141 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
Cooperative Relaying In Power Line Environment: A Survey and Tutorial
Exchange of information is essential in any society and the demand for faster, cheaper, and secure
communications is increasing every day. With other hi-tech initiatives like IPv6 and Internet-of-Things (IOT) already
in the horizon, demand for broadband is set to escalate beyond its current level. Inherently laden in the challenges
posed by this technology are fresh opportunities in terms of penetration of data services into rural communities and
development of innovative strategies for more efficient use of the grid. Though still in its developmental phase/stage,
Power Line Communication (PLC) has grown beyond theoretical fantasy to become a reality. The proofs are the
readily available PLC systems that can be purchased off the shelfto achieve in-house networking and the much talked
about, smart metering technology; generally regarded as the “new bride” in utilities industry. One of the biggest gains
of PLC is its use of existing electrical cables, thereby eliminating cost of installation and maintenance of data cables.
However, given that the power infrastructure was traditionally built to deliver electricity, data signals do suffer various
forms of distortions and impairments as they transit it. This paper presents a tutorial on the deployed wireless system
technique which is to be adapted to PLC scenario for the purpose of managing the available source energy for
achieving reliable communication system. One of these techniques is the cooperative diversity. Its application and
deployment in power line environment is explored. The improvement achieved through cooperative diversity in some
PLC systems were presented along with the associated limitations. Finally, future areas of research which will further
improve the reliability of PLC systems and reduce its power consumption during transmission is shown
Stochastic Geometry Analysis of a Class of Cooperative Relaying Protocols
This thesis examines wireless relay networks that use hybrid-ARQ protocols. Relays networks efficiently combat fading and exploit the spatial diversity present in the channel. Hybrid-ARQ involves retransmitting the signal if it is not decoded correctly. In conventional HARQ, the retransmission comes from the source, but in cooperative HARQ the retransmission could come from a relay that has successfully decoded the message, thus attaining transmit diversity.;A Markov chain model is conceived and used to compute the effective throughput and outage probability in the presence of Rayleigh fading. The analytical results are validated with simulations. The spatial configuration of the network plays an important role in the performance of the network. The behavior of the protocols for fixed network topologies and random topologies is examined. The impact of parameters such as path loss exponent, number of relays, and Signal to Noise Ratio are determined.;Spatial averaging is helpful in capturing the spatial variations present in the system. When network topology is random, the analysis proceeds by first assuming the number of relays is fixed, in which case they are drawn from a Binomial Point Process (BPP). For each network realization, the outage probability, throughput and effective throughput are found, and the spatial average of these quantities are found by averaging over a large number of network realizations. Moreover, the maximum throughput is found for each network realization, leading to a characterization of the distribution of throughputs achievable in a random network. Finally, networks with a random number of relays are considered, including the important case that the number of relays in a given area is Poisson distributed, in which case they are drawn from a Poisson Point Process (PPP)
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
Performance analysis of spatially-distributed cooperative networks
PhD ThesisApplications of cooperative communications have attracted considerable attention
in academia and industry in the past decade for their potential to exploit network
densi cation in meeting the growing demand for data services. However, analytical
methods capable of explicitly capturing the impact of the spatial domain on system
performance are still rare. The aim of this thesis is to study cooperation between
spatially-distributed nodes with the purpose to enhance relevant analytical methods.
New approaches to performance analysis of node cooperation and several useful relations
are developed in this work in the following three areas.
First part of this thesis investigates broadcasting as an important method for
TV and network signalling distribution. Cooperative broadcasting (CB) has been
generally studied under the assumptions of asymptotically dense or large networks,
which rarely hold in practice. In this work, a method to analyse the latency of
CB in nite networks is developed using stochastic geometry. New useful relations
and inter-node distance distributions are derived, highlighting interesting network
characteristics.
Second part of this thesis studies relay selection (RS), recognised as a way to reduce
overheads arising from cooperative communications. In this thesis, a method
for analysing RS is developed based on point processes theory. Presented approach is
simpler and more intuitive compared to known methods. This has allowed obtaining
exact expressions for outage probability of relay-assisted communication. Additionally,
analysis of the sources' contention for relays has revealed that relays can be
treated as a scarce resource.
Finally, proposed methods are further extended to account for imperfect channel
state information (CSI). Practical RS in presence of CSI imperfections remains an
active research area, however the aspect of cooperating nodes' spatial distribution
remains unexplored. This thesis introduces a novel approach to account for variable
levels of CSI accuracy and for the spatial distribution cooperating relays
- …