Wireless communications has gone through tremendous growth in the past decades.
There has been a shift in wireless network research from spectral efficiency and quality
of service (QoS) constraints to energy efficiency and green communications to reduce
power consumption. Green energy resources such as solar, wind, thermal and mechan-
ical vibrations can be employed to increase the energy efficiency of energy-constrained
networks such as wireless sensor networks. Converting the available energy in the sur-
rounding area into electricity, energy harvesting (EH), has been the subject of recent
research. EH from radio frequency (RF) signals can be utilized to prolong the lifetime
of devices in energy-constrained systems. Wireless power transmission (WPT) for EH
is a promising solution to provide a reliable source of energy for devices which are
di cult to service due to mobility and/or hard to reach locations.
The integration of relaying into conventional wireless networks is promising to
increase the coverage area and reduce power consumption. However, the extra power
consumed to relay signals may be a problem that can be mitigated by WPT. WPT
has made it possible for relays to power themselves by capturing ambient energy
wirelessly. The received signal at the relay can be utilized to both forward information
and harvest energy.
This dissertation focuses on practical energy harvesting schemes in wireless com-
munication networks. Further, the broadcast nature of wireless systems makes wire-
less transmissions more vulnerable to eavesdropping compared to wired signals. The
goal of this work is to develop EH schemes that are capable of supplying sustainable
energy to the relays and overcoming the secrecy hazards from potential eavesdroppers.
Power splitting (PS) and time switching (TS) are studied in communication networks
to prolong the lifetime of an energy-constrained relay. First, a dual hop system with
an amplify and forward (AF) relay employing wireless information and power transfer
(WIPT) via power splitting is studied. Optimal transmit antenna selection that max-
imizes the end-to-end signal to noise ratio (SNR) at the destination is considered and
the outage probability is derived. It is shown that the outage probability increases
with the number of transmit antennas but this also increases the system complexity.
Since the spectral efficiency with two-way relaying is higher than with one-way
relaying, a two-way EH-based relay network with an eavesdropper is investigated.
The secrecy capacity at the users is derived for two diversity combining cases at
the eavesdropper, selection combining (SC) and maximal ratio combining (MRC).
A friendly jammer is introduced to increase the secrecy capacity of the users by
reducing the received signal to noise ratio at the eavesdropper since the signal of the
jammer is considered as noise at the eavesdropper. The corresponding optimization
problem is reformulated using the single condensation method (SCM) and geometric
programming (GP) into a convex optimization problem. Then, GP is used to jointly
optimize the power splitting factor of the relay and transmit powers of the two users
and jammer to maximize the secrecy capacity of the system. Imperfect cancellation
of the jamming signal at the relay is assumed. It is shown that increasing the power
allocated to the jammer decreases the secrecy capacity at the users. However, when
perfect jamming signal cancellation is assumed, increasing the power allocated to
the jammer increases the secrecy capacity at the users. The secrecy capacity is also
shown to be greater with a jammer than without a jammer. Channel state information
uncertainty at the eavesdropper is also considered as an extra noise source.
TS at the relay of a two-way EH-based relay network was also considered. GP
is used to jointly optimize the time switching ratio of the relay and transmit powers
of the two users and jammer to maximize the secrecy capacity of the system. It is
shown that PS two-way relaying achieves a better secrecy capacity than TS two-way
relaying. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/13858 |
| Date | 14 April 2022 |
| Creators | Hayajneh, Maymoona |
| Contributors | Gulliver, T. Aaron |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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