Hasan S. Mir

Passive Direction Finding Using Airborne Vector Sensors in the Presence of Manifold Perturbations

This paper studies direction finding of electromagnetic energy sources using passive vector sensor arrays whose manifold is only nominally known. The problem of direction finding is studied in the context of an airborne array, thus facilitating the observation of a ground-based source from multiple look-angles. A calibration algorithm explicitly accounting for the polarization diverse nature of the vector sensor is developed. It is also shown that the direction finding performance provided by a conventional array calibration algorithm is greatly enhanced with usage of the proposed polarization diverse calibration algorithm

Passive Source Localization Using an Airborne Sensor Array in the Presence of Manifold Perturbations

This paper studies localizing sources of electromagnetic energy using a passive sensor array whose manifold is only nominally known. The problem of source localization is studied in the context of an airborne array that is able to observe a ground-based source from multiple angles. External and self-calibration algorithms are developed as a means to obtain accurate source localization estimates when the sensor manifold is perturbed. External calibration establishes the expected difference between the actual and modeled array manifold using signals at known locations. Self-calibration assumes that this expected difference is known only approximately and relies on signals of opportunity in the environment to provide updates. Several novel calibration algorithms are proposed, and their performance is tested on experimental data. The results indicate that significant performance gains are achieved with the use of the proposed calibration algorithms

Variable Dwell Time Task Scheduling for Multifunction Radar

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 Low-Cost High-Performance Digital Radar Test Bed

This paper describes the design of a dual-channel S-band digital radar test bed. The test bed combines stretch processing with a novel and cost-effective hardware architecture that enables it to achieve an in-band dynamic range of 60 dB over 600 MHz of instantaneous bandwidth. The dual digital receiver channels allow for adaptive digital beamforming which can be used to mitigate a directional source of interference. Experimental test and verification results are presented to demonstrate system performance.

Cyclic Task Scheduling for Multifunction Radar

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.

Optimum transmitter/receiver design for a narrowband overlay in noncoordinated subscriber lines

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.

A Generalized Transfer-Function Based Array Calibration Technique for Direction Finding

This correspondence studies direction finding on sources of electromagnetic energy using a passive sensor array whose manifold is only nominally known. The problem of direction finding is studied in the context of an array that can observe a ground-based source from multiple angles, such as an airborne system. An array calibration technique utilizing multiple calibration matrices with angle dependent corrections is developed. Results on experimental data and comparisons with other array calibration techniques are shown to verify the efficacy of the proposed technique.

Self-calibration of an airborne array

Unlike external array calibration, array self-calibration does not assume that source angles of arrival are known. This paper studies novel self-calibration algorithms and tests them on experimental data. Results indicate that self-calibration algorithms based on an appropriate cost function may achieve source-localization performance comparable to that of external array calibration and better than without calibration.

Task scheduling algorithm for an air and missile defense radar

An algorithm for scheduling tasks for an air and missile defense radar is proposed. The algorithm consists of two sub-algorithms: a task interleaving algorithm followed by a distributed greedy scheduling algorithm. The interleaving algorithm efficiently interleaves range-unambiguous and range-windowed tasks (such as BMD-track tasks) based on knowledge of the task dwell characteristics. The output of the interleaving algorithm and the remaining tasks are then input to a greedy scheduling algorithm which attempts to schedule as many tasks as possible while maintaining temporal regularity between the task update intervals. Simulation results are provided to demonstrate the behavior of the proposed algorithm.

Cognitive workload estimation due to vague visual stimuli using saccadic eye movements.

Visual perception is affected by the quality of stimulus. In this paper, we investigate the rise in cognitive workload of an individual performing visual task due to vague visual stimuli. We make use of normalized average peak saccadic velocity to estimate the cognitive workload. Results obtained from 16 human subjects show that the mean of peak saccadic velocity increases with workload indicating that faster saccades are required to obtain information as the workload increases. This technique should find application in assessment of vigilance and cognitive performance in many demanding professional, industrial and transportation situation.