Performance comparison of different dynamic channel allocation techniques for mobile satellite systems

Different dynamic channel allocation (DCA) approaches based on the evaluation of a cost function are proposed. The scenario considered is low earth orbit and geostationary orbit mobile satellite systems. A suitable user mobility model has been defined to generate interbeam handover requests. Different alternatives to manage interbeam handovers have been investigated. Among them, the most promising solution seems to be the queuing of handover requests. The quality of service parameters that have been considered are: blocking probability for new call arrivals, handover failure probability and the probability of incompletely served call owing to the initial blocking or to the failure of a subsequent handover request. Comparisons among the proposed DCA techniques and the fixed channel allocation technique have been carried out to find a solution that represents a good trade-off between the blocking performance and the required signalling load.

In little more than two decades, communications satellite technology has gone from being revolutionary to commonplace, from an idea to world wide service. In both industrialized and developing countries, economic and social progress depends on improved telecommunications. Like other means of transport, telephones, computers, satellites and fiber optic cables and their proper interfaces are essential for moving commercial goods and services. Benefits of satellite communications should in the 1990's be extended to users in all parts of the world through the use of smaller, inexpensive and less sophisticated Earth stations for two way (voice and data), and one way (video, data) use. While earlier satellite systems have been designed and implemented using C and S band communications with satellites in geostationary orbits (GEO), K band communications using VSATs (Very Small Aperture Terminals) have enabled the communications across areas of the US and the world where extensive telecommunications networks did not exist and/or were not affordable. In addition, several systems have been proposed (being built) to provide for the global communication of the mobile users using clusters of smaller, less complex satellites in low Earth orbit (LEG) and medium Earth orbit (MEO). Mobile satellite systems are the future of the satellite communications technology applications. In this presentation, we will briefly summarize the status for satellite communications and then present a comparison of the enabling mobile satellite communications technologies and mobile satellite systems currently being developed. We will also review applications of these systems in public and commercial areas in this presentation. >

This paper deals with the spectral efficiency comparison between Code Division Multiple Access (CDMA) and a modified version of Packet Reservation Multiple Access (PRMA), called PRMA with Hindering States (PRMA-HS), in a Low Earth Orbit — Mobile Satellite System (LEO-MSS). The same Rice channel model, available bandwidth, source and channel coding, energy per bit, satellite antenna system and satellite constellation altitude have been assumed in both cases. A performance analysis of both CDMA and PRMA-HS has permitted to evaluate their spectral efficiency. We have obtained that PRMA-HS has not a satisfactory performance when the fading margin is low, especially if also the Rice factor is low. Whereas CDMA maintains a certain capacity also for low fading margin values.

A traffic simulator is presented along with various simulation results for an ICO and LEO type constellations. The simulator permits the calculation of the traffic at the satellite footprint and spotbeam level in various instances of the satellites trajectory. By using these traffic simulation results as input to a satellite resource management simulator, the fixed channel allocation (FCA) and the dynamic channel allocation (DCA) techniques were evaluated. Simulations results are presented for the various parameters in both systems.

