| 1. |
- Amani, Navid, 1985, et al.
(författare)
-
Array Configuration Effect on the Spatial Correlation of MU-MIMO Channels in NLoS Environments
- 2020
-
Ingår i: 14th European Conference on Antennas and Propagation, EuCAP 2020. ; 2020:March
-
Konferensbidrag (refereegranskat)abstract
- In this paper, three different base-station antenna (BSA) configurations are compared in terms of inter-user spatial correlation in a two dimensional (2D) non-line-of-sight (NLoS) environment. The three configurations are: (i) a regular uniform linear array (ULA); (ii) a periodic sparse array; and (iii) an aperiodic sparse array. Electromagnetic modeling of the NLoS channel is proposed where scatterers are considered as resonant dipoles confined in clusters of scatterers (CoSs). While the probability of facing highly correlated user-equipments (UEs) in a multi-user multiple-input multiple-output (MU-MIMO) system is decreasing as the richness of mutipath increases, the sparsity (increased inter-element spacing) is seen to be capable of reducing this probability as well. This is due to the larger spatial variations experienced by the sparse array. Moreover, the results show that further improvement can be achieved by deploying an aperiodic distribution of antenna elements into the sparse antenna aperture.
|
|
| 2. |
- Meyer, E., et al.
(författare)
-
The state of the art in beyond 5G distributed massive multiple-input multiple-output communication system solutions
- 2022
-
Ingår i: Open Research Europe. - : F1000 Research Ltd. - 2732-5121. ; 2
-
Forskningsöversikt (refereegranskat)abstract
- Beyond fifth generation (5G) communication systems aim towards data rates in the tera bits per second range, with improved and flexible coverage options, introducing many new technological challenges in the fields of network architecture, signal pro- cessing, and radio frequency front-ends. One option is to move towards cell-free, or distributed massive Multiple-Input Multiple-Output (MIMO) network architectures and highly integrated front-end solutions. This paper presents an outlook on be- yond 5G distributed massive MIMO communication systems, the signal processing, characterisation and simulation challenges, and an overview of the state of the art in millimetre wave antennas and electronics.
|
|
| 3. |
|
|
| 4. |
- Athley, F., et al.
(författare)
-
Analysis of Massive MIMO with hardware impairments and different channel models
- 2015
-
Ingår i: 9th European Conference on Antennas and Propagation, EuCAP 2015, Lisbon, Portugal, 13-17 May 2015. - 9788890701856
-
Konferensbidrag (refereegranskat)abstract
- Massive Multiple-Input Multiple-Output (MIMO) is foreseen to be one of the main technology components in next generation cellular communications (5G). In this paper, fundamental limits on the performance of downlink massive MIMO systems are investigated by means of simulations and analytical analysis. Signal-to-noise-and-interference ratio (SINR) and sum rate for a single-cell scenario multi-user MIMO are analyzed for different array sizes, channel models, and precoding schemes. The impact of hardware impairments on performance is also investigated. Simple approximations are derived that show explicitly how the number of antennas, number of served users, transmit power, and magnitude of hardware impairments affect performance.
|
|
| 5. |
- Augutis, Kristin, et al.
(författare)
-
Cerebrospinal fluid biomarkers of β-amyloid metabolism in multiple sclerosis.
- 2013
-
Ingår i: Multiple sclerosis (Houndmills, Basingstoke, England). - : SAGE Publications. - 1477-0970 .- 1352-4585. ; 19:5, s. 543-52
-
Tidskriftsartikel (refereegranskat)abstract
- Amyloid precursor protein (APP) and amyloid β (Aβ) peptides are intensely studied in neuroscience and their cerebrospinal fluid (CSF) measurements may be used to track the metabolic pathways of APP in vivo. Reduced CSF levels of Aβ and soluble APP (sAPP) fragments are reported in inflammatory diseases, including multiple sclerosis (MS); but in MS, the precise pathway of APP metabolism and whether it can be affected by disease-modifying treatments remains unclear.
|
|
| 6. |
|
|
| 7. |
- Chen, Hui, 1992, et al.
(författare)
-
MCRB-based Performance Analysis of 6G Localization under Hardware Impairments
- 2022
-
Ingår i: 2022 IEEE International Conference on Communications Workshops, ICC Workshops 2022. ; , s. 115-120
-
Konferensbidrag (refereegranskat)abstract
- Location information is expected to be the key to meeting the needs of communication and context-aware services in 6G systems. User localization is achieved based on delay and/or angle estimation using uplink or downlink pilot signals. However, hardware impairments (HWIs) distort the signals at both the transmitter and receiver sides and thus affect the localization performance. While this impact can be ignored at lower frequencies where HWIs are less severe, modeling and analysis efforts are needed for 6G to evaluate the localization degradation due to HWIs. In this work, we model various types of impairments and conduct a misspecified Cramér-Rao bound analysis to evaluate the HWI-induced performance loss. Simulation results with different types of HWIs show that each HWI leads to a different level of degradation in angle and delay estimation performance.
|
|
| 8. |
- Devarakonda, Sravani, et al.
(författare)
-
Low-grade intestinal inflammation two decades after pelvic radiotherapy.
