Publications

List of Publications of Dr.D.Venkata Ratnam

National Journal Papers

1. P. Babu Sree Harsha and D. Venkata Ratnam,"Fuzzy Logic-based Adaptive Extended Kalman Filter Algorithm for GNSS Receivers'.Defence Science Journal, Vol. 68, No. 6, November 2018, pp. 560-565, DOI : 10.14429/dsj.68.12313

2. Swapna Raghunath and D. Venkata Ratnam, “Detection of Ionospheric Spatial and Temporal Gradients for Ground Based Augmentation System Applications”, Indian Journal of Radio Science and Space Physics, Apr 2016.

3. M. Venu Gopala Rao and D. Venkata Ratnam, “Faster Aquasation Technique for GNS Software Defined Radio”Defence Journal,DRDO,India,Dec. 2014.

4. Quddusa Sultana*, Dhiraj Sunehra, D Venkata Ratnam, P V D Somasekhar Rao** & A D Sarma,” Significance of Instrumental Biases and DOP in the context of GAGAN”, Indian Journal of Radio science and Space Physics, Vol 36, October 2007, pp. 405 – 410.

5. A.D.Sarma, D.Venkata Ratnam, K,Ravi Chandra, and D. Krishna Reddy, “Modeling of Indian Ionosphere for GNSS Augmentation Systems ”, Location Bi –monthly Magazine, January – February 2007 .

6. D.Venkata Ratnam and A. D Sarma, “Modeling of Indian Ionosphere using MMSE model for GAGAN Applications” IGU journal, October, 2006, Vol: 10 No: 4 pp 303-312.

b) International (in chronological order, latest to oldest)

International Journal papers

1. KCT, Swamy, Devanaboyina, Venkata Raranam, Shaik, TA. Double difference method with zero and short base length carrier phase measurements for Navigation with Indian Constellation satellites L5 (1176.45 MHz) signal quality analysis. Int J Satell Commun Network. 2022; 1- 11. doi:10.1002/sat.1441

2. K Siri Lakshatha, D Venkata Ratnam, K Sivakrishna. Applicability of NeQuick G ionospheric model for single-frequency GNSS users over India[J]. AIMS Geosciences, 2022, 8(1): 127-136. doi: 10.3934/geosci.2022008

3. T. V. Rao, M. Sridhar and D. V. Ratnam, "An Automatic CADI’s Ionogram Scaling Software Tool for Large Ionograms Data Analytics," in IEEE Access, vol. 10, pp. 22161-22168, 2022, doi: 10.1109/ACCESS.2022.3153470.

4. Khan, Pathan I., Devanaboyina V. Ratnam, Perumal Prasad, Ghouse Basha, Jonathan H. Jiang, Rehana Shaik, Madineni V. Ratnam, and Pangaluru Kishore. 2022. "Observed Climatology and Trend in Relative Humidity, CAPE, and CIN over India" Atmosphere 13, no. 2: 361. https://doi.org/10.3390/atmos13020361

5. Vankadara, Ram K., Sampad K. Panda, Christine Amory-Mazaudier, Rolland Fleury, Venkata R. Devanaboyina, Tarun K. Pant, Punyawi Jamjareegulgarn, Mohd A. Haq, Daniel Okoh, and Gopi K. Seemala. 2022. "Signatures of Equatorial Plasma Bubbles and Ionospheric Scintillations from Magnetometer and GNSS Observations in the Indian Longitudes during the Space Weather Events of Early September 2017" Remote Sensing 14, no. 3: 652. https://doi.org/10.3390/rs14030652

6. Shafi, S., Ratnam, D.V. A trust based energy and mobility aware routing protocol to improve infotainment services in VANETs. Peer-to-Peer Netw. Appl. 15, 576–591 (2022). https://doi.org/10.1007/s12083-021-01272-6.

7. G. Sivavaraprasad, I. Lakshmi Mallika, K. Sivakrishna, D. Venkata Ratnam,A novel hybrid Machine learning model to forecast ionospheric TEC over Low-latitude GNSS stations,Advances in Space Research,Volume 69, Issue 3,2022,Pages 1366-1379,ISSN 0273-1177,https://doi.org/10.1016/j.asr.2021.11.033.

8. Simi, K.G., Akala, A.O., Siva Krishna, K., Amaechi, P.O., Ogwala, A., Venkata Ratnam, D., Oyedokun, O.J. Responses of the Indian Equatorial Ionization Anomaly to two CME-induced geomagnetic storms during the peak phase of solar cycle 24(2021) 68 (8), pp. 3417-3434.

