| dc.description.abstract | Spectrum scarcity is one of the most important challenges in wireless communications
networks due to the sky-rocketing growth of multimedia applications. As the latest
member of the multiple access family, non-orthogonal multiple access (NOMA) has
been recently proposed for 3GPP Long Term Evolution (LTE) and envisioned to be
a key component of the 5th generation (5G) mobile networks for its potential ability on
spectrum enhancement. The feature of NOMA is to serve multiple users at the same
time/frequency/code, but with di erent power levels, which yields a signi cant spectral
e ciency gain over conventional orthogonal multiple access (OMA). This thesis provides
a systematic treatment of this newly emerging technology, from the basic principles of
NOMA, to its combination with simultaneously information and wireless power transfer
(SWIPT) technology, to apply in cognitive radio (CR) networks and Heterogeneous
networks (HetNets), as well as enhancing the physical layer security and addressing the
fairness issue.
First, this thesis examines the application of SWIPT to NOMA networks with spatially
randomly located users. A new cooperative SWIPT NOMA protocol is proposed, in
which near NOMA users that are close to the source act as energy harvesting relays in
the aid of far NOMA users. Three user selection schemes are proposed to investigate
the e ect of locations on the performance. Besides the closed-form expressions in terms
of outage probability and throughput, the diversity gain of the considered networks is
determined.
Second, when considering NOMA in CR networks, stochastic geometry tools are used to
evaluate the outage performance of the considered network. New closed-form expressions
are derived for the outage probability. Diversity order of NOMA users has been analyzed
based on the derived outage probability, which reveals important design insights regarding the interplay between two power constraints scenarios.
Third, a new promising transmission framework is proposed, in which massive multipleinput
multiple-output (MIMO) is employed in macro cells and NOMA is adopted in
small cells. For maximizing the biased average received power at mobile users, a massive
MIMO and NOMA based user association scheme is developed. Analytical expressions
for the spectrum e ciency of each tier are derived using stochastic geometry. It is
con rmed that NOMA is capable of enhancing the spectrum e ciency of the network
compared to the OMA based HetNets.
Fourth, this thesis investigates the physical layer security of NOMA in large-scale networks
with invoking stochastic geometry. Both single-antenna and multiple-antenna
aided transmission scenarios are considered, where the base station (BS) communicates
with randomly distributed NOMA users. In addition to the derived exact analytical
expressions for each scenario, some important insights such as secrecy diversity order
and large antenna array property are obtained by carrying the asymptotic analysis.
Fifth and last, the fundamental issues of fairness surrounding the joint power allocation
and dynamic user clustering are addressed in MIMO-NOMA systems in this thesis. A
two-step optimization approach is proposed to solve the formulated problem. Three
e cient suboptimal algorithms are proposed to reduce the computational complexity.
To further improve the performance of the worst user in each cluster, power allocation
coe cients are optimized by using bi-section search. Important insights are concluded
from the generated simulate results. | en_US |
