Satellite Diversity Research Articles

LEO Satellite Diversity in 6G Non-Terrestrial Networks: OFDM vs. OTFS

LEO Satellite Diversity in 6G Non-Terrestrial Networks: OFDM vs. OTFS

Optimizing Quality of Service in LEO Satellite Networks: A Comprehensive Review of Handoff Algorithms and Satellite Diversity Strategies

Optimizing Quality of Service in LEO Satellite Networks: A Comprehensive Review of Handoff Algorithms and Satellite Diversity Strategies

Deficient mismatch repair is detected in large-to-giant congenital melanocytic naevi: providing new insight into aetiology and diagnosis.

The aetiologies of large-to-giant congenital melanocytic naevi (LGCMN) remain ambiguous. A previous study discovered signatures associated with deficient mismatch repair (dMMR) in patients with LGCMN. However, a screening diagnostic immunohistochemistry (IHC) panel of dMMR in patients with LGCMN has not been performed to date. To identify the MMR status and aetiologies of LGCMN. A total of 110 patients with CMN, including 30 giant CMN, 30 large CMN, 30 medium CMN and 20 small CMN, underwent diagnostic IHC (for MSH6, MSH2, PMS2 and MLH1) screening of dMMR. The control group comprised normal skin samples from 20 healthy people. MMR proteins with little effect (MSH3 and PMS1) on the MMR system were stained in all samples. The surgical procedures conducted on each patient were noted because they might alter the behaviour of CMN and confound the results. Binary logistic regression analyses were performed between the phenotypic data and MMR status to identify associations. Whole-exome sequencing was performed on the main naevi, satellite naevi and normal skin tissues of four patients to detect variants. Mutational signature analyses were conducted to explore the aetiologies of LGCMN. dMMR was detected in 37% (11 of 30) of giant, 23% (7 of 30) of large and 7% (2 of 30) of medium CMNs, but were not identified in small CMNs or normal skin tissues. Moreover, multiple LGCMNs had a much higher dMMR rate than did single LGCMNs. The regression analyses showed that MMR status was significantly associated with CMN size and the presence of satellites, but was not correlated with age, sex, location, satellite diversity or tissue expansion. Notably, the pattern of protein loss in LGCMN mainly consisted of PMS2 loss. Mutational signature analyses detected dMMR-related signatures in patients with LGCMN. Additionally, rare deleterious germline mutations in DNA repair genes were detected in LGCMN, mainly in MSH6, ATM, RAD50, BRCA1 and ERCC8. These germline mutations were single-patient variants with unknown significance. dMMR is one of the aetiologies underlying LGCMN, particularly in patients with giant main lesions and multiple satellite lesions. Further studies are necessary to investigate the role of the DNA repair system, particularly MMR, in LGCMN.

Single Frequency WAAS Augmentation Observations (L1 vs. L5) on a Ground Based GPS L1 C/A Solution

This paper presents observations on the WAAS L1 and L5 signals quality and their impact on the robustness of the navigation solution by quantifying the contributions of each broadcasted differential correction. This work is undertaken with the intent of defining performance benefits of L5 by dual frequency WAAS users and is to provide useful material for Minimum Operational Performance Standard (MOPS) development. In this perspective, a study of the WAAS signal characteristics is first carried out. The information gathered is then used to compare various GPS solutions in terms of frequency diversity, satellite diversity, pseudorange noise and different signal corrections and their impacts. These solutions are compared against a reference standalone GPS solution. All statistics are computed with respect to a post-processed Novatel Waypoint Real-Time Kinematics (RTK) GPS L1/L2 semi-codeless static solution, considered as the reference. A discussion on some simplifications with respect to specifications (i.e. MOPS) that could be considered by receiver manufacturers closes the paper. It is confirmed that the current WAAS navigation message definition is the same on both the L1 and L5 frequencies, the latter further being Manchester coded, thus avoiding data ambiguity. The +5 dB SNR on L5 has minor impacts in terms of reliability and continuous availability in the presented scenarios, but would become especially beneficial in hostile environments, despite a greater number of pulsed interferers. Another demonstration is that the WAAS message varies slightly from one WAAS satellite to another, even if corrections are generated centrally. Finally, it is observed that WAAS and GPS signals pseudorange noise are comparable on a “per frequency” basis.

