Chapter 1 Introduction.- 1.1 Overview.- 1.1.1 History: From 1G to 6G.- 1.1.

2 Requirements and application of 6G.- 1.2 An Overview of Heterogeneous Networks.- 1.2.1 Architecture of Heterogeneous Networks.- 1.3 An overview of NOMA.

- 1.3.1 NOMA Architecture.- 1.3.2 Superposition coding.- 1.3.

3 Successive interference cancellation.- 1.3.4 NOMA in Downlink Transmission.- 1.4 An Introduction of SWIPT.- 1.4.

1 Definition and overview.- 1.4.2 Importance in Modern Wireless Networks.- 1.4.3 SWIPT Architecture.- 1.

4.3.1 Time Switching (TS).- 1.4.3.2 Power Splitting (PS).- 1.

4.3.3 Hybrid Architectures.- 1.5 An Introduction of RIS.- 1.5.1 Definition and overview.

- 1.5.2 Role in Modern Wireless Communication.- 1.5.3 Fundamental Concepts of RIS.- 1.5.

3.1 Structure and Functionality.- 1.5.3.2 Physics of Metasurfaces.- 1.5.

3.3 Beamforming and Phase Shifting.- 1.5.4 Integration of RIS in Wireless Networks.- 1.5.4.

1 Benefits of RIS in 5G and Beyond.- 1.5.4.2 Comparison with Traditional Techniques.- Chapter 2 Joint Impact of HPA Non-linearity and Imperfect SIC in NOMA Enabled HCN.- 2.1 Introduction and System Model.

- 2.2 Instantaneous received SINR.- 2.2.1 A typical user connected to MBS tier.- 2.2.2 A typical user connected to PBS tier (PU) without NOMA.

- 2.2.3 PU (NOMA with perfect SIC).- 2.2.4 PU (NOMA with i-SIC).- 2.2.

5 PU (NOMA with non-linear HPA).- 2.2.6 PU (NOMA with i-SIC & non-linear HPA).- 2.3 Performance Matrix.- 2.3.

1 Outage Probability.- 2.3.2 Asymptotic Outage Probability.- 2.3.3 Ergodic Rate Analysis.- 2.

3.4 System throughput.- 2.3.5 Energy Efficiency.- 2.4 Results and Discussions.- Chapter 3 Performance of NOMA-empowered HCN: A Stochastic Geometry Approach Considering Imperfect SIC and CSI.

- 3.1 Introduction and System Model.- 3.2 Instantaneous received SINR.- 3.2.1 MBS User's SINR.- 3.

2.2 PBS User's SINR (i-CSI, excluding NOMA).- 3.2.3 PBS User's SINR (i-CSI, NOMA with i-SIC).- 3.3 Performance Matrix.- 3.

3.1 Outage Probability.- 3.3.2 Asymptotic Outage Probability.- 3.3.3 System throughput.

- 3.3.4 Energy Efficiency.- 3.4 Results and Discussions.- Chapter 4 SWIPT Enabled Cooperative NOMA in Heterogeneous Networks.- 4.1 Network Model.

- 4.1.1 Spatial Distribution of BS.- 4.1.2 Signal Model.- 4.1.

3 Association Criteria.- 4.2 Carrier Sensing.- 4.2.1 Modelling BS tiers.- 4.2.

2 Neighborhood Success Probability.- 4.2.3 Repulsive point process.- 4.3 Comparison of PS and TS architectures.- 4.4 Power Beacon and Intermediate Node.

- 4.5 Performance Metrics.- 4.5.1 Outage Probability.- 4.5.2 System Throughput.

- 4.5.3 Energy Efficiency.- 4.6 Results and Discussions.- Chapter 5 Performance of HCN with Non-Linear HPA in SWIPT-Enabled Cooperative-NOMA.- 5.1 Introduction and System Model.

- 5.2 Multi-tier SINR analyses.- 5.2.1 MBS user's SINR.- 5.2.2 PBS user's SINR excluding NOMA.

- 5.2.3 PBS user's SINR (NOMA with non-linear PA and Energy Harvesting).- 5.2.3.1 Energy Harvesting.- 5.

2.3.2 Bussgang's linearization theory.- 5.2.3.3 Information Transmission.- 5.

3 Performance Matrix.- 5.3.1 Outage Probability.- 5.3.4 System throughput.- 5.

3.5 Energy Efficiency.- 5.4 Results and Discussions.- Chapter 6 Performance of RIS-Aided NOMA Network.- 6.1 System Model.- 6.

2 Signal Model.- 6.3 Instantaneous received SNR.- 6.4 Performance Matrix.- 6.4.1 Outage Probability.

- 6.4.2 Asymptotic Outage Probability.- 6.4.3 Ergodic Capacity.- 6.4.

4 Average Symbol Error Rate.- 6.4.4.1 Rectangular QAM.- 6.4.4.

2 Cross QAM.- 6.4.4.3 Hexagonal QAM.- 6.5 Results and Discussions.- Chapter 7 Conclusion and Future Works.

- 7.1 Conclusion.- 7.2 Future Works.