The Experts below are selected from a list of 39 Experts worldwide ranked by ideXlab platform
Mikko Valkama - One of the best experts on this subject based on the ideXlab platform.
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GLOBECOM Workshops - Impact of Power Amplifier Nonlinearities in Multi-User Massive MIMO Downlink
2015 IEEE Globecom Workshops (GC Wkshps), 2015Co-Authors: Yaning Zou, Orod Raeesi, Lauri Antilla, Aki Hakkarainen, Joao Vieira, Fredrik Tufvesson, Qimei Cui, Mikko ValkamaAbstract:In this paper, we investigate the impact of power amplifier (PA) nonlinear distortion in pre-coded multi-user large antenna or massive MIMO Downlink systems. First, detailed Signal and sys-tem models are derived for the received Signal at single-antenna user equipment (UE) under channel-aware linear precoding in the base-station combined with behavioral models for the individ-ual PA units, covering both single-carrier and multi-carrier modulation schemes. Based on the derived models, it is shown that the PA induced nonlinear distortion can also combine coherently in the channel, depending on the relative differences between the phase characteristics of the different PA units and the corresponding distortion terms. Furthermore, it is also shown that the impact of nonlinear PAs and the resulting linear and nonlinear multi-user interference, quantified in terms of the received Signal-to- interference-plus-noise ratio (SINR), is largely dependent on the effective or observable linear gain in the UE receiver demodulation stage. By observing only the instantaneous direct linear gain, the PA induced nonlinear distortion has a substantial impact on the effective SINR, even if very large number of TX antennas is adopted relative to the number of spatially multiplexed UEs. On the other hand, if the statistically averaged linear gain can be observed, the impact of nonlinear PAs is far less severe. These findings give thus new insight, not only to the core impact of nonlinear PAs in massive MIMO systems but also to the Downlink Reference Signal design, radio frame design and radio resource management in time, in order to facilitate the estimation of the statistically averaged linear gains in the receivers within the scheduled transmission and processing blocks.
Yaning Zou - One of the best experts on this subject based on the ideXlab platform.
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GLOBECOM Workshops - Impact of Power Amplifier Nonlinearities in Multi-User Massive MIMO Downlink
2015 IEEE Globecom Workshops (GC Wkshps), 2015Co-Authors: Yaning Zou, Orod Raeesi, Lauri Antilla, Aki Hakkarainen, Joao Vieira, Fredrik Tufvesson, Qimei Cui, Mikko ValkamaAbstract:In this paper, we investigate the impact of power amplifier (PA) nonlinear distortion in pre-coded multi-user large antenna or massive MIMO Downlink systems. First, detailed Signal and sys-tem models are derived for the received Signal at single-antenna user equipment (UE) under channel-aware linear precoding in the base-station combined with behavioral models for the individ-ual PA units, covering both single-carrier and multi-carrier modulation schemes. Based on the derived models, it is shown that the PA induced nonlinear distortion can also combine coherently in the channel, depending on the relative differences between the phase characteristics of the different PA units and the corresponding distortion terms. Furthermore, it is also shown that the impact of nonlinear PAs and the resulting linear and nonlinear multi-user interference, quantified in terms of the received Signal-to- interference-plus-noise ratio (SINR), is largely dependent on the effective or observable linear gain in the UE receiver demodulation stage. By observing only the instantaneous direct linear gain, the PA induced nonlinear distortion has a substantial impact on the effective SINR, even if very large number of TX antennas is adopted relative to the number of spatially multiplexed UEs. On the other hand, if the statistically averaged linear gain can be observed, the impact of nonlinear PAs is far less severe. These findings give thus new insight, not only to the core impact of nonlinear PAs in massive MIMO systems but also to the Downlink Reference Signal design, radio frame design and radio resource management in time, in order to facilitate the estimation of the statistically averaged linear gains in the receivers within the scheduled transmission and processing blocks.
Mikael Sternad - One of the best experts on this subject based on the ideXlab platform.
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Low-Overhead Cyclic Reference Signals for Channel Estimation in FDD Massive MIMO
IEEE Transactions on Communications, 2019Co-Authors: Rikke Apelfrojd, Wolfgang Zirwas, Mikael SternadAbstract:Massive multiple input multiple output (MIMO) transmission and coordinated multipoint transmission are candidate technologies for increasing data throughput in evolving 5G standards. Frequency division duplex (FDD) is likely to remain predominant in large parts of the spectrum below 6 GHz for future 5G systems. Therefore, it is important to estimate the Downlink FDD channels from a very large number of antennas, while avoiding an excessive Downlink Reference Signal overhead. We here propose and investigate a three part solution. First, massive MIMO Downlinks use a fixed grid of beams. For each user, only a subset of beams will then be relevant, and require estimation. Second, sets of coded Reference Signal sequences, with cyclic patterns over time, are used. Third, each terminal estimates its most relevant channels. We here propose and compare a linear mean square estimation and a Kalman estimation. Both utilize frequency and antenna correlation, and the later also utilizes temporal correlation. In extensive simulations, this scheme provides channel estimates that lead to an insignificant beamforming performance degradation as compared to full channel knowledge. The cyclic pattern of coded Reference Signals is found to be important for reliable channel estimation, without having to adjust the Reference Signals to specific users.
