Control-Data Separation With Decentralized Edge Control in Fog-Assisted Uplink Communications

Kang, Jinkyu,Simeone, Osvaldo,Kang, Joonhyuk,Shamai Shitz, Shlomo IEEE 2018 IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS Vol.17 No.6

<P>Fog-aided network architectures for 5G systems encompass wireless edge nodes, referred to as remote radio systems (RRSs), as well as remote cloud center (RCC) processors, which are connected to the RRSs via a fronthaul access network. RRSs and RCC are operated via network functions virtualization, enabling a flexible split of network functionalities that adapts to network parameters such as fronthaul latency and capacity. This paper focuses on uplink communications and investigates the cloud-edge allocation of two important network functions, namely, the control functionality of rate selection and the data-plane function of decoding. Three functional splits are considered: 1) distributed radio access network, in which both functions are implemented in a decentralized way at the RRSs; 2) cloud RAN, in which instead both functions are carried out centrally at the RCC; and 3) a new functional split, referred to as fog RAN (F-RAN), with separate decentralized edge control and centralized cloud data processing. The model under study consists of a time-varying uplink channel with fixed scheduling and cell association in which the RCC has global but delayed channel state information due to fronthaul latency, while the RRSs have local but more timely CSI. Using the adaptive sum-rate as the performance criterion, it is concluded that the F-RAN architecture can provide significant gains in the presence of user mobility.</P>

Time-Asynchronous Robust Cooperative Transmission for the Downlink of C-RAN

Seok-Hwan Park,Simeone, Osvaldo,Shitz, Shlomo Shamai IEEE Signal Processing Society 2016 IEEE signal processing letters Vol.23 No.10

<P>This letter studies the robust design of downlink precoding for cloud radio access network (C-RAN) in the presence of asynchronism among remote radio heads (RRHs). Specifically, a C-RAN downlink system is considered in which nonideal fronthaul links connecting two RRHs to a baseband unit (BBU) may cause a time offset, as well as a phase offset, between the transmissions of the two RRHs. The offsets are a priori not known to the BBU. With the aim of counteracting the unknown time offset, a robust precoding scheme is considered that is based on the idea of correlating the signal transmitted by one RRH with a number of delayed versions of the signal transmitted by the other RRH. For this transmission strategy, the problem of maximizing the worst-case minimum rate is tackled while satisfying per-RRH transmit power constraints. Numerical results are reported that verify the advantages of the proposed robust scheme as compared to the conventional nonrobust design criteria as well as noncooperative transmission.</P>

Fronthaul Compression and Precoding Design for C-RANs Over Ergodic Fading Channels

Kang, Jinkyu,Simeone, Osvaldo,Kang, Joonhyuk,Shamai, Shlomo IEEE 2016 IEEE Transactions on Vehicular Technology VT Vol.65 No.7

<P>This paper investigates the joint design of fronthaul compression and precoding for the downlink of cloud radio access networks (C-RANs). In a C-RAN, a central unit (CU) controls a cluster of radio units (RUs) through low-latency fronthaul links. Most previous works on the design of fronthaul compression and precoding assume constant channels and instantaneous channel state information (CSI) at the CU. This paper, in contrast, concentrates on a more practical scenario with block-ergodic channels and considers either instantaneous or stochastic CSI at the CU. Moreover, the analysis encompasses two types of CU-RU functional splits at the physical layer, which we refer to as compression-after-precoding (CAP) and compression-before-precoding (CBP). With the CAP approach, which is the standard C-RAN solution, all baseband processing is done at the CU. With the CBP scheme, channel encoding and precoding are instead performed at the RUs: The CU does not perform precoding but rather forwards separately the information messages of a subset of mobile stations (MSs) along with the compressed precoding matrices to each RU. Optimization algorithms over fronthaul compression and precoding for both CAP and CBP are proposed, which are based on a stochastic successive upper bound minimization (SSUM) approach. Numerical results yield insights into the optimal RU-CU functional split for C-RANs. As a general conclusion, the relative advantages of the two functional splits depend on the interplay between the enhanced interference management abilities of CAP, particularly for dense networks, and the lower fronthaul requirements of CBP in terms of precoding information overhead, particularly for large coherence periods and with stochastic, rather than instantaneous, CSI.</P>

Multivariate Fronthaul Quantization for Downlink C-RAN

Wonju Lee,Simeone, Osvaldo,Joonhyuk Kang,Shamai, Shlomo Institute of Electrical and Electronics Engineers 2016 IEEE transactions on signal processing Vol.64 No.19

