This paper introduces a data-driven model for generating synthetic satellite users based on population and geographical factors. The model applies the logarithmic opinion pool to combine complementary perspectives on user distribution, such as population density and rural predominance. This principled aggregation captures realistic spatial disparities in connectivity and improves the representativeness of satellite constellation simulations. The approach supports the development of adaptive non-terrestrial network (NTN) strategies aligned with both orbital topology and terrestrial demand.

We propose a fully decentralized, adaptive routing system that exploits the dynamic topology of Walker Delta Low Earth Orbit (LEO) constellations to achieve efficient traffic distribution and improved reliability without requiring global link-state information. The system addresses scalability challenges in mega-constellations, where congestion, limited ground infrastructure, and uneven user distribution degrade service quality in high-demand regions. Although inter-satellite links provide diverse routing paths, the lack of multibeam support in some terminals complicates routing and can increase path length during cross-plane communication. Our evaluation of a Hop-by-Hop based strategy in Walker Delta constellations shows that it achieves performance comparable to optimal congestion-minimization algorithms and outperforms source-routing methods, while maintaining near-minimal hop counts for low-latency communication.

The availability of abundant solar energy is driving renewed interest in orbital computing infrastructures hosted on Sun-Synchronous Orbit (SSO) constellations. However, these constellations suffer from limited instantaneous Earth coverage and constrained direct-to-ground, which is clearly incompatible with the connectivity and responsiveness requirements of datacenter clients. In this paper, we propose a hybrid architecture where SSO satellites offload traffic through Low Earth Orbit (LEO) Walker constellations—such as OneWeb and Starlink—which act as a dynamic relay layer toward the ground. We design and evaluate dynamic inter-orbital link topologies enabling SSO-to-Walker connectivity and analyze their performance in terms of link availability, relay opportunities, path continuity, and network resilience. Our results show that leveraging Walker constellations as relays significantly improves SSO systems, effectively compensating for their coverage limitations.

Key Exchange mechanisms (KE or KEMs) such as the Diffie-Hellman protocol have proved to be a cornerstone conciliating the efficiency of symmetric encryption and the practicality of public key primitives. Such designs however assume the non-compromission of the long term asymmetric key in use. To relax this strong security assumption, and allow for modern security features such as Perfect Forward Secrecy (PFS) or Post Compromise Security (PCS), Ratcheted-KE (RKE) have been proposed. This work proposes to turn the Hamming Quasi-Cyclic (HQC) cryptosystem into such a Ratcheted-KE, yielding the first code-based such construction. Interestingly, our design allows indifferently one party to update the key on-demand rather than the other, yielding a construction called bi-directionnal RKE, which compares favorably to generic transformations. Finally, we prove that the resulting scheme satisfies the usual correctness and key-indistinguishability properties, and suggest concrete sets of parameters, assuming different reallife use cases.

Low Earth Orbit (LEO) constellations are transforming today’s modern communication era by enabling highspeed, low-latency, and reliable broadband services at a global scale. Despite their huge potential, designing efficient mechanisms for satellite networks is challenging due to the dynamic nature of LEO satellites. In this paper, we focus on routing in LEO constellations including Inter-Satellite Links (ISLs) with several constraints like e.g. minimising the maximum link utilisation. We propose a static approach aiming to find optimal paths to transmit traffic demands in the network graph. We consider Linear Programming (LP) to formulate problems for different network constraints and show that we are able to provide solutions respecting the various constraints, including those related to quality of service (QoS).

The development of online applications for services such as package delivery, crowdsourcing, or taxi dispatching has caught the attention of the research community to the domain of online multi-agent multi-task allocation. In online service applications, tasks (or requests) to be performed arrive over time and need to be dynamically assigned to agents. Such planning problems are challenging because: (i) few or almost no information about future tasks is available for long-term reasoning; (ii) agent number, as well as, task number can be impressively high; and (iii) an efficient solution has to be reached in a limited amount of time. In this paper, we propose SKATE, a successive rank-based task assignment algorithm for online multi-agent planning. SKATE can be seen as a meta-heuristic approach which successively assigns a task to the best-ranked agent until all tasks have been assigned. We assessed the complexity of SKATE and showed it is cubic in the number of agents and tasks. To investigate how multi-agent multi-task assignment algorithms perform under a high number of agents and tasks, we compare three multi-task assignment methods in synthetic and real data benchmark environments: Integer Linear Programming (ILP), Genetic Algorithm (GA), and SKATE. In addition, a proactive approach is nested to all methods to determine near-future available agents (resources) using a receding-horizon. Based on the results obtained, we can argue that the classical ILP offers the better quality solutions when treating a low number of agents and tasks, i.e. low load despite the receding-horizon size, while it struggles to respect the time constraint for high load. SKATE performs better than the other methods in high load conditions, and even better when a variable receding-horizon is used.

