Sangkyu Baek

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.

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.

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.

Comparison Analysis of Outdoor Channel Characteristics at 28 GHz and 2 GHz Using 3D Ray-Tracing Technique

Broadband wireless systems operating in millimeter wave (mmWave) frequency band has been used for short-range wireless communication and point-to- point wireless backhaul. Due to lack of research work on outdoor radio propagation characteristics in mmWave frequency band, the question of feasibility of cellular communication including long-range and non-line of sight (NLoS) environments in mmWave frequency band is unanswered. In this paper, we investigate the radio propagation characteristics at 28 GHz and 2 GHz using 3D ray-tracing simulation based on Manhattan-like grid model. LoS and NLoS results of outdoor radio propagation characteristics considering beamforming effects at 28 GHz are provided. Results of 2 GHz in the same geometry are also provided. In LoS environment, the radio propagation with 25 dBi beamforming gain at 28 GHz has similar characteristics with 2 GHz. In NLoS environment, even if the transmitter has 25 dBi beamforming gain at 28 GHz, the received power is 10 to 25 dB lower than 2 GHz. The received power loss because of narrow beam usage at 28 GHz is negligible in both LoS and NLoS environments.

A study on correlation properties of shadow fading of millimeter wave frequency spectrum

Correlation properties of shadow fading are the essential part of a large-scale channel model to evaluate system-level performance. The recent interest on mmWave frequency band naturally requires the study of these correlation properties so that new cellular system based on the new spectrum on mmWave band can be identified to be feasible. To the best of our knowledge, the correlation study has been done in only legacy band, below 6 GHz, and the study of these correlation properties in mmWave channel is required. In this paper, we investigate the correlation of shadow fading in mmWave frequency band by comparing this with the results in conventional cellular frequency band, i.e., under 6 GHz. In detail, decorrelation distance and site-to-site correlation as the correlation parameters are obtained from the results of the ray-tracing simulation at 28 GHz and 2 GHz frequencies in the area of downtown of Ottawa. The simulation results show the similarity of the decorrelation distance which is statistically independent of frequency. Also, 28 GHz and 2 GHz have similar site-to-site correlation values to each other. From these results, we claim that the correlation parameters for mmWave frequency band can be adopted from the parameters of the conventional cellular frequency band.

Performance analysis of IEEE 802.15.4 superframe structure with the inactive period

Abstract We analyze the performance of IEEE 802.15.4 MAC with superframe structure including the inactive period where each device is in non-saturated conditions. The superframe structure with a inactive period has the following two primary characterizations: (i) deferment of packet transmission until the following active period due to insufficient backoff slots for completing the packet transmission, (ii) high competition in the head part of the active period due to packets which were deferred from the previous active period and were arrived during the previous inactive period. These characterizations complicate the construction of a mathematical model of MAC with the superframe structure including a inactive period. In this paper, we construct a discrete time Markov chain (DTMC) model which takes into account these characterizations. By analyzing the DTMC, we obtain the main performance measures such as throughput, packet delay distribution, packet loss probability and energy consumptions of devices and the PAN coordinator. We demonstrate high accuracy of the proposed model by comparing the numerical results with simulation results. Finally, we optimize the lengths of the beacon interval and the active period to maximize the battery life of devices while satisfying quality-of-service (QoS) constraints on packet delay and packet loss probability.

Energy efficient IP reachability for push service in NATted LTE systems

As smartphones have become increasingly pervasive, large amount of mobile data traffic has started to overwhelm the networks. Surprisingly, according to [1], the main cause of network congestion in cellular networks today is not only the data traffic generated by smartphones, but also the underlying signaling from the smartphone applications such as push email, instant messaging, and social network services. Such signaling is inevitable as the service providers need to provide always connected service to users. Among multiple signaling burdens, we consider “keepalive” message that is widely used to make a persistent IP connection for most push services in order to keep Network Address Translation (NAT) tables refreshed. Keepalive messages not only overburden the cellular network due to accompanied signaling traffics, but also significantly reduce the battery life of smartphones. In this paper, we propose a method that makes the push service possible without a keepalive mechanism for NATted network system. When the application servers have data to send to some UE given that the UEs information such as IP address and port number is not available in the servers, they first request this information from the network instead of maintaining a persistent IP connection. Our proposal helps increasing the battery life of the smartphone and relieving the overhead of the network. Simulation results show that the proposed scheme can reduce both battery power consumption and signaling traffic of UE by more than about 30% and 20%, respectively, compared to the keepalive-based legacy mechanism.