Wheatstone Project

Background The $29 billion Wheatstone Project is one of Australia’s largest resource projects, located 12 km west of Onslow on the Pilbara coast of WA. Objective NewSat was selected to provide vital communication services to the Wheatstone Project as the supplier of the Operations Satellite System to deliver remote internet, voice, video, and data services for LNG operations, OH&S compliance, backup communications, and onsite staff welfare. A project as large and complex as the Wheatstone Project required a range of solutions to overcome multiple communication challenges due to the large and varied number of users and diverse and harsh onsite weather conditions. With long standing relationships with Australian oil and gas service providers, NewSat had the reputation and experience to deliver the satellite services required. Solution NewSat worked closely with the Wheatstone engineering and design team to ensure the project had the best possible satellite service available and the highest amount of design options as the Project matured. The final design was a meshed satellite network, linking the onshore production facility at Onslow, the offshore platform, and the Perth head office. As a 24 x 7 x 365 operation, the project required an always-on satellite service. NewSat’s wide range of satellites provided line-of-site and satellite diversity to ensure there was no single point of failure across the satellite network. As well as providing the best infrastructure, NewSat integrated Adaptive Coding and Modulation (ACM) into the network to overcome the varying atmospheric challenges inherent in the region.

The influence of imperfect accretion and radial mixing on ice:rock ratios in the Galilean satellites

We investigate the origin of the steep compositional gradient inferred for the Galilean satellites. We analyze N-body simulations of satellite accretion (Ogihara, M., Ida, S. [2012]. Astrophys. J. 753, 60) to: (1) determine the extent to which individual satellites accrete material from different semi-major axes (‘radial mixing’); and (2) calculate the change in rock:ice ratios due to vapor production or physical erosion during collisions. Because of inwards migration, satellites experience enough radial mixing that any initial compositional gradient is efficiently smoothed out. Mean-motion resonances generally prevent large proto-satellites from colliding with each other; as a result, neither vapor production nor physical erosion are capable of explaining the steep compositional gradient. According to the models presented here, even combining an initial compositional gradient with impact-related mass loss cannot reproduce the observed gradient. Some other physical process must have been responsible, perhaps tidally-driven volatile loss at Io and Europa. Impact-related mass loss was probably more important in the saturnian system, and may explain some of the observed satellite diversity there.

A generative MIMO channel model encompassing single satellite and satellite diversity cases

This paper addresses the statistical modelling of MIMO-LMS fading channels. In the absence of accurate experimental results, a statistical model for the characterization of MIMO-LMS channels is proposed based on consolidation of available experimental results for SISO-LMS, SIMO-LMS and MISO-LMS as well as on their extrapolation to the MIMO-LMS and satellite diversity cases of interest.

Multi-Satellite MIMO Communications at Ku-Band and Above: Investigations on Spatial Multiplexing for Capacity Improvement and Selection Diversity for Interference Mitigation

This paper investigates the applicability of multiple-input multiple-output (MIMO) technology to satellite communications at the Ku-band and above. After introducing the possible diversity sources to form a MIMO matrix channel in a satellite environment, particular emphasis is put on satellite diversity. Two specific different topics from the field of MIMO technology applications to satellite communications at these frequencies are further analyzed: (i) capacity improvement achieved by MIMO spatial multiplexing systems and (ii) interference mitigation achieved by MIMO diversity systems employing receive antenna selection. In the first case, a single-user capacity analysis of a satellite MIMO spatial multiplexing system is presented and a useful analytical closed form expression is derived for the outage capacity achieved. In the second case, a satellite MIMO diversity system with receive antenna selection is considered, adjacent satellite cochannel interference on its forward link is studied and an analytical model predicting the interference mitigation achieved is presented. In both cases, an appropriate physical MIMO channel model is assumed which takes into account the propagation phenomena related to the frequencies of interest, such as clear line-of-sight operation, high antenna directivity, the effect of rain fading, and the slant path lengths difference. Useful numerical results obtained through the analytical expressions derived are presented to compare the performance of multi-satellite MIMO systems to relevant single-input single-output (SISO) ones.

