1,720,972 research outputs found
Random Access in DVB-RCS2: Design and Dynamic Control for Congestion Avoidance
No full textIn the current DVB generation, satellite terminals are expected to be interactive and capable of transmission in the return channel with satisfying quality. Considering the bursty nature of their traffic and the long propagation delay, the use of a random access technique is a viable solution for such a Medium Access Control (MAC) scenario. In this paper, random access communication design in DVB-RCS2 is considered with particular regard to the recently introduced Contention Resolution Diversity Slotted Aloha (CRDSA) technique. This paper presents a model for design and tackles some issues on performance evaluation of the system by giving intuitive and effective tools. Moreover, dynamic control procedures that are able to avoid congestion at the gateway are introduced. Results show the advantages brought by CRDSA to DVB-RCS2 with regard to the previous state of the art
Interference calculation in asynchronous random access protocols using diversity
No full textThe use of Aloha-based random access protocols is interesting when channel sensing is either not possible or not convenient and the traffic from terminals is unpredictable and sporadic. In this paper an analytic model for packet interference calculation in asynchronous random access protocols using diversity is presented. The aim is to provide a tool that avoids time-consuming simulations to evaluate packet loss and throughput in case decodability is still possible when a certain interference threshold is not exceeded. Moreover the same model represents the groundbase for further studies in which iterative interference cancellation is applied to received frame
64-APSK Constellation and Mapping Optimization for Satellite Broadcasting Using Genetic Algorithms
No full textDVB-S2 and DVB-SH satellite broadcasting standards currently deploy 16-And 32-Amplitude phase shift keying (APSK) modulation using the consultative committee for space data systems (CCSDS) mapping. Such standards also include hierarchical modulation as a mean to provide unequal error protection in highly variable channels over satellite. Foreseeing the increasing need for higher data rates, this paper tackles the optimization of 64-APSK constellations to minimize the mean square error between the original and received symbol. Optimization is performed according to the sensitivity of the data to the channel errors, by means of genetic algorithms, a well-known technique currently used in a variety of application domains, when close form solutions are impractical. Test results show that through non-uniform constellation and asymmetric symbol mapping, it is possible to significantly reduce the distortion while preserving bandwidth efficiency. Tests performed on real signals based on perceptual quality measurements allow validating the proposed scheme against conventional 64-APSK constellations and CCSDS mapping
CRDSA, CRDSA++ and IRSA: Stability and performance evaluation
No full textIn the recent past, new enhancements based on the well established Aloha technique (CRDSA, CRDSA++, IRSA) have demonstrated the capability to reach higher throughput than traditional SA, in bursty traffic conditions and without any need of coordination among terminals. In this paper, retransmissions and related stability for these new techniques are discussed. A model is also formulated in order to provide a basis for the analysis of the stability and the performance both for finite and infinite users population. This model can be used as a framework for the design of such a communication system
Average power limitations in sliding window contention resolution diversity slotted Aloha
No full textRecently a new Random Access technique based on Aloha and using Interference Cancellation (IC) named Sliding Window Contention Resolution Diversity Slotted Aloha (SW-CRDSA) has been introduced. Differently from classic CRDSA that operates grouping slots in frames, this technique operates in an unframed manner yielding to better throughput results and smaller average packet delay with respect to frame-based CRDSA. However as classic CRDSA also SW-CRDSA relies on multiple transmission of the same packet. While this can be acceptable in systems where the only limit resides in the peak transmission power, it could represent a problem when constraints on the average power (e.g. at the transponder of a satellite system) are present. In this paper, a comparison in terms of normalized efficiency is carried out between Slotted Aloha and the two CRDSA technique
The Role of Satellite Communications in the Smart Grid
