151 research outputs found
A Comparison of Hybrid Beamforming and Digital Beamforming with Low-Resolution ADCs for Multiple Users and Imperfect CSI
For 5G it will be important to leverage the available millimeter wave
spectrum. To achieve an approximately omni- directional coverage with a similar
effective antenna aperture compared to state of the art cellular systems, an
antenna array is required at both the mobile and basestation. Due to the large
bandwidth and inefficient amplifiers available in CMOS for mmWave, the analog
front-end of the receiver with a large number of antennas becomes especially
power hungry. Two main solutions exist to reduce the power consumption: hybrid
beam forming and digital beam forming with low resolution Analog to Digital
Converters (ADCs). In this work we compare the spectral and energy efficiency
of both systems under practical system constraints. We consider the effects of
channel estimation, transmitter impairments and multiple simultaneous users.
Our power consumption model considers components reported in literature at 60
GHz. In contrast to many other works we also consider the correlation of the
quantization error, and generalize the modeling of it to non-uniform quantizers
and different quantizers at each antenna. The result shows that as the SNR gets
larger the ADC resolution achieving the optimal energy efficiency gets also
larger. The energy efficiency peaks for 5 bit resolution at high SNR, since due
to other limiting factors the achievable rate almost saturates at this
resolution. We also show that in the multi-user scenario digital beamforming is
in any case more energy efficient than hybrid beamforming. In addition we show
that if different ADC resolutions are used we can achieve any desired
trade-offs between power consumption and rate close to those achieved with only
one ADC resolution.Comment: Submitted to JSTSP. arXiv admin note: text overlap with
arXiv:1610.0290
Arbitrary Beam Synthesis of Hybrid Beamforming Systems for Beam Training
For future millimeter Wave (mmWave) mobile com-
munication systems, the use of analog/hybrid beamforming is
envisioned to be an important aspect. The synthesis of beams
is a key technology to enable the best possible operation during
beam search and data transmission. The method for synthesizing
beams developed in this work is based on previous work in radar
technology considering only phased array antennas. With this
technique, it is possible to generate a desired beam of any shape
with the constraints of the desired target transceiver antenna
frontend. It is not constraint to a certain antenna array geometry,
and can handle 1D, 2D and even 3D antenna array geometries,
e.g. cylindrical arrays. The numerical examples show that the
method can synthesize beams by considering a user defined trade-
off between gain, transition width and passband ripples. Since
this beam synthesis method is computational complex, it is only
suitable for offline calculation during the design or calibration
of a devic
Performance Analysis of FBMC and CP-OFDM in the Presence of Phase Noise
Multi-Carrier (MC) modulation schemes like Or-
thogonal Frequency Division Multiplexing (OFDM) are highly
sensitive to Phase Noise (PN). In the case of air interfaces
operating in higher frequencies, e.g. the range between 6 and
100 GHz frequently called millimeter wave (mmWave), the PN
generated by the local oscillators is even more accentuated.
Alternative MC systems are being considered for future mmWave
wireless communications. In this contribution, we analytically
derive expressions for an upper bound for the interference power
generated by the PN in OFDM, DFT-Spread-OFDM and Filter
Bank Multi-Carrier (FBMC). Then, we evaluate the performance
degradation due to that imperfection in terms of coded and
uncoded BER
Nonlinear Digital Self-Interference Cancellation with Reduced Complexity for Full Duplex Systems
Full duplex transmission is currently viewed as an important technology component for the future 5G and beyond mobile broadband technology. In order to realize its promised theoretical gain, sufficient cancellation of the self-interference must be achieved. The focus throughout this work will be on the digital cancellation, which main target is to cancel the residual self-interference resulting from the insufficient analog cancellation due to hardware imperfections, along with non-linearities existing in the transmitter chain. A novel pre-transmission transformation based on the Cholesky decomposition is presented, that aims at enhancing the digital cancellation performance. A digital cancellation based on the transversal recursive least squares with the exploitation of the dichotomous coordinate descent algorithm to lower the computational complexity is presented. The analysis was extended to include the existence of a received signal of interest, while simultaneously canceling the self-interference signal. By means of numerical simulations, a performance evaluation was carried out and results showed that the level of residual interference after the digital canceler reaches the simulated noise floor power level
Nonparametric Bayesian inference for perturbed and orthologous gene regulatory networks
Motivation: The generation of time series transcriptomic datasets collected under multiple experimental conditions has proven to be a powerful approach for disentangling complex biological processes, allowing for the reverse engineering of gene regulatory networks (GRNs). Most methods for reverse engineering GRNs from multiple datasets assume that each of the time series were generated from networks with identical topology. In this study, we outline a hierarchical, non-parametric Bayesian approach for reverse engineering GRNs using multiple time series that can be applied in a number of novel situations including: (i) where different, but overlapping sets of transcription factors are expected to bind in the different experimental conditions; that is, where switching events could potentially arise under the different treatments and (ii) for inference in evolutionary related species in which orthologous GRNs exist. More generally, the method can be used to identify context-specific regulation by leveraging time series gene expression data alongside methods that can identify putative lists of transcription factors or transcription factor targets.