Study on ISL network structure in LEO satellite communication systems

Many parameters have to be taken into account in designing an LEO satellite constellation including transmission delay, service coverage, minimum elevation angle, and the effects of space radiation. We selected the 2 π constellation for the NeLS ISL study to maintain continuous ISL connections, which is expressed by using a Walker notation of 120/10/1 with 55° of inclination. The satellite orbit parameters were examined under conditions where at least two satellites were always visible from the user terminal to enable satellite diversity. The optimum inclination angle for the 2 π constellation was directly derived from the spherical triangle formed by three adjacent satellites. To evaluate the NeLS's ISL performance, the structure for ISL connections was simplified by using constellation parameters of 121/11/0 instead of 120/10/1. The ISL network had a bi-directional MSN structure with these parameters. The inter-orbital ISL, especially, achieved a ring network shaped like a figure-of-eight using n to n - 1 connections. The bi-directional MSN topology of ISL connections is also discussed. A combination of constellation parameters P , S , and F were found to have simple relations in the n to n - 1 connections of inter-orbital ISLs. Finally, optimum parameters for the NeLS constellation are discussed, and a candidate parameter ( T / P / F = 132 / 11 /- 1 , h = 1100 km , and I = 57 . 92 ∘ ) is proposed.

QoS handover management for multimedia LEO satellite networks

Low earth orbit (LEO) satellite systems gained considerable interest towards the end of the previous decade by virtue of some of the appealing features that are endowed with, such as low propagation delay and the ability to communicate with handheld terminals. However, after the limited commercial success of the first networks of this kind, future satellite networks are now conceived as complementary rather than competitive to terrestrial networks. In this paper, we focus on one of the most influential factors in system performance, that is, the handover of a call. First, we provide a succinct review of the handover strategies that have been proposed in the literature. Then we propose two different satellite handover techniques for broadband LEO satellite systems that capitalize upon the satellite diversity that a system may provide. The proposed schemes cater for multimedia traffic and are based on the queuing of handover requests. Moreover, a deallocation scheme is also proposed according to which capacity reservation requests are countermanded when the capacity that they strive to reserve is unlikely to be used. Simulation studies further document and confirm the positive characteristics of the proposed handover schemes.

Diversity Systems Comparison of Satellite Visibility Improvement for Designing Mobile Broadcasting Satellite System

This paper presents the experimental comparison of two diversity systems, namely, satellite diversity (Sat. D) and time-delayed diversity (TDD), in order to design a digital mobile broadcast satellite system (MBSS) using a geostationary satellite orbit (GSO) satellite. In order to design the digital MBSS using the GSO satellite, the attenuation characteristics due to urban buildings, trees, etc., must be studied. The measurements of the characteristics of diversity systems were carried out using Global Positioning System (GPS) signals with a limited elevation angle. By processing the measured data, the satellite visibility characteristics can be improved for the Sat. D and TDD systems. By using the Sat. D system, about 90% satellite visibility can be achieved in Sapporo and Asahikawa cities. Furthermore, the averaged satellite visibility can be improved by a factor of almost two by using the TDD system for the GSO satellite with a delay time of about 3~6 min. An example of the TDD system application for a quasi-zenith satellite system is also discussed

Outer loop power control in CDMA satellite systems with on-board power constraints

