[Paper Review] Multi-Beam UAV Communication in Cellular Uplink: Cooperative Interference Cancellation and Sum-Rate Maximization

Liang Liu, Shuowen Zhang+1 more|arXiv (Cornell University)|Aug 1, 2018

UAV Applications and Optimization20 references45 citations

TL;DR

This paper introduces a cooperative interference cancellation strategy for multi-beam UAV uplink in cellular networks, maximizing UAV sum-rate while protecting occupied GBSs under interference constraints, and analyzes DoF in high-SNR.

ABSTRACT

Integrating unmanned aerial vehicles (UAVs) into the cellular network as new aerial users is a promising solution to meet their ever-increasing communication demands in a plethora of applications. Due to the high UAV altitude, the channels between UAVs and the ground base stations (GBSs) are dominated by the strong line-of-sight (LoS) links, thus severe interference may be generated to/from the GBSs in the uplink/downlink, which renders the interference management with coexisting terrestrial and aerial users a more challenging problem to solve. In this paper, we study the uplink communication from a multi-antenna UAV to a set of GBSs in its signal coverage region. Among these GBSs, we denote available GBSs as the ones that do not serve any terrestrial users at the assigned resource block (RB) of the UAV, and occupied GBSs as the rest that are serving their respectively associated terrestrial users in the same RB. We propose a new cooperative interference cancellation strategy for the multi-beam UAV uplink communication, which aims to eliminate the co-channel interference at each of the occupied GBSs and in the meanwhile maximize the sum-rate to the available GBSs. Specifically, the multi-antenna UAV sends multiple data streams to selected available GBSs, which in turn forward their decoded data streams to their backhaul-connected occupied GBSs for interference cancellation. To draw useful insights, the maximum degrees-of-freedom (DoF) achievable by the multi-beam UAV communication for sum-rate maximization in the high signal-to-noise ratio (SNR) regime is first characterized, subject to the stringent constraint that all the occupied GBSs do not suffer from any interference in the UAV's uplink transmission. Then, based on the DoF-optimal design, the achievable sum-rate at finite SNR is maximized, subject to given maximum allowable interference power constraints at each occupied GBS.

Motivation & Objective

• Motivate cellular-enabled UAV uplink to meet high data-rate demands for UAV payload and control signals.
• Develop a cooperative interference cancellation strategy leveraging backhaul connections between adjacent GBSs.
• Characterize the maximum degrees-of-freedom (DoF) for the UAV uplink under interference constraints.
• Maximize UAV sum-rate at finite SNR using a DoF-guided beamforming design.
• Compare performance with benchmarks like cognitive beamforming, NOMA, and CoMP.

Proposed method

• Model a UAV with M antennas transmitting to N GBSs, dividing GBSs into occupied and available groups.
• Propose cooperative interference cancellation where available GBSs decode UAV streams and forward to connected occupied GBSs for interference cancellation.
• Formulate a sum-rate maximization problem under interference temperature constraints, with joint design of data streams J, associations Λj, beamformers wj, and rates Rj.
• Perform DoF analysis in the high-SNR regime using zero-forcing constraints to maximize J feasible under backhaul-assisted cancellation.
• Develop a finite-SNR beamforming algorithm via successive convex approximation, guided by the DoF-optimal associations.
• Provide numerical results comparing with cognitive beamforming, NOMA, and CoMP benchmarks.

Experimental results

Research questions

• RQ1 How to maximize UAV uplink sum-rate while protecting terrestrial uplink in occupied GBSs via cooperative interference cancellation?
• RQ2 What is the maximum achievable DoF for multi-beam UAV uplink under interference constraints and backhaul-aided cancellation?
• RQ3 How should data streams be associated with available GBSs to enable backhaul-based interference cancellation?
• RQ4 What finite-SNR beamforming strategy achieves near-optimal sum-rate under the interference-temperature constraints?

Key findings

• The cooperative interference cancellation strategy enables more data streams to be transmitted under interference constraints than cognitive beamforming or NOMA.
• The DoF analysis shows higher DoF with the proposed strategy than benchmarks, under zero-interference requirements at occupied GBSs.
• A DoF-optimal data-stream association guides a practical finite-SNR beamforming design via successive convex approximation.
• The finite-SNR beamforming algorithm achieves significant sum-rate gains over cognitive beamforming in simulations.
• Numerical results validate the DoF insights and demonstrate performance gains against benchmark schemes.