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Secure Degrees of Freedom of MIMO XChannels With Output Feedback and Delayed CSIT
 IEEE Transactions on Information Forensics and Security
, 2013
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Topological interference management with alternating connectivity: The Wynertype three user interference channel.” [Online]. Available: http://arxiv.org/ abs/1310.2385
, 2013
"... Abstract—Interference management in a threeuser interference channel with alternating connectivity with only topological knowledge at the transmitters is considered. The network has a Wynertype channel flavor, i.e., for each connectivity state the receivers observe at most one interference signal ..."
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Abstract—Interference management in a threeuser interference channel with alternating connectivity with only topological knowledge at the transmitters is considered. The network has a Wynertype channel flavor, i.e., for each connectivity state the receivers observe at most one interference signal in addition to their desired signal. Degrees of freedom (DoF) upper bounds and lower bounds are derived. The lower bounds are obtained from a scheme based on joint encoding across the alternating states. Given a uniform distribution among the connectivity states, it is shown that the channel has 2+1/9 DoF. This provides an increase in the DoF as compared to encoding over each state separately, which achieves 2 DoF only. I.
Resolving entanglements in topological interference management with alternating connectivity
 in Proc. IEEE ISIT
, 2014
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Retroactive AntiJamming for MISO Broadcast Channels∗
, 2014
"... Jamming attacks can significantly impact the performance of wireless communication systems. In addition to reducing the capacity, such attacks may lead to insurmountable overhead in terms of retransmissions and increased power consumption. In this paper, we consider the multipleinput singleoutput ..."
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Jamming attacks can significantly impact the performance of wireless communication systems. In addition to reducing the capacity, such attacks may lead to insurmountable overhead in terms of retransmissions and increased power consumption. In this paper, we consider the multipleinput singleoutput (MISO) broadcast channel (BC) in the presence of a jamming attack in which a subset of the receivers can be jammed at any given time. Further, countermeasures for mitigating the effects of such jamming attacks are presented. The effectiveness of these antijamming countermeasures is quantified in terms of the degreesoffreedom (DoF) of the MISO BC under various assumptions regarding the availability of the channel state information (CSIT) and the jammer state information at the transmitter (JSIT). The main contribution of this paper is the characterization of the DoF region of the two user MISO BC under various assumptions on the availability of CSIT and JSIT. Partial extensions to the multiuser broadcast channels are also presented. 1
Inseparability of the Multiple Access Wiretap Channel
"... Abstract—We examine the separability of the parallel multiple access wiretap channel. Separability, when exists, is useful as it enables us to code separately over parallel channels, and still achieve the optimum overall performance. It is wellknown that the parallel singleuser channel, parallel m ..."
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Abstract—We examine the separability of the parallel multiple access wiretap channel. Separability, when exists, is useful as it enables us to code separately over parallel channels, and still achieve the optimum overall performance. It is wellknown that the parallel singleuser channel, parallel multiple access channel (MAC) and parallel broadcast channel (BC) are all separable, however, the parallel interference channel (IC) is not separable in general. In this paper, we show that, while MAC is separable MAC wiretap channel is not separable in general. We prove this via a specific linear deterministic MAC wiretap channel. We then show that even the Gaussian MAC wiretap channel is inseparable in general. Finally, we show that, when the channel gains are drawn from continuous distributions, and when the secure degrees of freedom (s.d.o.f.) region is considered, then the Gaussian MAC wiretap channel is almost surely separable. I.
Topological Interference Management for Hexagonal Cellular Networks
"... Abstract—We consider the topological interference management problem for a downlink hexagonal cellular network, where the channel state information at the transmitters is limited to just the network topology. Recent work by Jafar showed that if interference is limited to only near the cell boundary ..."
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Abstract—We consider the topological interference management problem for a downlink hexagonal cellular network, where the channel state information at the transmitters is limited to just the network topology. Recent work by Jafar showed that if interference is limited to only near the cell boundary, then, an aligned frequency reuse pattern achieves the optimal value of 6/7 degrees of freedom (DoF) per cell, as opposed to the conventional frequency reuse baseline of 1/3 DoF per cell. We generalize the setting to include interference from multiple layers of adjacent cells and characterize how the gains of the optimal solution over basic frequency reuse diminish with increasing number of interference layers. Next, we focus on singlelayer interference and explore the sensitivity of the idealized assumptions behind the connectivity model of Jafar, which achieves higher DoF but only at the cost of a higher effective noise floor than the baseline, and under idealized placements of users. A modified connectivity model that operates at a comparable noisefloor to the baseline is then studied, and its DoF are shown to be bounded above by 6/11 and below by 1/2. Through numerical simulations, we compare the solutions that achieve 6/7, 1/2, and 1/3 DoF per cell and find that, while both the 6/7 and the 1/2 DoF solutions beat the baseline 1/3 figure, between them, the 1/2 DoF aligned frequency reuse pattern is more robust for small cell networks particularly for random users ’ distribution on the cell boundaries. Index Terms—Hexagonal cellular network, degree of freedom, aligned frequency reuse, topological interference management. I.
1Towards FullDuplex Multihop Multiflow — A Study of NonLayered Two Unicast Wireless Networks
"... Abstract—Starting from the elemental 2 2 2 interference channel, there has been much progress in the understanding of multihop multiflow wireless networks through degrees of freedom (DoF) studies that have produced important ideas such as (aligned) interference neutralization. However, much of thi ..."
