Pooja Gupta

MUSIC and improved MUSIC algorithm to estimate direction of arrival

The DOA estimation in array signal processing is one of the important and emerging research area. The effectiveness of this direction of arrival estimation greatly determines the performance of smart antennas. It works on the digitized output from each sensor array. The estimation results for coherent signals, broadband signals and multiple signals are of greater consideration. Various information of the parameters relating to a particular wave can be obtained by analyzing the incoming wave that is received by a sensor or an array of sensors. The accuracy in the estimation of direction of arrival is very crucial in array signal processing. DOA estimation has vital applications in radar, sonar, seismology, earthquake, astronomy, biomedicine and communication. This paper presents an overview of direction of arrival estimation using the MUSIC algorithm. This algorithm is a peak search method to estimate the arrival angle. The paper emphasizes on the factors that can affect the results of the estimation process and describes the concept of estimating the arrival angle. The MATLAB simulations shown here highlight the factors that can improve accuracy. The factors include the array element spacing, number of array elements, number of snapshots and the signal incidence angle difference. Attempts are made to bring about better resolution and contrast. As the conventional MUSIC algorithm is found to have less efficiency for coherent signals, better simulations using an improved MUSIC algorithm in provided in this paper.

Comparison of conventional and subspace based algorithms to estimate Direction of Arrival (DOA)

The Direction of Arrival (DOA) technology and researches are evolving areas in array signal processing. Biomedicine, sonar, radar, seismology, astronomy communication and earthquake widely use this estimation. We receive an incoming wave by sensing an array or a set of arrays, this sensed wave can be processed to derive many related estimation information of the associated wave. The Direction of arrival angle even known as the arrival angle estimation is one such vital parameter. The two broad classifications of estimations that can be employed to find out this direction of arrival are the conventional method of estimation and the subspace based methods. The beam forming and null steering forms the base for the conventional methods whereas the subspace based methods continuously exploit the data matrix of the narrowband received signal. The conventional methods are limited with resolution, so we need to move towards the subspace methods. The two conventional estimation approaches discussed here are the delay and sum method and the Capons method. A comparison plot for these two conventional approaches is also carried out. Multiple Signal Classification (MUSIC) and ESPRIT (Estimation of Signal Parameter through Rotational Invariance Technique) are the two widely used subspace based estimation methods. In this paper the concepts of the arrival angle estimation and some MATLAB simulations to highlight the factors that can especially improve accuracy of the MUSIC algorithm are discussed and attempts are made to bring about better resolution and contrast.

Bilateral facial weakness following dengue fever

Samir Patel1, Rajeev Ranjan1, Ritu Verma2, C. S. Agrawal1, Pooja Gupta1 1Department of Neurology, Sir Ganga Ram Hospital, New Delhi 110060, India. 2Department of Nuclear Medicine, Sir Ganga Ram Hospital, New Delhi 110060, India. Dengue, an acute viral disease transmitted by Aedes mosquitoes, is highly endemic in many tropical and subtropical areas of the world. Dengue has a wide clinical spectrum, ranging from mild clinical febrile illness to severe life-threatening conditions like dengue hemorrhagic fever and dengue shock syndrome. Neurological complications of dengue infection have been observed more frequently in the recent past. They are widespread and may involve almost all parts of nervous system through various pathogenic mechanisms. We report a case of a 30-year old male who developed bilateral facial weakness after dengue fever.

Meningitis with polymerase chain reaction for varicella zoster positivity in cerebrospinal flid of a young immunocompetent adult.

Meningitis caused by varicella zoster virus (VZV) is quite rare among young immunocompetent adults though immunocompromised patients are often seen to be affected by reactivation of VZV presenting with primary clinical features of dermatomal rashes and neurological sequelae. Here, we report the clinical scenario of a young, healthy male who had presented with fever, headache, and onset of dermatomal rashes later than the fever and was eventually diagnosed to be a case of VZV meningitis. We would like to highlight the fact that even young immunocompetent patients though rarely, might contract VZV meningitis and clinicians should have a high index of suspicion and keen eyes to catch the more obvious features of VZV infection on complete physical examination and must not harbor any reservations in ordering polymerase chain reaction for VZV DNA or initiating aggressive antiviral therapy.

Longitudinally extensive transverse myelitis as presenting manifestation of lung adenocarcinoma

Longitudinally extensive transverse myelitis (LETM) is an unusual manifestation of systemic malignancy. It has been mainly reported with lung cancers and lymphoproliferative malignancy. LETM in systemic malignancy can be caused by either intramedullary metastases or paraneoplastic syndrome. Occurrence of LETM as the first manifestation of malignancy has been rarely reported. We present clinical, laboratory, and imaging findings of a 66-year-old man with nonsmall-cell lung (adeno) carcinoma, who presented with LETM without having any cardinal manifestations of lung malignancy. The rarity of the disease and especially such a presentation can cause considerable delay in the diagnosis and treatment.

Takayasu’s arteritis - aphasia as an initial presentation

Takayasu arteritis (TA) is an uncommon disease of young women, characterized by granulomatous vasculitis of medium and large arteries. Neurological involvement is reported in only a minority of patients and occurrence of neurological syndromes as the first manifestation of disease has been rarely reported. We present clinical, laboratory and imaging findings of a 40 years old lady with TA, who initially presented with clinical manifestations of stroke in form of aphasia. The rarity of the disease and especially such a presentation can cause considerable delay in the diagnosis and treatment.