By Topic

Aerospace and Electronic Systems, IEEE Transactions on

Issue 4 • Date OCTOBER 2011

Filter Results

Displaying Results 1 - 25 of 64
  • Contents

    Page(s): c1
    Save to Project icon | Request Permissions | PDF file iconPDF (146 KB)  
    Freely Available from IEEE
  • [Inside front cover]

    Page(s): c2
    Save to Project icon | Request Permissions | PDF file iconPDF (130 KB)  
    Freely Available from IEEE
  • From the Editor

    Page(s): 2305 - 2307
    Save to Project icon | Request Permissions | PDF file iconPDF (532 KB)  
    Freely Available from IEEE
  • Quadrature Bandpass Sampling Rules for Single- and Multiband Communications and Satellite Navigation Receivers

    Page(s): 2308 - 2316
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3315 KB) |  | HTML iconHTML  

    In this paper, we examine how existing rules for bandpass sampling rates can be applied to quadrature bandpass sampling. We find that there are significantly more allowable sampling rates and that the minimum rate can be reduced. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • X-Ray Pulsar-Based Relative Navigation using Epoch Folding

    Page(s): 2317 - 2328
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4804 KB) |  | HTML iconHTML  

    How the relative position between two spacecraft can be estimated utilizing signals emitted from X-ray pulsars is explained. The mathematical models of X-ray pulsar signals are developed, and the pulse delay estimation problem is formulated. The Cramér-Rao lower bound (CRLB) for any unbiased estimator of the pulse delay is presented. To retrieve the pulsar photon intensity function, the epoch folding procedure is characterized. Based on epoch folding, two different pulse delay estimators are introduced, and their performance against the CRLB is studied. One is obtained by solving a least squares problem, and the other uses the cross correlation function between the empirical rate function and the true one. The effect of absolute velocity errors on position estimation is also studied. Numerical simulations are performed to verify the theoretical results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optimizations of Multisite Radar System with MIMO Radars for Target Detection

    Page(s): 2329 - 2343
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2613 KB) |  | HTML iconHTML  

    This paper proposes a novel multisite radar system (MSRS) with multiple-input and multiple-output (MIMO) radars, i.e., MIMO-MSRS system, to improve the detection performance of fluctuating targets. The proposed MIMO-MSRS system increases the local signal-to-noise ratio (SNR) by using digital beamforming (DBF) among all transmitting and receiving channels in a single site. Then it smoothes the target's fluctuation via spatial diversity among the DBF outputs of different sites. For the MIMO-MSRS system, we derive the likelihood ratio test (LRT) detector at first based on the proposed signal model and spatial diversity conditions. Furthermore, with the derived statistics of the LRT detector in the fixed noise background, three optimization problems are discussed on the MIMO-MSRS system configurations, i.e., the numbers of sites and collocated channels in different sites. The first problem is to detect the lowest SNR target with a given probability of false alarm (PF), probability of detection (PD) and total system degrees of freedom (DOF). The second is to detect a target with the highest PD for a given PF, target SNR, and system DOF. The third is on the minimal system DOF to detect a target with a given PF, PD, and target SNR. For the uniform MIMO-MSRS system, both the standard optimal site number, i.e., the diversity DOF, and its closed-form approximation of the above three problems are obtained. Finally, some numerical results are also provided to demonstrate the effectiveness of the proposed MIMO-MSRS systems. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multitarget Tracking using Probability Hypothesis Density Smoothing

    Page(s): 2344 - 2360
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4414 KB) |  | HTML iconHTML  

