In this paper GPS RADIO OCCULTATION has been introduced as a way to extract the electron density of the ionosphere. A GPS RADIO OCCULTATION occurs when a receiver on-board a LEO spacecraft tracks a GPS satellite as it sets or rises through the earth’s atmosphere. The recorded occulted signal phase and amplitude of the tracked satellite can then be analyzed to derive atmospheric electron density. TEC Monitoring has been studied to correct the error caused by the ionospher electron density in the telecommunication satellite global positioning system are briefly introduced as a tool for this method. One OCCULTATION event studied near one of the brazilion oson destations and the electron density curves obtained from the data reported Brazil Ionosonde are compared with RADIO methods.

Atmospheric wet refractivity indices, which are dependent on the water vapor, are one of the most important parameters for analyzing climate change in an area. Wet refractivity indices can be estimated from RADIOsonde stations measurement or calculated from numerical meteorological models. But due to low temporal and spatial resolution of RADIOsonde stations and severe variations of water vapor in the lower levels of Atmosphere, today’s numerical meteorological models provide low accuracy for atmospheric parameters. But nowadays, by growing number of stations that can use global positioning satellite measurements, atmospheric parameter can be estimated via remote sensing measurements in wide temporal and spatial resolutions. Wet refractivity indices cause delay in GPS measurement signals thus this delay have information about distribution of wet refractivity indices in atmosphere. By the use of global positioning satellites that can estimate atmospheric wet delay and tomography method, wet refractivity indices can be estimated. One of the growing methods for measuring the atmosphere parameters is the RADIO OCCULTATION technique. By increasing the number of low earth orbit satellites that carry GNSS receiver, this technique can provide observation in all of the globe, which its observations are obtained directly from the type of atmosphere parameters. The aim of this study is to use a combination of RO and GPS observation in 3D and 4D atmospheric tomography. But since tomography problem are ill-posed because of the poor distribution of GPS observations in network, a functional model has been implemented to estimate the wet refractivity indices from of the atmospheric tomography problem. By expanding tomography’s unknowns to base functions coefficients, the number of unknowns will be decreased and problem will become well-posed and unknowns can be estimated from inverse problem. In the three-dimensional functional model, combination of spherical cap harmonics and empirical orthogonal functions have been used to solve the inverse problem. Spherical cap harmonics are used to represent the wet refractivity indices in horizontal distribution and empirical orthogonal functions are used for the vertical distribution of the unknown coefficients. Eventually, the B-spline is used to represent the four-dimensional functional model and the dependence of coefficients to the time. After implementing 3D and 4D functional models, the relative weight of RO data with comparison to GPS data has been calculated using variance component method. The US region of California has been selected as the study network due to its high tectonic importance and the large number of GPS stations. The results in two considered tomography epochs have been validated with RADIOsonde station data in the network and also have been compared with ERA5 reanalysis data. Comparison of the profiles obtained from tomography and the ERA5 data profiles with the RADIOsonde wet refractivity indices shows that the results obtained from the functional model tomography are better than those of the ERA5 data. The results of the combination illustrate that using RO data in both 3D and 4D models, the RMSE has been decreased and showed improvement of about 7 to 10 percent compared to uncombined tomographic models. Also, it is seen that using RO data in the 4D model has higher accuracy compared to the 3D model due to the use of a time-dependent functional model that increases the functional model's accuracy.

One of the main challenges in tracking RADIO OCCULTATION (RO) signals of open loop approach is the excess Doppler estimation accuracy in lower troposphere. Propagation of RO signals through the lower troposphere with severe refractivity gradient results in high phase acceleration and low signal to noise ratio (SNR) signal. Because of the high refractivity in the lower moist troposphere, the received RO signals by global navigation satellite system (GNSS) receivers can have large excess Doppler which may vary rapidly. Due to limitation on bandwidth and transmitted information to post processing, we can' t use very high sampling rate at GNSS receivers at LEO satellite. Therefore, try to enhance the accuracy of the Doppler predicted models in the satellite makes the GNSS-RO receivers by using efficiently frequency estimation method at GNSS receivers. In this regard, we investigate the event of RO signal and then the various frequency estimation methods to improve the estimates of the Doppler frequency in post processing are evaluated. The various frequency estimation methods are investigated from performance and computational complexity perspective. Via simulation, the excess Doppler estimation accuracy in post processing for different frequency estimation methods are compared by its root mean squared error. Based on simulation results, it is seen that both ESPRIT and Jacobsen with Bias schemes have the better performance and the estimation error of them are less than that of other methods.

