Waveform diversity: Hardware demonstration

Multibeam radars (MBRs) enable multiple independent channels by simultaneously exploiting spatial and waveform diversity. Orthogonal waveforms are employed to form multiple independent antenna beams, each one providing a different function and using different dedicated radar resources. This paper investigates sidelobe levels in MBRs and presents a comparison with those of an Electronic Steerable Array (ESA) that employs a single waveform in transmission to generate multiple simultaneous beams. Simulations are carried out for a 3-channel MBR transmitting quasi-orthogonal Linear Frequency Modulated (LFM) waveforms at Ku band. The response of the MBR to an ideal point target as a function of aspect angle as well as that to multiple targets in different locations has been investigated. Results corroborate the analytical findings and show that the sidelobe levels with respect to angle, at the target range, are attenuated by the cross-ambiguity function properties between the waveforms employed. The range response to a target in low channel isolation suffers from cross-channel interference that may alter the noise floor characteristics of the radar, hence stressing the importance of suitable waveform selection.

Multiple-input multiple-output radar waveform diversity design has received much attention, but many of existing waveforms are lack of a large time-bandwidth product. This paper proposes an orthogonal frequency division multiplexing (OFDM) chirp waveform diversity design scheme to generate four waveforms with good correlation properties, ambiguity performance and Doppler tolerance. The method jointly utilizes classic chirp waveform and OFDM to conduct multi-carrier modulation. This scheme enables us to exploit full bandwidth for each waveform and thus has an high frequency utilization efficiency. The modulation and demodulation of the four OFDM chirp waveforms are presented. The performance of the designed waveforms is analyzed by the correlation and ambiguity functions. Simulation results validate that our proposal can generate more orthogonal waveforms without significant performance degradation.

Ground moving target indication (GMTI) plays an important role in surveillance and reconnaissance applications, but it is a difficult problem due to the impacts of stationary clutter. This paper proposes a multichannel synthetic aperture radar (SAR) using waveform diversity, namely, multiple-input multiple-output (MIMO) SAR and distinct carrier frequency for GMTI applications. The proposed approach employs MIMO configuration with multiple antennas in azimuth and orthogonal waveform diversity. In doing so, multiple independent transmit-receive channels are formulated at the receiver. Since each antenna uses both waveform diversity and distinct carrier frequency, after clutter cancellation and noise suppression by the displaced phase center antenna (DPCA) and along-track interferometry (ATI) combined processing algorithm, the cross-track velocity is estimated through double-interferometry processing. Next, the Doppler parameters of moving targets are estimated with the fractional Fourier transform algorithm and then GMTI is obtained by a joint signal processing algorithm. Finally, the moving targets are focused with a general chirp scaling imaging algorithm. All the proposed methods are verified by simulation results.

Orthogonal and quasi-orthogonal waveforms are used in a multibeam radar (MBR) to isolate different channels and reduce cross-channel interference. Each channel provides an independent radar beam that performs a specific functionality without interfering with adjacent channels. The MBR signal model is presented that shows how spatial and waveform diversity are employed to successfully separate multiple channels. In this paper, the theoretical predictions of channel isolation are experimentally confirmed with an analysis of micro-Doppler signatures of a rotating target obtained by applying short-time Fourier transform (STFT).

Unmanned aerial vehicles (UAV) can be used to cover large areas searching for targets. However, sensors on UAVs are typically limited in their accuracy of localization of targets on the ground. On the other hand, unmanned ground vehicles (UGV) can be deployed to accurately locate ground targets, but they have the disadvantage of not being able to move rapidly or see through such obstacles as buildings or fences. In this paper, we describe how we can exploit this synergy by creating a seamless network of UAVs and UGVs. The keys to this are our framework and algorithms for search and localization, which are easily scalable to large numbers of UAVs and UGVs and are transparent to the specificity of individual platforms. We describe our experimental testbed, the framework and algorithms, and some results

Testing is an essential part of any aero engine development programme. Combinations of flight and safety critical hardware and software are tested on various platforms before integrating on engine. Extensive tests are carried out to exercise the engine in various modes to ensure reliable performance. One of the vital element of on board safety critical embedded controller software is control algorithms also known as Control Law (CLAW). The Control Laws are coded in C language by the Software House and are extensively tested with the participation of the Independent Verification and Validation (IV & V) group. Various validation techniques are emoloyed before onboard safety critical software flies. A method known as Non- Real Time (NRT) testing is adopted to test the on board safety critical code. In this paper a new approach to conduct NRT testing is addressed. This method helped engine house for formal clearance of onboard safety critical software. The new approach i.e. Gray Box Non-Real Time (NRT) Testing methodology is deployed to cater various tests (normal & Stress) on the Target Control Law (On-board Software). It is a Gray-Box- End to End functionality testing technique without any execution time constraint (Frame by Frame execution) which allows testing of Target Control Law (On-board Software) with static/dynamic inputs, which could cause a system failure and trap the defect.

Starting with early 1960's a new approach has been followed by researchers and specialists in developing instructional applications. This new approach was related to the use, as an experiment, of the Natural Language Processing (NLP) in the development of next generation of instructional software. Soon, the experiment has became a reality and a necessity in the context that the quantity of information which had to be processed by students, regardless the domain or discipline, has increased considerably. One of the main goals chased constantly by the researchers and specialists in NLP was related to the improvement of the systems, methods, and techniques used for students' knowledge assessment using NLP facilities. A great opportunity to reach valuable results has arisen once the Intelligent Tutoring Systems (ITS) have been considered into the equation. Taking into consideration the ITS declared purposes to address instructional specific activities such as, teaching, learning, performance assessment and feedback generation/communication/analysis, a merge of the ITS and NLP took place and this merge was in the evident benefit of both, teachers and students. Of course, in all these changes a central role has been played by the progress related to the Information and Communication Technologies (ITC) and mainly by the development of few critical hardware and software components, such as, computers, mobile devices, operating systems for these devices and programming languages. This paper is presenting the author proposal of an automatic system for generating questions and performing the analysis of the students' answers, the system being encapsulated in an ITS using NLP and which is applicable to the Computers Programming and C language discipline. Also, the author will present briefly the algorithm used for the development of the proposed system, with the primary target to detect the incorrect answers based on off-topic/on-topic method.