    In general, for multitarget problems where the number of targets and their states are time varying, the optimal Bayesian multitarget tracking is computationally demanding. The Probability Hypothesis Density (PHD) filter, which is the first-order moment approximation of the optimal one, is a computationally tractable alternative. By evaluating the PHD, the number of targets as well as their individual states can be extracted. Recent sequential Monte Carlo (SMC) implementations of the PHD filter have paved the way to its application to realistic nonlinear non-Gaussian problems. It is observed that the particle implementation of the PHD filter is dependent on current measurements, especially in the case of low observable target problems (i.e., estimates are sensitive to missed detections and false alarms). In this paper a PHD smoothing algorithm is proposed to improve the capability of PHD-based tracking system. It involves forward multitarget filtering using the standard PHD filter recursion followed by backward smoothing recursion using a novel recursive formula. Smoothing, which produces delayed estimates, results in better estimates for target states and a better estimate for the number of targets. Multiple model PHD (MMPHD) smoothing, which is an extension of the proposed technique to maneuvering targets, is also provided. Simulations are performed with the proposed method on a multitarget scenario. Simulation results confirm improved performance of the proposed algorithm. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Joint Multitarget Tracking and Sensor Localization in Collaborative Sensor Networks

    Page(s): 2361 - 2375
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4051 KB) |  | HTML iconHTML  

    Multitarget tracking methods in a sensor network often assume the knowledge of the locations of the sensor nodes. However, in reality sensor nodes are randomly deployed with no prior knowledge about their positions. We propose a method to track an unknown and variable number of targets in the presence of false detections with the positions of sensor nodes estimated jointly to avoid the need of extra localization hardware. Moreover, as low-power consumption is a requirement in sensor networks, a collaborative estimation scheme is presented. For each target in the field under observation there is only a small set of sensor nodes that are active while the others remain in an idle state. The proposed technique is based on a Rao-Blackwellized sequential Monte Carlo (SMC) method that takes advantage of the fact that the state space of the unknown variables is separable. Therefore the problem is divided in two parts. The first one generates samples to estimate the number of targets and solves the association uncertainty between measurements and targets; while the second one is a multiple target tracking problem that can be solved with a modified unscented Kalman filter (MUKF) for each sample. It is shown through simulations that it is possible to track the multiple targets and also get accurate estimates of the unknown locations of the sensor nodes. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Persymmetric Adaptive Radar Detectors

    Page(s): 2376 - 2390
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5319 KB) |  | HTML iconHTML  

    In the general framework of radar detection, estimation of the Gaussian or non-Gaussian clutter covariance matrix is an important point. This matrix commonly exhibits a particular structure: for instance, this is the case for active systems using a symmetrically spaced linear array with constant pulse repetition interval. We propose using the particular persymmetric structure of the covariance matrix to improve the detection performance. In this context, this work provides two new adaptive detectors for Gaussian additive noise and non-Gaussian additive noise which is modeled by the spherically invariant random vector (SIRV). Their statistical properties are then derived and compared with simulations. The vast improvement in their detection performance is demonstrated by way of simulations or experimental ground clutter data. This allows for the analysis of the proposed detectors on both real Gaussian and non-Gaussian data. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Detection and Mitigation of Reference Receiver Faults in Differential Carrier Phase Navigation Systems

    Page(s): 2391 - 2404
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB) |  | HTML iconHTML  

    In this paper, a methodology is developed to evaluate differential carrier phase navigation architectures subject to reference receiver faults. Carrier phase measurements can be used to provide high accuracy estimates of a user's position. But in applications that involve safety-of-life, such as in precision approach for autonomous shipboard landing, integrity also plays a critical role. One source of integrity risk is the potential for GPS reference receiver failure. Integrity risk in these situations is typically mitigated by equipping the reference station with redundant receivers. However, various approaches to utilize redundant carrier phase measurements from multiple reference receivers are possible. In this paper, we describe two new methods: an averaging approach where different position solutions are averaged in the position domain, and a coupled estimation approach where the measurements from all reference receivers are coupled in the range domain and used to estimate a unified position solution. Furthermore, we investigate the impact of using these methods on accuracy and integrity from several perspectives, including availability performance, cycle resolution capabilities, implementation complexity, and computational efficiency. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optimal Flow Models for Multiscan Data Association

    Page(s): 2405 - 2422
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4064 KB) |  | HTML iconHTML  

