An efficient HARQ scheme for applications in multicast communication systems

This paper deals with the performance evaluation and optimization of an efficient hybrid automatic repeat request (HARQ) scheme suitable for applications delivered over lossy multicast communication channels. In particular, different from previously investigated strategies, this paper proposes a modified HARQ scheme based on the symbol combining principle (MHARQ‐SC) where multiple copies of a same packet are consecutively transmitted at each transmission opportunity. By considering as the performance metrics, the mean packet delivery delay, and the energy consumption per information packet, this paper presents suitable performance evaluation and optimization strategies tailored for multicast communications. For the sake of comparisons, it has been also analyzed, under the same operational conditions, the performance of different HARQ schemes optimized for multicast communications. Numerical results have been provided to validate the proposed performance evaluation and optimization approaches in the case of the MHARQ‐SC scheme. An important result devised here is that the reported analytical results clearly highlight the performance gain of the proposed strategy in comparison with all the other considered alternatives. Copyright © 2013 John Wiley & Sons, Ltd.     

Measured versus simulated transient disturbances induced on asystem harness

The increasing complexity of electronic payloads on satellites and aircraft has resulted in an increase in electromagnetic compatibility (EMC) test campaign costs and duration. Affordable simulation tools can help system engineers to reduce costs and prevent damage during tests. A method of moments (MOM) based simulation tool for the analysis of electrostatic discharge (ESD) interactions with systems has been assessed. Comparisons between experimental and simulated results are reported together with the adopted setup modeling philosophy. The results showed a very good performance of the simulation tool and the need to characterize and include in the computation the experimental current probe model     

Conformational stability of muscle acylphosphatase: the role of temperature, denaturant concentration, and pH

The conformational stability (delta G) of muscle acylphosphatase, a small alpha/beta globular protein, has been determined as a function of temperature, urea concentration, and pH. A combination of thermally induced and urea-induced unfolding, monitored by far-UV circular dichroism, was used to define the conformational stability over a wide range of temperature. Through analysis of all these data, the heat capacity change upon unfolding (delta Cp) could be estimated, allowing the determination of the temperature dependence of the main thermodynamic functions (delta G, delta H, delta S). Thermal unfolding in the presence of urea made it possible to extend such thermodynamic analysis to examine these parameters as a function of urea concentration. The results indicate that acylphosphatase is a relatively unstable protein with a delta G(H2O) of 22 +/- 1 kJ mol-1 at pH 7 and 25 degrees C. The midpoints of both thermal and chemical denaturation are also relatively low. Urea denaturation curves over the pH range 2-12 have allowed the pH dependence of delta G to be determined and indicate that the maximum stability of the protein occurs near pH 5.5. While the dependence of delta G on urea (the m value) does not vary with temperature, a significant increase has been found at low pH values, suggesting that the overall dimensions of the unfolded state are significantly affected by the number of charges within the polypeptide chain. The comparison of these data with those from other small proteins indicates that the pattern of conformational stability is defined by individual sequences and not by the overall structural fold.     

Turbo soft combining hybrid ARQ techniques: Theory and application to 3G wireless networks

This paper deals with the application of Hybrid Automatic Repeat reQuest (h-arq) techniques to allow reliable data communications in wireless 3G networks. Basically, retransmission of coded data is endowed with soft combining schemes applied, respectively, to packet replicas, or to decoding algorithm outputs. In particular, the proposed coding scheme takes advantage of error correction capabilities of the turbo codes, while the combining algorithm follows the diversity approach. The performance of the proposedh-arq schemes has been derived by means of a suitable analytical approach and numerical simulations in the case of a typical umts environment. The results highlight the good behavior of the proposed scheme in term of error rate, throughput, packet delivery delay and power reduction.     

Inter-comparison among different TLD-based techniques in a standard multisphere assembly for the characterisation of neutron fields

In the framework of collaboration among the ENEA Radiation Protection Institute (Bologna), the ENEA Fusion Department (Frascati) and the INFN-LNF-Radiation Protection Group (Frascati), an experimental campaign was organised on the usage of thermoluminescence dosemeters (TLDs) for the dosimetric and spectrometric characterisation of neutron fields. Commercially available TLDs of different material and different sensitivity to photons and thermal neutrons were selected, namely TLD600H and TLD700H from Harshaw, GR206 and GR207 from SSDML (China), MCP-6s from TLD Poland. The detectors were first calibrated in standard fields of photons ((60)Co) and thermal neutrons at the ENEA-IRP Secondary Standard Calibration Laboratory of Bologna, then exposed in fast neutron standard fields of different energy, using a standard multisphere moderating assembly. The paper compares the dosimetric characteristics of the studied TL detectors, underlining the (n-gamma) discrimination capability, and discusses their spectrometric performances addressed to radiation protection applications.     

