| dc.description.abstract | Wireless Internet access is almost pervasive nowadays, and many types of wireless
networks can be used to access the Internet. However, along with this growth,
there is an even greater concern about the energy consumption and efficiency of mobile
devices as well as of the supporting networks, triggering the appearance of the
concept of green communication. While some efforts have been made towards this
direction, challenges still exist and need to be tackled from diverse perspectives.
Cellular networks, WLANs, and ad hoc networks in the form of wireless mesh
networks are the most popular technologies for wireless Internet access. The availability
of such a variety of access networks has also paved the way to explore synergistic
approaches for Internet access, leading to the concept of hybrid networks
and relay communications. In addition, many mobile devices are being equipped
with multiple interfaces, enabling them to operate in hybrid networks. In contrast,
the improvements in the battery technology itself have not matched the pace of the
emerging mobile applications. The situation becomes more sophisticated when a
mobile device functions also as a relay node to forward other station’s data. In the
literature, energy efficiency of mobile devices has been addressed from various perspectives
such as protocol-level efforts, battery management efforts, etc. However,
there is little work on energy efficiency in hybrid mobile and wireless networks
and devices with heterogeneous connections. For example, when there are multiple
networks available to a mobile device, how to achieve optimum long-term energy
consumption of such a device is an open question.
Furthermore, in today’s cellular networks, micro-, pico-, and femto-cells are the
most popular network topologies in order to support high data rate services and
high user density. With the growth of such small-cell solutions, the energy consumption
of these networks is also becoming an important concern for operators.
Towards this direction, various solutions have been proposed, ranging from deployment
strategies for base stations to cooperative techniques etc. However, as base
stations have the largest share in a network’s energy consumption, methods that allow
lightly-loaded base stations sleep or be switched off are possible means as a
feasible step towards green communications.
In this dissertation, we tackle the above mentioned problems from two perspectives,
i.e., mobile station’s and operator’s perspectives. More specifically, by taking
into account the amount of transferred data in uplinks and downlinks individually
for various components in a hybrid network, strategies are proposed to reduce mobile
station’s battery energy consumption. For this purpose, other parameters such as link distance and remaining battery energy can also be considered for handover
decision making, in order to maximize energy efficiency of the mobile station. To
optimize long-term energy consumption of the mobile stations operated in such
scenarios, a Markov decision process-based methodology is proposed as our contribution
to this topic. Moreover, from operator’s perspective, a network energy
conservation scheme which may switch off a base station is proposed for micro- or
pico-cells scenarios. Both deterministic and probabilistic schemes are proposed for
network energy conservation. The problems considered and the solutions proposed
in this dissertation advance the frontiers of the research work within the theme of energy
efficiency for mobile devices as well as hybrid mobile and wireless networks. | no_NO |
