| 1. |
- Ding, Liqin, 1988, et al.
(författare)
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Bayesian Integrity Monitoring for Cellular Positioning - A Simplified Case Study
- 2023
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Ingår i: 2023 IEEE International Conference on Communications Workshops, ICC Workshops 2023. ; , s. 1050-1056
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Konferensbidrag (refereegranskat)abstract
- Bayesian receiver autonomous integrity monitoring (RAIM) algorithms are developed for the snapshot cellular positioning problem in a simplified one-dimensional (1D) linear Gaussian setting. They allow for position estimation, multi-fault detection and exclusion, and protection level (PL) computation by the efficient and exact computation of the position posterior probabilities via message passing along a factor graph. Numerical simulations show that the proposed Bayesian RAIM algorithms achieve significant performance improvement over a baseline advanced RAIM algorithm by providing tighter protection levels (PLs) that meet the target integrity risk (TIR) requirements.
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| 2. |
- Ding, Liqin, 1988, et al.
(författare)
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Degrees of Freedom in 3D Linear Large-Scale Antenna Array Communications—A Spatial Bandwidth Approach
- 2022
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Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 40:10, s. 2805-2822
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Tidskriftsartikel (refereegranskat)abstract
- For wireless communications using linear large-scale antenna arrays, we define a receiving coordinate system and parameterization strategy to facilitate the study of the impact of three-dimensional position and rotation of the arrays on the achievable spatial degrees of freedom (DoF) in line-of-sight (LOS) channels. An analytical framework based on spatial bandwidth analysis is developed, under which three elementary problems corresponding to three basic orthogonal receiving directions are investigated. For each of them, accurate, simple, and interpretable closed-form approximations for the achievable spatial DoF are derived, and the spatial region where a sufficient amount of spatial DoF is expected available is determined. The expressions can easily be integrated into large-scale system-level simulations. Some interesting and surprising observations are made from simulation studies based on the analytical results. For instance, the spatial bandwidth is shown to be approximately constant in almost the entire spatial multiplexing region. Moreover, in significant parts of this region, the optimal receive array orientation is not parallel with the transmitting array.
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| 3. |
- Ding, Liqin, 1988, et al.
(författare)
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Shannon Capacity of LOS MIMO Channels with Uniform Circular Arrays
- 2022
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Ingår i: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC. ; 2022-September
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Konferensbidrag (refereegranskat)abstract
- The Shannon capacity for the line-of-sight (LOS) multiple-input multiple-output (MIMO) channel between two perfectly aligned uniform circular arrays (UCAs) is derived from the first principles in a tutorial fashion. It is well known that harmonically related complex exponentials (also known in the literature as orbital angular momentum (OAM) modes) are eigenmodes for the spatially continuous channel. We show that the corresponding eigenvalues can be expressed as Bessel functions of the first kind. We also show that the spatially discrete channel between two UCAs with the same finite number of Hertzian dipole antennas on both sides has eigenmodes that are spatially sampled continuous OAM modes, and discrete eigenvalues that are aliased versions of the continuous eigenvalues. Through numerical solution of Maxwell's equations, we verify that the discrete eigenvalues for UCAs with realistic dipole antennas are the same as with the Hertzian dipoles for the studied geometries (1~km hop distance, UCA radius 1 and 2 m, carrier frequency 70 GHz) as long as antenna spacing is not very dense.
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| 4. |
- Ding, Liqin, 1988, et al.
(författare)
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Spatial Bandwidth Asymptotic Analysis for 3D Large-Scale Antenna Array Communications
- 2024
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Ingår i: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 23:4, s. 2638-2652
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we study the spatial bandwidth for line-of-sight (LOS) channels with linear large-scale antenna arrays (LSAAs) in 3D space. We provide approximations to the spatial bandwidth at the center of the receiving array, of the form $C R^{-B}$, where $R$ is the radial distance, and $C$ and $B$ are directional-dependent and piecewise constant in $R$. The approximations are valid in the entire radiative region, that is, for $R$ greater than a few wavelengths. When the length of the receiving array is small relative to $R$, the product of the array length and the spatial bandwidth provides an estimate of the available spatial degree-of-freedom (DOF) in the channel. In a case study, we apply these approximations to the evaluation of spatial multiplexing regions under random orientation conditions. The goodness-of-fit of the approximations is demonstrated and some interesting findings about the DOF performance of the channel under 3D and 2D orientation restrictions are obtained, e.g., that, under some conditions, it is better to constrain the receiving array orientation to be uniform over the unit circle in the 2D ground plane rather than uniform over the 3D unit sphere.
