacy systems are assumed to be noncooperative, as is appropriate for some pragmatic scenarios. A composite figure of merit is used consisting of a weighted sum of the mean-squared error (MSE) of the (new) overlay system plus the excess MSE in the legacy system caused by the introduction of the overlay system. Necessary conditions on the transmitter and receiver that jointly optimize the above metric are derived. The effects of varying key parameters such as the loop length (range) and transmitter power are investigated via computational examples.