    Multiscan data association can significantly enhance tracking performance in critical radar surveillance scenarios involving multiple targets, low detection probability, high false alarm probability, evasive target maneuvers, and finite radar resolution. Unfortunately, however, this approach is affected by the curse of dimensionality which hinders its real-time application for tracking problems with short scan periods and/or a high number of scans of the association logics and/or many measurements per scan. It is shown here how the formulation of the multiscan association as a multi-commodity or single-commodity flow optimization problem allows a relaxation of the association problem which, on one hand, provides close-to-optimal association performance and, on the other hand, implies a significant reduction of the computational load. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Robust Nonlinear Control Approach for Tip Position Tracking of Flexible Spacecraft

    Page(s): 2423 - 2434
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3804 KB) |  | HTML iconHTML  

    In this paper, the problem of attitude control of a 3D nonlinear flexible spacecraft is investigated. Two nonlinear controllers are presented. The first controller is based on dynamic inversion, while the second approach is composed of dynamic inversion and γ-synthesis schemes. The extension of dynamic inversion approach to flexible spacecraft is impeded by the nonminimum phase characteristics when the panel tip position is taken as the output of the system. To overcome this problem, the controllers are designed by utilizing the modified output redefinition approach. It is assumed that only three torques in three directions on the hub are used. Actuator saturation is also considered in the design of controllers. To evaluate the performance of the proposed controllers, an extensive number of simulations on a nonlinear model of the spacecraft are performed. The performances of the proposed controllers are compared in terms of nominal performance, robustness to uncertainties, vibration suppression of panel, sensitivity to measurement noise, environment disturbance, and nonlinearity in large maneuvers. Simulation results confirm the ability of the proposed controller in tracking the attitude trajectory while damping the panel vibration. It is also verified that the perturbations, environment disturbances, and measurement errors have only slight effects on the tracking and damping performances. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Hierarchical Fault Diagnosis and Fuzzy Rule-Based Reasoning for Satellites Formation Flight

    Page(s): 2435 - 2456
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3760 KB) |  | HTML iconHTML  

    Formation flying is an emerging area in the Earth and space science and technology domains that utilize multiple inexpensive spacecraft by distributing the functionalities of a single platform spacecraft among miniature inexpensive platforms. Traditional spacecraft fault diagnosis and health monitoring practices involve around-the-clock monitoring, threshold checking, and trend analysis of a large amount of telemetry data by human experts that do not scale well for multiple space platforms. A novel hierarchical fault diagnosis framework and methodology is presented here that enables a systematic utilization of fuzzy rule-based reasoning to enhance the level of autonomy achievable in fault diagnosis at ground stations. Fuzzy rule-based fault diagnosis schemes for satellite formation flight are developed and investigated at different levels in the hierarchy for a leader-follower architecture. Our formation level fault diagnosis is found to be useful as a supervisory diagnosis scheme that can prompt the operators to have a closer look at the potential faulty components to determine the sources of a fault. Effectiveness of our proposed fault diagnosis methodology is demonstrated by utilizing synthetic formation flying data of five satellites that are configured in the leader-follower architecture, and are subjected to nonabrupt intermittent faults in the attitude control subsystem (ACS) and the electrical power subsystem (EPS) of the follower satellites. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Optimal Maneuvers for Aircraft Conflict Resolution Based on Efficient Genetic Webs

    Page(s): 2457 - 2472
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2021 KB) |  | HTML iconHTML  

    The problem of designing optimal conflict-free maneuvers for planar multiple aircraft encounters is studied. The maneuvers propose suitable heading changes for aircraft in a cooperative manner. The new mathematical approach provides optimal aircraft trajectories to resolve a wide variety of conflicts, especially in the presence of high-altitude clear air turbulence (CAT), normally encountered during en-route flights. The proposed approach effectively uses Genetic Algorithms (GA), together with modified webs, to quickly find conflict-resolving maneuvers. Different case studies show the method is fast enough to be used for real-time applications when resolving conflicts involving two aircraft. It is also efficient enough to resolve conflicts involving as many as 26 aircraft, which would be helpful in designing acrobatic maneuvers or in congested airspaces where emergency plans are needed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Radon-Fourier Transform for Radar Target Detection (II): Blind Speed Sidelobe Suppression