- 2023
-
Ingår i: EBioMedicine. - 2352-3964. ; 94
-
Tidskriftsartikel (refereegranskat)abstract
- Radiotherapy is effective in the treatment of cancer but also causes damage to non-cancerous tissue. Pelvic radiotherapy may produce chronic and debilitating bowel symptoms, yet the underlying pathophysiology is still undefined. Most notably, although pelvic radiotherapy causes an acute intestinal inflammation there is no consensus on whether the late-phase pathophysiology contains an inflammatory component or not. To address this knowledge gap, we examined the potential presence of a chronic inflammation in mucosal biopsies from irradiated pelvic cancer survivors.We biopsied 24 cancer survivors two to 20 years after pelvic radiotherapy, and four non-irradiated controls. Using tandem mass tag (TMT) mass spectrometry and mRNA sequencing (mRNA-seq), we charted proteomic and transcriptomic profiles of the mucosal tissue previously exposed to a high or a low/no dose of radiation. Changes in the immune cell populations were determined with flow cytometry. The integrity of the protective mucus layers were determined by permeability analysis and 16S rRNA bacterial detection.942 proteins were differentially expressed in mucosa previously exposed to a high radiation dose compared to a low radiation dose. The data suggested a chronic low-grade inflammation with neutrophil activity, which was confirmed by mRNA-seq and flow cytometry and further supported by findings of a weakened mucus barrier with bacterial infiltration.Our results challenge the idea that pelvic radiotherapy causes an acute intestinal inflammation that either heals or turns fibrotic without progression to chronic inflammation. This provides a rationale for exploring novel strategies to mitigate chronic bowel symptoms in pelvic cancer survivors.This study was supported by the King Gustav V Jubilee Clinic Cancer Foundation (CB), The Adlerbertska Research Foundation (CB), The Swedish Cancer Society (GS), The Swedish State under the ALF agreement (GS and CB), Mary von Sydow's foundation (MA and VP).
|
|
| 9. |
|
|
| 10. |
|
|
| 11. |
|
|
| 12. |
|
|
| 13. |
- Fager, Christian, 1974, et al.
(författare)
-
Voltage/Current mode class D amplifiers and their applications
- 2008
-
Ingår i: Proc. IEEE Radio Wireless Symposium (Workshop: Transmitter Design for High Power Efficiency: The path from device to advanced system architectures).
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 14. |
- Farsaei, A., et al.
(författare)
-
On the Outage Performance of Line-Of-Sight Massive MIMO with a Fixed-Length Uniform Linear Sparse Array
- 2019
-
Ingår i: Proceedings of the 2019 9th IEEE-APS Topical Conference on Antennas and Propagation in Wireless Communications, APWC 2019. ; , s. 345-348
-
Konferensbidrag (refereegranskat)abstract
- Increasing the inter-element spacing of a uniform linear sparse array results in reducing the mutual coupling and simplifying the heat dissipation control of the array. However, increasing the inter-element spacing may result in the appearance of grating lobes in the field-of-view (FoV). In this paper, 0.05-outage capacity is used as the performance metric to optimize the inter-element spacing for a given array size in line-of-sight scenarios. For the case of two users, we propose to increase the inter-element spacing as long as the 0.05-outage capacity does not reduce more than 1% compared to the capacity achieved when the two users have orthogonal channel vectors. Radiated power at the base station is adjusted to have the same effective isotropic radiated power for different arrays. Simulation results for an array size of 40λ show that for FoVs of 60° to 120°, the inter-element spacing can be increased from 0.5λ to more than 1.14λ.
|
|
| 15. |
- Gustavsson, Ulf, 1975, et al.
(författare)
-
A composite amplifier, a radio terminal and a method for improving the efficiency of the composite amplifier
- 2009
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The present invention relates to a composite amplifier, a radio terminal including such composite amplifier and to a method for improving the efficiency of such composite amplifier in particular. The composite amplifier according to embodiments of the present invention is arranged to be connected to an output combiner network and to a load. The output combiner network comprising at least one dynamically tuneable reactance. The instantaneous efficiency of the composite amplifier is increased by tuning the impedances/admittances seen by each of said at least two power amplifiers. The amplifiers being differently driven and they may further be part of a Chireix outphasing system or a pair of a Doherty amplifier.
|
|
| 16. |
- Gustavsson, Ulf, 1975, et al.
(författare)
-
A general method for passband quantization noise suppression in pulsed transmitter architectures.
- 2009
-
Ingår i: Microwave Symposium Digest, 2009. MTT '09. IEEE MTT-S International.. - 0149-645X. ; , s. 1529 - 1532
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we describe a novel method for selective bandpass cancellation of the quantization-noise that occurs in pulsed transmitter architectures, where the signal is partially or completely quantized. A carrier bursting transmitter architecture, where the amplitude part is quantized and then recombined with a phase-modulated RF carrier, is used as a general example to demonstrate the principles of the method proposed. Measurements on a high efficiency 10 W LDMOS PA working at 1 GHz are used to verify the theoretical results.
|
|
| 17. |
- Gustavsson, Ulf, 1975, et al.
(författare)
-
An RF Carrier Bursting System using Partial Quantization Noise Cancellation
- 2012
-
Ingår i: IEEE Transactions on Circuits and Systems I: Regular Papers. - 1549-8328 .- 1558-0806. ; 59:3, s. 515-528
-
Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a novel method for bandpass cancellation of the quantization noise occurring in high efficiency, envelope pulsed transmitter architectures - or carrier bursting. An equivalent complex baseband model of the proposed system, including the Sigma Delta-modulator and cancellation signal generation, is developed. Analysis of the baseband model is performed, leading to analytical expressions of the power amplifier drain efficiency, assuming the use of an ideal class B power amplifier. These expressions are further used to study the impact of key system parameters, i.e. the compensation signal variance and clipping probability, on the class~B power amplifier drain efficiency and signal-to-noise ratio.The paper concludes with simulations followed by practical measurements in order to validate the functionality of the method and to evaluate the performance-trend predictions made by the theoretical framework in terms of efficiency and spectral purity.
|
|
| 18. |
|
|
| 19. |
- Gustavsson, Ulf, 1975, et al.
