Youn-Sun Kim

Full-dimension MIMO (FD-MIMO) for next generation cellular technology

This article considers a practical implementation of massive MIMO systems [1]. Although the best performance can be achieved when a large number of active antennas are placed only in the horizontal domain, BS form factor limitation often makes horizontal array placement infeasible. To cope with this limitation, this article introduces full-dimension MIMO (FD-MIMO) cellular wireless communication system, where active antennas are placed in a 2D grid at BSs. For analysis of the FD-MIMO systems, a 3D spatial channel model is introduced, on which system-level simulations are conducted. The simulation results show that the proposed FD-MIMO system with 32 antenna ports achieves 2-3.6 times cell average throughput gain and 1.5-5 times cell edge throughput gain compared to the 4G LTE system of two antenna ports at the BS.

Coordinated multipoint transmission and reception in LTE-advanced systems

Advanced interference mitigation techniques relying on multipoint coordination have attracted significant attention from the wireless industry and academia in the past few years. In 3GPP LTE-Advanced, a work item on Coordinated Multiple Point transmission and reception (CoMP) was initiated in September 2011, and it is one of the core features of Release 11. The objective of this work item is to provide the necessary specification support to efficiently realize the benefits of cooperative transmission in the downlink and cooperative reception in the uplink. This article discusses the specification support for CoMP and the motivations behind the specific design choices. The deployment scenarios that were considered for the application of CoMP in Release 11 are also presented.

Non-ablative 1550-nm erbium-glass and ablative 10 600-nm carbon dioxide fractional lasers for acne scars: a randomized split-face study with blinded response evaluation

Background  Non‐ablative 1550‐nm erbium‐doped fractional photothermolysis systems (FPS) and 10 600‐nm carbon dioxide fractional laser systems (CO2 FS) have been effectively used to treat scars.

Infrastructure Relay Transmission With Cooperative MIMO

An infrastructure relay system that transfers information from a base station to a randomly located mobile station (MS) using fixed-location relay stations (RSs) is studied. Transmission rates are derived for serial, parallel, and hybrid relay transmissions, considering the utilization of RSs as a means to extend the dimensionality of a multiple-input-multiple-output (MIMO) transmission. The derived transmission rate for the serial relay transmission is optimized by determining the optimal locations of the RSs and the number of hops. In addition, selection schemes for determining which RSs to activate to maximize the transmission rate are provided for parallel and hybrid relay topologies. Based on the analytic findings, numerical results are obtained for various deployment scenarios to compare and evaluate different relay topologies and design characteristics of a relay system.

Full dimension mimo (FD-MIMO): the next evolution of MIMO in LTE systems

Full dimension MIMO, or FD-MIMO, has attracted significant attention in the wireless industry and academia in the past few years as a candidate technology for the next generation evolution toward beyond fourth generation and 5G cellular systems. FD-MIMO utilizes a large number of antennas placed in a 2D antenna array panel for realizing spatially separated transmission links to a large number of mobile stations. The arrangement of these antennas on a 2D panel allows the extension of spatial separation to the elevation domain as well as the traditional azimuth domain. This article discusses features and performance benefits of FD-MIMO along with the ongoing standardization efforts in 3GPP to incorporate FD-MIMO features into the next evolution of LTE. Furthermore, a design of a 2D antenna array, which plays a key role in the implementation of FD-MIMO, is also discussed. Finally, in order to demonstrate performance benefits of FD-MIMO, system-level evaluation results are provided.

Evolution of reference signals for LTE-advanced systems

3GPP LTE Release 10 standards (also known as LTE-Advanced) adopted some of the state-of-the-art radio access technologies that include carrier aggregation, eight-layer downlink spatial multiplexing, and four-layer uplink spatial multiplexing. For facilitating these enhancements, reference signals have significantly evolved in LTE-Advanced. This article examines underlying design principles of the LTE-Advanced reference signals. Specifically, newly introduced dedicated demodulation reference signals and channel state information reference signals for downlink and improvements of demodulation reference signals and sounding reference signals in uplink are discussed.

Performance of an MC-CDMA system with frequency offsets in correlated fading

The performance of an MC-CDMA system with carrier frequency offsets in correlated multipath fading is mathematically analyzed. The bit error rate is obtained from such analysis for the uplink Rayleigh fading channel. The derived results show that the performance of the MC-CDMA system is sensitive to the frequency offset, and the correlation of the subcarriers. That is, the performance degradation of the MC-CDMA system is caused by both carrier frequency offset and correlation among subcarriers. From the derived results, however, the performance degradation due to correlation among subcarriers is more severe than effect of frequency offset.

Fulfilling the promise of massive MIMO with 2D active antenna array

In this paper, we study practical 2-Dimensional (2D) active antenna array configurations for Massive MIMO systems and evaluate the system-level performance with the form factor at the base stations operating in cellular frequency band. To this end, we develop a 3-Dimensional Spatial Channel Model (3D SCM) to facilitate accurate performance evaluation and to build insights for system design. System-level simulation is conducted for various 2D antenna array configurations (8Hx8V, 8Hx4V) by using the 3D SCM developed. Simulation results show that 2-5 times cell average throughput gain and 1.5-9 times cell edge throughput gain can be achieved compared to the 4G LTE system.

Coordinated multi-point transmission in heterogeneous networks: A distributed antenna system approach

With the frequency reuse approaching one and the networks becoming more and more heterogeneous, cooperative multi-point MIMO has become a key candidate technology in the design of future wireless networks and is nowadays an active research topic in the academia and the industry. In 3GPP LTE-Adv. Rel. 11, a new study item on Coordinated Multi-Point transmission and reception (commonly denoted as CoMP) has been initiated in December 2010 and is expected to be one of the major features of Rel. 11. A particularly interesting deployment scenario is the distributed antenna system (DAS) where cooperative transmission is applied between distributed transmission points belonging to a common cell. In this paper, we discuss the pros and cons of distributed antenna systems versus classical heterogeneous networks like picocells, the appropriate cooperative schemes and the design challenges. We confirm the benefits of such technology through system level performance evaluations compliant with LTE-Adv.

Overview of Full-Dimension MIMO in LTE-Advanced Pro

Multiple-input multiple-output (MIMO) systems with a large number of base station antennas, often called massive MIMO, have received much attention in academia and industry as a means to improve the spectral efficiency, energy efficiency, and processing complexity of next generation cellular systems. The mobile communication industry has initiated a feasibility study of massive MIMO systems to meet the increasing demand of future wireless systems. Field trials of the proof-of-concept systems have demonstrated the potential gain of the Full-Dimension MIMO (FD-MIMO), an official name for the MIMO enhancement in the 3rd generation partnership project (3GPP). 3GPP initiated standardization activity for the seamless integration of this technology into current 4G LTE systems. In this article, we provide an overview of FD-MIMO systems, with emphasis on the discussion and debate conducted on the standardization process of Release 13. We present key features for FD-MIMO systems, a summary of the major issues for the standardization and practical system design, and performance evaluations for typical FD-MIMO scenarios.