Satellite Network

The number of sensors for Earth environmental observation is growing. Several new sensors have been announced for the near future and several proposals for smart sensors have been proposed. In particular, distributed sensors, sensor network and sensor integration are being taken into account, and smart sensors, intelligent sensors, sensor’s autonomy, etc. is beginning to be used in future earth observing satellites. This paper investigates the development of sensors in Earth observing (EO) satellites, analyzes the current high-resolution EO satellites and presents the tendency of new imaging systems in future Earth observing satellite. The purpose of this paper is to contribute to the growing interest in knowing and keeping track of the details of the imaging system of earth observing satellites. This project is of particular interest to those who are developing the skills to measure and understand the detail of our Earth environment through analysis of satellite data. 1.

In an integrated cellular/satellite system for mobile communications a satellite subsystem cooperates with a terrestrial cellular network for providing user services. The paper addresses the problems related of the reuse of the procedures of the GSM cellular standard in an integrated system, allowing at most changes only at the mobile terminal and/or in the satellite network. The results of the study show that most of the GSM procedures can be reused in an integrated system (in a few cases with limited protocol variations) but some others would require modifications to the cellular network. The results of this study shall also be useful for the suitable definition of the protocols of an integrated satelliteherrestrial system for the next generation of mobile and personal communication services.

In satellite networks, voice over IP performance is degraded by long delays and low bandwidth. Both call setup time and quality of service (QoS) for voice calls are affected. Separate studies have been undertaken for these performance metrics. In this paper, we have carried out experiments using different voice codecs to evaluate SIP call setup time and QoS parameters together.

The IP-based Broadband Aeronautical Satellite Network will provide numerous new applications and services for both airspace system operations and passenger communications. However, the performance of data communications protocols and applications over such systems is dramatically degraded, especially the Internet TCP/IP protocol suite. In this paper, we propose a new transport protocols for satellite network supporting Internet and data services. Based on the observation that it is difficult for an endto-end TCP solution to solve the performance problem effectively, we propose a new splitting based TCP protocol, called Aeronautical Transport Control Protocol (AeroTCP), which takes advantage of the specific properties of satellite channel. Our simulation results show that AeroTCP improves satellite channel utilization and fairness.

This paper identifies key research issues and technologies that we envision will be important to the continued evolution of satellite networking and its integration as a core component of a Future Internet that offers reliable, robust and pervasive networking and access to network services.

Satellites play a significant role in communication, early warning systems, global broadcasting, meteorology, navigation, reconnaissance, remote sensing, and surveillance.Satellite services cover practically every sector, from mobile cellular communication to telemedicine, so any interference with them could have a serious effect. Satellites are a strategic asset for any country and are considered as " critical infrastructure, " therefore they are considerable as privileged targets for a possible cyber attack.

In this paper, we study a constraint-based routing strategy using label switching in a multi-layered hierarchical satellite constellation such as transformational communications architecture. Both quality (bit error rate on free space optical and radio inter-satellite links) and bandwidth availability on a satellite link are taken into account when setting up routes for high priority real-time traffic such as VoIP, which is sensitive to delay and jitter. To protect the real-time traffic from being swamped by bursty best-effort traffic we propose to have a ...

Wireless and satellite networks often have non-negligible packet corruption rates that can significantly degrade TCP performance. This is due to TCP's assumption that every packet loss is an indication of network congestion (causing TCP to reduce the transmission rate). This problem has re- ceived much attention in the literature. In this paper, we take a broad look at the problem

Designing efficient transmission mechanisms for advanced satellite networks is a demanding task, requiring the definition and the implementation of protocols and architectures well suited to this challenging environment. In particular, transport protocols performance over satellite networks is impaired by the characteristics of the satellite radio link, specifically by the long propagation delay and the possible presence of segment losses due to physical channel errors. The level of impact on performance depends upon the link design (type of constellation, link margin, coding and modulation) and operational conditions (link obstructions, terminal mobility, weather conditions, etc.). To address these critical aspects a number of possible solutions have been presented in the literature, ranging from limited modifications of standard protocols (e.g. TCP, transmission control protocol) to completely alternative protocol and network architectures. However, despite the great number of different proposals (or perhaps also because of it), the general framework appears quite fragmented and there is a compelling need of an integration of the research competences and efforts. This is actually the intent of the transport protocols research line within the European SatNEx (Satellite Network of Excellence) project. Stemming from the authors' work on this project, this paper aims to provide the reader with an updated overview of all the possible approaches that can be pursued to overcome the limitations of current transport protocols and architectures, when applied to satellite communications. In the paper the possible solutions are classified in the following categories: optimization of TCP interactions with lower layers, TCP enhancements, performance enhancement proxies (PEP) and delay tolerant networks (DTN). Advantages and disadvantages of the different approaches, as well as their interactions, are investigated and discussed, taking into account performance improvement, complexity, and compliance to the standard semantics. From this analysis, it emerges that DTN architectures could integrate some of the most efficient solutions from the other categories, by inserting them in a new rigorous framework. These innovative architectures therefore may represent a promising solution for solving some of the important problems posed at the transport layer by satellite networks, at least in a medium-tolong-term perspective.

