In this paper, we investigate and characterize the effects of multi-channel and rendezvous protocols on the connectivity of dynamic spectrum access networks using percolation theory. In particular, we focus on the scenario where the secondary nodes have plenty of vacant channels to choose from a phenomenon which we define as channel abundance. To cope with the existence of multi-channel, we use two types of rendezvous protocols: naive ones which do not guarantee a common channel and advanced ones which do. We show that, with more channel abundance, even with the use of either type of rendezvous protocols, it becomes difficult for two nodes to agree on a common channel, thereby, potentially remaining invisible to each other. We model this invisibility as a Poisson thinning process and show that invisibility is even more pronounced with channel abundance. Following the disk graph model, we represent the multiple channels as parallel edges in a graph and build a multi-layered graph (MLG) in R2. In order to study the connectivity, we show how percolation occurs in the MLG by coupling it with a typical discrete percolation. Using a Boolean model and the MLG, we study both cases of primaries' absence and presence. For both cases, we define and characterize connectivity of the secondary network in terms of the available number of channels, deployment densities, number of simultaneous transmissions per node, and communication range. When primary users are absent, we derive the critical number of channels which maintains supercriticality of the secondary network. When primary users are present, we characterize and analyze the connectivity for all the regions: channel abundance, optimal, and channel deprivation. For each region we show the requirement and the outcome of using either type of rendezvous techniques. Moreover, we find the tradeoff between deployment-density versus rendezvous probability which results in a connected network. Our results can be used to decide on the goodness of any channel rendezvous algorithm by computing the expected resultant connectivity. They also provide a guideline for achieving connectivity using minimal resources.
Abstract
The aim of the present research is to identify the test wisdom and the preoccupation with learning and psychological tension among postgraduate students at the University of Samarra according to the variables of the department, gender, age, and employee or non-employee, and revealing the relationship between the test wisdom and the preoccupation with learning and psychological tension. The research sample consisted of (75) students randomly selected from postgraduate students at the college of Education. The researcher applies test –wisdom of (Mellman & Ebel) and measurement of preoccupation with learning prepared by (Al-zaabi 2013) also, the researcher used the scale of t
... Show MoreInnovative various Schiff bases and their Co(II), Ni(II) and Cu(II) and Hg(II) compounds made by the condensation of 4-amino antipyrine with derived aminobenzoic acid (2-aminobenzoic acid, 3-aminobenzoic acid, and 4-aminobenzoic acid ) have been prepared by conventional approaches. These complexes were described by magnetic sensibility analysis, FT-IR spectra, and molar-conductance and elemental analysis. Analytical values appeared which the mixed-ligand complexes presented ratio about 2:1 (ligand: metal) with the chelation 4 or 6. The prepared compounds offered a good effect on the organisms; bacteria Staphylococcus-aurous, Escherichia-coli and fungi C. albicans, A. niger. Also, the biological products signalize which the mixed compl
... Show MoreSteps were taken to obtain the Kojic acid crystals from local fungal isolation A. flavus WJF81 by separating the fermentation products from the fungus mycelium from the production plant at the centrifuge at a speed of 5000 cycles for 10 minutes. The extraction was followed by ethyl acetate then supernatant concentrate by using rotary evaporator, and dried with heat oven 37ºC. Long, yellowish, pristine acid crystals were obtained that examined the optical microscope with a magnification force of 10x and 40x. The melting point of kojic acid was determined between 152.9-153.5 °C Results of the diagnosis of Kojic acid by applying High pressure liquid chromatography HPLC technique showed that the acid was at one peak, which was close to the
... Show MoreLet R be a commutative ring with identity. R is said to be P.P ring if every principle ideal of R is projective. Endo proved that R is P.P ring if and only if Rp is an integral domain for each prime ideal P of R and the total quotient ring Rs of R is regular. Also he proved that R is a semi-hereditary ring if and only if Rp is a valuation domain for each prime ideal P of R and the total quotient Rs of R is regular. , and we study some of properties of these modules. In this paper we study analogue of these results in C.F, C.P, F.G.F, F.G.P R-modules.
In dealing with media management phenomenon, concept and elements, we have tried, as much as possible, to build an abstract concept that can be analyzed and measured by analyzing the elements and components of the concept mentioned and explain it.
Before further consideration of the management of media campaigns, it is necessary to restore some points of media management so as not to understand the subject of campaign management as if it is independent of the concept of media management and the objectives that we seek to ensure its achievement. As we have noted that the concept of media management frames the administration mentioned as:
- Authority to manage the media institution.
- Operations supervised by the me
... Show MoreIn modules there is a relation between supplemented and π-projective semimodules. This relation was introduced, explained and investigated by many authors. This research will firstly introduce a concept of "supplement subsemimodule" analogues to the case in modules: a subsemimodule Y of a semimodule W is said to be supplement of a subsemimodule X if it is minimal with the property X+Y=W. A subsemimodule Y is called a supplement subsemimodule if it is a supplement of some subsemimodule of W. Then, the concept of supplemented semimodule will be defined as follows: an S-semimodule W is said to be supplemented if every subsemimodule of W is a supplemen
... Show MoreBackground: Gingival recession is defined as the apical migration of the gingival margin below the cementoenamel junction (CEJ), resulting in exposure of the root surface and it is one of the main esthetic complaints of patients. The management of gingival recession and its sequelae is based on a thorough assessment of the etiological factors and the degree of tissue involvement.
This research aims to deal with contemporary knowledge methodology to correlate between operations strategy and technological change or modernization in productive paths for industrial organizations depend on practical indicators for competitive priorities that is objectives of operations performance.
The research is based on main hypothesis, concentrates on determination of technological change which is decided by the level of technology deterioration in current operations path compared with the competitors leaders-technology leaders.
We apply these concepts on hypothetical case to two similar companies in their production nature and te
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