Ashish K Shukla

Rain Attenuation Modeling in the 10-100 GHz Frequency Using Drop Size Distributions for Different Climatic Zones in Tropical India

Rain drop size distributions (DSD) are measured with disdrometers at flve difierent climatic locations in the Indian tropical region. The distribution of drop size is assumed to be lognormal to model the rain attenuation in the frequency range of 10{100GHz. The rain attenuation is estimated assuming single scattering of spherical rain drops. Difierent attenuation characteristics are observed for difierent regions due to the dependency of DSD on climatic conditions. A comparison shows that signiflcant difierences between ITU-R model and DSD derived values occur at high frequency and at high rain rates for difierent regions. At frequencies below 30GHz, the ITU-R model matches well with the DSD generated values up to 30mm/h rain rate but difier above that. The results will be helpful in understanding the pattern of rain attenuation variation and designing the systems at EHF bands in the tropical region.

Two-Shell Ionospheric Model for Indian Region: A Novel Approach

In the U.S. Wide Area Augmentation System, European Geostationary Navigation Overlay Service, and Indian Global Positioning System Aided Geo Augmented Navigation, a near real-time grid-based single-shell model is proposed to correct the ionospheric delay at the user aircrafts. The single-shell model is based on the assumption that the whole ionosphere is compressed at a fixed altitude at 350 km. This assumption may not be appropriate for the Indian region, which falls in the Equatorial Ionospheric Anomaly belt. In this paper, a two-shell model which incorporates two different shells, at 300- and 500-km altitudes, having different weights at different time domains has been implemented. A statistical comparison between single- and two-shell models has been done for all quiet days of year 2005. Based on the results, it is observed that there is at least 60% improvement in the performance of the two-shell model in comparison to the single-shell model for the Indian region.

Regional Variability of Rain Drop Size Distribution Model in India

Present study shows the development of integrated rain drop size distribution (DSD) model and gives a comparative study with DSDs of difierent regions in India. This work is useful for estimation of rain induced attenuation. Rain data of flve difierent regions (Ahmedabad, Shillong, Thiruvananthapuram, Kharagpur and Hasan) was used for this work. Attenuation characteristics are difierent for difierent regions because DSD varies according to the climatic conditions. Development of DSD model for each location is not feasible. It is a demand to develop a integrated DSD model which gives the tolerable error in DSD for difierent regions, so that, it can be adjusted in fade margin of the communication system. The result of this work shows the good correlation between the proposed integrated DSD model and DSDs of difierent regions.

A comparison study of voxel based multi-and two-layer ionospheric tomography models over the Indian region using GPS data

Three dimensional multi- and two-layer ionospheric tomographic models have been developed for the Indian region, which may provide an alternative approach for total electron content (TEC) estimation and ionospheric propagation delay correction for user aircraft for Global Positioning System Aided Geo Augmented Navigation (GAGAN). A comparative study has been carried out between multi- and two-layer models with different voxel sizes. Further comparison of two-layer models with different voxel sizes shows that from 0006 to 0017 h UT, the root mean square error (RMSE) of the slant total electron content (STEC) is least for a 10° × 10° voxel size and for the remaining hours the RMSE of the STEC is least for the 15° × 15° voxel size. The main conclusion of the analysis is that the two-layer model performs around 50% better than the multi-layer model over the Indian region.

Variation in extinction cross-section of rain drops with temperature

In this research work the variation in extinction cross-section of rain drops with temperature is analyzed. Rain degrades signals at microwave and millimeter wave frequencies. The attenuation value at these frequencies depends upon the extinction cross-section of the rain drops. In the present work variation in extinction cross-section with temperature has been estimated which will be helpful in studying the temporal and spatial distribution of rain attenuation in future work. The present analysis is done at 30 GHz.

Frequency scaling of slant path rain attenuation for fade mitigation in satellite communication

Fade mitigation techniques are widely used in mm wave satellite communication systems. Proposed work shows estimation and frequency scaling of rain induced attenuation which is useful in fade mitigation. Rain attenuation has been evaluated at downlink frequency and then scaled to uplink frequency, so that uplink power can be adjusted accordingly. IPSTAR beacon data at 20 GHz of two years has been used for this work. Proposed analysis is very useful for the study of uplink power control algorithms to counter rain induced attenuation.