| 1. |
- Apelfröjd, Rikke, 1986-, et al.
(författare)
-
Kalman Smoothing for Irregular Pilot Patterns : A Case Study for Predictor Antennas in TDD Systems
- 2018
-
Ingår i: 2018 IEEE 29TH ANNUAL INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS (PIMRC). - : IEEE. - 9781538660096
-
Konferensbidrag (refereegranskat)abstract
- For future large-scale multi-antenna systems, channel orthogonal downlink pilots are not feasible due to extensive overhead requirements. Instead, channel reciprocity can be utilized in time division duplex (TDD) systems so that the downlink channel estimates can be based on pilots transmitted during the uplink. User mobility affects the reciprocity and makes the channel state information outdated for high velocities and/or long downlink subframe durations. Channel extrapolation, e.g. through Kalman prediction, can reduce the problem but is also limited by high velocities and long downlink subframes. An alternative solution has been proposed where channel predictions are made with the help of an extra antenna, e.g. on the roof of a car, so called predictor antenna, with the primary objective to measure the channel at a position that is later encountered by the rearward antenna(s). The predictor antenna is not directly limited by high velocities and allows the channel in the downlinks to be interpolated rather than extrapolated. One remaining challenge here is to obtain a good interpolation of the uplink channel estimate, since a sequence of uplink reference signals (pilots) will be interrupted by downlink subframes. We here evaluate a Kalman smoothing estimate of the downlink channels and compare it to a cubic spline interpolation. These results are also compared to results where uplink channels are estimated through Kalman filters and predictors. Results are based on measured channels and show that with Kalman smoothing, predictor antennas can enable accurate channel estimates for a longer downlink period at vehicular velocities. The gaps in the uplink pilot stream, due to downlink subframes, can have durations that correspond to a vehicle movement of up to 0.75 carrier wavelengths in space, for Rayleigh-like non-line-of-sight fading.
|
|
| 2. |
- Björsell, Joachim, 1991-, et al.
(författare)
-
Channel Interpolation of Fading Channels and the Pilot Density Required for Predictor Antennas
-
Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359.
-
Tidskriftsartikel (refereegranskat)abstract
- Predictor antennas (PAs) are a potential solution to severe channel aging that can occur at high vehicular velocities in non line-of-sight (NLOS) environments. Channel aging reduces the performance of many advanced communication schemes based on channel state information at the transmitter (CSIT). Although PAs have been shown to work in combination with dense pilots in time and space, prediction performance can be reduced when channel estimates are sparse. This paper answers how densely pilots must be placed for PAs to be feasible when performing basic interpolation between channel estimates. This is important, especially for establishing upper limits on the length of the downlink (DL) frames required in a time-division duplex (TDD) system with PAs. First, nearest-neighbor, linear, and spline interpolation are analyzed when applied to stochastic radio channels. A theoretical expression is derived for the power of the expected interpolation error for any interpolation method that can be expressed as a linear function of a set of measured values. The interpolation methods are evaluated on three theoretical channels with Rayleigh, flat, and Rician fading, and on two sets of channel measurements. For a given requirement on interpolation normalized mean-squared error (NMSE), a minimum pilot density is extracted, both for theoretical channels and measured channels. The interpolation techniques are used to evaluate the PA channel prediction for different distances between pilots. The results indicate that linear and spline interpolation can be used with down to five and three samples per wavelength, respectively, without affecting the PA-based prediction NMSE. At two samples per wavelength, the prediction NMSE is still at a level that can be useful for precoding design in massive multiple-input multiple-output (M-MIMO) systems. These results can be used to adapt the uplink/downlink frame rate in TDD to the speed of the terminals, if technically possible.
|
|
| 3. |
- Björsell, Joachim, 1991-, et al.
