騫 申

This paper investigates short-packet communications over a diamond relay network with two untrusted relays (potential eavesdroppers) with the purpose of guaranteeing reliability and security si- multaneously. As the performance metric, reliable-and-secure probability (RSP), considering both reliability and secrecy, is defined from the perspective of physical layer security. An analytical approach is proposed to investigate reliability and security by taking into account the characteristics of the short-packet transmission. RSPs are numerically obtained via the analytical framework by utilizing the source-channel separation theorem for the source-to-relay transmission and chief executive officer (CEO) problem analyses for the relay-to-destination transmission. It is found that the optimal RSP is achieved when the contributions from the source-relay transmission and the relay-destination transmission are balanced, even without support from a friendly jamming signal or artificial noise.

We develop a joint source-channel coding (JSCC) scheme based on an unequal power allocation strategy, in which different levels of power are allocated according to a priori probability distribution of the information bits. Two protograph low-density parity-check codes are used as the source code and the channel code, respectively, in the proposed JSCC scheme. With fixed row weight and row element alphabet, optimization on the source code is conducted via random search to obtain a best-found base matrix with the lowest decoding threshold among all the searched base matrices. Simulation results show that the new JSCC scheme outperforms the traditional equal power allocation based JSCC by exploiting the source statistics at the decoder. Moreover, theoretical threshold analysis is in agreement with the practical simulation results.

We analyze the outage probability for the orthogonal space-time block code based multiple-input multiple-output (MIMO) relay networks, composed of one source, one relay, and a single destination. The relay forwards the decoded and interleaved information sequence even though the information part may contain error(s), according to the lossy forward strategy. In spatially independent MIMO channels, we find that the diversity order of the relay network can be interpreted and formulated by the well-known max-flow min-cut theorem. Moreover, we extend the analysis to the case of spatially correlated MIMO channels. Approximated explicit expressions for the outage probabilities are obtained in high signal-to-noise ratio regime.