9. Sri Harsha, N.C., Anudeep, Y.G.V.S., Vikash, K., Ratnam, D.V., Performance Analysis of Machine Learning Algorithms for Smartphone-Based Human Activity Recognition, (2021) 121 (1), pp. 381-398.

10. Dey, A., Chhibba, R., Ratnam, D.V., Sharma, N.A, combined iCEEMDAN and VMD method for mitigating the impact of ionospheric scintillation on GNSS signals,(2021) Acta Geophysica, 69 (5), pp. 1933-1948.

11. Kiruthiga, S., Mythili, S., Mukesh, R., Vijay, M., Venkata Ratnam, D.Analysis of TEC values predicted by OKSM amongst low, mid and high latitude GPS stations during X 9.3 solar flare(2021) Astrophysics and Space Science, 366 (8), art. no. 80, .

12. de Dieu Nibigira, J., Sivavaraprasad, G., Ratnam, D.V.Performance analysis of IRI-2016 model TEC predictions over Northern and Southern Hemispheric IGS stations during descending phase of solar cycle 24(2021) Acta Geophysica, 69 (4), pp. 1509-1527.

13. Ruwali, A., Kumar, A.J.S., Prakash, K.B., Sivavaraprasad, G., Ratnam, D.V.Implementation of Hybrid Deep Learning Model (LSTM-CNN) for Ionospheric TEC Forecasting Using GPS Data,(2021) IEEE Geoscience and Remote Sensing Letters, 18 (6), art. no. 9093827, pp. 1004-1008.

14. Rao, T.V., Sridhar, M., Ratnam, D.V., Harsha, P.B.S. Comparative analysis of ionosonde spread F and GPS ionospheric scintillations over Hyderabad,(2021) Journal of Astrophysics and Astronomy, 42 (1), art. no. 7.

15. Abhigna, M.S.R., Sridhar, M., Harsha, P.B.S., Krishna, K.S., Ratnam, D.V.Broadcast ionospheric delay correction algorithm using reduced order adjusted spherical harmonics function for single-frequency GNSS receivers(2021) Acta Geophysica, 69 (1), pp. 335-351.

16. Priyanka, Ch., Venkata Ratnam, D., Sai Krishna Santosh, G.A review on design of low noise amplifiers for global navigational satellite system(2021) AIMS Electronics and Electrical Engineering, 5 (3), pp. 206-228.

17. Siva Krishna, K., Venkata Ratnam, D.Analysis of differential code biases and inter-system biases for GPS and NavIC satellite constellations(2021) AIMS Electronics and Electrical Engineering, 5 (3), pp. 194-205.

18. Rao, T.V., Sridhar, M., Ratnam, D.V., Harsha, P.B.S., Srivani, I.A Bidirectional Long Short-Term Memory-Based Ionospheric foF2 and hmF2 Models for a Single Station in the Low Latitude Region,(2021) IEEE Geoscience and Remote Sensing Letters, .

19. Vishnu Vardhan, A., Babu Sree Harsha, P., Venkata Ratnam, D., Upadhayaya, A.K.Low latitude ionospheric response to March 2015 geomagnetic storm using multi-instrument TEC observations over India,(2020) Astrophysics and Space Science, 365 (12), art. no. 187, .

20. Harsha, P.B.S., Ratnam, D.V., Nagasri, M.L., Sridhar, M., Padma Raju, K.,Kriging-based ionospheric TEC, ROTI and amplitude scintillation index (S4) maps for India(2020) IET Radar, Sonar and Navigation, 14 (11), pp. 1827-1836.

21. Sivavaraprasad, G., Venkata Ratnam, D., Sridhar, M., Sivakrishna, K.Modelling and forecasting of ionospheric TEC irregularities over a low latitude GNSS station(2020) Astrophysics and Space Science, 365 (10), art. no. 168, .

22. Mallika I, L., Ratnam, D.V., Raman, S., Sivavaraprasad, G.Machine learning algorithm to forecast ionospheric time delays using Global Navigation satellite system observations(2020) Acta Astronautica, 173, pp. 221-231.

23. Mallika I, L., Ratnam, D.V., Raman, S., Sivavaraprasad, G.Performance analysis of Neural Networks with IRI-2016 and IRI-2012 models over Indian low-latitude GPS stations(2020) Astrophysics and Space Science, 365 (7), art. no. 124, .