International audience

This study investigates the importance of choosing the first (respectively last) hop to access (respectively to exit) a Low Earth Orbit (LEO) satellite constellation, which is of upmost importance for the LEO routing performance. Usually, basic routing strategies connect a ground station to its nearest satellite, and this strategy does not always lead to the optimal routing path. We propose to select this first/last satellites within a subset of k-nearest satellites. After performing routing simulations over one of the next-generation satellite constellations, preliminary results show that this in/out hop selection strategy leads to a better link capacity usage and a lower data loss rate, allowing a faster TCP bulk data transfer.

Time-Sensitive Networking (TSN) describes a set of features extending the functionalities and Quality of Service (QoS) of standard Ethernet to enable determinism, reliability and reconfigurability, key requirements for Industry 4.0. The TSN profile for industrial automation (IEC/IEEE 60802 standard) defines specific options to favor reliability and reconfigurability. Nevertheless, there are multiple possible options for scheduling to guarantee determinism. Today, the scheduling standards in TSN can be categorized according to the implemented communication paradigm: asynchronous or synchronous. This paradigm is of utmost importance to quantify the synchronization need and the reconfigurability effort. The main contribution of this work is the specification of an asynchronous TSN-compliant network for Industry 4.0, FactoRing, that bridges the gap between both paradigms to guarantee low bounded jitters and latencies, without the need of synchronization and complex network planning. Moreover, FactoRing supports ring-based topologies to significantly reduce installation wiring and costs. In this paper, we first present the main industry 4.0 requirements and assess the ability of recommended TSN mechanisms for industrial automation versus such requirements. Afterwards, we detail the main features of Factoring including QoS, reliability and reconfiguration management. Finally, preliminary results on performance metrics like jitters, latencies and buffer usage are discussed and the first conclusions on the promises of Factoring to meet Industry 4.0 requirements are derived.

In this paper, we introduce a protocol to securely exchange data on chain while varying its price according to their freshness, maturity and lifetime. The exchange protocol, implemented as a smart contract, is best applied to crowdsourcing systems for fast depreciating digital goods, in which information is publicly shared after a given delay. The smart contract acts as a trusted intermediary to make sure that the funds of a client are delivered to the provider if and only if the data were really transferred. It also ensures that the data will be freely shared on the blockchain when the data has sufficiently depreciated. We demonstrate our work with an available prototype for specific space tracking data exchange.

We introduce a XOR-based source routing (XSR) scheme as a novel approach to enable fast forwarding and low-latency communications. XSR uses linear encoding operation to both 1) build the path labels of unicast and multicast data transfers; 2) perform fast computational efficient routing decisions compared to standard table lookup procedure without any packet modification all along the path. XSR specifically focuses on decreasing the complexity of forwarding router operations. This allows packet switches (e.g, link-layer switch or router) to perform only simple linear operations over a binary vector label which embeds the path. XSR provides the building blocks to speed up the forwarding plane and can be applied to different data planes such as MPLS or IPv6. Compared to recent approaches based on modular arithmetic, XSR computes the smallest label possible and presents strong scalable properties allowing to be deployed over any kind of core vendor or datacenter networks. At last but not least, the same computed label can be used interchangeably to cross the path forward or reverse in the context of unicast communication.