(författare)
-
Efficient amplifer operation
- 2023
-
Patent (övrigt vetenskapligt/konstnärligt)abstract
- Efficient amplifier operation. In one aspect, there is a radio transceiver device. The radio transceiver device includes a distorting unit configured to receive an input signal and distort the received input signal, thereby producing a distorted input signal. The radio transceiver device further includes a limiter configured to receive the distorted input signal and produce a limited signal based on the received distorted input signal. The radio transceiver device further includes a power amplifier configured to receive the limited signal and amplify the limited signal, thereby producing an amplified limited signal.
|
|
| 20. |
- Gustavsson, Ulf, 1975
(författare)
-
From Noise-Shaped Coding to Energy Efficiency - One bit at the time
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Three parameters that drive the research and development of future RF transmitter technologies for high speed wireless communication today are energy efficiency, flexibility and reduction of the physical footprint. This thesis treats the use of single-bit quantization in conjunction with a method called Noise-Shaped Coding (NSC), as an enabler for these parameters, foremost in terms of energy efficiency.The first part of the thesis provides a short introduction to the common Radio Frequency Power Amplifier (RFPA) power efficiency enhancement techniques. The pulsed RF transmitter is introduced in which the RFPA is used as a switch, modulated by a single-bit quantized signal which allows it to operate solely at its two most efficient states.The second part of the thesis provides an introduction to the concept of NSC and the underlying idea of how high signal quality can be achieved with one bit quantization of the signal amplitude. A particular method of implementing NSC, namely the ΣΔ-modulator, is introduced and some common methods for design and analysis are discussed. An optimization-based approach to ΣΔ-modulator design is proposed and benchmarked against conventional methods in terms of its ability to shape the power spectral density of the quantization noise according to a given reconstruction filter response, minimizing the reconstructed error metric.The third and final part of the thesis focuses specifically on the application of ΣΔ-modulation in a pulsed RF transmitter context. The concepts of band-pass and baseband ΣΔ-modulation are introduced. A few important challenges related to the use of ΣΔ-modulation in a pulsed RF-transmitter context are identified. A ΣΔ-modulator topology which handles a complex input signal is investigated in great detail and advantages compared to conventional methods for using ΣΔ-modulation are unveiled by means of theoretical analysis and simulations. A method for suppressing the quantization noise within a frequency band surrounding the modulated RF carrier, enabling the use of more wideband reconstruction filter and moderate pulse-rates, is also presented. A detailed theoretical analysis reveals how optimized Noise-Shaped Coding, as provided by the optimization method introduced in the second part, can be deployed in order to improve the system performance. Finally, the method is validated by experimental measurements on two different high efficiency RFPAs at 1 and 3.5 GHz respectively, showing promising results.
|
|
| 21. |
- Gustavsson, Ulf, 1975, et al.
(författare)
-
Implementation challenges and opportunities in beyond-5G and 6G communication
- 2021
-
Ingår i: IEEE Journal of Microwaves. - 2692-8388. ; 1:1, s. 86-100
-
Tidskriftsartikel (refereegranskat)abstract
- As 5G New Radio (NR) is being rolled out, research effort is being focused on the evolution of what is to come in the post-5G era. In order to meet the diverse requirements of future wireless communication in terms of increased capacity and reduced latency, technologies such as distributed massive Multiple-Input Multiple-Output (MIMO), sub-millimeter wave and Tera-hertz spectrum become technology components of interest. Furthermore, to meet the demands on connectivity anywhere at anytime, non-terrestrial satellite networks will be needed, which brings about challenges both in terms of implementation as well as deployment. Finally, scaling up massive Internet-of-Things (IoT), energy harvesting and Simultaneous Wireless Information and Power Transfer (SWIPT) is foreseen to become important enablers when deploying a large amount of small, low-power radios. In this paper, we will discuss some of the important opportunities these technologies bring, and the challenges faced by the microwave and wireless communication communities.
|
|
| 22. |
- Gustavsson, Ulf, 1975
(författare)
-
Improved amplifying device
- 2009
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The present invention concerns a composite amplifier and a method for controlling the amplitude of a composite amplifier in a node of a wireless communication system. The composite amplifier comprises a first amplifier and a second amplifier that are arranged to be connected via an output combiner network to a load. The method comprises decomposing an input signal into a first signal component and a second signal component. Further, the method comprises differentiating the amplitude on the first signal component from the amplitude on the second signal component. the differentiation is made such that the aggregated efficiency of the composite amplifier is increased. The present invention also oncerns a radio transmission device comprising a composite amplifier.
|
|
| 23. |
- Gustavsson, Ulf, 1975, et al.
(författare)
-
Linearization of non-linear amplifiers
- 2023
-
Patent (övrigt vetenskapligt/konstnärligt)abstract
- A linearization device (380) is disclosed, which is configured to determine pre-distortion parameters associated with a plurality of non-linear amplifiers (331, 332, 333, 334), each associated with a non-linear amplifier characteristic. The linearization device comprises determination circuitry (383), a first port (381) and a second port (382). The first port is configured to receive a plurality of channel coefficients indicative of channel characteristics of a plurality of communication paths (391, 392, 393, 394) between the plurality of non-linear amplifiers and a transmit observation receiver (370). The second port is configured to receive, from the transmit observation receiver, a sum of transmission signals generated by the plurality of non-linear amplifiers and transferred over the plurality of communication paths. The determination circuitry is configured to determine the pre-distortion parameters based on the received plurality of channel coefficients, the received sum of transmission signals, and a model of the non-linear amplifier characteristics of the non-linear amplifiers. Corresponding arrangement, wireless transmitter node, cloud based server node, method and computer program product are also disclosed.
|
|
| 24. |
|
|
| 25. |
- Gustavsson, Ulf, 1975, et al.
