Maximum likelihood azimuth estimation applied to SSR/IFF systems

A conventional (nonmonopulse) secondary surveillance radar (SSR) is significantly cheaper than a monopulse SSR but exhibits much greater azimuthal error, especially when some of the replies are missing. Estimation techniques and their performance are discussed with special reference to SSR applications, and a novel estimator for conventional SSR is described. The proposed technique is a close approximation of the maximum-likelihood estimator (MLE), taking into account the receiver characteristics as well as the missed replies. Estimator performance obtained by analysis and computer simulation is compared with that of conventional estimators that are based on the leading and trailing edges of binary sequences and shows significantly improved accuracy     

Design and Evaluation of an Adaptive MTI Filter

The design and evaluation of an adaptive moving target indicator (MTI) filter, the adaptive canceler for extended clutter (ACEC) is dealt with, taking into consideration adaptivity to clutter mean Doppler frequency. This consideration is one of the most important operational requirements in adaptive MTI's and permits a relatively simple hardware implementation as compared to more general optimization and adaptivity criteria (briefly described). The ACEC's algorithm compensates in real time for the clutter mean Doppler frequency. Performances have been obtained by digital computer simulation in various operational conditions.     

When gestures show us the way: Co-thought gestures selectively facilitate navigation and spatial memory

How does gesturing during route learning relate to subsequent spatial performance? We examined the relationship between gestures produced spontaneously while studying route directions and spatial representations of the navigated environment. Participants studied route directions, then navigated those routes from memory in a virtual environment, and finally had their memory of the environment assessed. We found that, for navigators with low spatial perspective-taking performance on the Spatial Orientation Test, more gesturing from a survey perspective predicted more accurate memory following navigation. Thus, co-thought gestures accompanying route learning relate to performance selectively, depending on the gesturers’ spatial ability and the perspective of their gestures. Survey gestures may help some individuals visualize an overall route that they can retain in memory.     

Evaluation of Collapsing Losses in Digital Radar Detection

The collapsing losses, due to multiple channel combinations, are evaluated for some digital radar detection schemes including the moving window detector.     

Separation of SSR Signals by Array Processing in Multilateration Systems

Location and identification of cooperating aircraft in the airport area (and beyond) may be implemented by multilateration (MLAT) systems using the secondary surveillance radar (SSR) mode S signals. Most of these signals, spontaneously emitted from on-board mode S transponders at a fixed carrier frequency, arrive randomly at the receiving station, as well as many mode A/C replies from legacy transponders still in use. Several SSR signals are, then, overlapped in multiple aircraft situations. Therefore, the aim of this work is the separation of overlapped SSR signals, i.e., signals superimposed in time at receiving stations. We improve the MLAT receiving station by replacing the single antenna by an array of m elements and using array signal processing techniques. In the literature, several algorithms address the general source separation problem, but a very few of them are specifically designed for a mixture of overlapping SSR replies. Unfortunately, all of them have either some shortcomings, or an expensive computational cost, or no simple practical implementation. In this paper, we use the time sparsity property of the sources to propose more reliable, simpler, and more effective algorithms based on projection techniques to separate multiple SSR signals. Real recorded signals in a live environment are used to demonstrate the effectiveness of our method.     

The Space Systems Technical Panel

The Space Systems Technical Panel of the IEEE Aerospace and Electronic Systems Society (AESS) was conceived in 2000 and established in 2001. The aims and main activities of the panel are highlighted together with an overview of the status of some ongoing key European space programs.     

Effectiveness of the Nash strategies in competitive multi-team target assignment problems

The Nash strategy in game theory has often been criticized as being ineffective in competitive multi-team target assignment problems, especially when compared with other simplistic strategies such as the random or greedy targeting strategies. This criticism arises from the fact that the Nash strategies may yield unpredictable results when paired with non-Nash strategies in non-zero sum games. In addition, the Nash equilibrium is generally more difficult to compute than strategies which do not attempt to anticipate the strategy of the other side. The authors seek to show that in multi-team target assignment problems the Nash strategy is superior to such simplistic strategies while also remaining computationally feasible. To demonstrate this point, an attrition model was considered, consisting of two teams of nonhomogeneous fighting units simultaneously targeting each other and compare the outcomes when various combinations of four targeting strategies are used on each side. The four strategies are: 1) the random strategy where each unit selects its target randomly, 2) the unit greedy strategy where each unit chooses the target that optimizes its own performance only, 3) the team optimal strategy where the units coordinate their choice of targets so as to optimize the overall team performance while ignoring the possible strategy choices by the other team, and 4) the team Nash strategy, calculated under the assumption that the other team is also using a Nash strategy. Because the computational requirements for calculating the team Nash strategies may become unfeasibly large, an efficient method was discussed for approximating the Nash strategies using a neighborhood search algorithm called unit level team resource allocation (ULTRA). The results were compared for all 16 possible combinations of these four targeting strategies and show that for each team the Nash strategy outperforms all other strategies irrespective of the strategy employed by the other team     

Space-based SSR constellation for global air traffic control

Advanced surveillance and communications are the main functions needed for an efficient Air Traffic Control/Management (ATC/ATM). In order to perform them over the entire Earth, a novel architecture is described and evaluated. It supplies the surveillance and data link capabilities of advanced Secondary Surveillance Radar (SSR) Mode S world-wide by means of a constellation of medium orbit satellites carrying SSR Mode S interrogators with phased-array antennas; no new equipment is required on-board aircraft, because the standard transponders are used. The rationale for the study, the system geometry, the link budget computation, the accuracy requirements as well as the subsequent design of the payload and of the optimized constellations needed for global coverage with high location accuracy are described. Moreover, details are given about the design of the spacecraft and of the main units of the space segment. The encouraging results of this overall system study pave the way to a demonstration based on simulators and ground prototypes of the critical parts     

Angular Accuracy of the Binary Moving Window Radar Detector

The angular accuracy of a search radar depends on the extraction technique. For the case of a binary moving window extractor, the accuracy is evaluated in different operational conditions including target scintillation. A beam-splitting technique that was devised to improve the accuracy is also evaluated and compared with the binary moving window.