16,036 research outputs found
Interference, Cooperation and Connectivity - A Degrees of Freedom Perspective
We explore the interplay between interference, cooperation and connectivity
in heterogeneous wireless interference networks. Specifically, we consider a
4-user locally-connected interference network with pairwise clustered decoding
and show that its degrees of freedom (DoF) are bounded above by 12/5.
Interestingly, when compared to the corresponding fully connected setting which
is known to have 8/3 DoF, the locally connected network is only missing
interference-carrying links, but still has lower DoF, i.e., eliminating these
interference-carrying links reduces the DoF. The 12/5 DoF outer bound is
obtained through a novel approach that translates insights from interference
alignment over linear vector spaces into corresponding sub-modularity
relationships between entropy functions.Comment: Submitted to 2011 IEEE International Symposium on Information Theory
(ISIT
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
Elements of Cellular Blind Interference Alignment --- Aligned Frequency Reuse, Wireless Index Coding and Interference Diversity
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
interference-free signal space at each receiver fluctuates differently from
other receivers, creating opportunities for robust applications of blind
interference alignment principles
Multiple Unicast Capacity of 2-Source 2-Sink Networks
We study the sum capacity of multiple unicasts in wired and wireless multihop
networks. With 2 source nodes and 2 sink nodes, there are a total of 4
independent unicast sessions (messages), one from each source to each sink node
(this setting is also known as an X network). For wired networks with arbitrary
connectivity, the sum capacity is achieved simply by routing. For wireless
networks, we explore the degrees of freedom (DoF) of multihop X networks with a
layered structure, allowing arbitrary number of hops, and arbitrary
connectivity within each hop. For the case when there are no more than two
relay nodes in each layer, the DoF can only take values 1, 4/3, 3/2 or 2, based
on the connectivity of the network, for almost all values of channel
coefficients. When there are arbitrary number of relays in each layer, the DoF
can also take the value 5/3 . Achievability schemes incorporate linear
forwarding, interference alignment and aligned interference neutralization
principles. Information theoretic converse arguments specialized for the
connectivity of the network are constructed based on the intuition from linear
dimension counting arguments.Comment: 6 pages, 7 figures, submitted to IEEE Globecom 201
Ultra-Reliable Communication in 5G Wireless Systems
Wireless 5G systems will not only be "4G, but faster". One of the novel
features discussed in relation to 5G is Ultra-Reliable Communication (URC), an
operation mode not present in today's wireless systems. URC refers to provision
of certain level of communication service almost 100 % of the time. Example URC
applications include reliable cloud connectivity, critical connections for
industrial automation and reliable wireless coordination among vehicles. This
paper puts forward a systematic view on URC in 5G wireless systems. It starts
by analyzing the fundamental mechanisms that constitute a wireless connection
and concludes that one of the key steps towards enabling URC is revision of the
methods for encoding control information (metadata) and data. It introduces the
key concept of Reliable Service Composition, where a service is designed to
adapt its requirements to the level of reliability that can be attained. The
problem of URC is analyzed across two different dimensions. The first dimension
is the type of URC problem that is defined based on the time frame used to
measure the reliability of the packet transmission. Two types of URC problems
are identified: long-term URC (URC-L) and short-term URC (URC-S). The second
dimension is represented by the type of reliability impairment that can affect
the communication reliability in a given scenario. The main objective of this
paper is to create the context for defining and solving the new engineering
problems posed by URC in 5G.Comment: To be presented at the 1st International Conference on 5G for
Ubiquitous Connectivit
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
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