• Journal of Astronomy and Space Sciences
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• v.38 no.4
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• pp.217-227
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• 2021

In this study, we describe an analytical process for designing a low Earth orbit constellation for discontinuous regional coverage, to be used for a surveillance and reconnaissance space mission. The objective of this study was to configure a satellite constellation that targeted multiple areas near the Korean Peninsula. The constellation design forms part of a discontinuous regional coverage problem with a minimum revisit time. We first introduced an optimal inclination search algorithm to calculate the orbital inclination that maximizes the geometrical coverage of single or multiple ground targets. The common ground track (CGT) constellation pattern with a repeating period of one nodal day was then used to construct the rest of the orbital elements of the constellation. Combining these results, we present an analytical design process that users can directly apply to their own situation. For Seoul, for example, 39.0° was determined as the optimal orbital inclination, and the maximum and average revisit times were 58.1 min and 27.9 min for a 20-satellite constellation, and 42.5 min and 19.7 min for a 30-satellite CGT constellation, respectively. This study also compares the revisit times of the proposed method with those of a traditional Walker-Delta constellation under three inclination conditions: optimal inclination, restricted inclination by launch trajectories from the Korean Peninsula, and inclination for the sun-synchronous orbit. A comparison showed that the CGT constellation had the shortest revisit times with a non-optimal inclination condition. The results of this analysis can serve as a reference for determining the appropriate constellation pattern for a given inclination condition.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.3
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• pp.1260-1283
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• 2019

Low earth orbit (LEO) satellite broadband network is a crucial part of the space information network. LEO satellite constellation design is a top-level design, which plays a decisive role in the overall performance of the LEO satellite network. However, the existing works on constellation design mainly focus on the coverage criterion and rarely take network performance into the design process. In this article, we develop a unified framework for constellation optimization design in LEO satellite broadband networks. Several design criteria including network performance and coverage capability are combined into the design process. Firstly, the quality of service (QoS) metrics is presented to evaluate the performance of the LEO satellite broadband network. Also, we propose a network stability model for the rapid change of the satellite network topology. Besides, a mathematical model of constellation optimization design is formulated by considering the network cost-efficiency and stability. Then, an optimization algorithm based on non-dominated sorting genetic algorithm-II (NSGA-II) is provided for the problem of constellation design. Finally, the proposed method is further evaluated through numerical simulations. Simulation results validate the proposed method and show that it is an efficient and effective approach for solving the problem of constellation design in LEO satellite broadband networks.

• Journal of the Korea Institute of Military Science and Technology
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• v.23 no.2
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• pp.125-138
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• 2020

One of the most important steps to consider in utilizing micro-satellites for surveillance or reconnaissance operations is the design of the satellite constellation. The Walker-Delta constellation which is commonly used in designing satellite constellations is not ideal for this operation in which military satellites are required to monitor specific regions continuously in a stable manner. This study aims to discuss the methodology for designing a satellite constellation that is capable of monitoring the fixed region at the fixed time each day by using the Sun synchronous Orbit. The BB(Beach Ball) constellation that we propose outperforms the Walker-Delta constellation in terms of robustness and it holds the merit of being simple in its design, thereby making future expansions more convenient. We expect the BB constellation will have a high applicability as the operational concept of military surveillance satellites is established in the near future.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.2
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• pp.334-343
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• 2017

The optimum design of an SAR (Synthetic Aperture Radar) satellite constellation is developed herein using a genetic algorithm. The performance of Earth observations using a satellite constellation can be improved by minimizing the maximum revisit time. Classical orbit design using analytic methods has limitations when addressing orbit dynamics due to various disturbances. To overcome this issue, an optimization technique based on a genetic algorithm is used. STK (Systems Tool Kit) is utilized to propagate the satellite orbit when considering external disturbances, and the maximum revisit time on the earth observation area is calculated. By minimizing the performance index using a genetic algorithm, the optimum orbit of the satellite constellation is designed. Numerical results are provided to demonstrate the performance of the proposed method.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.6
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• pp.401-412
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• 2022