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| 5. |
- Li, Huafu, et al.
(författare)
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Air-to-Ground Channel Modeling and Performance Analysis for Cellular-Connected UAV Swarm
- 2023
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Ingår i: IEEE Communications Letters. - 1558-2558 .- 1089-7798. ; 27:8, s. 2172-2176
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Tidskriftsartikel (refereegranskat)abstract
- In this letter, we investigate the air-to-ground (A2G) channel model and transmission performance for a cellular-connected massive multiple-input multiple-output unmanned aerial vehicle (UAV) swarm system. First, we propose a spatially and temporally correlated A2G channel model that focuses on non-isotropic scattering, line-of-sight (LoS) propagation, and moving scatterers. Second, we derive a novel closed-form signal-to-interference-and-noise ratio expression for uplink transmission, taking into account the effect of channel aging with strong LoS. The results show that the frame length, pilot overhead, and UAV swarm scale can be pre-designed in a fine-grained manner depending on the propagation environment and transmission task. For example, for a low-speed scenario, a long frame can be configured due to the negligible channel aging effect. Moreover, more pilots may mitigate the damage of channel aging, but it is no better when a short frame is needed for transmission such as ultra-reliable and low-latency communications.
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| 6. |
- Li, Huafu, et al.
(författare)
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Impact of Channel Aging on Massive MIMO Vehicular Networks in Non-isotropic Scattering Scenarios
- 2021
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Ingår i: 2021 IEEE Global Communications Conference, GLOBECOM 2021 - Proceedings.
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Konferensbidrag (refereegranskat)abstract
- Massive multiple-input multiple-output (MIMO) relies on accurate channel estimation for precoding and receiving to achieve its claimed performance advantages. When serving vehicular users, the rapid channel aging effect greatly hinders its advantages, and a careful system design is required to ensure an efficient use of wireless resources. In this paper, we investigate this problem for the first time in a non-isotropic scattering scenario. The von Mises distribution is adopted for the angle of arrival (AoA), resulting in a tunable channel temporal correlation coefficient (TCC) model, which can adapt to different AoA spread conditions through the k parameter and incorporates the isotropic Jakes-Clarke model as a special case. The simulated results in a Manhattan grid-type multi-cell network clearly demonstrate the impact of channel aging on the uplink spectral efficiency (SE) performance and moreover, in order to maximize the area average SE, the size of the transmission block should be optimally selected according to some linear equations of k.
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| 7. |
- Li, Huafu, et al.
(författare)
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Performance Analysis and Transmission Block Size Optimization for Massive MIMO Vehicular Network with Spatially and Temporally Correlated Channels
- 2024
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Ingår i: IEEE Internet of Things Journal. - 2327-4662. ; 11:5, s. 8989-9003
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effect of spatially and temporally correlated channels on the transmission performance of multi-cell multi-user massive multiple-input multiple-output (MIMO) vehicular networks in generic non-isotropic scattering environments. A new channel model is established to evaluate the harmfulness of the non-isotropic-scattered angle-of-departure/angle-of-arrival (AoD/AoA) spread and the high mobility of users on the uplink transmission. We derive the expressions of achievable spectral efficiency (SE), taking into account the effects of line-of-sight propagation, channel aging, and pilot contamination. Specifically, two novel receive combining schemes, namely the aging-aware maximum ratio combining and the aging-aware minimum mean square error combining, are presented to mitigate the SE decline caused by outdated channel state information. A low-complexity pilot assignment algorithm is proposed to suppress pilot contamination. We find that the quasi-static assumption of the channel may be unsafe for the system design of the vehicular networks even within a single transmission block period lasting from hundreds of microseconds to a few milliseconds. We observe that there exists an optimal block size Copt that maximizes area spectral efficiency. Especially, Copt can be expressed as a function of movement speed, AoD spread, and AoA spread. Numerical results are presented to validate the efficacy of the proposed schemes and highlight the importance of correct performance evaluation for practical massive MIMO system designs.
