Hybrid MANET–DTN and a New Algorithm for Relay Nodes Selection

In this paper, a new way to a selection of the secure relay nodes in hybrid MANET–DTN networks based on the cooperation between routing, trust and game theory mechanisms is introduced. The hybrid MANET–DTN enables delivering the data or messages in the situation when communication paths are disconnected or broken and also in the emergency situations. We focus on the situations when MANET routing protocol cannot establish the end-to-end connection between source and destination nodes. In this situation, it is necessary to select relay nodes, that will be able to transport data or messages between isolated islands of mobile terminals with limited connectivity to other terminals. The proposed algorithm enables to select the relay nodes, that will come into contact with other mobile nodes located in different network areas with regards to trust and game theory. The parameter trust is computed for all mobile nodes and relies on a parameter obtained during routing and data transport processes. The game theory provides a powerful tool to select one candidate from a number of possible nodes with respect to confidence and security. Moreover, we propose a new mechanism to compute and select the trusted node, that can be used for transportation of the secure data in this hostile and disconnected environment. In order to verify the functionalities of this mechanism, we implement this mechanism into the OPNET modeler simulation environment and introduce performance analysis.     

Learning-Based Relay Selection for Cooperative Networks with Space–Time Network Coding

Wireless Personal Communications - Space–time network coding has recently been used in cooperative communication to mitigate the problem of transmission delay in wireless systems as well as...     

A Comparison of Performance between Macro-mobility Protocol and Micro-mobility Protocol

1　IntroductionAlthoughthemobileIP protocol[1～3] workswellinthemacromobilitysituation ,someproblemsoccurinthemicromobilitysituation .Therearetwomainconcerns.First,theregistrationdelaycon tributestothehandoffdelay .Thedelayissignifi cantwhenanMNisfarawayfromhomeandcausessignificantpacketdropanddrasticreductionincom municationthroughput.Second ,frequentlocationupdatesincurextensiveoverheadforlocationcachemanagementinrouteoptimizationthatrequiresac curatelocationinformationinordertotunnelIPda…     

Spontaneous Hybrid Nano-Domain Behavior of the Organic–Inorganic Hybrid Perovskites

In hybrid perovskites, the organic molecules and inorganic frameworks exhibit distinct static and dynamic characteristics. Their coupling will lead to fascinating phenomena, such as large polarons, dynamic Rashba–Dresselhaus effects, etc. In this paper, deep potential molecular dynamics (DPMD) is employed, a large-scale MD simulation scheme with DFT accuracy, to study hybrid perovskites formamidinium lead iodide (FAPbI₃) and methylamonium lead iodide (MAPbI₃). A spontaneous hybrid nano-domain behavior, namely multiple molecular rotation nano-domains embedded into a single [PbI₆]⁴⁻ octahedra rotation domain, is first discovered at low temperatures. The behavior originates from the interplay between the long range order of molecular rotation and local lattice deformation, and clarifies the puzzling structural features of FAPbI₃ at low temperatures. The work provides new insights into the structural characteristics and stability of hybrid perovskite, as well as new ideas for the structural characterization of organic–inorganic coupled systems.     

Performance Analysis of Joint Relay and Transmit–Receive Antenna Selection for Low Density Parity Check-Asynchronous Distributed Space Time Block Coded Cooperative Diversity System

In this work we propose a joint relay and transmit–receive antenna selection method for amplify and forward asynchronous distributed space time block coded (ADSTBC) system. To the LDPC coded signal received from the source at the relays, we apply linear dispersion codes which are optimized over the delay profile of the system to produce the ADSTBC. Selection of the best transmit–receive antenna pair between source and selected relays, and that of between the selected relays and destination is done on the basis of instantaneous signal to noise ratio (SNR) of the respective paths. The relays and transmit-receive antenna pairs are selected by maximizing the end-to-end instantaneous SNR. Performance analysis of the system is done on the basis of pair wise error probability and outage probability (P_out).     

Selection of Parameters of the Primary Feed of the Luneberg Lens for the Sum–Difference Operating Mode

Excitation of the Luneberg lens by an arc antenna array of open-ended rectangular waveguides forming the H₁₀ wave is studied. Technical limitations imposed on the array of primary feeds in order to form the sum and difference operating modes of the antenna system are discussed.     

