1,463 research outputs found
Cooperative Symbol-Based Signaling for Networks with Multiple Relays
Wireless channels suffer from severe inherent impairments and hence
reliable and high data rate wireless transmission is particularly challenging to
achieve. Fortunately, using multiple antennae improves performance in wireless
transmission by providing space diversity, spatial multiplexing, and power gains.
However, in wireless ad-hoc networks multiple antennae may not be acceptable
due to limitations in size, cost, and hardware complexity. As a result, cooperative
relaying strategies have attracted considerable attention because of their abilities
to take advantage of multi-antenna by using multiple single-antenna relays.
This study is to explore cooperative signaling for different relay networks,
such as multi-hop relay networks formed by multiple single-antenna relays and
multi-stage relay networks formed by multiple relaying stages with each stage
holding several single-antenna relays. The main contribution of this study is the
development of a new relaying scheme for networks using symbol-level
modulation, such as binary phase shift keying (BPSK) and quadrature phase shift
keying (QPSK). We also analyze effects of this newly developed scheme when it
is used with space-time coding in a multi-stage relay network. Simulation results
demonstrate that the new scheme outperforms previously proposed schemes:
amplify-and-forward (AF) scheme and decode-and-forward (DF) scheme
Generalized Area Spectral Efficiency: An Effective Performance Metric for Green Wireless Communications
Area spectral efficiency (ASE) was introduced as a metric to quantify the
spectral utilization efficiency of cellular systems. Unlike other performance
metrics, ASE takes into account the spatial property of cellular systems. In
this paper, we generalize the concept of ASE to study arbitrary wireless
transmissions. Specifically, we introduce the notion of affected area to
characterize the spatial property of arbitrary wireless transmissions. Based on
the definition of affected area, we define the performance metric, generalized
area spectral efficiency (GASE), to quantify the spatial spectral utilization
efficiency as well as the greenness of wireless transmissions. After
illustrating its evaluation for point-to-point transmission, we analyze the
GASE performance of several different transmission scenarios, including
dual-hop relay transmission, three-node cooperative relay transmission and
underlay cognitive radio transmission. We derive closed-form expressions for
the GASE metric of each transmission scenario under Rayleigh fading environment
whenever possible. Through mathematical analysis and numerical examples, we
show that the GASE metric provides a new perspective on the design and
optimization of wireless transmissions, especially on the transmitting power
selection. We also show that introducing relay nodes can greatly improve the
spatial utilization efficiency of wireless systems. We illustrate that the GASE
metric can help optimize the deployment of underlay cognitive radio systems.Comment: 11 pages, 8 figures, accepted by TCo
Optimal Relay Selection for Physical-Layer Security in Cooperative Wireless Networks
In this paper, we explore the physical-layer security in cooperative wireless
networks with multiple relays where both amplify-and-forward (AF) and
decode-and-forward (DF) protocols are considered. We propose the AF and DF
based optimal relay selection (i.e., AFbORS and DFbORS) schemes to improve the
wireless security against eavesdropping attack. For the purpose of comparison,
we examine the traditional AFbORS and DFbORS schemes, denoted by T-AFbORS and
TDFbORS, respectively. We also investigate a so-called multiple relay combining
(MRC) framework and present the traditional AF and DF based MRC schemes, called
T-AFbMRC and TDFbMRC, where multiple relays participate in forwarding the
source signal to destination which then combines its received signals from the
multiple relays. We derive closed-form intercept probability expressions of the
proposed AFbORS and DFbORS (i.e., P-AFbORS and P-DFbORS) as well as the
T-AFbORS, TDFbORS, T-AFbMRC and T-DFbMRC schemes in the presence of
eavesdropping attack. We further conduct an asymptotic intercept probability
analysis to evaluate the diversity order performance of relay selection schemes
and show that no matter which relaying protocol is considered (i.e., AF and
DF), the traditional and proposed optimal relay selection approaches both
achieve the diversity order M where M represents the number of relays. In
