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Allerton Conference on Communication, Control, and Computing

The interference wiretap channel with an arbitrarily varying eavesdropper: Aligning interference with artificial noise

Xiang He, Aylin Yener

Published Oct 1, 2012• 8 citations
Publisher

Abstract

In this work, a Gaussian two-user MIMO interference channel is considered in the presence of an external eavesdropper whose channel is completely unknown to the legitimate communication parties and can be varying in an arbitrary fashion from one channel use to the next. We improve our recent result by deriving a larger achievable secrecy degrees of freedom region. In the achievable scheme, the transmitter injects artificial noise to confuse the eavesdropper, and at the same time aligns the injected noise with the interference from the other user at the intended receiver. The achieved secure degrees of freedom are shown to be closely connected to the rank of the effective channel matrix through which the eavesdropper observes the artificial noise. The precoding matrix is then designed to ensure that this rank cannot be reduced under any possible Eve's channel state.

DOI
10.1109/allerton.2012.6483219

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IEEE Transactions on Information Theory•Jun 20, 2013•67 citations
In this work, a Gaussian two-user MIMO interference channel is considered in the presence of an external eavesdropper whose channel is completely unknown to the legitimate communication parties and can be varying in an arbitrary fashion from one channel use to the next. We improve our recent result by deriving a larger achievable secrecy degrees of freedom region. In the achievable scheme, the transmitter injects artificial noise to confuse the eavesdropper, and at the same time aligns the injected noise with the interference from the other user at the intended receiver. The achieved secure degrees of freedom are shown to be closely connected to the rank of the effective channel matrix through which the eavesdropper observes the artificial noise. The precoding matrix is then designed to ensure that this rank cannot be reduced under any possible Eve's channel state.
In this work we considered the Gaussian two-user interference channel where the eavesdropper channel is arbitrarily varying, all channel matrices have rank less than or equal to 2, and the eavesdropper has 1 antenna. We identify a class of these channel models for which the secrecy degrees of freedom (s.d.o.f.) region is achieved by letting only one user transmit a time. We also provided a non-trivial example for which such a transmission strategy is sub-optimal in terms of s.d.o.f. region. The achievable scheme for this example introduces a new technique to achieve secrecy for MIMO wiretap channels, in which the transmitter-receiver pair uses linear precoding so that effectively the signals are beam-formed toward a direction that can not be attained by the eavesdropper and is at the same time orthogonal to interference from the other user.
In this paper, a class of information theoretic secrecy problems is addressed where the eavesdropper channel state is completely unknown to the legitimate parties. In particular, a Gaussian MIMO wiretap channel is considered, where the eavesdropper channel state can vary from one channel use to the next, and the overall channel state sequence is known only to the eavesdropper. When the eavesdropper has fewer antennas than the transmitter and its intended receiver, a positive secrecy rate in the sense of strong secrecy is proved to be achievable and shown to match with the converse in secure degrees of freedom. This yields the conclusion that secure communication is possible regardless of the location or channel states of the eavesdropper. Additionally, it is observed that, the present setting renders the secrecy capacity problems for some multiterminal wiretap-type channels more tractable as compared to the case with full or partial knowledge of eavesdropper channel states. To demonstrate this observation, secure degrees of freedom regions are derived for the Gaussian MIMO multiple access (MAC) wiretap channel and the two-user Gaussian MIMO broadcast (BC) wiretap channel, where the transmitter(s) and intended receiver(s) have the same number of antennas.
In this work, a class of information theoretic secrecy problems is addressed where the eavesdropper channel states are completely unknown to the legitimate parties. In particular, MIMO wiretap channel models are considered where the channel of the eavesdropper is arbitrarily varying over time. Assuming that the number of antennas of the eavesdropper is limited, the secrecy rate of the MIMO wiretap channel in the sense of strong secrecy is derived, and shown to match with the converse in secure degrees of freedom. It is proved that there exists a universal coding scheme that secures the confidential message against any sequence of channel states experienced by the eavesdropper. This yields the conclusion that secure communication is possible regardless of the location or channel states of (potentially infinite number of) eavesdroppers. Additionally, it is observed that, the present setting renders the secrecy capacity problems for multi-terminal wiretap-type channels more tractable as compared the case with full or partial knowledge of eavesdropper channel states. To demonstrate this observation, secure degrees of freedom regions are derived for the Gaussian MIMO multiple access wiretap channel (MIMO MAC-WT) and the Gaussian MIMO broadcast wiretap channel (MIMO BC-WT) where the transmitter(s) and the intended receiver(s) have the same number of antennas.
A two-receiver MIMO broadcast-wiretap channel is considered where the channel state of the eavesdropper is arbitrarily varying. It is assumed that the eavesdropper knows this channel state perfectly whereas the legitimate nodes have no knowledge of it. It is further assumed that the eavesdropper experiences no additive noise. The channel between the transmitter and the two legitimate receivers is a constant MIMO Gaussian broadcast channel. This paper establishes the secrecy degrees of freedom region for transmitting a common-confidential message as well as a private- confidential message to each receiver. It is observed that a straightforward extension of single user random binning does not achieve the optimal secrecy degrees of freedom (s.d.o.f.) region. The proposed coding scheme that achieves the s.d.o.f. region involves simultaneous diagonalization of the channel matrices of the two legitimate receivers using the generalized singular value decomposition (GSVD) as well as a particular \emph{structured binning} across codebooks that minimizes the rate of the fictitious message. While the focus is on achieving weak secrecy for ease of exposition, an outline is provided on how the results can be extended for achieving strong secrecy.
A usual concern against physical layer security is that the legitimate parties would need to have (partial) channel state information (CSI) of the eavesdropper in order to design transmission schemes that provide secrecy. In this work, to overcome this concern, we consider the model where the eavesdropper's CSI is completely unknown at the legitimate transmitter(s) and the receiver. A static channel setting, and multiple antennas are considered for all parties, and it is assumed that the eavesdropper has perfect self-CSI. In this setting, assuming that the legitimate parties can employ a larger number of antennas than the eavesdropper, we provide a positive secure communication rate in the sense of strong secrecy. The achievable (guaranteed) secrecy rate we derive for the MIMO wiretap channel matches its converse in terms of secure degrees of freedom. As a side result of our approach, we also derive the secure degrees of freedom region for the MIMO MAC-wiretap channel where the transmitters and the intended receiver have the same number of antennas.
A two-transmitter Gaussian multiple access wiretap channel with multiple antennas at each of the nodes is investigated. The channel matrices of the legitimate users are fixed and revealed to all the terminals, whereas the channel matrices of the eavesdropper are arbitrarily varying and only known to the eavesdropper. The secrecy degrees of freedom (s.d.o.f.) region under a strong secrecy constraint is characterized. A transmission scheme that orthogonalizes the transmit signals of the two users at the intended receiver, and uses a single-user wiretap code for each user, is shown to achieve the s.d.o.f. region. The converse involves establishing an upper bound on a weighted-sum-rate expression. This is accomplished by using induction, where at each step one combines the secrecy and multiple-access constraints associated with an adversary eavesdropping a carefully selected group of sub-channels.