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Srilatha Indira Dutt, V. B. S.
- Imaging of Ionospheric Electron Density Profile Over the Visakhapatnam Region for GPS Precise Position Applications
Authors
1 Dept of ECE, GITAM University, IN
Source
Wireless Communication, Vol 6, No 3 (2014), Pagination: 90-94Abstract
The electron density profile of the Ionosphere is one of the extreme interests of the Radio navigation and positioning communities. For Global Positioning System users in particular, the unknown distribution of electrons in the ionosphere is the single largest natural error source in the position fix. The GPS navigation solution is significantly affected by the refraction of the GPS signal in atmosphere. This refraction of the ionosphere causes an error of 10-30m. This refraction of the GPS signal in the atmosphere especially in ionosphere is due to the presence of electrons. With the aid of local differential corrections this error term may be eliminated. However, it is better to provide the user with real-time representation of the user-local ionosphere in order to provide the GPS signal correction at the receiver. This real time representation of the local ionosphere electron density can be achieved by several models such as spherical harmonic analysis, Tomography, International Reference Ionosphere etc. In this paper, using Spherical Harmonic analysis, Image of the electron density profile of the atmosphere is estimated over the Visakhapatnam (Lat: 17042‟00‟‟ N and Long: 83018‟00‟‟) region for the entire day of 13th January 2013. Along with electron density profile, Total Electron Content of the entire day of 13th January 2013 is also estimated and analyzed.Keywords
Electron Density, Total Electron Content, Refraction.
- Effect of Fragment SIZE and Contention Window on the Performance of IEEE 802.11 WLANs
Authors
1 Department of ECE, GITAM Institute of Technology, GITAM University, Visakhapatnam, A.P., IN
Source
Wireless Communication, Vol 4, No 9 (2012), Pagination: 467-471Abstract
Wireless communications is, by any measure, the fastest growing segment of the communications industry. The IEEE has standardized the 802.11 protocol for Wireless Local Area Networks. The IEEE 802.11 standard has defined two different access mechanisms in order to allow multiple users to access a common channel, the Distributed Coordination Function (DCF) and a centrally controlled access mechanism called the Point Coordination Function (PCF). DCF is a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) scheme with Binary Exponential Backoff algorithm (BEB). DCF describes two techniques to employ for packet transmission: the two-way handshaking technique called basic access mechanism and an optional four way handshakin technique, known as request-to send/clear-to-send (RTS/CTS) mechanism. In noisy channel, data packets become erroneous, and retransmission reduces the throughput. IEEE 802.11 allows fo fragmentation tuning and rate selection to achieve highest throughput in bad channel conditions. If an error rate is known, the parameters like fragment size and contention window can be adjusted to obtain the maximum throughput. In this paper, an analytic model is developed to evaluate the throughput of IEEE 802.11 wireless networks over noisy channels using constant backoff window. The optimal Contention window and fragment size are calculated using this model.
Keywords
IEEE 802.11b, BER, Fragmentation, Contention Window.- GPS Navigation Solution Performance Analysis due to Solar Eclipses in the Context of Indian Subcontinent
Authors
1 Department of Electronics & Communication Engineering, University College of Engineering, Andhra University, Visakhapatnam-530003, IN
2 Department of Electronics & Communication Engineering, Andhra University, Visakhapatnam, IN