Abstract:
The evolution of next-generation communication systems, driven by applications like smart cities, factories of future, and autonomous vehicles, has led to a surge in communication devices and applications facilitated by 5G-and-beyond networks. While legacy orthogonal multiple access (OMA) schemes struggle to meet the demands of these applications, non-orthogonal multiple access (NOMA) has gained prominence for its potential to provide more links, lower access latency, and higher spectral efficiency. This thesis delves into the disruptive sparse code multiple access (SCMA) scheme proposed by H. Nikopour and H. Baligh, exploring its performance in various scenarios. Firstly, a novel codebook (CB) is designed for SCMA-based visible light communication (VLC) systems, addressing shot noise issues. An iterative algorithm optimizes the CB, and theoretical bit error rate (BER) expressions are derived, showing superior performance in simulations compared to existing literature. The study extends to an intelligent reflecting surface (IRS)-aided downlink SCMA system for sum-rate maximization, considering constraints like minimum user data rate, total power, SCMA CB structure, and IRS channel coefficients. An alternating optimization (AO) algorithm tackles the non-convex joint optimization problem, demonstrating significant performance improvements over the IRS-aided SCMA system without IRS. In the realm of unmanned aerial vehicles (UAVs), the report shifts focus to a SCMA- assisted UAV system. The objective is to optimize resource utilization and maximize the system data rate within energy constraints. We explore UAV 3D placement optimization, optimal UAV 3D trajectory computation, and spectral resource and transmit power allocation, showcasing the benefits of SCMA in enhancing communication systems through UAV assistance. Further, the investigation extends to SCMA with multiple UAVs, addressing challenges of inter-UAV and intra-UAV interference. The complexities involve equitable user allocation, frequency reuse-based subchannel assignment, and iterative algorithms for power and bandwidth allocation, presenting a comprehensive approach to optimize system performance in multi-UAV scenarios. In conclusion, this comprehensive study demonstrates the versatility and effectiveness of SCMA across diverse scenarios, ranging from VLC to IRS-aided systems and UAV- assisted networks, showcasing its potential to revolutionize next-generation communication systems.