Impact of XPM on the Performance of Microwave Photonic Switching with NOLM

The impact of XPM on the microwave photonic switching with NOLM is analyzed by the split-step Fourier method (SSFM) that can solve the coupled nonlinear Schr?dinger equation (CNLSE). The simulation results show that XPM induces the distortion of waveforms and the leak of side lobes. And the larger the modulation bandwidth is, the larger the leak of side lobes is. Furthermore, the power transmission function of NOLM Tm is distorted because of the XPM-induced nonreciprocity: Tm decreases when the splitting ratio of the coupler f ∈(0,0.5) and increases when f ∈(0.5,1.0).     

Registration Cost Performance Analysis of a Hierarchical Mobile Internet Protocol Network

1　Introduction　MobileIP[1～3] isanetworklayersolutiontonodemobilityintheInternet.ItmeansthatMobileIPaccomplishesitstaskbysettinguptheroutingtablesinappropriatenodes,suchthatIPpacketscanbesenttomobilenodesnotconnectedtotheirhomenetworklinks.　AlthoughMobileIPissuitedformacro mobility ,itfailstosupportmicro mobilityefficiently[4～5] .MobileIPrequirestheMobileNode (MN)toregis terwiththeHomeAgent (HA)andtheCorrespon dentNode (CN)whenitchangesitspointofattach mentintheInternet.Therefor…     

Forward Link Performance Analysis in CDMA Distributed Antenna Systems with Imperfect Channel Estimation

1　Introduction　The Distributed Antenna (DA) system has been proposedas a promising antenna architecture for the future wirelesscommunication systems[1~10].　In the DA systems, with remote antennas, the presentcellular structure is removed and cells are not divided geo graphically, but according to the user needs. That is, ac cording to the channel estimates computed via pilot signals,the Processing Node (PN) continuously measures the chan nels between the mobiles and the remote ante…     

Study of the Improvement on Network Management Performance with Mobile Agent

1　IntroductionWiththerapiddevelopmentofInternet,thenetworkisbecominglargerandmorecomplex ,whichcallsformoresophisticatednetworkmanage mentstrategiestobeadoptedinordertoguaranteeadequatelevelsofperformance .Confrontedwiththepresentstatusofnetworkmanagement,manyschol arsmakegreateffortstoinventnewapproachesforthepurposeofimprovingtheperformanceofnet workmanagement.MobileAgenttechnologiesandtheirapplicationtonetworkmanagementaread vancedunderthisbackground .Althoughalotofworkhasstilltobedone ,t…     

Performance of joint source–channel decoding with iterative bit combining and detection

A joint source–channel decoding scheme (JSCD) with iterative bit combining (IBC) is proposed, which exploits two types of a priori information. The first one is the a priori bit probabilities obtained from source statistics, and the second is the channel a priori probabilities obtained from saved extrinsic information of previous transmissions. The JSCD-IBC scheme also incorporates iterative detection as both a stopping criteria and mechanism for triggering retransmissions. This adds an implicit adaptivity to the system and prevents excess iterations/retransmissions from being effected. The performance of the JSCD-IBC scheme is evaluated with four different iterative detection schemes and also two different types of variable length codes, Huffman and reversible variable length codes. Simulation results show that a significant performance gain in terms of bit error rate, throughput, and number of iterations can be achieved with the JSCD-IBC scheme as compared to a separate decoding scheme.     

Analysis of Outage Probability in Wavelength Diversity Based FSO Link Under Gamma–Gamma Fading with Varying Atmospheric Attenuation

Wireless Personal Communications - Free space optical (FSO) communication links offers an emerging alternative to RF communication links because of high speed, secure and cost-effective options to...     

