Uplink Cooperative NOMA for Cellular-Connected UAV (1809.03657v3)

Abstract: Aerial-ground interference mitigation is a challenging issue in the cellular-connected unmanned aerial vehicle (UAV) communications. Due to the strong line-of-sight (LoS) air-to-ground (A2G) channels, the UAV may impose/suffer more severe uplink/downlink interference to/from the cellular base stations (BSs) than the ground users. To tackle this challenge, we propose to apply the non-orthogonal multiple access (NOMA) technique to the uplink communication from a UAV to cellular BSs, under spectrum sharing with the existing ground users. However, for our considered system, traditional NOMA with local interference cancellation (IC), termed non-cooperative NOMA, may provide very limited gain compared to the OMA. This is because there are many co-channel BSs due to the LoS A2G channels and thus the UAV's rate performance is severely limited by the BS with the worst channel condition with the UAV. To improve the UAV's achievable rate, a new cooperative NOMA scheme is proposed by exploiting the backhaul links among BSs. Specifically, some BSs with better channel conditions are selected to decode the UAV's signals first, and then forward the decoded signals to their backhaul-connected BSs for IC. To investigate the optimal design of cooperative NOMA, we maximize the weighted sum-rate of the UAV and ground users by jointly optimizing the UAV's rate and power allocations over multiple resource blocks. However, this problem is hard to be solved optimally. To obtain useful insights, we first consider two special cases with egoistic and altruistic transmission strategies of the UAV, respectively, and solve their corresponding problems optimally. Next, we consider the general case and propose an efficient suboptimal solution via the alternating optimization. Numerical results show that the proposed cooperative NOMA yields significant throughput gains than the OMA and the non-cooperative NOMA benchmark.

• The paper introduces a cooperative NOMA scheme leveraging inter-base station backhaul links for efficient interference cancellation in UAV uplink communication.
• A weighted sum-rate maximization framework optimizes UAV rate and power allocation across multiple resource blocks, examining egoistic and altruistic transmission strategies.
• Numerical simulations confirm significant throughput gains over traditional OMA and non-cooperative NOMA, enhancing UAV performance in dense cellular networks.

Overview of Uplink Cooperative NOMA for Cellular-Connected UAV

The paper critically examines aerial-ground interference mitigation for cellular-connected unmanned aerial vehicles (UAVs) by leveraging the non-orthogonal multiple access (NOMA) technique. Due to the strong line-of-sight (LoS) channels characteristic of UAV communication, UAVs can suffer from more severe uplink/downlink interference compared to terrestrial users. The authors propose a novel cooperative NOMA scheme aiming to effectively alleviate this interference without excessively degrading the UAV’s achievable rate.

Technical Contributions

The paper introduces a cooperative NOMA scheme that involves leveraging backhaul links among base stations (BSs) to facilitate cooperative interference cancellation. This technique is distinct because, unlike traditional NOMA that utilizes local interference cancellation at individual BSs, cooperative NOMA employs a broader approach whereby BSs with preferred channel conditions decode the UAV's signals first and then communicate decoded information through backhaul connections for interference cancellation with corresponding BSs.

To explore optimal cooperative NOMA design, the authors establish a weighted sum-rate maximization framework wherein the UAV’s rate and power allocations are optimized over multiple resource blocks. They extensively investigate two UAV transmission strategies—egoistic and altruistic—and aptly solve their corresponding optimization problems to furnish insights into cooperative NOMA design. Later, for the general problem case, a suboptimal solution is developed using alternating optimization and successive convex approximation techniques, which offer efficient computational feasibility.

Numerical Results and Analysis

Numerical simulations demonstrably exhibit that the proposed cooperative NOMA scheme results in substantial throughput gains compared to both traditional orthogonal multiple access (OMA) and non-cooperative NOMA benchmarks. Such improvements underscore the efficacy of the cooperative NOMA approach in mitigating UAV's uplink interference and advancing UAV’s communication capability in dense cellular environments.

Implications and Future Directions

The research implies that cooperative interference cancellation can potentially alter strategic NOMA applications in modern cellular systems, particularly given the burgeoning deployment of UAVs within various civilian domains. Moreover, this cooperative approach poses intriguing possibilities for broader cellular ecosystem integration without necessitating substantial network infrastructural overhauls.

In prospect, theoretical and practical developments could be geared towards accommodating multi-UAV scenarios, addressing downlink challenges, and refining cooperative interference cancellation under stochastic channel conditions. Moreover, embracing user-centric scenarios and pliable network designs undoubtedly presents compelling opportunities for advancing NOMA deployment.

This paper propels the discourse forward in aerial-ground communications, substantiating the cooperative NOMA’s progressiveness, aptitude, and adaptability within emergent UAV cellular networks.