OFDM based low-complexity time of arrival estimation in active sonar

Khyam, MO ORCiD: 0000-0002-1988-2328Estimation of bottom profile is one of the important geo-acoustic reversal problems in underwater acoustics that gives an idea about depth and structure of the sub-bottom layers of the ocean. Estimation of time of arrival (TOA) of bottom and sub-bottom reflections are the key to these estimations. To estimate TOAs from different bottom layers, an active sonar transmits a signal and receive its bottom reflections. In the literature, chirp, a frequency modulated signal is described as the best candidate for the transmitted signal. In this paper, it is shown that an orthogonal frequency modulated (OFDM) signal can also be used as a strong candidate for transmitted signal in active sonar. The proposed OFDM based TOA estimation technique is expected to give superior results in terms of complexity, parallelism, noise reduction and memory requirement compared to the existing chirp based technique

Integrating a brain into a bat robot

Khyam, MO ORCiD: 0000-0002-1988-2328The sophisticated biosonar systems of horseshoe bats have enabled these animals to navigate and pursue prey in complex environments. A conspicuous peripheral dynamics in which the animals' noseleaves and pinnae change during biosonar behaviors could play an important role in enabling these capabilities. It may be hypothesized that for the integration between peripheral dynamics and neural signal processing/estimation to be maximally effective, the periphery should be controlled by feedback from the output of the subsequent neural echo processing. In the way, the specifics of sensory information encoding in the periphery could be controlled based on the needs of the neural signal processing. As a first step towards such an integration in a biomimetic sonar head, a computational model for the inner ear and the auditory nerve's spike code has been integrated with a dynamic periphery that—like the computational models—mimics horseshoe bats. For each model stage, alternative versions with different levels of complexity have been implemented to test how module complexity and the values of the associated parameters affect the capacity of the echo representation to encode sensory information. These effects have been tested based on a large dataset of 220 000 echoes collected in natural forest environments

Information-theoretic evaluation of brain-inspired sonar signal representation

Khyam, MO ORCiD: 0000-0002-1988-2328Many bat species, such as horseshoe bats, move their external auditory periphery (noseleaf and pinnae) during emission/reception of their biosonar signals. This peripheral dynamics has already been shown to enhance sensory information encoding at the level of the analog echo waveforms. However, the bats' brains do not process any analog waveforms directly but rely on spike codes generated in the auditory nerve instead. Hence, it is desirable to evaluate the effect of the peripheral dynamics at the level of these spike codes. As input for this analysis, natural foliage echoes akin to the forest environments experienced by bats were recorded using a biomimetic robot with a dynamic periphery similar to that of horseshoe bats. The echoes were converted into neural spike trains through a signal-processing model of the bats' cochlea/auditory nerve. The effect of the dynamic periphery was then investigated using information-theoretic techniques. As a first step, entropy was estimated to quantify coding capacity. The results showed an increased entropy within signals corresponding to a dynamic periphery when compared to a static periphery. For the next steps, the variability in characteristic spike train features such as spike timing, spike rates, and spike intervals will be characterized with additional information-theoretic methods

Biomimetic spike representation for the encoding of sonar signals

Khyam, MO ORCiD: 0000-0002-1988-2328Biosonar echoes received by bats in their natural habitats are short, highly time-variant acoustic waveforms. Because of these signals properties, the way in which the bats' auditory nerve represents the echoes could be a model for how sparse neural time-code can capture salient signal features. Here, the spike-encoding of natural echoes has been studied based on a large data set containing about 220 00 echoes that were collected by hand-carrying a biomimetic robotic sonar head through forest environments. The sonar head was equipped with flexible noseleaf and pinna shapes that could deform during pulse emission/echo reception in a similar fashion to what horseshoe bats do. This peripheral dynamics was turned on for half of the recoded echoes and turned off for the other half. The echo waveforms were transformed into spike trains using two spike-generation models, each with different levels of complexity: The simplest version was a “leaky integrate-and-fire model"; in the more complex version, a response kernels was added to model the refractory behavior of the neurons. The input to the spike generation models were the outputs of three different basiliar membrane models of varying complexity levels. The coding capacity of the spike trains has been evaluated using information-theoretic methods

Robust welding seam tracking and recognition

Khyam, MO ORCiD: 0000-0002-1988-2328In the process of automatic welding based on structured light vision, the precise localization of the welding seam in an image has an important influence on the quality of the welding. However, in practice, there is much interference, such as spatter and arc, which introduces great challenges for accurate welding seam localization. In this paper, we considered welding seam localization problem as visual target tracking and based on that, we proposed a robust welding seam tracking algorithm. Prior to the start of welding, the seam is separated using a cumulative gray frequency, which is utilized to adaptively determine the initial position and size of the search window. During the welding process, large seam motion range may result in only a portion of the welding seam exists in the search window. To prevent that, a tracking-by-detection method is used to calculate the location of the search window. Usually, the intersection of seam and noise, e.g., spatter, has a severe influence on the accuracy of feature points localization. In order to solve this problem, a sequence gravity method (SGM) for extracting a smoother center line of welding seam is proposed, which is able to reduce the impact of interference. The double-threshold recursive least square method is used to fit the curve obtained by SGM with the aim of improving the real-time performance and accuracy of the system. Finally, the superiority of the proposed algorithm is well demonstrated by comparison with other solutions for seam tracking and recognition through extensive experiments

