Minimum Collision Probability Research Articles

Combined Global and Local Search for Optimization with Gaussian Process Models

Gaussian process (GP) model based optimization is widely applied in simulation and machine learning. In general, it first estimates a GP model based on a few observations from the true response and then uses this model to guide the search, aiming to quickly locate the global optimum. Despite its successful applications, it has several limitations that may hinder its broader use. First, building an accurate GP model can be difficult and computationally expensive, especially when the response function is multimodal or varies significantly over the design space. Second, even with an appropriate model, the search process can be trapped in suboptimal regions before moving to the global optimum because of the excessive effort spent around the current best solution. In this work, we adopt the additive global and local GP (AGLGP) model in the optimization framework. The model is rooted in the inducing points based GP sparse approximations and is combined with independent local models in different regions. With these properties, the AGLGP model is suitable for multimodal responses with relatively large data sizes. Based on this AGLGP model, we propose a combined global and local search for optimization (CGLO) algorithm. It first divides the whole design space into disjoint local regions and identifies a promising region with the global model. Next, a local model in the selected region is fit to guide detailed search within this region. The algorithm then switches back to the global step when a good local solution is found. The global and local natures of CGLO enable it to enjoy the benefits of both global and local search to efficiently locate the global optimum. Summary of Contribution: This work proposes a new Gaussian process based algorithm for stochastic simulation optimization, which is an important area in operations research. This type of algorithm is also regarded as one of the state-of-the-art optimization algorithms for black-box functions in computer science. The aim of this work is to provide a computationally efficient optimization algorithm when the baseline functions are highly nonstationary (the function values change dramatically across the design space). Such nonstationary surfaces are very common in reality, such as the case in the maritime traffic safety problem considered here. In this problem, agent-based simulation is used to simulate the probability of collision of one vessel with the others on a given trajectory, and the decision maker needs to choose the trajectory with the minimum probability of collision quickly. Typically, in a high-congestion region, a small turn of the vessel can result in a very different conflict environment, and thus the response is highly nonstationary. Through our study, we find that the proposed algorithm can provide safer choices within a limited time compared with other methods. We believe the proposed algorithm is very computationally efficient and has large potential in such operational problems.

Analytical Framework for Space Debris Collision Avoidance Maneuver Design

An analytical formulation for collision avoidance maneuvers involving a spacecraft and a space debris is presented, including solutions for the maximum deviation and minimum collision probability cases. Gauss’s planetary equations and relative motion equations are used to map maneuvers at a given time to displacements at the predicted close approach. The model is then extended to map changes in state between two times, allowing one to propagate covariance matrices. The analytical formulation reduces the optimization problem to an eigenproblem, for both maximum deviation and minimum collision probability. Two maximum deviation cases, total deviation and impact parameter, are compared for a large set of spacecraft–debris conjunction geometries derived from European Space Agency’s Meteoroid and Space Debris Terrestrial Environment Reference (MASTER-2009) model. Moreover, the maximum impact parameter and minimum collision probability maneuvers are compared assuming covariances known at the maneuver time, to evaluate the net effect of lead time in collision probability. In all cases, solutions are analyzed in the b-plane to leverage its natural separation of phasing and geometry change effects. Both uncertainties and maximum deviation grow along the time axis for long lead times, limiting the reduction in collision probability.

Introducing MISS, a new tool for collision avoidance analysis and design

The core aspects and latest developments of Manoeuvre Intelligence for Space Safety (MISS), a new software tool for the analysis and design of collision avoidance manoeuvres involving a spacecraft and a space debris, are presented. The tool leverages analytical and semi-analytical methods for the efficient modelling of the orbit modifications due to different control strategies, such as impulsive or low-thrust manoeuvres, and maps them into displacements at the nominal close approach using relative motion equations. B-plane representations are then used to separate the phasing-related and geometry-related components of the displacement. Both maximum miss distance and minimum collision probability collision avoidance manoeuvres are considered. The tool also allows for the computation of state transition matrices and propagation of uncertainties. Several test cases are provided to assess the capabilities and performance of the tool.

Analysis of MAC Protocol for Reliable Broadcast

In wireless communication It is important to find a reliable broadcasting protocol that is especially designed for an optimum performance of public-safety and data travelling related applications. Using RSU and OBU, there are four novel ideas presented in this research work, namely choosing the nearest following node as the network probe node, headway-based segmentation, non-uniform segmentation and application adaptive. The integration of these ideas results in a protocol that possesses minimum latency, minimum probability of collision in the acknowledgment messages and unique robustness at different speeds and traffic volumes. Wireless communications are becoming the dominant form of transferring information,and the most active research field. In this dissertation, we will present one of the most applicable forms of Ad-Hoc networks; the Vehicular Ad-Hoc Networks (VANETs). VANET is the technology of building a robust Ad-Hoc network between mobile vehicles and each other, besides, between mobile vehicles and roadside units.

Application of time dependent probabilistic collision state checkers in highly dynamic environments.

