590 research outputs found
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
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 Outage Probability of the Full-Duplex Interference-Limited Relay Channel
In this paper, we study the performance, in terms of the asymptotic error
probability, of a user which communicates with a destination with the aid of a
full-duplex in-band relay. We consider that the network is
interference-limited, and interfering users are distributed as a Poisson point
process. In this case, the asymptotic error probability is upper bounded by the
outage probability (OP). We investigate the outage behavior for well-known
cooperative schemes, namely, decode-and-forward (DF) and compress-and-forward
(CF) considering fading and path loss. For DF we determine the exact OP and
develop upper bounds which are tight in typical operating conditions. Also, we
find the correlation coefficient between source and relay signals which
minimizes the OP when the density of interferers is small. For CF, the
achievable rates are determined by the spatial correlation of the
interferences, and a straightforward analysis isn't possible. To handle this
issue, we show the rate with correlated noises is at most one bit worse than
with uncorrelated noises, and thus find an upper bound on the performance of
CF. These results are useful to evaluate the performance and to optimize
relaying schemes in the context of full-duplex wireless networks.Comment: 30 pages, 4 figures. Final version. To appear in IEEE JSAC Special
Issue on Full-duplex Wireless Communications and Networks, 201
Cognitive Multihop Wireless Sensor Networks over Nakagami-m Fading Channels
This work is supported by the National Science Foundation of China (NSFC) under Grant 61372114, by the National 973 Program of China under Grant 2012CB316005, by the Joint Funds of NSFC-Guangdong under Grant U1035001, and by Beijing Higher Education Young Elite Teacher Project (no. YETP0434)
A Comparative Study of Relaying Schemes with Decode-and-Forward over Nakagami-m Fading Channels
Utilizing relaying techniques to improve performance of wireless systems is a
promising avenue. However, it is crucial to understand what type of relaying
schemes should be used for achieving different performance objectives under
realistic fading conditions. In this paper, we present a general framework for
modelling and evaluating the performance of relaying schemes based on the
decode-and-forward (DF) protocol over independent and not necessarily
identically distributed (INID) Nakagami-m fading channels. In particular, we
present closed-form expressions for the statistics of the instantaneous output
signal-to-noise ratio of four significant relaying schemes with DF; two based
on repetitive transmission and the other two based on relay selection (RS).
These expressions are then used to obtain closed-form expressions for the
outage probability and the average symbol error probability for several
modulations of all considered relaying schemes over INID Nakagami-m fading.
Importantly, it is shown that when the channel state information for RS is
perfect, RS-based transmission schemes always outperform repetitive ones.
Furthermore, when the direct link between the source and the destination nodes
is sufficiently strong, relaying may not result in any gains and in this case
it should be switched-off.Comment: Submitted to Journal of Computer Systems, Networks, and
Communication
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