An Efficient Decoding Algorithm for Block Codes Based on the Communication Channel Reliability Information

For channel codes in communication systems, an efficient algorithm that controls error is proposed. It is an algorithm for soft decision decoding of block codes. The sufficient conditions to obtain the optimum decoding are deduced so that the efficient method which explores candidate code words can be presented. The information vector of signal space codes has isomorphic coherence. The path metric in the coded demodulator is the selected components of scaled regions. The carrier decision is derived by the normalized metric of synchronized space. An efficient algorithm is proposed based on the method. The algorithm finds out a group of candidate code words, in which the most likely one is chosen as a decoding result. The algorithm reduces the complexity, which is the number of candidate code words. It also increases the probability that the correct code word is included in the candidate code words. It is shown that both the error probability and the complexity are reduced. The positions of the first hard-decision decoded errors and the positions of the unreliable bits are carefully examined. From this examination, the candidate codewords are efficiently searched for. The aim of this paper is to reduce the required number of hard-decision decoding and to lower the block error probability

Two-Way Physical Layer Security Protocol for Gaussian Channels

In this paper we propose a two-way protocol of physical layer security using the method of privacy amplification against eavesdroppers. First we justify our proposed protocol by analyzing the physical layer security provided by the classic wiretap channel model (i.e. one-way protocol). In the Gaussian channels, the classic one-way protocol requires Eve's channel to be degraded w.r.t. Bob's channel. However, this channel degradation condition depends on Eve's location and whether Eve's receiving antenna is more powerful than Bob's. To overcome this limitation, we introduce a two-way protocol inspired in IEEE TIT (1993) that eliminates the channel degradation condition. In the proposed two-way protocol, on a first phase, via Gaussian channel, Bob sends randomness to Alice, which is partially leaked to Eve. Then, on a second phase, Alice transmits information to Bob over a public noiseless channel. We derive the secrecy capacity of the two-way protocol when the channel to Eve is also Gaussian. We show that the capacity of the two-way protocol is always positive. We present numerical values of the capacities illustrating the gains obtained by our proposed protocol. We apply our result to simple yet realistic models of satellite communication channels

Physical Layer Security Protocol for Poisson Channels for Passive Man-in-the-middle Attack

In this work, we focus on the classical optical channel having Poissonian statistical behavior and propose a novel secrecy coding-based physical layer protocol. Our protocol is different but complementary to both (computationally secure) quantum immune cryptographic protocols and (information theoretically secure) quantum cryptographic protocols. Specifically, our (information theoretical) secrecy coding protocol secures classical digital information bits at photonic level exploiting the random nature of the Poisson channel. It is known that secrecy coding techniques for the Poisson channel based on the classical one-way wiretap channel (introduced by Wyner in 1975) ensure secret communication only if the mutual information to the eavesdropper is smaller than that to the legitimate receiver. In order to overcome such a strong limitation, we introduce a two-way protocol that always ensures secret communication independently of the conditions of legitimate and eavesdropper channels. We prove this claim showing rigorous comparative derivation and analysis of the information theoretical secrecy capacity of the classical one-way and of the proposed two-way protocols. We also show numerical calculations that prove drastic gains and strong practical potential of our proposed two-way protocol to secure information transmission over optical channels