24. Sridhar, K.M., Sridhar, M., Raghunath, S., Venkata Ratnam, D.Ionospheric anomaly detection and Indian ionospheric climatology from GAGAN receivers(2020) Acta Geodaetica et Geophysica, 55 (2), pp. 223-235.

25. Siridhara, A.L., Ratnam, D.V. Mitigation of Multipath Effects Based on a Robust Fractional Order Bidirectional Least Mean Square (FOBLMS) Beamforming Algorithm for GPS Receivers(2020) Wireless Personal Communications, 112 (2), pp. 743-761.

26. Siva Krishna, K., Ratnam, D.V. Determination of NavIC differential code biases using GPS and NavIC observations(2020) Geodesy and Geodynamics, 11 (2), pp. 97-105.

27. Krishna, K.S., Ratnam, D.V., Sridhar, M., Harsha, P.B.S., Sivavaraprasad, G. Performance Evaluation of Adjusted Spherical Harmonics Ionospheric Model over Indian Region(2020) IEEE Access, 8, pp. 172610-172622.

28. Babu Harsha, P., Venkata Ratnam, D. Generation of Regional Ionospheric TEC Maps with EIA Nowcasting/Forecasting Capability during Geomagnetic Storm Conditions(2020) IEEE Access, 8, art. no. 9044338, pp. 57879-57890.

29. Lakshmi Mallika, I., Venkata Ratnam, D., Raman, S., Sivavaraprasad, G.A New Ionospheric Model for Single Frequency GNSS User Applications Using Klobuchar Model Driven by Auto Regressive Moving Average (SAKARMA) Method over Indian Region(2020) IEEE Access, 8, art. no. 9039612, pp. 54535-54553.

30. Pasumarthi, B.S.H., Devanaboyina, V.R. Generation of Assimilated Indian Regional Vertical TEC Maps(2020) GPS Solutions, 24 (1), art. no. 21, .DOI: 10.1007/s11277-021-08641-7

31. AL Siridhara, D Venkata Ratnam, Multipath mitigation in GPS receiver using Taylor integrated bidirectional least mean square algorithm, Transactions on Emerging Telecommunications Technologies 30 (12), e3760,2019.

32. JRKK Dabbakuti, Y Mallika, MV Rao, KR Rao, DV Ratnam, Modeling of GPS-TEC using QR-decomposition over the low latitude sector during disturbed geomagnetic conditions Advances in Space Research 64 (10), 2088-2103,2019

33. MR Kumar, M Sridhar, DV Ratnam, PBS Harsha, SN Sri,Estimation of ionospheric gradients and vertical total electron content using dual-frequency NAVIC measurements, Astrophysics and Space Science 364 (3), 49,2019.

34. S Shafi, DV Ratnam, ,A Cross Layer Cluster Based Routing Approach for Efficient Multimedia Data Dissemination with Improved Reliability in VANETs, Wireless Personal Communications, 1-18,2019.

35. SahithiKaranam, D.Venkata Ratnam, J.R.K.Kumar Dabbakuti, ,Ionospheric time delay corrections based on the extended single layer model over low latitude region, geodesy and geodynamics, April 2019. 10.1016/j.geog.2019.02.002

36. K.Sahithi,M.Sridhar,SaratK,.Kotamraju,K.Ch.SriKavya,G.Sivavaraprasad,D.VenkataRatnam,Ch.Deepthi, Characteristics of ionospheric scintillation climatology over Indian low-latitude region during the 24th solar maximum period, geodesy and geodynamics, Jan 2019. DOI:10.1016/j.geog.2018.11.006

37. I. Srivani, G. S. V. Prasad and D. Venkata Ratnam, "A Deep Learning-Based Approach to Forecast Ionospheric Delays for GPS Signals," in IEEE Geoscience and Remote Sensing Letters., 2019.doi: 10.1109/LGRS.2019.2895112 .

38. D. Venkata Ratnam, Vishnu T. R and P. Babu Sree Harsha Ionospheric Gradients Estimation and Analysis of S-Band Navigation Signals for NAVIC system over Low Latitude Station, IEEE Access, Nov 2018, DOI: 10.1109/ACCESS.2018.2876795.

