13 research outputs found
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
TDMA is Optimal for All-unicast DoF Region of TIM if and only if Topology is Chordal Bipartite
The main result of this work is that an orthogonal access scheme such as TDMA
achieves the all-unicast degrees of freedom (DoF) region of the topological
interference management (TIM) problem if and only if the network topology graph
is chordal bipartite, i.e., every cycle that can contain a chord, does contain
a chord. The all-unicast DoF region includes the DoF region for any arbitrary
choice of a unicast message set, so e.g., the results of Maleki and Jafar on
the optimality of orthogonal access for the sum-DoF of one-dimensional convex
networks are recovered as a special case. The result is also established for
the corresponding topological representation of the index coding problem
Topological Interference Management: Trade-off Between DoF and SIR for Cellular Systems
International audienceTopological interference management (TIM) allows studying the degrees of freedom (DoF) of partially connected linear interference communication networks, where the channel state information at the transmitters (CSIT) is restricted to the topology of the network, i.e., a knowledge of which interference links are weak and which are strong. In this paper, we consider TIM for an infinite downlink cellular network in the one-dimensional (1D) linear and the two-dimensional (2D) hexagonal models. We consider uniformly distributed users in each cellular cell, effectively creating a continuous distribution of users, aiming to study user classes based on different interference profiles rather than on actual individual users' positions. We also consider the construction of the TIM network topology by analyzing different interference thresholds. Unlike previous works, we use TIM at the user class level to find the system's DoF independent of the actual user position. Finally, after proposing a fractional coloring scheme that can achieve the optimal DoF solution, a trade-off between DoF and SIR is given
On the Impact of Normalized Interference Threshold for Topological Interference Management
International audienceThis paper presents a new formulation to build an interference topology for the multiuser unicast Topological Interference Management (TIM) based wireless network problem. Based on our interference topology formulation, we are able to evaluate the achievable rate's theoretical limit, in the asymptotic signal to noise ratio (SNR) regime, for the underlying wireless network and not just for its topological interference representation. This new formulation allows us to cope with the finite SNR regime and not just with the asymptotic SNR regime with the Degrees of Freedom (DoF) analysis. A new SNR independent interference threshold parameter is proposed and we evaluate the achievable symmetric rates of the wireless network in both the finite SNR regime and the asymptotic SNR regime. Finally, we present outer bound solutions on the new normalized interference threshold parameter for interference topologies with half-DoF-feasibility, considering both an orthogonal resource allocation and Interference Alignment (IA). These bounds specify if a given half-DoF-feasible interference topology can be, in terms of the achievable rate, the best topology or not. Using this result, we limit the search space in the normalized interference threshold parameter range, to find half-DoF-feasible interference topologies having the possibility to be the best topologies in terms of the achievable rate
Topological Interference Management With Transmitter Cooperation
Interference networks with no channel state information at the transmitter except for the knowledge of the connectivity graph have been recently studied under the topological interference management framework. In this paper, we consider a similar problem with topological knowledge but in a distributed broadcast channel setting, i.e., a network where transmitter cooperation is enabled. We show that the topological information can also be exploited in this case to strictly improve the degrees of freedom (DoF) as long as the network is not fully connected, which is a reasonable assumption in practice. Achievability schemes from graph theoretic and interference alignment perspectives are proposed. Together with outer bounds built upon generator sequence, the concept of compound channel settings, and the relation to index coding, we characterize the symmetric DoF for the so-called regular networks with constant number of interfering links, and identify the sufficient and/or necessary conditions for the arbitrary network topologies to achieve a certain amount of symmetric DoF
Topological Interference Management with Transmitter Cooperation
Interference networks with no channel state information at the transmitter
(CSIT) except for the knowledge of the connectivity graph have been recently
studied under the topological interference management (TIM) framework. In this
paper, we consider a similar problem with topological knowledge but in a
distributed broadcast channel setting, i.e. a network where transmitter
cooperation is enabled. We show that the topological information can also be
exploited in this case to strictly improve the degrees of freedom (DoF) as long
as the network is not fully connected, which is a reasonable assumption in
practice. Achievability schemes based on selective graph coloring, interference
alignment, and hypergraph covering, are proposed. Together with outer bounds
built upon generator sequence, the concept of compound channel settings, and
the relation to index coding, we characterize the symmetric DoF for so-called
regular networks with constant number of interfering links, and identify the
sufficient and/or necessary conditions for the arbitrary network topologies to
achieve a certain amount of symmetric DoF.Comment: 46 pages, 10 figures, short version presented at the International
Symposium on Information Theory 201