Enabling UAV Cellular with Millimeter-Wave Communication: Potentials and Approaches (1602.03654v1)

Abstract: To support high data rate urgent or ad hoc communications, we consider mmWave UAV cellular networks and the associated challenges and solutions. To enable fast beamforming training and tracking, we first investigate a hierarchical structure of beamforming codebooks and design of hierarchical codebooks with different beam widths via the sub-array techniques. We next examine the Doppler effect as a result of UAV movement and find that the Doppler effect may not be catastrophic when high gain directional transmission is used. We further explore the use of millimeter wave spatial division multiple access and demonstrate its clear advantage in improving the cellular network capacity. We also explore different ways of dealing with signal blockage and point out that possible adaptive UAV cruising algorithms would be necessary to counteract signal blockage. Finally, we identify a close relationship between UAV positioning and directional millimeter wave user discovery, where update of the former may directly impact the latter and vice versa.

• The paper's main contribution is introducing hierarchical beamforming strategies that address UAV mobility challenges.
• It shows that high gain directional transmissions can effectively counteract Doppler effects in mmWave UAV communications.
• The study demonstrates that using mmWave SDMA significantly boosts network capacity while mitigating signal blockage issues.

Overview of Millimeter-Wave UAV Cellular Networks

The paper "Enabling UAV Cellular with Millimeter-Wave Communication: Potentials and Approaches" by Zhenyu Xiao, Pengfei Xia, and Xiang-Gen Xia offers a meticulous exploration into the intricacies of employing millimeter wave (mmWave) technology within unmanned aerial vehicle (UAV) cellular networks. These networks are envisaged to support high data rate and urgent communications, specifically in scenarios where fixed infrastructure networks either do not exist or are inoperative.

Fundamental Challenges and Proposed Solutions

This paper identifies several key challenges associated with implementing mmWave communications in UAV-based cellular networks, primarily due to the inherent mobility of UAVs which complicates typical cellular network dynamics.

1. Beamforming Training and Tracking: The paper explores the use of hierarchical structures for beamforming codebooks. By designing codebooks with varying beam widths via sub-array techniques, the authors aim to expedite the beamforming training and tracking processes in response to the rapid movements of UAV BS.
2. Doppler Effect Considerations: Contrary to initial assumptions, the research demonstrates that high gain directional transmission in mmWave communications may mitigate catastrophic impacts stemming from the Doppler effect resulting from UAV movements.
3. Spatial Division Multiple Access (SDMA): The deployment of mmWave SDMA is highlighted as a mechanism to significantly enhance network capacity. By allocating distinct spatial beams to different users, simultaneous multi-user access without severe interference is achievable.
4. Signal Blockage Mitigation: Adaptability concerning signal blockage is a notable discussion point. UAVs, by virtue of their mobility, can employ adaptive cruising algorithms to counteract blocked signals effectively, mitigating a major limitation of stationary mmWave networks.
5. Interconnection Between UAV Positioning and User Discovery: The paper reveals a dynamic relationship between UAV positioning and mmWave user discovery, suggesting that updates in UAV positioning could directly influence user discovery procedures, and vice versa.

Numerical Results and Implications

The paper provides empirical results showing that hierarchical beamforming codebooks, notably the BMW-SS design, outperform conventional approaches in detecting line-of-sight (LOS) components during beam searches, particularly in sparse multipath environments. Moreover, it concludes that mmWave UAV cellular systems can potentially deliver superior multi-user capacities when juxtaposed with low-frequency cellular systems, leveraging broader signal bandwidths and effective SDMA practices.

Theoretical and Practical Implications

The advancements proposed in this paper promise to enhance the robustness and efficiency of UAV-based cellular networks using mmWave technology. Practically, these insights hence hold significance for emergency scenarios where rapid deployment of communication systems is crucial. Theoretically, this research contributes to the growing field of mmWave communications by addressing and potentially overcoming its long-standing limitations, such as dominance of signal blockage and rapid channel variation.

Future Directions

Future research could delve more deeply into the optimization of adaptive cruising algorithms for UAVs to further reduce blockage impact. Furthermore, the integration of real-time data regarding UAV movement and environmental variations could optimize beamforming and user discovery processes more effectively. The continued enhancement of SDMA protocols to accommodate more complex multi-user scenarios is also a promising avenue for exploration.

The contributions of this paper lay a robust foundation for advancing UAV mmWave communications, positing solutions that adapt seamlessly to the inherent dynamism of UAV operations while maximizing system capacity and reliability.