Browsing by Author "Jokhakar Jignesh, D."

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    Performance enhancement of optical QPSK systems with coherent reception for high speed links
    (2013) Jokhakar Jignesh, D.; Sripati, U.; Kulkarni, M.
    Coherent optical QPSK systems have attracted the attention of the research community and the Optical industry on account of features such as low power requirement and high receiver sensitivity. This can bring about a reduction in the transmitter power levels as well as the link margin to maintain a required BER. However, in order to realize a coherent detection system, the local oscillator laser needs to be synchronized with the transmitter laser diode. This can be achieved by using an optical (Phase Lock Loop) PLL at the receiver for medium data rate (Mbps). But for high data rate applications (data rates in terms of Gbps), optical PLLs are not practically realizable. In this paper, we have analyzed the use of Viterbi and Viterbi Phase Estimation Algorithm for phase synchronization. We have carried out the BER calculations and determined the BER performance degradation when compared to ideal uncoded QPSK BER performance when synchronization is not maintained. The use of Viterbi and Viterbi phase estimation algorithm brings about an improvement in BER even in the absence of an optical synchronizing arrangement. This performance improvement is further enhanced with the use of suitable error control codes. A comparison has been made between various Error Control Codes such as Reed-Solomon (RS) codes, Concatenated codes comprising of a RS and convolutional code and Low Density Parity check (LDPC) codes. We have quantified the improvement achievable with the use of these codes. © 2013 IEEE.
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    Performance of QPSK modulation for FSO geo-synchronous satellite communication link under atmospheric turbulence
    (2013) Jokhakar Jignesh, D.; Sripati, U.; Kulkarni, M.
    In recent years, free space optical (FSO) communication has gained a considerable interest amongst the researchers due to certain benefits it has to offer over RF links such as availability of large unlicensed bandwidth, high data rates, negligible electromagnetic interference, ease of installation etc. However the conventionally used FSO systems use On-Off Keying (OOK) as the modulation technique. Such a link requires high levels of transmit power. In this paper, we have suggested the use of QPSK modulation technique which allows us to reap the benefits of coherent detection. Our calculations show that QPSK is more inert to the changes in atmospheric conditions like temperature, air pressure, humidity, aerosol concentration etc. © 2013 IEEE.