With the rapid deployment of the Internet of Things and cloud computing, it is necessary to enhance authentication protocols to reduce attacks and security vulnerabilities which affect the correct ...performance of applications. In 2019 a new lightweight IoT-based authentication scheme in cloud computing circumstances was proposed. According to the authors, their protocol is secure and resists very well-known attacks. However, when we evaluated the protocol we found some security vulnerabilities and drawbacks, making the scheme insecure. Therefore, we propose a new version considering login, mutual authentication and key agreement phases to enhance the security. Moreover, we include a sub-phase called evidence of connection attempt which provides proof about the participation of the user and the server. The new scheme achieves the security requirements and resists very well-known attacks, improving previous works. In addition, the performance evaluation demonstrates that the new scheme requires less communication-cost than previous authentication protocols during the registration and login phases.
The design of Networks-on-Chip (NoCs) components implies a wide range of techniques and methods to address the microarchitecture of the packet-forwarding components, where routers and switches are ...the most complex because they constitute the NoC's backbone. Due to this complex design space, several works use approaches limiting architectural exploration, focusing only on achieving high-performance levels; therefore, they are inadequate for designing NoC components when particular functionalities are demanded, as in real applications with specific protocols and interfaces. This paper presents a design methodology based on a top-down approach with NoC-oriented abstraction levels to systematically generate a microarchitecture and its hardware description according to system requirements. The design flow transforms a high-level functional model into a microarchitecture model through a refinement process at each abstraction level. This structured approach involves integrating details on how the data is functionally managed within the component according to the system requirements and the processing granularity of each level, allowing testing alternatives in the early stages of the design when necessary. The models of each abstraction level can be described and simulated using the simulator OMNet++. Thus, the obtained microarchitecture model will be directly translated into a Hardware Description Language (HDL). The methodology is tested via the design of a NoC switch for a Software Defined Radio (SDR) system. Performance analysis and implementation results in a field-programmable gate array (FPGA) show that the proposed design is functional and comparable in both area and frequency to other similar state-of-the-art components, and it is also configurable to build star topologies of up to 16 nodes.
The use of antenna arrays is indispensable in radar and multiple-input multiple-output (MIMO) wireless communications areas, as it permits the treatment of wavefronts in the spatial domain, enabling ...important applications such as beamforming and target detection. Spatial information is commonly given in terms of spatial correlation functions (SCFs), but its representation in terms of angular domain, such as the power azimuth spectrums (PASs), is sometimes more convenient. Therefore, transforming from SCF to PAS, and vice versa, is often required. This is commonly done by employing so-called beamformers, where the Bartlett beamformer (BB) is the most commonly utilized. However, the use of beamformers alone is not enough for retrieving PAS information from a given SCF. Particularly, this paper shows that a non-linear operation is missing in relating SCFs to PASs as provided by current beamformers. The paper also shows the mathematical expressions that correctly relate SCFs to PASs and wavenumber spectrums (WNSs) for the general case of systems with antenna arrays. The developed theory results in two new beamformers, which, corroborated by simulation results, solve any previous inconsistency in estimating PASs from SCFs.
Modern communication systems are based on orthogonal frequency division multiplexing (OFDM). They are designed for dealing with frequency selective channels considering invariance within the ...time-span of an OFDM symbol. However, this assumption is no longer valid when the transceivers operate in higher mobility scenarios or higher carrier frequencies. This condition provokes inter-carrier interference (ICI) that greatly degrades system performance. State-of-the-art approaches that satisfactorily mitigate this problem have a complexity of O(N 3 ), which makes them infeasible with current technology. In this paper, a novel channel estimation algorithm to cope with this problem is presented. It is based on a subspace approach using two-dimensional Prolate functions, achieving a complexity of only O(N 2 ). It depends only on the maximum delay spread and maximum Doppler spread while being robust in the sense that it is independent of the particular channel scattering function. Performance analysis of the proposed algorithm is presented. Simulation results under the WiMAX standard show that this algorithm improves previous results, achieving a bit error rate (BER) close to the one obtained with perfect channel state information (CSI) in very-fast transceiver mobility, as high as 874 Km/h over a 2.4 Ghz carrier frequency.
Maximum likelihood sequence estimation (MLSE) and maximum a posteriori probability (MAP) equalizers are optimum receivers for dealing with intersymbol interference (ISI) in time-dispersive channels. ...However, their high complexity and latency limit their widespread implementation; therefore, research into reducing their complexity is an open topic. This paper proposes a novel modification to reduce the computational complexity of the aforementioned algorithms, which exploits the representation of the communication channels in a time-delay-domain basis expansion model (BEM). It is shown that an appropriate basis is a set of modified prolate functions, in which the transmitter and receiver filters are considered in the kernel construction. Simulation results show that a reduction in sums and multiplications on the order of 55% can be obtained, maintaining the same bit error rate performance as in the traditional implementation.
