| 1. |
- Cai, Xuesong, et al.
(author)
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A Centralized and Scalable Uplink Power Control Algorithm in Low SINR Scenarios
- 2021
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In: IEEE Transactions on Vehicular Technology. - 0018-9545. ; 70:9, s. 9583-9587
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Journal article (peer-reviewed)abstract
- Power control is becoming increasingly essential for the fifth-generation (5G) and beyond systems. An example use-case, among others, is the unmanned-aerial-vehicle (UAV) communications where the nearly line-of-sight (LoS) radio channels may result in very low signal-to-interference-plus-noise ratios (SINRs). The authors in (Chiang et al., 2007) proposed to efficiently and reliably solve this kind of non-convex problem via a series of geometrical programmings (GPs) using condensation approximation. However, it is only applicable for a small-scale network with several communication pairs and practically infeasible with more (e.g., tens of) nodes to be jointly optimized. We therefore in this paper aim to provide new insights into this problem. By properly introducing auxiliary variables, the problem is transformed to an equivalent form which is simpler and more intuitive for condensation. A novel condensation method with linear complexity is also proposed based on the form. The enhancements make the GP-based power control feasible for both small- and especially large-scale networks that are common in 5G and beyond. The algorithm is verified via simulations. A preliminary case study of uplink UAV communications also shows the potential of the algorithm.
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| 2. |
- Cai, Xuesong, et al.
(author)
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Characterizing the Small-Scale Fading for Low Altitude UAV Channels
- 2021
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In: ICWMC 2021 : The Seventeenth International Conference on Wireless and Mobile Communications - The Seventeenth International Conference on Wireless and Mobile Communications. - 9781612088785 ; , s. 16-19
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Conference paper (peer-reviewed)abstract
- In this contribution, a recently conducted measurement campaign in a suburban scenario for the Unmanned Aerial Vehicle (UAV) Air-to-Ground (A2G) radio channel is introduced.The downlink signals in an in-service Long Term Evolution (LTE) network were collected and utilized to extract the Channel Impulse Responses (CIRs). A high-resolution parameter estimation algorithm derived based on the Space-Alternating Generalized Expectation-maximization (SAGE) principle is applied to estimate the delays, Doppler frequencies and complex amplitudes of Multi Path Components (MPCs) from the CIRs. Based on the MPC estimation results, fast fading characteristics of the A2G channels are investigated. It is found that the Rician distribution models the fast fading the best compared to Nakagami, Lognormal and Rayleigh distributions. Rician K factors are also calculated for the A2G channels.
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| 3. |
- Cai, Xuesong, et al.
(author)
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Empirical Low-Altitude Air-to-Ground Spatial Channel Characterization for Cellular Networks Connectivity
- 2021
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In: IEEE Journal on Selected Areas in Communications. - 0733-8716. ; 39:10, s. 2975-2991
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Journal article (peer-reviewed)abstract
- Cellular-connected unmanned aerial vehicles (UAVs) have recently attracted a surge of interest in both academia and industry. Understanding the air-to-ground (A2G) propagation channels is essential to enable reliable and/or high-throughput communications for UAVs and protect the ground user equipments (UEs). In this contribution, a recently conducted measurement campaign for the A2G channels is introduced. A uniform circular array (UCA) with 16 antenna elements was employed to collect the downlink signals of two different Long Term Evolution (LTE) networks, at the heights of 0-40m in three different, namely rural, urban and industrial scenarios. The channel impulse responses (CIRs) have been extracted from the received data, and the spatial, including angular, parameters of the multipath components in individual channels were estimated according to a high-resolution-parameter-estimation (HRPE) principle. Based on the HRPE results, clusters of multipath components were further identified. Finally, comprehensive spatial channel characteristics were investigated in the composite and cluster levels at different heights in the three scenarios.
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| 4. |
- Cai, Xuesong, et al.
(author)
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Power Allocation for Uplink Communications of Massive Cellular-Connected UAVs
- 2023
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In: IEEE Transactions on Vehicular Technology. - 0018-9545. ; 72:7, s. 8797-8811
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Journal article (peer-reviewed)abstract
- Cellular-connected unmanned aerial vehicle (UAV) has attracted a surge of research interest in both academia and industry. To support aerial user equipment (UEs) in the existing cellular networks, one promising approach is to assign a portion of the system bandwidth exclusively to the UAV-UEs. This is especially favorable for use cases where a large number of UAV-UEs are exploited, e.g., for package delivery close to a warehouse. Although the nearly line-of-sight (LoS) channels can result in higher powers received, UAVs can in turn cause severe interference to each other in the same frequency band. In this contribution, we focus on the uplink communications of massive cellular-connected UAVs. Different power allocation algorithms are proposed to either maximize the minimal spectrum efficiency (SE) or maximize the overall SE to cope with severe interference based on the successive convex approximation (SCA) principle. One of the challenges is that a UAV can affect a large area meaning that many more UAV-UEs must be considered in the optimization problem, which is essentially different from that for terrestrial UEs. The necessity of single-carrier uplink transmission further complicates the problem. Nevertheless, we find that the special property of large coherent bandwidths and coherent times of the propagation channels can be leveraged. The performances of the proposed algorithms are evaluated via extensive simulations in the full-buffer transmission mode and bursty-traffic mode. Results show that the proposed algorithms can effectively enhance the uplink SEs. This work can be considered the first attempt to deal with the interference among massive cellular-connected UAV-UEs with optimized power allocations.
