QUIC is emerging as the de facto transport protocol for modern applications and forms the basis of HTTP/3. Within the European Space Agency (ESA) project QUICoS, we developed QUIC-Wave, a satellite-tailored extension of QUIC designed to address the limitations of TCP-based transport in high-latency and lossy satellite environments (GEO, MEO, LEO). Unlike Performance Enhancing Proxy (PEP) approaches, QUIC-Wave preserves end-to-end semantics and encryption while enhancing congestion control. The protocol extensions are engineered to sustain throughput and responsiveness under satellite-specific conditions such as long RTTs, bandwidth variability, and mobility-induced handovers, while maintaining compliance with QUIC specifications and interoperability with terrestrial networks. To validate QUIC-Wave, we conducted extensive real experiments using standard browsers and servers. Results show that QUIC-Wave supports interactive web browsing and multimedia streaming with improved performance over satellite links, without compromising either end-to-end encryption or protocol integrity.

Wave is a disruptive rate control protocol based on the burst transmission paradigm, developed in the Linux kernel for TCP. The main technical innovation leverages a burst-based transmission against the traditional Congestion Window ( cwnd ) paradigm, demonstrating good performance in harsh communication scenarios and supporting common Web applications. Recently, the advent of QUIC moved congestion and loss control up to the application layer, using UDP as transport protocol. Such a migration implied the adaptation and validation of the CCAs within the QUIC framework, based on new data encapsulation methods of both data and acknowledgment frames, and new timers with user space granularity, enabling various options for error control and bandwidth estimation, mainly tailored to BBR. The latter, together with Cubic and NewReno, are the current QUIC CCA. In this context, the original contribution of the paper includes the adaptation of the Wave algorithm within the QUIC implementation and the verification of its better effectiveness with respect to the CCAs already included in the latest QUIC implementations. In particular, an enhanced Wave algorithm has been designed and adapted to QUIC, adding a new state named “recovery mode” to handle possible ACK frame encapsulation into QUIC packets. The resulting QUIC Wave has been implemented in ngtcp2 and integrated into a network testbed, allowing extensive performance evaluation over different challenging communication scenarios for an exhaustive protocol validation. Results confirm the TCP Wave working principles and the overall performance efficiency, paving the way for future experimentation on real networks.

Traditional transport layer protocols, such as TCP and UDP, have long served as the foundation for Internet communications. In particular, TCP seeks to avoid network congestion through a Congestion Control Algorithm (CCA), which typically relies on outdated paradigms, such as ACK-clocked transmission and congestion window regulation based on packet loss. Recently, the standardization of QUIC by the IETF has led to a more flexible and efficient transport protocol, offering integrated security, reduced signaling latency, and multiplexing capabilities. Within this evolving landscape, TCP Wave (TCPW) emerged as a novel transport-layer protocol that adopts different CCA paradigms with respect to traditional ones. Decoupling transmission from ACK reception and adopting a burst-based proactive congestion control strategy, Wave presents a promising direction for next-generation network protocols.This paper addresses the feasibility of integrating TCP Wave’s core principles into the QUIC protocol. We provide an overview of the TCP Wave congestion control algorithm and evaluate a preliminary implementation across two representative QUIC stacks. Through an experimental analysis, we examine the impact of burst transmission on throughput and acknowledgment behavior. The results of this study may serve as a foundational step towards the full implementation of the Wave CCA within the QUIC protocol, laying the groundwork for future research on congestion control within QUIC.

Current 3GPP specifications (Rel. 17) enable connectivity to the 5G core network through alternative non-3GPP access technologies (e.g., WiFi), introducing also the support of multicast and broadcast services, but only within the New Radio (NR) framework. Thus, the standard leaves a significant gap when users want to access multicast and broadcast services through non-3GPP access networks.In a near future, when heterogeneous connectivity will be the norm and device density continues to grow, this limitation may hinder efficient content distribution and strain unicast-dominated infrastructures.This paper envisions a future in which multicast and broadcast services are natively integrated into the non-3GPP access domain, enabling smarter resource allocation and reduced bandwidth consumption. We outline key technical challenges, propose architectural considerations, and explore the transformative potential of unified multicast services in next-generation multi-access 5G environments.

