1,455 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
Power Allocation and Cooperative Diversity in Two-Way Non-Regenerative Cognitive Radio Networks
In this paper, we investigate the performance of a dual-hop block fading
cognitive radio network with underlay spectrum sharing over independent but not
necessarily identically distributed (i.n.i.d.) Nakagami- fading channels.
The primary network consists of a source and a destination. Depending on
whether the secondary network which consists of two source nodes have a single
relay for cooperation or multiple relays thereby employs opportunistic relay
selection for cooperation and whether the two source nodes suffer from the
primary users' (PU) interference, two cases are considered in this paper, which
are referred to as Scenario (a) and Scenario (b), respectively. For the
considered underlay spectrum sharing, the transmit power constraint of the
proposed system is adjusted by interference limit on the primary network and
the interference imposed by primary user (PU). The developed new analysis
obtains new analytical results for the outage capacity (OC) and average symbol
error probability (ASEP). In particular, for Scenario (a), tight lower bounds
on the OC and ASEP of the secondary network are derived in closed-form. In
addition, a closed from expression for the end-to-end OC of Scenario (a) is
achieved. With regards to Scenario (b), a tight lower bound on the OC of the
secondary network is derived in closed-form. All analytical results are
corroborated using Monte Carlo simulation method
Relay Selection for Bidirectional AF Relay Network with Outdated CSI
Most previous researches on bidirectional relay selection (RS) typically
assume perfect channel state information (CSI). However, outdated CSI, caused
by the the time-variation of channel, cannot be ignored in the practical
system, and it will deteriorate the performance. In this paper, the effect of
outdated CSI on the performance of bidirectional amplify-and-forward RS is
investigated. The optimal single RS scheme in minimizing the symbol error rate
(SER) is revised by incorporating the outdated channels. The analytical
expressions of end-to-end signal to noise ratio (SNR) and symbol error rate
(SER) are derived in a closed-form, along with the asymptotic SER expression in
high SNR. All the analytical expressions are verified by the Monte-Carlo
simulations. The analytical and the simulation results reveal that once CSI is
outdated, the diversity order degrades to one from full diversity. Furthermore,
a multiple RS scheme is proposed and verified that this scheme is a feasible
solution to compensate the diversity loss caused by outdated CSI.Comment: accepted by IEEE Transactions on Vehicular Technolog
Opportunistic Relaying in Time Division Broadcast Protocol with Incremental Relaying
In this paper, we investigate the performance of time division broadcast protocol (TDBC) with incremental relaying (IR) when there are multiple available relays. Opportunistic relaying (OR), i.e., the “best” relay is select for transmission to minimize the system’s outage probability, is proposed. Two OR schemes are presented. The first scheme, termed TDBC-OIR-I, selects the “best” relay from the set of relays that can decode both flows of signal from the two sources successfully. The second one, termed TDBC-OIR-II, selects two “best” relays from two respective sets of relays that can decode successfully each flow of signal. The performance, in terms of outage probability, expected rate (ER), and diversity-multiplexing tradeoff (DMT), of the two schemes are analyzed and compared with two TDBC schemes that have no IR but OR (termed TDBC-OR-I and TDBC-OR-II accordingly) and two other benchmark OR schemes that have no direct link transmission between the two sources
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