24 research outputs found
Impact of Mobility on MIMO Green Wireless Systems
This paper studies the impact of mobility on the power consumption of
wireless networks. With increasing mobility, we show that the network should
dedicate a non negligible fraction of the useful rate to estimate the different
degrees of freedom. In order to keep the rate constant, we quantify the
increase of power required for several cases of interest. In the case of a
point to point MIMO link, we calculate the minimum transmit power required for
a target rate and outage probability as a function of the coherence time and
the number of antennas. Interestingly, the results show that there is an
optimal number of antennas to be used for a given coherence time and power
consumption. This provides a lower bound limit on the minimum power required
for maintaining a green network.Comment: Accepted for EUSIPCO conference. 5 page
Cross-layer distributed power control: A repeated games formulation to improve the sum energy-efficiency
The main objective of this work is to improve the energy-efficiency (EE) of a
multiple access channel (MAC) system, through power control, in a distributed
manner. In contrast with many existing works on energy-efficient power control,
which ignore the possible presence of a queue at the transmitter, we consider a
new generalized cross-layer EE metric. This approach is relevant when the
transmitters have a non-zero energy cost even when the radiated power is zero
and takes into account the presence of a finite packet buffer and packet
arrival at the transmitter. As the Nash equilibrium (NE) is an
energy-inefficient solution, the present work aims at overcoming this deficit
by improving the global energy-efficiency. Indeed, as the considered system has
multiple agencies each with their own interest, the performance metric
reflecting the individual interest of each decision maker is the global
energy-efficiency defined then as the sum over individual energy-efficiencies.
Repeated games (RG) are investigated through the study of two dynamic games
(finite RG and discounted RG), whose equilibrium is defined when introducing a
new operating point (OP), Pareto-dominating the NE and relying only on
individual channel state information (CSI). Accordingly, closed-form
expressions of the minimum number of stages of the game for finite RG (FRG) and
the maximum discount factor of the discounted RG (DRG) were established. The
cross-layer model in the RG formulation leads to achieving a shorter minimum
number of stages in the FRG even for higher number of users. In addition, the
social welfare (sum of utilities) in the DRG decreases slightly with the
cross-layer model when the number of users increases while it is reduced
considerably with the Goodman model. Finally, we show that in real systems with
random packet arrivals, the cross-layer power control algorithm outperforms the
Goodman algorithm.Comment: 36 pages, single column draft forma
Cross-Layer Design for Green Power Control
In this work, we propose a new energy efficiency metric which allows one to
optimize the performance of a wireless system through a novel power control
mechanism. The proposed metric possesses two important features. First, it
considers the whole power of the terminal and not just the radiated power.
Second, it can account for the limited buffer memory of transmitters which
store arriving packets as a queue and transmit them with a success rate that is
determined by the transmit power and channel conditions. Remarkably, this
metric is shown to have attractive properties such as quasi-concavity with
respect to the transmit power and a unique maximum, allowing to derive an
optimal power control scheme. Based on analytical and numerical results, the
influence of the packet arrival rate, the size of the queue, and the
constraints in terms of quality of service are studied. Simulations show that
the proposed cross-layer approach of power control may lead to significant
gains in terms of transmit power compared to a physical layer approach of green
communications.Comment: Presented in ICC 201
Optimal control for a mobile robot with a communication objective
In this paper, we design control strategies that minimize the time required by a mobile robot to accomplish a certain task (reach a target) while transmitting/receiving a message. To better illustrate the solution we consider a simple model for the robot dynamics. The message delivery is done over a wireless network, and we account for path-loss, i.e., the transmission rate depends on the distance to the wireless antenna. In this work, we consider only one wireless antenna and disregard any shadowing phenomena. To render the problem interesting from a practical point of view we assume that the robot cannot move with innite velocity. The general problem involves a switching control signal due to the complementarity of the objectives (message transmission can require to approach the antenna situated in the opposite direction of the nal target to reach). Our minimal-time control design is based on the use of Pontryagin maximum principle. A numerical example illustrates the theoretical results
Decentralized control for guaranteed individual costs in a linear multi-agent system: A satisfaction equilibrium approach
International audienceThis work focuses on the design of decentralized feedback control gains that aims at optimizing individual costs in a multi-agent synchronization problem. As reported in the literature, the optimal control design for synchronization of agents using local information is NP-hard. Consequently, we relax the problem and use the notion of satisfaction equilibrium from game theory to ensure that each individual cost is guaranteed to be lower than a given threshold. Our main results provide conditions in the form of linear matrix inequalities (LMIs) to check if a given set of control gains are in satisfaction equilibrium i.e. all individual costs are upper-bounded by the imposed threshold. Moreover, we provide an algorithm in order to synthesize gains that are in satisfaction equilibrium. Finally, we illustrate this algorithm with numerical examples
Transmission power policies for energy-efficient wireless control of nonlinear system
We present a controller and transmission policy design procedure for
nonlinear wireless networked control systems. Our objective is to ensure the
stability of the closed-loop system, in a stochastic sense, together with given
control performance, while minimizing the average power used for
communications. The controller is designed by emulation, i.e., ignoring the
network, and the transmission power is given by threshold policies. These
policies involve waiting a given amount of time since the last successful
transmission instant, as well as requiring that the measured wireless channel
gain is above a given threshold, before attempting a new transmission. Two
power control laws are investigated: i) a constant power and ii) a power level
inversely proportional to the channel gain. We explain how to select the
waiting time, the channel threshold and the power level to minimize the induced
average communication power, while ensuring the desired control objectives
Transmit power policies for stochastic stabilisation of multi-link wireless networked control systems
Transmit power control is one of the most important issues in wireless
networks, where nodes typically operate on limited battery power. Reducing
communicating power consumption is essential for both economic and ecologic
reasons. In fact, transmitting at unnecessarily high power not only reduces
node lifetime, but also introduces excessive interference and electromagnetic
pollution. Existing work in the wireless community mostly focus on designing
transmit power policies by taking into account communication aspects like
quality of service or network capacity. Wireless networked control systems
(WNCSs), on the other hand, have different and specific needs such as
stability, which require transmit power policies adapted to the control
context. Transmit power design in the control community has recently attracted
much attention, and available works mostly consider linear systems or specific
classes of non-linear systems with a single-link view of the system. In this
paper, we propose a framework for the design of stabilising transmit power
levels that applies to much larger classes of non-linear plants, controllers,
and multi-link setting. By exploiting the fact that channel success
probabilities are related to transmit power in a non-linear fashion, we first
derive closed-loop stability conditions that relate channel probabilities with
transmission rate. Next, we combine these results together with well-known and
realistic interference models to provide a design methodology for stabilising
transmit power in non-linear and multi-link WNCSs.Comment: 18 pages, 3 figure