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Abstract—Starting from the elemental 2 2 2 interference channel, there has been much progress in the understanding of multihop multiflow wireless networks through degrees of freedom (DoF) studies that have produced important ideas such as (aligned) interference neutralization. However, much of this progress has been limited to layered connectivity models that are essentially motivated by the assumption that wireless networks can only operate in halfduplex mode. Motivated by recent breakthroughs in fullduplex radio technology, in this work we expand the 2 2 2 interference channel model beyond layered connectivity in order to study the impact of fullduplex operation. In particular we study the impact of intralayer connectivity between relays that are in the same layer, the impact of direct interlayer connectivity between sources and destinations, and the impact of intermediate interlayer connectivity that connects sources or destinations, not directly to each other, but to relay nodes in nonadjacent layers in a 2 2 2 2 interference channel. We show that intralayer links and intermediate interlayer interference links do not cause a collapse of DoF while direct interference links do cause a collapse of DoF. Index Terms—Capacity, degrees of freedom, fullduplex, interference neutralization, multihop multiflow I.
SECURE DEGREES OF FREEDOM OF WIRELESS NETWORKS
, 2014
"... This dissertation studies the security of wireless interference networks from an informationtheoretic point of view. In this setting, several transmitterreceiver pairs wish to have secure communication against the eavesdropper(s). The central goal of this dissertation is to develop a framework bas ..."
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This dissertation studies the security of wireless interference networks from an informationtheoretic point of view. In this setting, several transmitterreceiver pairs wish to have secure communication against the eavesdropper(s). The central goal of this dissertation is to develop a framework based on informationtheoretic principles to determine the complete solutions for the signaling schemes in different wireless interference networks with large transmit powers, and derive the corresponding fundamental limits in terms of the secure degrees of freedom (s.d.o.f.). First, we study onehop wireless networks by considering four fundamental wireless network structures: Gaussian wiretap channel with helpers, Gaussian broadcast channel (BC) with confidential messages, Gaussian interference channel (IC) with confidential messages, and Gaussian multiple access (MAC) wiretap channel. The secrecy capacity of the canonical Gaussian wiretap channel does not scale with the transmit power, and hence, the s.d.o.f. of the Gaussian wiretap channel with no helpers is zero. We show that the exact s.d.o.f. of the Gaussian wiretap channel with a helper is 1. Our achievable scheme is based on real interference alignment 2 and cooperative jamming, which renders the message signal and the cooperative jamming signal separable at the legitimate receiver, but aligns them perfectly at the eavesdropper preventing any reliable decoding of the message signal. Our converse is based on two key lemmas. The first lemma quantifies the secrecy penalty by showing that the net effect of an eavesdropper on the system is that it eliminates one of the independent channel inputs. The second lemma quantifies the role of a helper by developing a direct relationship between the cooperative jamming signal of a helper and the message rate. We extend this result to the case of M helpers, and show that the exact s.d.o.f. in this case is M. We then generalize this approach to more
1TwoHop Interference Channels: Impact of Linear Schemes
"... We consider the twohop interference channel (IC), which consists of two sourcedestination pairs communicating with each other via two relays. We analyze the degrees of freedom (DoF) of this network when the relays are restricted to perform linear schemes, and the channel gains are constant (i.e., ..."
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We consider the twohop interference channel (IC), which consists of two sourcedestination pairs communicating with each other via two relays. We analyze the degrees of freedom (DoF) of this network when the relays are restricted to perform linear schemes, and the channel gains are constant (i.e., slow fading). We show that, somewhat surprisingly, by using vectorlinear strategies at the relays, it is possible to achieve 4/3 sumDoF when the channel gains are real. The key achievability idea is to alternate relaying coefficients across time, to create different endtoend interference structures (or topologies) at different times. Although each of these topologies has only 1 sumDoF, we manage to achieve 4/3 by coding across them. Furthermore, we develop a novel outer bound that matches our achievability, hence characterizing the sumDoF of twohop interference channels with linear schemes. As for the case of complex channel gains, we characterize the sumDoF with linear schemes to be 5/3. We also generalize the results to the multiantenna setting, characterizing the sumDoF with linear schemes to be 2M − 1/3 (for complex channel gains), where M is the number of antennas at each node. I.
1Secure Degrees of Freedom of MIMO XChannels with Output Feedback and Delayed CSI
, 2013
"... We investigate the problem of secure transmission over a twouser multiinput multioutput (MIMO) Xchannel with noiseless local feedback and delayed channel state information (CSI) available at transmitters. The transmitters are equipped with M antennas each, and the receivers are equipped with N ..."
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We investigate the problem of secure transmission over a twouser multiinput multioutput (MIMO) Xchannel with noiseless local feedback and delayed channel state information (CSI) available at transmitters. The transmitters are equipped with M antennas each, and the receivers are equipped with N antennas each. For this model, we characterize the optimal sum secure degrees of freedom (SDoF) region. We show that, in presence of local feedback and delayed CSI, the sum SDoF region of the MIMO Xchannel is same as the SDoF region of a twouser MIMO BC with 2M antennas at the transmitter and N antennas at each receiver. This result shows that, upon availability of feedback and delayed CSI, there is no performance loss in sum SDoF due to the distributed nature of the transmitters. Next, we show that this result also holds if only global feedback is conveyed to the transmitters. We also study the case in which only local feedback is provided to the transmitters, i.e., without CSI, and derive a lower bound on the sum SDoF for this model. Furthermore, we specialize our results to the case in which there are no security constraints. In particular, similar to the setting with security constraints, we show that the optimal sum degrees of freedom (sum DoF) region of the (M,M,N,N)MIMO Xchannel is same of