558 research outputs found
Outage Performance of Two-Hop OFDM Systems with Spatially Random Decode-and-Forward Relays
In this paper, we analyze the outage performance of different multicarrier
relay selection schemes for two-hop orthogonal frequency-division multiplexing
(OFDM) systems in a Poisson field of relays. In particular, special emphasis is
placed on decode-and-forward (DF) relay systems, equipped with bulk and
per-subcarrier selection schemes, respectively. The exact expressions for
outage probability are derived in integrals for general cases. In addition,
asymptotic expressions for outage probability in the high signal-to-noise ratio
(SNR) region in the finite circle relay distribution region are determined in
closed forms for both relay selection schemes. Also, the outage probabilities
for free space in the infinite relay distribution region are derived in closed
forms. Meanwhile, a series of important properties related to cooperative
systems in random networks are investigated, including diversity, outage
probability ratio of two selection schemes and optimization of the number of
subcarriers in terms of system throughput. All analysis is numerically verified
by simulations. Finally, a framework for analyzing the outage performance of
OFDM systems with spatially random relays is constructed, which can be easily
modified to analyze other similar cases with different forwarding protocols,
location distributions and/or channel conditions
Cooperative Relaying in Wireless Networks under Spatially and Temporally Correlated Interference
We analyze the performance of an interference-limited, decode-and-forward,
cooperative relaying system that comprises a source, a destination, and
relays, placed arbitrarily on the plane and suffering from interference by a
set of interferers placed according to a spatial Poisson process. In each
transmission attempt, first the transmitter sends a packet; subsequently, a
single one of the relays that received the packet correctly, if such a relay
exists, retransmits it. We consider both selection combining and maximal ratio
combining at the destination, Rayleigh fading, and interferer mobility.
We derive expressions for the probability that a single transmission attempt
is successful, as well as for the distribution of the transmission attempts
until a packet is transmitted successfully. Results provide design guidelines
applicable to a wide range of systems. Overall, the temporal and spatial
characteristics of the interference play a significant role in shaping the
system performance. Maximal ratio combining is only helpful when relays are
close to the destination; in harsh environments, having many relays is
especially helpful, and relay placement is critical; the performance improves
when interferer mobility increases; and a tradeoff exists between energy
efficiency and throughput
Mode Selection for 5G Heterogeneous and Opportunistic Networks
5G and beyond networks will offer multiple communication modes including device-to-device
and multi-hop cellular (or UE-to-network relay) communications. Several studies have shown that these
modes can signi_cantly improve the Quality of Service (QoS), the spectrum and energy ef_ciency, and the
network capacity. Recent studies have demonstrated that further gains can be achieved when integrating
demand-driven opportunistic networking into Multi-Hop Cellular Networks (MCN). In opportunistic MCN
connections, devices can exploit the delay tolerance of many mobile data services to search for the most
ef_cient connections between nodes. The availability of multiple communication modes requires mode
selection schemes capable to decide the optimum mode for each transmission. Mode selection schemes
have been previously proposed to account for the introduction of D2D and MCN. However, existing mode
selection schemes cannot integrate opportunistic MCN connections into the selection process. This paper
advances the state of the art by proposing the _rst mode selection scheme capable to integrate opportunistic
MCN communications within 5G and beyond networks. The conducted analysis demonstrates the potential
of opportunistic MCN communications, and the capability of the proposed mode selection scheme to select
the most adequate communication mode.This work was supported in part by the Spanish Ministry of Economy, Industry, and Competitiveness, AEI, and FEDER funds under Grant
TEC2017-88612-RGrant TEC2014-57146-Rand in part by the Generalitat Valenciana under Grant GV/2016/049
Energy Harvesting Wireless Communications: A Review of Recent Advances
This article summarizes recent contributions in the broad area of energy
harvesting wireless communications. In particular, we provide the current state
of the art for wireless networks composed of energy harvesting nodes, starting
from the information-theoretic performance limits to transmission scheduling
policies and resource allocation, medium access and networking issues. The
emerging related area of energy transfer for self-sustaining energy harvesting
wireless networks is considered in detail covering both energy cooperation
aspects and simultaneous energy and information transfer. Various potential
models with energy harvesting nodes at different network scales are reviewed as
well as models for energy consumption at the nodes.Comment: To appear in the IEEE Journal of Selected Areas in Communications
(Special Issue: Wireless Communications Powered by Energy Harvesting and
Wireless Energy Transfer
Principles of Physical Layer Security in Multiuser Wireless Networks: A Survey
This paper provides a comprehensive review of the domain of physical layer
security in multiuser wireless networks. The essential premise of
physical-layer security is to enable the exchange of confidential messages over
a wireless medium in the presence of unauthorized eavesdroppers without relying
on higher-layer encryption. This can be achieved primarily in two ways: without
the need for a secret key by intelligently designing transmit coding
strategies, or by exploiting the wireless communication medium to develop
secret keys over public channels. The survey begins with an overview of the
foundations dating back to the pioneering work of Shannon and Wyner on
information-theoretic security. We then describe the evolution of secure
transmission strategies from point-to-point channels to multiple-antenna
systems, followed by generalizations to multiuser broadcast, multiple-access,
interference, and relay networks. Secret-key generation and establishment
protocols based on physical layer mechanisms are subsequently covered.
Approaches for secrecy based on channel coding design are then examined, along
with a description of inter-disciplinary approaches based on game theory and
stochastic geometry. The associated problem of physical-layer message
authentication is also introduced briefly. The survey concludes with
observations on potential research directions in this area.Comment: 23 pages, 10 figures, 303 refs. arXiv admin note: text overlap with
arXiv:1303.1609 by other authors. IEEE Communications Surveys and Tutorials,
201
Cooperative Relaying in a Poisson Field of Interferers: A Diversity Order Analysis
This work analyzes the gains of cooperative relaying in interference-limited
networks, in which outages can be due to interference and fading. A stochastic
model based on point process theory is used to capture the spatial randomness
present in contemporary wireless networks. Using a modification of the
diversity order metric, the reliability gain of selection decode-and-forward is
studied for several cases. The main results are as follows: the achievable
\emph{spatial-contention} diversity order (SC-DO) is equal to one irrespective
of the type of channel which is due to the ineffectiveness of the relay in the
MAC-phase (transmit diversity). In the BC-phase (receive diversity), the SC-DO
depends on the amount of fading and spatial interference correlation. In the
absence of fading, there is a hard transition between SC-DO of either one or
two, depending on the system parameters.Comment: 5 pages, 2 figures. To be presented at ISIT 201
MIMO Relay Networks: Scheduling and Outage Probability
We present an analytical characterization of the ergodic capacity for an amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay network over asymmetric chan- nels. In the two-hop system that we consider, the source-relay and relay-destination channels undergo Rayleigh and Rician fading, respectively. Considering arbitrary-rank means for the relay- destination channel, we first investigate the marginal distribution of an unordered eigenvalue of the cascaded AF channel, and we provide an analytical expression for the ergodic capacity of the system. The closed-form expressions that we derive are computationally efficient and validated by numerical simulation. Our results also show the impact of the signal-to-noise ratio and of the Rician factor on this asymmetric relay network
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