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| 5. |
- Huang, Ziwei, et al.
(author)
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A Mixed-Bouncing Based Non-Stationarity and Consistency 6G V2V Channel Model with Continuously Arbitrary Trajectory
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In: IEEE Transactions on Wireless Communications. - 1536-1276.
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Journal article (peer-reviewed)abstract
- In this paper, a novel three-dimensional (3D) irregularshaped geometry-based stochastic model (IS-GBSM) is proposedfor sixth-generation (6G) millimeter wave (mmWave) massivemultiple-input multiple-output (MIMO) vehicle-to-vehicle(V2V) channels. To investigate the impact of vehicular trafficdensity (VTD) on channel statistics, clusters are divided into staticclusters and dynamic clusters, which are further distinguishedinto static/dynamic single/twin-clusters to capture the mixed bouncingpropagation. A new method, which integrates thevisibility region and birth-death process methods, is developedto model space-time-frequency (S-T-F) non-stationarity of V2Vchannels with time-space (T-S) consistency. The continuouslyarbitrary vehicular movement trajectory (VMT) and soft clusterpower handover are modeled to further ensure channel T-Sconsistency. From the proposed model, key channel statistics arederived. Simulation results show that S-T-F non-stationarity ofchannels with T-S consistency is modeled and the impacts of VTDand VMT on channel statistics are analyzed. The generality ofthe proposed model is validated by comparing simulation resultsand measurement/ray-tracing (RT)-based results.
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| 6. |
- Huang, Ziwei, et al.
(author)
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A Non-Stationary 6G V2V Channel Model with Continuously Arbitrary Trajectory
- 2023
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In: IEEE Transactions on Vehicular Technology. - 0018-9545. ; 72:1, s. 4-19
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Journal article (peer-reviewed)abstract
- In this paper, a novel three-dimensional (3D) massive multiple-input multiple-output (MIMO) millimeter wave (mmWave) geometry-based stochastic model (GBSM) is proposed for sixth-generation (6G) vehicle-to-vehicle (V2V) channels. In the proposed GBSM, clusters in the environment are divided into static clusters and dynamic clusters. Furthermore, the time-variant acceleration together with the integration of time during the transmission distance update are exploited. As a result, the continuously arbitrary trajectory of the transceiver and dynamic clusters is successfully captured. To jointly model space-time-frequency (S-T-F) non-stationarity of 6G V2V channels, a new method, which properly integrates the frequency-dependent factor, birth-death (BD) process, and selective evolution of static and dynamic clusters, is developed. Key channel statistics, including the space-time-frequency correlation function (STF-CF), time stationary interval, and Doppler power spectral density (DPSD) are obtained. Simulation results demonstrate that S-T-F non-stationarity is modeled and the impacts of vehicular traffic density (VTD) and vehicular movement trajectory (VMT) on channel statistics are further analyzed thoroughly. Finally, the generality and accuracy of the proposed GBSM are validated through the comparison of simulation results and available measurement data.
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| 7. |
- Song, Jian, et al.
(author)
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Bounded Path-Loss Model for UAV-to-UAV Communications
- 2021
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In: ICWMC 2021 : The Seventeenth International Conference on Wireless and Mobile Communications - The Seventeenth International Conference on Wireless and Mobile Communications. - 9781612088785
-
Conference paper (peer-reviewed)abstract
- In this paper, we focus on ultra-dense network modelingwhere both the Base Stations (BSs) and Mobile Terminals(MTs) are UAVs. In this case, two communication nodes canbe very close to each other. However, existing cellular networkanalyses typically use the standard unbounded path loss modelwhere received power decays like r^beta over a distance r. Thisstandard model is a good approximation for the path-loss inwireless communications over large values of r but is not validfor small values of r due to the singularity at 0. This model is oftenused along with a random uniform node distribution, even thoughin a group of uniformly distributed nodes some may be arbitrarilyclose to one another, thus, it will lose accuracy and may benot applicable for UAV-to-UAV communications. To tackle thisproblem, by using mathematical tool behind stochastic geometry,we propose tractable analytical frameworks of coverage and ratebased on the novel unbounded path-loss model with a constantdistance factor r_0 for analyzing the UAV-to-UAV communications.
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