| 1. |
- Valecha, Neharika, et al.
(författare)
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Angle estimation using mmWave RSS measurements with enhanced multipath information
- 2024
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Ingår i: 2024 IEEE Wireless Communications and Networking Conference.
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Konferensbidrag (refereegranskat)abstract
- mmWave communication has come up as the unexplored spectrum for 5G services. With new standards for 5G NR positioning, more off-the-shelf platforms and algorithms are needed to perform indoor positioning. An object can be accurately positioned in a room either by using an angle and a delay estimate or two angle estimates or three delay estimates. We propose an algorithm to jointly estimate the angle of arrival (AoA) and angle of departure (AoD), based only on the received signal strength (RSS). We use mm-FLEX, an experimentation platform developed by IMDEA Networks Institute that can perform real-time signal processing for experimental validation of our proposed algorithm. Codebook-based beampatterns are used with a uniquely placed multi-antenna array setup to enhance the reception of multipath components and we obtain an AoA estimate per receiver thereby overcoming the line-of-sight (LoS) limitation of RSS-based localization systems. We further validate the results from measurements by emulating the setup with a simple ray-tracing approach.
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| 2. |
- Bengtsson, Erik L, et al.
(författare)
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Simulation of Multiple-Antenna Terminal Performance in Massive MIMO Systems based on Indoor Measurements
- 2020
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545. ; 69:1, s. 418-427
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Tidskriftsartikel (refereegranskat)abstract
- In massive MIMO systems the uplink pilot signalstransmitted by a terminal define the channel seen by the basestation. This gives the terminal some degree of freedom selectingan uplink pilot transmission strategy. In this paper, we investigatethe benefit of different pilot transmission strategies when increasingthe number of antennas in the terminal. Building on previouswork on a simulation framework for Multiple-antenna terminalsin 5G massive MIMO systems, this paper presents simulatedperformance results for various transmission schemes. The resultsare calibrated to reflect a real communication situation in a largeauditorium. Emulating the measurement set-up, we show that theframework can be tuned to generate channel distributions thatmatch measured data. Under generalized conditions, we performsimulations for different terminal transmission-strategies, bothrelated to single stream and multiple streams. All evaluations arebased on terminals with four antennas integrated into real SonyXperia smartphone-chassis, tuned to 3.7 GHz. The measurementsare conducted by using the Lund University Massive MIMOtestbed with its 100 antennas. The results clearly show theadvantage of increasing the antenna-count also at the terminalside in massive MIMO systems.
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| 3. |
- Sanchez, Juan, et al.
(författare)
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Optimal, Low-Complexity Beamforming for Discrete Phase Reconfigurable Intelligent Surfaces
- 2021
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Ingår i: 2021 IEEE Global Communications Conference, GLOBECOM 2021 - Proceedings. - 9781728181042
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Konferensbidrag (refereegranskat)abstract
- Reflective reconfigurable intelligent surface (RIS) technology is regarded as an innovative, cost- and power-effective solution that aims at influencing the wireless channel through controlled scattering. The technology can be realized by using metamaterials and/or resonant elements that scatter electromagnetic waves with a configurable phase shift. Most of the previous work on beamforming techniques for RIS assumes ideal hardware and, thus, continuous phase shifts. However, hardware constraints limit the phase shift resolution, manifested into the amount of discrete phase shifts that can be configured into each RIS element. This paper aims to offer a discrete phase shift beamforming algorithm for reflective RISs that targets minimization of the quantization error resulting from discretization of continuous phase shifts. The beamforming solution proves to be optimal under perfect channel knowledge for any discrete set of uniformly distributed phase shifts. The required complexity to find the optimal beamforming vector for our approach is found to be linear with the number of RIS elements, the minimum needed to obtain optimal results. Simulated behavior is validated by measurements, showing robustness against angle misalignments and distance variations.
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| 4. |
- Al-Ameri, Ali, et al.