Dynamic multicast link selections for buffer‐aided relaying networks

The management of small cell is considered a key point in next‐generation cellular networks for providing higher data rates, and the relay nodes are expected to be useful to improve the coverage area. Moreover, multicast services have gained importance to disseminate common data to subscribers. The use of buffer‐aided relay for multicast communications is analysed in the paper, and different policies to perform the optimal link selections are compared. These policies are based on the knowledge of the instantaneous link quality indicators as well as the status of the relay buffer and dynamically select the better link according to a suitable probabilistic criterion by improving the aggregate multicast flows. The parameters of these multicast policies are optimized via a Markov chain theoretical framework. The performance for all the proposed methods is analytically derived and validated through computer simulations conducted in different multicast scenarios. The advantages of the proposed schemes are pointed out in terms of multicast throughput, buffer occupancy for different buffer and multicast group size. Copyright © 2016 John Wiley & Sons, Ltd.     

QoS provisioning in GEO satellite with onboard processing using predictor algorithms

Recently, IP satellite networks have attracted considerable interest as a technology to deliver high-bandwidth IP-based multimedia services to nationwide areas. In particular, IP satellite networks seem to be one of the most promising technologies for connecting users in rural areas, where a wired high-speed network (e.g., xDSL) is not foreseen to be used. However, one of the main problems arising here is to guarantee specific quality of service constraints in order to have good performance for each traffic class. Among various QoS approaches used in the Internet, recently the DiffServ technique has become the most promising solution, mainly for its scalability with respect to the IntServ approach. Moreover, in satellite communication systems, DiffServ computational capabilities are placed at the edge points, reducing the implementation complexity of the satellite onboard equipment. This article deals with the problem of QoS provisioning for packet traffic by considering some resource allocation schemes, including bandwidth allocation techniques and priority-driven onboard switching algorithms. As to the first aim, the proposed technique takes advantage of proper statistical traffic modeling to predict future bandwidth requests. This approach takes into consideration DiffServ-based traffic management to guarantee QoS priority among different users. Moreover, the satellite onboard switching problem has been addressed by considering a suitable implementation of the DiffServ policy based on a cellular neural network.     

Studies on enzymatic activity and conformational stability of muscle acylphosphatase mutated at conserved lysine residues

An oligonucleotide-directed mutagenesis study was carried out on the five acylphosphatase conserved lysine residues to assess their possible participation in enzyme active site formation and their contribution to the enzyme conformational stability. The study was designed to eliminate the ambiguity arising from the presence of a sulfate ion, an enzyme competitive inhibitor, bound to lysine 32 and 68 in the crystal structure of the erythrocyte isoenzyme. Furthermore, previous kinetic studies suggested the presence of residues with pKa=7.9 and 11, tentatively identified as two lysines. The kinetic parameters for the mutants under investigation are not significantly different from those of the wild-type enzyme, demonstrating that none of the lysine residues are involved in catalysis or in substrate binding. In addition, thermal and urea denaturation experiments performed by circular dichroism indicate that the mutated lysine residues do not play a significant role in the enzyme structural stabilization, as the destabilizing energy averages 1.40 kJ/mol. Such results are in agreement with those obtained with other proteins indicating that lysine residues make little contribution to the stability of the native structure.      

Perspectives for present and future CDMA-based communications systems

In this article the main boosters of future CDMA communication systems are presented and described in order to highlight the ways to cope with the more challenging requirements of future systems and services. Particular attention is devoted to the inherent weak points of CDMA systems and detection techniques that can be used to overcome their impairments. Moreover, high-data-rate transmissions in wireless channels require proper link adaptation techniques; these are thoroughly described as well. Finally, the last part of this article focuses on the design of suitable protocol strategies for new heterogeneous multimedia packet services characterized by strict QoS requirements