Random Access (RA) protocols have considerably evolved in satellite communications, especially after the introduction of Contention Resolution Diversity Slotted Aloha (CRDSA). However, CRDSA finds itself in a deadlock when the number of users is important. A complementary treatment Multireplica Decoding using Correlation based Localization (MARSALA) has hence been proposed to unlock CRDSA. This is fulfilled by localizing then combining replicas of the same undecoded packets using correlations. Based on a prior knowledge of the potential frame content by the receiver, a random Shared POsition Technique for Interfered random Transmissions (SPOTiT) is proposed to reduce MARSALA's localization complexity. As a matter of fact, random SPOTiT highlights a manner for the receiver to be aware of time slot positions and the preamble used by each subscriber. Then it uses this information to target a lower number of slots for localization correlations. In this paper we propose a hybrid solution that mixes both DAMA and Random Access in order to lower the Packet Loss Ratio (PLR) floor. In fact, a centralized computing can manage replicas positions and preambles to use, in a way that no loops are created. This also allows to keep a simple packet localization as in SPOTiT. Hereafter, we provide an optimal distribution of frame content using two replicas per packet which is evaluated through simulation.

Erasure codes are widely used in today's storage systems to cope with failures. Most of them use the finite field arithmetic. In this paper, we propose an implementation and a coding speed evaluation of an original method called PYRIT (PolYnomial RIng Transform) to perform operations between elements of a finite field into a bigger ring by using fast transforms between these two structures. Working in such a ring is much easier than working in a finite field. Firstly, it reduces the coding complexity by design. Secondly, it allows simple but efficient xor-based implementations by unrolling the operations thanks to the properties of the ring structure. We evaluate this proposition for Maximum Distance Separable erasure codes and we show that our method has better performances than common codes. Compared to the best known implementations, the coding speeds are increased by a factor varying from 1.5 or 2.

The complexity of software implementations of MDS erasure codes mainly depends on the efficiency of the finite field operations implementation. In this paper, we propose a method to reduce the complexity of the finite field multiplication by using simple transforms between a field and a ring to perform the multiplication in a ring. We show that moving to a ring reduces the complexity of the operations. Then, we show that this construction allows the use of simple scheduling to reduce the number of operations.

Multi-replicA decoding using corRelation baSed LocALisAtion (MARSALA) is a recent random access technique designed for satellite return links. It follows the multiple transmission and interference cancellation scheme of Contention Resolution Diversity Slotted Aloha (CRDSA). In addition, at the receiver side, MARSALA uses autocorrelation to localise replicas of a same packet so as to coherently combine them. Previous work has shown good performance of MARSALA with an assumption of ideal channel state information and perfectly coherent combining of the different replicas of a given packet. However, in a real system, synchronisation errors such as timing offsets and phase shifts between the replicas on separate timeslots will result in less constructive combining of the received signals. This paper describes a method to estimate and compensate the timing and phase differences between the replicas, prior to their combination. Then, the impact of signal misalignment in terms of residual timing offsets and phase shifts, is modeled and evaluated analytically. Finally, the performance of MARSALA in realistic channel conditions is assessed through simulations, and compared to CRDSA in various scenarios.

Recent work have shown that Reed-Müller (RM) codes achieve the erasure channel capacity. However, this performance is obtained with maximum-likelihood decoding which can be costly for practical applications. In this paper, we propose an encoding/decoding scheme for Reed-Müller codes on the packet erasure channel based on Plotkin construction. We present several improvements over the generic decoding. They allow, for a light cost, to compete with maximum-likelihood decoding performance, especially on high-rate codes, while significantly outperforming it in terms of speed.

Avionics implementation with less cables will clearly improve the efficiency of aircraft while reducing weight and maintenance costs. To fulfill these emerging needs, an innovative avionics communication architecture, based on Gigabit Full Duplex Ethernet ring, is proposed in this paper. To adapt this COTS technology to safety-critical avionics, an adequate tuning process of the communication protocol and the choice of reliability mechanisms to achieve timely and reliable communications are first detailed. Then, efficient timing analyses of such a proposal based on Network Calculus are conducted, accounting the impact of a ring topology and the specified reliability mechanisms. Third, these general analyses are illustrated in the case of a realistic avionic application, to replace the AFDX backup network with AeroRing, to reduce wires, while guaranteeing timely communications.