The fifth-generation (5G) mobile network is designed to provide a better user experience than its predecessors. To reach this goal, in addition to the standard radio access, it is foreseen that users can connect to 5G services via different access networks (e.g., Wi-Fi), through the well-defined non-3GPP access technology. Based on some security aspects, it can be distinguished as trusted and untrusted non-3GPP access.This paper aims to show how to improve overall 5G non-3GPP access performance by optimizing data rate and strengthening security, achieved through the selection of the most suitable ciphering and authentication algorithm combination. After providing a detailed comparison between trusted and untrusted access types and related differences, we describe how to maximize the available bandwidth using fast and secure IPSec authentication and encryption algorithms, ensuring an optimal trade-off between performance and security. A surprising outcome of this study reveals that, although users are expected to experience higher data rates on trusted non-3GPP access due to the absence of encryption overhead, the use of new-generation ciphers such as AEAD (Authenticated Encryption with Associated Data), which ensures both confidentiality and message authenticity through a single, efficient operation, can achieve up to a twofold increase in throughput compared to historical approaches considering encryption and authentication as separate operations.

The Integrated Access Backhaul (IAB) is deemed to reduce the deployment costs of ultra-dense 5G millimetre-wave (mmWave) networks, using wireless backhaul links to relay the access traffic. ESA funded the project SATIABLE to investigate technical issues to use the satellite for this kind of service, aiming to draw recommendations for IAB features or extensions for scenarios integrating NTN networks, to provide an analytical baseline and a simulation tool for the assessment of benefits for further studies towards the 3GPP Release 18. The paper briefly describes the project objectives and outcomes.

Network virtualization and centralized resource orchestration is gaining importance thanks to cutting-edge 5G communication paradigms. Although satellite networks are often characterized by legacy technologies customized for specific application requirements, an update of the satellite platforms following the process encompassed by the mobile network operators can help a future efficient integration of terrestrial and satellite resource to offer added-value services. The main objective of the SURPRISE project, funded by ESA, is the virtualization of the satellite gateway, which is of paramount importance, needing a careful design, development and testing of the ground software components to control, manage and share combined digitalized services/resources provided by flexible high throughput satellites and terrestrial networks to multiple end users and service providers. It just ended the reference scenario definition phase, arriving to valuable results to share with the scientific community. Thus, the aim of this paper is to describe the use cases and the reference scenarios so far defined.

5G represents the latest currently available and the state of the art of mobile cellular networks. 5G is defined on the basis of new concepts like Software Defined Network (SDN), Network Function Virtualization (NFV) and Network Slicing, enabling a wide set of use-cases and applications. An innovative feature introduced in 5G since 3GPP Release 16 is Access Traffic Steering, Splitting and Switching (ATSSS), which gives the possibility to the user equipment (UE) connected to a 5G network using a 3GPP link (i.e., the gNB New Radio access) and a non-3GPP one (e.g., a public WLAN access point) to access 5G services using both links simultaneously. ATSSS can improve the user-experience, maximizing the throughput and improving resilience to network faults by downloading or uploading data using both channels at the same time or selecting the best link where to transmit for each data flow. In this paper, we analyze in depth the ATSSS functionality and the associated Multipath TCP (MP-TCP) mode in a Linux simulation testbed, including an Open Source 5G Core Network, with the full implementation of the User Plane and 3GPP and non-3GPP access links, using Free5GC, UERANSIM and a custom implementation of N3IWF. In this testbed setup, we run real traffic and assess the MP-TCP configuration and performance in realistic conditions, when the non-3GPP access is performed wither via terrestrial wireless or a high latency satellite link.