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PIMRC - Key solutions for a massive MIMO FDD system
2017 IEEE 28th Annual International Symposium on Personal Indoor and Mobile Radio Communications (PIMRC), 2017Co-Authors: Wolfgang Zirwas, Mikael Sternad, Rikke ApelfrojdAbstract:The ongoing standardization within 3GPP for the so called new radio (NR) system has identified massive multiple-input multiple output (MIMO) transmission, also called full dimension MIMO, as one of the main contributors to higher spectral efficiency for the mobile broadband case. In particular for radio frequencies below 6 GHz, channel estimation has to be supported in frequency division duplex (FDD) as well as time division duplex (TDD) operation. In TDD we may obtain Downlink channels by estimating uplink channels, assuming reciprocity. For FDD, codebook based design as well as some type of explicit feedback is under discussion. Separately, there are also ongoing discussions of the question if massive MIMO in combination with FDD is a reasonable choice at all. Here we highlight some of our recent results obtained within several 5G research projects. To our understanding they overcome some of the inherent limitations of massive MIMO for FDD. As indicated by simulations, the resulting concept enables a grid of beam (GoB) and Reference Signal design with a reasonable Downlink Reference Signal overhead of around 10 percent, together with reasonable feedback overhead of several hundred kbit/s per UE. Such a design attains around 90 percent of the massive MIMO system performance with ideal channel state information.
Qimei Cui - One of the best experts on this subject based on the ideXlab platform.
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GLOBECOM Workshops - Impact of Power Amplifier Nonlinearities in Multi-User Massive MIMO Downlink
2015 IEEE Globecom Workshops (GC Wkshps), 2015Co-Authors: Yaning Zou, Orod Raeesi, Lauri Antilla, Aki Hakkarainen, Joao Vieira, Fredrik Tufvesson, Qimei Cui, Mikko ValkamaAbstract:In this paper, we investigate the impact of power amplifier (PA) nonlinear distortion in pre-coded multi-user large antenna or massive MIMO Downlink systems. First, detailed Signal and sys-tem models are derived for the received Signal at single-antenna user equipment (UE) under channel-aware linear precoding in the base-station combined with behavioral models for the individ-ual PA units, covering both single-carrier and multi-carrier modulation schemes. Based on the derived models, it is shown that the PA induced nonlinear distortion can also combine coherently in the channel, depending on the relative differences between the phase characteristics of the different PA units and the corresponding distortion terms. Furthermore, it is also shown that the impact of nonlinear PAs and the resulting linear and nonlinear multi-user interference, quantified in terms of the received Signal-to- interference-plus-noise ratio (SINR), is largely dependent on the effective or observable linear gain in the UE receiver demodulation stage. By observing only the instantaneous direct linear gain, the PA induced nonlinear distortion has a substantial impact on the effective SINR, even if very large number of TX antennas is adopted relative to the number of spatially multiplexed UEs. On the other hand, if the statistically averaged linear gain can be observed, the impact of nonlinear PAs is far less severe. These findings give thus new insight, not only to the core impact of nonlinear PAs in massive MIMO systems but also to the Downlink Reference Signal design, radio frame design and radio resource management in time, in order to facilitate the estimation of the statistically averaged linear gains in the receivers within the scheduled transmission and processing blocks.
Fredrik Tufvesson - One of the best experts on this subject based on the ideXlab platform.
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GLOBECOM Workshops - Impact of Power Amplifier Nonlinearities in Multi-User Massive MIMO Downlink
2015 IEEE Globecom Workshops (GC Wkshps), 2015Co-Authors: Yaning Zou, Orod Raeesi, Lauri Antilla, Aki Hakkarainen, Joao Vieira, Fredrik Tufvesson, Qimei Cui, Mikko ValkamaAbstract:In this paper, we investigate the impact of power amplifier (PA) nonlinear distortion in pre-coded multi-user large antenna or massive MIMO Downlink systems. First, detailed Signal and sys-tem models are derived for the received Signal at single-antenna user equipment (UE) under channel-aware linear precoding in the base-station combined with behavioral models for the individ-ual PA units, covering both single-carrier and multi-carrier modulation schemes. Based on the derived models, it is shown that the PA induced nonlinear distortion can also combine coherently in the channel, depending on the relative differences between the phase characteristics of the different PA units and the corresponding distortion terms. Furthermore, it is also shown that the impact of nonlinear PAs and the resulting linear and nonlinear multi-user interference, quantified in terms of the received Signal-to- interference-plus-noise ratio (SINR), is largely dependent on the effective or observable linear gain in the UE receiver demodulation stage. By observing only the instantaneous direct linear gain, the PA induced nonlinear distortion has a substantial impact on the effective SINR, even if very large number of TX antennas is adopted relative to the number of spatially multiplexed UEs. On the other hand, if the statistically averaged linear gain can be observed, the impact of nonlinear PAs is far less severe. These findings give thus new insight, not only to the core impact of nonlinear PAs in massive MIMO systems but also to the Downlink Reference Signal design, radio frame design and radio resource management in time, in order to facilitate the estimation of the statistically averaged linear gains in the receivers within the scheduled transmission and processing blocks.