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39
Ergodic interference alignment
 in Proceedings of the International Symposium on Information Theory (ISIT 2009), (Seoul, South Korea
, 2009
"... Abstract—Consider a Kuser interference channel with timevarying fading. At any particular time, each receiver will see a signal from most transmitters. The standard approach to such a scenario results in each transmitterreceiver pair achieving a rate proportional to 1 the single user rate. However ..."
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Cited by 96 (24 self)
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Abstract—Consider a Kuser interference channel with timevarying fading. At any particular time, each receiver will see a signal from most transmitters. The standard approach to such a scenario results in each transmitterreceiver pair achieving a rate proportional to 1 the single user rate. However, given two K well chosen time indices, the channel coefficients from interfering users can be made to exactly cancel. By adding up these two signals, the receiver can see an interferencefree version of the desired transmission. We show that this technique allows each user to achieve at least half its interferencefree ergodic capacity at any SNR. Prior work was only able to show that half the interferencefree rate was achievable as the SNR tended to infinity. We examine a finite field channel model and a Gaussian channel model. In both cases, the achievable rate region has a simple description and, in the finite field case, we prove it is the ergodic capacity region. I.
Subspace alignment chains and the degrees of freedom of the threeuser MIMO interference channel
 IEEE Trans. Inf. Theory
, 2014
"... We show that the 3user MT ×MR MIMO interference channel where each transmitter is equipped with MT antennas and each receiver is equipped with MR antennas has d(M,N) 4 ..."
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Cited by 36 (12 self)
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We show that the 3user MT ×MR MIMO interference channel where each transmitter is equipped with MT antennas and each receiver is equipped with MR antennas has d(M,N) 4
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
MISO Broadcast Channels with Delayed FiniteRate Feedback: Predict or Observe?
"... Abstract—Most multiuser precoding techniques require accurate channel state information at the transmitter (CSIT) to maintain orthogonality between the users. Such techniques have proven quite fragile in timevarying channels because the CSIT is inherently imperfect due to quantization error and fe ..."
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Cited by 10 (2 self)
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Abstract—Most multiuser precoding techniques require accurate channel state information at the transmitter (CSIT) to maintain orthogonality between the users. Such techniques have proven quite fragile in timevarying channels because the CSIT is inherently imperfect due to quantization error and feedback delay. An alternative approach recently proposed by MaddahAli and Tse (MAT) allows for significant multiplexing gain in the multiinput singleoutput (MISO) broadcast channel (BC) even with CSIT that is “completely stale”, i.e., uncorrelated with the current channel state. With K users, their scheme claims to lose only a log(K) factor relative to the full K degrees of freedom (DoF) attainable in the MISO BC with perfect CSIT for large K. However, their result does not consider the cost of the feedback, which is potentially very large in high mobility (short channel coherence time). In this paper, we more closely examine the MAT scheme and compare its maximum net DoF gain to single user transmission (which always achieves 1 DoF) and partial CSIT linear precoding (which achieves up to K). In particular, assuming the channel coherence time isN symbol periods and the feedback delay is Nfd, we show that when N < (1+o(1))K logK (short coherence time), single user transmission performs best, whereas for N> (1+o(1))(Nfd+K / logK)(1−log−1K)−1 (long coherence time), zeroforcing precoding outperforms the other two. The MAT scheme is optimal for intermediate coherence times, which for practical parameter choices is indeed quite a large and significant range, even accounting for the feedback cost. Index Terms—MIMO, channel state information, quantization. I.
Aligned image sets under channel uncertainty: Settling a conjecture by lapidoth, shamai and wigger on the collapse of degrees of freedom under finite precision csit,” arXiv preprint arXiv:1403.1541
"... A conjecture made by Lapidoth, Shamai and Wigger at Allerton 2005 (also an open problem presented at ITA 2006) states that the degrees of freedom (DoF) of a two user broadcast channel, where the transmitter is equipped with 2 antennas and each user is equipped with 1 antenna, must collapse under fin ..."
