Results 1  10
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100
Computeandforward: Harnessing interference through structured codes
 IEEE TRANS. INF. THEORY
, 2009
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Aligned interference neutralization and the degrees of freedom of the 2×2×2 interference channel with . . .
, 2010
"... Previous work showed that the 2×2×2 interference channel, i.e., the multihop interference network formed by concatenation of two 2user interference channels, achieves the mincut outer bound value of 2 DoF. This work studies the 2×2×2 interference channel with one additional assumption that two re ..."
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Cited by 52 (14 self)
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Previous work showed that the 2×2×2 interference channel, i.e., the multihop interference network formed by concatenation of two 2user interference channels, achieves the mincut outer bound value of 2 DoF. This work studies the 2×2×2 interference channel with one additional assumption that two relays interfere with each other. It is shown that even in the presence of the interfering links between two relays, the mincut outer bound of 2 DoF can still be achieved for almost all values of channel coefficients, for both fixed or timevarying channel coefficients. The achievable scheme relies on the idea of aligned interference neutralization as well as exploiting memory at source and relay nodes.
Aiming perfectly in the dark  blind interference alignment through staggered antenna switching
 IEEE Transactions on Signal Processing
, 2011
"... We propose a blind interference alignment scheme for the vector broadcast channel where the transmitter is equipped with M antennas and there are K receivers, each equipped with a reconfigurable antenna capable of switching among M preset modes. Without any knowledge of the channel coefficient value ..."
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Cited by 48 (7 self)
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We propose a blind interference alignment scheme for the vector broadcast channel where the transmitter is equipped with M antennas and there are K receivers, each equipped with a reconfigurable antenna capable of switching among M preset modes. Without any knowledge of the channel coefficient values at the transmitters and with only mild assumptions on the channel coherence structure we show that MKM+K−1 degrees of freedom are achievable. The key to the blind interference alignment scheme is the ability of the receivers to switch between reconfigurable antenna modes to create short term channel fluctuation patterns that are exploited by the transmitter. The achievable scheme does not require cooperation between transmit antennas and is therefore applicable to the M ×K X network as well. Only finite symbol extensions are used, and no channel knowledge at the receivers is required to null the interference. ar X iv
On secrecy capacity scaling in wireless networks
"... We study a random extended network, where the legitimate and eavesdropper nodes are assumed to be placed according to Poisson point processes in a square region of area n. It is shown that, when the legitimate nodes have unit intensity, λ = 1, and the eavesdroppers have an intensity of λe = O ( (lo ..."
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Cited by 45 (3 self)
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We study a random extended network, where the legitimate and eavesdropper nodes are assumed to be placed according to Poisson point processes in a square region of area n. It is shown that, when the legitimate nodes have unit intensity, λ = 1, and the eavesdroppers have an intensity of λe = O ( (log n) −2) , almost all of the nodes achieve a perfectly
Repair optimal erasure codes through Hadamard designs
 THE 49TH ANNUAL ALLERTON CONFERENCE ON COMMUNICATION, CONTROL AND COMPUTATION
, 2011
"... In distributed storage systems that employ erasure coding, the issue of minimizing the total communication required to exactly rebuild a storage node after a failure arises. This repair bandwidth depends on the structure of the storage code and the repair strategies used to restore the lost data. De ..."
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Cited by 41 (5 self)
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In distributed storage systems that employ erasure coding, the issue of minimizing the total communication required to exactly rebuild a storage node after a failure arises. This repair bandwidth depends on the structure of the storage code and the repair strategies used to restore the lost data. Designing highrate maximumdistance separable (MDS) codes that achieve the optimum repair communication has been a wellknown open problem. In this work, we use Hadamard matrices to construct the first explicit 2parity MDS storage code with optimal repair properties for all single node failures, including the parities. Our construction relies on a novel method of achieving perfect interference alignment over finite fields with a finite file size, or number of extensions. We generalize this construction to design mparity MDS codes that achieve the optimum repair communication for single systematic node failures and show that there is an interesting connection between our mparity codes and the systematicrepair optimal permutationmatrix based codes of Tamo et al. [21] and Cadambe et al. [22], [23].
Topological interference management through index coding
, 2013
"... While much recent progress on interference networks has come about under the assumption of abundant channel state information at the transmitters (CSIT), a complementary perspective is sought in this work through the study of interference networks with no CSIT except a coarse knowledge of the topolo ..."
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Cited by 30 (14 self)
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While much recent progress on interference networks has come about under the assumption of abundant channel state information at the transmitters (CSIT), a complementary perspective is sought in this work through the study of interference networks with no CSIT except a coarse knowledge of the topology of the network that only allows a distinction between weak and significant channels and no further knowledge of the channel coefficients ’ realizations. Modeled as a degreesoffreedom (DoF) study of a partially connected interference network with no CSIT, the problem is found to have a counterpart in the capacity analysis of wired networks with arbitrary linear network coding at intermediate nodes, under the assumption that the sources are aware only of the end to end topology of the network. The wireless (wired) network DoF (capacity) region, expressed in dimensionless units as a multiple of the DoF (capacity) of a single point to point channel (link), is found to be bounded above by the capacity of an index coding problem where the antidotes graph is the complement of the interference graph of the original network and the bottleneck link capacity is normalized to unity. The problems are shown to be equivalent under linear solutions over the same field. An interference alignment
InformationTheoretic Operating Regimes of Large Wireless Networks
"... Abstract—In analyzing the pointtopoint wireless channel, insights about two qualitatively different operating regimes—bandwidthand powerlimited—have proven indispensable in the design of good communication schemes. In this paper, we propose a new scaling law formulation for wireless networks tha ..."
