Mathieu Gineste

Effect of Residual Channel Estimation Errors in Random Access Methods for Satellite Communications

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.

On the Impact of Link Layer Retransmissions on TCP for Aeronautical Communications

In this article, we evaluate the impact of link layer retransmissions on the performance of TCP in the context of aeronautical communications. We present the architecture of aeronautical networks, which is manly driven by an important channel access delay, and the various retransmission strategies that can be implemented at both link and transport layers. We consider a worst case scenario to illustrate the benefits provided by the ARQ scheme at the link layer in terms of transmission delay. We evaluate the trade-off between allowing a fast data transmission and a low usage of satellite capacity by adjusting link layer parameters.

Estimation of Timing Offsets and Phase Shifts between Packet Replicas in MARSALA Random Access

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.

Multipath TCP Architecture for Infotainment Multimedia Applications in Vehicular Networks

The large deployment of Internet resources has facilitated the accelerated development of Intelligent Transport Systems (ITS) including a large diversity of distributed applications such as non-safety infotainment vehicular applications. In vehicular networks, nodes can connect to Internet using Road Side Units (RSUs), but the complete deployment of RSUs along all the transport network seems unfeasible. So, we can take advantage of multihomed devices using complementary access network technologies, such as satellite networks, in order to maintain the connectivity. Several solutions have been implemented in order to take advantage of multihoming and multipath capabilities of mobile nodes. However, in dynamic network scenarios involving multipath communication channels, the QoS requirements of these applications is not always globally managed and guaranteed. Moreover, specific multimedia semantics of the transmitted data is not usually considered by the available transmission mechanisms and protocols. In this work, we present a Multipath TCP communication architecture that take full advantage of the intrinsic multimedia QoS semantics based in Deep Packet Inspection in order to self-manage the available resources and to provide a more compliant e2e transport service.

Dynamic satellite system QoS architecture integrated with IP Multimedia Subsystem core network

Summary n nConvergence is one of the most important challenges for Next Generation Networks (NGN). This includes service convergence as well as fixed-mobile convergence. The integration of satellite telecommunication system into NGN is a key to increasing the coverage of future networks and opening satellite access networks to a wider range of terrestrial solutions. Digital Video Broadcast (DVB) Return Channel via Satellite system (DVB-RCS) and its evolution (DVB-RCS2) are widely used European standards that are specified for broadband satellite systems using dynamic capacity assignment and multifrequency TDMA. This paper introduces a new QoS architecture derived from terrestrial IP Multimedia Subsystem solutions to provide advanced end-to-end QoS support, and defines cross-layer optimization paths suited to the satellite context and in particular using DVB standards. Copyright

An autonomic traffic analysis proposal using Machine Learning techniques

Network analysis has recently become in one of the most challenging tasks to handle due to the rapid growth of communication technologies. For network management, accurate identification and classification of network traffic is a key task. For example, identifying traffic from different applications is critical to manage bandwidth resources and to ensure Quality of Service objectives. Machine learning emerges as a suitable tool for traffic classification; however, it requires several steps that must be followed adequately in order to achieve the goals. In this paper, we proposed an architecture to perform traffic analysis based on Machine Learning techniques and autonomic computing. We analyze the procedures to perform Machine Learning over traffic network classification, and at the same time we give guidelines to introduce all these procedures into the architecture proposed. The main contribution of our proposal is the reconfiguration of the traffic classifier that will change according to the knowledge acquired from the traffic analysis process.

Making H-ARQ Suitable for a Mobile TCP Receiver over LEO Satellite Constellations

This paper investigates strategies to carry out delay tolerant services over LEO satellite constellations for mobile receiver. In this context, LEO constellations are characterized by important delay variations where propagation impairments are mostly localized on the Land Mobile Satellite (LMS) channel (i.e. on the last hop). To cope with this issue, distinct reliability schemes can be introduced at the physical or link layers. Although their capacity to cope with transmission errors has been demonstrated, these recovery schemes may induce a high jitter that could severely damage TCP’s internal timers and reliability schemes. As a matter of fact, transport and link layers’ reliability schemes exhibit a clear discrepancy. Following temporal traces representing the delay between a mobile terminal and the last hop satellite from a LEO constellation, we assess how HARQ mechanisms impact on the RTO based retransmission and the duplicate acknowledgments of TCP. Based on ns-2 simulations, we propose a layer-2 buffer that let both link and transport layers to conjointly perform. Our evaluations show an end-to-end data rate increase and more generally illustrate the benefit of re-ordering packets at the link layer when link-layer erasure coding recovery mechanisms are used conjointly with TCP.

Enhancing satellite system throughput using adaptive HARQ for delay tolerant services in mobile communications

In this paper we propose the introduction of adaptive hybrid automatic repeat request (HARQ) in the context of mobile satellite communications. HARQ schemes which are commonly used in terrestrial links, can be adapted to improve the throughput for delay tolerant services. The proposed method uses the estimation of the mutual information between the received and the sent symbols, in order to estimate the number of bits necessary to decode the message at next transmission. We evaluate the performance of our method by simulating a land mobile satellite (LMS) channel. We compare our results with the static HARQ scheme, showing that our adaptive retransmission technique has better efficiency while keeping an acceptable delay for services.