Time-frequency Grassmannian signalling for MIMO multi-channel-frequency-flat systems

In this paper, we consider the application of non-coherent Grassmannian signalling in practical multi-channel-frequency-flat multiple-input multiple-output (MIMO) wireless communication systems. In these systems, Grassmannian signalling, originally developed for single-channel block-fading systems, is not readily applicable. In particular, in such systems, the channel coefficients are constant across time and frequency, which implies that spectrally-efficient signalling ought to be jointly structured over these domains. To approach this goal, we develop a concatenation technique that yields a spectrally-efficient time-frequency Grassmannian signalling scheme, which enables the channel coherence bandwidth to be regarded as an additional coherence time. This scheme is shown to achieve the high signal-to-noise ratio non-coherent capacity of MIMO channels when the fading coefficients are constant over a time-frequency block. This scheme is also applicable in fast fading systems with coherence bandwidth exceeding that of one subchannel. The proposed scheme is independent of the symbol duration, i.e., the channel use duration, and is thus compatible with the transmit filter designs in current systems.The work of the first and second authors is supported, in part, by the Natural Sciences and Engineering Research Council of Canada (NSERC). This work is also supported, in part, by Huawei Canada Co., Ltd., in part, by the Ontario Ministry of Economic Development and Innovation's ORF-RE (Ontario Research Fund-Research Excellence) program, and, in part, by the Ministerio de Ciencia e Innovacion (project number TEC2011-27723-C02-02). The associate editor coordinating the review of this paper and approving it for publication was Z. Wang.Fouad, YMM.; Gohary, RH.; Cabrejas Peñuelas, J.; Yanikomeroglu, H.; Calabuig Soler, D.; Roger Varea, S.; Monserrat Del Río, JF. (2015). Time-frequency Grassmannian signalling for MIMO multi-channel-frequency-flat systems. IEEE Communications Letters. 19(3):475-478. https://doi.org/10.1109/LCOMM.2014.2386873S47547819

Non-Coherent Open-Loop MIMO Communications Over Temporally-Correlated Channels

[EN] This paper investigates the use of non-coherent communication techniques for open-loop transmission over temporally-correlated Rayleigh-fading MIMO channels. These techniques perform data detection without knowing the instantaneous channel coefficients. Three non-coherent Multiple Input Multiple Output (MIMO) schemes, namely, differential unitary space-time modulation, differential space-time block code, and Grassmannian signaling, are compared with several state-of-the-art training-based coherent schemes. This paper shows that the non-coherent schemes are meaningful alternatives to training-based communication, specially as the number of transmit antennas increases. In particular, for more than two transmit antennas, non-coherent communication provides a clear advantage in medium to high mobility scenarios.This work was supported in part by the Ministerio de Economia y Competitividad, Spain, under Grant TEC2014-60258-C2-1-R, in part by the European Regional Development Fund, in part by the European Union through the H2020 Project METIS-II under Grant 671680, in part by Huawei Canada Company, Ltd., and in part by the Ontario Ministry of Economic Development and Innovation's through the Ontario Research Fund-Research Excellence Program.Cabrejas Peñuelas, J.; Roger Varea, S.; Calabuig Soler, D.; Fouad, YMM.; Gohary, RH.; Monserrat Del Río, JF.; Yanikomeroglu, H. (2016). Non-Coherent Open-Loop MIMO Communications Over Temporally-Correlated Channels. IEEE Access. 4:6161-6170. https://doi.org/10.1109/ACCESS.2016.2580680S61616170

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10 years; 78.2% included were male with a median age of 37 years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

Chinese Remainder Theorem Based Sequence Design for Resource Block Assignment in Relay-Assisted Internet-of-Things Communications

Terminal relays are prospected to play a key role in facilitating the communication between base stations and low-cost power-constrained cellular Internet of Things (IoT) devices. However, these mobile relays require a mechanism by which they can autonomously assign the available resource blocks (RBs) to their assisted IoT devices in the absence of channel state information (CSI) and with minimal assignment conflicts. To address this problem, in this work, we develop an autonomous sequence-based RB assignment scheme that dispenses with CSI. The sequences underling the proposed scheme are designed using the Chinese remainder theorem (CRT). In particular, the CRT is used to combine the cyclic sequences generated by simple cyclic group structures into longer ones. The combining process introduces additional degre

Number-Theoretic Sequence Design for Uncoordinated Autonomous Multiple Access in Relay-Assisted Machine-Type Communications

Terminal relaying is expected to offer an effective means for realizing machine-Type communications (MTC) in wireless cellular networks. In the absence of channel quality indicators, the effective utilization of relaying terminals (RTs) requires a mechanism by which RTs can autonomously assign available resource blocks (RBs) to potentially large numbers of uncoordinated MTC devices with minimal conflicts. Unlike random RB assignments, which do not offer performance guarantees, using prescribed RB assignment sequences provides an opportunity for obtaining performance gains. However, realizing these gains requires optimizing RB assignments over a large set of lengthy sequences. One technique for selecting assignment seq

An efficient greedy-based autonomous resource block assignment scheme for 5G cellular networks with self-organizing relaying terminals

In future cellular networks, self-organizing relaying terminals (RTs) are expected to play a crucial role in assisting the communication between base stations and wireless terminals (WTs), which include, not only active user terminals, but also machine-type communication devices. In the absence of channel quality indicators, the effective utilization of RTs requires a mechanism by which these RTs can assign available resource blocks (RBs) to a potentially large number of WTs with minimal conflicts. This requires optimizing RB assignments over a large set of lengthy sequences, which is computationally prohibitive for networks with large numbers of RTs. To alleviate the difficulty in designing such sequences, we develop a greedy algorithm