Results: The hierarchical inference outperforms related (but non-hierarchical) approaches when the networks used to generate the data were identical, and performs comparably even when the networks used to generate data were independent. The method was subsequently used alongside yeast one hybrid and microarray time series data to infer potential transcriptional switches in Arabidopsis thaliana response to stress. The results confirm previous biological studies and allow for additional insights into gene regulation under various abiotic stresses.
Availability: The methods outlined in this article have been implemented in Matlab and are available on request
Waveforms for sub-THz 6G: Design Guidelines
The projected sub-THz (100 - 300 GHz) part of the upcoming 6G standard will
require a careful design of the waveform and choice of slot structure. Not only
that the design of the physical layer for 6G will be driven by ambitious system
performance requirements, but also hardware limitations, specific to sub-THz
frequencies, pose a fundamental design constraint for the waveform. In this
contribution, general guidelines for the waveform design are given, together
with a non-exhaustive list of exemplary waveforms that can be used to meet the
design requirements.Comment: Paper presented at EuCNC 2023, June 6-9 2023, Gothenburg, Swede
Electroweak radiative corrections to single Higgs-boson production in e+e- annihilation
We have calculated the complete electroweak O(alpha) radiative corrections to
the single Higgs-boson production processes e+ e- --> nu_l anti-nu_l H
(l=e,mu,tau) in the electroweak Standard Model. Initial-state radiation beyond
O(alpha) is included in the structure-function approach. The calculation of the
corrections is briefly described, and numerical results are presented for the
total cross section. In the G_mu scheme, the bulk of the corrections is due to
initial-state radiation, which affects the cross section at the level of -7% at
high energies and even more in the ZH threshold region. The remaining bosonic
and fermionic corrections are at the level of a few per cent. The confusing
situation in the literature regarding differing results for the fermionic
corrections to this process is clarified.Comment: 11 pages, latex, 7 postscript files, some references added, final
version to appear in Phys.Lett.
Impact of valve morphology, hypertension and age on aortic wall properties in patients with coarctation: a two-centre cross-sectional study
Objective: We aimed to investigate the combined effects of arterial hypertension, bicuspid aortic valve disease (BAVD) and age on the distensibility of the ascending and descending aortas in patients with aortic coarctation.
Design: Cross-sectional study.
Setting: The study was conducted at two university medical centres, located in Berlin and London.
Participants: A total of 121 patients with aortic coarctation (ages 1-71 years) underwent cardiac MRI, echocardiography and blood pressure measurements.
Outcome measures: Cross-sectional diameters of the ascending and descending aortas were assessed to compute aortic area distensibility. Findings were compared with age-specific reference values. The study complied with the Strengthening the Reporting of Observational Studies in Epidemiology statement and reporting guidelines.
Results: Impaired distensibility (below fifth percentile) was seen in 37% of all patients with coarctation in the ascending aorta and in 43% in the descending aorta. BAVD (43%) and arterial hypertension (72%) were present across all ages. In patients >10 years distensibility impairment of the ascending aorta was predominantly associated with BAVD (OR 3.1, 95% CI 1.33 to 7.22, p=0.009). Distensibility impairment of the descending aorta was predominantly associated with arterial hypertension (OR 2.8, 95% CI 1.08 to 7.2, p=0.033) and was most pronounced in patients with uncontrolled hypertension despite antihypertensive treatment.
Conclusion: From early adolescence on, both arterial hypertension and BAVD have a major impact on aortic distensibility. Their specific effects differ in strength and localisation (descending vs ascending aorta). Moreover, adequate blood pressure control is associated with improved distensibility. These findings could contribute to the understanding of cardiovascular complications and the management of patients with aortic coarctation
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