Today most operational Earth observing satellites reside in low Earth orbits (LEO) at less than 1,000 km altitude, and in geostationary Earth orbits (GEO) at ~35,800 km altitude. These orbits have been the venues of choice for observations, albeit for very different reasons. LEO provides high spatial resolution with low temporal resolution while GEO provides for low spatial resolution, but high temporal resolution. NOAA utilizes both venues for their environmental satellites. The NOAA Polar-orbiting Operational Environmental Satellites (POES) reside in LEO Sun synchronous orbits at approximately 830 km in altitude, as do the Defense Meteorological Satellite Program (DMSP) satellites of the Department of Defense. In the near future the POES and DMSP satellites will be merged into a new satellite system referred to as the National Polar-orbiting Operational Environmental Satellite System (NPOESS). The NOAA Geostationary Operational Environmental Satellite (GOES) system, as the name specifies, resides at the other preferred observational venue of GEO. The Jet Propulsion Laboratory (JPL), under contract to NOAA, has been studying the characteristics of medium Earth orbits (MEO), at altitudes between 1000 and 35,800 km, as an observation venue to answer the question as to whether MEO might capture the attributes of the two traditional venues. This on-going study initially focused on determining the optimal altitude for MEO observations, through numerous trade studies involving altitude, instrument complexity, coverage, radiation environment, data temporality, revisit time, data rates, downlink requirements and other parameters including cost and launch complexity. Once the optimal altitude of 10,400 km had been determined the study proceeded to explore single through multiple MEO satellite constellation performance capabilities using two instrument types, a visible through infrared (IR) imager and IR sounder as the satellites’ payload. The MEO performance capabilities were compared to comparable LEO and GEO satellite constellation capabilities. This portion of the study concluded that indeed for global coverage a constellation of satellites operating in the MEO venue could capture the attributes of those operating in the LEO and GEO venues. Three 8-satellite constellations configurations - Walker, ICO, and Equatorial-Polar (EP) - then were studied to develop more constellation coverage statistics including robustness to individual satellite failure. That study phase concluded that the EP constellation was superior to both the ICO and Walker configurations. The study is presently examining if, and to what extent, the equatorial portion of the EP constellation might provide substantive supplemental data to that collected by the NPOESS and GOES satellite constellations.

Novel strategies for automatic satellite constellation design with satellite diversity and radio resource management are proposed. The automatic satellite constellation design means that some parameters of satellite constellation design can be determined simultaneously. The total number of satellites, the altitude of a satellite, the angle between planes, the angle shift between satellites and the inclination angle are considered in the design. Satellite constellation design is modelled using a multiobjective genetic algorithm. This method is applied to low Earth orbit (LEO), medium Earth orbit (MEO) and hybrid constellations. The use of a genetic algorithm allows automatic satellite constellation design while achieving dual satellite diversity statistics. Furthermore, a strategy for dynamic channel allocation is proposed that uses a genetic algorithm for use in mobile satellite systems (MSS) networks. The main idea behind this algorithm is to use the minimum cost as a metric to provide optimum channel solutions for specified interference constraints. The simulation is designed for a MEO satellite constellation. Using this algorithm, the proposed model outperforms conventional dynamic channel assignment (DCA) schemes in terms of call blocking and call dropping probability. Generally, genetic algorithms are robust to dynamic variations in satellite constellation design and provide resource allocation improvements in DCA in MSS networks.

Due to increasing demand of cellular communication services, determining a spectrum efficient and conflict-free allocation of channel among the cells while satisfying both the interference constrains and the traffic demand, become a NP - hard channel allocation problem. Minimizing call blocking probability may raise interference, which may increase call dropping probability. In order to minimize call blocking probability in presence of co channel and co site interference with varying traffic demand, Genetic Algorithm approach with interference graph based fitness function is proposed. Integer genetic representation allow to select multiple fittest chromosomes in one generation, so less number of generations are required to get the desired output, leading to less computation time. The result shows reduction in call blocking probability, for both Uniform and Non uniform traffic demand, than the reported literature for 49 cell Benchmark problem with Hybrid channel allocation.

Low earth orbit (LEO) satellite system becomes an emerging non-terrestrial network solution for future radio communications. To maximize the system capacity, an LEO satellite could utilize circularly polarized planar antenna array with the frequency reuse technique to form multiple earthmoving beams. With the increasing number of LEO satellites, inline interference from the geosynchronous equatorial orbit (GEO) satellite is an important issue to be resolved when the spectrum resource is shared. With the frequency hopping phenomena in earth-moving LEO networks, the inline interference could be minimized if the GEO users also perform the similar frequency hopping via coordination between LEO and GEO satellite networks. This paper proposes eight spectrum sharing schemes for GEO satellite networks to produce the frequency hopping sequence in earth-moving LEO network. We evaluate the system capacity, fairness between LEO and GEO users, and time costs of all schemes. Simulation results validate the advantage obtained from coordination, and show that the simple greedy scheme performs as good as the optimal scheme due to fixed frequency hopping patterns.