The 5G service-based architecture brought a high degree of flexibility in the dynamic network management and configuration, enabling several Network Functions (NFs) cooperating to customize a communication service based on requirements of a specific vertical. Since rel. 15, the 3GPP introduced a Network Data Analytic Function (NWDAF) for the collection of data from other NFs and the delivery of data analytics services. This paper addresses a compelling use case with a hybrid satellite terrestrial backhaul, with the NWDAF that can be used to catch the slice statistics on the user plane and to drive the enabling of a supplementary satellite backhaul link for performance optimization in compliance with the service requirements. Thus, an optimized configuration of the 5GC is proposed highlighting the NFs involved in the analytics as well as the data sources and the data interfaces.

5G is a cornerstone in the evolution of mobile communication networks, representing the most advanced and available standard at the state of art. Characterized by higher data rate and capacity, actually the real revolution of 5G relies in its capability to offer advanced and heterogeneous services by the full abstraction and slicing of network resources, realizing a service-oriented full-IP high-performance network over a common infrastructure, even belonging to different operators. Another key aspect, which is specifically addressed in this paper, is the possibility to access the services offered by the 5G network using non-3GPP access, and in particular Wi-Fi. This feature can allow access from home Access Points or using public Hotspots, even where there is no 5G coverage or roaming. At the same time, other types of IP access, including terrestrial wired options, are allowed by 3GPP specifications. Such a flexibility allows, although not explicitly mentioned, to consider as well satellite-based non-3GPP access methods, thus enabling wide-coverage use-cases and rural areas coverage. In the paper we discuss the network function required to enable non-3GPP access to 5G Core Networks, namely N3IWF, and the impact in using as access network a VSAT satellite link. After a focus on protocol stacks and signalling procedures, we implemented such an access on a real time Linux testbed including a 5G rel. 15 compliant Core Network, a N3IWF network function and a satellite emulation to assess control procedures timings, User plane latency and overhead.

The adoption of the Narrowband-Internet of Things technology in satellite communications intends to boost Internet of Things services beyond the boundaries imposed by the current terrestrial infrastructures. Apart from link-level studies in the scientific literature and preliminary 3GPP technical reports, the overall debate is still open. To provide a further step forward in this direction, the work presented herein pursues a novel service-oriented methodology to design an effective solution, meticulously stitched around application requirements and technological constraints. To this end, it conducts link-level and system-level investigations to tune physical transmissions, satellite constellation, and protocol architecture, while ensuring the expected system behavior. To offer a real smart agriculture service operating in Europe, the resulting solution exploits 24 low-Earth orbit satellites, grouped into eight different orbits, moving at an altitude of 500 km. The configured protocol stack supports the transmission of tens of bytes generated at the application layer, by also counteracting the issues introduced by the satellite link. Since each satellite has the whole protocol stack onboard, terminals can transmit data without the need for the feeder link. This ensures communication latencies ranging from 16 to 75 min, depending on the served number of terminals and the physical transmission settings. Moreover, the usage of the early data transmission scheme reduces communication latencies up to 40%. These results pave the way toward the deployment of an effective proof of concept, which drastically reduces the time to market imposed by the current state of the art.

Satellite communications (SatCom) have a role of advanced service enablers in the new virtual networks, following 3GPP specifications. Specifically, the satellite peculiar characteristics are of paramount importance to dynamically activate capabilities, such as multicast and broadcast channels, sudden traffic offloading, capacity bonding, and cost-efficient coverage of uncovered areas. A key aspect to achieve a seamless and efficient integration between satellite and terrestrial infrastructures is to make satellite resource management dynamic and with a centralised control of a single orchestrator that has visibility of the end-to-end network. Considering the adoption of Software Defined Networking (SDN) and Network Function Virtualization (NFV) paradigms and the upcoming 5thgeneration of mobile communications (5G), this paper presents the ongoing work within the European Space Agency (ESA) ANChOR project, whose main output will be a data-driven Network Controller and Orchestrator for SatCom networks. This tool will be based on Artificial Intelligence (AI) / Machine Learning (ML)-based techniques to properly allocate resources exploiting some feedback knowledge of the network and it aims to support different services over 5G integrated satellite-terrestrial networks.

