• Journal of Computing Science and Engineering
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• v.7 no.2
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• pp.81-88
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• 2013

In cognitive radio or dynamic spectrum access networks, a rendezvous represents meeting two or more users on a common channel, and negotiating to establish data communication. The rendezvous problem is one of the most challenging tasks in cognitive radio ad hoc networks. Generally, this problem is simplified by using two well-known mechanisms: the first uses a predefined common control channel, while the second employs a channel hopping procedure. Yet, these two mechanisms form a life cycle, when they simplify the rendezvous problem in cognitive radio networks. The main purpose of this paper is to point out how and why this cycle forms.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06d
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• pp.294-296
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• 2012

In cognitive radio ad hoc networks, secondary users need to exchange control information before data transmission. This task is not trivial in cognitive radio networks due to the dynamic nature of environment. This problem is sometime called rendezvous problem of cognitive radio network. The rendezvous problem is normally tackled by using two famous approaches: the use of common control channel (CCC) and using channel hopping (a.k.a sequence-based protocols). However, these two famous solutions form a vicious cycle while solving the rendezvous problem. The main purpose of this paper is to point out how and why this vicious cycle is formed.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.10
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• pp.4738-4753
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• 2018

Efficient rendezvous node selection and routing algorithm (RNSRA) for wireless sensor networks with mobile sink that visits rendezvous node to gather data from sensor nodes is proposed. In order to plan an optimal moving tour for mobile sink and avoid energy hole problem, we develop the RNSRA to find optimal rendezvous nodes (RN) for the mobile sink to visit. The RNSRA can select the set of RNs to act as store points for the mobile sink, and search for the optimal multi-hop path between source nodes and rendezvous node, so that the rendezvous node could gather information from sensor nodes periodically. Fitness function with several factors is calculated to find suitable RNs from sensor nodes, and the artificial bee colony optimization algorithm (ABC) is used to optimize the selection of optimal multi-hop path, in order to forward data to the nearest RN. Therefore the energy consumption of sensor nodes is minimized and balanced. Our method is validated by extensive simulations and illustrates the novel capability for maintaining the network robustness against sink moving problem, the results show that the RNSRA could reduce energy consumption by 6% and increase network lifetime by 5% as comparing with several existing algorithms.

• Convergence Security Journal
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• v.21 no.1
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• pp.209-219
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• 2021

The problem of congestion in the licensed radio channels spectrum can be solved by Cognitive Radio Networks (CRN). Several algorithms exist to ensure the rendezvous between Secondary Users (SUs), they are increasingly efficient, allowing faster rendezvous under multiple scenarios. In parallel, several jamming algorithms are developed to counter rendezvous which are also improving. The goal in CRN is to ensure the rendezvous by warding such jammers with robust algorithms. In this paper, we classify various jamming techniques and analyze the performance of various well-known rendezvous algorithms under jamming attacks.

• Proceedings of the KIEE Conference
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• 2001.11c
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• pp.84-86
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• 2001

A new navigation method is developed and implemented for mobile robot. The mobile robot navigation problem has traditionally been decomposed into the path planning and path following. Unlike tracking-based system, which minimize intercept time and moved mobile robot distance for optimal rendezvous point selection. To research of random moving object uses algorithm of Adaptive Control using Auto-regressive Model. A fine motion tracking object's trajectory is predicted of Auto-regressive Algorithm. Thus, the mobile robot can travel faster than the target wi thin the robot's workspace. The can select optimal rendezvous point of various intercept time.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.11a
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• pp.125-129
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• 2001

A Software development of space launch vehicle danamics and control simulation is presented in this study. The Dynamics for a two body problem including pertubations for various effect show on this paper. Mission analysis for space launch vehicle is included rendezvous mission. The software develpoment is intended to maintain generality to the extent possible through objected approach for future modification and expansion. This result shows various pertubation effect is also important.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.11
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• pp.1072-1078
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• 2008

An adaptive control algorithm for spacecraft rendezvous and docking in a Keplerian orbit is presented. The equations of relative motion of two spacecrafts expressed in a local-vertical-local-horizontal rectangular frame are converted to a general Hamiltonian form, then an adaptive control method developed for the uncertain Hamiltonian system is applied to the rendezvous and docking problem. A smooth projection algorithm is applied to keep the parameter estimates inside a singularity-free region, and a numerical example shows that the developed controller successfully deals with the unknown mass of the chaser spacecraft.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.3
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• pp.1204-1227
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• 2020

The tradeoff between energy conservation and traffic balancing is a dilemma problem in Wireless Sensor Networks (WSNs). By analyzing the intrinsic relationship between cluster properties and long distance transmission energy consumption, we characterize three node sets of the cluster as a theoretical foundation to enhance high performance of WSNs, and propose optimal solutions by introducing rendezvous and Mobile Elements (MEs) to optimize energy consumption for prolonging the lifetime of WSNs. First, we exploit an approximate method based on the transmission distance from the different node to an ME to select suboptimal Rendezvous Point (RP) on the trajectory for ME to collect data. Then, we define data transmission routing sequence and model rendezvous planning for the cluster. In order to achieve optimization of energy consumption, we specifically apply the economic theory called Diminishing Marginal Utility Rule (DMUR) and create the utility function with regard to energy to develop an adaptive energy consumption optimization framework to achieve energy efficiency for data collection. At last, Rendezvous Transmission Algorithm (RTA) is proposed to better tradeoff between energy conservation and traffic balancing. Furthermore, via collaborations among multiple MEs, we design Two-Orbit Back-Propagation Algorithm (TOBPA) which concurrently handles load imbalance phenomenon to improve the efficiency of data collection. The simulation results show that our solutions can improve energy efficiency of the whole network and reduce the energy consumption of sensor nodes, which in turn prolong the lifetime of WSNs.

• Journal of Astronomy and Space Sciences
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• v.15 no.1
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• pp.221-228
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• 1998

The effect of air drag was researched when a low-earth orbit spacecraft using power-limited thruster rendezvoused another low-earth orbit spacecraft. The air density was assumed to decrease exponentially. The radius of parking orbit was 6655.935km and that of target orbit was 7321.529km. From the trajectories of active vehicles, the fuelconsumption and the magnitude of thrust acceleration, we could conclude that the effect of air drag had to be considered in fuel optimal rendezvous problem between low-earth orbit spacecrafts. In multiple-revolution rendezvous case, the air drag was more effective.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.9
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• pp.775-783
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• 2017

In this paper, an impulsive rendezvous problem by using minimum energy of spacecraft in different orbits is addressed. In particular, the orbits considered in this paper are the general orbits including the elliptic orbit, while most of the orbits considered in the literature have been restricted within co-planar or circular orbits. The constraints for solving this optimization problem are the Kepler's equation formulated with the universal variable, and the final position and velocity of two spacecraft. Also, the Lagrange coefficients, sometimes called as f and g solution, are used to describe the orbit transfer. The proposed method technique is demonstrated through numerical simulation by considering the minimum energy, and both the minimum energy and the wait time, respectively. Finally, it is also verified by comparing with the Hohmann transfer known as the minimum energy trajectory. Although a closed-form solution cannot be obtained, it shows that the suggested technique can provide a new insight to solve various orbital transfer problems.