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.
Tension caused by a lack of water (water stress or drought stress) represents the continuous and continuous threat to the survival of the plant, as many of the plants in which phenotypic or physiological modification takes place may not be able to continue and remain in the environment in which they live due to the water stress on it or the low soil moisture content. This of course is related to the prevailing weather conditions (lack of rain, high temperature, increased wind speed, low relative humidity in the atmosphere … etc.), so dry soil is defined as the shortage of soil water needed to the extent that its readiness for the plant decreases (that is, the threshold at which the
The city is often discussed in barren, eviscerated terms and in technical jargon by urban professionals as if it were a lifeless, detached being. In fact, it is a sensory, emotional, lived experience. How often do strategic urban plans start with the words ‘beauty’, ‘love’, ‘happiness’ or ‘excitement’, as opposed to ‘bypass’, ‘spatial outcome’ or ‘planning framework, So the research problem was formed by the weakness of the sensory perception of cities and the weakness of the sense of different spaces, which in turn leads to weakness of belonging, identity and clarity, Therefor we focus here on the sensory perception. The hypothesis Recognize Senses as helpful tool in increasing people's understanding of differe
... Show MoreThis review highlights the importance of photodynamic therapy in periodontology. It can be confirmed that the photodynamic therapy as adjunct to classical scaling and root planing can be recommended as treatment option, which can by no means replace the classical therapy concepts. But even over an observation period of six months a slightly higher improvement of the clinical parameters was achieved than with SRP alone.
Since the widespread use of the concept of human security in 1994, and as stated in the report of human development (UNDP) issued by the United Nations Development Programmer,And framed it with multiple dimensions of political, economical, social and cultural. This concept has became beyond the state and its security ,and covered all what, can threaten human life and humanitarian groups, according to the humanitarian needs in the following aspects: The economic, the food,health,environmental , individual, community and the political aspect,which totally means ,the disability of the security traditional perspective to deal with these issues.The achievement of human security,that handles the maintenance of human dignity for meeting their b
... Show MoreMultiple Sclerosis (MS) is a progressive neurological disease characterized by periods of quiescence and exacerbation, epidemiological data suggest the notion that MS is an acquired autoimmune disease caused by environmental factors, probably infectious, in genetically susceptible individuals.The submitted research was attempted to study the possible viral (Paramyxoviruses) role in MS, the sera of 57 MS patients were assayed for anti-measles and anti-mumps IgG antibodies using ELISA technique, the results were compared in order to establish the presence or absence of a significant difference regarding both number of positive cases and antibodies titer between the two groups, the results revealed that there is no in number of measles posit
... Show MoreThe problem of informal settlements in Iraqi is one of the most serious problems due
to its economic, social and security impacts which jeopardize the society safety and stability.
This study investigates the present situation of informal settlements in the Baghdad
governorates as well as approaches followed in making decisions to either upgrade or remove
those areas. Requirements of each decision are also discussed.
Study methods relied on both office and field studies to collect data and information
needed. The study revealed important findings that would help take appropriate measures that
deal with the informal settlements in Iraqi. The study also proposes effective mechanisms to
preclude both an increase in c
Most media studies on the development of the agenda have focused on the relationship between the content of the media and the audience of these media, and the extent of its impact on the agenda of the media, in addition to comparing it to the extent of interest in the agenda of those means. While in the construction of the agenda, we focus on the relationship between news sources and the media and the role of these sources in the process Building the agenda.These sources are institutions, parties, pressure groups, interest groups, the head of state and other media. The impact of these sources on the process of building the agenda are shown through the process of the selection of resources by the channel and communicators, and the technic
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