39. Mallika I, D Venkata Ratnam, Y,Otsuka, G.Sivavaraprasad, Raman, “Implementation of Hybrid Ionospheric TEC Forecasting Algorithm Using PCA-NN Method, IEEE: JSTARS, DOI: 10.1109/JSTARS.2018.2877445.

40. G. Sivavaraprasad1, D. Venkata Ratnam1 and Yuichi Otsuka, “Multicomponent Analysis of Ionospheric Scintillation Effects Using the Synchrosqueezing Technique for Monitoring and Mitigating their Impact on GNSS Signals, “, Journal Navigation, Nov2018.

41. Raghavendra Neeli ·J R K Kumar Dabbakuti ·V. Rajesh Chowdhary ·Nitin K. Tripathi Venkata Ratnam D, " Modeling of local ionospheric time varying characteristics based on singular value decomposition over low-latitude GPS stations" Astrophys Space Sci (2018)363:182 DOI:10.1007/s10509-018-3403-1,

42. Shaik Shafi, B.N.Bhandari, D.Venkata Ratnam,”An Efficient Cross Layer Routing Protocol for Safety Message Dissemination in VANETS with Reduced Routing Cost and Delay Using IEEE 802.11p”, Wireless Personal Communications, Springer, April 2018.

43. D. Venkata. Ratnam, J R K Kumar DabbakutiandN V V N J Sri Lakshmi,Improvement of Indian-Regional Klobuchar Ionospheric Model Parameters for Single-frequency GNSS Users, IEEE GRSL letters April 2018.

44. D. Venkata Ratnam, JRK Kumar and G Sivavaraprasad,l., Development ofMultivariate Ionospheric TEC Forecasting Algorithm using Linear Time Series Model and ARMA over Low-latitude GNSS Station, March 2018, Advances in Space Research

45. Suraj, P.S., Kumar Dabbakuti, J.R.K., Chowdhary, Venkata.Ratnam. et al, Linear time series modeling of GPS-derived TEC observations over the Indo-Thailand region,. J Geodesy (2017). https://doi.org/10.1007/s00190-017-1099-6.

46. D Venkata Ratnam, Senior Member, IEEE, J. R. K. Kumar Dabbakuti, and Surendra Sunda,” Modeling of Ionospheric Time Delays Based on a Multishell Spherical Harmonics Function Approach”. IEEE JOURNAL OF SELECTED TOPICS IN APPLIED EARTH OBSERVATIONS AND REMOTE SENSING , Digital Object Identiﬁer 10.1109/JSTARS.2017.2743695, 2017.

47. M Sridhar, D Venkata Ratnam, KP Raju, DS Praharsha,” Ionospheric scintillation forecasting model based on NN-PSO technique”‘ Astrophysics and Space Science (Springer), 2017.

48. Raghavendra Vishnu Tadivaka, Bhanu Priyanka Paruchuri,Sridhar Miriyala, Padma Raju Koppireddi and Venkata Ratnam Devanaboyina, Detection of ionospheric scintillation effects using LMD–DFA, Acta Geophys. (2017). doi:10.1007/s11600- 017-0058-1.

49. D. Venkata Ratnam, Vindhya JRK Kumar, Ionospheric forecasting model using fuzzy logic-based gradientdescentmethod,GeodesyandGeodynamics(2017),http://dx.doi.org/10.1016/j.geog.2017.05.003

50. Cheerla, S., Venkata Ratnam, D., Meghana, S.R. et al,” Pathloss Study for 61 GHZ Wave D2D Communications in Indoor Environment”, Wireless Personal Communications, Springer, 2017.

51. Sivavaraprasad G, D.Venkata Ratnam , “Short-term Forecasting of Ionospheric Total Electron Content over a Low-latitude Global Navigation Satellite System Station”, IET Radar, Sonar & Navigation, April 2017.

52. Swapna Raghunath and D. Venkata Ratnam, “Maximum-Minimum Eigen Detector for Ionospheric Irregularities over Low Latitude Region”, IEEE Geosciences and Remote Sensing letters, 2017.

53. Sivavaraprasad G, D.Venkata Ratnam "Application of Synchrosqueezing Transform (SST) to Forecast Ionospheric Delays using GPS Observations", IET Radar, Sonar & Navigation, February 2017.

54. Sivavaraprasad G, D.Venkata Ratnam "Performance Evaluation of Ionospheric Time Delay Forecasting Models using GPS Observations at a Low-latitude Station", Advances in Space Research, 2017.

