Conference Papers

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    Using RBF neural networks and kullback-leibler distance to classify channel models in Free Space Optics
    (2012) Prakash, G.; Kulkarni, M.; Sripati, U.
    Free Space Optical (FSO) communication systems offer a license free and cost effective access performance. FSO systems provide virtually unlimited bandwidth. Since the laser beams used in these systems are spatially confined, the links are very secure. However FSO links perform well only in clear weather conditions. Clouds, fog, aerosols, and turbulence drastically affect the performance of FSO systems and lead to fluctuations in both the intensity and phase of the received signal. FSO links can suffer from data packet corruption and erasure. Various statistical models have been proposed to describe the atmospheric turbulence channels. The choice of the appropriate model for varying level of turbulence is dependent on the atmospheric parameters. In this paper we classify the channels using Radial Basis Function Neural Networks to decide the best fit. We also use Kullback-Leibler distance as a measure between the reference distribution and the distribution of observed data. © 2012 IEEE.
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    BER performance and energy efficiency of Luby Transform codes with varying BPSK thresholds over the Free Space Optical channel
    (2013) Prakash, G.; Kulkarni, M.; Sripati, U.
    In this paper we analyse the Bit Error Rate(BER) performance and energy efficiency of Luby Transform (LT) codes when the signals are Binary Phase shift Keying (BPSK )modulated with varying thresholds and transmitted over the Free Space Optical (FSO)Channel in a wireless sensor network. We model the FSO channel using the Gamma-Gamma distribution function and compare the performance for varied turbulence parameters. We also show how the distribution of the BPSK symbols varies as the distribution varies when the turbulence changes from strong to weak. Use of forward error correction helps in the recovery of the original signal even if some transmitted signals are corrupted during transmission. We analyse the FSO system, which employs Luby Transform Codes, which do not have a fixed code rate. They are considered Rateless, and as many codewords are generated as required to recover all the message bits. We show an increase in SNR and reduced energy per bit for the same BER with LT codes as the BPSK threshold increases. © 2013 IEEE.
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    On the improved performance of luby transform codes over selective repeat ARQ in turbulent free space optical links
    (2013) Prakash, G.; Nayak, A.; Kulkarni, M.; Acharya, S.
    Free Space Optical (FSO) links are capable of offering high data transfer rates, secure and low interference links for connectivity as a last mile solution. However, atmospheric turbulence can degrade the performance for distances over 1 km. This degradation is in the form of packet loss and hence drop in the error performance. Error Control Coding (ECC) can be used to mitigate the effects of the atmospheric turbulence. In this paper we prove analytically and verify through simulations that Luby Transform(LT) Codes show an improved performance over Automatic Repeat Request(ARQ) schemes for FSO transmission. FSO systems are limited by the safety limits of the input power to the laser transmitter. A notable contribution in this paper is that we prove that this improvement with LT codes is within Maximum Permissible Exposure (MPE) limit for an FSO link for a BER performance of 10-5. © 2013 IEEE.