808 research outputs found
Asymptotic Capacity of Large Fading Relay Networks with Random Node Failures
To understand the network response to large-scale physical attacks, we
investigate the asymptotic capacity of a half-duplex fading relay network with
random node failures when the number of relays is infinitely large. In this
paper, a simplified independent attack model is assumed where each relay node
fails with a certain probability. The noncoherent relaying scheme is
considered, which corresponds to the case of zero forward-link channel state
information (CSI) at the relays. Accordingly, the whole relay network can be
shown equivalent to a Rayleigh fading channel, where we derive the
-outage capacity upper bound according to the multiple access (MAC)
cut-set, and the -outage achievable rates for both the
amplify-and-forward (AF) and decode-and-forward (DF) strategies. Furthermore,
we show that the DF strategy is asymptotically optimal as the outage
probability goes to zero, with the AF strategy strictly suboptimal
over all signal to noise ratio (SNR) regimes. Regarding the rate loss due to
random attacks, the AF strategy suffers a less portion of rate loss than the DF
strategy in the high SNR regime, while the DF strategy demonstrates more robust
performance in the low SNR regime.Comment: 24 pages, 5 figures, submitted to IEEE Transactions on Communication
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
Divide-and-conquer: Approaching the capacity of the two-pair bidirectional Gaussian relay network
The capacity region of multi-pair bidirectional relay networks, in which a
relay node facilitates the communication between multiple pairs of users, is
studied. This problem is first examined in the context of the linear shift
deterministic channel model. The capacity region of this network when the relay
is operating at either full-duplex mode or half-duplex mode for arbitrary
number of pairs is characterized. It is shown that the cut-set upper-bound is
tight and the capacity region is achieved by a so called divide-and-conquer
relaying strategy. The insights gained from the deterministic network are then
used for the Gaussian bidirectional relay network. The strategy in the
deterministic channel translates to a specific superposition of lattice codes
and random Gaussian codes at the source nodes and successive interference
cancelation at the receiving nodes for the Gaussian network. The achievable
rate of this scheme with two pairs is analyzed and it is shown that for all
channel gains it achieves to within 3 bits/sec/Hz per user of the cut-set
upper-bound. Hence, the capacity region of the two-pair bidirectional Gaussian
relay network to within 3 bits/sec/Hz per user is characterized.Comment: IEEE Trans. on Information Theory, accepte
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