<P>The cloud-radio access network (C-RAN) cellular architecture relies on the transfer of complex baseband signals to and from a central unit (CU) over digital fronthaul links to enable the virtualization of the baseband processing functionalities of distributed radio units (RUs). The standard design of digital fronthauling is based on either scalar quantization or on more sophisticated point-to-point compression techniques operating on baseband signals. Motivated by network-information theoretic results, techniques for fronthaul quantization and compression that improve over point-to-point solutions by allowing for joint processing across multiple fronthaul links at the CU have been recently proposed for both the uplink and the downlink. For the downlink, a form of joint compression, known in network information theory as multivariate compression, was shown to be advantageous under a nonconstructive asymptotic information-theoretic framework. In this paper, instead, the design of a practical symbol-by-symbol fronthaul quantization algorithm that implements the idea of multivariate compression is investigated for the C-RAN downlink. As compared to current standards, the proposed multivariate quantization (MQ) only requires changes in the CU processing while no modification is needed at the RUs. The algorithm is extended to enable the joint optimization of downlink precoding and quantization, reduced-complexity MQ via successive block quantization, and variable-length compression. Numerical results, which include performance evaluations over standard cellular models, demonstrate the advantages of MQ and the merits of a joint optimization with precoding.</P>

Multi-Tenant C-RAN With Spectrum Pooling: Downlink Optimization Under Privacy Constraints

Park, Seok-Hwan,Simeone, Osvaldo,Shamai, Shlomo IEEE 2018 IEEE Transactions on Vehicular Technology VT Vol.67 No.11

<P>Spectrum pooling allows multiple operators, or tenants, to share the same frequency bands. This paper studies the optimization of spectrum pooling for the downlink of a multi-tenant cloud radio access network system in the presence of inter-tenant privacy constraints. The spectrum available for downlink transmission is partitioned into private and shared subbands, and the participating operators cooperate to serve the user equipment (UEs) on the shared subband. The network of each operator consists of a cloud processor (CP) that is connected to proprietary radio units (RUs) by means of finite-capacity fronthaul links. In order to enable inter-operator cooperation, the CPs of the participating operators are also connected by finite-capacity backhaul links. Inter-operator cooperation may, hence, result in loss of privacy. Fronthaul and backhaul links are used to transfer quantized baseband signals. Standard quantization is considered first. Then, a novel approach based on the idea of correlating quantization noise signals across RUs of different operators is proposed to control the trade-off between distortion at UEs and inter-operator privacy. The problem of optimizing the bandwidth allocation, precoding, and fronthaul/backhaul compression strategies is tackled under constraints on backhaul and fronthaul capacity, as well as on per-RU transmit power and inter-operator privacy. For both cases, the optimization problems are tackled using the concave convex procedure, and extensive numerical results are provided.</P>

Layered Downlink Precoding for C-RAN Systems With Full Dimensional MIMO

Kang, Jinkyu,Simeone, Osvaldo,Kang, Joonhyuk,Shamai, Shlomo IEEE 2017 IEEE Transactions on Vehicular Technology VT Vol.66 No.3

<P>The implementation of a cloud radio access network (C-RAN) with full dimensional (FD) multiple-input multiple-output (MIMO) is faced with the challenge of controlling the fronthaul overhead for the transmission of baseband signals as the number of horizontal and vertical antennas grows larger. This paper proposes to leverage the special low-rank structure of the FD-MIMO channel, which is characterized by a time-invariant elevation component and a time-varying azimuth component, by means of a layered precoding approach, to reduce the fronthaul overhead. According to this scheme, separate precoding matrices are applied for the azimuth and elevation channel components, with different rates of adaptation to the channel variations and correspondingly different impacts on the fronthaul capacity. Moreover, we consider two different central unit (CU)-radio unit (RU) functional splits at the physical layer, namely, the conventional C-RAN implementation and an alternative one in which coding and precoding are performed at the RUs. Via numerical results, it is shown that the layered schemes significantly outperform conventional nonlayered schemes, particularly in the regime of low fronthaul capacity and a large number of vertical antennas.</P>

Management pathway for emergency department patients in the setting of the opioid epidemic and emergency department overcrowding

Kiersten Gurley,Churchill Onyeii,Jonathan Burstein,Shamai Grossman 대한응급의학회 2020 Clinical and Experimental Emergency Medicine Vol.7 No.2

