Vignan University

About: Vignan University is a education organization based out in Guntur, Andhra Pradesh, India. It is known for research contribution in the topics: Computer science & Control theory. The organization has 1138 authors who have published 1381 publications receiving 7798 citations.

Enhanced Distributed Coordination Function of MAC for VoIP Services Using IEEE802.11 Networks

Abstract: Voice over Internet Protocol (VoIP) is an important service with strict Quality-of-Service (QoS) requirements with in wireless local area networks. The popular Distributed Coordination Function (DCF) of IEEE802.11 Medium Access Control (MAC) protocol adopts Multiplicative Increase and linear Decrease procedure to reduce the packet collision probability in WLANs. In DCF, the size of contention window is doubled upon a collision regardless of the network loads. This paper presents an enhanced DCF scheme to improve the QoS of VoIP in WLANs. This scheme applies a threshold of the collision rate to switch between two different functions for increasing the size of contention window based on the status of network loads. The performance of this scheme investigated and compared to the original DCF using the network simulator NS-2. Under the high traffic loads the packet loss probability decreases with the enhanced DCF compared to the original DCF. Some other parameters like throughput and access delay is decreased with the enhanced DCF.

Analysis of DRA with Different Shapes for X-Band Applications

Abstract: Geometry of dielectric resonator antenna has a significant effect on the design parameter. In this paper, the comparison of spherical type DRA has been carried out with cylindrical and conical shapes DRA to exhibit the best results for X-band applications. The proposed antennas (cylindrical, spherical, and conical) have been designed to operate at 9 GHz resonant frequency using Rogers TMM 13i material of permittivity = 12 with substrate Rogers RO3010 (lossy) used. The proposed antenna uses a combination of two resonating structures for making the operation feasible. The results have been analyzed and confirmed that spherical type exhibits better gain 7.97 dB and directivity is 8.48 dB and return loss is −39.02 dB and good bandwidth because of above characteristics and simplicity of the designers may prefer the spherical configuration for X-band applications.

Spectrum aware opportunistic routing in multi-interface multi-channel CRWMN

Abstract: Cognitive radio opportunistically identifies the spectrum holes and efficiently share the resources among the secondary users (SU). Routing in highly dynamic networks is an intimidating task without spectrum reflections. Thus, the proposed spectrum-aware routing protocol can justify the need for three key components such as analyzing primary users activity on the channel, accurate selection of next hop relay nodes to form reliable and stable paths to maximize the end-to-end throughput. In this way, a novel routing metric is used to achieve the requirement of primary user activity on the channel that helps to select a next-hop relay node to perform the routing. Thus, the opportunistic transmission time (OTT) metric is used to determine the reliable path to transfer the data between the nodes in the network. The proposed spectrum aware opportunistic routing protocol is simulated using the network simulator (ns-2). The simulation results demonstrate the routing has improved the performance of the network compared to the existing routing protocols in cognitive radio networks.

Identification and structural characterization of lactose adduct impurities in isosorbide dinitrate and hydralazine hydrochloride tablets by liquid chromatography‐mass spectrometry and nuclear magnetic resonance studies

Abstract: Isosorbide dinitrate and hydralazine hydrochloride tablets are approved for the treatment of heart failure, prolonged hospitalization for heart failure, and enhanced patient-reported functional status. It has been administered orally. Isosorbide dinitrate and hydralazine hydrochloride tablets contained two additional major unknown peaks (Degradation Product 1 and Degradation Product 2) in the stability studies (25°C/60% relative humidity and 40°C/75% relative humidity). These two unknown degradation peaks formed due to the heat (thermal) and humidity stress of hydralazine hydrochloride. Liquid chromatography separated these unknown degradant peaks. Initially, liquid chromatography-mass spectrometry assessed the degradation pathways and mass of two degradants. Afterward, preparative-liquid chromatography isolated the two major unknown degradation impurities formed under heat (thermal) and humidity stress conditions. Further, to confirm the structures, nuclear magnetic resonance spectroscopy evaluated these two degradants. The liquid chromatography-mass spectrometry and nuclear magnetic resonance spectral data confirmed that the two degradation impurities are hydralazine lactosone ring-opened adduct (Degradation Product 1) and s-triazolo [3,4-α] phthalazine (Degradation Product 2).