Rapporto finale del progetto NeGeFEC2021

Since the 2018 IAEA FEC Conference, FTU operations have been devoted to several experiments covering a large range of topics, from the investigation of the behaviour of a liquid tin limiter to the runaway electrons mitigation and control and to the stabilization of tearing modes by electron cyclotron heating and by pellet injection. Other experiments have involved the spectroscopy of heavy metal ions, the electron density peaking in helium doped plasmas, the electron cyclotron assisted start-up and the electron temperature measurements in high temperature plasmas. The effectiveness of the laser induced breakdown spectroscopy system has been demonstrated and the new capabilities of the runaway electron imaging spectrometry system for in-flight runaways studies have been explored. Finally, a high resolution saddle coil array for MHD analysis and UV and SXR diamond detectors have been successfully tested on different plasma scenarios.

Rapporto finale del progetto NeGeFEC20

Final Report of the research contract "Rate adaptive and Generalized Floorless LDPC codes" about future FEC solutions for optical communications.

This paper evaluates the performance of the NORM multicast transport protocol, when used in mobile satellite channels that behave as in delay-tolerant and disruptive networks (DTN). Comparisons are made between multicast transmissions with and without interleaver when NORM is used in "confirmed delivery" mode.

In case of video streaming services via satellite towards vehicular clients, very long blockage periods due to road infrastructures, vegetation, and so on, may lead to a complete channel outage, which may result in the loss of all packets transmitted during that period, even in the presence of interleaving and FEC techniques. But if these periods are predictable, as in the presence of known routes traced by means of a GPS navigator, it may be advisable to alert the transmitter in advance, in order to counteract the incoming outage interval. We refer to this technique as Smart Mode. In the following we will detail how Smart Mode takes advantage of FEC and interleaving techniques, in order to improve the Quality of Experience and to reduce the waste of bandwidth in satellite multimedia streaming.

Quality of experience (QoE) is becoming an important parameter for estimating the end user perceived video quality. Video coding algorithms are currently increasing the compression performances by exploiting the temporal and spatial correlations of multimedia information. Such a trend is self-defeating in hybrid networks, due to the frequent channel impairments experienced. In this paper, we present a cross layer approach to reduce the channel impairments that a multimedia communication undergoes when broadcasting a video stream through an hybrid infrastructure constituted by satellite and terrestrial wireless links. We present a detailed statistical description of the terrestrial wireless channel, and we exploit it to design the optimal parameters for tuning our algorithm. Simulations results show that our approach not only performs better than the error recovery techniques currently used, but it also experiences a significant reduction in bandwidth overhead.

Optimizing the end-to-end throughput of a TCP connection (goodput) over geostationary satellite links is a challenging research topic. This is because the high delay-bandwidth product, together with a non-negligible random loss of packets, is a condition that considerably differs from the environments TCP was originally designed for. As a result, TCP performance is significantly impaired by the channel bit error rate. The literature is full of suggestions for improving TCP goodput, most based on modifications of the protocol itself. We only investigated the application of different FEC (forward error correction) types for TCP goodput optimization, leaving the end-to-end protocol unaltered. Using a method midway between analysis and simulation to evaluate the goodput of TCP long-lived connections, we first studied the influence of packet loss rate, introduced by errors on the channel, on the TCP goodput. We showed that, in some cases, the packet loss rate does not need to be negligible with respect to that caused by congestion, as it is widely-held opinion. We then applied physical-level FEC techniques, such as convolutional encoding/Viterbi decoding, Reed Solomon, link-level erasure codes and their combinations, over a wide field of signal to noise conditions of the satellite channel. For each FEC type, we found the FEC rate that maximizes the TCP goodput, in each channel condition. We finally compared the results of all FECs used between them, and presented the case of multiple TCP connections sharing the same link as well

Optimizing the end-to-end throughput of a TCP connection (goodput) over geostationary satellite links is a challenging research topic. This is because the high delay-bandwidth product, together with a non-negligible random loss of packets, is a condition that considerably differs from the environments TCP was originally designed for. As a result, TCP performance is significantly impaired by the channel bit error rate. The literature is full of suggestions for improving TCP goodput, most based on modifications of the protocol itself. We only investigated the application of different FEC (forward error correction) types for TCP goodput optimization, leaving the end-to-end protocol unaltered. Using a method midway between analysis and simulation to evaluate the goodput of TCP long-lived connections, we first studied the influence of packet loss rate, introduced by errors on the channel, on the TCP goodput. We showed that, in some cases, the packet loss rate does not need to be negligible with respect to that caused by congestion, as it is widely-held opinion. We then applied physical-level FEC techniques, such as convolutional encoding/Viterbi decoding, Reed Solomon, linklevel erasure codes and their combinations, over a wide field of signal to noise conditions of the satellite channel. For each FEC type, we found the FEC rate that maximizes the TCP goodput, in each channel condition. We finally compared the results of all FECs used between them, and presented the case of multiple TCP connections sharing the same link as well.