On the Selection of Random Numbers in the ElGamal Algorithm

Generally speaking, parameter selection in all cryptographic algorithms and protocols is a mixture of art and science and exerts various subtle influences on a system, which is related to application requirements, security policies, the compromise between security and the overheads of computation, storage and communications, the balance between security and availability, and to the efficiency of software /hardware implementation, etc. Usually, simplistic, insecure or impractical textbook crypto…     

Frequency Performance Compensation of Operational Amplifiers with the ‘T’ Feedback Network

A simple T network can be used in the feedback path of a conventional voltage feedback operational amplifier (VFOA) to avoid using a large feedback resistor. However detailed analysis shows that the bandwidth of amplifier will be degraded. In this paper, a capacitive compensation method for the T network is described which yields a significant improvement in closed-loop bandwidth of the amplifier.     

In Situ Fabrication of Metal–Organic Framework Thin Films with Enhanced Pervaporation Performance

The intrinsic porosity in the periodic structures of metal–organic frameworks (MOFs) endows them with a great potential for membrane separation. However, facile fabrication of crystalline MOF membranes has been challenging and limited to few materials for economic and environmental considerations. Herein, a continuous Zr-MOF thin film with a thickness of ≈180 nm has been fabricated via in situ recrystallization of MOF nanoparticles on the porous support under formic acid vapor. Owing to the inherent microporosity and the well-established hydrophilicity during membrane fabrication, the MOF thin films exhibit excellent pervaporation performance with separation factors of 2630, 501 and fluxes of 1.45, 1.41 kg m⁻² h⁻¹) for n-butanol dehydration and methanol/methyl tert-butyl ether (MeOH/MTBE) separation, respectively. The structural stability of the film has been further confirmed by its steady performance in the 10-day pervaporation test. This in situ recrystallization method induced by a trace amount of acid vapor with no extra ingredients opens a new avenue for the facile membrane fabrication of various MOF materials to feasibly realize their versatile potential as membrane materials.     

Design and Performance Evaluation of Space–time Receivers with Dynamically Adjustable Tap Delays

The delay elements of a conventional two-dimensional space–time receiver are fixed. The rather inflexible design is inappropriate since the received signals among the antenna branches are correlated due to limited spacing, and the fading environment is time-varying. In this paper we propose a dynamic finger assignment strategy for a space–time receiver, where the delay taps are adjusted dynamically, based on the theory of finite projective planes, to improve the signal-to-noise ratio in correlated antenna branches. The proposed finite projective plane (FPP) based finger assignment scheme maximizes the collected energy by dynamically setting the tap delays depending on the correlation among antenna branches and the delay spread of the channel. In the performance evaluation, we demonstrate that the FPP based finger assignment scheme can improve the signal-to-noise ratio significantly in comparison to the conventional mesh-grid configuration when the correlation among antenna branches is high and the channel dispersion is relatively long in comparison to the overall span of the fingers. However, the gain is moderate if the channel dispersion ratio is short, where the gain of reduced correlation among antenna branches must compensate for the reduced signal-to-noise ratio due to the missed signals.

Optimizing the Oxygen-Catalytic Performance of Zn–Mn–Co Spinel by Regulating the Bond Competition at Octahedral Sites

By using the more electro-negative Mn³⁺ ion to partially replace Co³⁺ at the octahedral site of spinel ZnCo₂O₄, i.e., forming ternary Zn–Mn–Co spinel oxide, the electrocatalytic oxygen reduction/evolution activity is found to be significantly increased. Considering the physical characterization and theoretical calculations, it demonstrated that the bond competition played a key role in regulating the cobalt valence state and the electrocatalytic activity. The partial replacement of octahedral-site-occupied Co³⁺ by Mn³⁺ can effectively modulate the adjacent Co–O bond and induce the Jahn–Teller effect, thus changing the originally stable crystal structure and optimizing the binding strength between the active center and reaction intermediates. Certainly, the Mn-substituted ZnMn_1.4Co_0.6O₄/NCNTs exhibit higher electrocatalytic oxygen reduction reaction (ORR) activity than that of ZnCo₂O₄/NCNTs and ZnMn₂O₄/NCNTs, supporting that the Co–O bond covalency determines the ORR activity of spinel ZnCo₂O₄. This study offers the competition between adjacent Co–O and Mn–O bonds via the B_Oh–O–B_Oh edge-sharing geometry. The ion substitution at octahedral sites by less electronegative cations can be a new and effective way to improve the electrocatalytic performance of cobalt-based spinel oxides.