16,045 research outputs found
Robust Signaling for Bursty Interference
This paper studies a bursty interference channel, where the presence/absence
of interference is modeled by a block-i.i.d.\ Bernoulli process that stays
constant for a duration of symbols (referred to as coherence block) and
then changes independently to a new state. We consider both a quasi-static
setup, where the interference state remains constant during the whole
transmission of the codeword, and an ergodic setup, where a codeword spans
several coherence blocks. For the quasi-static setup, we study the largest rate
of a coding strategy that provides reliable communication at a basic rate and
allows an increased (opportunistic) rate when there is no interference. For the
ergodic setup, we study the largest achievable rate. We study how non-causal
knowledge of the interference state, referred to as channel-state information
(CSI), affects the achievable rates. We derive converse and achievability
bounds for (i) local CSI at the receiver-side only; (ii) local CSI at the
transmitter- and receiver-side, and (iii) global CSI at all nodes. Our bounds
allow us to identify when interference burstiness is beneficial and in which
scenarios global CSI outperforms local CSI. The joint treatment of the
quasi-static and ergodic setup further allows for a thorough comparison of
these two setups.Comment: 67 pages, 39 figure
Interference Channel with a Half-Duplex Out-of-Band Relay
A Gaussian interference channel (IC) aided by a half-duplex relay is
considered, in which the relay receives and transmits in an orthogonal band
with respect to the IC. The system thus consists of two parallel channels, the
IC and the channel over which the relay is active, which is referred to as
Out-of-Band Relay Channel (OBRC). The OBRC is operated by separating a multiple
access phase from the sources to the relay and a broadcast phase from the relay
to the destinations. Conditions under which the optimal operation, in terms of
the sum-capacity, entails either signal relaying and/or interference forwarding
by the relay are identified. These conditions also assess the optimality of
either separable or non-separable transmission over the IC and OBRC.
Specifically, the optimality of signal relaying and separable coding is
established for scenarios where the relay-to-destination channels set the
performance bottleneck with respect to the source-to-relay channels on the
OBRC. Optimality of interference forwarding and non-separable operation is also
established in special cases.Comment: 5 pages, 5 figures, to appear in Proceedings of IEEE ISIT 201
Capacity of wireless erasure networks
In this paper, a special class of wireless networks, called wireless erasure networks, is considered. In these networks, each node is connected to a set of nodes by possibly correlated erasure channels. The network model incorporates the broadcast nature of the wireless environment by requiring each node to send the same signal on all outgoing channels. However, we assume there is no interference in reception. Such models are therefore appropriate for wireless networks where all information transmission is packetized and where some mechanism for interference avoidance is already built in. This paper looks at multicast problems over these networks. The capacity under the assumption that erasure locations on all the links of the network are provided to the destinations is obtained. It turns out that the capacity region has a nice max-flow min-cut interpretation. The definition of cut-capacity in these networks incorporates the broadcast property of the wireless medium. It is further shown that linear coding at nodes in the network suffices to achieve the capacity region. Finally, the performance of different coding schemes in these networks when no side information is available to the destinations is analyzed
Ergodic Interference Alignment
This paper develops a new communication strategy, ergodic interference
alignment, for the K-user interference channel with time-varying fading. At any
particular time, each receiver will see a superposition of the transmitted
signals plus noise. The standard approach to such a scenario results in each
transmitter-receiver pair achieving a rate proportional to 1/K its
interference-free ergodic capacity. However, given two well-chosen time
indices, the channel coefficients from interfering users can be made to exactly
cancel. By adding up these two observations, each receiver can obtain its
desired signal without any interference. If the channel gains have independent,
uniform phases, this technique allows each user to achieve at least 1/2 its
interference-free ergodic capacity at any signal-to-noise ratio. Prior
interference alignment techniques were only able to attain this performance as
the signal-to-noise ratio tended to infinity. Extensions are given for the case
where each receiver wants a message from more than one transmitter as well as
the "X channel" case (with two receivers) where each transmitter has an
independent message for each receiver. Finally, it is shown how to generalize
this strategy beyond Gaussian channel models. For a class of finite field
interference channels, this approach yields the ergodic capacity region.Comment: 16 pages, 6 figure, To appear in IEEE Transactions on Information
Theor
On the Capacity Region of the Two-user Interference Channel with a Cognitive Relay
This paper considers a variation of the classical two-user interference
channel where the communication of two interfering source-destination pairs is
aided by an additional node that has a priori knowledge of the messages to be
transmitted, which is referred to as the it cognitive relay. For this
Interference Channel with a Cognitive Relay (ICCR) In particular, for the class
of injective semi-deterministic ICCRs, a sum-rate upper bound is derived for
the general memoryless ICCR and further tightened for the Linear Deterministic
Approximation (LDA) of the Gaussian noise channel at high SNR, which disregards
the noise and focuses on the interaction among the users' signals. The capacity
region of the symmetric LDA is completely characterized except for the regime
of moderately weak interference and weak links from the CR to the destinations.
The insights gained from the analysis of the LDA are then translated back to
the symmetric Gaussian noise channel (GICCR). For the symmetric GICCR, an
approximate characterization (to within a constant gap) of the capacity region
is provided for a parameter regime where capacity was previously unknown. The
approximately optimal scheme suggests that message cognition at a relay is
beneficial for interference management as it enables simultaneous over the air
neutralization of the interference at both destinations
Uplink CoMP under a Constrained Backhaul and Imperfect Channel Knowledge
Coordinated Multi-Point (CoMP) is known to be a key technology for next
generation mobile communications systems, as it allows to overcome the burden
of inter-cell interference. Especially in the uplink, it is likely that
interference exploitation schemes will be used in the near future, as they can
be used with legacy terminals and require no or little changes in
standardization. Major drawbacks, however, are the extent of additional
backhaul infrastructure needed, and the sensitivity to imperfect channel
knowledge. This paper jointly addresses both issues in a new framework
incorporating a multitude of proposed theoretical uplink CoMP concepts, which
are then put into perspective with practical CoMP algorithms. This
comprehensive analysis provides new insight into the potential usage of uplink
CoMP in next generation wireless communications systems.Comment: Submitted to IEEE Transactions on Wireless Communications in February
201
On Constant Gaps for the Two-way Gaussian Interference Channel
We introduce the two-way Gaussian interference channel in which there are
four nodes with four independent messages: two-messages to be transmitted over
a Gaussian interference channel in the direction, simultaneously
with two-messages to be transmitted over an interference channel (in-band,
full-duplex) in the direction. In such a two-way network, all
nodes are transmitters and receivers of messages, allowing them to adapt
current channel inputs to previously received channel outputs. We propose two
new outer bounds on the symmetric sum-rate for the two-way Gaussian
interference channel with complex channel gains: one under full adaptation (all
4 nodes are permitted to adapt inputs to previous outputs), and one under
partial adaptation (only 2 nodes are permitted to adapt, the other 2 are
restricted). We show that simple non-adaptive schemes such as the Han and
Kobayashi scheme, where inputs are functions of messages only and not past
outputs, utilized in each direction are sufficient to achieve within a constant
gap of these fully or partially adaptive outer bounds for all channel regimes.Comment: presented at 50th Annual Allerton Conference on Communication,
Control, and Computing, Monticello, IL, October 201
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