A return-to-zero differential quadrature phase-shift keying (DQPSK) modulation scheme is proposed for all-optical orthogonal frequency-division multiplexing transmission systems. The system uses coupler-based inverse fast Fourier transform/fast Fourier transform to support a 700 km single-mode fiber link and a transmission rate of 40 Gb∕s without any nonlinear compensation. The performance of the proposed system is evaluated using simulation and four performance measures are obtained, namely, the eye diagram, the eyeopening penalty (EOP), the power spectral broadening, and the bit error rate (BER). The effect of self-phase modulation is taken into account in the performance evaluation. In addition, the performance of the proposed system is compared to that of a traditional one adopting a non-return-to-zero DQPSK scheme. Our results reveal that the proposed system outperforms the traditional one in all four aforementioned performance measures, yet the spectral efficiency is almost preserved. Specifically, for an input average power of 12 dBm, a reduction in both the required optical-signal-to-noise ratio of about 4 dB (to achieve a BER of 10 −6 ) and the EOP of about 5 dB are reported when adopting the proposed system, as compared to the traditional one.

In this paper, as part of the adaptive resource allocation and management (ARAM) system (Alagöz, 2001), we propose an adaptive admission control strategy, which is aimed at combating link congestion and compromised channel conditions inherent in multimedia satellite networks. We present the performance comparisons of a traditional (fixed) admission control strategy versus the new adaptive admission control strategy for a direct broadcast satellite (DBS) network with return channel system (DBS-RCS). Performance comparisons are done using the ARAM simulator. The traffic mix in the simulator includes both available bit rate (ABR) traffic and variable bit rate (VBR) traffic. The dynamic channel conditions in the simulator reflect time variant error rates due to external effects such as rain. In order to maximize the resource utilization, both for fixed and adaptive approaches, assignment of the VBR services are determined based on the estimated statistical multiplexing and other system attributes, namely, video source, data transmission, and channel coding rates. In this paper, we focus on the admission control algorithms and assess their impact on quality-of-service (QoS) and forward link utilization of DBS-RCS. We show that the proposed adaptive admission control strategy is profoundly superior to the traditional admission control strategy with only a marginal decrease in QoS. Since the ARAM system has several parameters and strategies that play key roles in terms of the performance measures, their sensitivity analysis are also studied to verify the above foundations.

Very Small Aperture Terminal (VSAT) satellite networks have so far been successful in the provision of specific communication services to geographically dispersed users. However, user demands are becoming more complex, and VSAT networks are expected to provide a much wider range of services (voice, data and multimedia). We investigate how this service integration could be achieved and show that performance improvements are possible if efficient multi-access protocols and speech compression with voice activity detection techniques are used. We also discuss the future role VSATs could play in the provision of access to the Integrated Broadband Communications Network to remote users. It is shown that it could be possible to use VSATs for ATM service provision, but there are limitations on the system's performance from the satellite delay and limited link capacity. Careful consideration of these limitations is required in designing a system that could guarantee a particular Quality of Service.

An enhanced adaptive scheme based on threshold method with a reduced complexity that combine adaptive modulation and coding with diversity combining is presented for throughput maximization in broadband code division multiple access (CDMA) satellite networks. The proposed algorithm is a modify, enhanced, and more robust version of the existing algorithms for adaptive transmission rate and modulation in CDMA networks. The rate compatible punctured turbo-coded (RCPT), which has been found to give improved throughput performance in a direct sequence (DS) CDMA is exploited. A semianalytical process and simulations were carried out. It is found that there are significant improvement in the average throughput and the bit-error performance. The proposed algorithm using adaptive coding and modulation (instead of variable spreading gain) outperforms other systems such as Selective Power Control with Active Link Protection (SPC-ALP) algorithm proposed for adaptive transmission rate and power control in CDMA networks.

