On Strong Secrecy for Multiple Access Channels with States and Causal CSI

TL;DR

This paper investigates strong secrecy over state-dependent multiple access channels with causal channel state information, proposing new coding schemes and bounds, and identifying conditions where these schemes are optimal.

Contribution

It introduces two novel block Markov coding schemes for secure communication with causal CSI and characterizes their performance and optimality in certain cases.

Findings

The first coding scheme with backward decoding can achieve larger regions.

Both coding schemes are optimal in capacity-achieving cases with degraded message sets.

Inner bounds reduce to known results in special cases.

Abstract

Strong secrecy communication over a discrete memoryless state-dependent multiple access channel (SD-MAC) with an external eavesdropper is investigated. The channel is governed by discrete memoryless and i.i.d. channel states and the channel state information (CSI) is revealed to the encoders in a causal manner. Inner and outer bounds are provided. To establish the inner bound, we investigate coding schemes incorporating wiretap coding and secret key agreement between the sender and the legitimate receiver. Two kinds of block Markov coding schemes are proposed. The first one is a new coding scheme using backward decoding and Wyner-Ziv coding and the secret key is constructed from a lossy description of the CSI. The other one is an extended version of the existing coding scheme for point-to-point wiretap channels with causal CSI. A numerical example shows that the achievable region given by the first coding scheme can be strictly larger than the second one. However, these two schemes do not outperform each other in general and there exists some numerical examples that in different channel models each coding scheme achieves some rate pairs that cannot be achieved by another scheme. Our established inner bound reduces to some best-known results in the literature as special cases. We further investigate some capacity-achieving cases for state-dependent multiple access wiretap channels (SD-MAWCs) with degraded message sets. It turns out that the two coding schemes are both optimal in these cases.