Impact of Spatial Filtering on Distortion from Low-Noise Amplifiers in Massive MIMO Base Stations

In massive MIMO base stations, power consumption and cost of the low-noise amplifiers (LNAs) can be substantial because of the many antennas. We investigate the feasibility of inexpensive, power efficient LNAs, which inherently are less linear. A polynomial model is used to characterize the nonlinear LNAs and to derive the second-order statistics and spatial correlation of the distortion. We show that, with spatial matched filtering (maximum-ratio combining) at the receiver, some distortion terms combine coherently, and that the SINR of the symbol estimates therefore is limited by the linearity of the LNAs. Furthermore, it is studied how the power from a blocker in the adjacent frequency band leaks into the main band and creates distortion. The distortion term that scales cubically with the power received from the blocker has a spatial correlation that can be filtered out by spatial processing and only the coherent term that scales quadratically with the power remains. When the blocker is in free-space line-of-sight and the LNAs are identical, this quadratic term has the same spatial direction as the desired signal, and hence cannot be removed by linear receiver processing

Out-of-Band Radiation Measure for MIMO Arrays with Beamformed Transmission

The spatial characteristics of the out-of-band radiation that a multiuser MIMO system emits in the environment, due to its power amplifiers (modeled by a polynomial model) are nonlinear, is studied by deriving an analytical expression for the continuous-time cross-correlation of the transmit signals. At a random spatial point, the same power is received at any frequency on average with a MIMO base station as with a SISO base station when the two radiate the same amount of power. For a specific channel realization however, the received power depends on the channel. We show that the power received out-of-band only deviates little from the average in a MIMO system with multiple users and that the deviation 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 total radiated power is lower compared to SISO systems and that requirements on spectral regrowth can be relaxed in MIMO systems without causing more total out-of-band radiation

Spatial Characteristics of Distortion Radiated from Antenna Arrays with Transceiver Nonlinearities

The distortion from massive MIMO (multiple-input--multiple-output) base stations with nonlinear amplifiers is studied and its radiation pattern is derived. The distortion is analyzed both in-band and out-of-band. By using an orthogonal Hermite representation of the amplified signal, the spatial cross-correlation matrix of the nonlinear distortion is obtained. It shows that, if the input signal to the amplifiers has a dominant beam, the distortion is beamformed in the same way as that beam. When there are multiple beams without any one being dominant, it is shown that the distortion is practically isotropic. The derived theory is useful to predict how the nonlinear distortion will behave, to analyze the out-of-band radiation, to do reciprocity calibration, and to schedule users in the frequency plane to minimize the effect of in-band distortion

Chapter 1 Examining the illusion of accountability

Do EU citizens have real opportunities to hold decision-makers accountable, or does the current institutional set-up in the Union merely create an illusion of accountability? That is the central question of this volume. There are widespread and growing concerns that the political system of the EU does not, in fact, afford citizens appropriate mechanisms of accountability. The aim of the current study is to ascertain whether such concerns are warranted

Modelado estadístico de amplificadores no lineales

Complexity relaxations in wireless communication systems operating at the boundaries of components performance are foreseen. Due to this matter, a need to properly characterize hardware impairments degrading the performance of communications links has been recognized in previous studies. Statistical models might be the definitive tool for assessing the impact of these non-idealities. Particularly, the non-linearity of power amplifiers in multi-antenna scenarios was examined in this thesis. To this matter, a full revision of a novel method capable of capturing this limitation for a single-antenna and thus, a single power amplifier, was carried out. Thereafter, the strategy was to commence with the simplest multiantenna case and to increase the number of antennas and users until a general model was achieved. Results of the developed models in the thesis are provided concluding that these kind of approaches are valid to model the non-linear nature of power amplifiers in MIMO systems. Another studies of the evolution of this distortion when varying the number of antennas and users are also presented and analyzed

Chapter 1 Examining the illusion of accountability

Do EU citizens have real opportunities to hold decision-makers accountable, or does the current institutional set-up in the Union merely create an illusion of accountability? That is the central question of this volume. There are widespread and growing concerns that the political system of the EU does not, in fact, afford citizens appropriate mechanisms of accountability. The aim of the current study is to ascertain whether such concerns are warranted

On the Impact of Hardware Impairments on Massive MIMO

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.Comment: 7 pages, 9 figures, Accepted for presentation at Globe-Com workshop on Massive MIM

Fast Timing for High-Rate Environments with Micromegas

The current state of the art in fast timing resolution for existing experiments is of the order of 100 ps on the time of arrival of both charged particles and electromagnetic showers. Current R&D on charged particle timing is approaching the level of 10 ps but is not primarily directed at sustained performance at high rates and under high radiation (as would be needed for HL-LHC pileup mitigation). We demonstrate a Micromegas based solution to reach this level of performance. The Micromegas acts as a photomultiplier coupled to a Cerenkov-radiator front window, which produces sufficient UV photons to convert the ~100 ps single-photoelectron jitter into a timing response of the order of 10-20 ps per incident charged particle. A prototype has been built in order to demonstrate this performance. The first laboratory tests with a pico-second laser have shown a time resolution of the order of 27 ps for ~50 primary photoelectrons, using a bulk Micromegas readout.Comment: MPGD2015 (4th Conference on Micro-Pattern Gaseous Detectors, Trieste, Italy, 12 - 15 October, 2015). 5 pages, 8 figure

Solvent Effect on the Singlet Excited-state Dynamics of 5-Fluorouracil in Acetonitrile as Compared with Water

The excited-state dynamics of 5-fluorouracil in acetonitrile has been investigated by femtosecond fluorescence upconversion spectroscopy in combination with quantum chemistry TD-DFT calculations ((PCM/TD-PBE0). Experimentally, it was found that when going from water to acetonitrile solution the fluorescence decay of 5FU becomes much faster. The calculations show that this is related to the opening of an additional decay channel in acetonitrile solution since the dark n/* excited state becomes near degenerate with the bright /* state, forming a conical intersection close to the Franck-Condon region. In both solvents, a S1-S0 conical intersection, governed by the out-of-plane motion of the fluorine atom, is active, allowing an ultrafast internal conversion to the ground state

Do fluorescence and transient absorption probe the same intramolecular charge transfer state of 4- ( dimethylamino ) benzonitrile?

We present here the results of time-resolved absorption and emission experiments for 4-(dimethylamino)benzonitrile in solution, which suggest that the fluorescent intramolecular charge transfer (ICT) state may differ from the twisted ICT (TICT) state observed in transient [email protected]