3,362 research outputs found
Weighted Sum Rate Maximization for Downlink OFDMA with Subcarrier-pair based Opportunistic DF Relaying
This paper addresses a weighted sum rate (WSR) maximization problem for
downlink OFDMA aided by a decode-and-forward (DF) relay under a total power
constraint. A novel subcarrier-pair based opportunistic DF relaying protocol is
proposed. Specifically, user message bits are transmitted in two time slots. A
subcarrier in the first slot can be paired with a subcarrier in the second slot
for the DF relay-aided transmission to a user. In particular, the source and
the relay can transmit simultaneously to implement beamforming at the
subcarrier in the second slot. Each unpaired subcarrier in either the first or
second slot is used for the source's direct transmission to a user. A benchmark
protocol, same as the proposed one except that the transmit beamforming is not
used for the relay-aided transmission, is also considered. For each protocol, a
polynomial-complexity algorithm is developed to find at least an approximately
optimum resource allocation (RA), by using continuous relaxation, the dual
method, and Hungarian algorithm. Instrumental to the algorithm design is an
elegant definition of optimization variables, motivated by the idea of
regarding the unpaired subcarriers as virtual subcarrier pairs in the direct
transmission mode. The effectiveness of the RA algorithm and the impact of
relay position and total power on the protocols' performance are illustrated by
numerical experiments. The proposed protocol always leads to a maximum WSR
equal to or greater than that for the benchmark one, and the performance gain
of using the proposed one is significant especially when the relay is in close
proximity to the source and the total power is low. Theoretical analysis is
presented to interpret these observations.Comment: 8 figures, accepted and to be published in IEEE Transactions on
Signal Processing. arXiv admin note: text overlap with arXiv:1301.293
Novel Subcarrier-pair based Opportunistic DF Protocol for Cooperative Downlink OFDMA
A novel subcarrier-pair based opportunistic DF protocol is proposed for
cooperative downlink OFDMA transmission aided by a decode-and-forward (DF)
relay. Specifically, user message bits are transmitted in two consecutive
equal-duration time slots. A subcarrier in the first slot can be paired with a
subcarrier in the second slot for the DF relay-aided transmission to a user. In
particular, the source and the relay can transmit simultaneously to implement
beamforming at the subcarrier in the second slot for the relay-aided
transmission. Each unpaired subcarrier in either the first or second slot is
used by the source for direct transmission to a user without the relay's
assistance. The sum rate maximized resource allocation (RA) problem is
addressed for this protocol under a total power constraint. It is shown that
the novel protocol leads to a maximum sum rate greater than or equal to that
for a benchmark one, which does not allow the source to implement beamforming
at the subcarrier in the second slot for the relay-aided transmission. Then, a
polynomial-complexity RA algorithm is developed to find an (at least
approximately) optimum resource allocation (i.e., source/relay power,
subcarrier pairing and assignment to users) for either the proposed or
benchmark protocol. Numerical experiments illustrate that the novel protocol
can lead to a much greater sum rate than the benchmark one.Comment: 6 pages, accepted by 2013 IEEE Wireless Communications and Networking
Conferenc
Optimal Power Allocation for Two-Way Decode-and-Forward OFDM Relay Networks
This paper presents a novel two-way decode-and-forward (DF) relay strategy
for Orthogonal Frequency Division Multiplexing (OFDM) relay networks. This DF
relay strategy employs multi-subcarrier joint channel coding to leverage
frequency selective fading, and thus can achieve a higher data rate than the
conventional per-subcarrier DF relay strategies. We further propose a
low-complexity, optimal power allocation strategy to maximize the data rate of
the proposed relay strategy. Simulation results suggest that our strategy
obtains a substantial gain over the per-subcarrier DF relay strategies, and
also outperforms the amplify-and-forward (AF) relay strategy in a wide
signal-to-noise-ratio (SNR) region.Comment: 5 pages, 2 figures, accepted by IEEE ICC 201
MIMO-OFDM Based Energy Harvesting Cooperative Communications Using Coalitional Game Algorithm
This document is the Accepted Manuscript version. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this paper, we consider the problem of cooperative communication between relays and base station in an advanced MIMO-OFDM framework, under the assumption that the relays are supplied by electric power drawn from energy harvesting (EH) sources. In particular, we focus on the relay selection, with the goal to guarantee the required performance in terms of capacity. In order to maximize the data throughput under the EH constraint, we model the transmission scheme as a non-transferable coalition formation game, with characteristic function based on an approximated capacity expression. Then, we introduce a powerful mathematical tool inherent to coalitional game theory, namely: the Shapley value (Sv) to provide a reliable solution concept to the game. The selected relays will form a virtual dynamically-configuredMIMO network that is able to transmit data to destination using efficient space-time coding techniques. Numerical results, obtained by simulating the EH-powered cooperativeMIMO-OFDMtransmission with Algebraic Space-Time Coding (ASTC), prove that the proposed coalitional game-based relay selection allows to achieve performance very close to that obtained by the same system operated by guaranteed power supply. The proposed methodology is finally compared with some recent related state-of-the-art techniques showing clear advantages in terms of link performance and goodput.Peer reviewe
- …