55. G. Sivavaraprasad, R. Sree Padmaja, and D. Venkata Ratnam, “Mitigation of Ionospheric Scintillation Effects on GNSS Signals Using Variational Mode Decomposition”, IEEE Geoscience and Remote Sensing Letters, 14(3), pp- 389 - 393 March 2017.

56. G. Sivavaraprasad, D. Venkata Ratnam, R. Sree Padmaja, V. Sharvani, G. Saiteja, Y.S. R. Mounika, P. Babu Sree Harsha, “Detection of ionospheric anomalies during intense space weather over a low-latitude GNSS station”, Acta Geodaetica et Geophysica (Springer), Dec-2016.doi:10.1007/s40328-016-0190-4

57. D. Venkata Ratnam, G. Sivavaraprasad and N.S.M.P. Latha Devi, “Analysis of Ionosphere Variability over Low-latitude GNSS Stations during 24th Solar Maximum Period” Advances in Space Research, 2016 .

58. P. B. Sree Harsha and D. Venkata Ratnam, Implementation of Advanced Carrier Tracking Algorithm Using Adaptive- Extended Kalman Filter for GNSS Receivers, IEEE Geoscience and Remote Sensing leters, March 2016.

59. J R K Kumar Dabbakuti, Venkata Ratnam D, K S Ramesh, “Analysis of Local Ionospheric variability based on SVD and MDS at low latitude GNSS stations”, Earth Planet Space, 68(94), pp.1-11,2016.

60. Swapna Raghunath and D. Venkata Ratnam , “Ionospheric Spatial Gradient Detector Based on GLRT method Using GNSS observations”, IEEE Geoscience and Remote Sensing leters, March 2016.

61. JRKK Dabbakuti, D Venkata Ratnam m, “Characterization of ionospheric variability in TEC using EOF and wavelets over low-latitude GNSS stations”,- Advances in Space Research, 2016.

62. Swapna Raghunath and D. Venkata Ratnam, “Detection of Low-Latitude Ionospheric Irregularities from GNSS Observations”, IEEE JSTARS,, Aug 2015.

63. J R K Kumar D, D. Venkata Ratnam, Surendra Sunda,” Modelling Of Ionospheric Time Delays For Satellite Based Navigation Systems Based On Adjusted Spherical Harmonic Analysis”, journal of aviation, July 2015.

64. D.Venkata Ratnam, G Shiva Prasad, and Jiyun Lee, “ An Automatic Ionospheric scintillation detector for GNSS receivers”, ”. IET Radar Sonar Navig (UK)., 2015.

65. M. Sridhar, K. Padma Raju, Ch. Srinivasa Rao and D. Venkata Ratnam, Mitigation of Ionospheric Scintillations for GPS signals under geomagnetic storm conditions using LMS adaptive filter, Int. J. of Information and Communication Technology (Inderscience Journal), Oct 2014.

66. D.Venkata Ratnam, “Estimation and Analysis of User IPP Delays using Bi-linear Model for Satellite Based Augmented Navigation Systems”, Taylor and Francis Journal of Aviation, June 2013(Scopus Indexed).

67. D.Venkata Ratnam, and A.D.Sarma, “Modelling of Low Latitude Ionosphere using GPS Data with SHF Model”, IEEE transactions on Geoscience and Remote Sensing, September,2011. Digital Object Identifier: 10.1109/TGRS.2011.2163639.

68. Venkata Ratnam, D., A. D. Sarma, V. Satya Srinivas, and P. Sreelatha (2011), Performance evaluation of selected ionospheric delay models during geomagnetic storm conditions in low-latitude region, AGU Radio Science., 46, RS0D08, doi:10.1029/2010RS004592.

69. A.D.Sarma, D. Venkata Ratnam and D. Krishna Reddy “ Modelling Low Latitude Ionosphere using modified planar fit method for GAGAN”. IET Radar Sonar Navig (UK)., 2009, Vol. 3, Iss. 6, pp. 609–619 609, doi: 10.1049/iet-rsn.2009.0022.

70. Smitha V Thampi, Sudha Ravindran, C V Devasia1, P. Sreelatha, Tarun K Pant, R. Sridharan, D. Venkata Ratnam, A.D. Sarma, C. Raghava Reddi, Jessy Jose and J.H. Sastri4 “Coherent Radio Beacon Experiment (CRABEX) for tomographic imaging of the equatorial ionosphere in the Indian longitudes- Preliminary results” , Advances in Space Research, 40, 436-441, 2007.