The acoustic world of bat biosonar

Khyam, MO ORCiD: 0000-0002-1988-2328Bats and toothed whales (odontocetes) have both independently evolved sophisticated biosonar systems. This raises the question how similar the functional principles of these systems are. Could, for example, insights gained from bats be assumed to hold for odontocetes or vice versa? Could both systems be lumped together as a single source of inspiration for novel engineering approaches to sonar sensing? Similarities and differences between the biosonar systems of bats and odontocetes are likely to depend on the respective acoustic environments in which these systems have evolved as well as on the evolutionary starting points and capabilities for adaptations of these two very different phylogenetic groups. In this presentation, the focus will be on comparing the acoustic environments of bats and odontocetes. The acoustics of biosonar sensing can be organized into three different aspects: (i) the properties of the propagation medium, (ii) the geometry and material of the boundaries that limit the propagation channel (this includes targets of interest and clutter), and (iii) the time-frequency and spatial properties of the sources. In this presentation, these aspects will be reviewed for the in-air biosonar of bats. In the companion talk, the same will be done for the underwater biosonar of the odontocetes

Energy harvesting two-way relaying with antenna selection scheme

Khyam, MO ORCiD: 0000-0002-1988-2328This study investigates the performance of a bidirectional/two-way relaying scheme with an energy-harvesting relay while amplify-and-forward relaying is performed. With multiple antennas at the relay, the authors propose the use of the max- min antenna selection scheme in the context of an energy harvesting scenario. They show that the proposed scheme attains diversity gain, whereby its end-to-end symbol error probability performance improves with increments in the number of energy harvesting relay antennas. For limited battery capacity at the energy harvesting node, they derive the lower bound of the outage probabilities and observe a good match between the analytical and simulated results. For this scenario, a simple power provisioning technique is proposed to optimise the end nodes' transmission powers. It is observed that the proposed technique saves significantly more transmission energy than the conventional equal power provisioning technique

A robust welding seam identification method

Khyam, MO ORCiD: 0000-0002-1988-2328As an automatic welding process may experience some disturbances caused by, e.g., splashes and/or welding fumes, misalignments/poor positioning, thermally induced deformations, strong arc lights, diversified welding joints/grooves, etc., precisely identifying the welding seam has an great influence on the welding quality achieved. In this paper, a robust method for identifying this seam is proposed. Firstly, after a welding image obtained from a/the structured-light vision sensor is filtered, in a sufficiently small area, the extended Kalman filter (EKF) is used to search for the/its laser stripe in order to prevent possible disturbances. Secondly, to realize the extraction of the profile of welding seam, the least square method is used to fit a sequence of centroids determined by the scanning result of columns displayed on the tracking window. Thirdly, this profile is then qualitatively described and matched using a proposed character string method. Finally, the advantages of this method are compared with those of other approaches through repeated experiments

Multiple access chirp-based ultrasonic positioning

Khyam, MO ORCiD: 0000-0002-1988-2328Distance-based ultrasonic positioning systems (UPSs) using trilateration have been adopted in various types of applications across a wide variety of fields. Recently, the use of a chirp signal in conjunction with cross correlation has drawn a considerable amount of attention for UPSs. However, when a chirp signal is used for positioning, these algorithms suffer from problems due to signal interference. In this paper, to solve this problem, we propose using four sets of orthogonal chirps, each of which contains three waveforms. The first three sets use chirp rates as a mechanism for assigning uniquely modulated chirp signals to transmitters while the basic idea behind the last one is to exploit the orthogonality of the subcarriers of a chirp waveform, i.e., the discrete frequency components of a chirp waveform. All the waveforms contained in each set have good orthogonality (i.e., the waveforms contained in sets 1 to 3 and set 4 are, respectively, quasi-orthogonal and perfectly orthogonal) and also have all the advantages of a classic chirp waveform. First, the performance of the waveforms is investigated through correlation analysis and then, in an indoor environment, evaluated through simulations and experiments for ultrasonic positioning. For sets 1 to 4, for an operational range of approximately 1000 mm, the positioning root-mean-square-errors 90% error were 6.20 9.13 mm, 6.05 8.90 mm, 7.38 10.85 mm, and 4.54 6.68 mm, respectively

Pseudo-orthogonal chirp-based multiple ultrasonic transducer positioning

Khyam, MO ORCiD: 0000-0002-1988-2328Distance-based ultrasonic positioning systems (UPSs) using the trilateration algorithm have been adopted in various types of applications across a wide variety of fields. Recently, the use of a chirp signal in conjunction with cross-correlation has drawn a considerable amount of attention for UPSs. However, when they use a chirp signal for positioning, they suffer from the multiple-access problem due to signal interference. In this paper, to solve this problem, we propose two sets of pseudo-orthogonal chirp waveforms. The basic idea behind the first one is to exploit the orthogonality of the sub-carriers of a chirp waveform, i.e., the discrete frequency components of a chirp waveform, whereas the second one not only exploits the orthogonality of the sub-carriers of a chirp waveform but also chirp rates as a mechanism for assigning uniquely modulated chirp signals to the transmitters. All the waveforms contained in each set have good orthogonality and all the advantages of a classic chirp waveform. First, the performances of the waveforms are investigated through correlation analysis and then, in an indoor environment, evaluated through simulations and experiments for ultrasonic positioning