End-to-end (E2E) reliable communication in Delay Tolerant Network (DTN) is a challenging task due to long delay and frequent link disruptions. To enable reliability, the IETF is currently looking at strategies to integrate erasure coding mechanisms inside DTN architecture. The objective is to extend the ability of the existing DTN bundle fragmentation mechanism to support cases where bundles have a high probability of being lost. To date, discussions agree that an intermediate node can re-encode bundles, leaving all decoding process at the destination node in order to let intermediate node operations be as simple as possible. We propose to study and analyze possible re-encoding strategies at intermediate nodes using an on-the-fly coding paradigm. We also investigate how re-encoding and acknowledgment strategies based on this coding scheme would enable E2E reliable communication. Finally, we propose an adaptive mechanism with low complexity that deals with both re-routing events and network dynamics which are common in the context of DTN. Simulation results show that re-encoding at the relay and the adaptive mechanism allows a significant reduction in terms of network overhead injected by erasure codes while ensuring the E2E reliability.

This paper introduces Rest, a reliable streaming protocol for lossy networks. Rest ensures full reliability while recovering losses as soon as possible thanks to the proactive injection of redundancy packets encoded following an on-the-fly scheme. It dynamically adapts the sending of codes depending on the estimation of the packet error rate with periodic acknowledgments to limit feedback dependency and protocol overhead. Results show that data are smoothly delivered to the receiving application with minimum overhead when errors are uniform. For systems with limited processing capacity, we propose to use a bounded encoding window to deliver data more uniformly while limiting decoding matrices size. We study the performance of Rest under different network conditions and highlight the underlying trade-offs behind each system parameter. We show that an optimal acknowledgement frequency can be estimated to minimize overhead while meeting system requirements in terms of delivery delay and computational power.

This paper proposes "LD-Tetrys" (Late Decoding Tetrys), a solution based on an on-the-fly erasure code that attempts to solve the problem of late decoded packets usually considered as lost by the video decoder. LD-Tetrys has the following advantages: i) it drastically improves the trade-off between throughput and quality without modifying the codecs or adding complexity at the encoder side ii) it allows a simple but robust configuration. The only cost is a minor modification of the decoding process and a slight increase in the video decoding complexity. Last but not least, LD-Tetrys requires a much smaller playout buffer to obtain the same perceived video quality, bringing benefits for interactive applications.

This paper proposes a new method for data reception over a random access channel in a satellite communication system. The method is called Multi-replicA decoding using corRelation baSed locALisAtion (MARSALA). It uses the same transmission scheme as in Contention Resolution Diversity Slotted Aloha (CRDSA) where each user sends several replicas of the same packet over the frame. MARSALA is a new decoding technique that localises all the replicas of a packet using a correlation based method, then combines them to decode the data. With MARSALA, the system can achieve a normalized throughput higher than 1.2, resulting in a significant gain compared to CRDSA, while adding a relatively low implementation complexity at the receiver. We also highlight on the practical issues related to channel estimation and how to perform coherent signal combination in MARSALA.

In recent random access methods used for satellite communications, collisions between packets are not considered as destructive. In fact, to deal with the collision problem, successive interference cancellation is performed at the receiver. Generally, it is assumed that the receiver has perfect knowledge of the interference. In practice, the interference term is affected by the transmission channel parameters, i.e., channel attenuation, timing offsets, frequency offsets and phase shifts, and needs to be accurately estimated and canceled to avoid performance degradation. In this paper, we study the performance of an enhanced channel estimation technique combining estimation using an autocorrelation based method and the Expectation-Maximization algorithm integrated in a joint estimation and decoding scheme. We evaluate the effect of residual estimation errors after successive interference cancellation. To validate our experimental results, we compare them to the Cramer-Rao lower bounds for the estimation of channel parameters in case of superimposed signals.

Broadcasting systems have to deal with channel variability in order to offer the best spectrum efficiency to the receivers. However, the transmission parameters that optimize the spectrum efficiency generally leads to a large link unavailability. In this paper, we study the performance of hierarchical and non-hierarchical modulations in terms of spectrum efficiency and link unavailability for DVB-S2 systems. Our first contribution is the design of the hierarchical 16-APSK for the DVB-S2 standard. Then we introduce the link unavailability to compare the performance of hierarchical and non-hierarchical modulations in terms of spectrum efficiency and link unavailability. The results show that hierarchical modulation is a good alternative to non-hierarchical modulation for the DVB-S2 standard.