(författare)
-
On the Impact of Hardware Impairments on Massive MIMO
- 2014
-
Ingår i: IEEE Globecom 2014 Workshop - Massive MIMO: From Theory to Practice, 2014-12-08, Austin, Texas, USA. - 9781479974702 ; , s. 294-300
-
Konferensbidrag (refereegranskat)abstract
- Massive multi-user (MU) multiple-input multiple-output (MIMO) systems are one possible key technology for next generation wireless communication systems. Claims have been made that massive MU-MIMO will increase both the radiated energy efficiency as well as the sum-rate capacity by orders of magnitude, because of the high transmit directivity. However, due to the very large number of transceivers needed at each base-station (BS), a successful implementation of massive MU-MIMO will be contingent on of the availability of very cheap, compact and power-efficient radio and digital-processing hardware. This may in turn impair the quality of the modulated radio frequency (RF) signal due to an increased amount of power-amplifier distortion, phase-noise, and quantization noise. In this paper, we examine the effects of hardware impairments on a massive MU-MIMO single-cell system by means of theory and simulation. The simulations are performed using simplified, well-established statistical hardware impairment models as well as more sophisticated and realistic models based upon measurements and electromagnetic antenna array simulations.
|
|
| 26. |
- Gustavsson, Ulf, 1975
(författare)
-
Quantization and Noise-Shaped Coding for High Efficiency Transmitter Architectures
- 2009
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Three driving parameters in the development of transmitter technologies for wireless communication today is: energy efficiency, flexibility and footprint reduction. This thesis investigates the use of 1-bit oversampled signal representation, mainly as a power efficiency enhancement technique for the transmitter, but also as a path toward reduced footprint and increased flexibility. Common transmitter architectures comprising this representation of the signal on either baseband or RF level are discussed and analyzed. Two common methods of mapping a complex baseband signal to different characteristics of a pulse-train, Pulse Width Modulation and Pulse Density Modulation are discussed. Noise-Shaped Coding, an inherent feature of Pulse Density Modulation, is illustrated and discussed. The implementation of Pulse Density Modulation and the determination of the Noise-Shaped Coding properties are explored within a class of oversampled A/D-converters commonly referred to as the ΣΔ-modulators. A few different approaches of analyzing the ΣΔ-modulator is discussed and a novel ΣΔ-modulator representation is introduced. Further on, an algorithm designed to achieve arbitrary Noise Shaped Coding by optimized selection of the loop-filter coefficients in the ΣΔ-structure is developed. This algorithm uses a Monte Carlo-based technique in combination with a differentiable approximation of the quantizer element and a damped Gauss-Newton search.Finally, a novel method for quantization noise suppression close to the RF-carrier is proposed. The method is based on the superposition of a selective amplitude variation onto the quantized signal. Simulations are performed on an equivalent baseband model comprising a generalized memory polynomial model for linearization. The method is then successfully demonstrated with measurements in a carrier bursting transmitter working on a high efficiency, 10 W Si-LDMOS power amplifier.
|
|
| 27. |
- Gustavsson, Ulf, 1975, et al.
(författare)
-
Quantization Noise Minimization in ΣΔ-modulation based RF Transmitter Architectures
- 2010
-
Ingår i: IEEE Transactions on Circuits and Systems I: Regular Papers. - 1549-8328 .- 1558-0806. ; 57:12, s. 3082-3091
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we describe an optimization method for minimization of quantization noise in ΣΔ-based RF transmitters. The aim of the method is to enable the use of reconstruction filters with wider passband, or alternatively, a lower switch-rate. The method uses a general representation of the ΣΔ-converters in combination with a differentiable approximation of the quantizer. Based on this, a Monte-Carlo based algorithm is developed around the damped Gauss-Newton iteration. As a result of the suggested algorithm, the residual quantization noise after reconstruction filtering is significantly decreased. Finally, simulations using a bandlimited signal with a Gaussian distribution are used to demonstrate the capabilities of the suggested algorithm when applied with the proposed ΣΔ-modulator representation. The resulting performance is compared to several cases of traditional integrator based ΣΔ-converters, demonstrating significant improvements in terms of reduced reconstruction normalized mean square error (NMSE). This implicates that the transmitter efficiency can be improved with minor changes in the modulator implementation.
|
|
| 28. |
- Hausmair, Katharina, 1982, et al.
(författare)
-
Digital Predistortion for Multi-Antenna Transmitters Affected by Antenna Crosstalk
- 2018
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 66:3, s. 1524-1535
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a digital predistortion (DPD) technique for wideband multi-antenna transmitters is proposed. The proposed DPD compensates for the combined effects of power amplifier (PA) nonlinearity, antenna crosstalk and impedance mismatch. The proposed technique consists of a linear crosstalk and mismatch model block shared by all transmit paths, and a dual-input DPD block in every transmit path. By avoiding the use of multi-input DPD blocks in every transmit path, the complexity of the proposed technique is kept low and scales more favorably with the number of antennas than competing techniques. It is shown that all blocks can be identified from measurements of the PA output signals using least-squares estimation. Measurement results of a four-path transmitter are presented and used to evaluate the proposed DPD technique against existing techniques. The results show that the performance of the proposed DPD technique is similar to those of existing techniques, while the complexity is lower.
|
|
| 29. |
- Hausmair, Katharina, 1982, et al.
