Nishesh Tiwari

Ultra-high frequency near-ground short-range propagation measurements in forest and plantation environments for wireless sensor networks

The growing interest in applications of wireless sensor networks (WSNs) in vegetation environment has made it important to understand and predict the impact of vegetation on coverage and signal quality. As most of the proposed vegetation attenuation models are mainly based on measurements in temperate climate their prediction accuracy needs to be tested in tropical climate. With the presence of high humidity and high temperature in the tropical climate the attenuation because of vegetation is bound to increase. Very few researches have been reported about the attenuation because of vegetation related to WSN applications in scrub forest and plantation environments from the regions having tropical climate in Indian subcontinent. This study focuses on short-range, near to ground received signal strength measurements at 915 and 2400 MHz to evaluate vegetation attenuation models for planning and deployment of wireless sensor communications/networks in tropical climate for precision agriculture and plantation management applications. The measurements have been done in scrub forest, mango and guava plantation environment. It is found that International Telecommunication Union (ITU) Recommendation (ITU-R) and Weissberger models under predict vegetation because of attenuation, whereas the Cost 235 model has high prediction accuracy in the scrub forest and plantation environments in tropical climate.

A switched beam antenna array with butler matrix network using substrate integrated waveguide technology for 60 GHz communications

A switched beam antenna array based on substrate integrated waveguide (SIW) technology is designed and simulated for 60 GHz communications. The antenna array is fed by 4×4 planar butler matrix network in order to achieve the switched beam characteristic. The use of SIW technology offers a low cost and a planar design. Each of the components is designed and verified through simulations in electromagnetic field simulation tool, CST MWS. The components are integrated later to form the switched beam antenna array. The return losses and isolations are lower than -10 dB from 57 GHz to 64 GHz for all of the input ports. The peak gain for the switched beam antenna array is 16 dBi at 60 GHz.

Intra-vehicular RF propagation measurements at UHF for Wireless Sensor Networks

Received Signal Strength (RSS) propagation measurements were made in a vehicular environment (Intra-Car) atUHF range (433/868/915/2400 MHz)utilizing RF equipment and Matlab simulations. Pathloss and Pathloss Exponent values were deduced from the measured RSS from various positions in a Multi Utility Vehicle (MUV). The research work reported in this paper is predominately focuses on characterizing radio link for Wireless Sensor Communications/Networks for vehicular environments at very short-range.

UHF short-range pathloss measurements in forest & plantation environments for wireless sensor networks

This work presents received signal strength at UHF, 868/915/2400 MHz utilizing radio frequency equipment and Matlab simulations in forest and plantation (Mango & Guava) environments. Path loss, path loss exponent, root mean square error and corresponding cumulative distribution function values were deduced from the measured data at various positions in foliage environments using omnidirectional antennas at 1.0 m height from the ground. Empirical foliage loss prediction models such as COST 235, ITU-R and Weissberger models were compared with the experimental results. The research work reported in this paper is predominately targeted towards characterizing short-range near ground radio link for wireless sensor communications/networks in vegetation environments.

60 GHz radio wave propagation studies in an indoor office environment

60 GHz radio channel propagation characteristics in indoor office environment are addressed in this paper using full 3-Dimensional ray tracing of Wireless InSite and a simple deterministic 2-Dimensional model utilizing Ray-tracing technique. The comparisons are made with free space model and site-general prediction model of ITU-R. Values of the path gain, rms delay spread for sectoral horn and omni-directional antennas are presented. Also, path loss exponent and channel capacity values deduced from the simulation investigations.

DESIGN AND ANALYSIS OF WIDEBAND MONOPOLE ANTENNAS FOR FLEXIBLE/WEARABLE WIRELESS DEVICE APPLICATIONS

Compact wideband flexible monopole antennas are designed and analyzed for its performance for Body Centric Wireless Communications (BCWC). Two antennas with identical radiators on different substrates are designed and fabricated on polyamide and teslin paper substrates, deploying a modified rectangle-shaped radiator. With the aid of modifications in the radiating plane and defecting the ground plane, the polyamide based antenna is designed to operate between 1.8 and 13.3 GHz, and teslin paper based antenna is designed to operate between 1.45 and 13.4 GHz to cover the wireless communication technology frequencies and ultra-wideband range for various wireless applications. The reflection coefficient characteristics of the fabricated antennas on free space and on various sites of the body are measured and match reasonably well with the simulated reflection coefficient characteristics. The specific absorption rate (SAR) analysis is also carried out by placing the antennas on tissue layered model.

Design of SIW fed antipodal linearly tapered slot antennas with curved and hat shaped dielectric loadings at 60 GHz for wireless communications

A substrate integrated waveguide (SIW) based antipodal linear tapered slot antenna (ALTSA) with dielectric loading at 60 GHz for wireless communication applications are presented. The antenna ALTSA 1 with hat-shaped dielectric loading has gain of 17.29 dB. The gain of another antenna ALTSA 2 is 18.18 dB which is constructed by adding a curved dielectric slab loading on top of ALTSA 1 and showed good efficiency of about 95%. The ALTSA 1 designed using Rogers RT/Duroid 6002 material with dielectric constant 2.94 and thickness of 0.254 mm. And, Rogers Ultralam 1217 with dielectric constant 2.17 and thickness of 1 mm is used for ALTSA 2. Ansys HFSS and CST MWS were used for the electromagnetic (EM) simulation and computation of antennas.

Short-range near floor path gain measurements in indoor corridors at UHF for wireless sensor communications

Near to floor/ground radio frequency propagation path gain measurements at short distances at antenna height of 50 cm from the ground were made in typical narrow and wide straight indoor corridors at 433/868/915/2400 MHz in a modern multi-storied building. The measurement was performed utilizing RF equipment and comparisons were made with Matlab simulations of ray tracing technique, free space model and ITU-R model along with Full-3D ray tracing model of Wireless Insite software. Measured PG values showed good agreement with Wireless Insite model in all cases. Path loss exponent values ranging from 1.22 to 2.13 were deduced from the measured data. The research work reported in this paper is predominately geared towards characterizing radio link for wireless sensor communications / networks in typical indoor corridor environments.