Interference Alignment (IA) and Coordinated Multi-Point (CoMP) with IEEE802.11ac feedback compression: testbed results

We have implemented interference alignment (IA) and joint transmission coordinated multipoint (CoMP) on a wireless testbed using the feedback compression scheme of the new 802.11ac standard. The performance as a function of the frequency domain granularity is assessed. Realistic throughput gains are obtained by probing each spatial modulation stream with ten different coding and modulation schemes. The gain of IA and CoMP over TDMA MIMO is found to be 26% and 71%, respectively under stationary conditions. In our dense indoor office deployment, the frequency domain granularity of the feedback can be reduced down to every 8th subcarrier (2.5MHz), without sacrificing performance.Comment: To appear in ICASSP 201

Foreword

In this paper, theoretical properties of a maximum-likelihood (ML) estimator of signal-to-noise ratio (SNR) is discussed. The three-parameter sine fit algorithm is employed on a finite and coherently sampled measurement set corrupted by additive white Gaussian noise. Under the Gaussian noise model, the least squares solution provided by the three-parameter sine fit is also ML estimator. Exact distribution and finite sample properties of the SNR estimate are derived. Moreover, an explicit expression for the mean squared error (MSE) of the estimator is given. Simulation results are shown to verify the underlying theoretical results.QC 20131216</p

Interference Alignment — Practical Challenges and Test-bed Implementation

Data traffic over wireless communication networks has experienced a tremendous growth in the last decade, and it is predicted to exponentially increase in the next decades. Enabling future wireless networks to fulfill this expectation is a challenging task both due to the scarcity of radio resources (e.g. spectrum and energy), and also the inherent characteristics of the wireless transmission medium. Wireless transmission is in general subject to two phenomena: fading and interference. The elegant interference alignment concept reveals that with proper transmission signalling design, different interference signals can in fact be aligned together, such that more radio resources can be assigned to the desired transmission. Although interference alignment can achieve a larger data rate compared to orthogonal transmission strategies, several challenges should be addressed to enable the deployment of this technique in future wireless networks For instance, to perform interference alignment, normally, global channel state information (CSI) is required to be perfectly known at all terminals. Clearly, acquiring such channel knowledge is a challenging problem in practice and proper channel training and channel state feedback techniques need to be deployed. In addition, since the channels are time-varying proper adaptive transmission is needed. This chapter review recent advances in practical aspects of interference alignment. It also presents recent test-bed implementations of signal processing algorithms for the realization of interference alignment.Comment: Book Chapter accepted for publication in the book entitled: Contemporary Issues in Wireless Communications, ISBN: 978-953-51-4101-3, Khatib, M. (Ed.), to be published by INTECH Publishers. Expected month of publication: November 201

Decorrelation Distance Characterization of Long Term Fading of CW MIMO Channels in Urban Multicell Environment

An analysis of long-term fading properties of 4×4 CW MIMO channels is presented in this paper. The main focus has been on the long-term variability of MIMO channels in urban cellular environments, with emphasis on the decorrelation distance over mid range distances along the mobile trajectory for different base station antenna heights. A model that characterizes the decorrelation distance at different probability levels of distribution of the decorrelation distance is proposed. The model predicts that at some probability level all measured decorrelation distances will be within ½Δx0and 2Δx0, where Δx0is the decorrelation distance at the e-1 level of the autocorrelation function

Impact of Major RF Impairments on mm-wave Communications using OFDM Waveforms

In this paper, we study the joint impact of three major RF im-pairments, namely, oscillator phase noise, power amplifier non-linearity and I/Q imbalance on the performance of a mm-wave communication link based on OFDM modulation. General im-pairment models are first derived for describing the joint effects in each TX, each RX as well as a mm-wave communication link. Based on the obtained signal models and initial air interface de-sign from the mmMAGIC project, we numerically evaluate the impact of RF impairments on channel estimation in terms of channel-to-noise ratio (CNR) and also channel fluctuation due to common phase error (CPE) caused by phase noise within the channel coherence time. Then the impact on the link performance in terms of maximum sum rate is evaluated using extensive com-puter simulations. The simulation results show that the used air interface design is generally robust to the presence of RF impair-ments. With regard to the use of high order modulation alphabet and implementation of low-power and low-cost RF transceivers in mm-wave communication, special attention needs to be paid on phase noise where the inter-carrier-interference (ICI) can become a major limiting factor

Plasma neurodegeneration biomarker concentrations associate with glymphatic and meningeal lymphatic measures in neurological disorders

Clearance of neurotoxic brain proteins via cerebrospinal fluid (CSF) to blood has recently emerged to be crucial, and plasma biomarkers of neurodegeneration were newly introduced to predict neurological disease. This study examines in 106 individuals with neurological disorders associations between plasma biomarkers [40 and 42 amino acid-long amyloid-β (Aβ40 and Aβ42), total-tau, glial fibrillary acidic protein (GFAP), and neurofilament light (NfL)] and magnetic resonance imaging measures of CSF-mediated clearance from brain via extra-vascular pathways (proxy of glymphatic function) and CSF-to-blood clearance variables from pharmacokinetic modeling (proxy of meningeal lymphatic egress). We also examine how biomarkers vary during daytime and associate with subjective sleep quality. Plasma concentrations of neurodegeneration markers associate with indices of glymphatic and meningeal lymphatic functions in individual- and disease-specific manners, vary during daytime, but are unaffected by sleep quality. The results suggest that plasma concentrations of neurodegeneration biomarkers associate with measures of glymphatic and meningeal lymphatic function