Sooyoung Hur

Millimeter Wave Beamforming for Wireless Backhaul and Access in Small Cell Networks

Recently, there has been considerable interest in new tiered network cellular architectures, which would likely use many more cell sites than found today. Two major challenges will be i) providing backhaul to all of these cells and ii) finding efficient techniques to leverage higher frequency bands for mobile access and backhaul. This paper proposes the use of outdoor millimeter wave communications for backhaul networking between cells and mobile access within a cell. To overcome the outdoor impairments found in millimeter wave propagation, this paper studies beamforming using large arrays. However, such systems will require narrow beams, increasing sensitivity to movement caused by pole sway and other environmental concerns. To overcome this, we propose an efficient beam alignment technique using adaptive subspace sampling and hierarchical beam codebooks. A wind sway analysis is presented to establish a notion of beam coherence time. This highlights a previously unexplored tradeoff between array size and wind-induced movement. Generally, it is not possible to use larger arrays without risking a corresponding performance loss from wind-induced beam misalignment. The performance of the proposed alignment technique is analyzed and compared with other search and alignment methods. The results show significant performance improvement with reduced search time.

Proposal on Millimeter-Wave Channel Modeling for 5G Cellular System

This paper presents 28 GHz wideband propagation channel characteristics for millimeter wave (mmWave) urban cellular communication systems. The mmWave spectrum is considered as a key-enabling feature of 5G cellular communication systems to provide an enormous capacity increment; however, mmWave channel models are lacking today. The paper compares measurements conducted with a spherical scanning 28 GHz channel sounder system in the urban street-canyon environments of Daejeon, Korea and NYU campus, Manhattan, with ray-tracing simulations made for the same areas. Since such scanning measurements are very costly and time-intensive, only a relatively small number of channel samples can be obtained. The measurements are thus used to quantify the accuracy of a ray-tracer; the ray-tracer is subsequently used to obtain a large number of channel samples to fill gaps in the measurements. A set of mmWave radio propagation parameters is presented based on both the measurement results and ray-tracing, and the corresponding channel models following the 3GPP spatial channel model (SCM) methodology are also described.

Synchronous channel sounder using horn antenna and indoor measurements on 28 GHz

The millimeter wave band will be a key component in the next generation wireless communication system (5G), and a proper channel model is needed for developing the future 5G cellular technologies. This paper introduces a 28 GHz channel sounder based on automatically rotating horn antennas with time synchronization ability between the transmitter (TX) and the receiver (RX). We have developed a sounding method for synchronized measurement using the proposed channel sounder system which records time-stamping to measure the relative propagation time from the transmitter to receiver. The proposed approach allows us to generate an omni-like channel measurements by synthesizing all directional measurements, which have been verified by comparison with the measurements of omni-directional antennas. Subsequently, the omni-directional propagation measurement results are provided in an in-building environment similar to a small shopping mall. From the measurements, the clustering analysis has been done including its power distribution. This paper provides the first channel sounder and initial results to obtain the synthesized omni-directional results in millimeter wave 28 GHz band.

5G 3GPP-Like Channel Models for Outdoor Urban Microcellular and Macrocellular Environments

For the development of new 5G systems to operate in bands up to 100 GHz, there is a need for accurate radio propagation models at these bands that currently are not addressed by existing channel models developed for bands below 6 GHz. This document presents a preliminary overview of 5G channel models for bands up to 100 GHz. These have been derived based on extensive measurement and ray tracing results across a multitude of frequencies from 6 GHz to 100 GHz, and this document describes an initial 3D channel model which includes: 1) typical deployment scenarios for urban microcells (UMi) and urban macrocells (UMa), and 2) a baseline model for incorporating path loss, shadow fading, line of sight probability, penetration and blockage models for the typical scenarios. Various processing methodologies such as clustering and antenna decoupling algorithms are also presented.

Multilevel millimeter wave beamforming for wireless backhaul

Due to the projected increased demand for high data rate mobile services, interest has grown in new cellular network architectures such as a tiered networks. This paper proposes a beam searching algorithm and a codebook design for multilevel beamforming in outdoor millimeter wave communication systems. In an outdoor millimeter wave scenario, the received signal suffers from severe path loss and various attenuation factors. Beamforming is an essential component to establish the wireless link in 60GHz up to 80GHz. A millimeter wave beamforming method based on joint transmitter-receiver searching of an adaptive codebook is described. To reduce search complexity, an adaptive beam width beamforming technique is developed based on a sub-array method using squinting angles. A multilevel codebook having a hierarchical tree-structure on different beam width is adaptively designed. The performance of the proposed codebook design is analyzed, and the joint search algorithm is compared with other search methods. The proposed search method and the codebook design show performance improvement with small complexity.