The construction industry recognizes that significant gains can be achieved using e-business. However, ebusiness platforms need to progress toward new emerging paradigms; beyond the dematerialization of processes, e-business must integrate collaborative tools, support social networking mechanisms, and enhance interoperability between systems in order to improve collaboration, develop trust, and implement strategic approaches to network relationships. The Social e-business concept presented in this paper defines this innovative e-business vision, which integrates web-based collaborative tools, emphasizes the importance of social capital and social networking, and enhances the role of supply chain management. The proposed Satellite Network model fits in with this collaborative working logic, defining a functional approach to enhance the social network behavior in a project-based web platform for the construction industry. A case study is presented demonstrating the implementation of the Social e-business concept and the Social Network model in an innovative electronic platform for the construction industry.

Nongeostationary satellite constellations with intersatellite links are a challenge for networking due to their continuously changing topology. In order to make maximal use of the network's capacities, special attention has to be paid to routing and traffic engineering. Multiprotocol label switching (MPLS) as underlying protocol is an interesting candidate for this task since it offers many possibilities to exert influence on traffic flows and supports today's dominating Internet protocol traffic very well. This paper describes a general MPLS-based networking concept for satellite networks and discusses different scenarios considering the particularities and constraints of the dynamic topology. Functional elements of MPLS like ingress, egress, or core routers have to be mapped onto the physical entities of the network and prerequisites for traffic engineering are discussed. Routing and rerouting of paths is of key interest since this affects route computation effort and routing performance. Thus, an analytical estimation of routing effort is deduced and numerical and simulation results are presented.

Satellites offer a promising alternative for mobile access to the Internet by both pedestrians, and more importantly, from vehicles. As such, satellites provide an essential complement to the cellular radio (UMTS) infrastructure in sparsely populated areas where high bandwidth UMTS cells cannot be economically deployed. In this paper, we analyse various mobile Internet applications in representative urban scenarios for two LEO constellations (one with polar orbits and the other with inclined orbits), as well as for some simple GEO configurations. To this end, we develop a satellite channel propagation model that includes shadowing from surrounding building skylines based on actual data in a built-up area.

We study the problem of carrying voice calls over a low-earth-orbit satellite network and present an analytical model for computing call-blocking probabilities for a single orbit of a satellite constellation. We have devised a method to solve the corresponding Markov process efficiently for orbits of up to five satellites. For orbits consisting of a larger number of satellites, we have developed an approximate decomposition algorithm to compute the call-blocking probabilities by decomposing the system into smaller subsystems and iteratively solving each subsystem in isolation using the exact Markov process. Our approach can capture blocking due to handoffs for both satellite-fixed and earth-fixed constellations. Numerical results demonstrate that our method is accurate for a wide range of traffic patterns and for orbits with a number of satellites that is representative of commercial satellite systems.

Amplitude scintillation data from GPS were analyzed. The objective is to estimate the impact of ionospheric scintillations at Satellite Based Augmentation Systems Ranging and Integrity Monitoring Station (SBAS RIMS) level and at GPS user level. For this purpose, a new approach to the problem was considered. Data were studied from the point of view of the impact of scintillations on the calculation of VTEC at pierce points and ionospheric grid points. An ionospheric grid of 5°× 5°surface squares was assumed. From geometrical considerations and taking into account the basic principle to compute VTEC at grid points, with the data analyzed it is shown that scintillations very seldom affect the calculation of a grid point VTEC. Data from all the RIMS and for the entire GPS satellites network must be analyzed simultaneously to describe a realistic scenario for the impact of scintillations on SBAS. Finally, GPS scintillation data were analyzed at user level: service availability problems were encountered.

Currently many efforts are undertaken to develop and install communication networks based on low earth orbit (LEO) and intermediate circular orbit (ICO) satellites. However, many problems are to be solved until the final operation of such networks. This paper deals with basic design problems of LEODCO-based networks. In the first part, the topology of the satellite network is considered and estimates for the necessary number of satellites, orbits and number of communication channels per satellite are derived. Features and consequences of intersatellite links are discussed. In the second part of the paper, the number of communication channels per link is derived with a more elaborate model. This includes the radio links from the satellites to mobile users and to gateways, as well as intersatellite links and terrestrial lines. We introduce a formal model for LEO/ICO-based networks and propose a method for the evaluation of link capacities, given the network topology and the trafflc requirements. As an example, two constellations are investigated in detail. One of these constellations is the Iridium system proposed by Motorola, the other one is the LEONET concept developed in an ESA study. Finally, the influence of unequal traffic distribution is discussed.

