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Maximization of Users’ Fairness in an Imbalanced-NOMA Network scenario with More Far-Users, by means of Multiple Near-Field Relays
Author(s)
Ligwa, Mario
Date Issued
2024
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
The development of 5G networks is currently prominent in the mobile network industry. This is
due to the need for increased network performances, such as more capacity and reliability
(users’ fairness); which the current 4G networks fall short of delivering. Non-Orthogonal
Multiple Access (NOMA) technology has been identified by others, as key elements for the
realization of 5G networks; thus, the design of NOMA networks has recently gained popularity.
NOMA technology implies serving 2 or more users in the same frequency band and
discriminating their respective information by assigning different power levels to each (PDNOMA).
In the case of 2 users per frequency band, a base-station with N-antennas must serve
2N users at the time. Initial works in the NOMA-networks’ design often assumed that the 2Nusers
to be served consist of N-far field users and N-near field users. This scenario is referred
to as the “balanced-NOMA” scenario. Initial power-allocation algorithms (Initial FM-PAA) have
been proposed to maximize users’ fairness of NOMA networks in this scenario, and have
yielded relatively good results. However, there can be a case where there are more far-users
than near-users in the 2N set to be served; it is referred to as an “imbalanced NOMA” scenario.
In this case, if the “initial FM-PAA” is used straight, it will only serve possible pairs, leaving
many far-users unserved. This will result in very poor user fairness for the network.
To address this problem, first, an “intermediate PAA”, which executes NOMA combined with
OMA, was designed, implemented and tested. The algorithm consists of an inter-beam powersharing
stage, to distribute the base station’s power across respective antennas; and an intrabeam
power-sharing stage, only applicable to the NOMA pairs formulated. Both stages
employed the “OCTR-ratios convergence concept”. The results indicated that the proposed
“intermediate-PAA” considerably improves the fairness of the imbalanced-NOMA network
scenario; compared to when the “initial FM-PAA” is used straight. However, since it does not
serve all users, it therefore constitutes an intermediate solution to the problem stated.
Furthermore, the research proposed an “advanced-PAA” solution, to completely address the
problem. The solution consists of placing relays in the near-field of the base station. Each relay
serves as the near-user to one of the unpaired far-users, and it will be served with the
information intended for the other unpaired far-user. This turns the system into a perfectly
balanced NOMA scenario. Then, a power-allocation algorithm, which combines an “initial FMPAA”,
and a “relay management system”, was designed, implemented and tested. The “initial
FM-PAA” was designed based on the “OCTR-ratios convergence” concept. The “relaymanagement
system” was based on the “decode and forward” concept. The results
demonstrated that the proposed “advanced PAA” maximizes the fairness of the imbalanced-
NOMA network scenario; and as such, outshines, both the “intermediate PAA” and the “initial
FM-PAA” used straight. Therefore, it provides an optimal solution to the stated problem.
due to the need for increased network performances, such as more capacity and reliability
(users’ fairness); which the current 4G networks fall short of delivering. Non-Orthogonal
Multiple Access (NOMA) technology has been identified by others, as key elements for the
realization of 5G networks; thus, the design of NOMA networks has recently gained popularity.
NOMA technology implies serving 2 or more users in the same frequency band and
discriminating their respective information by assigning different power levels to each (PDNOMA).
In the case of 2 users per frequency band, a base-station with N-antennas must serve
2N users at the time. Initial works in the NOMA-networks’ design often assumed that the 2Nusers
to be served consist of N-far field users and N-near field users. This scenario is referred
to as the “balanced-NOMA” scenario. Initial power-allocation algorithms (Initial FM-PAA) have
been proposed to maximize users’ fairness of NOMA networks in this scenario, and have
yielded relatively good results. However, there can be a case where there are more far-users
than near-users in the 2N set to be served; it is referred to as an “imbalanced NOMA” scenario.
In this case, if the “initial FM-PAA” is used straight, it will only serve possible pairs, leaving
many far-users unserved. This will result in very poor user fairness for the network.
To address this problem, first, an “intermediate PAA”, which executes NOMA combined with
OMA, was designed, implemented and tested. The algorithm consists of an inter-beam powersharing
stage, to distribute the base station’s power across respective antennas; and an intrabeam
power-sharing stage, only applicable to the NOMA pairs formulated. Both stages
employed the “OCTR-ratios convergence concept”. The results indicated that the proposed
“intermediate-PAA” considerably improves the fairness of the imbalanced-NOMA network
scenario; compared to when the “initial FM-PAA” is used straight. However, since it does not
serve all users, it therefore constitutes an intermediate solution to the problem stated.
Furthermore, the research proposed an “advanced-PAA” solution, to completely address the
problem. The solution consists of placing relays in the near-field of the base station. Each relay
serves as the near-user to one of the unpaired far-users, and it will be served with the
information intended for the other unpaired far-user. This turns the system into a perfectly
balanced NOMA scenario. Then, a power-allocation algorithm, which combines an “initial FMPAA”,
and a “relay management system”, was designed, implemented and tested. The “initial
FM-PAA” was designed based on the “OCTR-ratios convergence” concept. The “relaymanagement
system” was based on the “decode and forward” concept. The results
demonstrated that the proposed “advanced PAA” maximizes the fairness of the imbalanced-
NOMA network scenario; and as such, outshines, both the “intermediate PAA” and the “initial
FM-PAA” used straight. Therefore, it provides an optimal solution to the stated problem.
Additional information
Thesis (DEng (Electrical Engineering))--Cape Peninsula University of Technology, 2024
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