2,013 research outputs found
Spectral-energy efficiency trade-off of relay-aided cellular networks
Wireless communication networks are traditionally designed to operate at high spectral
e ciency with less emphasis on power consumption as it is assumed that endless
power supply is available through the power grid where the cells are connected to. As
new generations of mobile networks exhibit decreasing gains in spectral e ciency, the
mobile industry is forced to consider energy reform policies in order to sustain the
economic growth of itself and other industries relying on it. Consequently, the energy
e ciency of conventional direct transmission cellular networks is being examined
while alternative green network architectures are also explored. The relay-aided cellular
network is being considered as one of the potential network architecture for energy
e cient transmission. However, relaying transmission incurs multiplexing loss due to
its multi-hop protocol. This, in turn, reduces network spectral e ciency. Furthermore,
interference is also expected to increase with the deployment of Relay Stations
(RSs) in the network. This thesis examines the power consumption of the conventional
direct transmission cellular network and contributes to the development of the
relay-aided cellular network.
Firstly, the power consumption of the direct transmission cellular network is investigated.
While most work considered transmitter side strategies, the impact of the
receiver on the Base Station (BS) total power consumption is investigated here. Both
the zero-forcing and minimum mean square error weight optimisation approaches are
considered for both the conventional linear and successive interference cancellation
receivers. The power consumption model which includes both the radio frequency
transmit power and circuit power is described. The in
uence of the receiver interference
cancellation techniques, the number of transceiver antennas, circuit power
consumption and inter-cell interference on the BS total power consumption is investigated.
Secondly, the spectral-energy e ciency trade-o in the relay-aided cellular network is
investigated. The signal forwarding and interference forwarding relaying paradigms
are considered with the direct transmission cellular network taken as the baseline.
This investigation serves to understand the dynamics in the performance trade-o .
To select a suitable balance point in the trade-o , the economic e ciency metric is
proposed whereby the spectral-energy e ciency pair which maximises the economic
pro tability is found. Thus, the economic e ciency metric can be utilised as an alternative
means to optimise the relay-aided cellular network while taking into account
the inherent spectral-energy e ciency trade-o .
Finally, the method of mitigating interference in the relay-aided cellular network is
demonstrated by means of the proposed relay cooperation scheme. In the proposed
scheme, both joint RS decoding and independent RS decoding approaches are considered
during the broadcast phase while joint relay transmission is employed in the
relay phase. Two user selection schemes requiring global Channel State Information
(CSI) are considered. The partial semi-orthogonal user selection method with reduced
CSI requirement is then proposed. As the cooperative cost limits the practicality of
cooperative schemes, the cost incurred at the cooperative links between the RSs is
investigated for varying degrees of RS cooperation. The performance of the relay
cooperation scheme with di erent relay frequency reuse patterns is considered as well.
