33 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
Outage Capacity of Incremental Relaying at Low Signal-to-Noise Ratios
We present the \epsilon-outage capacity of incremental relaying at low
signal-to-noise ratios (SNR) in a wireless cooperative network with slow
Rayleigh fading channels. The relay performs decode-and-forward and repetition
coding is employed in the network, which is optimal in the low SNR regime. We
derive an expression on the optimal relay location that maximizes the
\epsilon-outage capacity. It is shown that this location is independent of the
outage probability and SNR but only depends on the channel conditions
represented by a path-loss factor. We compare our results to the
\epsilon-outage capacity of the cut-set bound and demonstrate that the ratio
between the \epsilon-outage capacity of incremental relaying and the cut-set
bound lies within 1/\sqrt{2} and 1. Furthermore, we derive lower bounds on the
\epsilon-outage capacity for the case of K relays.Comment: 5 pages, 4 figures, to be presented at VTC Fall 2009 in Anchorage,
Alask
Outage Capacity of Bursty Amplify-and-Forward with Incremental Relaying
We derive the outage capacity of a bursty version of the amplify-and-forward
(BAF) protocol for small signal-to-noise ratios when incremental relaying is
used. We show that the ratio between the outage capacities of BAF and the
cut-set bound is independent of the relay position and that BAF is outage
optimal for certain conditions on the target rate R. This is in contrast to
decode-and-forward with incremental relaying, where the relay location strongly
determines the performance of the cooperative protocol. We further derive the
outage capacity for a network consisting of an arbitrary number of relay nodes.
In this case the relays transmit in subsequent partitions of the overall
transmission block and the destination accumulates signal-to-noise ratio until
it is able to decode.Comment: 5 pages, 3 figures, submitted to IEEE International Symposium on
Information Theory, Austin, TX, June 13-18, 201
On the Non-Coherent Wideband Multipath Fading Relay Channel
We investigate the multipath fading relay channel in the limit of a large
bandwidth, and in the non-coherent setting, where the channel state is unknown
to all terminals, including the relay and the destination. We propose a
hypergraph model of the wideband multipath fading relay channel, and show that
its min-cut is achieved by a non-coherent peaky frequency binning scheme. The
so-obtained lower bound on the capacity of the wideband multipath fading relay
channel turns out to coincide with the block-Markov lower bound on the capacity
of the wideband frequency-division Gaussian (FD-AWGN) relay channel. In certain
cases, this achievable rate also meets the cut-set upper-bound, and thus
reaches the capacity of the non-coherent wideband multipath fading relay
channel.Comment: 8 pages, 4 figures, longer version (including proof) of the paper in
Proc. of IEEE ISIT 201
Comparing the Outage Capacity of Transmit Diversity and Incremental Relaying
We present the e-outage capacity of incremental relaying at low signal-to-noise ratios (SNR) in a wireless cooperative network with slow Rayleigh fading channels. The relay performs decode-and-forward and repetition coding is employed in the network, which is optimal in the low SNR regime. We derive an expression on the optimal relay location that maximizes the e-outage capacity. It is shown that this location is independent of the outage probability and SNR but only depends on the channel conditions represented by a path-loss factor. We compare our results to the e-outage capacity of the cut-set bound and demonstrate that the ratio between the e-outage capacity of incremental relaying and the cut-set bound lies within 1/wurzel2 and 1. Furthermore, we derive lower bounds on the e-outage capacity for the case of K relays