Alessio Meloni

Sliding window-based Contention Resolution Diversity Slotted ALOHA

Contention Resolution Diversity Slotted ALOHA (CRDSA) and its burst degree optimizations (CRDSA++, IRSA) make use of MAC burst repetitions and Interference Cancellation (IC) making possible to reach throughput values as high as T ≃ 0.8 in practical implementations, whereas for the traditional slotted ALOHA T ≃ 0.37. However, these new techniques introduce a frame-based access to the channel that limits the performance in terms of throughput and packet delivery delay. In this paper, a new technique named Sliding Window CRDSA (SW-CRDSA) and its counterpart for irregular repetitions (SW-IRSA) are introduced in order to exploit the advantages of MAC burst repetition and Interference Cancellation (IC) with an unframed access scheme. Numerical results are also provided in order to validate the statement of better performance.

CRDSA, CRDSA++ and IRSA: Stability and performance evaluation

In 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.

The Role of Satellite Communications in the Smart Grid

The 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.

64-APSK Constellation and Mapping Optimization for Satellite Broadcasting Using Genetic Algorithms

DVB-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.

Random Access in DVB-RCS2: Design and Dynamic Control for Congestion Avoidance

In 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.

A cloud-based and RESTful Internet of Things platform to foster Smart Grid technologies integration and re-usability

Currently, one of the hottest topics in the Internet of Things (IoT) research domain regards the issue to overcome the heterogeneity of proprietary technologies and systems so as to enable the integration of applications and devices developed for different environments in a single interoperable framework. Towards this objective, virtualization is widely used to foster integration and creation of new services and applications. Similar benefits are expected by its application in the smart grid arena. The use of a virtualization middleware is expected to enrich the capabilities and opportunities related to the use of smart grid devices. In this paper, we propose key features for an interoperable, re-usable, elastic and secure smart grid architecture which is cloud-based and relies on REST APIs. To highlight the benefits, a practical case study is presented, where outlined functionalities are implemented in a cloud-based IoT platform. The advantages brought by the proposed middleware in terms of interoperability, re-usability, privacy and elasticity of the underlying infrastructure are discussed.

Average power limitations in Sliding Window Contention Resolution Diversity Slotted Aloha

Recently 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 techniques.

PMU-Based Distribution System State Estimation with Adaptive Accuracy Exploiting Local Decision Metrics and IoT Paradigm

A novel adaptive distribution system state estimation (DSSE) solution is presented and discussed, which relies on distributed decision points and exploits the Cloud-based Internet of Things (IoT) paradigm. Up to now, DSSE procedures have been using fixed settings regardless of the actual values of measurement accuracy, which is instead affected by the actual operating conditions of the network. The proposed DSSE is innovative with respect to previous literature, because it is adaptive in the use of updated accuracies for the measurement devices. The information used in the estimation process along with the rate of the execution are updated, depending on the indications of appropriate local metrics aimed at detecting possible variations in the operating conditions of the distribution network. Specifically, the variations and the trend of variation of the rms voltage values obtained by phasor measurement units (PMUs) are used to trigger changes in the DSSE. In case dynamics are detected, the measurement data are sent to the DSSE at higher rates and the estimation process runs consequently, updating the accuracy values to be considered in the estimation. The proposed system relies on a Cloud-based IoT platform, which has been designed to incorporate heterogeneous measurement devices, such as PMUs and smart meters. The results obtained on a 13-bus system demonstrate the validity of the proposed methodology that is efficient both in the estimation process and in the use of the communication resources.

IoT cloud-based distribution system state estimation: Virtual objects and context-awareness

This paper presents an IoT cloud-based state estimation system for distribution networks in which the PMUs (Phasor Measurement Units) are virtualized with respect to the physical devices. In the considered system only application level entities are put in the cloud, whereas virtualized PMUs are running in the communication network edge (i.e. closer to the physical objects) in order to have a certain degree of local logic, which allows to implement a bandwidth-efficient and smart data transmission to the involved applications in the cloud. The major contributions of the paper are the following: we demonstrate that a cloud-based architecture is capable of achieving the QoS level required by the specific state estimation application; we show that implementing a certain local logic for data transmission in the cloud, the result of the state estimation is not degraded with respect to the case of an estimation that takes place frequently at fixed intervals; we show the results in terms of latency and reduced network load for a reference smart grid network.

Random access congestion control in DVB-RCS2 interactive satellite terminals

The 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 fluctuations.