Objective The United States is currently in the midst of a major opioid addiction epidemic, of which the primary drivers are a sharp increase in prescription opioid pain medications, their misuse, and the inordinate illicit use of opioids. Declared a national health emergency, the opioid crisis puts enormous pressure on various systems, including increasing overcrowding in emergency departments (EDs) and forced changes in prescribing practices. We are piloting a newly-developed ED opiate pathway to streamline ED care for patients who frequently present at the ED for chronic pain management or other recurrent pain-causing medical problems. Methods Patients at risk of possible opioid addiction are identified and their records are reviewed. If there is no narcotics agreement in place, the ED care team contacts the primary care physician and any other service providers involved in the patient’s care to create a comprehensive pain management program. Results Our pathway is simple and geared toward streamlining and improving care for patients with opioid addiction and misuse. We looked at seven patients in this pilot study with mixed results regarding decreasing future ED visits. Conclusion This strategy may both limit opioid usage and abuse as well as limit ED visits and overcrowding by streamlining ED care for patients who frequently present for chronic pain management or other recurrent medical problems.

Getting to the heart of the issue: senior emergency resident electrocardiogram interpretation and its impact on quality assurance events

Leslie A Bilello1,Céline Pascheles,Kiersten Gurley,Douglas Rappaport,David T Chiu,Shamai A. Grossman,Carlo L Rosen 대한응급의학회 2020 Clinical and Experimental Emergency Medicine Vol.7 No.3

Objective Electrocardiogram (ECG) interpretation skills are of critical importance for diagnostic accuracy and patient safety. In our emergency department (ED), senior third-year emergency medicine residents (EM3s) are the initial interpreters of all ED ECGs. While this is an integral part of emergency medicine education, the accuracy of ECG interpretation is unknown. We aimed to review the adverse quality assurance (QA) events associated with ECG interpretation by EM3s. Methods We conducted a retrospective study of all ED ECGs performed between October 2015 and October 2018, which were read primarily by EM3s, at an urban tertiary care medical center treating 56,000 patients per year. All cases referred to the ED QA committee during this time were reviewed. Cases involving a perceived error were referred to a 20-member committee of ED leadership staff, attendings, residents, and nurses for further consensus review. Ninety-five percent confidence intervals (CIs) were calculated. Results EM3s read 92,928 ECGs during the study period. Of the 3,983 total ED QA cases reviewed, errors were identified in 268 (6.7%; 95% CI, 6.0%–7.6%). Four of the 268 errors involved ECG misinterpretation or failure to act on an ECG abnormality by a resident (1.5%; 95% CI, 0.0%–2.9%). Conclusion A small percentage of the cases referred to the QA committee were a result of EM3 misinterpretation of ECGs. The majority of emergency medicine residencies do not include the senior resident as a primary interpreter of ECGs. These findings support the use of EM3s as initial ED ECG interpreters to increase their clinical exposure.

Emergency department point-of-care ultrasonography improves time to pericardiocentesis for clinically significant effusions

Evan Avraham Alpert,Uri Amit,Larisa Guranda,Rafea Mahagna,Shamai A. Grossman,Ariel Bentancur 대한응급의학회 2017 Clinical and Experimental Emergency Medicine Vol.4 No.3

Objective Our objective was to determine the utility of point-of-care ultrasound (POCUS) to identify and guide treatment of tamponade or clinically significant pericardial effusions in the emergency department (ED). Methods This was a retrospective cohort study of non-trauma patients who were diagnosed with large pericardial effusions or tamponade by the ED physician using POCUS. The control group was composed of those patients later diagnosed on the medical wards or incidentally in the ED by other means such as a computed tomography. The following data were abstracted from the patient’s file: demographics, medical background, electrocardiogram results, chest radiograph readings, echocardiogram results, and patient outcomes. Results There were 18 patients in the POCUS arm and 55 in the control group. The POCUS arm had a decreased time to pericardiocentesis (11.3 vs. 70.2 hours, P=0.055) as well as a shorter length of stay (5.1 vs. 7.0 days, P=0.222). A decreased volume of pericardial fluid was drained (661 vs. 826 mL, P=0.139) in the group diagnosed by POCUS. Conclusion This study suggests that POCUS may effectively identify pericardial effusions and guide appropriate treatment, leading to a decreased time to pericardiocentesis and decreased length of hospital stay. Pericardial tamponade or a large pericardial effusion should be considered in all patients presenting to the ED with clinical, radiographic, or electrocardiographic signs of cardiovascular compromise.