135 research outputs found
Optimization Framework and Graph-Based Approach for Relay-Assisted Bidirectional OFDMA Cellular Networks
This paper considers a relay-assisted bidirectional cellular network where
the base station (BS) communicates with each mobile station (MS) using OFDMA
for both uplink and downlink. The goal is to improve the overall system
performance by exploring the full potential of the network in various
dimensions including user, subcarrier, relay, and bidirectional traffic. In
this work, we first introduce a novel three-time-slot time-division duplexing
(TDD) transmission protocol. This protocol unifies direct transmission, one-way
relaying and network-coded two-way relaying between the BS and each MS. Using
the proposed three-time-slot TDD protocol, we then propose an optimization
framework for resource allocation to achieve the following gains: cooperative
diversity (via relay selection), network coding gain (via bidirectional
transmission mode selection), and multiuser diversity (via subcarrier
assignment). We formulate the problem as a combinatorial optimization problem,
which is NP-complete. To make it more tractable, we adopt a graph-based
approach. We first establish the equivalence between the original problem and a
maximum weighted clique problem in graph theory. A metaheuristic algorithm
based on any colony optimization (ACO) is then employed to find the solution in
polynomial time. Simulation results demonstrate that the proposed protocol
together with the ACO algorithm significantly enhances the system total
throughput.Comment: 27 pages, 8 figures, 2 table
A Comprehensive Survey of Potential Game Approaches to Wireless Networks
Potential games form a class of non-cooperative games where unilateral
improvement dynamics are guaranteed to converge in many practical cases. The
potential game approach has been applied to a wide range of wireless network
problems, particularly to a variety of channel assignment problems. In this
paper, the properties of potential games are introduced, and games in wireless
networks that have been proven to be potential games are comprehensively
discussed.Comment: 44 pages, 6 figures, to appear in IEICE Transactions on
Communications, vol. E98-B, no. 9, Sept. 201
Energy Harvesting for Secure OFDMA Systems
Energy harvesting and physical-layer security in wireless networks are of
great significance. In this paper, we study the simultaneous wireless
information and power transfer (SWIPT) in downlink orthogonal
frequency-division multiple access (OFDMA) systems, where each user applies
power splitting to coordinate the energy harvesting and information decoding
processes while secrecy information requirement is guaranteed. The problem is
formulated to maximize the aggregate harvested power at the users while
satisfying secrecy rate requirements of all users by subcarrier allocation and
the optimal power splitting ratio selection. Due to the NP-hardness of the
problem, we propose an efficient iterative algorithm. The numerical results
show that the proposed method outperforms conventional methods.Comment: Accepted by WCSP 201
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
Jointly Optimal Channel and Power Assignment for Dual-Hop Multi-channel Multi-user Relaying
We consider the problem of jointly optimizing channel pairing, channel-user
assignment, and power allocation, to maximize the weighted sum-rate, in a
single-relay cooperative system with multiple channels and multiple users.
Common relaying strategies are considered, and transmission power constraints
are imposed on both individual transmitters and the aggregate over all
transmitters. The joint optimization problem naturally leads to a mixed-integer
program. Despite the general expectation that such problems are intractable, we
construct an efficient algorithm to find an optimal solution, which incurs
computational complexity that is polynomial in the number of channels and the
number of users. We further demonstrate through numerical experiments that the
jointly optimal solution can significantly improve system performance over its
suboptimal alternatives.Comment: This is the full version of a paper to appear in the IEEE Journal on
Selected Areas in Communications, Special Issue on Cooperative Networking -
Challenges and Applications (Part II), October 201
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