59 research outputs found
Link Quality Control Mechanism for Selective and Opportunistic AF Relaying in Cooperative ARQs: A MLSD Perspective
Incorporating relaying techniques into Automatic Repeat reQuest (ARQ)
mechanisms gives a general impression of diversity and throughput enhancements.
Allowing overhearing among multiple relays is also a known approach to increase
the number of participating relays in ARQs. However, when opportunistic
amplify-and-forward (AF) relaying is applied to cooperative ARQs, the system
design becomes nontrivial and even involved. Based on outage analysis, the
spatial and temporal diversities are first found sensitive to the received
signal qualities of relays, and a link quality control mechanism is then
developed to prescreen candidate relays in order to explore the diversity of
cooperative ARQs with a selective and opportunistic AF (SOAF) relaying method.
According to the analysis, the temporal and spatial diversities can be fully
exploited if proper thresholds are set for each hop along the relaying routes.
The SOAF relaying method is further examined from a packet delivery viewpoint.
By the principle of the maximum likelihood sequence detection (MLSD),
sufficient conditions on the link quality are established for the proposed
SOAF-relaying-based ARQ scheme to attain its potential diversity order in the
packet error rates (PERs) of MLSD. The conditions depend on the minimum
codeword distance and the average signal-to-noise ratio (SNR). Furthermore,
from a heuristic viewpoint, we also develop a threshold searching algorithm for
the proposed SOAF relaying and link quality method to exploit both the
diversity and the SNR gains in PER. The effectiveness of the proposed
thresholding mechanism is verified via simulations with trellis codes.Comment: This paper has been withdrawn by the authors due to an improper proof
for Theorem 2. To avoid a misleading understanding, we thus decide to
withdraw this pape
Cooperative strategies design based on the diversity and multiplexing tradeoff
This thesis focuses on designing wireless cooperative communication strategies that are
either optimal or near-optimal in terms of the tradeoff between diversity and multiplexing
gains. Starting from classical cooperative broadcast, multiple-access and relay channels
with unit degree of freedom, to more general cooperative interference channels with
higher degrees of freedom, properties of different network topologies are studied and
their unique characteristics together with several advanced interference management
techniques are exploited to design cooperative transmission strategies in order to enhance
data rate, reliability or both at the same time. Moreover, various algorithms are
proposed to solve practical implementation issues and performance is analyzed through
both theoretical verifications and simulations
Multi-Source Cooperative Communication with Opportunistic Interference Cancelling Relays
In this paper we present a multi-user cooperative protocol for wireless
networks. Two sources transmit simultaneously their information blocks and
relays employ opportunistically successive interference cancellation (SIC) in
an effort to decode them. An adaptive decode/amplify-and-forward scheme is
applied at the relays to the decoded blocks or their sufficient statistic if
decoding fails. The main feature of the protocol is that SIC is exploited in a
network since more opportunities arise for each block to be decoded as the
number of used relays NRU is increased. This feature leads to benefits in terms
of diversity and multiplexing gains that are proven with the help of an
analytical outage model and a diversity-multiplexing tradeoff (DMT) analysis.
The performance improvements are achieved without any network synchronization
and coordination. In the final part of this work the closed-form outage
probability model is used by a novel approach for offline pre-selection of the
NRU relays, that have the best SIC performance, from a larger number of NR
nodes. The analytical results are corroborated with extensive simulations,
while the protocol is compared with orthogonal and multi-user protocols
reported in the literature.Comment: in IEEE Transactions on Communications, 201
Outage probability of an optimal cooperative MAC protocol in Nakagami-m channels
A new cooperative access protocol is presented in the context of IEEE 802.11-based fixed ad hoc networks. The protocol achieves optimal diversity-multiplexing tradeoff thanks to two known functionalities: on-demand cooperation and selection of the best relay. The on-demand approach allows maximization of the spatial multiplexing gain. The selection of the best relay allows maximization of the spatial diversity order. The main contribution of this paper consists in the design of a proactive mechanism in order to select the best relay. The mechanism is centralized at the destination terminal. Destination terminals maintain lists of relays for all possible source terminals by overhearing ongoing transmissions. So when cooperation is needed, a destination terminal just picks the best relay for a specific source terminal in the corresponding table. Hence, collision among relay candidates is now avoided. Moreover, only terminals that can improve the direct transmission are selected. This guarantees the usefulness of relaying. This study focusses on Nakagami-m wireless channel models in order to encompass a wide variety of fading models
Relay Selection for Wireless Communications Against Eavesdropping: A Security-Reliability Tradeoff Perspective
This article examines the secrecy coding aided wireless communications from a
source to a destination in the presence of an eavesdropper from a
security-reliability tradeoff (SRT) perspective. Explicitly, the security is
quantified in terms of the intercept probability experienced at the
eavesdropper, while the outage probability encountered at the destination is
used to measure the transmission reliability. We characterize the SRT of
conventional direct transmission from the source to the destination and show
that if the outage probability is increased, the intercept probability
decreases, and vice versa. We first demonstrate that the employment of relay
nodes for assisting the source-destination transmissions is capable of
defending against eavesdropping, followed by quantifying the benefits of
single-relay selection (SRS) as well as of multi-relay selection (MRS) schemes.
More specifically, in the SRS scheme, only the single "best" relay is selected
for forwarding the source signal to the destination, whereas the MRS scheme
allows multiple relays to participate in this process. It is illustrated that
both the SRS and MRS schemes achieve a better SRT than the conventional direct
transmission, especially upon increasing the number of relays. Numerical
results also show that as expected, the MRS outperforms the SRS in terms of its
SRT. Additionally, we present some open challenges and future directions for
the wireless relay aided physical-layer security.Comment: 16 pages, IEEE Network, 201
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