The management of public utilities represents a complex issue even in normal operational conditions. In case of emergency the degree of complexity increases exponentially and the variables to take into account, the data to process, the useful expected outcomes and the decision processes need to be supported by technology.For these reasons, the eUmaP project aims to design and develop an open platform through which local authorities will be able to plan and manage the demand and supply of building utilities in case of quarantine or lock down. It will be based on the rational of Earth observation, and the recording of the required network information in open BIM platforms of five European capital cities (Rome, Berlin, Athens, Vilnius, Nicosia).The paper is focused on the architecture definition discussing the pros and cons of three different architectural schemes.

Due to satellite physical constraints in terms of available power and area, data processing capacity is low, storage and security are limited. It is a challenge to protect satellite network from illegal information access and use storage space effectively. In this paper, a blockchain technology-based on authentication and privacy protection scheme is proposed for a satellite communication network. to this aim, an architecture consisting of both conventional and restricted devices connected to the blockchain via a wireless heterogeneous network is deployed. The communication is carried out through registration, authentication and revocation. In this scheme, the satellite will forward the collected information to the ground base station, which will record all key parameters on the distributed blockchain and all malicious node certificates will be cleared from the blockchain by the ground base station. The simulation results show that the scheme has been greatly improved in terms of communication security and communication overhead.

The advent of 5G with the three identified use case classes (eMBB, mMTC, URLLC) requires to adequately define system architectures including all the technological segments that can contribute to satisfactorily reach the target performance. For this reason, satellite systems must be duly considered because their intrinsic characteristics are well suitable to support 5G services. In particular, as concerns mMTC/NB-IoT class an ongoing ESA project is demonstrating the feasibility and the usefulness of the inclusion of the satellite segment in the system architecture and has identified peculiar use cases. The paper presents some of the outcomes of the project so far achieved, both in terms of scenario identification and implementation issues in compliance with 3GPP standard architectures.

The QUIC (Quick UDP Internet Connection) protocol suite is going to approach its final stages of standardization to become part of the official Internet standards (RFCs) and of the new HTTP/3 specification. Some of its disruptive characteristics, such as the 0-RTT establishment of secure communications and a connection-oriented management over a UDP-based connection-less transport, can be reused and tailored in the framework of a Performance Enhancing Proxy (PEP) architecture for the effective management of multiple links. In this paper, we describe the design and implementation of a QUIC-based splitting solution to enhance the communication across multiple backhaul links, each associated with a different network technology (e.g., satellite and terrestrial). After discussing the working principles of the designed QUIC-based proxy, we present a software implementation, as well as preliminary results obtained, through a set of meaningful test-cases deployed over a Linux based testbed.

In the definition of advanced 5G scenarios, one of the possible configurations including the satellite link is to consider it to provide a supplementary capacity to enhance backhauling towards data networks. The peculiar satellite physical characteristics and the resulting challenging communication environment (i.e., large propagation delays, possible losses, etc.) are usually tackled with the introduction of Performance Enhancing Proxies (PEPs) agents aimed to improve performance. In this regard, 5G offers the cutting-edge capability to exploit virtualization and slicing concepts, so that PEP can be implemented as a set of Virtualized Network Functions (VNFs) to be dynamically deployed into the network responding to the specific requirement of the target service slice. In this paper we discuss this approach, validated in the frame of an European Space Agency (ESA) project, where a hybrid terrestrial-satellite backhaul is envisaged to enhance performance and system. In particular, we present a QUIC proxy as distributed VNFs aimed to efficiently manage the hybrid link allowing an efficient failover in case of terrestrial link outage or unavailability.