(författare)
-
Modeling and Linearization of Multi-Antenna Transmitters Using Over-the-Air Measurements
- 2018
-
Ingår i: Proceedings - IEEE International Symposium on Circuits and Systems. - 0271-4310. ; 2018-May
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we present a technique to model and linearize a multi-antenna transmitter using only a small set of observation receivers that perform over-the-air measurements. We assume that the transmitter suffers from distortion due to power amplifier (PA) nonlinearities but not from crosstalk. By avoiding the use of an observation receiver in every transmitter branch, the hardware complexity and cost of multi-antenna transmitters can be reduced. First, equations are developed to extract PA models from observation receivers. Based on the extracted PA models, predistorters can then be identified for every transmit branch. We present simulation results that demonstrate that it is indeed possible to model and linearize a set of PAs using only one single observation receiver.
|
|
| 30. |
- Hausmair, Katharina, 1982, et al.
(författare)
-
Prediction of Nonlinear Distortion in Wideband Active Antenna Arrays
- 2017
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 65:11, s. 4550-4563
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we propose a technique for comprehensive analysis of nonlinear and dynamic characteristics of multi-antenna transmitters (TXs). The analysis technique is enabled by the development of a Volterra series-based dual-input model for power amplifiers (PAs), which is capable of taking into account the joint effects of PA nonlinearity, antenna crosstalk and mismatch for wideband modulated signals. By combining multiple instances of the PA model with linear dynamic antenna simulations we develop the analysis technique. The proposed method allows the prediction of the output signal of every antenna in an arbitrarily sized TX array, as well as the total far-field radiated wave of the TX for any input signal with low computational effort. A 2.12 GHz four-element TX demonstrator based on GaAs PAs is implemented to verify simulation results with measurements. The proposed technique is a powerful tool to study hardware characteristics, as for example the effects of antenna design and element spacing. It can be used in cases where experiments are not feasible, and thus aid the development of next generation wireless systems.
|
|
| 31. |
- Jacobsson, Sven, 1990, et al.
(författare)
-
Beamformed transmission using a precoder
- 2023
-
Patent (övrigt vetenskapligt/konstnärligt)abstract
- There is provided mechanisms for beamformed transmission using a precoder. A method is performed by a radio transceiver device. The radio transceiver device comprises hard ware. The hardware impacts transmission of signals from the radio transceiver device. The method comprises acquiring channel conditions of a radio propagation channel between the radio transceiver device and at least one other radio transceiver device. The method comprises determining a precoder, in form of a linear precoding matrix, for beam formed transmission towards the at least one other radio transceiver device. The precoder is determined according to the channel conditions and a model of how the hardware impacts the transmission of signals from the radio transceiver device. The method comprises transmitting, using the precoder, a signal towards the at least one other radio transceiver device.
|
|
| 32. |
- Jacobsson, Sven, 1990, et al.
(författare)
-
Massive MU-MIMO-OFDM Uplink with Hardware Impairments: Modeling and Analysis
- 2018
-
Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. ; 2018-October, s. 1829-1835
-
Konferensbidrag (refereegranskat)abstract
- © 2018 IEEE. We study the impact of hardware impairments at the base station (BS) of an orthogonal frequency-division multiplexing (OFDM)-based massive multiuser (MU) multiple-input multiple-output (MIMO) uplink system. We leverage Bussgang's theorem to develop accurate models for the distortions caused by nonlinear low-noise amplifiers, local oscillators with phase noise, and oversampling finite-resolution analog-to-digital converters. By combining the individual effects of these hardware models, we obtain a composite model for the BS-side distortion caused by nonideal hardware that takes into account its inherent correlation in time, frequency, and across antennas. We use this composite model to analyze the impact of BS-side hardware impairments on the performance of realistic massive MU-MIMO-OFDM uplink systems.
|
|
| 33. |
- Jacobsson, Sven, 1990, et al.
(författare)
-
One-Bit Massive MIMO: Channel Estimation and High-Order Modulations
- 2015
-
Ingår i: 2015 IEEE International Conference on Communication Workshop, ICCW 2015. - 9781467363051 ; , s. 1304-1309
-
Konferensbidrag (refereegranskat)abstract
- We investigate the information-theoretic throughout achievable on a fading communication link when the receiver is equipped with one-bit analog-to-digital converters (ADCs). The analysis is conducted for the setting where neither the transmitter nor the receiver have a priori information on the realization of the fading channels. This means that channel-state information needs to be acquired at the receiver on the basis of the one-bit quantized channel outputs. We show that least-squares (LS) channel estimation combined with joint pilot and data processing is capacity achieving in the single-user, single-receive-antenna case. We also investigate the achievable uplink throughput in a massive multiple-input multiple-output system where each element of the antenna array at the receiver base-station feeds a one-bit ADC. We show that LS channel estimation and maximum-ratio combining are sufficient to support both multiuser operation and the use of high-order constellations. This holds in spite of the severe nonlinearity introduced by the one-bit ADCs.
|
|
| 34. |
- Jacobsson, Sven, 1990, et al.
(författare)
-
Throughput Analysis of Massive MIMO Uplink With Low-Resolution ADCs
- 2017
-
Ingår i: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 16:6, s. 4038-4051
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the uplink throughput achievable by a multiple-user (MU) massive multiple-input multiple-output (MIMO) system, in which the base station is equipped with a large number of low-resolution analog-to-digital converters (ADCs). Our focus is on the case where neither the transmitter nor the receiver have any a priori channel state information. This implies that the fading realizations have to be learned through pilot transmission followed by channel estimation at the receiver, based on coarsely quantized observations. We propose a novel channel estimator, based on Bussgang's decomposition, and a novel approximation to the rate achievable with finite-resolution ADCs, both for the case of finite-cardinality constellations and of Gaussian inputs, that is accurate for a broad range of system parameters. Through numerical results, we illustrate that, for the 1-bit quantized case, pilot-based channel estimation together with maximal-ratio combing, or zero-forcing detection enables reliable multi-user communication with high-order constellations, in spite of the severe nonlinearity introduced by the ADCs. Furthermore, we show that the rate achievable in the infinite-resolution (no quantization) case can be approached using ADCs with only a few bits of resolution. We finally investigate the robustness of low-ADC-resolution MU-MIMO uplink against receive power imbalances between the different users, caused for example by imperfect power control.
|
|
| 35. |
- Landin, Per, 1983, et al.
