91 research outputs found
Topological Interference Management through Index Coding
This work studies linear interference networks, both wired and wireless, with
no channel state information at the transmitters (CSIT) except a coarse
knowledge of the end-to-end one-hop topology of the network that only allows a
distinction between weak (zero) and significant (non-zero) channels and no
further knowledge of the channel coefficients' realizations. The network
capacity (wired) and DoF (wireless) are found to be bounded above by the
capacity of an index coding problem for which the antidote graph is the
complement of the given interference graph. The problems are shown to be
equivalent under linear solutions. An interference alignment perspective is
then used to translate the existing index coding solutions into the wired
network capacity and wireless network DoF solutions, as well as to find new and
unified solutions to different classes of all three problems.Comment: Revised for the IEEE Transactions on Information Theor
Topological Interference Management with Alternating Connectivity: The Wyner-Type Three User Interference Channel
Interference management in a three-user interference channel with alternating
connectivity with only topological knowledge at the transmitters is considered.
The network has a Wyner-type 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.Comment: 4 pages, 3 figure
On Critical Index Coding Problems
The question of under what condition some side information for index coding
can be removed without affecting the capacity region is studied, which was
originally posed by Tahmasbi, Shahrasbi, and Gohari. To answer this question,
the notion of unicycle for the side information graph is introduced and it is
shown that any edge that belongs to a unicycle is critical, namely, it cannot
be removed without reducing the capacity region. Although this sufficient
condition for criticality is not necessary in general, a partial converse is
established, which elucidates the connection between the notion of unicycle and
the maximal acylic induced subgraph outer bound on the capacity region by
Bar-Yossef, Birk, Jayram, and Kol.Comment: 5 pages, accepted to 2015 IEEE Information Theory Workshop (ITW),
Jeju Island, Kore
Multilevel Topological Interference Management
The robust principles of treating interference as noise (TIN) when it is
sufficiently weak, and avoiding it when it is not, form the background for this
work. Combining TIN with the topological interference management (TIM)
framework that identifies optimal interference avoidance schemes, a baseline
TIM-TIN approach is proposed which decomposes a network into TIN and TIM
components, allocates the signal power levels to each user in the TIN
component, allocates signal vector space dimensions to each user in the TIM
component, and guarantees that the product of the two is an achievable number
of signal dimensions available to each user in the original network.Comment: To be presented at 2013 IEEE Information Theory Worksho
Topological Interference Management with Alternating Connectivity
The topological interference management problem refers to the study of the
capacity of partially connected linear (wired and wireless) communication
networks with no channel state information at the transmitters (no CSIT) beyond
the network topology, i.e., a knowledge of which channel coefficients are zero
(weaker than the noise floor in the wireless case). While the problem is
originally studied with fixed topology, in this work we explore the
implications of varying connectivity, through a series of simple and
conceptually representative examples. Specifically, we highlight the
synergistic benefits of coding across alternating topologies
A New Index Coding Scheme Exploiting Interlinked Cycles
We study the index coding problem in the unicast message setting, i.e., where
each message is requested by one unique receiver. This problem can be modeled
by a directed graph. We propose a new scheme called interlinked cycle cover,
which exploits interlinked cycles in the directed graph, for designing index
codes. This new scheme generalizes the existing clique cover and cycle cover
schemes. We prove that for a class of infinitely many digraphs with messages of
any length, interlinked cycle cover provides an optimal index code.
Furthermore, the index code is linear with linear time encoding complexity.Comment: To be presented at the 2015 IEEE International Symposium on
Information Theory (ISIT 2015), Hong Kon
Optimality of Orthogonal Access for One-dimensional Convex Cellular Networks
It is shown that a greedy orthogonal access scheme achieves the sum degrees
of freedom of all one-dimensional (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
two-dimensional convex cellular networks nor for one-dimensional non-convex
cellular networks, thus revealing a fundamental limitation that exists only
when both one-dimensional 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
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