Yasser Albagory

Handover Performance of Unstable-Yaw Stratospheric High-Altitude Stations

Abstract Stratospheric platform (SP) is a new technique for providing mobile and data communications and is capable to add many advantages to the users compared to conventional terrestrial and satellite systems. A very competing problem of this emerging system is the positional instability of SP which affects the system performance. In this paper, one main problem of SP positional instabilities—which is the rotation drift—is described and analyzed and its impact on the call handover in cellular systems is also investigated. The total handover due to both user mobility and platform positional instability is explained and determined. In addition, an expression for the number of handed calls is deduced which has been shown as function of user density, distribution, platform angular shift due to rotation, cell geometry, and number of active calling users. The analysis of this number shows the serious effects of the rotational motion instability on the system performance.

A modified array processing technique based on Kaiser window for concentric circular arrays

In this paper, an efficient beamforming technique is proposed where the Kaiser window is designed and applied to the uniform concentric circular arrays (UCCA) for sidelobe reduction. This technique is based on tapering the current amplitudes of the rings in the array, where all elements in an individual ring are weighted in amplitude by the same value. Based on establishing some mapping curves, this modified tapering window is optimized in its parameters to have the lowest possible sidelobe level that can be 45 dB below the main lobe level and these optimum weights are found to be function of the number of elements of the innermost ring and the number of rings in the array.

IoT-RTP and IoT-RTCP: Adaptive Protocols for Multimedia Transmission over Internet of Things Environments

Recently, the Internet of Things (IoT) has attracted the interest of network researchers all over the world. Multimedia transmission through IoT presents an important challenge owing to nodes diversity. In this paper, adaptive versions of the real-time transport protocol (RTP) and real-time control protocol (RTCP), i.e., IoT-RTP and IoT-RTCP, are proposed. In these versions, the nature of IoT environments, such as transmission channels heterogeneity, sudden change in session size, and different multimedia sources, is considered. The basic idea of the proposed adaptive versions is to divide the large multimedia sessions into simple sessions with awareness of network status. To achieve this target, additional fields are added to the RTP and RTCP headers. These fields work under certain conditions to decrease the network overload. Finally, to test the performance of the proposed IoT-RTP and IoT-RTCP, a simulation environment is constructed using the network simulation package (NS2).The results of intensive simulations proved that the proposed adaptive versions of the multimedia protocols outperform the basic ones in terms of end-to-end delay, delay jitter, number of receiver reports, packet loss, throughput, and energy consumption.

Overview on modeling and design of stratospheric mobile cellular system

In this paper, cellular communications from Stratospheric Platforms (SPs) is studied and the footprint analysis and design are demonstrated. In the analysis part two coverage schemes are discussed; flat-earth and real-earth models and the cell footprint is determined in each case. The flat-earth provides simple footprint equations describing the cell dimensions especially for cells of higher elevation angles while more accurate coverage equations can be obtained from the real-earth scheme which well determine the geometry of the cells of lower elevation angles. The design of a cellular system using the proposed coverage models is then demonstrated through a procedure that determines the cells locations and dimensions on the ground according. The procedure takes into consideration the cell broadening when going outwardly from the central cell to the outer cells and an update for the conventional terrestrial equations must be performed to properly locate the cells. The convergence in calculating the cell parameters have been shown to be fast and reach the final values after few updating cycles.

Handover Analysis for Yaw-Shifted High-Altitude Platforms

High-Altitude Platforms (HAP) is an emerging technology for mobile broadband communications and is capable of providing many advantages compared to conventional terrestrial and satellite systems. On the other hand, positional instabilities of HAP affect the system performance greatly. In this paper, a main problem concerning the rotation motion or yaw-shift of HAP is described, analyzed, and its impact on the handover of cellular systems is also investigated. The total handover due to both user mobility and platform rotational positional instability is discussed and determined. An expression for the number of calls subjected to handover is deduced where it will be a function of users’ density and their distribution in the cell, platform angular shift due to rotation, cell geometry, and number of active calling users. The analysis of this number shows the serious effects of the yaw-shift instability on the system performance.