(författare)
-
Enabling Multi-User M-MIMO for High-Mobility Users with Predictor Antennas : A Deep Analysis Based on Experimental NLOS Measurements
- 2022
-
Ingår i: IEEE Transactions on Vehicular Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9545 .- 1939-9359. ; 71:7, s. 7456-7471
-
Tidskriftsartikel (refereegranskat)abstract
- Predictor antenna channel measurements from a 64-antenna base station are used to investigate the effects of channel aging on the precoder design for high-mobility users in a non-line-of-sight (NLOS) massive multiple-input multiple-output (M-MIMO) environment. The effects are evaluated in terms of received downlink (DL) signal-to-interference-and-noise ratio (SINR) and the corresponding ergodic capacity bound. A simulated velocity of 150 km/h is used with a carrier frequency of 2.18 GHz. Maximum ratio (MR) and a codebook-based precoders are used to evaluate single-user transmission and zero-forcing (ZF), regularized zero-forcing (RZF), and minimum mean-squared error (MMSE) precoders are used to evaluate multi-user transmission with up to nine active users in a cell. Furthermore, predictor antenna predictions are evaluated as a mean of combating channel aging. It is also investigated how the predictor antenna can be used during data reception. Simulations show that outdated channel estimates significantly reduce the SINR and consequently the capacity for all investigated transmission techniques. Basic predictor antenna predictions outperform the use of outdated channel estimates for delays larger than 0.6 ms. In single-user transmission, channel prediction can improve the capacity by 6–14%. The gain from multi-user transmission typically disappears when using outdated channel estimates older than 1 ms. In contrast, the use of predictor antennas enables multi-user MIMO for these high-mobility users, which is demonstrated to increase the capacity bound by 100% compared to 1 ms old channel estimates.
|
|
| 4. |
- D’Amico, Valeria, et al.
(författare)
-
EU FP7 INFSO-ICT-247223 ARTIST4G, D1.2 Innovative advanced signal processing algorithms for interference avoidance
- 2010
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This document provides an overview of the proposed innovations and activities in Task 1.1 of Work Package 1 (WP1) of the ARTIST4G project, related to interference avoidance. Focus is on the technical approaches applicable at the physical layer, which are grouped into four different classes of innovations related to single-cell multi-user MIMO schemes, multi-cell multi-user MIMOschemes, advanced 3D beamforming and enabling functionalities. Descriptions of the proposed innovations are given including basic ideas, potential of performance, simulation results, realization options and possible implementation restrictions.
|
|
| 5. |
- Guo, Hao, 1992, et al.
(författare)
-
Electromagnetic Field Exposure Avoidance thanks to Non-Intended User Equipment and RIS
- 2022
-
Ingår i: GLOBECOM - IEEE Global Telecommunications Conference. - 9781665459754 ; , s. 1537-1542
-
Konferensbidrag (refereegranskat)abstract
- On the one hand, there is a growing demand for high throughput which can be satisfied thanks to the deployment of new networks using massive multiple-input multiple-output (MIMO) and beamforming. On the other hand, in some countries or cities, there is a demand for arbitrarily low electromagnetic field exposure (EMFE) of people not concerned by the ongoing communication, which slows down the deployment of new networks. Recently, it has been proposed to take the opportunity, when designing the future 6th generation (6G), to offer, in addition to higher throughput, a new type of service: arbitrarily low EMFE. Recent works have shown that a reconfigurable intelligent surface (RIS), jointly optimized with the base station (BS) beamforming can improve the received throughput at the desired location whilst reducing EMFE everywhere. In this paper, we introduce a new concept of a non-intended user (NIU). An NIU is a user of the network who requests low EMFE when he/she is not downloading/uploading data. An NIU lets his/her device, called NIU equipment (NIUE), exchange some control signaling and pilots with the network, to help the network avoid exposing NIU to waves that are transporting data for another user of the network: the intended user (IU), whose device is called IU equipment (IUE). Specifically, we propose several new schemes to maximize the IU throughput under an EMFE constraint at the NIU (in practice, an interference constraint at the NIUE). Several propagation scenarios are investigated. Analytical and numerical results show that proper power allocation and beam optimization can remarkably boost the EMFE-constrained system's performance with limited complexity and channel information.
|
|
| 6. |
- Guo, Hao, 1992, et al.
