8,271 research outputs found
Approximate Capacity of Gaussian Relay Networks
We present an achievable rate for general Gaussian relay networks. We show
that the achievable rate is within a constant number of bits from the
information-theoretic cut-set upper bound on the capacity of these networks.
This constant depends on the topology of the network, but not the values of the
channel gains. Therefore, we uniformly characterize the capacity of Gaussian
relay networks within a constant number of bits, for all channel parameters.Comment: This paper is submited to 2008 IEEE International Symposium on
Information Theory (ISIT 2008) -In the revised format the approximation gap
(\kappa) is sharpene
Nested Lattice Codes for Gaussian Relay Networks with Interference
In this paper, a class of relay networks is considered. We assume that, at a
node, outgoing channels to its neighbors are orthogonal, while incoming signals
from neighbors can interfere with each other. We are interested in the
multicast capacity of these networks. As a subclass, we first focus on Gaussian
relay networks with interference and find an achievable rate using a lattice
coding scheme. It is shown that there is a constant gap between our achievable
rate and the information theoretic cut-set bound. This is similar to the recent
result by Avestimehr, Diggavi, and Tse, who showed such an approximate
characterization of the capacity of general Gaussian relay networks. However,
our achievability uses a structured code instead of a random one. Using the
same idea used in the Gaussian case, we also consider linear finite-field
symmetric networks with interference and characterize the capacity using a
linear coding scheme.Comment: 23 pages, 5 figures, submitted to IEEE Transactions on Information
Theor
On the Capacity Region of the Deterministic Y-Channel with Common and Private Messages
In multi user Gaussian relay networks, it is desirable to transmit private
information to each user as well as common information to all of them. However,
the capacity region of such networks with both kinds of information is not easy
to characterize. The prior art used simple linear deterministic models in order
to approximate the capacities of these Gaussian networks. This paper discusses
the capacity region of the deterministic Y-channel with private and common
messages. In this channel, each user aims at delivering two private messages to
the other two users in addition to a common message directed towards both of
them. As there is no direct link between the users, all messages must pass
through an intermediate relay. We present outer-bounds on the rate region using
genie aided and cut-set bounds. Then, we develop a greedy scheme to define an
achievable region and show that at a certain number of levels at the relay, our
achievable region coincides with the upper bound. Finally, we argue that these
bounds for this setup are not sufficient to characterize the capacity region.Comment: 4 figures, 7 page
Efficiently Finding Simple Schedules in Gaussian Half-Duplex Relay Line Networks
The problem of operating a Gaussian Half-Duplex (HD) relay network optimally
is challenging due to the exponential number of listen/transmit network states
that need to be considered. Recent results have shown that, for the class of
Gaussian HD networks with N relays, there always exists a simple schedule,
i.e., with at most N +1 active states, that is sufficient for approximate
(i.e., up to a constant gap) capacity characterization. This paper investigates
how to efficiently find such a simple schedule over line networks. Towards this
end, a polynomial-time algorithm is designed and proved to output a simple
schedule that achieves the approximate capacity. The key ingredient of the
algorithm is to leverage similarities between network states in HD and edge
coloring in a graph. It is also shown that the algorithm allows to derive a
closed-form expression for the approximate capacity of the Gaussian line
network that can be evaluated distributively and in linear time. Additionally,
it is shown using this closed-form that the problem of Half-Duplex routing is
NP-Hard.Comment: A short version of this paper was submitted to ISIT 201
Approximate Capacity of a Class of Gaussian Interference-Relay Networks
In this paper, we study a Gaussian relay-interference network, in which relay (helper) nodes are to facilitate competing information flows between different source-destination pairs. We focus on two-stage relay-interference networks where there are weak cross links, causing the networks to behave like a chain of Z Gaussian channels. Our main result is an approximate characterization of the capacity region for such ZZ and ZS networks. We propose a new interference management scheme, termed interference neutralization, which is implemented using structured lattice codes. This scheme allows for over-the-air interference removal, without the transmitters having complete access the interfering signals. This scheme in conjunction a new network decomposition technique provides the approximate characterization. Our analysis of these Gaussian networks is based on insights gained from an exact characterization of the corresponding linear deterministic model
Gaussian 1-2-1 Networks: Capacity Results for mmWave Communications
This paper proposes a new model for wireless relay networks referred to as
"1-2-1 network", where two nodes can communicate only if they point "beams" at
each other, while if they do not point beams at each other, no signal can be
exchanged or interference can be generated. This model is motivated by
millimeter wave communications where, due to the high path loss, a link between
two nodes can exist only if beamforming gain at both sides is established,
while in the absence of beamforming gain the signal is received well below the
thermal noise floor. The main result in this paper is that the 1-2-1 network
capacity can be approximated by routing information along at most paths,
where is the number of relays connecting a source and a destination through
an arbitrary topology
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