    Page(s): 2473 - 2489
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4595 KB) |  | HTML iconHTML  

    This paper gives a detailed performance analysis for the novel radar long-time coherent integration method, i.e., Radon-Fourier transforms (RFT). Some important properties of RFT, e.g., two-dimensional (2D) impulse response, 2D translational invariance, multitarget linear additivity, linear signal-to-noise ratio gain in additive white Gaussian noise (AWGN), as well as the 2D correlation function of transformed AWGN, are derived for continuous and discrete RFT, respectively. However, because of discrete pulse sampling, finite range resolution, and limited integration time, the "blind-speed sidelobes (BSSL)" of discrete RFT may inevitably appear in real applications. Although the BSSL are reduced with the increase of the blind-speed integer, they may still lead to false alarms or loss detections in a real multitarget scenario. Based on the analytic expression derived for BSSL, the causes of BSSL are analyzed and the effective BSSL suppression methods are proposed. Finally, numerical experiments are also provided to demonstrate the effectiveness of the proposed methods. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Near-Optimal Terrain Collision Avoidance Trajectories using Elevation Maps

    Page(s): 2490 - 2501
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (6203 KB) |  | HTML iconHTML  

    The main attempt of this paper is to present a new methodology to model a generic low-level flight close to terrain, which guarantees terrain collision avoidance. Benefiting the advantages of high-speed computer technology, this method uses satellite elevation maps to generate so-called "quad-tree forms." The latter is then used to find the optimal trajectories for low-level flights. The novelty of this approach, entitled the "cost map," lies in the integration of aircraft dynamics into the segmented map. This procedure results in some near-optimal trajectories with respect to aircraft dynamics that could easily be used for minimization of flight path together with pilot effort. Different simulations show the method is applicable wherever there is no need for sharp changes in flight level. Nevertheless, the current method could be expanded to three-dimensional terrain avoidance/terrain following flights. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Nonlinear-Phase Model-Based Human Detector for Radar

    Page(s): 2502 - 2513
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2502 KB) |  | HTML iconHTML  

    Radar offers unique advantages over other sensors for the detection of humans, such as remote operation during virtually all weather and lighting conditions, increased range, and better coverage. Many current radar-based human detection systems employ some type of Fourier analysis, such as Doppler processing. However, in many environments, the signal-to-noise ratio (SNR) of human returns is quite low. Furthermore, Fourier-based techniques assume a linear variation in target phase over the aperture, whereas human targets have a highly nonlinear phase history. The resulting phase mismatch causes significant SNR loss in the detector itself. In this paper, human target modeling is used to derive a more accurate nonlinear approximation to the true target phase history. The likelihood ratio is optimized over unknown model parameters to enhance detection performance. Cramer-Rao bounds on parameter estimates and receiver operating characteristic curves are used to validate analytically the performance of the proposed method and to evaluate simulation results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Near-Optimal Iterative Algorithm via Alternately Optimizing Sensor and Fusion Rules in Distributed Decision Systems

    Page(s): 2514 - 2529
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (822 KB) |  | HTML iconHTML  

    For parallel distributed sensor systems with statistically independent sensor decision rules, Chair and Varshney in [2] has obtained the optimal fusion rule. On the other hand, under a given fusion rule, the optimal sensor compression rules have been proposed by Zhu et al. in [21], [23] for generally distributed and dependent sensor observations. An open problem is how to simultaneously obtain an optimal fusion rule and optimal sensor compression rules for general parallel distributed sensor decision systems. Obviously, the exhaustive method for searching for the optimal fusion rule is computationally intractable. For general parallel distributed sensor decision systems, we provide necessary conditions of an optimal fusion rule and optimal sensor compression rules and propose a computationally efficient iterative algorithm to simultaneously/alternately search for a fusion rule and sensor compression rules by combining both Zhu's and Chair and Varshney's methods. Moreover, the algorithm is extended to multiple bit compression and Network decision systems. Numerical examples show that the fusion rule obtained by the algorithm is in most cases the same as the optimal fusion rule obtained by the exhaustive method, therefore, it is effective and near optimal. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High Resolution ISAR Imaging of Targets with Rotating Parts