TCP Wave is an innovative transport protocol adopting a burst-based transmission approach, instead of the traditional window-based one. In TCP Wave the underlying IP packet transmission process results completely changed because of an internal timer to schedule bursts, which replaces the ACK-clocked transmission of all TCP versions. So far, TCP Wave capabilities have been assessed in a large gamut of scenarios but mainly limited to unidirectional bulk-like transfers involving a TCP sender and a TCP receiver. In this paper, TCP Wave behavior and performance are evaluated for the first time with real HTTP running applications, which are characterized by: a request/response interactive traffic model, a short and, in some cases, spaced objects transmissions and a mutual role of TCP peers that can act either as sender or receiver according to the application operations. TCP Wave procedures were accurately adapted to be suitable in this scenario and will be described in details. Finally, ns-3 simulator was setup and test campaign was performed, including both a real Web server and an HTTP client.

New paradigms for web applications have motivated in recent years a series of proposals to update the Internet protocols. One of the proposed protocols is called SPDY, endorsed and developed by Google. This protocol at application layer is able to optimize Web page loading time, allowing additional features such as multiplexing, flow control and priority, and providing security as well. Some SPDY working principles can be particularly effective in a satellite context, aspect not yet well covered by present literature. This paper assesses the use of SPDY in a satellite-based scenario, in particular focusing on the multiplexing feature, which is one of the main innovations. The main objective is to demonstrate how SPDY approach relying on few TCP connections (one in the optimal case) to carry all the Web objects brings a relevant performance improvement. The analysis is supported by experiments over a Linux based testbed introducing a long latency link to the data patch, including a reference SPDY implementation.

An efficient resource allocation is of paramount importance to guarantee the best performance with a fair distribution of satellite capacity, even for Multi-beam High Throughput Satellites (HTS) platforms. These platforms are recently gaining relevance for broadband Internet access and are nowadays able to provide xDSL like services. Although the available bandwidth for HTS is greater than previous platforms, it is still fundamental to use it wisely and avoiding abuses, which may jeopardize the service performance of the installed user-base. This paper focuses on the commercial system using the KA-SAT platform by Eutelsat, where a Deep Packet Inspection (DPI) solution is adopted to allow multi-dimensional per-user and per-application priority. Simulation and emulation tests have been executed to identify both the optimal DPI configuration and the amount of satellite capacity to procure in order to meet user requirements. Test achievements are then used to provide useful inputs for the real platform configuration in the frame of the Lift Off ESA project.

SPDY is a recent Web technology aimed to improve webpages load time and resource utilization, through the implementation of: multiplexing and prioritization of webpage objects, header compression, resource pushing and encryption. Most of these techniques are already implemented in Performance Enhancing Proxies (PEPs), which are adopted in geostationary satellite systems to optimize TCP-based application performance. Thus, SPDY is expected to provide benefits for satellite communications resource management. This paper provides a careful assessment of SPDY performance over satellite links, compliant to DVB-RCS standard, with return link resources assigned on demand through a Demand Assignment Multiple Access (DAMA) method. Such a reference scenario constitutes a challenging communication environment due to both the limited return link bandwidth and the relatively high latency. Performance evaluation has been carried out through a satellite network emulator, which reproduces physical layer satellite impairments, while running real implementations of both TCP/IP stack and SPDY.

TCP Noordwijk manages very efficiently Internet traffic when a satellite link is included in the path. The improvement of the bandwidth estimator can further increase performance, especially in presence of competing traffic using other TCP protocols, and the exploitation of innovative service paradigms, first of all, cloud computing. In this respect, a meaningful increase of data transfers with different requirements in terms of size and interactivity will be experienced and large bulk data transfers can imply congestion on the bottleneck link of the core networks, impairing performance of real-time data transfers. This issue is further emphasized when a satellite link is included on the path, since resources are limited and the large latency affects congestion recovery mechanisms. Flow control differentiation capability can be the solution to exploit cloud computing efficiently. In this paper, we propose to manage flows priority at the transport layer introducing a proxy agent installed before each satellite terminal exploiting cloud computing service, which can use different transport protocols and parameters according to the flow priority. The proxy includes the new TCP Noordwijk+ (TCPN+), which allows establishing efficient transfer of low-priority bulk data along with efficient handling of interactive data, keeping a degree of friendliness with existing standard TCP connections. The results, outcome of Ns-2 simulation, confirm the efficiency of the proposed solution.

