95 research outputs found
Power Allocation for Conventional and Buffer-Aided Link Adaptive Relaying Systems with Energy Harvesting Nodes
Energy harvesting (EH) nodes can play an important role in cooperative
communication systems which do not have a continuous power supply. In this
paper, we consider the optimization of conventional and buffer-aided link
adaptive EH relaying systems, where an EH source communicates with the
destination via an EH decode-and-forward relay. In conventional relaying,
source and relay transmit signals in consecutive time slots whereas in
buffer-aided link adaptive relaying, the state of the source-relay and
relay-destination channels determines whether the source or the relay is
selected for transmission. Our objective is to maximize the system throughput
over a finite number of transmission time slots for both relaying protocols. In
case of conventional relaying, we propose an offline and several online joint
source and relay transmit power allocation schemes. For offline power
allocation, we formulate an optimization problem which can be solved optimally.
For the online case, we propose a dynamic programming (DP) approach to compute
the optimal online transmit power. To alleviate the complexity inherent to DP,
we also propose several suboptimal online power allocation schemes. For
buffer-aided link adaptive relaying, we show that the joint offline
optimization of the source and relay transmit powers along with the link
selection results in a mixed integer non-linear program which we solve
optimally using the spatial branch-and-bound method. We also propose an
efficient online power allocation scheme and a naive online power allocation
scheme for buffer-aided link adaptive relaying. Our results show that link
adaptive relaying provides performance improvement over conventional relaying
at the expense of a higher computational complexity.Comment: Submitted to IEEE Transactions on Wireless Communication
Study on Generalized Buffer-State-Based Relay Selection in Cooperative Cognitive Radio Networks
学位の種別: 修士University of Tokyo(東京大学
Effective Capacity Analysis of H-ARQ Assisted Cooperative Communication Systems
In this paper, the effective capacity of cooperative communication (CC)
systems with hybrid Automatic repeat request (HARQ) is derived. The derived
expressions are valid for any channel distribution and with any arbitrary
number of retransmissions by the source and relay for both HARQ-repetition
redundancy (RR) and HARQ-incremental redundancy (IR) over asymmetric channels.
As an example, we use the derived EC expression over Rayleigh fading channels.
Several results are obtained for a low rate and signal-to-noise ratio (SNR). We
can see that the EC attends its maximum value with a small number of
retransmissions. As expected when the relay-destination channel has low SNR, it
is better than the relay does not participate especially when we assign a large
number of transitions at the relay. For high data rates and strict quality of
service (QoS) constraints, it is better to increase the number of relay
transmissions. Finally, when we increase the number of source retransmissions,
the effective capacity improves even for low values.Comment: 30 pages, 6 figure
Buffer-aided relay selection with reduced packet delay in cooperative networks
Applying data buffers at relay nodes significantly improves the outage performance in relay networks, but the performance gain is often at the price of long packet delays. In this paper, a novel relay selection scheme with significantly reduced packet delay is proposed. The outage probability and average packet delay of the proposed scheme under different channel scenarios are analyzed. Simulation results are also given to verify the analysis. The analytical and simulation results show that, compared with non-buffer-aided relay selection schemes, the proposed scheme has not only significant gain in outage performance but also similar average packet delay when the channel signal-to-noise ratio (SNR) is high enough, making it an attractive scheme in practice
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
Truncated-ARQ aided adaptive network coding for cooperative two-way relaying networks: cross-layer design and analysis
Network Coding (NC) constitutes a promising technique of improving the throughput of relay-aided networks. In this context, we propose a cross-layer design for both amplifyand- forward (AF-) and decode-and-forward two-way relaying (DF-TWR) based on the NC technique invoked for improving the achievable throughput under specific Quality of Service (QoS) requirements, such as the maximum affordable delay and error rate.We intrinsically amalgamate adaptive Analog Network Coding (ANC) and Network Coded Modulation (NCM) with truncated Automatic Repeat reQuest (ARQ) operating at the different OSI layers. At the data-link layer, we design a pair of improved NC-based ARQ strategies based on the Stop-andwait and the Selective-repeat ARQ protocols. At the physical layer, adaptive ANC/NCM are invoked based on our approximate packet error ratio (PER). We demonstrate that the adaptive ANC design can be readily amalgamated with the proposed protocols. However, adaptive NC-QAM suffers from an SNR-loss, when the transmit rates of the pair of downlink (DL) channels spanning from the relay to the pair of destinations are different. Therefore we develop a novel transmission strategy for jointly selecting the optimal constellation sizes for both of the relay-to-destination links that have to be adapted to both pair of channel conditions. Finally, we analyze the attainable throughput, demonstrating that our truncated ARQ-aided adaptive ANC/NCM schemes attain considerable throughput gains over the schemes dispensing with ARQ, whilst our proposed scheme is capable of supporting bidirectional NC scenarios
Max-gain relay selection scheme for wireless networks
© 2020 Karabuk University Next generation wireless systems are supposed to handle high amount of data with broader coverage and high quality of service (QoS). When a signal travels from a source to destination, the signal quality may suffer from the fading, which makes it difficult to receive correct messages. To handle the impact of fading, various diversity techniques are performed with Multiple Input Multiple Output (MIMO). Considering cooperative wireless networks, virtual MIMOs are being used, which also called cooperative diversity. In this paper, we propose a max-gain relay selection scheme (MGRS) for buffer-aided wireless cooperative networks. This scheme determines the best link using the maximum gain based on quality of link and available buffer size. The time slot is divided into two parts, one is used to choose the best link from the source to relay transmission (odd slot) and another time slot (even) is used based on the selection of the best link from the relay to destination. Markov chain model is use to measure buffer status and QoS parameters to evaluate the performance. The proposed scheme provides better QoS (12%) compared to the existing relay selection schemes with respect to throughput, end-to-end delay and outage probability
Cooperative Diversity with Mobile Nodes: Capacity Outage Rate and Duration
The outage probability is an important performance measure for cooperative
diversity schemes. However, in mobile environments, the outage probability does
not completely describe the behavior of cooperative diversity schemes since the
mobility of the involved nodes introduces variations in the channel gains. As a
result, the capacity outage events are correlated in time and second-order
statistical parameters of the achievable information-theoretic capacity such as
the average capacity outage rate (AOR) and the average capacity outage duration
(AOD) are required to obtain a more complete description of the properties of
cooperative diversity protocols. In this paper, assuming slow Rayleigh fading,
we derive exact expressions for the AOR and the AOD of three well-known
cooperative diversity protocols: variable-gain amplify-and-forward,
decode-and-forward, and selection decode-and-forward relaying. Furthermore, we
develop asymptotically tight high signal-to-noise ratio (SNR) approximations,
which offer important insights into the influence of various system and channel
parameters on the AOR and AOD. In particular, we show that on a
double-logarithmic scale, similar to the outage probability, the AOR
asymptotically decays with the SNR with a slope that depends on the diversity
gain of the cooperative protocol, whereas the AOD asymptotically decays with a
slope of -1/2 independent of the diversity gain.Comment: IEEE Transactions on Information Theory (2011
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