Several existing and emerging applications of Space Situational Awareness (SSA) relate directly to spacecraft Rendezvous, Proximity Operations, and Docking (RPOD) and Formation / Cluster Flight (FCF). Observation correlation of nearby objects, control authority estimation, sensor-track re-acquisition, formation re-conguration feasibility, ‘stuck’ thrusters, and worst-case passive safety analysis are some areas where analytical reachability methods have potential utility. Existing reachability theory is applied to RPOD and FCF regimes. An optimal control policy is developed to maximize the reachability set and optimal control law discontinuities (switching) are examined. Necessary conditions for maximum position reachability are developed, allowing for a reduction in reachable set computation dimensionality. The nonlinear relative equations of Keplerian motion are introduced and used for all reachable position set determinations. The linearized ClohessyWiltshire equations of motion are normalized to accentuate relative control authority for spacecraft propulsion systems at both Low Earth Orbit (LEO) and Geostationary Earth Orbit (GEO). Several examples with traditional and low thrust propulsion systems in LEO and GEO are explored to illustrate the eects of relative control authority on the timevarying reachability set surface using the nonlinear equations of motion. Both monopropellant spacecraft at LEO and Hall thruster spacecraft at GEO are shown to be strongly actuated while Hall thruster spacecraft at LEO are found to be weakly actuated. Weaknesses with the current implementation are discussed and future numerical improvements and analytical eorts are discussed.

Adaptive quality management schemes in Voice over IP (VoIP) Network have a constructive impact on the improvement of voice quality level received by end-users. These schemes are used for persistent monitoring of quality level leading to better management of network services. In this paper, a model is introduced to improve the voice quality level and optimize resource utilization. In the proposed model, the VoIP network makes the decision for configuration adaptively and modifies itself by means of Hidden Markov Model (HMM). Depending on the quality level and consumed bandwidth evaluated in the receiver side this adaptive self-modification takes place. During this procedure, acceptable weights for Quality and Quality of Service (QoS) parameters, namely, End-to-End Delay, Packet Loss, and Jitter are determined. These acquired weights help HMM model predict next optimum state properly. Another important objective of this work is to find a relation between Quality of Experience (in terms of Mean Opinion Score) and Quality of Service (in terms of End-to-End Delay and Jitter) parameters. This mapping provides a tangible understanding of how QoS parameters affect MOS. Simulation results demonstrate that the proposed technique lessens the impact of jitter and packet loss on voice quality level.

The European Space Agency's satellite ARTEMIS will support data links between spacecraft in low earth orbit, ARTEMIS in geostationary orbit and ground stations in Europe. The links between spacecraft in low earth orbit and ARTEMIS will operate at S-band (2 GHz), Ka-band (25 GHz) or optical wavelength (800 nm). This paper addresses the S-band and Ka-band links, which both operate via a steerable 2.85 m diameter reflector antenna on ARTEMIS. The link design has been performed to minimize the signal degradations, and has led to rather demanding requirements on the flatness of the amplitude and group delay distortion versus frequency, on the phase noise and on the linearity of the payload. The measured values for these parameters are presented. In S-band, the antenna pointing is performed in open loop according to a preloaded table, while in Ka-band a closed loop pointing system is implemented and open loop pointing is back-up. The design, test and operation of the antenna pointing system are presented. The European Space Agency (ESA) participates in the Satellite Network Interoperability Panel (SNTP) together with NASA and NASD A. SNTP has established a set of interoperability parameters making it possible for low earth spacecraft from the three agencies to operate through the relay satellites of NASA, NASDA and ESA. ARTEMIS will be the first ESA satellite to offer data relay services, and its performances are compared to the interoperability parameters established by SNIP. Inter Orbit Links Spacecraft in low earth orbit (LEO) are restricted in their ability to communicate with the ground, because of the limited time a spacecraft in LEO is visible from a single ground station. ARTEMIS, located in the geostationary orbit, will significantly increase the communication time between the spacecraft in LEO and a single ground station. This is illustrated in Fig. 1. When a spacecraft is flying over the cross hatched areas in Fig. 1 at 300km altitude, no contact is possible via ARTEMIS. This area is slightly increased for a spacecraft at 1000km altitude as marked by the contour. Spacecraft can maintain contact to ground via ARTEMIS, when they are over SouthAmerica, eastern part of North-America, the Atlantic, Europe, Africa, most of Asia, the Indian Ocean and the polar regions The data relay function is provided by communication links between the ground and ARTEMIS named feeder links and links between ARTEMIS and the LEO spacecraft named inter orbit links (IOL). The feeder link operates at 20 GHz from ARTEMIS to ground (i.e. return feeder link) and at 30 GHz from ground to ARTEMIS (i.e. forward feeder link). The IOL can operate in three different bands namely S-Band (i.e 2.025 to 2.110 GHz for the forward IOL from ARTEMIS to LEO spacecraft and Copyright © 1997 by J. Sandberg. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission.