We study the performance of Selective Acknowledgments with TCP over the ATM-UBR service c ategory. We examine various UBR drop policies, TCP mechanisms and network con gurations to recommend optimal parameters for TCP over UBR. We discuss various TCP congestion control mechanisms compare their performance for LAN and WAN networks. We describe the e ect of satellite delays on TCP performance over UBR and present simulation results for LAN, WAN and satellite networks. SACK TCP improves the performance of TCP over UBR, especially for large delay networks. Intelligent drop policies at the switches are an important factor for good p erformance i n l o c al area networks.

The standardization of a Return Channel via Satellite (DVB-RCS) and satellite community efforts in term of interoperability over the last few years lead to quite a positive outcome: Geostationary satellite networks are intended to provide broadband access to interactive multimedia services in low infrastructure areas. However, in order to take in account real-time multimedia traffic, an efficient resource management scheme is still necessary to maximize the scarce uplink capacities usage.

... of UDL Mesh Satellite Networks Using DVB-S Technology", Proceedings Asia Pacific Conference on Communications (APCC2003), Penang, Malaysia Sept 21-24, 2003 [9] Nihal KG Samaraweera, "Return Link ... [14] Jehan-Franc,ois Paris, Steven W. Carter, Darrell DE Longz ...

The next generation satellite networks will provide broadband communications at low cost. The recent developments in satellites technology, transmission techniques, antennas, and launch capabilities have enabled a new generation of services to be made available to users especially when communications satellites have been widely considered to complement the terrestrial systems. In this paper, a survey of next generation satellite networks through the satellite background are discussed. The satellite network requirements for the future mobile system are presented. The proposed satellite-UMTS which have been accepted for the third generation wireless network is showned to be internetworked with the proposed all IP network. This consideration is inevitable because of highspeed transmission requirements and roaming capability that the next generation network system demand.

Real-time transmission over asymmetric satellite IP links is challenging, since satellite systems commonly exhibit long propagation delays, while bandwidth asymmetry often enforces a variable and infrequent rate of acknowledgment packets (ACKs) across the upstream channel with several undesirable implications. In this context, we formulate an analytical model in order to quantify the impact of satellite systems and link asymmetry on TCP performance and real-time delivery. We emphasize on the effects of asymmetric links, and especially on the implications that cause interruptions in the sending rate, and eventually disturb smooth delivery. Since TCP performance is in part throttled by the rate of arriving ACKs, we additionally investigate the impact of delayed ACKs. Although delayed ACKs occasionally diminish the transmission rate, we uncover notable gains in terms of smoothness and real-time delivery. Furthermore, we demonstrate conclusive performance studies tackling the supportive role of selective acknowledgments (SACK) and the effect of varying bit error rates. Our simulation results illustrate that most existing end-to-end solutions do not comply with the stringent Quality of Service (QoS) provisions of time-sensitive applications, resulting in ineffective bandwidth utilization and varying delays in data delivery. Finally, with the absence of a satellite-optimized TCP implementation for real-time transmission, we identify the most prominent end-to-end solutions that manage to alleviate most of the impairments induced by asymmetric satellite links, sustaining a relatively smooth transmission rate.

Session Initiation Protocol (SIP) is an application layer signalling protocol used in the IP- based Universal Mobile Telecommunication Systems (UMTS) network for establishing multimedia sessions. With a satellite component identified to play an integral role in UMTS, there is a need also to support SIP-based session establishment over Satellite-UMTS (S-UMTS) to achieve end-to-end seamless IP-based terrestrial/satellite network integration. Due to

This paper describes current and proposed protocols for mobility management for public land mobile network (PLMN)-based networks, mobile Internet protocol (IP), wireless asynchronous transfer mode (ATM), and satellite networks. The integration of these networks will be discussed in the context of the next evolutionary step of wireless communication networks. First, a review is provided of location management algorithms for personal communication systems (PCS) implemented over a PLMN network. The latest protocol changes for location registration and handoff are investigated for Mobile IP, followed by a discussion of proposed protocols for wireless ATM and satellite networks. Finally, an outline of open problems to be addressed by the next generation of wireless network service is discussed.

We consider optimal control for general networks with both wireless and wireline components and time varying channels. A dynamic strategy is developed to support all traffic whenever possible, and to make optimally fair decisions about which data to serve when inputs exceed network capacity. The strategy is decoupled into separate algorithms for flow control, routing, and resource allocation, and allows each user to make decisions independent of the actions of others. The combined strategy is shown to yield data rates that are arbitrarily close to the optimal operating point achieved when all network controllers are coordinated and have perfect knowledge of future events. The cost of approaching this fair operating point is an end-to-end delay increase for data that is served by the network. Analysis is performed at the packet level and considers the full effects of queueing.