This paper aims at clarifying the role of the outer loop power control for CDMA satellite systems with on-board power constraints. If the inner loop of the power control is perfect, the channel turns into a AWGN channel and there is no need of the outer loop. In satellite CDMA systems, due to the longer propagation delay with respect to a terrestrial system, the inner loop of power control is only partly able to track power variations due to fast fading. Moreover, the Rice factor, which characterizes the channel statistics, can widely vary even if the user does not move but just because of the change of the elevation angle. Because of that, a wide range of target SNIR (and larger than in typical terrestrial systems) may be necessary to get the same BER performance. Therefore, the outer loop power control turns out to be essential to minimize the dynamic of the power link margins and avoid capacity degradations induced by the systematic use of static link margins. A semi-analytical model for the capacity evaluation has been developed, which is specifically intended for the power-limited satellite-to-mobile link with multi satellite reception. We found that the capacity gain with respect to a pure SNIR-based strategy (i.e., only inner loop) can reach the 40% of the total capacity in a single reception scheme. A smaller, but still noticeable capacity gain of the order of 20 - 30% is observed in presence of satellite diversity. Therefore, any dimensioning of CDMA satellite systems should not neglect this component of the power control.

Outer loop power control in CDMA systems with on-board power constraints

This paper aims at clarifying the role of the outer loop power control for CDMA satellite systems with on-board power constraints. If the inner loop of the power control is perfect, the channel turns into a AWGN channel and there is no need of the outer loop. In satellite CDMA sytsems, due to the longer propagation delay with respect to a terrestrial system, the inner loop of power control is only partly able to track power variations due to fast fading. Moreover, the Rice factor, which characterizes the channel statistics, can widely vary even if the user does not move but just because of the change of the elevation angle. Because of that, a wide range of target SNIR (and larger than in typical terrestrial systems) may be necessary to get the same BER performance. Therefore, the outer loop power control turns out to be essential to minimize the dynamic of the power link margins and avoid capacity degradations induced by the systematic use of static link margins. A semi-analytical model for the capacity evaluation has been developed, which is specifically intended for the power-limited satellite-to-mobile link with multi satellite reception. We found that the capacity gain with respect to pure SNIR-based strategy (i.e. only inner loop) can reach the 40% of the total capacity in a single reception scheme. A smaller, but still noticeable capacity gain of the order of 20-30% is observed in the presence of satellite diversity. Therefore, any dimensioning of CDMA satellite systems should neglet this component of the power control.

Design issues and QoS handover management for broadband LEO satellite systems

Today, the wider spectrum of applications that wireless networks are called to support, presses the designers of low earth orbit (LEO) satellite systems for a more efficient exploitation of the limited radio spectrum. The limited commercial success of the first LEO satellite networks, which were geared towards narrowband services, has been the main motive for the reconsideration of the set of services that these networks should provide. In this context, a broadband LEO satellite system is examined in the paper. In this kind of networks, the handing-over of a call between contiguous cells or satellites is one of the dominant factors that degrade the quality of the provided services. In the paper, a satellite handover technique is proposed and evaluated for systems that present partial satellite diversity in order to provide an efficient handover strategy and QoS in multimedia applications, examining the impact of the footprint's overlapping area on the system performance as well.

Satellite handover techniques for LEO networks

AbstractLow earth orbit satellite constellations could play an important role in future mobile communication networks due to their characteristics, such as global coverage and low propagation delays. However, because of the non‐stationarity of the satellites, a call may be subjected to handovers, which can be cell or satellite handovers. Quite many techniques have been proposed in the literature dealing with the cell handover issue. In this paper, a satellite handover procedure is proposed, that investigates and exploits the partial satellite diversity (namely, the existing common coverage area between contiguous satellites) in order to provide an efficient handover strategy, based always on a tradeoff of blocking and forced termination probabilities for a fair treatment of new and handover calls. Three different criteria were examined for the selection of a satellite. Each one of them could be applied either to new or handover calls, therefore we investigated nine different service schemes. A simulation tool was implemented in order to compare the different service schemes and simulation results are presented at the end of the paper. Copyright © 2004 John Wiley & Sons, Ltd.