The optimization of the end-to-end throughput of a TCP connection over geostationary satellite links is a challenging research topic. This is because the high delay-bandwidth product, together with a non-negligible random loss of packets, are conditions which differ considerably from the original environment for which TCP was originally designed. As a result TCP performance is significantly impaired by the channel bit error rate. The literature is full of suggestions for improving TCP goodput, most based on modifications of the protocol itself. We only investigated the application of different FEC (forward error correction) types for TCP goodput optimization, leaving the end-to-end protocol unaltered. Using a method midway between analysis and simulation to evaluate the throughput of a TCP long-lived connection, we first disprove the widely-held opinion that the packet loss rate, introduced by errors on the channel, should be negligible with respect to that caused by congestion. We then compare physical-level FEC techniques, such as convolutional encoding/Viterbi decoding, Reed Solomon, link-level erasure codes and their combinations, over a wide field of signal to noise conditions of the satellite channel. Furthermore, the case of multiple TCP connections sharing the same link is presented as well.

All other conditions being equal, the end-to-end throughput of a TCP connection depends on the packet loss rate at the IP level. This is an issue when IP runs on a wireless link, where the bit error rate is variable and typically much higher than it is on fixed links. Especially on physical links where the bandwidth delay product is high, TCP performance is significantly impaired by apparently low values of the bit error rate. Generally speaking, on a wireless link bandwidth can be traded for information quality (error rate), the simplest method being to change the type or parameters of forward error correction. On this basis, we show a general method of taking advantage of this trade-off in order to maximize the throughput of a TCP connection.

The optimization of the end-to-end throughput of a TCP connection over geostationary satellite links is a challenging research topic because the high delay-bandwidth product, together with a non-negligible random loss of packets, are conditions which differ considerably from the original environment for which TCP was originally designed. As a result, TCP performance is significantly impaired by the channel bit error rate. In this paper we investigate the application of different FEC (forward error correction) types/rates and different bit rates, for the optimization of TCP goodput, in transmissions over a rain-faded geostationary satellite channel, provided that the end-to-end protocols are left unaltered. We compare physical-level FEC techniques, such as convolutional encoding/Viterbi decoding and Reed Solomon, link-level erasure codes and their combinations, over a wide field of signal-to-noise conditions of the satellite channel. The case of multiple connections per link is also analyzed, in addition to that of a single connection per link. In order to evaluate the throughput of a TCP long-lived connection we used a method that is midway between analysis (fluid model) and simulation.

The optimisation of the end-to-end throughput of a TCP connection over geostationary satellite links is a challenging research topic. This because the high delay-bandwidth product, together with a non negligible random loss of packets, are conditions which differ pretty much from the original environment TCP was originally designed for. As a result TCP performance is significantly impaired by the channel bit error rate. The literature is full of suggestions to improve TCP goodput, most of them are based on modifications of the protocol itself. We only investigate on the application of different FEC (forward error correction) types for TCP optimisation, leaving the end-to-end protocol unaltered. Using a method, which is a midway between analysis and simulation, to evaluate the throughput of a TCP long run connection, we first disprove the widely diffused opinion that the packet loss rate, introduced by errors on the channel, should be negligible with respect to that caused by congestion. We then compare physical-level FEC techniques such as convolutional encoding/Viterbi decoding and Reed Solomon, link-level erasure codes and their combinations, over a wide field of signal to noise conditions of the satellite channel. Furthermore, the case of multiple connections per link is compared with the single connection per link case.

This paper describes a complete fade countermeasure system, designed for thin route user-oriented and fully meshed satellite networks. The signal degradation due to the residual up-link attenuation after up-power control intervention, plus the down-link attenuation, is compensated for by varying the FEC coding and bit rates of the data. Down and up-link signal degradations are evaluated separately: the former by collecting statistics of quantized levels of the demodulated PSK signal, and the latter by using a narrow band signal level estimator. Measurement times are optimized using a model to evaluate the scintillation variance. The performance evaluation of the whole system in the presence of additive white Gaussian noise (AWGN), shows that very small link power margins can be adopted.