In this study, we investigated the design methods of satellite constellations to conduct near-real-time surveillance reconnaissance of the Korean Peninsula. Also, we designed satellite constellations utilizing the Walker-Delta method and repeat-ground-track method, and taking into account the target area and the feasible number of satellites. The constrains of the Electro-Optical and Synthetic Aperture Radar equipment were also considered in performance analysis. As a result, the designed constellation has mean revisit time of less than 30 min which enables near-real-time surveillance reconnaissance of the Korean Peninsula. This research provides the strategy to design the satellite constellation for reconnaissance. Furthermore, it contributes to suggesting an operating strategy for micro-satellites constellation and guidelines for establishing space force.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.1
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• pp.54-62
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• 2017

For the Earth observation satellite for ISR mission, a satellite constellation can be utilized to observe a specific area periodically and ultimately increase the effectiveness of the mission. The Walker-Delta method was applied to design constellation orbits with four satellites, which could detect abnormal activities in AoI(Area of Interest). To evaluate the effectiveness of the mission, a revisiting time was selected as a key requirement. This paper presents the mission analysis process for four SAR satellites constellation as well as the result of constellation configuration design to meet the requirements. Figure of Merits analysis was performed based on algorithm developed. Finally, it was confirmed that the constellation orbit with four different orbital planes is likely to be appropriate for ISR mission.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.3
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• pp.398-404
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• 2020

In this paper, we propose a new design method of signal constellation of the spiral quadrature amplitude modulation (QAM) exploiting a modified gradient descent search algorithm and its binary mapping rule. Unlike the conventional method, the new method, which uses and the constellation optimization algorithm and the maximum number of iterations as a parameter for the iterative design, is more robust to phase noise. And the proposed binary mapping rule significantly reduces the average Hamming distance of the spiral constellation. As a result, the proposed spiral QAM constellation has much improved error performance compared to the conventional ones even in a very severe phase noise environment. It is, therefore, considered that the proposed QAM may be a useful modulation format for coherent optical communication systems and orthogonal frequency division multiplexing (OFDM) systems.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.8
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• pp.65-69
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• 2012

We introduce a rotated square QAM constellation with low peak-to-average-power ratio (PAPR) for coordinate interleaved orthogonal design (CIOD). The proposed signal constellation has much lower PAPR than the ordinary square QAM constellations for CIOD while it keeps almost the same coordinate product distance (CPD).

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.10
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• pp.2149-2156
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• 2011

In this paper, design of a new 3-dimensional (3-D) 16-ary signal constellation with constant envelope is presented and analyzed. Unlike the conventional 16-ary constellations, all signal points of the new constellation are uniformly located on the surface of a sphere so that they have a unique amplitude level and a symmetrical structure. When average power of the constellations is normalized, the presented 16-ary constellation has around 11.4% increased minimum Euclidean distance (MED) as compared to the conventional ones that have non-constant envelope. As a result, a digital communication system which exploits the presented constellation has 1.2dB improved symbol error rate (SER). While signal points of the conventional constant-envelope constellation are not distributed uniformly on the surface of a sphere, those of the proposed constellation has a completely symmetric distribution. In addition, the new signal constellation has much lower computational complexity for practical implementation than the conventional one. Hence, the proposed 3-D 16-ary signal constellation is appropriate for the application to a communication system which strongly requires a constant-envelope characteristic.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.2
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• pp.91-102
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• 2021

In this paper, a fully reconfigurable Software Defined Radio (SDR) for multi-constellation and multi-frequency Global Navigation Satellite System (GNSS) receivers is presented. The reconfigurability with respect to the data structure, variability of signal and receiver parameters, and receiver's internal functionality is presented. The configuration file, that is modified to lead to an entirely different operation of the SDR in response to specific target signal scenarios, directly determines the operating characteristics of the SDR. In this manner, receiver designers can effectively reduce the effort to develop many different combinations of multi-constellation and/or multi-frequency GNSS receivers. Finally, the implementation of the presented fully reconfigurable SDR is included with the experimental processing results such as acquisition, tracking, navigation for the received signals in the realistic fields.