90 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
Adaptive OFDM Index Modulation for Two-Hop Relay-Assisted Networks
In this paper, we propose an adaptive orthogonal frequency-division
multiplexing (OFDM) index modulation (IM) scheme for two-hop relay networks. In
contrast to the traditional OFDM IM scheme with a deterministic and fixed
mapping scheme, in this proposed adaptive OFDM IM scheme, the mapping schemes
between a bit stream and indices of active subcarriers for the first and second
hops are adaptively selected by a certain criterion. As a result, the active
subcarriers for the same bit stream in the first and second hops can be varied
in order to combat slow frequency-selective fading. In this way, the system
reliability can be enhanced. Additionally, considering the fact that a relay
device is normally a simple node, which may not always be able to perform
mapping scheme selection due to limited processing capability, we also propose
an alternative adaptive methodology in which the mapping scheme selection is
only performed at the source and the relay will simply utilize the selected
mapping scheme without changing it. The analyses of average outage probability,
network capacity and symbol error rate (SER) are given in closed form for
decode-and-forward (DF) relaying networks and are substantiated by numerical
results generated by Monte Carlo simulations.Comment: 30 page
Outage Performance Analysis of Multicarrier Relay Selection for Cooperative Networks
In this paper, we analyze the outage performance of two multicarrier relay
selection schemes, i.e. bulk and per-subcarrier selections, for two-hop
orthogonal frequency-division multiplexing (OFDM) systems. To provide a
comprehensive analysis, three forwarding protocols: decode-and-forward (DF),
fixed-gain (FG) amplify-and-forward (AF) and variable-gain (VG) AF relay
systems are considered. We obtain closed-form approximations for the outage
probability and closed-form expressions for the asymptotic outage probability
in the high signal-to-noise ratio (SNR) region for all cases. Our analysis is
verified by Monte Carlo simulations, and provides an analytical framework for
multicarrier systems with relay selection
Green Holographic MIMO Communications With A Few Transmit Radio Frequency Chains
Holographic multiple-input multiple-output (MIMO) communications are widely
recognized as a promising candidate for the next-generation air interface. With
holographic MIMO surface, the number of the spatial degrees-of-freedom (DoFs)
considerably increases and also significantly varies as the user moves. To
fully employ the large and varying number of spatial DoFs, the number of
equipped RF chains has to be larger than or equal to the largest number of
spatial DoFs. However, this causes much waste as radio frequency (RF) chains
(especially the transmit RF chains) are costly and power-hungry. To avoid the
heavy burden, this paper investigates green holographic MIMO communications
with a few transmit RF chains under an electromagnetic-based communication
model. We not only look at the fundamental capacity limits but also propose an
effective transmission, namely non-uniform holographic pattern modulation
(NUHPM), to achieve the capacity limit in the high signal-to-noise (SNR)
regime. The analytical result sheds light on the green evaluation of MIMO
communications, which can be realized by increasing the size of the antenna
aperture without increasing the number of transmit RF chains. Numerical results
are provided to verify our analysis and to show the great performance gain by
employing the additional spatial DoFs as modulation resources.Comment: 10 figures; has been accepted by TGC
Paving the Way for Distributed Artificial Intelligence over the Air
Distributed Artificial Intelligence (DAI) is regarded as one of the most
promising techniques to provide intelligent services under strict privacy
protection regulations for multiple clients. By applying DAI, training on raw
data is carried out locally, while the trained outputs, e.g., model parameters,
from multiple local clients, are sent back to a central server for aggregation.
Recently, for achieving better practicality, DAI is studied in conjunction with
wireless communication networks, incorporating various random effects brought
by wireless channels. However, because of the complex and case-dependent nature
of wireless channels, a generic simulator for applying DAI in wireless
communication networks is still lacking. To accelerate the development of DAI
applied in wireless communication networks, we propose a generic system design
in this paper as well as an associated simulator that can be set according to
wireless channels and system-level configurations. Details of the system design
and analysis of the impacts of wireless environments are provided to facilitate
further implementations and updates. We employ a series of experiments to
verify the effectiveness and efficiency of the proposed system design and
reveal its superior scalability
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