A novel approach is proposed for correlated multiple-input multiple-output (MIMO) channel estimation based on reduced-rank (RR) technique and partial channel state information (CSI). In contrast to ...previous proposals that used the channel correlation matrix (CCM) and its eigendecomposition, this paper shows that close linear minimum mean-square-error (LMMSE) performance can be achieved with the use of predefined bases derived from the knowledge of the maximum angular dispersion. A theoretical framework to synthesize a suitable set of bases is provided, from which discrete prolate spheroidal sequences (DPSSs) are identified as one of the appropriate predefined bases for spatial channel representation. The robustness of the proposed estimator allows changes in the propagation scenario to be managed according to the demands of realistic communications systems. The performance analysis of the channel estimator is shown and corroborated with simulation results.
An in-plane radial sensitivity interferometer that uses the divergent illumination for displacement measurement in the radial direction is presented. A description and mathematical model for ...calculating the sensitivity vector are also presented. The interferometer has two polarizing filters: a circular one and a linear one to implement the phase stepping technique. A measurement of the radial deformation by thermal expansion is performed over an aluminium plate in order to test the interferometer. The results indicate that the maximum contribution of the out-of-plane with respect to the radial-in-plane sensitivity vector is less than 3% and decreases by less than 1% when measurements are performed near the optical axis. The measurement is compared with the results obtained by a finite element analysis on a virtual specimen model.
Polycrystalline samples of layered cobaltites LnBaCo2O5+δ (Ln=La, Eu) were synthesized by standard solid state reaction. Structural, magnetic and carbon dioxide gas sensing properties of the samples ...were carefully investigated. The polycrystalline LnBaCo2O5+δ samples showed typical sequences of magnetic transitions according to the nonstoichiometric oxygen (δ) content. Well-defined hysteresis loops were observed at different temperatures (270K for EuBaCo2O5+δ), which supports the existence of a ferromagnetic order in the samples. Thick films were prepared with the as-prepared powders for the gas sensing evaluation. Considerable response to CO2 gas was measured for the first time on sensors based on LnBaCo2O5+δ powders. The resistance of the sensors increases with an increase of CO2 concentration, with dry air as base gas. The gas sensing response of the sensors is fast and shows good reproducibility. The EuBaCo2O5+δ, and LaBaCo2O5+δ cobaltites show distinct behavior upon increase in the CO2 concentration, which might be associated with the value of δ for each system. The probable carbon dioxide gas sensing mechanism of the studied cobaltites is discussed.
The increasing use of smaller technologies in the manufacture of analog front-ends (AFEs) for communication systems has increased the impact their non-ideal components produce. This results in a ...significant degradation of the system performance that must be identified and addressed. In particular, the I/Q imbalance is commonly estimated and compensated via digital signal processing techniques using training sequences. In order to preclude the rise of other non-idealities, such as the non-linearity of the power amplifier (PA), these training sequences should be chosen to have a low peak-to-average power ratio (PAPR). In addition, it is desirable that these techniques have reduced computational complexity for minimizing estimation times and area resources. This paper presents a novel I/Q imbalance estimation algorithm that is computationally simple, it only requires adders and shifters, while exhibiting a PAPR ≤ 2. It can include the transmitter and receiver I/Q imbalances as well as the multipath phenomena. It is based on a newly used property of Golay complementary sequences (GCS). The statistical efficiency and low complexity of the proposed algorithm are proved, while its flexibility is illustrated under several extreme test cases.
One of the main problems of multiple-input multiple-output (MIMO) high-speed interconnect (HSI) circuits that use single-ended signaling is crosstalk phenomena. Crosstalk is an unintentional coupling ...of the transmitted signals due to close spacing between transmission lines that distorts the information bearing symbols. A novel model for uniform or nonuniform multiconductor transmission line based on the S-parameters is proposed. It allows representation of an HSI as a MIMO channel. In addition, a linear precoding scheme stands on the aforementioned signal model and wireless digital precoding. The precoder generates eigen-beam patterns designed to avoid crosstalk. This research employs practical HSI circuits used in system-in-package at data rates of 2 Gb/s. Statistical link simulation results are presented to analyze and verify the performance and benefits in terms of signal integrity quality of the signal model and the linear precoder proposed.
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