89 research outputs found
Fundamental Limits of Energy-Efficient Resource Sharing, Power Control and Discontinuous Transmission
The achievable gains via power-optimal scheduling are investigated. Under the
QoS constraint of a guaranteed link rate, the overall power consumed by a
cellular BS is minimized. Available alternatives for the minimization of
transmit power consumption are presented. The transmit power is derived for the
two-user downlink situation. The analysis is extended to incorporate a BS power
model (which maps transmit power to supply power consumption) and the use of
DTX in a BS. Overall potential gains are evaluated by comparison of a
conventional SOTA BS with one that employs DTX exclusively, a power control
scheme and an optimal combined DTX and power control scheme. Fundamental limits
of the achievable savings are found to be at 5.5 dB under low load and 2 dB
under high load when comparing the SOTA consumption with optimal allocation
under the chosen power model.Comment: 12 pages, ISBN 978-1-4577-0928-9. In Future Network & Mobile Summit
(FutureNetw), 201
Enhancing the energy efficiency of radio base stations
This thesis is concerned with the energy efficiency of cellular networks. It
studies the dominant power consumer in future cellular networks, the Long Term
Evolution (LTE) radio Base Station (BS), and proposes mechanisms that enhance
the BS energy efficiency by reducing its power consumption under target rate
constraints. These mechanisms trade spare capacity for power saving.
First, the thesis describes how much power individual components of a BS
consume and what parameters affect this consumption based on third party
experimental data. These individual models are joined into a component power
model for an entire BS. The component model is an essential step in analysis but is
too complex for many applications. It is therefore abstracted into a much simpler
parameterized model to reduce its complexity. The parameterized model is further
simplified into an affine model which can be applied in power minimization.
Second, Power Control (PC) and Discontinuous Transmission (DTX) are identified as promising power-saving Radio Resource Management (RRM) mechanisms
and applied to multi-user downlink transmission. PC reduces the power consumption
of the Power Amplifier (PA) and is found to be most effective at high
traffic loads. DTX mostly reduces the power consumption of the Baseband (BB)
unit while interrupting transmission and is better applied in low traffic loads.
Joint optimization of these two techniques is found to enable additional power-saving
at medium traffic loads and to be a convex problem which can be solved
efficiently. The convex problem is extended to provide a comprehensive power-saving
Orthogonal Frequency Division Multiple Access (OFDMA) frame resource
scheduler. The proposed scheduler is shown to reduce power consumption by
25-40% in computer simulations, depending on the traffic load.
Finally, the thesis investigates the influence of interference on power consumption
in a network of multiple power-saving BSs. It discusses three popular alternative
distributed uncoordinated methods which align DTX mode between neighbouring
BSs. To address drawbacks of these three, a fourth memory-based DTX alignment
method is proposed. It decreases power consumption by up to 40% and
retransmission probability by around 20%, depending on the traffic load
Minimizing Base Station Power Consumption
We propose a new radio resource management algorithm which aims at minimizing
the base station supply power consumption for multi-user MIMO-OFDM. Given a
base station power model that establishes a relation between the RF transmit
power and the supply power consumption, the algorithm optimizes the trade-off
between three basic power-saving mechanisms: antenna adaptation, power control
and discontinuous transmission. The algorithm comprises two steps: a) the first
step estimates sleep mode duration, resource shares and antenna configuration
based on average channel conditions and b) the second step exploits
instantaneous channel knowledge at the transmitter for frequency selective
time-variant channels. The proposed algorithm finds the number of transmit
antennas, the RF transmission power per resource unit and spatial channel, the
number of discontinuous transmission time slots, and the multi-user resource
allocation, such that supply power consumption is minimized. Simulation results
indicate that the proposed algorithm is capable of reducing the supply power
consumption by between 25% and 40%, dependend on the system load.Comment: 27 page
Energy-Efficient Resource Allocation Optimization for Multimedia Heterogeneous Cloud Radio Access Networks
The heterogeneous cloud radio access network (H-CRAN) is a promising paradigm
which incorporates the cloud computing into heterogeneous networks (HetNets),
thereby taking full advantage of cloud radio access networks (C-RANs) and
HetNets. Characterizing the cooperative beamforming with fronthaul capacity and
queue stability constraints is critical for multimedia applications to
improving energy efficiency (EE) in H-CRANs. An energy-efficient optimization
objective function with individual fronthaul capacity and inter-tier
interference constraints is presented in this paper for queue-aware multimedia
H-CRANs. To solve this non-convex objective function, a stochastic optimization
problem is reformulated by introducing the general Lyapunov optimization
framework. Under the Lyapunov framework, this optimization problem is
equivalent to an optimal network-wide cooperative beamformer design algorithm
with instantaneous power, average power and inter-tier interference
constraints, which can be regarded as the weighted sum EE maximization problem
and solved by a generalized weighted minimum mean square error approach. The
mathematical analysis and simulation results demonstrate that a tradeoff
between EE and queuing delay can be achieved, and this tradeoff strictly
depends on the fronthaul constraint
Optimal Cell Clustering and Activation for Energy Saving in Load-Coupled Wireless Networks
Optimizing activation and deactivation of base station transmissions provides
an instrument for improving energy efficiency in cellular networks. In this
paper, we study optimal cell clustering and scheduling of activation duration
for each cluster, with the objective of minimizing the sum energy, subject to a
time constraint of delivering the users' traffic demand. The cells within a
cluster are simultaneously in transmission and napping modes, with cluster
activation and deactivation, respectively. Our optimization framework accounts
for the coupling relation among cells due to the mutual interference. Thus, the
users' achievable rates in a cell depend on the cluster composition. On the
theoretical side, we provide mathematical formulation and structural
characterization for the energy-efficient cell clustering and scheduling
optimization problem, and prove its NP hardness. On the algorithmic side, we
first show how column generation facilitates problem solving, and then present
our notion of local enumeration as a flexible and effective means for dealing
with the trade-off between optimality and the combinatorial nature of cluster
formation, as well as for the purpose of gauging the deviation from optimality.
Numerical results demonstrate that our solutions achieve more than 60% energy
saving over existing schemes, and that the solutions we obtain are within a few
percent of deviation from global optimum.Comment: Revision, IEEE Transactions on Wireless Communication
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