Abstract-The existing cellular networks are being modified under the umbrella of fifth generation (5G) networks to provide high data rates with optimum coverage. Current cellular systems operating in ultra high frequency (UHF) bands suffer from severe bandwidth congestion hence 5G enabling technologies such as millimeter wave (mmWave) networks focus on significantly higher data rates. In this paper, we explore the impact of coexistance of massive Multiple-Input Multiple-Output (MIMO) that provides large array gains and mmWave small cells on coverage. We investigate the downlink performance in terms of coverage and rate of a three tier network where a massive MIMO macro base stations (MBSs) are overlaid with small cells operating at sub-6GHz and mmWave frequency bands. Based on the existing stochastic models, we investigate user association, coverage probability and data rate of the network. Numerical results clearly show that massive MIMO enabled MBSs alongside mmWave small cells enhance the performance of heterogeneous networks (HetNets) significantly.

Massive multiple antenna systems in conjunction with millimeter (mmWave) communication have gained tremendous attention in the recent years owing to their high speed data delivery. However, security in these networks has been overlooked; thereby necessitating a comprehensive study. This paper analyzes the physical layer security performance of the downlink of a massive multiple-input multiple-output (MIMO)-based hybrid heterogeneous network (HetNet) where both mmWave and sub-6 GHz small cells coexist. Specifically, a tractable approach using stochastic geometry is proposed to analyze the secrecy outage probability, secrecy energy efficiency (SEE) and secrecy spectrum efficiency (SSE) of the hybrid HetNets. Our study further characterizes the impact of large antenna arrays, directional beamforming gains, transmit power, and cell density on the above mentioned secrecy performance measures. The results show that at low transmit power operation, the secrecy performance enhances for higher small cell density. It has also been observed that the higher directivity gains at mmWave cells lead to a drop in secrecy performance of the network; thus a tradeoff exists between better coverage or secrecy.This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TGCN.2019.2956433, IEEE Transactions on Green Communications and Networking complex solution for the protection of confidential information in complex wireless networks [8]. Particularly, PLS in massive MIMO-enabled hybrid HetNets with mmWave small cells is important since the aforementioned networks present the most common deployment scenario for the future 5G communication networks. This paper analyses the PLS in massive MIMO-enabled hybrid HetNets by digging into unique advantageous properties of massive MIMO and mmWave channel.

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Microscopic polyangiitis (MPA) is an idiopathic autoimmune disease characterized by necrotizing vasculitis without granulomatous inflammation that predominantly affects small vessels. It most commonly presents in elderly patients but can occur at any age. Here we present a case of an elderly patient who presented with exertional dyspnea and fatigue in the setting of anemia and was diagnosed with microscopic polyangiitis. The patient had a past medical history significant for chronic kidney disease stage IIIb with worsening creatinine over the last four months along with feeling fatigued and intermittently dyspneic associated with black stools for the previous three weeks. A kidney biopsy revealed fibro-cellular crescents consistent with microscopic polyangiitis, and the patient was started on intravenous pulse dose steroids and later put on hemodialysis for worsening creatinine. He was later discharged home on rituximab and oral steroids. MPA is a rare vasculitis that presents with renal dysfunction and occasionally with pulmonary involvement. Gastrointestinal bleeding is rarely associated with the MPO and is thought to be caused by arterial aneurysms. Therefore, MPO should be considered in mind while evaluating GI bleeding in patients with worsening kidney function.