DVB-S/S2 is used to provide multimedia broadcasting and unidirectional IP based services over satellite networks, while DVB-RCS enhances transmission in a bidirectional way, enabling transmission over the satellite return channel. Streaming Encapsulation (GSE) protocols are defined to transport 'P datagrams over DVB. They provide several benefits over Multiprotocol Encapsulation (MPE), typically used in DVB for transporting 'P data. While the security mechanism defined within DVB-RCS standard supports MPE encapsulation, there is no identified security mechanism for both ULE and GSE protocols. This paper proposes an enhanced security framework for DVBRCS security specifications adopting ULE encapsulation to provide secure lightweight encapsulation.

ESA Satlabs proposed a splitting architecture, named Interoperable-Performance Enhancing Proxy (I-PEP), which defines a protocol stack for the edges of a Digital Video Broadcasting-Return Channal over Satellite (DVB-RCS) link with the aim of improving performance of Transmission Control Protocol (TCP)-based applications. At the transport layer of I-PEPs, the Space Communications Protocols Standards-Transport Protocol (SCPS-TP) provides a reliable connection to upper layers, although resulting in very poor performance in tests. In fact, standard congestion-control mechanisms under-perform mainly due to long latency and Demand Assignment Multiple Access (DAMA) access schemes, especially in the case of short transfers, as for Web traffic, when optimum window may not be reached. In this paper, a burst-based TCP, named TCP Noordwijk (TCPN), is introduced to improve on these aspects. To evaluate performance, the protocol has been implemented on the Network Simulator NS-2. Definitively, details on the protocol design, implementation, and a vast gamut of results coming from simulations are reported.

DVB-RCS links, as well as most of VSAT systems, to improve TCP performance usually consider a PEP solution. The SatLabs group of the European Space Agency issued I-PEP, selecting SCPS-TP as transport protocol, which supports two congestion control schemes: TCP Vegas (default) and van Jacobson's Slow Start and Congestion Avoidance. In both cases the most popular TCP-based applications, i.e. Web browsing and e-mail, achieve very poor performance especially when DAMA schemes run at the MAC layer. In this frame, TCP Noordwijk has been specifically designed to optimize performance of short TCP- based data transfers over DVB-RCS DAMA links, meeting the requirement to be compatible with I-PEP specifications. This paper presents an overview of TCP-based application criticalities over DVB-RCS links and shows how TCP Noordwijk improves performance.

In a mobile communication scenario handover functions must be supported in order to keep connection alive while switching between different points of access. Moreover, if the infrastructure is composed of different networks or technologies, intersegment handover is necessary to roam from a component to another. The handover function is implemented either for necessity or to improve performance. Necessity means that the terminal must perform a handover because its current network connection is worsening; in the other case switching to another network can help to achieve better performance even if the current network connection is fine. Furthermore, the handover can be soft or hard, according to the possible overlap in the connection of the two segments involved. This paper illustrates the behavior of TCP during intersegment handovers in an architecture including two segments: satellite and WLAN. In particular, the goal is to carry out a thorough analysis of a cross-layer based mechanism applicable during handovers to optimize the TCP performance. Such a mechanism is validated with an ad-hoc software simulator written in C++ and the most meaningful results are shown.

The integration of a satellite system with a HAPS segment appears very suitable to provide communication services, including Internet access, for a large set of applications. In fact, the satellite capability to provide wide coverage and broadband access can be enhanced by the use of cost-effective, mobile/portable and low-power consuming user terminals, when HAPS acts as an intermediate repeater. Moreover, also TCP-based applications, which suffer from long latency introduced by the satellite link and in general by errors, can get benefits in terms of end-to-end performance. In this frame, this paper deals with the introduction, on board the HAPS, of an efficient CAC scheme in order to guarantee an optimal utilization of the precious radio resources. In particular, we propose an innovative TCP driven CAC algorithm, which shall take into account not only the QoS requirements, but also TCP statistics obtained through a proxy installed on the HAPS. Results show that the overall system performance in terms of both average throughput and blocking probability is significantly improved.