(författare)
-
Distortion mitigation in RF transmitters with cascaded nonlinear and efficient power amplifiers
- 2014
-
Ingår i: 2014 IEEE 15th Annual IEEE Wireless and Microwave Technology Conference, WAMICON 2014. - 9781479946082 ; , s. Art. no. 6857778-
-
Konferensbidrag (refereegranskat)abstract
- The requirements on the linearization algorithm stemming from the use of a nonlinear amplifier to drive the power amplifier is investigated. It is theoretically shown under which conditions the nonlinear driver amplifier does not create additional nonlinear dynamic effects that have to be compensated. Experimental results using two cascaded Doherty amplifiers show that this cascade setup creates nonlinear distortion which the standard memory polynomial (MP) cannot properly linearize. A solution in the form of the vector-switched MP is shown to properly linearize the system. Experiments also show that it is possible to bias the driver Doherty amplifier's main branch in deeper class-AB without loosing linearity when an appropriate linearization algorithm is used.
|
|
| 36. |
- Lebrero-Fernandez, Cristina, et al.
(författare)
-
Altered expression of Butyrophilin (BTN) and BTN-like (BTNL) genes in intestinal inflammation and colon cancer
- 2016
-
Ingår i: Immunity Inflammation and Disease. - : Wiley. - 2050-4527. ; 4:2, s. 191-200
-
Tidskriftsartikel (refereegranskat)abstract
- Several Butyrophilin (BTN) and Btn-like (BTNL) molecules control T lymphocyte responses, and are genetically associated with inflammatory disorders and cancer. In this study, we present a comprehensive expression analysis of human and murine BTN and BTNL genes in conditions associated with intestinal inflammation and cancer. Using real-time PCR, expression of human BTN and BTNL genes was analyzed in samples from patients with ulcerative colitis, irritable bowel syndrome, and colon tumors. Expression of murine Btn and Btnl genes was examined in mouse models of spontaneous colitis (Muc2(-/-)) and intestinal tumorigenesis (Apc(Min/+)). Our analysis indicates a strong association of several of the human genes with ulcerative colitis and colon cancer; while especially BTN1A1, BTN2A2, BTN3A3, and BTNL8 were significantly altered in inflammation, colonic tumors exhibited significantly decreased levels of BTNL2, BTNL3, BTNL8, and BTNL9 as compared to unaffected tissue. Colonic inflammation in Muc2(-/-) mice significantly down-regulated the expression of particularly Btnl1, Btnl4, and Btnl6 mRNA, and intestinal polyps derived from Apc(Min/+) mice displayed altered levels of Btn1a1, Btn2a2, and Btnl1 transcripts. Thus, our data present an association of BTN and BTNL genes with intestinal inflammation and cancer and represent a valuable resource for further studies of this gene family.
|
|
| 37. |
- Marinovic, Tomislav, et al.
(författare)
-
Effect of antenna array element separation on capacity of MIMO systems including mutual coupling
- 2019
-
Ingår i: 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting, APSURSI 2019 - Proceedings. ; , s. 415-416
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we study the effect of element separation in a base station array (BSA) on the downlink line-of-sight achievable sum-rate of MIMO systems in the presence of mutual coupling at the BSA. The channel matrix H is modeled using the embedded field patterns of the BSA and is used to analyze the outage performance for two single-element user equipments assuming no inter-user coupling.
|
|
| 38. |
- Mashad Nemati, Hossein, 1980, et al.
(författare)
-
An efficiency optimized controlling scheme for dynamic load modulation of power amplifiers
- 2008
-
Ingår i: European Microwave Conf., Proc., Oct. 2008. ; , s. 583-586
-
Konferensbidrag (refereegranskat)abstract
- An efficiency optimized controlling scheme for dynamic load modulation (DLM) of power amplifiers (PAs) is proposed. In this scheme, both the input signal and load impedance are controlled to allow high efficiency operation of PAs for a desired output signal modulation. The proposed technique is demonstrated by two 1 GHz, LDMOS, switched mode power amplifiers (SMPAs) which are characterized by varying the input power during load-pull measurements. It is shown that the power-added efficiency (PAE) of the PAs in back-off operation can significantly be improved by the optimum controlling scheme.
|
|
| 39. |
|
|
| 40. |
- Mashad Nemati, Hossein, 1980, et al.
(författare)
-
Characterization of switched mode LDMOS and GaN power amplifiers for optimal use in polar transmitter architectures
- 2008
-
Ingår i: IEEE MTT-S International Microwave Symposium Digest. - 0149-645X. - 9781424417810 ; , s. 1505-1508
-
Konferensbidrag (refereegranskat)abstract
- In this paper, switched mode power amplifiers with different classes of operation and device technologies are characterized versus input power and output supply voltage. The results are used to identify optimal control schemes for use in polar transmitter architectures. Then the effects of different control schemes on the requirements for the power amplifier, and the envelope amplifier, as the main building blocks of this architecture, are investigated.
|
|
| 41. |
- Mashad Nemati, Hossein, 1980, et al.