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| 8. |
- Nie, Xuefang, et al.
(författare)
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Modeling and Analysis of FeICIC in OFDMA HetNets with Limited Backhaul Capacity
- 2018
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Ingår i: 2018 10th International Conference on Wireless Communications and Signal Processing, WCSP 2018. - 9781538661208
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Konferensbidrag (refereegranskat)abstract
- Heterogeneous networks (HetNets) with dense deployment of small cells in co-channel manner are recognized as a key solution to boost network capacity. However, in addition to the severe inter-Tier interference, the non-ideal backhaul is also a bottleneck in improving the performance of HetNets. This paper proposes an analytical model of further-enhanced intercell interference coordination (FeICIC) in orthogonal frequency division multiple access (OFDMA) HetNets with limited backhaul capacity, and further evaluates the performance of HetNets. Stochastic geometry is applied to derive the expression of rate coverage in two-Tier HetNets, while modeling the BS interference in the context of OFDMA. The accuracy of analytical results is validated by Monte Carlo simulation. The superiority of FeICIC for rate coverage of HetNets is demonstrated, and the proper parameter settings are further investigated to provide design guidelines for future dense networks.
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| 9. |
- Wu, Peng, et al.
(författare)
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V2V-Assisted V2I MmWave Communication for Cooperative Perception with Information Value-Based Relay
- 2021
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Ingår i: Proceedings - IEEE Global Communications Conference, GLOBECOM. - 2334-0983 .- 2576-6813. ; 2021
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Konferensbidrag (refereegranskat)abstract
- Millimeter-wave (mmWave) vehicular communication is a key technology that enables autonomous vehicles to collaborate in environment perception, thereby improving traffic efficiency and safety to a new level. Many recent works have focused on relay-based solutions to overcome the inherent defects of mmWave, such as the severe path loss and its sensitivity to blockages. However, the selfishness of the vehicles is often ignored. Considering the application-oriented nature of vehicular communication, we propose an information value-based relay strategy for mmWave vehicle-to-infrastructure (V2I) transmission in this paper. Specifically, the vehicles are allowed to make relay decisions based on the evaluation of the value of messages from their own perspectives. To this end, a simple relay probability model based on the required awareness range is introduced. Through the use of stochastic geometry to model the vehicular network, the outage performance is analyzed and the results are validated by simulations. Impacts of both network and application related parameters on the outage performance are investigated. These preliminary results laid the foundation for the further expansion of the information value-based relay strategies to a wider range of network settings.
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| 10. |
- Xue, Kai, et al.
(författare)
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Spaceborne miniaturized UHF dual band helix antenna with a small frequency ratio
- 2021
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Ingår i: Microwave and Optical Technology Letters. - : Wiley. - 1098-2760 .- 0895-2477. ; 63:6, s. 1767-1773
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Tidskriftsartikel (refereegranskat)abstract
- This study proposes a novel miniaturized circularly polarized (CP) ultrahigh frequency (UHF) quadrifilar helix antenna for spaceborne applications. The dual-band operation is realized using four inverted-U shaped helical strips (IUSHSs) that are rotated and alternately arranged on the four faces of a hollow polyimide cuboid in a sequential rotation manner, which effectively reduces the size of the antenna. Furthermore, the four IUSHSs are connected by a cross-shape strip at the top of the antenna to control the dual resonant frequencies, resulting in a small dual-band frequency ratio. The proposed antenna is both lightweight and robust when compared with the conventional miniaturized CP antennas operating at similar bands with similar performance. In particular, its compact radiator provides effective miniaturized spaceborne solution without the need of high-dielectric coefficient materials. A device for spaceborne application that operates at 402/505 MHz is designed, fabricated, measured, and in-orbit tested with a weight of 651 g and an effective size of 0.161 × 0.161 × 0.228 λ3402MHz (λ402MHz is the wavelength at 402 MHz). The measured gain and axial ratio of the proposed antenna are better than 5.32 dBi and 2.18 dB, respectively, within 2 and 12 MHz bandwidth for the two bands. The test results proved that the methods used to design the proposed antenna are effective.
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