Heesang Chung

A study on millimeter-wave beamforming for high-speed train communication

This paper investigates three millimeter-wave beamforming (BF) scenarios for high-speed train (HST) communication that can potentially help to meet the explosively growing demand for Internet services in HSTs. Throughout the paper, we introduce the BF schemes based on the beam pattern that we designed and show the performance of three BF scenarios via the simulation, which demonstrates that in the case of adaptive BF applied to both transmitter (TX) and receiver (RX), the highest SINR can be obtained. It is also shown that the different BF schemes are appropriate for different HST location and the fixed BF can achieve very similar performance to that of adaptive BF in most of time. Consequently, we have gained a valuable insight into designing a mmWave BF based HST communication system from feasibility and implementation perspective.

Performance Evaluation of Millimeter-Wave-Based Communication System in Tunnels

This report presents performance evaluation of a prototype of a millimeter-wave-based communication system in tunnel environments. The prototype could give 500 Mbps of data rate throughout 1.1 km on a straight route. The data rate dropped from 500 Mbps to 100 Mbps while a receiver of the prototype passed by 530-m point on a curved route. The results can be used to determine appropriate locations of trackside radio components to achieve enough coverages in a system deployment for railway communication networks.

Efficient Doppler mitigation for high-speed rail communications

Since the high-speed rail (HSR) communications are suffering from the huge Doppler shift, an efficient Doppler mitigation method is proposed in this paper. The proposed method mainly concerns about the mitigation of Doppler shift in OFDM based systems, especially for the case of employing mmWave with very high mobility. The proposed method can be used for both downlink and uplink of the system and it is quite robust to the time-varying mobility. Furthermore, the pilot-aided channel estimation for Doppler compensation is not necessary in most of the cases, which indicates the pilot density in time-domain can be reduced. Simulation results show that by using the proposed method, the residual Doppler shift can be compressed to 0 Hz with the probability of 90%.

Uplink control channel of mobile hotspot network

The need for more extended communication throughput for public transportations is gradually increased. Among several solutions, millimeter-wave-based backhaul system named as MHN is under development. In this paper, we propose architectures of uplink control channel for MHN. The proposed control channels are simulated over high-speed moving environment in Rician fading channel. The results show that the proposed control channels are affected by Doppler frequency shift over 100 km/h. The architecture and simulation results may be useful in designing uplink control channels for high-speed mobile communication.

From architecture to field trial: A millimeter wave based MHN system for HST Communications toward 5G

This report presents a mobile hotspot network system to provide mobile Internet services for the passengers in the high speed trains. 3GPP has been working on enhanced mobile broadband under many deployment scenarios such as indoor hotspots, dense urban, rural, high speed, etc. The high speed deployment scenario deals with continuous coverage along track in the high speed trains considering mobility of up to 500 km/h. The design concept of the mobile hotspot network system is in line with the 3GPP deployment scenario. The system will eventually provide the fifth generation mobile network services based on the very wide bandwidth of millimeter waves. The designs and architecture of the system will be disclosed. Also, the performance and mobility management issue will be addressed. A proof-of-concept demonstration with the system prototype will be presented.

Creation and control of handover zone using antenna radiation pattern for high-speed train communications in unidirectional networks

In order to successfully perform the break-before-make handover for high-speed train (HST) communications in unidirectional networks, it is well agreed that the handover zone should be created. In this paper, handover zone creation and control methods are proposed. Instead of intentionally create an engineered handover zone by overlapping the coverages of adjacent cells, the nature of antenna radiation pattern is adopted for creating the proposed handover zone. The analysis and simulation results employing the system parameters of mobile hotspot network (MHN) show that the proposed handover zone can be easily controlled by setting the parameters corresponding to the antenna radiation pattern, which enables its flexible use for handover in HST communication networks.

Synchronization and Cell Searcher Design over OFDM Frame Structure Based on Millimeter Waves

This report proposes two types of synchronization signal structure and corresponding cell searcher designs for use in orthogonal frequency division multiplexing transmission over millimeter waves. The performance of the cell searchers has been assessed in terms of detection error rate under a high-speed train environment. The simulation results provide an insight into how power spectral density (PSD) boosting is an efficient design tool to achieve both signal-to-noise ratio (SNR) gains and low implementation complexity. Accordingly, the PSD boosted design of the two proposed structures is capable of delivering SNR gains in detection probability, and low hardware complexity, at the same time. Additionally, the analysis deals with non-coherent energy combining as a useful way of improving the detection probability under various channel environments. It also revealed how trade-offs between time diversity and Doppler frequency shift under various mobility cases are tightly coupled with non-coherent energy combining.