Application-Level Forward Erasure Correction (AL-FEC) codes are a key element of telecommunication systems. They are used to recover from packet losses when retransmission are not feasible and to optimize the large scale distribution of contents. In this paper we introduce Reed-Solomon/LDPC-Staircase codes, two complementary AL-FEC codes that have recently been recognized as superior to Raptor codes in the context of the 3GPP-eMBMS call for technology [1]. After a brief introduction to the codes, we explain how to design high performance codecs which is a key aspect when targeting embedded systems with limited CPU/battery capacity. Finally we present the performances of these codes in terms of erasure correction capabilities and encoding/decoding speed, taking advantage of the 3GPP-eMBMS results where they have been ranked first.

Video transmission is sensitive to losses due to high compression efficiency. To tolerate the quality degradation from losses, Forward Error Correction (FEC) and error resilience schemes are commonly used. In this paper, we evaluate the performance of error tolerance schemes with the latest video coding standard, H.264/AVC. The analysis in three zones of packet loss rates (PLR) shows that no FEC scheme outperforms the others in a wide PLR range. We also compare the equal and unequal FEC schemes with the Flexible Macroblock Ordering (FMO) error resilience mechanism and find that FMO performs well in moving videos while FEC codes are better in rather static videos. Our results and analysis would give insights to design flexible applications which are able to adapt to the network dynamics.

A new class of erasure codes for delay-constraint applications, called on-the-fly coding, have recently been introduced for their improvements in terms of recovery delay and achievable capacity. Despite their promising characteristics, little is known about the complexity of the systematic and non-systematic variants of this code, notably for live multicast transmission of multimedia content which is their ideal use case. Our paper aims to fill this gap and targets specifically the metrics relevant to mobile receivers with limited resources: buffer size requirements and computation complexity of the receiver. As our contribution, we evaluate both code variants on uniform and bursty erasure channels. Results obtained are unequivocal and demonstrate that the systematic codes outperform the non-systematic ones, in terms of both the buffer occupancy and computation overhead.

We present a solution to evaluate the performance of transport protocols as a function of link layer reliability schemes (i.e. ARQ, FEC and Hybrid ARQ) applied to satellite physical layer traces. As modelling such traces is complex and may require approximations, the use of real traces will minimise the potential for erroneous performance evaluations resulting from imperfect models. Our Trace Manager Tool (TMT) produces the corresponding link layer output, which is then used within the ns-2 network simulator via the additionally developed ns-2 interface module. We first present the analytical models for the link layer with bursty erasure packets and for the link layer reliability mechanisms with bursty erasures. Then, we present details of the TMT tool and our validation methodology, demonstrating that the selected performance metrics (recovery delay and throughput efficiency) exhibit a good match between the theoretical results and those obtained with TMT. Finally, we present results showing the impact of different link layer reliability mechanisms on the performance of TCP Cubic transport layer protocol.

Video streaming for heterogeneous types of devices, where nodes have different devices characteristics in terms of computational capacity and display, is usually handled by encoding the video with different qualities. This is not well suited for Peer-To-Peer (P2P) systems, as a single peer group can only share content of the same quality, thus limiting the peer group size and efficiency. To address this problem, several existing works propose the use of Multiple Descriptions Coding (MDC). The concept of this type of video codec is to split a video in a number of descriptions which can be used on their own, or aggregated to improve the global quality of the video. Unfortunately existing MDC codes are not flexible, as the video is split in a defined number of descriptions. In this paper, we focus on the practical feasibility of using a Fountain MDC code with properties similar to existing Fountain erasure codes, including the ability to create any number of descriptions when needed (on the fly). We perform simulations using selected pictures to assess the feasibility of using these codes, knowing that they should improve the availability of the video pieces in a P2P system and hence the video streaming quality. We observe that, although this idea seems promising, the evaluated benefits, demonstrated by the PSNR values, are limited when used in a real P2P video streaming system.