Several satellite systems currently in operation or under development claim to support broadband Internet applications. In these scenarios, transmission control protocol (TCP) plays a critical role. Unfortunately, when used with satellite links, TCP suffers from a number of well-known performance problems, especially for higher data rates and high altitude satellites with longer delays. In response to these difficulties, the satellite and Internet research communities have developed a large gamut of solutions ranging from architectural modifications to changes in the TCP protocol. Among these, one approach requiring minimal modifications involves splitting the TCP connection in two or more segments with one segment connecting terrestrial nodes across the satellite network. In this paper, we consider an evolution of this idea: placing a TCP proxy on board the satellite that further subdivides the end-to-end connection into separate TCP connections between ground and space. We focus upon the efficient use of buffer resources on board the satellite, while at the same time enhancing TCP performance. We evaluate two TCP protocol versions, TCP NewReno and TCP Westwood. We consider various geosynchronous earth orbit satellite scenarios, with and without the split proxy, and with different channel error conditions (random errors, shadowing, etc.). Using simulation, we show that an on-board proxy provides a number of distinct advantages and can enhance throughput up to threefold for both TCP New Reno and TCP Westwood, in some scenarios, with relatively modest on-board buffering requirements. The main contributions of this paper are: the on-board split proxy concept, the buffer management strategy, the use of a realistic "urban shadowing" model in the evaluation, and the extensive comparison of the recently announced TCP Westwood with the traditional TCP New Reno.

Abstract Satellite system architectures based on geostationary or Low Earth Orbit (LEO)/Medium Earth Orbit (MEO) constellation suffer from their intrinsic limitations in terms of coverage or flexibility. Traffic requirements concerning broadband services are expected to be very uneven both in time and space. To match this requirement and to improve coverage an innovative satellite system architecture, composed of a LEO/MEO segment to complement a Geostationary Earth Orbit (GEO) segment, has been proposed. In this scenario, to achieve interworking and to make it possible to hold the call while switching between the two segments, efficient intersegment handover (ISHO) procedures must be identified. The paper, after introducing the classical ISHO schemes, aims at defining and analysing an ISHO procedure developed to perform handover in case of hybrid constellations based on the use of both GEO and LEO/MEO orbits. Performance evaluation will be carried out for different system configurations utilizing a dynamic satellite constellation simulator in the time domain. The execution delay and its complementary cumulative distribution have been evaluated for different constellation geometry at different distances from the gateway. Copyright © 2002 John Wiley & Sons, Ltd.

High errors and high delays create well-known problems with TCP. One established approach to solve this problem involves dividing TCP connections into segments, or splitting the connection. This paper takes this approach one step further by exploring the use of a TCP proxy on board a satellite for the purpose of enhancing end-to-end TCP performance. We show that this approach yields a number of important advantages, especially for small, mobile terminals, multi-segment systems, and multicast applications. As part of this architecture, we introduce a method of TCP backpressure using the advertised window, which optimizes memory usage on the satellite. Using simulation, we demonstrate that performance may improve by as much as three-fold.

The severe constraints characterising satellite communications and the need to reduce the user terminal requirements impose restrictions on obtaining high on-board performance. If satellite systems aim at providing a large set of multimedia services to a large set of users, as standalone systems or as a real complement to terrestrial networks, considering the scarce bandwidth allocation, pursuing the improvement of payload characteristics we can get the target performance. To reach this goal the use of multibeam antennas for coverage patterns as similar as possible to terrestrial cellular systems is practically mandatory. The increased number of beams allows greater spatial selectivity helping in alleviating interference constraints and in implementing fading countermeasure techniques. The increase of the number of beams has to be traded off among the co-channel interference, complexity, costs and the maximisation of the spectral efficiency. In this paper the problem of interference in multibeam satellite systems is described and the impact of antenna design on interference is quantified for a LEO constellation. The results of simulations carried out using a simulator capable of performing dynamic analysis varying the number of beams are presented.