18 research outputs found
Mean Field Energy Games in Wireless Networks
This work tackles the problem of energy-efficient distributed power control
in wireless networks with a large number of transmitters. The problem is
modeled by a dynamic game. Each transmitter-receiver communication is
characterized by a state given by the available energy and/or the individual
channel state and whose evolution is governed by certain dynamics. Since
equilibrium analysis in such a (stochastic) game is generally difficult and
even impossible, the problem is approximated by exploiting the large system
assumption. Under an appropriate exchangeability assumption, the corresponding
mean field game is well defined and studied in detail for special cases. The
main contribution of this work is to show how mean field games can be applied
to the problem under investigation and provide illustrative numerical results.
Our results indicate that this approach can lead to significant gains in terms
of energy-efficiency at the resulting equilibrium.Comment: IEEE Proc. of Asilomar Conf. on Signals, Systems, and Computers, Nov.
2012, Pacific Grove, CA, US
Long-Term Energy Constraints and Power Control in Cognitive Radio Networks
When a long-term energy constraint is imposed to a transmitter, the average
energy-efficiency of a transmitter is, in general, not maximized by always
transmitting. In a cognitive radio context, this means that a secondary link
can re-exploit the non-used time-slots. In the case where the secondary link is
imposed to generate no interference on the primary link, a relevant issue is
therefore to know the fraction of time-slots available to the secondary
transmitter, depending on the system parameters. On the other hand, if the
secondary transmitter is modeled as a selfish and free player choosing its
power control policy to maximize its average energy-efficiency, resulting
primary and secondary signals are not necessarily orthogonal and studying the
corresponding Stackelberg game is relevant to know the outcome of this
interactive situation in terms of power control policies.Comment: DSP 2011: 17th International Conference on Digital Signal Processing,
July 2011, Corfu, Greec
Stochastic Differential Games and Energy-Efficient Power Control
One of the contributions of this work is to formulate the problem of
energy-efficient power control in multiple access channels (namely, channels
which comprise several transmitters and one receiver) as a stochastic
differential game. The players are the transmitters who adapt their power level
to the quality of their time-varying link with the receiver, their battery
level, and the strategy updates of the others. The proposed model not only
allows one to take into account long-term strategic interactions but also
long-term energy constraints. A simple sufficient condition for the existence
of a Nash equilibrium in this game is provided and shown to be verified in a
typical scenario. As the uniqueness and determination of equilibria are
difficult issues in general, especially when the number of players goes large,
we move to two special cases: the single player case which gives us some useful
insights of practical interest and allows one to make connections with the case
of large number of players. The latter case is treated with a mean-field game
approach for which reasonable sufficient conditions for convergence and
uniqueness are provided. Remarkably, this recent approach for large system
analysis shows how scalability can be dealt with in large games and only relies
on the individual state information assumption.Comment: The final publication is available at
http://www.springerlink.com/openurl.asp?genre=article\&id=doi:10.1007/s13235-012-0068-
A Stochastic Game Formulation of Energy-Efficient Power Control: Equilibrium Utilities and Practical Strategies
Frequency non-selective time-selective multiple access channels in which
transmitters can freely choose their power control policy are considered. The
individual objective of the transmitters is to maximize their averaged
energy-efficiency. For this purpose, a transmitter has to choose a power
control policy that is, a sequence of power levels adapted to the channel
variations. This problem can be formulated as a stochastic game with
discounting for which there exists a theorem characterizing all the equilibrium
utilities (equilibrium utility region). As in its general formulation, this
theorem relies on global channel state information (CSI), it is shown that some
points of the utility region can be reached with individual CSI. Interestingly,
time-sharing based solutions, which are usually considered for centralized
policies, appear to be part of the equilibrium solutions. This analysis is
illustrated by numerical results providing further insights to the problem
under investigation.Comment: DSP 2011: 17th International Conference on Digital Signal Processing,
July 2011, Corfu, Greec
Introducing Hierarchy in Energy Games
In this work we introduce hierarchy in wireless networks that can be modeled
by a decentralized multiple access channel and for which energy-efficiency is
the main performance index. In these networks users are free to choose their
power control strategy to selfishly maximize their energy-efficiency.
Specifically, we introduce hierarchy in two different ways: 1. Assuming
single-user decoding at the receiver, we investigate a Stackelberg formulation
of the game where one user is the leader whereas the other users are assumed to
be able to react to the leader's decisions; 2. Assuming neither leader nor
followers among the users, we introduce hierarchy by assuming successive
interference cancellation at the receiver. It is shown that introducing a
certain degree of hierarchy in non-cooperative power control games not only
improves the individual energy efficiency of all the users but can also be a
way of insuring the existence of a non-saturated equilibrium and reaching a
desired trade-off between the global network performance at the equilibrium and
the requested amount of signaling. In this respect, the way of measuring the
global performance of an energy-efficient network is shown to be a critical
issue.Comment: Accepted for publication in IEEE Trans. on Wireless Communication