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Cited by 8 (1 self)
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A conjecture made by Lapidoth, Shamai and Wigger at Allerton 2005 (also an open problem presented at ITA 2006) states that the degrees of freedom (DoF) of a two user broadcast channel, where the transmitter is equipped with 2 antennas and each user is equipped with 1 antenna, must collapse under finite precision channel state information at the transmitter (CSIT). That this conjecture, which predates interference alignment, has remained unresolved, is emblematic of a pervasive lack of understanding of the degrees of freedom of wireless networks—including interference and X networks—under channel uncertainty at the transmitter(s). In this work we prove that the conjecture is true in all nondegenerate settings (e.g., where the probability density function of unknown channel coefficients exists and is bounded). The DoF collapse even when perfect channel knowledge for one user is available to the transmitter. This also settles a related recent conjecture by Tandon et al. The key to our proof is a bound on the number of codewords that can cast the same image (within noise distortion) at the undesired receiver whose channel is subject to finite precision CSIT, while remaining resolvable at the desired receiver whose channel is precisely known by the transmitter. We are also able to generalize the result
Elements of Cellular Blind Interference Alignment — Aligned Frequency Reuse
 Wireless Index Coding and Interference Diversity”, March 2012, eprint arXiv:1203.2384
"... We explore degrees of freedom (DoF) characterizations of partially connected wireless networks, especially cellular networks, with no channel state information at the transmitters. Specifically, we introduce three fundamental elements — aligned frequency reuse, wireless index coding and interferen ..."
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Cited by 7 (3 self)
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We explore degrees of freedom (DoF) characterizations of partially connected wireless networks, especially cellular networks, with no channel state information at the transmitters. Specifically, we introduce three fundamental elements — aligned frequency reuse, wireless index coding and interference diversity — through a series of examples, focusing first on infinite regular arrays, then on finite clusters with arbitrary connectivity and message sets, and finally on heterogeneous settings with asymmetric multiple antenna configurations. Aligned frequency reuse refers to the optimality of orthogonal resource allocations in many cases, but according to unconventional reuse patterns that are guided by interference alignment principles. Wireless index coding highlights both the intimate connection between the index coding problem and cellular blind interference alignment, as well as the added complexity inherent to wireless settings. Interference diversity refers to the observation that in a wireless network each receiver experiences a different set of interferers, and depending on the actions of its own set of interferers, the interferencefree signal space at each receiver fluctuates differently from other receivers, creating opportunities for robust applications of blind interference alignment principles. ar X iv
Dynamic interference mitigation for generalized partially connected quasistatic MIMO interference channel
 IEEE Transactions on Signal Processing
, 2011
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Degrees of Freedom of RankDeficient MIMO Interference Channels
"... Abstract — We characterize the degrees of freedom (DoF) of multipleinput and multipleoutput (MIMO) interference channels with rankdeficient channel matrices. For the twouser rankdeficient MIMO interference channel, we provide a tight outer bound to show that the previously known achievable DoF ..."
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Cited by 5 (4 self)
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Abstract — We characterize the degrees of freedom (DoF) of multipleinput and multipleoutput (MIMO) interference channels with rankdeficient channel matrices. For the twouser rankdeficient MIMO interference channel, we provide a tight outer bound to show that the previously known achievable DoF in the symmetric case is optimal and generalize the result to fully asymmetric settings. For the Kuser rankdeficient interference channel, we improve the previously known achievable DoF and provide a tight outer bound to establish optimality in symmetric settings. In particular, we show that for the Kuser rankdeficient interference channel, when all nodes have M antennas, all direct channels have rank D0, all cross channels are of rank D, and the channels are otherwise generic, the optimal DoF value per user is min(D0, M − (min(M, (K − 1)D)/2)). Notably for interference channels, the rankdeficiency of direct channels does not help and the rank deficiency of crosschannels does not hurt. The main technical challenge is to account for the spatial dependences introduced by rank deficiencies in the interference alignment schemes that typically rely on the independence of channel coefficients. Index Terms — Channel capacity, degrees of freedom, interference channel, multipleinput multipleoutput (MIMO), rank deficient channels, interference alignment I.
On blind interference alignment over homogeneous block fading channels
 IEEE Commun. Lett
, 2012
"... All intext references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately. ..."
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Cited by 4 (2 self)
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All intext references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.