(författare)
-
Design of Varactor-Based Tunable Matching Networks for Dynamic Load Modulation of High Power Amplifiers
- 2009
-
Ingår i: IEEE Transactions on Microwave Theory and Techniques. - 0018-9480 .- 1557-9670. ; 57:5, s. 1110-1118
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the design of varactor-based tunablematching networks for dynamic load modulation of high poweramplifiers (PAs) is presented. Design guidelines to overcome the common breakdown, and tunability problems of the varactors for high power applications are proposed. Based on the guidelines, using commercially available abrupt junction silicon varactors, a tunable matching network is built and measured. The matching network is then used for load modulation of a 1-GHz 7-W class-ELDMOS PA. Static measurements of the load modulated PA showthat the power-added efficiency of the PA is improved by an absolute value of 10% at 10-dB backoff. This promising result proves, for the first time, the feasibility of load modulation techniques for high-power applications in the gigahertz frequency range.
|
|
| 42. |
- Mashad Nemati, Hossein, 1980, et al.
(författare)
-
Practical realizations of high efficiency switched mode power amplifiers
- 2008
-
Ingår i: German Microwave Conference, GEMIC 2008; Hamburg University of Technology (TUHH)Hamburg-Harburg; Germany; 10 March 2008 through 12 March 2008. - 9783800730865
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- High efficiency switch-mode power amplifiers based on class E, F-1 and current-mode class-D are studied and designed utilizing same LDMOS devices. The possibilities of applying load modulation techniques as an efficient way to modulate the output power is also investigated.
|
|
| 43. |
- Mashad Nemati, Hossein, 1980, et al.
(författare)
-
Varactor-Based Dynamic Load Modulation of RF PAs
- 2011
-
Ingår i: European Microwave Conference, Manchester, Workshop "RF PA Efficiency Enhancement Techniques".
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)
|
|
| 44. |
- Mattsson, Niklas, 1979, et al.
(författare)
-
Amyloid-β metabolism in Niemann-Pick C disease models and patients.
- 2012
-
Ingår i: Metabolic brain disease. - : Springer Science and Business Media LLC. - 1573-7365 .- 0885-7490. ; 27:4, s. 573-85
-
Tidskriftsartikel (refereegranskat)abstract
- Niemann-Pick type C (NPC) is a progressive neurodegenerative lysosomal disease with altered cellular lipid trafficking. The metabolism of amyloid-β (Aβ) - previously mainly studied in Alzheimer's disease - has been suggested to be altered in NPC. Here we aimed to perform a detailed characterization of metabolic products from the amyloid precursor protein (APP) in NPC models and patients. We used multiple analytical technologies, including immunoassays and immunoprecipitation followed by mass spectrometry (IP-MS) to characterize Aβ peptides and soluble APP fragments (sAPP-α/β) in cell media from pharmacologically (U18666A) and genetically (NPC1 ( -/- ) ) induced NPC cell models, and cerebrospinal fluid (CSF) from NPC cats and human patients. The pattern of Aβ peptides and sAPP-α/β fragments in cell media was differently affected by NPC-phenotype induced by U18666A treatment and by NPC1 ( -/- ) genotype. U18666A treatment increased the secreted media levels of sAPP-α, AβX-40 and AβX-42 and reduced the levels of sAPP-β, Aβ1-40 and Aβ1-42, while IP-MS showed increased relative levels of Aβ5-38 and Aβ5-40 in response to treatment. NPC1 ( -/- ) cells had reduced media levels of sAPP-α and Aβ1-16, and increased levels of sAPP-β. NPC cats had altered CSF distribution of Aβ peptides compared with normal cats. Cats treated with the potential disease-modifying compound 2-hydroxypropyl-β-cyclodextrin had increased relative levels of short Aβ peptides including Aβ1-16 compared with untreated cats. NPC patients receiving β-cyclodextrin had reduced levels over time of CSF Aβ1-42, AβX-38, AβX-40, AβX-42 and sAPP-β, as well as reduced levels of the axonal damage markers tau and phosphorylated tau. We conclude that NPC models have altered Aβ metabolism, but with differences across experimental systems, suggesting that NPC1-loss of function, such as in NPC1 ( -/- ) cells, or NPC1-dysfunction, seen in NPC patients and cats as well as in U18666A-treated cells, may cause subtle but different effects on APP degradation pathways. The preliminary findings from NPC cats suggest that treatment with cyclodextrin may have an impact on APP processing pathways. CSF Aβ, sAPP and tau biomarkers were dynamically altered over time in human NPC patients.
|
|
| 45. |
- Mollén, Christopher, et al.
(författare)
-
Analysis of nonlinear low-noise amplifiers in massive MIMO base stations
- 2017
-
Ingår i: 2017 51st Asilomar Conference on Signals, Systems, and Computers. - 1058-6393. - 9781538618233 - 9781538618240 ; , s. 285-289
-
Konferensbidrag (refereegranskat)abstract
- Because of the large number of antennas at the base station, the power consumption and cost of the low-noise amplifiers (LNAs) can be substantial. Therefore, we investigate the feasibility of inexpensive, power efficient LNAs, which inherently are less linear. To characterize the nonlinear distortion, we describe the LNAs using a polynomial model, which allows for the derivation of the second-order statistics of the received signal and the distortion. A massive MIMO system that serves one user in line-of-sight is studied. It is shown that the distortion from the LNAs combines coherently and that the SINR of the symbol estimates therefore is limited by the linearity of the LNAs. Furthermore, the impact of a strong transmitter in the adjacent frequency band is investigated. The second-order statistics show how the power from that transmission leaks into the main band and interferes with the symbol estimates.
|
|
| 46. |
- Mollén, Christopher, et al.
