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.
HS Saeed, SS Abdul-Jabbar, SG Mohammed, EA Abed, HS Ibrahem, Solid State Technology, 2020
The aimes of this study is to investigate Optimism and Pessimism among university undergraduates including the first and fourth stage students ,the sample of this stoudy contained (326) students ,(166) male and (160) female, The researcher adopted a scale of Dember et al (1889) translated and adjusted to arabic version by Al-Dosoke (2001). The results have shown that students have optimism including the first and fourth stage and no significant difference between the students as far as ncluding the first and fourth study stage and gender, Implications of the results and recommendations for further research are discussed.
In this paper we show that if ? Xi is monotonically T2-space then each Xi is monotonically T2-space, too. Moreover, we show that if ? Xi is monotonically normal space then each Xi is monotonically normal space, too. Among these results we give a new proof to show that the monotonically T2-space property and monotonically normal space property are hereditary property and topologically property and give an example of T2-space but not monotonically T2-space.
Praise be to God, Lord of the Worlds, and prayers and peace be upon our Master Muhammad and upon all his family and companions:
And then: What most concerns rational people and reformers in the modern era is the moral deviation and delinquency that dominates childhood, due to family disintegration and the lack of discipline of most societies according to the religious and moral motives called for by the heavenly messages, especially Islam, which is the final message and guarantees the reform of people in life. Every time and place.
Islam has drawn attention to this issue (childhood) and made it the focus of its consideration, considering that the child is the nucleus of society and the preparation for the future, so it ordered that
Learning education in the Islamic legacy vision considers a completed The Islamic learning education took its bases from origins of Quran and honored prophet Suna , and stressed on education child a good education and providing him with principles of religion and semantic moral values and Messenger (peace on him) considers the higher example for man in his moral, behavior and goodness and witness on this Higher God said
(you had in God Messenger a good leadership for those were requesting God and last day and mentioned God a lot). Al- Ahzab Surah :21. learning education converts man from religion to another and from culture to another and teacher left his signs on the generation if he accept or refuse.
In his novel entitled Victory. Joseph Conrad asserts himself as a writer for man
as a moral agent in this universe. His characters exhibit the possibilities for isolation
and moral deterioration in modern life. The aim of this research is to investigate some
social issues that touch the core of humanity. In this novel, Conrad's perceptive eyes
has noted so many social issues that need to be tackled. Implicitly and explicitly,
Conrad launches so many controversial issues like : communication and
disengagement or skepticism , conflict between heart and mind ,fate, demonic
identification sense of guilt in man, men , women and homosexuality, the clash
between the civilized and the raw ,the disregarded local people and
The research aims to identify the educational plan for the private and public kindergartens. The researchers selected a sample consisted of (59) female teachers for the private kindergartens and (150) female teachers for the public kindergartens in the city of Baghdad. As for the research tool, the two researchers designed a questionnaire to measure the educational plan for the private and public kindergartens. The results revealed that private kindergartens have educational plans that contribute considerably to classroom interaction, the public kindergartens lack for educational plans. In light of the findings of the research, the researchers recommend the following: the need to set up a unified educational plan for the priv
... Show MoreIn this paper, for the first time we introduce a new four-parameter model called the Gumbel- Pareto distribution by using the T-X method. We obtain some of its mathematical properties. Some structural properties of the new distribution are studied. The method of maximum likelihood is used for estimating the model parameters. Numerical illustration and an application to a real data set are given to show the flexibility and potentiality of the new model.
This research includes theoretical and evaluation design of a polarizer filter of high transmission in the near IR region of (900-1200nm) for different incidence angles to obtain a long wave and short wave pass filter using analytical calculations. Results refer to a new configuration design in fewer layers than used in previous studies in the long wave pass at incidence angles (45o,50o,55o). Adopted Hafnium dioxide (HfO2) and Magnesium fluoride (MgF2) as coating material at design wavelength (933nm), the study also included design short wave pass polarizer by using the same coating material.