Seung Nam Choi

Development of Millimeter-Wave Communication Modem for Mobile Wireless Backhaul in Mobile Hotspot Network

The current cellular communications are optimized for low mobility users, meaning that their performance is degraded at high speed. Therefore, passengers in a high-speed train experience very poor radio link quality due to the significantly large number of simultaneous handovers. In addition, wireless data traffic is expanding exponentially in trains, subways and buses due to the widespread use of smartphones and mobile devices. To solve the inherent problem of cellular communication networks and meet the growing traffic demand, this paper proposes the mobile hotspot network of a millimeter-wave communication system as a mobile wireless backhaul. This paper describes the physical layer design of uplink and downlink in the proposed system, and the performances of uplink and downlink are evaluated under Rician fading channel conditions. The implemented baseband prototype of the proposed millimeter-wave communication modem is presented. This system can provide a Gbps data rate service in high-speed trains carrying hundreds of wireless Internet users.

Uplink Design of Millimeter-Wave Mobile Communication Systems for High-Speed Trains

Passengers in a high-speed train (350 km/h) experience very poor multimedia services and discontinuous connections due to the much more and simultaneous handovers in the cellular networks. To handle these problems, a millimeter-wave mobile communication system for high-speed trains was introduced and its downlink structure was presented. This paper proposes the uplink structure appropriate to the millimeter-wave mobile communication system. It also describes the frame structure, the multiple access method, and the pilot deployment of the uplink channel. Especially, the uplink pilot was designed to solve the Doppler problem in order to achieve a higher spectrum efficiency. The simulation results of the uplink channel show the spectral efficiency of 4.18 bps/Hz even in 400 km/h under the Rician fading channel conditions.

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.

Performance improvement of MHN-enhanced uplink with frequency offset compensation

This paper proposes an uplink frequency offset compensation scheme for the millimeter-wave (mmWave) based mobile hotspot network that provides a wireless backhaul link of high-speed railway communications. We designed new uplink control and shared channels to mitigate Doppler effects and also proved that the proposed automatic frequency control (AFC) scheme employing the newly designed uplink channels showes better block error rate performances than the original channel structures.

Filter design of interpolation-based SC-FDMA transmitter for random access preamble generation

The physical random access channel (PRACH) of a mobile hotspot network (MHN) is based on a single carrier frequency division multiple access (SC-FDMA). In this paper, we introduce a practical filter design of interpolation-based SC-FDMA transmitter for random access preamble generation. A multistage interpolation filter is used to increase the preamble sampling rate of 12.96 MHz to the system sampling rate of 184.32 MHz, while lowering the sidelobes below -60 dB. In the implementation point of view, this interpolation-based PRACH transmitter provides efficiency and reduction in complexity.

Short Data Transmission with Least Resource in Machine Type Communications

Machine type communications (MTC) is becoming an important part of a cellular network such as Long Term Evolution (LTE). Recently MTC was chosen as Work Item for standardizations and it will be included in 3GPP release 12. Diverse MTC devices transmit small amount of data occupying least resources. Therefore, this paper proposes efficient resource allocation methods for the short MTC uplink data based on the LTE channel structure. Among a few methods, we observed that time division multiplexing is advantageous and the transmit data deployment closer to demodulation reference signals shows a better detection performance.

Development of millimeter-wave communication modem for mobile wireless backhaul

Cellular communications are optimized for the low mobility users and their performances are degraded at high speed. So passengers in a high-speed train (350 km/h) experience very poor radio link qualities. This paper proposes mobile wireless backhaul based on millimeter-wave for mobile hotspot network. Prototype of the baseband modem was presented and the downlink/uplink performances for high-speed trains were analyzed in Rician fading channel conditions.

Uplink data channel in a mobile wireless backhaul of mmWave communications

This paper implemented the uplink data channel of a 27 GHz millimeter-wave mobile wireless backhaul system. The hardware architecture of the receiver was designed and a RTL timing diagram was illustrated. The floating-point/fixed-point simulations were performed under the Rician channel. The uplink data channel can provide a giga-bit data rate service for high speed vehicles in a millimeter-wave mobile wireless backhaul.