    Page(s): 2530 - 2543
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5562 KB) |  | HTML iconHTML  

    For a target with rotating parts, the ISAR image of its main body may be overshadowed by micro-Doppler signals, which are traditionally treated as interference and removed from radar echoes. However, it is potentially useful to perform imaging using micro-Doppler signals because they contain information on the geometrical structure of the rotating part. Inspired by the inverse Radon transform, well-known in the image processing community, this paper creates a data-recording model for two-dimensional (2D) ISAR imaging of rotating parts. Based on this model, the real-valued inverse Radon transform is applied to image formation in the range-slow time domain. Then we put forward a complex-valued inverse Radon transform for imaging of rotating parts, which utilizes both the sinusoidal modulus and the phase of the radar echoes. Additionally, we analyze possible problems when applying these algorithms in real world situations and provide corresponding solutions. Finally, the effectiveness of the algorithms is demonstrated using simulated and measured data. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Delayed PIC for Postcorrelation Mitigation of Continuous Wave and Multiple Access Interference in GPS Receivers

    Page(s): 2544 - 2557
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4817 KB) |  | HTML iconHTML  

    Several techniques are available to mitigate the problem of multiple access interference (MAI) caused by the limited dynamic range of the 1023-chip global positioning system (GPS) coarse acquisition Gold codes. MAI causes difficulties in several high-sensitivity applications, including indoor GPS and the use of pseudolites for GPS augmentation. This paper provides details on a variation on the existing techniques of successive interference cancellation (SIC) and parallel interference cancellation (PIC), but with the advantage of being more readily applied. This postcorrelation method is suitable for use in both hardware and software GPS receivers and is able to use commercially available GPS front-end chips employing 2-bit quantization of the received radio signal. The method can also be used to cancel some forms of continuous wave (CW) interference. Simulation results providing statistics on the effectiveness of the technique are provided, as well as results obtained when the technique was implemented in hardware on a GPS receiver based on a field programmable gate array correlator. The proposed method is also compared to some other MAI-mitigating techniques. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Maritime ATR using Classifier Combination and High Resolution Range Profiles

    Page(s): 2558 - 2573
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4279 KB) |  | HTML iconHTML  

    A maritime automatic target recognition system is developed that performs ship classification using one-dimensional high resolution range profiles. Five physically based features are defined and are extracted from both VV and HH polarizations resulting in a 10-dimensional feature vector. A nonlinear classifier combination approach involving a neural network combiner along with three individual classifiers (Bayes, nearest neighbor, and neural network) is proposed. A decision confidence measure based on the classifier discriminants is developed using a nonparametric estimation approach. The confidence measure enables the system to reject samples that have a low decision confidence. The performance of the proposed neural network based combination is compared with individual classifiers and a number of other combination rules. The results show that this combination can provide high recognition accuracy along with a high probability of declaration. The performance in the presence of samples from not-before-seen classes is also investigated. A new nearest neighbor confidence thresholding approach is developed to aid the neural network combiner in rejecting these samples. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Aircraft Power System Stability Study Including Effect of Voltage Control and Actuators Dynamic

    Page(s): 2574 - 2589
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (9054 KB) |  | HTML iconHTML  

    This paper describes a stability analysis of aircraft ac frequency-wild power systems with constant power loads (CPL). In contrast to previous publications, the proposed analysis method employs the dq modeling approach instead of the state-space averaging (SSA) and average-value modeling (AVM) methods to derive power-electronic converter models for stability studies. This results in lower order models and allows the modeling of vector-controlled converter elements where the SSA and AVM methods are not easily applicable. The resulting model can be combined with models of other power system elements expressed in terms of synchronously rotating frames (generators, front-end converters, vector-controlled drives, etc.). The paper analyzes the stability of frequency-wild power systems for both load and parameter variations and takes into account controlled generator voltage dynamics and electromechanical actuator dynamics. The stability margins are assessed and compared with those for power systems with the ideal voltage source and the ideal CPLs. The study is supported by intensive time domain simulations that support the theory. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multipath Insensitive Delay Lock Loop in GNSS Receivers

