Securing network traffic has always been a must requirement for any network application that employs insecure communication channel. The reason is to provide protection for the transmitted data over the network against unauthorized disclosure and modification of the messages between communicating parties. A Key exchange protocol is the cryptographic primitive that can establish a secure communication. The first Key exchange protocol was introduced by Diffie-Hellman. The purpose of the Diffie-Hellman protocol is to enable two parties to securely exchange a session key which can then be used for next symmetric encryption of messages. However, Diffie-Hellman itself does not authenticate the communicating entities. In this paper, we study on Diffie-Hellman Key exchange protocol. Subsequently describe authenticated key exchange protocol and One-pass key exchange protocol, which are the variants of Diffie-Hellman protocol.
OFDM with quadrature amplitude modulation (QAM) technique can be used for high speed optical applications. Increasing the order of modulation, the bit error rate (BER) increases. Forward Error correction (FEC) coding like LDPC coding is generally used to improve the BER performance. LDPC provides large minimum distance and also the power efficiency of the LDPC code increases significantly with the code length. In this paper we have compared the Soft decision and Hard decision algorithms of LDPC codes. A long Irregular LDPC code is simulated over the BIAWGN channel demonstrating the fact that LDPC coded OFDM with soft decision decoding provides very lower bit error rate as well as a larger gain in transmitter power and thus making the link more power efficient than the case with hard decision decoding. Through simulation, we have shown the advantages of using this long Irregular LDPC coded OFDM link in Optical wireless communication (OWC).
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