(författare)
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A Hybrid Antenna Switching Scheme for Dynamic Channel Sounding
- 2023
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Ingår i: 2023 IEEE 97th Vehicular Technology Conference, VTC 2023-Spring - Proceedings. - 9798350311143 - 9798350311150
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Konferensbidrag (refereegranskat)abstract
- Channel sounding is essential for the development of radio systems. One flexible strategy is the switched-array-based channel sounding, where antenna elements are activated at different time instants to measure the channel spatial characteristics. Although its hardware complexity is decreased due to fewer radio-frequency (RF) chains, sequentially switching the antenna elements can result in aliasing in the joint estimation of angles and Doppler frequencies of multipath components (MPCs). Therefore, pseudo-random switching has been proposed to mitigate such aliasing and increase estimation accuracy in both angular and Doppler domains. Nevertheless, the increased Doppler resolution could cause additional post-processing complexity of parameter estimation, which is relevant when the Doppler frequencies are not of interest, e.g., for spatial channel modeling. This paper proposes an improved hybrid sequential and random switching scheme. The primary purpose is to maintain the estimation accuracy of angles of MPCs while decreasing the resolution of Doppler frequencies for minimized complexity of channel parameter estimation. A simulated-annealing algorithm is exploited to obtain an optimized switching sequence. The effectiveness of the proposed scheme is also demonstrated with a realistic antenna array.
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| 5. |
- Bartoletti, Stefania, et al.
(författare)
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Positioning and Sensing for Vehicular Safety Applications in 5G and Beyond
- 2021
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Ingår i: IEEE Communications Magazine. - 0163-6804 .- 1558-1896. ; 59:11, s. 15-21
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Tidskriftsartikel (refereegranskat)abstract
- This article presents a shared vision among stakeholders across the value chain on the use of radio positioning and sensing for road safety in the 5G ecosystem. The key enabling technologies and architectural functionalities are explored, focusing on the extremely stringent localization and communication requirements. A case study for joint radar and communication using experimental data showcases the potential of the new enablers that are paving the way toward enhanced road safety in beyond 5G scenarios.
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| 6. |
- Björsell, Joachim, 1991-
(författare)
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Predictor Antennas : Enabling channel prediction for fast-moving vehicles in wireless broadband systems
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many advanced transmission techniques utilize channel state information (CSI) at the transmitter (CSIT) to improve throughput, spectral efficiency, power efficiency, and other performance metrics. Estimating CSI accurately is important to fully benefit from many of these techniques. In situations where users travel at high speed, the channel can change rapidly, especially in small-scale fading environments. In many systems, there is also a delay between measuring CSI and using it for transmission. If the channel changes significantly during this delay, CSI becomes outdated and the benefits of advanced transmission techniques are typically negatively affected. Long-range channel prediction can be used to counteract this delay and enable advanced transmission to vehicles that travel at high velocity. Conventional prediction methods use channel extrapolation and have a limited prediction horizon that does not support high vehicular velocities for the current size of these delays. The predictor antenna concept has been shown to increase the prediction horizon by at least an order-of-magnitude. It does so by placing an antenna array on the exterior of a vehicle, in the direction of travel. The first antenna can then measure the channel at positions that the following antennas will visit later.This thesis uses channel measurements to investigate how practical aspects affect the prediction performance of predictions based on predictor antennas. It also develops a general framework that can be used to calculate the predictions in a real system. This includes addressing the causality of all the processing methods involved and adapting these methods to the design of the system and the radio environment. In a massive multiple-inputmultiple-output (MIMO) system, multi-user transmission is enabled by channel prediction and increases the sum capacity by 100% compared to 1 ms old channel estimates at a velocity of 150 km/h. This is achieved with relatively dense pilots in time. The prediction performance of the proposed framework is shown to degrade if pilots are spread further than 0.3–0.5 wavelengths in space, if spline interpolation is used to interpolate between the channel estimates.
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| 7. |
- Brihuega, Alberto, et al.