(författare)
-
Predictor Antenna: A Technique to Boost the Performance of Moving Relays
- 2021
-
Ingår i: IEEE Communications Magazine. - 0163-6804 .- 1558-1896. ; 59:7, s. 80-86
-
Tidskriftsartikel (refereegranskat)abstract
- In future wireless systems, a large number of users may access the networks via moving relays (MRs) installed on top of vehicles. One of the main challenges of MRs is rapid channel variation which may make channel estimation, and its following procedures, difficult. To address these issues, various schemes are designed, among which predictor antenna (PA) is a candidate. The PA setup refers to a system with two (sets of) antennas on top of a vehicle, where the PA(s) positioned in front of the vehicle is(are) utilized to predict the channel state information required for data transmission to the receive antennas (RAs) aligned behind the PA. In this paper, we introduce the concept and the potentials of PA systems. Moreover, summarizing the field trials for PAs and the 3GPP attempts on (moving) relays, we compare the performance of different PA and non-PA methods for vehicle communications in both urban and rural areas with the PA setup backhauled through terrestrial or satellite technology, respectively. As we show, with typical parameter settings and vehicle speeds, a single-antenna PA-assisted setup can boost the backhaul throughput of MRs, compared to state-of-the-art open-loop schemes, by up to 50%.
|
|
| 7. |
- Li, Zexian, et al.
(författare)
-
5GCAR project D3.1 Intermediate 5G V2X Radio
- 2018
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The 5GCAR project aims to contribute to 5G network design, and specifically to design V2X technology components for V2X use case classes identified in the project. The requirements on reliability, latency, data rates, spectral and energy efficiency cannot be fully supported by today’s wireless networks and V2X solutions and call for novel and innovative approaches, including the design of a new radio interface.
|
|
| 8. |
|
|
| 9. |
- Phan-Huy, Dinh-Thuy, et al.
(författare)
-
Making 5G Adaptive Antennas Work for Very Fast Moving Vehicles
- 2015
-
Ingår i: IEEE Intelligent Transportation Systems Magazine. - 1939-1390 .- 1941-1197. ; 7:2, s. 71-84
-
Tidskriftsartikel (refereegranskat)abstract
- Wireless systems increasingly rely on the accurate knowledge at the transmitter side of the transmitter-to-receiver propagation channel, to optimize the transmission adaptively. Some candidate techniques for 5th generation networks need the channel knowledge for tens of antennas to perform adaptive beamforming from the base station towards the mobile terminal. These techniques reduce the radiated power and the energy consumption of the base station. Unfortunately, they fail to deliver the targeted quality of service to fast moving terminals such as connected vehicles. Indeed, due to the movement of the vehicle during the delay between channel estimation and data transmission, the channel estimate is outdated. In this paper, we propose three new schemes that exploit the "Predictor Antenna" concept. This recent concept is based on the observation that the position occupied by one antenna at the front of the vehicle, will later on be occupied by another antenna at the back. Estimating the channel of the "front" antenna can therefore later help beamforming towards the "back" antenna. Simulations show that our proposed schemes make adaptive beamforming work for vehicles moving at speeds up to 300 km/h.
|
|
| 10. |
- Phan-Huy, Dinh-Thuy, et al.
(författare)
-
Predictor Antenna for Robust Non Reciprocity based Beamforming at High Speed
- 2021
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we show for the first time, based on channels from real urban environments, that although non reciprocity based beamformers (such as Discrete Fourier Transform beamforming) are more robust to high velocity than reciprocity based beamformers (such as maximum ratio transmission), they can still benefit from predictor antenna based channel prediction, in non line-of-sight propagation environments, due to the impact of small-scale fading within beams. The evaluation was conducted with channels from a massive multiple input multiple output antenna with 64 elements.
|
|