Number of Paper Presentations:

a) National (in chronological order, latest to oldest)

1. D.Venkata Ratnam, G.Sivavaraprasad and Harshali Mane, “Forecasting of Ionospheric TEC Values Using Holt-Winters Method over Low Latitude Station”, National Conference on Research issues and Recent trends in Electronics & Communication Engineering West Godavari. Dist., A.P., INDIA, 24-25, Jan, 2014,.

2. Harshali Mane, G.Sivavaraprasad and D.Venkata Ratnam, “ ARMA Ionospheric Prediction Model for GAGAN Applications” ,NCRRECE 2014), SIR C.R.REDDY COLLEGE OF ENGINEERING,ELURU – 534007, West Godavari. Dist., A.P., INDIA, 24- 25, Jan, 2014,.

3. N.S.M. Latha Devi, , P.S.Brahmanadam, G.Uma, S. Gopi Krishna, D. Venkata Ratnam , and K.S.Ramesh, “ A comparative study on ionospheric parameters measured with ionosonde and predicted using IRI model at Japanees longitudes during an extremely low sun spot activity year”, Proceedings of national seminar on Role of radars in atmospheric and ionospheric studies, 4-5, Jan 2012, K L University, Vaddeswaram (ISBN No: 978- 14276-5344-4).

4. V. Nagi Reddy, M. Mallikarjun, R.Rahul and D.Venkata Ratnam, P.S. Brahmanadam, S. Gopi Krishna, “ Challenges in the migration to 4G mobile systems in India”, Proceedings of national seminar on Role of radars in atmospheric and ionospheric studies, 4-5, Jan 2012, K L University, Vaddeswaram (ISBN No: 978-14276-5344-4).

5. V. Nagi Reddy, S.Venkatesh, N. Shiva Kumar, D.Venkata Ratnam, P.S.Brahmanadam, “Study of GPS postional and DOP varations using single frequency GPS receiver at KL University”, Proceedings of national seminar on Role of radars in atmospheric and ionospheric studies, 4-5, Jan 2012, K L University, Vaddeswaram (ISBN No: 978-14276- 5344-4).

6. R. Revathi, G.Uma, K.S.Ramesh,S.Gopi Krishna, D.Venkata Ratnam and P.S.Brahmandam, “ Seismo- generated gravity waves and associated ionospheric fluctuations as observed by the ground based GPS receivers”. Proceedings of national seminar on Role of radars in atmospheric and ionospheric studies, 4-5, Jan 2012, K L University, Vaddeswaram (ISBN No: 978-14276-5344-4).

7. P.Karthik, V.Navithejesh, D.Venkata Ratnam, P.S.Brahmanadam and S.Gopi Krishna, “ Study of signal strength varations using single GPS receiver”, Proceedings of national seminar on Role of radars in atmospheric and ionospheric studies, 4-5, Jan 2012, K L University, Vaddeswaram (ISBN No: 978-14276-5344-4).

8. Dhiraj Sunehra, D.Venkata Ratnam, K. Ravichandra, V. Satya Srinivas, Md.Saleemulla andA.D. Sarma, “Hardware and Software Aspects of Dual Frequency GPS Receiver “ Sliver Jubilee National Symposium on Global Navigation Satellite Systems (GNSS) and its Applications at the NERTU, OU, Hyd during 25 -26 October 2007.

9. A.D.Sarma, D.Venkata Ratnam and V. Satya Srinivas, “ Salient aspects of TEC analysis using GPS data”, National Science Workshop Proceedings, 21-23, May 2007, NARL, Gadanki.

10. Venkata Ratnam, D. and Shiva Kumar, B., “Datum Transformations for GPS Applications”, National Symposium on Global Positioning System and its Applications, 19^th December, 2002, Hyderabad, India.

b) International (in chronological order, latest to oldest)

1. E Suneetha, D Venkata Ratnam, K Sivakrishna, Review Onspace based Ionospheric Probes and Payloads for Monitoring Ionospheric Weather, 2021 3rd International Conference on Advances in Computing, Communication Control and Networking (ICAC3N),PP. 1844-1850,2021.

2. Pasumarthi, B.S.H., Devanaboyina, V.R., Sinha, P.R., Ojha, D.K., Suneel Kumar, B.Regional ionospheric TEC data assimilation and forecasting during geomagnetic storm conditions for 17thand 18thMarch 2015 days(2020) WiSEE 2020 - 8th Annual IEEE International Conference on Wireless for Space and Extreme Environments, Proceedings, art. no. 9262646, pp. 95-100.