Line-of-sight communications links between satellites allow data to be transmitted directly from one satellite to another. The different types of links which can be implemented between satellites in geostationary orbit (GSO) and low Earth orbit (LEO), are illustrated. There are two main classes, interorbit links between LEO and GSO satellites, and intersatellite links (ISLs) between satellites which are both in GSO or LEO orbit. This paper is primarily concerned with ISLs between GSO satellites for military communications.

The efficient utilization of limited spectral resources in space presents a significant challenge given the rapidly increasing number of satellites (SATs) in various orbits. To address this challenge, it is paramount to enhance spectral efficiency by facilitating inter-operation between SATs in different orbits. In this letter, we investigate the impact of dynamic spectrum access (DSA) on the spectral efficiency of a SAT network that integrates geostationary (GEO) and low Earth orbit (LEO) SATs. Specifically, in the context of DSA, the secondary LEO SATs can opportunistically reuse the frequency bands originally assigned to primary GEO SATs. To characterize the resultant spectral efficiency in a realistic time-varying SAT network topology, we analyze the signal-to-interference-plus-noise ratio (SINR) at the nadir user of a randomly selected LEO SAT and an upper bound on average throughput of the LEO SAT. Simulation results demonstrate the significant advantages of DSA in enhancing the spectral efficiency of the integrated GEO-LEO SAT network.

Satellites in low Earth orbit (LEO) are accessible to an unprecedented number of users around the globe with numerous applications, especially with the recent rapid development in LEO satellite constellations for communications. Until a few years ago, advanced designs for satellite communications systems had focused on conventional geostationary Earth orbit (GEO) communications technologies which are not necessarily tailored to the LEO environment. Such sub-optimal designs were accommodated by the typical application of LEO satellites-remote sensing satellites-normally being large satellites with ever-increasing power and bandwidth and equipped with large ground stations. These days, the current trend of the satellite industry is towards smaller satellites and smaller terminals, made possible through continuous technological improvement. Advances in sensor and payload technology have permitted rapidly increasing amounts of data to be transferred. This, coupled with user demands for reliable, efficient data delivery from small satellites to even smaller terminals, calls for an urgent need to optimise the LEO communications link, particularly for payload data retrieval.

In recent years, low earth orbit (LEO) satellite constellation systems have been developed rapidly. However, the scarcity of satellite spectrum resources has become one of the major obstacles to this trend. LEO satellite constellation communication systems sharing the spectrum of incumbent geostationary earth orbit (GEO) satellite system is a feasible way to alleviate spectrum scarcity. Therefore, it has practical significance to study the optimization of satellite resources allocation (RA) in a spectrum sharing scenario. This paper focuses on the RA problem that LEO satellites share a GEO high throughput satellite’s spectrum in a beam-hopping (BH) manner. The GEO satellite system is served as the primary system and the LEO satellite constellation system is served as the secondary system whose frequency bands and transmitting power are strictly limited. Compared with conventional multibeam satellites, BH satellites have the advantage of flexibility in the time dimension. Therefore, we make full use of the flexibility of LEO BH satellites to realize the matching of traffic demand and traffic supply. The RA problem is decomposed into three sub-problems, namely, frequency band selection (FBS) problem, illuminated cell selection (ICS) problem, and transmitting power allocation (TPA) problem. We solve each sub-problem in order and finally form a complete RA scheme. The performance evaluation of the proposed RA scheme is carried out in real-time and simulation results show that the LEO BH satellite paired with the RA scheme we proposed has good adaptability to the uneven distribution of traffic demand in the spectrum sharing scenario.