Power and Channel Allocation for Non-orthogonal Multiple Access in 5G Systems: Tractability and Computation (1603.07576v1)

Abstract: Network capacity calls for significant increase for 5G cellular systems. A promising multi-user access scheme, non-orthogonal multiple access (NOMA) with successive interference cancellation (SIC), is currently under consideration. In NOMA, spectrum efficiency is improved by allowing more than one user to simultaneously access the same frequency-time resource and separating multi-user signals by SIC at the receiver. These render resource allocation and optimization in NOMA different from orthogonal multiple access in 4G. In this paper, we provide theoretical insights and algorithmic solutions to jointly optimize power and channel allocation in NOMA. For utility maximization, we mathematically formulate NOMA resource allocation problems. We characterize and analyze the problems' tractability under a range of constraints and utility functions. For tractable cases, we provide polynomial-time solutions for global optimality. For intractable cases, we prove the NP-hardness and propose an algorithmic framework combining Lagrangian duality and dynamic programming (LDDP) to deliver near-optimal solutions. To gauge the performance of the obtained solutions, we also provide optimality bounds on the global optimum. Numerical results demonstrate that the proposed algorithmic solution can significantly improve the system performance in both throughput and fairness over orthogonal multiple access as well as over a previous NOMA resource allocation scheme.

• The paper finds that joint power and channel allocation in NOMA is NP-hard and proposes an LDDP algorithm for solving intractable cases effectively.
• Numerical results show the proposed LDDP approach achieves significant performance gains, including a 20% throughput improvement over existing NOMA methods.
• These findings encourage practical NOMA adoption in 5G via effective resource allocation strategies and guide future research in this area.

Power and Channel Allocation for Non-Orthogonal Multiple Access in 5G Systems: Tractability and Computation

This paper addresses critical aspects of resource allocation in the evolving 5G cellular networks, particularly focusing on Non-Orthogonal Multiple Access (NOMA) with Successive Interference Cancellation (SIC) strategies. The paper posits NOMA as a promising multi-user access scheme, intended to significantly improve spectrum efficiency and network capacity. Unlike the traditional orthogonal multiple access (OMA) methods, such as OFDMA used in 4G LTE networks, NOMA allows simultaneous access to the same frequency-time resources by multiple users. This paper aims to resolve two main challenges: joint power and channel allocation optimization and the complexity analysis of the problem in NOMA systems.

The authors provide a comprehensive mathematical formulation for NOMA resource allocation problems under various utility functions. Through a combination of theoretical insights and algorithmic development, they establish that the joint power and channel allocation problem (JPCAP) is NP-hard, signifying significant computational challenges in targeting global optimality. For tractable scenarios, polynomial-time solutions are presented. Moreover, for the recognized intractable cases, an algorithmic framework combining Lagrangian duality and dynamic programming (LDDP) is developed, providing near-optimal solutions and performance bounds.

Among numerically validated results, the proposed approach demonstrates significant performance improvement over traditional OMA and previously proposed NOMA solutions in terms of throughput and fairness. Numerical analyses substantiate that the LDDP framework enhances system capabilities effectively, achieving an approximate 20% rise in throughput compared to existing NOMA strategies and substantial efficiency gains over OFDMA implementations.

Key Contributions and Findings

1. Theoretical Framework: The paper introduces mathematical models for evaluating power and channel allocations under NOMA with respect to utility maximization, addressing problem tractability through complexity analysis.
2. Algorithmic Development: An LDDP-based algorithmic framework is proposed. It combines Lagrangian duality approaches and dynamic programming to tackle intractable JPCAP cases, facilitating near-optimal solutions and providing upper bounds for solution quality evaluation.
3. Performance Evaluation: Numerical results indicate significant enhancements in network performance, highlighting improved throughput and fairness compared to conventional methods. Specifically, the paper quantifies a 20% throughput improvement over NOMA-FTPC.
4. Utility and Fairness Analysis: The paper explores both sum-rate (SR) and weighted sum-rate (WSR) utilities, ensuring balanced allocations between throughput maximization and fairness. It addresses fairness particularly by employing proportional fairness metrics during scheduling.
5. Practical Implications: The results encourage practical adoption of NOMA in 5G networks, where efficient power and channel allocation can lead to enhanced user experiences and greater system adaptability.

Implications for Future Research

The paper provides a stepping stone for further investigations into optimizing NOMA systems. It suggests directions like exploring max-min fairness solutions within a single scheduling instance and potentially integrating other interference management techniques. Furthermore, the tractability aspects discussed may pave the way for developing new scalable algorithms capable of adapting these principles to other emerging wireless communication standards.

Future research may include examining the impact of these optimization strategies in heterogeneous network environments, considering real-world constraints like varying traffic demands and user mobility patterns. Also, advances in machine learning could inform dynamic adjustments to these algorithms to provide adaptive real-time solutions in constantly changing network conditions.

In conclusion, this paper provides valuable insights and innovative solutions to the intricate problem of resource allocation in NOMA-based 5G systems, setting a precedent for addressing similar challenges in future wireless communication technologies.