Orthogonal discrete frequency coding waveform design based on chaos

Orthogonal waveforms with good correlation properties are required for target detection in MIMO radar. In this paper, a waveform optimization method for the phase-coded orthogonal frequency division multiplexing (PC-OFDM) signal is proposed. The pulse compression property of the spatial synthesized PC-OFDM signal is firstly analyzed by theoretical derivation. According to the analysis results, the frequency step of PC-OFDM signals is proved to be critical for the high sidelobes. So we optimize the frequency steps of PC-OFDM waveforms by utilizing the sequential quadratic programming (SQP) algorithm to obtain a better sidelobe distribution. Compared with the conventional waveform, the spatial synthesized signals of the optimized waveforms have much better pulse compression properties. Numerical results validate the effectiveness and superiority of the waveform optimization method.

SpChar: Characterizing the sparse puzzle via decision trees

While much of the technology associated with wireless smart sensors (WSS) has been available for over a decade, only a limited number of full-scale implementations have been realized for civil infrastructure, primarily due to the lack of critical hardware and software elements. Using the Imote2, a flexible WSS framework has been developed for full-scale, autonomous structural health monitoring (SHM) that integrates the necessary software and hardware elements, while addressing key implementation requirements for civil infrastructure. This paper discusses the recent advances in the development of this WSS framework and extensions to structural control. Their successful implementations at full-scale for SHM of the 2nd Jindo Bridge in South Korea and the Government Bridge at the Rock Island Arsenal in Illinois, USA, as well as for wireless control of a lab-scale structure are presented.

The Formation Flying Test Bed (FFTB) at NASA Goddard Space Flight Center (GSFC) is being developed as a modular, hybrid dynamic simulation facility employed for end-to-end guidance, navigation, and control (GN&C) analysis and design for formation flying clusters and constellations of satellites. The FFTB will support critical hardware and software technology development to enable current and future missions for NASA, other government agencies, and external customers for a wide range of missions, particularly those involving distributed spacecraft operations. The initial capabilities of the FFTB are based upon an integration of high fidelity hardware and software simulation, emulation, and test platforms developed at GSFC in recent years; including a high-fidelity GPS simulator which has been a fundamental component of the Guidance, Navigation, and Control Center's GPS Test Facility. The FFTB will be continuously evolving over the next several years from a tool with initial capabilities in GPS navigation hardware/software-in-the-loop analysis and closed loop GPS-based orbit control algorithm assessment to one with cross-link communications and relative navigation analysis and simulation capability. Eventually the FFTB will provide full capability to support all aspects of multi-sensor, absolute and relative position determination and control, in all (attitude and orbit) degrees of freedom, as well as information management for satellite clusters and constellations. In this paper we focus on the architecture for the FFTB as a general GN&C analysis environment for the spacecraft formation flying community inside and outside of NASA GSFC and we briefly reference some current and future activities which will drive the requirements and development.

Mobile computing has emerged as a pervasive technology that empowers its users with portable computation and context-aware communication. Smart systems and infrastructures can exploit portable and context-aware computing technologies to provide any time, any place digitized services on the go. Despite the offered benefits, such as portability, context-sensitivity, and high connectivity, mobile computing also faces some critical challenges. These challenges include resource poverty as well as data security and privacy that need to be addressed to increase the pervasiveness of mobile systems. We propose to provide a self-protection mechanism for mobile devices against the unforeseen security threats that can attack the critical resources of mobile devices. We have unified the concepts of autonomic computing and computer security to develop a framework that enables adaptive security to dynamically configure the security measures of a mobile device. We have developed a framework - an android-based prototype - that supports automation and user decision to protect the critical hardware and software resources of a device. Evaluation results demonstrate (i) framework’s accuracy for runtime detection and minimization of threats, and (ii) framework’s efficiency for device’s resource utilization.

A novel application of time-modulated arrays to multiple-input-multiple-output (MIMO) radar is presented and studied. The proposed scheme is to partition the transmit antenna of MIMO radar to a number of time-modulated subarrays that are overlapped. A series of orthogonal waveforms are emitted by these time-modulated subarrays with the unidirectional phase center motion time scheme. The resulting system can be referred to as subarrayed time-modulated MIMO (STM-MIMO) radar. As the tradeoff of conventional phased-array and MIMO radars, the STM-MIMO radar can obtain the coherent processing gain and waveform diversity gain simultaneously. The performance in terms of output signal-to-interference-plus-noise ratio and transmit/receive beampattern for the STM-MIMO radar is highlighted and compared to that of phased-array and MIMO radars. Simulation results validate the effectiveness of the proposed STM-MIMO radar technique.

The USA Air Force came to the conclusion in a 1995 migration to space study that there are no technical impediments to moving tactical surveillance radars to space. The main issue is the high cost of current space system designs $the Air Force must develop technologies that make these systems more affordable. Several examples of cost-effective satellite systems have been demonstrated in recent years: the most notable being the Iridium communications constellation. With this motivation, the enabling technologies for a new class of surveillance radar satellites for ground and airborne moving targets is being examined. A timetable for this development was set with the objective of technology readiness by 2005 for the ground surveillance mission, and 2010 for the air surveillance mission. This paper outlines the methodology and rationale for the critical enabling technologies needed for space based radar.