In a nutshell, the research presented in this thesis reveals the impact of the receiver on
the BS total power consumption in direct transmission cellular networks. The relayaided
cellular network is then presented as an alternative architecture for energy
e cient transmission. The economic e ciency metric is proposed to maximise the
economic pro tability of the relay network while taking into account the existing
spectral-energy e ciency trade-o . To mitigate the interference from the RSs, the
relay cooperation scheme for advanced relay-aided cellular networks is proposed
Link-State Based Decode-Forward Schemes for Two-way Relaying
In this paper, we analyze a composite decode-and-forward scheme for the
two-way relay channel with a direct link. During transmission, our scheme
combines both block Markov coding and an independent coding scheme similar to
network coding at the relay. The main contribution of this work is to examine
how link state impacts the allocation of power between these two distinct
techniques, which in turn governs the necessity of each technique in achieving
the largest transmission rate region. We analytically determine the link-state
regimes and associated relaying techniques. Our results illustrate an
interesting trend: when the user-to-relay link is marginally stronger than the
direct link, it is optimal to use only independent coding. In this case, the
relay need not use full power. However, for larger user-to-relay link gains,
the relay must supplement independent coding with block Markov coding to
achieve the largest rate region. These link-state regimes are important for the
application of two-way relaying in 5G networks, such as in D2D mode or
relay-aided transmission.Comment: To be presented at Globecom 2014, Emerging Technologies for 5G
Wireless Cellular Networks (Wi5G
Interference Alignment for Cognitive Radio Communications and Networks: A Survey
© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).Interference alignment (IA) is an innovative wireless transmission strategy that has shown to be a promising technique for achieving optimal capacity scaling of a multiuser interference channel at asymptotically high-signal-to-noise ratio (SNR). Transmitters exploit the availability of multiple signaling dimensions in order to align their mutual interference at the receivers. Most of the research has focused on developing algorithms for determining alignment solutions as well as proving interference alignment’s theoretical ability to achieve the maximum degrees of freedom in a wireless network. Cognitive radio, on the other hand, is a technique used to improve the utilization of the radio spectrum by opportunistically sensing and accessing unused licensed frequency spectrum, without causing harmful interference to the licensed users. With the increased deployment of wireless services, the possibility of detecting unused frequency spectrum becomes diminished. Thus, the concept of introducing interference alignment in cognitive radio has become a very attractive proposition. This paper provides a survey of the implementation of IA in cognitive radio under the main research paradigms, along with a summary and analysis of results under each system model.Peer reviewe
Energy Efficiency in MIMO Underlay and Overlay Device-to-Device Communications and Cognitive Radio Systems
This paper addresses the problem of resource allocation for systems in which
a primary and a secondary link share the available spectrum by an underlay or
overlay approach. After observing that such a scenario models both cognitive
radio and D2D communications, we formulate the problem as the maximization of
the secondary energy efficiency subject to a minimum rate requirement for the
primary user. This leads to challenging non-convex, fractional problems. In the
underlay scenario, we obtain the global solution by means of a suitable
reformulation. In the overlay scenario, two algorithms are proposed. The first
one yields a resource allocation fulfilling the first-order optimality
conditions of the resource allocation problem, by solving a sequence of easier
fractional problems. The second one enjoys a weaker optimality claim, but an
even lower computational complexity. Numerical results demonstrate the merits
of the proposed algorithms both in terms of energy-efficient performance and
complexity, also showing that the two proposed algorithms for the overlay
scenario perform very similarly, despite the different complexity.Comment: to appear in IEEE Transactions on Signal Processin
Energy-Aware Competitive Power Allocation for Heterogeneous Networks Under QoS Constraints
This work proposes a distributed power allocation scheme for maximizing
energy efficiency in the uplink of orthogonal frequency-division multiple
access (OFDMA)-based heterogeneous networks (HetNets). The user equipment (UEs)
in the network are modeled as rational agents that engage in a non-cooperative
game where each UE allocates its available transmit power over the set of
assigned subcarriers so as to maximize its individual utility (defined as the
user's throughput per Watt of transmit power) subject to minimum-rate
constraints. In this framework, the relevant solution concept is that of Debreu
equilibrium, a generalization of Nash equilibrium which accounts for the case
where an agent's set of possible actions depends on the actions of its
opponents. Since the problem at hand might not be feasible, Debreu equilibria
do not always exist. However, using techniques from fractional programming, we
provide a characterization of equilibrial power allocation profiles when they
do exist. In particular, Debreu equilibria are found to be the fixed points of
a water-filling best response operator whose water level is a function of
minimum rate constraints and circuit power. Moreover, we also describe a set of
sufficient conditions for the existence and uniqueness of Debreu equilibria
exploiting the contraction properties of the best response operator. This
analysis provides the necessary tools to derive a power allocation scheme that
steers the network to equilibrium in an iterative and distributed manner
without the need for any centralized processing. Numerical simulations are then
used to validate the analysis and assess the performance of the proposed
algorithm as a function of the system parameters.Comment: 37 pages, 12 figures, to appear IEEE Trans. Wireless Commu
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