1,611 research outputs found
Buffer-Aided Relaying with Adaptive Link Selection - Fixed and Mixed Rate Transmission
We consider a simple network consisting of a source, a half-duplex DF relay
with a buffer, and a destination. We assume that the direct source-destination
link is not available and all links undergo fading. We propose two new
buffer-aided relaying schemes. In the first scheme, neither the source nor the
relay have CSIT, and consequently, both nodes are forced to transmit with fixed
rates. In contrast, in the second scheme, the source does not have CSIT and
transmits with fixed rate but the relay has CSIT and adapts its transmission
rate accordingly. In the absence of delay constraints, for both fixed rate and
mixed rate transmission, we derive the throughput-optimal buffer-aided relaying
protocols which select either the source or the relay for transmission based on
the instantaneous SNRs of the source-relay and the relay-destination links. In
addition, for the delay constrained case, we develop buffer-aided relaying
protocols that achieve a predefined average delay. Compared to conventional
relaying protocols, which select the transmitting node according to a
predefined schedule independent of the link instantaneous SNRs, the proposed
buffer-aided protocols with adaptive link selection achieve large performance
gains. In particular, for fixed rate transmission, we show that the proposed
protocol achieves a diversity gain of two as long as an average delay of more
than three time slots can be afforded. Furthermore, for mixed rate transmission
with an average delay of time slots, a multiplexing gain of
is achieved. Hence, for mixed rate transmission, for
sufficiently large average delays, buffer-aided half-duplex relaying with and
without adaptive link selection does not suffer from a multiplexing gain loss
compared to full-duplex relaying.Comment: IEEE Transactions on Information Theory. (Published
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
Buffer-Aided Relaying with Adaptive Link Selection
In this paper, we consider a simple network consisting of a source, a
half-duplex decode-and-forward relay, and a destination. We propose a new
relaying protocol employing adaptive link selection, i.e., in any given time
slot, based on the channel state information of the source-relay and the
relay-destination link a decision is made whether the source or the relay
transmits. In order to avoid data loss at the relay, adaptive link selection
requires the relay to be equipped with a buffer such that data can be queued
until the relay-destination link is selected for transmission. We study both
delay constrained and delay unconstrained transmission. For the delay
unconstrained case, we characterize the optimal link selection policy, derive
the corresponding throughput, and develop an optimal power allocation scheme.
For the delay constrained case, we propose to starve the buffer of the relay by
choosing the decision threshold of the link selection policy smaller than the
optimal one and derive a corresponding upper bound on the average delay.
Furthermore, we propose a modified link selection protocol which avoids buffer
overflow by limiting the queue size. Our analytical and numerical results show
that buffer-aided relaying with adaptive link selection achieves significant
throughput gains compared to conventional relaying protocols with and without
buffers where the relay employs a fixed schedule for reception and
transmission.Comment: IEEE Journal on Selected Areas in Communications; Special Issue on
Theories and Methods for Advanced Wireless Relay
Adaptive Modulation and Coding and Cooperative ARQ in a Cognitive Radio System
In this paper, a joint cross-layer design of adaptive modulation and coding
(AMC) and cooperative automatic repeat request (C-ARQ) scheme is proposed for a
secondary user in a shared-spectrum environment. First, based on the
statistical descriptions of the channel, closed-form expressions of the average
spectral efficiency (SE) and the average packet loss rate (PLR) are presented.
Then, the cross-layer scheme is designed, with the aim of maximizing the
average SE while maintaining the average PLR under a prescribed level. An
optimization problem is formed, and a sub-optimal solution is found: the target
packet error rates (PER) for the secondary system channels are obtained and the
corresponding sub-optimal AMC rate adaptation policy is derived based on the
target PERs. Finally, the average SE and the average PLR performance of the
proposed scheme are presented
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