    Page(s): 2590 - 2609
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (9245 KB) |  | HTML iconHTML  

    The code measurement suffers from multiple error sources and especially multipath. The latter is unpredictable and changes in space and over time. Many interesting multipath mitigation techniques have been proposed. Most of them are not sufficiently effective for precise positioning using the code measurement. This paper presents a multipath insensitive delay lock loop that aims to improve the pseudorange measurement precision in the presence of multipath. This code loop is simple and does not require postprocessing of observables. Simulation and real implementation results showed that the proposed code loop dramatically improves the tracking error due to multipaths. Tracking error is limited to 1 m on pseudorange in typical multipath environments. This loop is more sensitive than the standard delay lock loop to thermal noise and applies predominantly to strong GNSS signals. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Throughput per Pass for Data Aggregation from a Wireless Sensor Network via a UAV

    Page(s): 2610 - 2626
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3536 KB) |  | HTML iconHTML  

    Data retrieval from a sensor field by means of unmanned aerial vehicle (UAV) has increasing interests for both commercial, military, and homeland security applications. In these situations, the design of energy-efficient communication links between sensor field and UAV is crucial, owing to battery powered sensor nodes. We propose an energy-efficient cooperative transmission scheme for wireless sensor networks (WSNs) where data gathered by sensor nodes need to be collected into a far receiver. In particular, we consider a network composed of sensor nodes that share a common message that has to be transmitted asynchronously toward a fusion center onboard a UAV. We consider that the communication channels between the nodes and the fusion center are subject to fading and noise. Due to the far communication distance and energy constraint at each node, the fusion center must be able to reliably receive the weak and noisy signals. In our approach the fusion center consists of a Rake receiver capable of collecting multiple replicas of the same information from the nodes in the WSN. The performance of the proposed cooperative diversity scheme is then studied in terms of throughput, bit error probability, and energy efficiency. The results obtained show that, as the number of nodes increases, the proposed approach increases network lifetime, communication reliability, and throughput. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Specific Length Trajectories Optimised for Maximum Acceleration using Conic Parameterised Clothoids

    Page(s): 2627 - 2636
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1218 KB) |  | HTML iconHTML  

    One current method of aircraft flightpath generation employs multi-segmented straight trajectories with each consecutive pair of segments filleted with arcs of constant radius. A difficulty of infeasibility immediately arises. In order for an aircraft to make the transition from a straight to a curved path segment (or vice versa) there is a physical requirement for a step acceleration, implying an infinite jerk. Clothoid curves provide a solution and have been investigated to fillet the consecutive segments. However, in this case, the mathematical definition of the clothoid is in terms of an integral that precludes closed-form solutions for critical guidance parameters. The attractiveness of the clothoid is to solve the physical infeasibility problem, however the mathematical intractability inherent in the approach has attracted limited attention despite being recognised as a major concern through early experiments. A method is presented here where double clothoid curves are used to fillet consecutive segments. This work goes beyond present practice to provide closed form solutions by using the hyperbola as a clothoid facsimile. Acceleration constraints have been enforced, both accumulative and maximum, and both the reference bank angle and bank angle rate have been expressed analytically in closed-form in terms of hyperbolic parameters. The solution can be optimised in terms of accumulative acceleration and path length, whilst simultaneously enforcing maximum acceleration constraints. This method of trajectory generation is attractive for implementation with air traffic management separation assurance, tunnel-in-the-sky, and other proposed cockpit display systems. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

IEEE Transactions on Aerospace and Electronic Systems focuses on the equipment, procedures, and techniques applicable to the organization, installation, and operation of functional systems designed to meet the high performance requirements of earth and space systems.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Lance Kaplan
Army Research Laboratory