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Before/After Precoding Massive MIMO Systems for Cloud Radio Access Networks
Park, Sangkyu,Chae, Chan-Byoung,Bahk, Saewoong The Korea Institute of Information and Commucation 2013 Journal of communications and networks Vol.15 No.4
In this paper, we investigate two types of in-phase and quadrature-phase (IQ) data transfer methods for cloud multiple-input multiple-output (MIMO) network operation. They are termed "after-precoding" and "before-precoding". We formulate a cloud massive MIMO operation problem that aims at selecting the best IQ data transfer method and transmission strategy (beamforming technique, the number of concurrently receiving users, the number of used antennas for transmission) to maximize the ergodic sum-rate under a limited capacity of the digital unit-radio unit link. Based on our proposed solution, the optimal numbers of users and antennas are simultaneously chosen. Numerical results confirm that the sum-rate gain is greater when adaptive "after/before-precoding" method is available than when only conventional "after-precoding" IQ-data transfer is available.
Sangkyu Park,Chan-Byoung Chae,Saewoong Bahk IEEE 2015 IEEE wireless communications Vol.22 No.3
<P>To satisfy the ever increasing capacity demand and quality of service requirements of users, 5G cellular systems will take the form of HetNets that consist of macrocells and small cells. To build and operate such systems, mobile operators have given significant attention to cloud radio access networks, C-RANs, due to their beneficial features of performance optimization and cost effectiveness. Along with the architectural enhancement of C-RAN, largescale antennas (a.k.a. massive MIMO) at cell sites contribute greatly to increased network capacity either with higher spectral efficiency or through permitting many users at once. In this article, we discuss the challenging issues of CRAN- based HetNets (H-CRAN), especially with respect to large-scale antenna operation. We provide an overview of existing C-RAN architectures in terms of large-scale antenna operation and promote a partially centralized approach. This approach remarkably reduces fronthaul overheads in C-RANs with large-scale antennas. We also provide some insights into its potential and applicability in the fronthaul bandwidth-limited H-CRAN with large-scale antennas.</P>
TSCH 네트워크에서 발생하는 충돌문제 원인 분석 및 검증
박정준(Jeongjun Park),박세웅(Saewoong Bahk) 한국통신학회 2022 한국통신학회 학술대회논문집 Vol.2022 No.2
본 논문은 사물 인터넷 (IoT) 환경 중 low-power and lossy networks (LLNs)에서 보편적으로 사용되는 time-slotted channel hopping (TSCH) 기반의 동작에서 다수의 송신자가 동시에 데이터를 전송할 때 겪는 충돌문제에 대하여 원인을 분석하고 이를 검증한다. 이를 위해 collision detection ratio (CDR)을 정의하고, 실제 테스트 베드에서 충돌문제를 측정함으로써 TSCH의 충돌문제를 검증한다.