3. Cheerla, S., Venkata Ratnam, D., Dabbakuti, J.R.K.K.An Optimized Path Loss Model for Urban Wireless Channels(2021) Lecture Notes in Electrical Engineering, 655, pp. 293-301.

4. S Salma, G Sivavaraprasad, BTP Madhav, DV Ratnam , Implementation of VARMA Model for Ionospheric TEC Forecast over an Indian GNSS Station,5th International Conference on Devices, Circuits, 2020.

5. Shaik Shafi, B.N.Bhandari, D.Venkata Ratnam, "An Improved Cross Layer Cooperative Routing for Vehicular Networks". IEEE- International Conference on Research Advances in Integrated Navigation Systems" (RAINS - 2016),April 06-07, 2016 Bangalore, India,Pages: 1 - 4, DOI: 10.1109/RAINS.2016.7764427.

6. Venkata Ratnam D, Swapna Ragunath, “Ionospheric Gradient Detection Methods for Ground Based Augmentation System”, IEEE International Conference on Electronics and Communication Systems.,Karpagam College of Engineering,Coimbatore,26-27, Feb, 2015(IEEE Digital Explorer and Scopus Indexed).

7. Venkata Ratnam D, Harshali Mane and Venu Gopala Rao Matcha, “Forecasting of Ionospheric time delays using ARMA model under Geomagnetic storm conditions”, 2nd IEEE international conference on Signal Processing and Integrated Networks, Amity Univeristy, Noida, 19-20, Feb 2015(IEEE Digital Explorer and Scopus Indexed).

8. P. Laxmikanth ,L. Surendra, D. Venkata Ratnam, “Enhancing the performance of AOA estimation in wireless communication using the MUSIC algorithm” , IEEE conference, SPACES -2015, KL University, Guntur, India, 2-3 Januarya 2015(IEEE Digital Explorer and Scopus Indexed).

9. M. Sridhar, K. Padma Raju, Ch. SrinivasaRao and D. VenkataRatnam, Spectral Analysis of Ionospheric Phase Scintillations using Hilbert – Huang Transform at a Low Latitude GNSS Station, IEEE conference, SPACES -2015, KL University, Guntur, India, 2-3 Januarya 2015(IEEE Digital Explorer and Scopus Indexed).

10. D. Venkata Ratnam and GRK Kumar , “Implementation Of An Adaptive Kalman Filter for Unmanned Air Vehicles (UAV)”, 3rd International Conference on Recent Advances in Design, Development and Operation of Micro Air Vehicles ICRAMAV-2014 -5-7 November 2014 at Jawaharlal Nehru Auditorium, Jawaharlal Nehru Technological University, Hyderabad-500 085, A. P. India. (Elsiever Indexed)

11. Sree Vardhan.C, D.Venkat Ratnam,Bhagyasree N ,Hema Dattu A, “Analysis of Path Loss Models for 4G Femtocells”, IEEE WCON Confere 12-13 September 2014, KL University, Guntur, India(IEEE Digital Explorer and Scopus Indexed).

12. D.Venkata Ratnam, P.R.V. Mounika,V. Sidhartha,V.Neelima, N. Reema,Harshali Mane Implementation of Ionospheric Prediction Algorithm Based On Huang Hilbert Transform, IEEE conferece ICSPCT – 2014, 12-12 July 2014, Ajmeer, India(IEEE Digital Explorer and Scopus Indexed).

13. M. Sridhar, K. Padma Raju, Ch. Srinivasa Rao, D. Venkata Ratnam, “Ionospheric Scintillation Monitoring at Low Latitude Indian station during Geo-magnetic storm”, International Conference on Electronics and Communication Systems.,Karpagam College of Engineering,Coimbatore,13-14, Feb, 2014 (IEEE Digital Explorer and Scopus Indexed) .

14. N.S.M.P.Latha Devi, D.VenkataRatnam, S.Venkatesh, “ TEC response due to Geomagnetic storm at low latitude GPS station”, the International Conference on Navigational Systems and Signal Processing Applications, Acharya Nagarjuna University, 13-13, Dec, 2013.

