Wireless Powered Communications with Non-Orthogonal Multiple Access (1511.01291v2)

Abstract: We study a wireless-powered uplink communication system with non-orthogonal multiple access (NOMA), consisting of one base station and multiple energy harvesting users. More specifically, we focus on the individual data rate optimization and fairness improvement and we show that the formulated problems can be optimally and efficiently solved by either linear programming or convex optimization. In the provided analysis, two types of decoding order strategies are considered, namely fixed decoding order and time- sharing. Furthermore, we propose an efficient greedy algorithm, which is suitable for the practical implementation of the time-sharing strategy. Simulation results illustrate that the proposed scheme outperforms the baseline orthogonal multiple access scheme. More specifically, it is shown that NOMA offers a considerable improvement in throughput, fairness, and energy efficiency. Also, the dependence among system throughput, minimum individual data rate, and harvested energy is revealed, as well as an interesting trade-off between rates and energy efficiency. Finally, the convergence speed of the proposed greedy algorithm is evaluated, and it is shown that the required number of iterations is linear with respect to the number of users.

• The paper analyzes wireless powered communication systems using non-orthogonal multiple access (NOMA) to optimize throughput and fairness, demonstrating advantages over TDMA via optimization techniques.
• The research optimizes system throughput and user fairness in wireless-powered NOMA, showing time-sharing improves minimum rates and enables greater flexibility.
• Numerical results show NOMA with time-sharing substantially improves minimum user throughput and fairness compared to TDMA schemes, contributing to energy-efficient networks.

Analysis of Wireless Powered Communications with Non-Orthogonal Multiple Access

Wireless-powered communications hold significant promise for enabling energy-efficient and sustainable wireless networks. The paper "Wireless Powered Communications with Non-Orthogonal Multiple Access" by Diamantoulakis et al. explores the integration of energy harvesting capabilities in wireless networks employing non-orthogonal multiple access (NOMA) schemes. This research focuses on optimizing system throughput and improving fairness among users, all within the context of a wireless-powered communication system. The detailed analysis encompasses the use of advanced optimization techniques such as linear programming and convex optimization, and the results show notable advantages over traditional orthogonal multiple access schemes like TDMA.

Optimization Objectives and Achievements

The paper addresses two significant optimization objectives in a wireless-powered NOMA setup: maximizing system throughput and maximizing equal individual data rates. The authors present solutions for these objectives both with and without employing a time-sharing strategy among users' decoding orders.

1. System Throughput Maximization: By employing a fixed decoding order based on descending channel gains, the scheme maximizes the system throughput efficiently. Furthermore, by considering the time-sharing configuration, the minimum individual data rate is improved without degrading total throughput. This approach allows the configuration to adopt the most advantageous points within the capacity region—a flexibility absent in fixed order schemes.
2. Equal Individual Data Rate Maximization: The authors also consider scenarios necessitating equal user rates, optimizing the shared system time (i.e., harvest time vs. transmit time) to achieve larger fairness. Here, a strategic balance between energy transfer and communication duration plays a pivotal role. Unlike fixed order decoding, the use of time-sharing succeeds in maximizing the achievable equal individual data rate within the network.

Comparative Insights

A thorough comparative investigation is conducted against TDMA-based schemes. The findings suggest that NOMA schemes not only assure enhanced system throughput but also better fairness among users—attributes that are critical when dealing with energy-limited wireless powered networks. Significantly, when maximizing equal individual data rates, NOMA consistently outperforms TDMA schemes, reflecting its robustness in diverse network conditions.

Noteworthy Numerical Results:

• Improvement in Minimum User Throughput: The paper highlights substantial improvements in the minimum user throughput when using NOMA with time-sharing over conventional TDMA.
• Fairness and Energy Efficiency: Evaluations using the Jain's fairness index elucidate the superior fairness levels achieved by NOMA approaches. Additionally, higher energy efficiency is reported, underlining the paper's emphasis on balancing energy harvesting with transmission efficiency.

Algorithmic Contribution:

The development of a greedy algorithm for time-sharing configuration is another key contribution. This algorithm optimally determines time-sharing permutations and demonstrates efficiency gains, reducing theoretical complexity from factorial dependency on the number of users to a manageable linear growth concerning iterations, hence facilitating practical implementation.

Future Directions and Implications

The findings have notable implications for the design of future wireless networks, particularly in contexts leaning towards ubiquitous energy sustainability like the Internet of Things (IoT). By unlocking higher efficiency in energy use and enabling fairer resource allocation, such strategies could be pivotal for the forthcoming 5G networks and beyond.

In terms of future developments, further research could focus on larger-scale implementations where more intricate user-channel interactions are considered, leading to deeper insights into the capabilities of NOMA within energy-harvesting frameworks. Another potential direction is the exploration of hybrid models that combine multiple power-saving techniques with NOMA to further enhance both theoretical and practical constraints in increasingly dense network environments.

In conclusion, the research provides a significant step forward in the understanding and design of energy-efficient NOMA systems, underscoring their potential to enhance throughput and fairness in future sustainable communication networks.