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On the Secure Degrees of Freedom of Wireless X Networks

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 Added by Tiangao Gou
 Publication date 2008
and research's language is English




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Previous work showed that the X network with M transmitters, N receivers has MN/(M+N-1) degrees of freedom. In this work we study the degrees of freedom of the X network with secrecy constraints, i.e. the X network where some/all messages are confidential. We consider the $M times N$ network where all messages are secured and show that N(M-1)/(M+N-1) degrees of freedom can be achieved. Secondly, we show that if messages from only M-1 transmitters are confidential, then MN/(M+N-1) degrees of freedom can be achieved meaning that there is no loss of degrees of freedom because of secrecy constraints. We also consider the achievable secure degrees of freedom under a more conservative secrecy constraint. We require that messages from any subset of transmitters are secure even if other transmitters are compromised, i.e., messages from the compromised transmitter are revealed to the unintended receivers. We also study the achievable secure degrees of freedom of the K user Gaussian interference channel under two different secrecy constraints where 1/2 secure degrees of freedom per message can be achieved. The achievable scheme in all cases is based on random binning combined with interference alignment.



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We explore the capacity and generalized degrees of freedom of the two-user Gaussian X channel, i.e. a generalization of the 2 user interference channel where there is an independent message from each transmitter to each receiver. There are three main results in this paper. First, we characterize the sum capacity of the deterministic X channel model under a symmetric setting. Second, we characterize the generalized degrees of freedom of the Gaussian X channel under a similar symmetric model. Third, we extend the noisy interference capacity characterization previously obtained for the interference channel to the X channel. Specifically, we show that the X channel associated with noisy (very weak) interference channel has the same sum capacity as the noisy interference channel.
After receiving useful peer comments, we would like to withdraw this paper.
In wireless data networks, communication is particularly susceptible to eavesdropping due to its broadcast nature. Security and privacy systems have become critical for wireless providers and enterprise networks. This paper considers the problem of secret communication over the Gaussian broadcast channel, where a multi-antenna transmitter sends independent confidential messages to two users with perfect secrecy. That is, each user would like to obtain its own message reliably and confidentially. First, a computable Sato-type outer bound on the secrecy capacity region is provided for a multi-antenna broadcast channel with confidential messages. Next, a dirty-paper secure coding scheme and its simplified version are described. For each case, the corresponding achievable rate region is derived under the perfect secrecy requirement. Finally, two numerical examples demonstrate that the Sato-type outer bound is consistent with the boundary of the simplified dirty-paper coding secrecy rate region.
In this paper, degrees of freedom (DoF) is investigated for the $Mtimes N$ single input single output (SISO) X channel with alternating channel state information at the transmitters (CSIT). It is known that the sum DoF of 2-user SISO X channel with synergistic alternating CSIT is the same as the sum DoF of 2-user $(M=N=2)$ SISO X channel with perfect CSIT [8]. In this paper, such 2-user X channel schemes are extended to the general $Mtimes N$ X channel. It is shown that the proposed $Mtimes N$ X channel schemes with synergistic alternating CSIT achieve $2M/(M+1)$ sum DoF. This DoF with $M=N=K$ is strictly lager than the best known DoF for the $K$-user X channel with delayed CSIT.
The Maddah-Ali and Tse (MAT) scheme is a linear precoding strategy that exploits Interference Alignment and perfect, but delayed, channel state information at the transmitters (delayed CSIT), improving the degrees of freedom (DoF) that can be achieved for the broadcast channel (BC). Since its appearance, many works have extended the concept of Retrospective Interference Alignment (RIA) to other multi-user channel configurations. However, little is known about the broadcast channel with multiple cells, i.e. the interference broadcast channel (IBC). In this work, the DoF are studied for the $K$-user $C$-cell multiple-input single-output (MISO) IBC with delayed CSIT (with $K/C$ users per cell). We show that the straightforward application of the MAT scheme over the IBC fails because it requires all interference to be received from the same source. Hence, in this case not all the interference can be cancelled, thus blocking the decoding of the received messages. We call this phenomenon as textit{interference coupling}, forcing to use the MAT scheme by serving just one cell at a time. In this work, we propose an extension, namely the uncoupled MAT scheme (uMAT), exploiting multiple cells, uncoupling the interference, and achieving the best known DoF inner bound for almost all settings.
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