There are many types of Performance Enhancing Proxies (PEPs). Different types of PEPs are used in different environments to overcome different link characteristics which affect protocol performance [1]. The main examples concerns satellite and wireless networks, which represent the most challenging environments.

This paper proposes a design for key management for secure multicast in hybrid satellite networks. Communication satellites offer an efficient way to extend IP multicast services for groups in wide-area networks. In order to be commercially viable, the multicast traffic should be accessible only to paying subscribers. Access control can be achieved by data encryption. This requires secure and efficient methods to generate, distribute and update the keys. Most current key management protocols do not scale well when applied to large dynamic groups in wide-area networks. This paper attempts to solve the above problem for groups in a hybrid network that is composed of terrestrial Ethernet LANs interconnected by ATM-based satellite channels. We investigate current group key management protocols, and design a framework for secure and scalable key management for the multicast routing architecture in the satellite network. The proposed framework is presented in detail, alongwith analysis and simulation results.

Rain and snow can have a distorting effect on Ku and Ka bands signal fidelity resulting in excessive digital transmission errors. This loss of signal attenuation is commonly referred to as rain fade. Rain fade impacts the Quality of Service in wireless and satellite networks. A decision support system is therefore necessary for service providers to accurately predict rain fade and establish mitigation planning by adaptively selecting appropriate power level, coding and modulation schemes. This paper establishes an important component of the decision support system by adaptively computing rainfall rate and rain attenuation at any location on earth using ITU-R models combined with bi-linear interpolation and frequency extrapolation. We also introduce a novel method for accurately determining rain attenuation as a function of frequency based on proceeding results from prediction weather database, since rain attenuation is considered a dominant impairment for wireless signals [1]- . Finally, a three dimensional relationship is proposed for rain attenuation with both frequency and probability to provide decision support system with an accurate

Designing an efficient routing algorithm for LEO satellite constellations is crucial for optimizing IP over Satellite (IPoS) network resources. Since there could be many shortest paths between two satellites, an efficient routing algorithm should provide better utilization of these paths. For this purpose, we propose a Priority-based Adaptive Routing (PAR) technique, which distributedly sets the shortest path through a destination. In this technique, a direction decision is made at each hop by a priority mechanism, depending on the past utilization and buffering information about the links. We further make some enhancements on PAR, and propose ePAR algorithm that also accounts for the contentions between packets with different source-destination pairs. We explore the performances of PAR and ePAR algorithms based on an extensive set of simulations, and compared their performances with static and adaptive routing techniques as a reference. Obtained results show that while the proposed PAR algorithm is promising for use in LEO satellite networks, ePAR algorithm may be more suitable for MEO satellite networks.

One of the key factors for the successful deployment of mobile satellite systems in 4G networks is the maximization of the technology commonalities with the terrestrial systems. An effective way of achieving this objective consists in considering the terrestrial radio interface as the baseline for the satellite radio interface. Since the 3GPP Long Term Evolution (LTE) standard will be one of the main players in the 4G scenario, along with other emerging technologies, such as mobile WiMAX; this paper analyzes the possible applicability of the 3GPP LTE interface to satellite transmission, presenting several enabling techniques for this adaptation. In particular, we propose the introduction of an inter-TTI interleaving technique that exploits the existing H-ARQ facilities provided by the LTE physical layer, the use of PAPR reduction techniques to increase the resilience of the OFDM waveform to non linear distortion, and the design of the sequences for Random Access, taking into account the requirements deriving from the large round trip times. The outcomes of this analysis show that, with the required proposed enablers, it is possible to reuse the existing terrestrial air interface to transmit over the satellite link.

he recent evolution of the Internet and the spread of networked multimedia applications have highlighted the need to investigate the techniques, tools, and device configurations to guarantee a certain level of quality of service (QoS) to end users. The characteristics of the network used are extremely important to get to the aim. Some types of networks, such as asynchronous transfer mode (ATM), were designed to support QoS for specific traffic flows. A statistic investigation to verify the availability of the resources to guarantee a fixed level of service is performed before accepting a new call entering the network. A call admission control (CAC) mechanism is used in this case. On the other hand, the Internet is a "best-effort" network (TCP/IP protocols were not designed to provide guaranteed QoS), and it only does its best. It is characterized by heterogeneity from the points of view of both algorithms and management, and physical links. There are high-speed channels, low-speed phone links, wireless multi-access channels, and satellite portions. Moreover, many organizations and providers manage the Internet. In the meanwhile, its development has been incremental, and the number of services and applications are growing more and more.