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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
Optimality of orthogonal access for onedimensional convex cellular networks
, 2013
"... It is shown that a greedy orthogonal access scheme achieves the sum degrees of freedom of all onedimensional (all nodes placed along a straight line) convex cellular networks (where cells are convex regions) when no channel knowledge is available at the transmitters except the knowledge of the netw ..."
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It is shown that a greedy orthogonal access scheme achieves the sum degrees of freedom of all onedimensional (all nodes placed along a straight line) convex cellular networks (where cells are convex regions) when no channel knowledge is available at the transmitters except the knowledge of the network topology. In general, optimality of orthogonal access holds neither for twodimensional convex cellular networks nor for onedimensional nonconvex cellular networks, thus revealing a fundamental limitation that exists only when both onedimensional and convex properties are simultaneously enforced, as is common in canonical information theoretic models for studying cellular networks. The result also establishes the capacity of the corresponding class of index coding problems.
INTERFERENCE CHANNELS WITH COORDINATED MULTIPOINT TRANSMISSION
, 2014
"... Coordinated MultiPoint (CoMP) transmission is an infrastructural enhancement under consideration for nextgeneration wireless networks. In this dissertation, the capacity gain achieved through CoMP transmission is studied in various models of wireless networks that have practical significance. The ..."
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Cited by 2 (2 self)
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Coordinated MultiPoint (CoMP) transmission is an infrastructural enhancement under consideration for nextgeneration wireless networks. In this dissertation, the capacity gain achieved through CoMP transmission is studied in various models of wireless networks that have practical significance. The capacity gain is analyzed through the degrees of freedom (DoF) criterion. The DoF available for communication provides an analytically tractable way to characterize the capacity of interference channels. The considered channel model has K transmitter/receiver pairs, and each receiver is interested in one unique message from a set of K independent messages. Each message can be available at more than one transmitter. The maximum number of transmitters at which each message can be available is defined as the cooperation order M. For fully connected interference channels, it is shown that the asymptotic per user DoF, as K goes to infinity, remains at 1 2 as M is increased from 1 to 2. Furthermore, the same negative result is shown to hold for all M ≥ 2 for any message assignment that satisfies a local cooperation constraint. On the other hand, when the assumption of full connectivity is relaxed to local connectivity, and each transmitter is connected only to its own receiver as well as L neighboring receivers, it is shown that local cooperation is optimal. The asymptotic per user DoF is shown to be at least max
On UplinkDownlink Duality for Cellular IA
"... In our previous work [1], [2] we considered the uplink of a hexagonal cellular network topology and showed that linear “oneshot ” interference alignment (IA) schemes are able to achieve the optimal degrees of freedom (DoFs) per user, under a decodedmessage passing framework that allows basestatio ..."
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In our previous work [1], [2] we considered the uplink of a hexagonal cellular network topology and showed that linear “oneshot ” interference alignment (IA) schemes are able to achieve the optimal degrees of freedom (DoFs) per user, under a decodedmessage passing framework that allows basestations to exchange their own decoded messages over local backhaul links. In this work, we provide the dual framework for the downlink of cellular networks with the same backhaul architecture, and show that for every “oneshot ” IA scheme that can achieve d DoFs per user in the uplink, there exists a dual “oneshot ” IA scheme that can achieve the same DoFs in the downlink. To enable “Cellular IA ” for the downlink, basestations will now use the same local backhaul links to exchange quantized versions of the dirtypaper precoded signals instead of user messages. I.
Index Terms
"... Interference alignment promises that, in Gaussian interference channels, each link can support half of a degree of freedom (DoF) per pair of transmitreceive antennas. However, in general, this result requires to precode the data bearing signals over a signal space of asymptotically large diversity, ..."
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Interference alignment promises that, in Gaussian interference channels, each link can support half of a degree of freedom (DoF) per pair of transmitreceive antennas. However, in general, this result requires to precode the data bearing signals over a signal space of asymptotically large diversity, e.g., over an infinite number of dimensions for timefrequency varying fading channels, or over an infinite number of rationally independent signal levels, in the case of timefrequency invariant channels. In this work we consider a wireless cellular system scenario where the promised optimal DoFs are achieved with linear precoding in oneshot (i.e., over a single timefrequency slot). We focus on the uplink of a symmetric cellular system, where each cell is split into three sectors with orthogonal intrasector multiple access. In our model, interference is “local”, i.e., it is due to transmitters in neighboring cells only. We consider a messagepassing backhaul network architecture, in which nearby sectors can exchange already decoded messages and propose an alignment solution that can achieve the optimal DoFs. To avoid signaling schemes relying on the strength of interference, we further introduce the notion of topologically robust schemes, which are able to guarantee a minimum rate (or DoFs) irrespectively of the strength of the interfering links. Towards this end, we design an alignment scheme which is topologically robust and still achieves the same optimum DoFs.