(författare)
-
Impact of Spatial Filtering on Distortion from Low-Noise Amplifiers in Massive MIMO Base Stations
- 2018
-
Ingår i: IEEE Transactions on Communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0090-6778 .- 1558-0857. ; 66:12, s. 6050-6067
-
Tidskriftsartikel (refereegranskat)abstract
- Because of the large number of antennas at the base station, the power consumption and cost of the low-noise amplifiers (LNAs) can be substantial. Therefore, we investigate the feasibility of inexpensive, power efficient LNAs, which inherently are less linear. To characterize the nonlinear distortion, the LNAs are described using a polynomial model, which allows for the derivation of the second-order statistics of the distortion. We show that some terms of the distortion from the LNAs combine coherently, and that the SINR of the symbol estimates therefore is limited by the linearity of the LNAs. Furthermore, the impact of a strong transmitter in the adjacent frequency band is investigated. The second-order statistics show how the power from that transmission leaks into the main band and interferes with the symbol estimates. The term that scales with the cube of the power received from the blocker can be filtered out by spatial processing. Only the coherent term that scales with the square of the power remains. Nonlinear distortion from the LNAs can be reduced by spatial processing in massive MIMO. However, it does not vanish as the number of antennas is increased.
|
|
| 47. |
- Mollén, Christopher, et al.
(författare)
-
Out-of-Band Radiation from Large Antenna Arrays
- 2018
-
Ingår i: IEEE Communications Magazine. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0163-6804 .- 1558-1896. ; 56:4, s. 196-203
-
Tidskriftsartikel (refereegranskat)abstract
- The radiation pattern of the out-of-band (oob) radiation from large arrays with nonlinear hardware is different from the radiation pattern of the beamformed inband signal. This is the main difference between the oob radiation from large arrays and from well-studied legacy systems. Beamforming might focus the oob radiation in certain directions but also significantly reduce the total power that has to be transmitted. For cost and power-consumption reasons, large arrays might have to be built from low-complexity hardware without advanced precompensation for linearization, which increases the relative amount of oob radiation. Given that large arrays will be used in future base stations, a correct understanding of the oob radiation is crucial to specify appropriate linearity requirements for the hardware. We show that the oob radiation from large arrays varies little between coherence times; it is isotropic in many cases; and, when it is beamformed, it is directed towards the served user in a very narrow beam with an array gain equal to or less than that of the in-band signal. We draw the conclusion that, compared to legacy systems, less stringent linearity requirements can be used in many systems with large arrays by virtue of the lower transmit power needed to upkeep the same received signal-to-noise ratio.
|
|
| 48. |
- Mollén, Christopher, 1987-, et al.
(författare)
-
Out-of-band radiation measure for MIMO arrays with beamformed transmission
- 2016
-
Ingår i: 2016 IEEE International Conference on Communications, ICC 2016, Kuala Lumpur, Malaysia, 22-27 May 2016. - : IEEE. - 1550-3607. - 9781479966646 ; , s. Art. no. 7511629-
-
Konferensbidrag (refereegranskat)abstract
- The spatial characteristics of the out-of-band radiation that a multiuser MIMO system emits, due to its power amplifiers (modeled by a polynomial model) being nonlinear, are studied by deriving an analytical expression for the continuous-time cross-correlation of the transmit signals. It is shown that, at any spatial point and on any frequency, the received power averaged over many channel realizations from a MIMO base station is the same as from a SISO base station when the two radiate the same amount of power. For a specific channel realization however, the received power can deviate from this average. We show that the deviations from the average are small in a MIMO system with multiple users and that the deviations can be significant with only one user. Using an ergodicity argument, we conclude that out-of-band radiation is less of a problem in massive MIMO, where precoding and array gain let us reduce the total radiated power compared to SISO systems. The requirements on spectral regrowth can therefore be relaxed in MIMO systems without causing more total out-of-band radiation.
|
|
| 49. |
- Sudow, Mattias, 1980, et al.
(författare)
-
SiC varactors for dynamic load modulation of high power amplifiers
- 2008
-
Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 29:7, s. 728-730
-
Tidskriftsartikel (refereegranskat)abstract
- SiC Schottky diode varactors with a high breakdown voltage, a high tuning ratio, and a low series resistance have been designed and fabricated. These characteristics are particularly necessary for the dynamic load modulation of high power amplifiers (PAs), which is an attractive alternative to other efficiency enhancement techniques. For a SiC Schottky diode varactor with a 50-µm radius fabricated by using a graded doping profile, a breakdown voltage of 40 V, a tuning range of 5.6, and a series resistance of 0.9 O were achieved. The results show the great potential of this type of varactors for the use in the dynamic load modulation of high power amplifiers. © 2008 IEEE.
|
|
| 50. |
- Wu, Yibo, 1996, et al.
(författare)
-
Frequency-domain digital predistortion for Massive MU-MIMO-OFDM Downlink
- 2022
-
Ingår i: GLOBECOM - IEEE Global Telecommunications Conference. ; , s. 579-584
-
Konferensbidrag (refereegranskat)abstract
- Digital predistortion (DPD) is a method commonly used to compensate for the nonlinear effects of power amplifiers (PAs). However, the computational complexity of most DPD algorithms becomes an issue in the downlink of massive multi-user (MU) multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM), where potentially up to several hundreds of PAs in the base station (BS) require linearization. In this paper, we propose a convolutional neural network (CNN)-based DPD in the frequency domain, taking place before the precoding, where the dimensionality of the signal space depends on the number of users, instead of the number of BS antennas. Simulation results on generalized memory polynomial (GMP)-based PAs show that the proposed CNN-based DPD can lead to very large complexity savings as the number of BS antenna increases at the expense of a small increase in power to achieve the same symbol error rate (SER).
|
|