In this paper, we propose a structured peer-to-peer (P2P) distribution scheme based on Fast Fourier Transform (FFT) graphs. We build a peer-to-peer network that reproduces the FFT graph initially designed for hardware FFT codecs. This topology allows content delivery with a maximum diversity level for a minimum global complexity. The resulting FFT-based network is a structured architecture with an adapted network coding that brings flexibility upon content distribution and robustness upon the dynamic nature of the network. This structure can achieve optimal capacity in terms of content recovery while solving the problem of last remaining blocks, even for large networks.

This paper introduces a robust point-to-point transmission scheme: Tetrys, that relies on a novel on-the-fly erasure coding concept which reduces the delay for recovering lost data at the receiver side. In current erasure coding schemes, the packets that are not rebuilt at the receiver side are either lost or delayed by at least one RTT before transmission to the application. The present contribution aims at demonstrating that Tetrys coding scheme can fill the gap between real-time applications requirements and full reliability. Indeed, we show that in several cases, Tetrys can recover lost packets below one RTT over lossy and best-effort networks. We also show that Tetrys allows to enable full reliability without delay compromise and as a result: significantly improves the performance of time constrained applications. For instance, our evaluations present that video-conferencing applications obtain a PSNR gain up to 7 dB compared to classic block-based erasure codes.

This paper presents a new construction of maximum-distance separable (MDS) Reed-Solomon erasure codes based on Fermat number transform (FNT). Thanks to FNT, these codes support practical coding and decoding algorithms with complexity O(n log n), where n is the number of symbols of a codeword. An open-source implementation shows that the encoding speed can reach 150 Mbps for codes of length up to several 10,000s of symbols. These codes can be used as the basic component of the information dispersal algorithm (IDA) system used in a several P2P systems.

Delay Tolerant Networks (DTN) do not provide any end to end connectivity guarantee. Thus, transporting data over such networks is a tough challenge as most of Internet applications assume a form of persistent end to end connection. While research in DTN has mainly addressed the problem of routing in various mobility contexts with the aim to improve bundle delay delivery and data delivery ratio, little attention has been paid to applications. This paper investigates the support of streaming-like applications over DTN. We identify how DTN characteristics impact on the overall performances of these applications and present Tetrys, a transport layer mechanism, which enables robust streaming over DTN. Tetrys is based on an on the fly coding mechanism able to ensure full reliability without retransmission and fast in-order bundle delivery in comparison to classical erasure coding schemes. We evaluate our Tetrys prototype on real DTN connectivity traces captured from the Rollerblading tour in Paris. Simulations show that on average, Tetrys clearly outperforms all other reliability schemes in terms of bundles delivery service.

Unequal protection mechanisms have been proposed at several layers in order to improve the reliability of multimedia contents, especially for video data. The paper aims at implementing a multi-layer unequal protection scheme, which is based on a Physical-Transport-Application cross-layer design. Hierarchical Modulation, in the physical layer, has been demonstrated to increase the overall user capacity of a wireless communication. On the other hand, unequal erasure protection codes at the transport layer turned out to be an efficient method to protect video data generated by the application layer by exploiting their intrinsic properties. In this paper, the two techniques are jointly optimized in order to enable recovering lost data in case the protection is performed separately. We show that the cross-layer design proposed herein outperforms the performance of hierarchical modulation and unequal erasure codes taken independently.

This paper presents new FEC codes for the erasure channel, LDPC-Band, that have been designed so as to optimize a hybrid iterative-Maximum Likelihood (ML) decoding. Indeed, these codes feature simultaneously a sparse parity check matrix, which allows an efficient use of iterative LDPC decoding, and a generator matrix with a band structure, which allows fast ML decoding on the erasure channel. The combination of these two decoding algorithms leads to erasure codes achieving a very good trade-off between complexity and erasure correction capability.

Although ironically it does not offer any real-time guarantee, Internet is a popular solution to support multimedia time-constrained applications (e.g. VoIP, Video Conferencing, ...).

Using a particular construction of generator matrices of the q-ary image of q/sup m/-ary cyclic codes, it is proved that some of these codes are invariant under the action of particular permutation groups. The equivalence of such codes with some two-dimensional (2-D) Abelian codes and cyclic codes is deduced from this property. These permutations are also used in the area of the soft-decision decoding of some expanded Reed-Solomon (RS) codes to improve the performance of generalized minimum-distance decoding.