(författare)
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Digital Predistortion for Multiuser Hybrid MIMO at mmWaves
- 2020
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Ingår i: IEEE Transactions on Signal Processing. - 1941-0476 .- 1053-587X. ; 68, s. 3603-3618
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Tidskriftsartikel (refereegranskat)abstract
- Efficient mitigation of power amplifier (PA) nonlinear distortion in multi-user hybrid precoding based broadband mmWave systems is an open research problem. In this article, we carry out detailed signal and distortion modeling in broadband multi-user hybrid MIMO systems, with a bank of nonlinear PAs in each subarray, while also take the inevitable crosstalk between the antenna/PA branches into account. Building on the derived models, we adopt and describe an efficient closed-loop (CL) digital predistortion (DPD) solution that utilizes only a single-input DPD unit per transmit chain or subarray, despite crosstalk, providing thus substantial complexity-benefit compared to the state-of-the art multi-dimensional DPD solutions. We show that under spatially correlated multipath propagation, each single-input DPD unit can provide linearization towards every intended user, or more generally, towards all spatial directions where coherent propagation is taking place, and that the adopted CL DPD system is robust against crosstalk. Extensive numerical results building on practical measurement-based mmWave PA models are provided, demonstrating and verifying the excellent linearization performance of the overall DPD system in different evaluation scenarios.
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| 8. |
- Cai, Xuesong, et al.
(författare)
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A Switched Array Sounder for Dynamic Millimeter-Wave Channel Characterization: Design, Implementation and Measurements
- 2024
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X.
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Tidskriftsartikel (refereegranskat)abstract
- A prerequisite for the design and evaluation of wireless systems is the understanding of propagation channels. While abundant propagation knowledge exists for bands below 6 GHz, the same is not true for millimeter-wave frequencies. In this paper, we present the design, implementation and measurement-based verification of a re-configurable 27.5-29.5 GHz channel sounder. Based on the switched array principle, our design is capable of characterizing 128×256 dynamic double-directional dual-polarized channels with snapshot times of around 600 ms. This is in sharp contrast to measurement times on the order of tens-of-minutes of sounders by rotating horn antennas. The antenna arrays at both link ends are calibrated in an anechoic chamber with high angular sampling intervals of 3 degrees in azimuth and elevation domains, which enables de-embedding the system responses of the sounder from the propagation channels. This is complemented with a bandwidth of up to 2 GHz, i.e., nanosecond-level delay resolution. The short measurement times and stable radio frequency design facilitate real-time processing of the received wavefronts to enhance measurement dynamic range. After disclosing the sounder design and implementation, we demonstrate its capabilities by presenting a measurement campaign at 28 GHz in an indoor lab environment.
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| 9. |
- Cai, Xuesong, et al.
(författare)
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Characterizing the Small-Scale Fading for Low Altitude UAV Channels
- 2021
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Ingår i: 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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Konferensbidrag (refereegranskat)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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| 10. |
- Cai, Xuesong, et al.
(författare)
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Dynamic mmWave Channel Emulation in a Cost-Effective MPAC with Dominant-Cluster Concept
- 2021
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X.
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Tidskriftsartikel (refereegranskat)abstract
- Millimeter-Wave (mmWave) massive multiple-input multiple-output (MIMO) has been considered as a key enabler for the fifth-generation (5G) communications. It is essential to design and test mmWave 5G devices under various realisticscenarios since the radio propagation channels pose intrinsic limitations on the performance. This requires emulating realistic dynamic mmWave channels in a reproducible manner in laboratories, which is the goal of this paper. In this contribution, we first illustrate the dominant-cluster(s) concept, where thenon-dominant clusters in the mmWave channels are pruned, for mmWave 5G devices applying massive MIMO beamforming. This demonstrates the importance and necessity to accurately emulate the mmWave channels at a cluster level rather than the composite-channel level. Thus, an over-the-air (OTA) emulationstrategy for dynamic mmWave channels is proposed based on the concept of dominant-cluster(s) in a sectored multiprobe anechoic chamber (SMPAC). The key design parameters including the probe number and the angular spacing of probes are investigated through comprehensive simulations. A cost-effective switch circuit is also designed for this purpose and validated in the simulation. Furthermore, a dynamic mmWave channel measured in an indoor scenario at 28-30 GHz is presented, where the proposed emulation strategy is also validated by reproducing the measured reality.
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