When computing the trajectory of an autonomous vehicle, inevitable collision states must be avoided at all costs, so no harm comes to the device or pedestrians around it. In dynamic environments, considering collisions as binary events is risky and inefficient, as the future position of moving obstacles is unknown. We introduce a time-dependent probabilistic collision state checker system, which traces a safe route with a minimum collision probability for a robot. We apply a sequential Bayesian model to calculate approximate predictions of the movement patterns of the obstacles, and define a time-dependent variation of the Dijkstra algorithm to compute statistically safe trajectories through a crowded area. We prove the efficiency of our methods through experimentation, using a self-guided robotic device.

Joint Cooperative Routing and Power Allocation for Collision Minimization in Wireless Sensor Networks With Multiple Flows

In this letter, a cross-layer cooperative routing algorithm is proposed for minimizing the collision probability subject to an end-to-end outage probability constraint. We develop a collision minimization algorithm by combining cooperative transmission, optimal power allocation, and route selection. The proposed cooperative routing algorithm, called minimum collision cooperative routing (MCCR), selects the route that causes minimum collision probability to other nodes in the network. Results show that MCCR can significantly reduce the collision probability compared with existing cooperative routing schemes.

An efficient and dynamic backoff algorithm for IEEE 802.11 networks

Performance of Wireless LAN can be improved at each layer of the protocol stack with respect to energy efficiency. The Media Access Control layer is responsible for the key functions like access control and flow control. During contention, Backoff algorithm is used to gain access to the medium with minimum probability of collision. After studying different variations of backoff algorithms, a new variant called History based Probabilistic Backoff Algorithm is proposed. Mathematical analysis and simulation results using NS-2 with parameters like retransmission counts, saturated throughput, transmission delay, different data sizes and different traffic patterns was carried out. It is seen that proposed History based Probabilistic Backoff algorithm outperforms the other backoff algorithms.

HISTORY BASED PROBABILISTIC BACKOFF ALGORITHM

Performance of Wireless LAN can be improved at each layer of the protocol stack with respect to energy efficiency. The Media Access Control layer is responsible for the key functions like access control and flow control. During contention, Backoff algorithm is used to gain access to the medium with minimum probability of collision. After studying different variations of back off algorithms that have been proposed, a new variant called History based Probabilistic Backoff Algorithm is proposed. Through mathematical analysis and simulation results using NS-2, it is seen that proposed History based Probabilistic Backoff algorithm performs better than Binary Exponential Backoff algorithm.

Performance Analysis of Optimum Interleaver based on Prime Numbers for Multiuser Iterative IDMA Systems

In recently proposed multiple access techniques like IDMA and OFDM-IDMA, the user separation is done by user specific interleavers in contrast to the conventional CDMA scheme, where user separation is assured with user-specific signature sequences. The user specific interleavers must demonstrate minimum probability of collision amongst each other in addition to other merits, including minimal consumption of bandwidth, least hardware for their generation, and least memory requirement. In this paper, the authors propose an interleaver based on prime numbers for the generation of user specific interleavers to remove the problem of high consumption of bandwidth. The simulation results demonstrate the optimal performance of prime interleaver (PI), which is based on prime numbers, apart from other merits in comparison to random and other interleavers.

The Effect of Type and Dosage of Frothers on Coarse Particles Flotation

Frothers have a profound effect on bubble size and also flotation efficiency. In present study the effect of type and dosage of frothers on the flotation response of coarse particles of quartz was investigated. Therefore, flotation response of coarse particles using frothers such as MIBC, pine oil, poly propylene glycol with concentration of 0, 25, 50 and 75 g/t, was obtained respectively. For all used frothers, maximum recovery was obtained around frother dosage of 25 g/t and with increasing frother dosage, flotation recovery decreased. With increasing frother dosage, bubble diameter, d32, decreased and when Poly Propylene Glycol, MIBC and Pine Oil were used as frother, bubble diameter increased. Maximum bubble diameter was obtained around Pine Oil and frother dosage of 25 g/t and minimum bubble diameter was obtained around Poly Propylene Glycol and frother dosage of 75 g/t. As the particle size increased, the probability of collision increased and with using Poly Propylene Glycol, MIBC and Pine Oil, probability of collision increased, respectively. Maximum collision probability was obtained around 65.46 % with Poly Propylene Glycol dosage of 75 g/t and particle size of 545 microns and minimum collision probability was obtained around 1.43 % with Pine Oil dosage of 25 g/t and particle size of 256 microns.

The effect of hydrodynamic parameters on probability of bubble–particle collision and attachment

In this study the dependence of the impeller speed on the particle size variation was investigated on the quartz particles using laboratory mechanical flotation cell. Maximum recovery was obtained at 1100 rpm. For either more quiescent (impeller speed <900 rpm) or more turbulent (impeller speed >1300 rpm) conditions, flotation recovery decreased steadily. Furthermore, amount of collision probabilities is calculated using various equations. According to this study, maximum collision probability was obtained around 48.35% with impeller speed of 1100 rpm, air flow rate of 15 l/h and particle size of 545 μm and minimum collision probability was obtained around 2.43% with impeller speed of 700 rpm, air flow rate of 15 l/h and particle size of 256 μm. Maximum attachment probability was obtained around 44.16% with impeller speed of 1300 rpm, air flow rate of 75 l/h and particle size of 256 μm. With using some frothers such as poly propylene glycol, MIBC and pine oil, probability of collision increased, respectively. Maximum collision probability was obtained around 65.46% with poly propylene glycol dosage of 75 g/t and particle size of 545 μm.