addition, numerical results show that for both AF and DF protocols, the
intercept probability performance of proposed optimal relay selection is
strictly better than that of the traditional relay selection and multiple relay
combining methods.Comment: 13 page
Intercept Probability Analysis of Cooperative Wireless Networks with Best Relay Selection in the Presence of Eavesdropping Attack
Due to the broadcast nature of wireless medium, wireless communication is
extremely vulnerable to eavesdropping attack. Physical-layer security is
emerging as a new paradigm to prevent the eavesdropper from interception by
exploiting the physical characteristics of wireless channels, which has
recently attracted a lot of research attentions. In this paper, we consider the
physical-layer security in cooperative wireless networks with multiple
decode-and-forward (DF) relays and investigate the best relay selection in the
presence of eavesdropping attack. For the comparison purpose, we also examine
the conventional direct transmission without relay and traditional max-min
relay selection. We derive closed-form intercept probability expressions of the
direct transmission, traditional max-min relay selection, and proposed best
relay selection schemes in Rayleigh fading channels. Numerical results show
that the proposed best relay selection scheme strictly outperforms the
traditional direct transmission and max-min relay selection schemes in terms of
intercept probability. In addition, as the number of relays increases, the
intercept probabilities of both traditional max-min relay selection and
proposed best relay selection schemes decrease significantly, showing the
advantage of exploiting multiple relays against eavesdropping attack.Comment: 5 pages. arXiv admin note: substantial text overlap with
arXiv:1305.081
Multi-Antenna Cooperative Wireless Systems: A Diversity-Multiplexing Tradeoff Perspective
We consider a general multiple antenna network with multiple sources,
multiple destinations and multiple relays in terms of the
diversity-multiplexing tradeoff (DMT). We examine several subcases of this most
general problem taking into account the processing capability of the relays
(half-duplex or full-duplex), and the network geometry (clustered or
non-clustered). We first study the multiple antenna relay channel with a
full-duplex relay to understand the effect of increased degrees of freedom in
the direct link. We find DMT upper bounds and investigate the achievable
performance of decode-and-forward (DF), and compress-and-forward (CF)
protocols. Our results suggest that while DF is DMT optimal when all terminals
have one antenna each, it may not maintain its good performance when the
degrees of freedom in the direct link is increased, whereas CF continues to
perform optimally. We also study the multiple antenna relay channel with a
half-duplex relay. We show that the half-duplex DMT behavior can significantly
be different from the full-duplex case. We find that CF is DMT optimal for
half-duplex relaying as well, and is the first protocol known to achieve the
half-duplex relay DMT. We next study the multiple-access relay channel (MARC)
DMT. Finally, we investigate a system with a single source-destination pair and
multiple relays, each node with a single antenna, and show that even under the
idealistic assumption of full-duplex relays and a clustered network, this
virtual multi-input multi-output (MIMO) system can never fully mimic a real
MIMO DMT. For cooperative systems with multiple sources and multiple
destinations the same limitation remains to be in effect.Comment: version 1: 58 pages, 15 figures, Submitted to IEEE Transactions on
Information Theory, version 2: Final version, to appear IEEE IT, title
changed, extra figures adde
Source-Channel Coding for the Multiple-Access Relay Channel
This work considers reliable transmission of general correlated sources over
the multiple-access relay channel (MARC) and the multiple-access broadcast
relay channel (MABRC). In MARCs only the destination is interested in a
reconstruction of the sources, while in MABRCs both the relay and the
destination want to reconstruct the sources. We assume that both the relay and
the destination have correlated side information. We find sufficient conditions
for reliable communication based on operational separation, as well as
necessary conditions on the achievable source-channel rate. For correlated
sources transmitted over fading Gaussian MARCs and MABRCs we find conditions
under which informational separation is optimal.Comment: Presented in ISWCS 2011, Aachen, German
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