Indoor 5G 3GPP-like channel models for office and shopping mall environments

Future mobile communications systems are likely to be very different to those of today with new service innovations driven by increasing data traffic demand, increasing processing power of smart devices and new innovative applications. To meet these service demands the telecommunications industry is converging on a common set of 5G requirements which includes network speeds as high as 10 Gbps, cell edge rate greater than 100 Mbps, and latency of less than 1 msec. To reach these 5G requirements the industry is looking at new spectrum bands in the range up to 100 GHz where there is spectrum availability for wide bandwidth channels. For the development of new 5G systems to operate in bands up to 100 GHz there is a need for accurate radio propagation models which are not addressed by existing channel models developed for bands below 6 GHz. This paper presents a preliminary overview of the 5G channel models for bands up to 100 GHz in indoor offices and shopping malls, derived from extensive measurements across a multitude of bands. These studies have found some extensibility of the existing 3GPP models (e.g. 3GPP TR36.873) to the higher frequency bands up to 100 GHz. The measurements indicate that the smaller wavelengths introduce an increased sensitivity of the propagation models to the scale of the environment and show some frequency dependence of the path loss as well as increased occurrence of blockage. Further, the penetration loss is highly dependent on the material and tends to increase with frequency. The small-scale characteristics of the channel such as delay spread and angular spread and the multipath richness is somewhat similar over the frequency range, which is encouraging for extending the existing 3GPP models to the wider frequency range. Further work will be carried out to complete these models, but this paper presents the first steps for an initial basis for the model development.

Millimeter-Wave Propagation: Characterization and modeling toward fifth-generation systems. [Wireless Corner]

The World Radiocommunication Conference 2015 (WRC-15) identified a number of frequency bands between 24 and 86 GHz as candidate frequencies for future cellular networks. In this article, an extensive review of propagation characteristics and challenges related to the use of millimeter wave (mm-wave) in future wireless systems is presented. Reference to existing path-loss models including atmospheric and material attenuation in recommendations of the International Telecommunication Union (ITU) in Geneva, Switzerland, is given, and the need for new multidimensional models and measurements is identified. A description of state-of-the-art mm-wave channel sounders for single and multiple antenna measurements is followed by a discussion of the most recent deterministic, semideterministic, and stochastic propagation and channel models. Finally, standardization issues are outlined with recommendations for future research.

A novel dual-slope mm-Wave channel model based on 3D ray-tracing in urban environments

To solve mobile traffic crunch, the usage of enormous bandwidth in millimeter wave (mm-Wave) is under discussion. In this paper, we investigate radio channel characteristics of mm-Wave frequency in the downtown area of Ottawa using 3D ray-tracing technique. In the results, important parameters of the radio channel model, such as path loss exponent, shadow fading, delay spread and angle spread, are provided. Especially, in case of path loss model in non-line of sight, a novel dual-slope approach is proposed for two conventional deployment scenarios. Comparing to traditional single-slope path loss model, the proposed method has smaller RMS errors in terms of local mean of path loss observations. We believe that the proposed method is appropriate to evaluate performance of the mm-Wave system in dense urban environments.

Millimeter-Wave Channel Measurements and Analysis for Statistical Spatial Channel Model in In-Building and Urban Environments at 28 GHz

The millimeter-wave (mm-wave) band will be a key component of fifth-generation (5G) wireless communication systems. This paper presents radio propagation measurements and analysis investigating the wideband directional channel characteristics of the mm-wave transmission for in-building and urban cellular communication systems in the 28-GHz band. Based on the measurements, we analyze and model the spatio-temporal channel characteristics such as multipath delay, angular statistics, and path loss. In particular we investigate the clustering of the multipath components, and investigate both the intra-cluster and inter-cluster distributions. Based on these investigations, we present a complete channel model suitable for system simulations in the in-building and urban environments.

3-Dimensional Large-Scale Channel Model for Urban Environments in mmWave Frequency

From the results of the ray-tracing simulation of 28 GHz frequency band over downtown of Ottawa and New York University campus, we propose 3D large-scale channel models for urban city which are applicable to a mmWave version of 3D spatial channel model. Due to the change of geographical topology dimension from 2D to 3D, the height information of the transmitter should be reflected to the parameters of the channel model such as line-of-sight probability, Ricean K factor, path loss and shadow fading accordingly. In the simulation results, the line-of-sight probability depends on the height of the transmitter compared to the 2D model. The dual-slope path loss model is still appropriate in 3D channel model. We also propose the linear standard deviation function of the shadow fading, which shows a large standard deviation and an increasing trend with the distance.