15. M. Venu Gopala Rao, D. Venkata Ratnam, “Faster GPS/IRNSS Acquisition via Sub Sampled Fast Fourier Transform (ssFFT) and Thresholding , INDICON 2013

16. ,“Impact of Engineering on Global Sustainability, IIT Bombay,13-15,Dec,2013. (IEEE Digital Explorer and Scopus Indexed).

17. D.Venkata Ratnam, Ashish Pasha, Swathi P, M.Venugopal Rao, “Acquisition of GPS L1 Signals Using Cooley-Tukey FFT Algorithm”,2013 IEEE International Conference on Signal Processing, Computing and Control (2013 IEEE ISPCC) , Jaypee University of Information Technology, Shimla, India, 26-28 September 2013 (IEEE Digital Explorer and Scopus Indexed).

18. N. S. M. P. Latha Devi, D.Venkata Ratnam, P.S.Brahmanandam, *G. Uma, and K.S.Ramesh, “An Assessment of IRI TEC predictions and Ground-based GPS- TEC Measurements over a Low Latitude Indian Station, Vaddeswaram”, 3rd International Conference on RF and Signal Processing, KL University,Vaddeswaram, Guntur, India, 26-27,July, 2013.

19. D.Venkata Ratnam, P. Karthik, S.G. Krishna, B.S.Siva Rao, and H. Khan "Ionospheric Prediction Model Based on ARMA Technique for GAGAN ION GNSS 2012 conference, Nashville, Tennessee on Sept 17-18,.

20. A.D. Sarma, V. Satya Srinivas, D. Venkata Ratnam and B.M. Reddy ,"Robust Ionospheric Threat Model for Low Latitude Stations in the Context of GBAS", Ionospheric Effects Symposium IES-2011, Alxandria, 17-19, May 2011.

21. A.D. Sarma, D. Venkata Ratnam, Sudha Ravindran and P.V. D. Somasekhar Rao, “Evaluation of Ionospheric Models Under Magnetic Storm Conditions for GAGAN System”, Beacon Satellite Sympoisum, Barcelona, Spain, June 7-11, 2010

22. D. Venkata Ratnam, CH. Sujatha, A. D. Sarma and Sudha Ravindran “Modelling of GAGAN TEC data using Spherical Harmonic Functions”, CODEC-09 international conference, December 14-16, Kolkota, 2009.

23.

D.Venkata Ratnam1, A.D. Sarma1, P.V.D. Somasekhar Rao and B.M.Reddy1 “Modified Ionospheric Tomography algorithm using GAGAN data” URSIGA2008 international conference 23-29 August 2008 in Chicago, USA.

24. D. Krishna Reddy, N .Sunanda, D. Venkata Ratnam and A.D.Sarma, “Mobile Positioning using RSS based Weighted Least Square Algorithm for LBS application” 3rd International conference on Positioning , Timing and Navigation (LOCATION 07), 8-9 Feb 2008, Noida, India,

25. D.Krishna Reddy1, N.Sunanda, D.Venkat Ratnam and A.D.Sarma, “Mobile Position Error Analysis of RSS Based Algorithms” INDICON 07, 6-8 September,2007, Bangalore, India.

26. D.Venkata Ratnam and A.D.Sarma “ 3-D Ionospheric model for GAGAN” CODEC 06 international conference, December 2006, Kolkata.

27. Dhiraj Sunehra, D.Venkata Ratnam and A.D.Sarma “Prominent methods for estimation of instrumental biases for GAGAN applications” CODEC 06 international conference, December 2006, Kolkata.

28. D.Krishna Reddy, A.D.Sarma, D.Venkata Ratnam and K.Satyanarayana “ Grid Based Field Strength Method for Mobile Positioning” , 2nd International conference on Positioning , Timing and Navigation (LOCATION 06), 7- 9th June 2006, Bangalore, India

29. K. Ravi Chandra, D.Krishna Reddy, D.Venkata Ratnam and A.D.Sarma “Integration of LRF Observables with GPS Datum for GIS Applications” ,ICORG 2006, JNTU,Hyderabad June 2006

30. A.D.Sarma, D.Venkata Ratnam and C.V.Devasia “Validation of TEC derived from CRABEX Receiver with GPS data at a Low Latitude Station " URSIGA2005 international conference 23-29 October 2005 in New Delhi, INDIA.

31. Sarma, A., D., Dhiraj Sunehra and D.Venkata Ratnam, “Prominent datum conversions for GPS Applications”, International conference CODEC04, Kolkata, January 2004.