A Survey on Energy-Efficient Communications
E. V. Belmega, S. Lasaulce
LSS (joint lab of CNRS, SUP
´
ELEC, Univ. Paris-Sud 11)
Gif-sur-Yvette Cedex, France
Email: belmega, lasaulce@lss.supelec.fr
M. Debbah
Alcatel-Lucent Chair on Flexible Radio
SUP
´
ELEC, Gif-sur-Yvette Cedex, France
Email: merouane.debbah@supelec.fr
Abstract—In this paper, we review the literature on physical
layer energy-efficient communications. The most relevant and
recent works are mainly centered around two frameworks: the
pragmatic and the information theoretical approaches. Both of
them aim at finding the best transmit and/or receive policies
which maximize the number of bits that can be reliably conveyed
over the channel per unit of energy consumed. Taking into
account both approaches, the analysis starts with the single user
SISO (single-input single-output) channel, and is then extended
to the MIMO (multiple-input multiple-output) and multi-user
scenarios.
I. INTRODUCTION
During the past decade, energy consumption has become
an increasingly important issue in wireless networks. For
instance, in the current cellular networks, the mobile terminals
are equipped with relatively large screens, required to offer
more and more functionalities and they need to operate at
higher transmission rates for a longer period of time. At the
fixed infrastructure level of these networks, the number of
base stations has increased dramatically implying important
energy costs. According to [2], these costs are expected to be
multiplied by a factor of six within the decade 2002–2012.
However, significant progress has been made in the art of
designing wireless transmitters and receivers. This includes
antennas and electronic circuits technology, signal processing
algorithms, channel coding techniques and network protocols.
The arising question is: Will technological progress be fast
enough to control and decrease the energy consumption at
the terminal and the network infrastructure sides? Answering
such a question is a difficult task and only partial answers can
be provided. For this purpose, different communication and
information theoretical tools will be used. An important tool
and one of the technological breakthroughs in communications
is the MIMO concept (i.e., systems composed of multiple
antenna terminals) [3][4][5]. It is well known that, for a point-
to-point communication, using multiple antenna terminals in
full diversity mode (i.e., all the transmmit antennas are used
to send the same information over the channel) allows one to
decrease the transmit power while ensuring a fixed quality of
transmission (e.g., the bit error rate).
In this paper, we overview the literature on energy-efficient
communications w.r.t. the number of bits that can be reliably
conveyed over the channel per unit of energy consumed.
The research on this topic has been focused on two main
approaches: a pragmatic approach based on practical modula-
tions, coding-decoding schemes, electronics and an informa-
tion theoretical approach. In Tab. I, we have summarized the
general assumptions for both approaches. The systems under
investigation consist either of single or multiple antenna ter-
minals. The multi-carrier scenario is a special case of MIMO
channel which can be solved in closed-form in the pragmatic
approach and, thus, will be considered separately. Regarding
the channel coherence time, in the pragmatic approach, the
quasi-static channel is considered assuming perfect channel
state information at the transmitters (CSIT). The transmitter
can adjust its power as a function of the channel state. In the
second scenario three types of channels are considered: a) the
static channel with perfect CSIT; b) the fast fading channel; c)
the slow fading channel. For b) and c) only the statistics of the
channel are required at the transmitter. In all scenarios, perfect
channel state information is needed at the decoder. The main
focus of this paper is the energy-efficiency power allocation
(PA) problem although different degrees of freedom are also
briefly reviewed. In most of the dedicated literature, only the
transmit power at the output of the RF circuits (or the transmit
power for reliable data) is considered. Even if this assumption
may not be realistic, it allows one to characterize the upper
bound on the maximum performance that can be achieved
in practice. However, we will also review some works that
have taken into account the consumed circuitry energy which
may have a critical impact on the system energy-efficiency.
Furthermore, only the single-user setting is investigated in the
information theoretical approach, whereas for the pragmatic
approach the multi-user scenario is also considered.
TABLE I
SYSTEM MODEL AND ASSUMPTIONS FOR THE TWO ENERGY-EFFICIENT APPROACHES
Pragmatic approach Information theoret-
ical approach
Dimensionality
SISO SISO
Multi-carrier -
MIMO MIMO
Number of users
Single-user Single-user
Multi-user -
Coherence time
Static channels,
CSIT
Quasi-static, CSIT Fast fading, CDIT
Slow fading, CDIT
Consumed power
RF signal power RF signal power
RF signal plus cir-
cuitry power
-
A. Notations
We define hereafter some general notations and acronyms
that will be used throughout the paper. Let R denote the
hal-00554951, version 1 - 11 Jan 2011
Author manuscript, published in "2010 IEEE 21st International Symposium on : Personal, Indoor and Mobile Radio Communications
Workshops (PIMRC Workshops), Turkey (2010)"