Full text linkThe dramatic drop in the price of equipment and services and the increase in efficiency have made satellite communications (SATCOM) an interesting choice for the deployment of major smart grid scenarios. As a matter of fact, SATCOM providers are offering more and more services dedicated to machine-To-machine communications, and they expect actors in the smart grid domain to be among the main users. However, to fruitfully integrate these communication technologies into smart grids, it is of utmost importance to understand the strengths and limits of the available satellite features in light of smart grid communication requirements and recent advancements in the SATCOM arena. Starting with a review of the latest trends in the satellite market for machine-To-machine communications, relevant smart grid requirements are classified and mapped to the most significant smart grid applications. Then, various features and trends of SATCOM are discussed to take stock of their suitability and to outline future challenges for the exploitation of SATCOM systems in smart grids
On the stability of asynchronous random access schemes
No full textSlotted Aloha-based Random Access (RA) techniques have recently regained attention in light of the use of Interference Cancellation (IC) as a mean to exploit diversity created through the transmission of multiple burst copies per packet content (CRDSA). Subsequently, the same concept has been extended to pure ALOHA-based techniques in order to boost the performance also in case of asynchronous RA schemes. In this paper, throughput as well as packet delay and related stability for asynchronous ALOHA techniques under geometrically distributed retransmissions are analyzed both in case of finite and infinite population size. Moreover, a comparison between pure ALOHA, its evolution (known as CRA) and CRDSA techniques is presented, in order to give a measure of the achievable gain that can be reached in a closed-loop scenario with respect to the previous state of the art
Random access congestion control in DVB-RCS2 interactive satellite terminals
No full textThe next generation of interactive satellite terminals is going to play a crucial role in the future of DVB standards. As a matter of fact in the current standard, satellite terminals are expected to be interactive thus offering apart from the possibility of logon signalling and control signalling also data transmission in the return channel with satisfying quality. Considering the nature of the traffic from terminals that is by nature bursty and with big periods of inactivity, the use of a Random Access technique could be preferred. In this paper Random Access congestion control in DVB-RCS2 is considered with particular regard to the recently introduced Contention Resolution Diversity Slotted Aloha technique, able to boost the performance compared to Slotted Aloha. The paper analyzes the stability of such a channel with particular emphasis on the design and on limit control procedures that can be applied in order to ensure stability of the channel even in presence of possible instability due to statistical fluctuation
On the genetic optimization of APSK constellations for satellite broadcasting
No full textBoth satellite transmissions and DVB applications over satellite present peculiar characteristics that could be taken into consideration in order to further exploit the optimality of the transmission. In this paper, starting from the state-of-the-art, the optimization of the APSK constellation through asymmetric symbols arrangement is investigated for its use in satellite communications. In particular, the optimization problem is tackled by means of Genetic Algorithms that have already been demonstrated to work nicely with complex non-linear optimization problems like the one presented hereinafter. This work aims at studying the various parameters involved in the optimization routine in order to establish those that best fit this case, thus further enhancing the constellation
Smart home energy management including renewable sources: A QoE-driven Approach
No full textSmart Home Energy Management (SHEM) systems can introduce adjustments in the working period and operations of the home appliances to allow for energy cost savings, which can however affect the Quality of Experience (QoE) perceived by the user. This paper analyses this issue and proposes a QoE-aware SHEM system, which relies on the knowledge of the annoyance suffered by the users when the operations of appliances are changed with respect to the ideal user's preferences. Accordingly, a number of profiles which describe different usages are created in the design phase. At the deployment stage, users behavior and annoyance are registered to assign one of these profiles per appliance. The assigned profile is then exploited by the QoE-aware Cost Saving Appliance Scheduling and the QoEaware Renewable Source Power Allocation algorithms. The former is aimed at scheduling controlled loads based on users profile preferences and electricity prices making use of a greedy approach. The latter re-allocates appliances' operations whenever a surplus of energy has been made available by renewable energy sources. Experimental results demonstrate that the annoyance perceived by the users is severely diminished with respect to a QoE-unaware strategy, at the expenses of only a limited reduction in energy saving
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