Satellite constellation design and radio resource management using genetic algorithm

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.

Neural network model for atmospheric attenuation retrieval between 20 and 50 GHz by means of dual‐frequency microwave radiometers

The propagation of signals through the atmosphere plays a major role in the quality of communications between ground terminals and satellites. Its characteristics have to be known accurately for appropriate communications equipment to be selected. In the band of frequencies used by operators in the future generation of satellites (beyond 20 GHz), the quality of transmission is especially affected by the attenuation of received signals because of rain, and by other less significant but much more frequent effects due to atmospheric gases, and nonprecipitating water. These phenomena have a direct impact on the availability ratio of a link between a ground terminal and a satellite. Our main goal in this study is to measure the atmospheric attenuation, using dual‐frequency ground‐based radiometers measuring the sky radiation at different pointing directions, so as to perform a statistical study. A new algorithm, based on a neural approach, is thus developed for estimating atmospheric attenuation, in various meteorological conditions, for several elevation angles and for frequencies between 20 and 50 GHz, from dual‐frequency radiometric measurements. A validation of the obtained algorithm is performed on Olympus experimental data for the 20 and 30 GHz channels. At the end of this paper some applications are then presented to underline the usefulness of this new algorithm. The applicability of the algorithm to satellite beacon calibration in Ka or Q band with accuracy of 0.1 dB is shown. Preliminary joint statistics between attenuation at various pointing directions obtained at 40 GHz show what improvement can be expected from satellite diversity in the case of satellite constellations.

Wide-band CDMA for the UMTS/IMT-2000 satellite component

This paper describes the main aspects relevant to the development of a third-generation radio transmission technology (RTT) concept identified as satellite wide-band CDMA (SW-CDMA), which has been accepted by the International Telecommunications Union (ITU) as one of the possible RTTs for the satellite component of International Mobile Telecommunications-2000 (IMT-2000). The main outcomes of the extensive system engineering effort that has led to the above ITU RTT are described. In particular, we address propagation channel characteristics, satellite diversity, power control, pilot channel, code acquisition, digital modulation and spreading format, interference mitigation, and resource allocation. Due to its similarity with respect to the terrestrial W-CDMA proposal from which it is derived, the SW-CDMA open air interface solution is described briefly, with emphasis only on the major adaptation required to best cope with the satellite environment. Quantitative results concerning the physical-layer performance over realistic channel conditions, for both forward and reverse link, are reported. A system capacity study case for a low-Earth-orbit constellation is also provided.

Shadowing correlation assessment and modeling for satellite diversity in urban environments

AbstractNon‐geostationary orbit satellite networks have dynamic, yet deterministic topologies. This paper deals with the consequences of relying on the use of multiple visible satellites to improve availability with time/locations through satellite diversity techniques. The assumption of independent blockage events in two different satellite‐to‐mobile links is generally not accurate and information on shadowing correlation should be taken into account in the assessment of availability.In this paper a shadowing correlation study for urban environments is presented and a model for the real environments, as well as for a generic urban environment is inferred. The model proposed here is simple and can be run on a computer. It also relates urban and constellation geometries thus allowing the identification of those cases for which satellite diversity gain should be expected. As a result of this analysis and modelling, we present empirical analytical expressions describing positive correlation coefficient as a function of satellite angular separation (azimuth and elevation). We also show that an angle exists above which correlation can be negative and satellite diversity can sensibly improve link availability. Copyright © 2002 John Wiley & Sons, Ltd.

Modified GSC for hybrid satellite constellation

A modified genetic satellite constellation (GSC) design is proposed for hybrid satellite constellations. The novelty of the proposed model is the automatic determination of satellite constellation parameters for hybrid LEO/MEO constellations. Illustrative results of satellite constellation parameters and dual satellite diversity statistics for hybrid LEO/MEO are presented.