One of the main challenges of the Open-Loop Signal Tracking method in GPS-RO space receivers, is Doppler prediction. Almost in all satellite communication systems, accurate carrier phase tracking under difficult conditions is depend on Doppler prediction accuracy. Obviously, there are several methods for producing a predicted Doppler model, and one of the earliest is Sokolovskiy. In this paper, we are analyzing the typical and operational atmospheric Doppler prediction models for the Open-Loop Signal Tracking of RADIO OCCULTATION, in satellite communications. A summary and comparison between these methods will be concluded in the end of this paper. finally we propose a prediction method can be used in national GPS-RO payloads for predicting atmospheric doppler based on combination of Sokolovsky and C.O. Ao methods.

We address the throughput maximization problem for downlink transmission in DF-relay-assisted cognitive RADIO networks (CRNs) based on simultaneous wireless information and power transfer (SWIPT) capability. In this envisioned network, multiple-input multiple-output (MIMO) relay and secondary user (SU) equipment are designed to handle both RADIO frequency (RF) signal energy harvesting and SWIPT functional tasks. Additionally, the cognitive base station (CBS) communicates with the SU only via the MIMO relay. Based on the considered network model, several combined constraints of the main problem complicate the solution. Therefore, in this paper, we apply heuristic guidelines within the convex optimization framework to handle this complexity. First, consider the problem of maximizing throughput on both sides of the relay separately. Second, each side progresses to solve the complex problem optimally by adopting strategies for solving sub-problems. Finally, these optimal solutions are synthesized by proposing a heuristic iterative power allocation algorithm that satisfies the combinatorial constraints with short convergence times. The performance of the optimal proposed algorithm (OPA) is evaluated against benchmark algorithms via numerical results on optimality, convergence time, constraints’ compliance, and imperfect channel state information (CSI) on the CBS-PU link.

The ideal government in the age of OCCULTATION is a government that has the advantages of existing governments and is free from their defects. The purpose of this research is to investigate the types of governments and to prove the best type of it during Absence. For this purpose, with a purely rational method, the types of existing governments can be classified as follows: Democratic, monarchy and Islamic government. From this point of view, it is proven with rational evidence that the Islamic Republic has all the advantages of democratic government and monarchy, but does not have their disadvantages. Of course, the reason for the ineffectiveness of the Islamic Republic in some areas, including "economic and livelihood" is not because of the structure, but because of the disobedience of some elites and some people to the "guardian of society". Elites by failing to enlighten people, and people by voting for incompetent and inefficient officials without investigation.

Although Allameh Mohammad Hossein Na’ini offered explicit support for Wilāyatīyah Governance during the Constitutional period, he also affirmed the general deputyship of jurists in the era of OCCULTATION. He regarded the scope and application of public welfare duties as much broader than what some scholars have defined under the categories of guardianship over the absent or the incapable. He extended the application of public welfare duties to include livelihood systems, social order, public administration, defense of borders, and governance over the people. Furthermore, if public welfare duties were to be confined to limited areas, he considered the organization of societal affairs to be more important than public welfare duties and believed in the certainty of juristic authority during the OCCULTATION. Na’ini's theory of governance rests upon the preservation of collective interests, prevention of harm to the public good, and avoidance of corruption in the political ecosystem. He rejects ownership-based governance (tamlīkiyyah)—where rulers view themselves as owning the people, acting arbitrarily, without oversight or accountability—arguing it is detrimental to society and contradicts the philosophy of governance and the people's welfare. This study explores Na’ini’s perspective on governance during the apparent absence of the Infallible Imam (peace be upon him), focusing on his profound insights into the philosophy of governance and the safeguarding of public interests. The research findings indicate that his view aligns with the affirmation of Wilayat Faqih, which he sees as a legitimate form of Wilāyatīyah (wilāyah-based) government. The methodology used is library research combined with a descriptive-analytical approach.

The possibility of Imam Mahdi's OCCULTATION and its forecast by some other Divine proofs, has been challenged by opponents at the present era. Challenging the reliability of documents, they try to ascribe it to shia scholars such as Numani and Sheikh Mofid. To remove these doubts, the author of the present paper has made an investigation of some hadiths issued by Infallible Imams and concluded that OCCULTATION is found in Infallible Imams forecast from the first century to the third one. There is little body of hadiths from the first century which also indicate that OCCULTATION had been regarded as a secret. The author finally concludes that the issue of OCCULTATION had been forecasted years before its occurrence and there are reliable hadiths in this regard.