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Cited by 26 (2 self)
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Abstract—In analyzing the pointtopoint wireless channel, insights about two qualitatively different operating regimes—bandwidthand powerlimited—have proven indispensable in the design of good communication schemes. In this paper, we propose a new scaling law formulation for wireless networks that allows us to develop a theory that is analogous to the pointtopoint case. We identify fundamental operating regimes of wireless networks and derive architectural guidelines for the design of optimal schemes. Our analysis shows that in a given wireless network with arbitrary size, area, power, bandwidth, etc., there are three parameters of importance: the shortdistance signaltonoise ratio (SNR), the longdistance SNR, and the power path loss exponent of the environment. Depending on these parameters, we identify four qualitatively different regimes. One of these regimes is especially interesting since it is fundamentally a consequence of the heterogeneous nature of links in a network and does not occur in the pointtopoint case; the network capacity is both power and bandwidth limited. This regime has thus far remained hidden due to the limitations of the existing formulation. Existing schemes, either multihop transmission or hierarchical cooperation, fail to achieve capacity in this regime; we propose a new hybrid scheme that achieves capacity. Index Terms—Ad hoc wireless networks, distributed MIMO, hierarchical cooperation, multihopping, operating regimes, scaling laws. I.
Network coding for three unicast sessions: Interference alignment approaches
 ALLERTON CONFERENCE ON COMMUNICATION, CONTROL, AND COMPUTING
, 2010
"... We propose interference alignment techniques, originally developed for wireless interference channels, for the problem of network coding across unicast sessions. We describe two general approaches (namely, coding at the edge or in the middle of the network) and one specific example of each approach ..."
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Cited by 23 (11 self)
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We propose interference alignment techniques, originally developed for wireless interference channels, for the problem of network coding across unicast sessions. We describe two general approaches (namely, coding at the edge or in the middle of the network) and one specific example of each approach (namely, symbol extension method and ergodic alignment, respectively). We discuss the conditions for feasibility of alignment and their relation to network structure. We also compare alignment to alternative approaches. For three unicast sessions with mincut one, we show that whenever alignment is possible, alternative approaches can also achieve half the mincut. However, for more than three sessions and/or for mincut per session greater than one, we show examples where alignment is necessary.
Exploiting channel correlations – simple interference alignment schemes with no CSIT
, 2009
"... We explore 5 network communication problems where the possibility of interference alignment, and consequently the total number of degrees of freedom (DoF) with channel uncertainty at the transmitters are unknown. These problems share the common property that in each case the best known outer bounds ..."
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Cited by 22 (6 self)
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We explore 5 network communication problems where the possibility of interference alignment, and consequently the total number of degrees of freedom (DoF) with channel uncertainty at the transmitters are unknown. These problems share the common property that in each case the best known outer bounds are essentially robust to channel uncertainty and represent the outcome with interference alignment, but the best inner bounds – in some cases conjectured to be optimal – predict a total collapse of DoF, thus indicating the infeasibility of interference alignment under channel uncertainty at transmitters. Our main contribution is to show that even with no knowledge of channel coefficient values at the transmitters, the knowledge of the channels ’ correlation structure can be exploited to achieve interference alignment. In each case, we show that under a staggered block fading model, the transmitters are able to align interference without the knowledge of channel coefficient values. The alignment schemes are based on linear beamforming – which can be seen as a repetition code over a small number of symbols – and involve delays of only a few coherence intervals.
Ergodic Secret Alignment
, 2012
"... In this paper, we introduce two new achievable schemes for the fading multiple access wiretap channel (MACWT). In the model that we consider, we assume that perfect knowledge of the state of all channels is available at all the nodes in a causal fashion. Our schemes use this knowledge together wit ..."
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Cited by 21 (17 self)
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In this paper, we introduce two new achievable schemes for the fading multiple access wiretap channel (MACWT). In the model that we consider, we assume that perfect knowledge of the state of all channels is available at all the nodes in a causal fashion. Our schemes use this knowledge together with the timevarying nature of the channel model to align the interference from different users at the eavesdropper perfectly in a onedimensional space while creating a higher dimensionality space for the interfering signals at the legitimate receiver, hence allowing for better chance of recovery. While we achieve this alignment through signal scaling at the transmitters in our first scheme (scalingbased alignment), we let nature provide this alignment through the ergodicity of the channel coefficients in the second scheme [ergodic secret alignment (ESA)] [1], [2]. For each scheme, we obtain the resulting achievable secrecy rate region. We show that the secrecy rates achieved by both schemes in the twouser fading MACWT scale with signaltonoise ratio (SNR) as 1 2 log(SNR). Hence, we show the suboptimality of the independent identically distributed (i.i.d.) Gaussian signalingbased schemes with and without cooperative jamming by showing that the secrecy rates achieved using i.i.d. Gaussian signaling with cooperative jamming do not scale with SNR. In addition, we introduce an improved version of our ESA scheme where we incorporate cooperative jamming to achieve higher secrecy rates. Moreover, we derive the necessary optimality conditions for the power control policy that maximizes the secrecy sum rate achievable by our ESA scheme when used solely and with cooperative jamming. Finally, we discuss the extension of the proposed schemes to the case where there are more than two users and show that, for theuser fading MACWT, each of the two schemes achieves secrecy sum rate that scales with SNR as 1 log(SNR).