Il-Gyu Kim

An efficient synchronization signal structure for OFDM-based cellular systems

OFDM has been a widely accepted technology in high rate and multimedia data service systems such as long term evolution (LTE) in the 3rd generation partnership project (3GPP). In this paper, we investigate a synchronization signal structure and corresponding cell search algorithm in the LTE system where two, primary and secondary synchronization signals are employed. We focus on the secondary synchronization signal which possesses two layered scrambling sequences in addition to basic sequences. These scrambling sequences minimize performance degradation in cell search, but incur a high complexity to a mobile station receiver. In this paper, we propose a new secondary synchronization signal structure which does not require additional scrambling sequences while maintaining almost the same performance as the current LTE scheme. We evaluate the performance of the proposed scheme under various channel environments by examining the impacts of multipath fading, frequency offset, and vehicular speed. We also compare the complexity of the proposed scheme with the LTE scheme.

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.

5G CHAMPION - Rolling out 5G in 2018

The 5G CHAMPION Consortium will provide the first fully integrated and operational 5G prototype in 2018 - this effort is a major leap ahead compared to existing punctual technology trials, such as, e.g., Proof-of-Concept platforms focusing on mmWave communication in specific bands, etc. This paper describes the overall set-up including a synergetic combination of technologies such as beamforming based mmWave & Satellite service provisioning, virtualized infrastructure, software reconfiguration across the entire stack, accurate positioning and high-speed solutions. The key enablers are described in detail and related efforts in standards and regulation organizations are discussed.

Design of Downlink Control Channels for Millimeter Wave Mobile Hotspot Network System

Recently, according to the survey, one of the most frequent place to use mobile internet is the moving vehicle, such as bus, subway and train. Therefore, the high speed data rate services for mobile group vehicles moving at high speed are severely required. We design and develop a new system, which can support upto 2.5Gbps data rate services for mobile group vehicles moving at high speed over 400km/h, e.g., KTX (Korea Train Express), TGV (Train a Grande Vitesse) and ICE (InterCity Express), etc. in ETRI (Electronics and Telecommunications Research Institute). In this paper, we propose and design a new structure of the physical layer downlink control channels, and furthermore, we verified the performance of the downlink control channels by computer simulation. Especially, we compared the performance between floating point simulation and fixed point simulation. We verified the performance gap is under 0.5dB. Currently, we develop the test-bed of MHN system and have a target to demonstrate the real time performance of the MHN system on the outdoor environment in 2014. Outdoor demonstration will be done in subway in 1st step. In this paper, we are focusing on the performance of MHN DL control channels, especially on the fixed performance to develop RTL design in test-bed system. We also show the performance of these channels meet the required SNR.

Performance analysis of uplink handover searcher in asynchronous WCDMA system

Unlike in the IS-95 based synchronous CDMA system, in the 3GPPs asynchronous WCDMA system, it is impossible for the network to estimate the round trip delay between the handover UE (user equipment) and the target base station (BS) before the handover execution, so the uplink handover search window size of the target BS becomes large. In order to get good link quality during handover execution, it is very important to reduce the uplink handover search time at the target BS. We propose an efficient uplink handover search scheme for an asynchronous WCDMA system. Average search time performance of the proposed scheme is analyzed for a fading channel environment. The effects of the non-coherent accumulation length of the search mode and that of the verification mode to the average search time performance are analyzed. The optimal threshold values of the search mode and the verification mode are investigated. The results analyzed in this paper may be useful for designing the uplink handover searcher of 3GPPs WCDMA base station.

A 2.59-GHz RF self-interference cancellation circuit with wide dynamic range for in-band full-duplex radio

A 2.59GHz self-interference cancellation (SIC) circuit is presented for in-band full-duplex radio. The SIC circuit is based on an analog vector modulator whose output can automatically track the time-varying self-interference signal through an analog LMS algorithm based weight calculation circuit. By adding a variable gain stage after the vector modulator, the total dynamic range is significantly widened so that the SIC can deal with large Tx power variation and/or Tx-to-Rx attenuation. Implemented in 16.4 × 11.9 cm2 printed circuit board, the circuit achieves the cancellation ratio of 39.2 dB and 39.4 dB for 5MHz and 10MHz bandwidth 16-QAM signal, respectively. Also, the dynamic range is increased from 22 dB to 40 dB by properly setting the variable gain.

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.

Massive MIMO test-bed design for next-generation long term evolution (LTE) mobile systems in the frequency division duplex (FDD) mode.

A massive MIMO test-bed under design is introduced as the pilot for next-generation long term evolution (LTE) mobile systems in the frequency division duplex (FDD) mode. In the design stage, computer simulations are performed and in a given conditions the results demonstrate that the test-bed algorithms possibly fulfill the capacity requirements of the fifth generation cellular system, which is one thousand times of that of the legacy LTE system. However, the complexity of the test-bed is not significantly increased with the adoption of new concepts like user grouping and beamforming, which enables the base station (BS) to use both smaller numbers of transmit pilot patterns and smaller amounts of channel state information feedback.

Enabling Technologies toward Fully LTE-Compatible Full-Duplex Radio

Full-duplex radio has potential to double spectral efficiency by simultaneously transmitting and receiving signals in the same frequency band, but at the expense of additional hardware and power consumption for self-interference cancellation. Hence, the deployment of a full-duplex cellular network can be realized by employing full-duplex functionality only at an eNodeB, which is supposed to have sufficient computation and power resources, and by scheduling pairs of half-duplex UEs that are in either downlink or uplink. By doing so, fast and smooth full-duplex deployment is possible while minimally affecting the legacy UEs and the rest of the network entities. In this article, we provide technical challenges and solutions for an LTE-compatible full-duplex cellular network, featuring wideband and wide dynamic range support for RF self-interference cancellation, and robust and efficient self-interference channel estimation for digital self-interference cancellation. Based on a realistic LTE-based cellular model, our full-duplex radio design is evaluated through system-level simulations and real-world testbed experiments. Simulation results show that a significant throughput gain can be achieved by the full-duplex technique despite the existence of physical limiting factors such as path loss, fading, and other-cell interference. Testbed measurements reveal that at a bandwidth of 20 MHz, self-interference cancellation up to 37 dB is achieved in the RF domain, and most of the residual self-interference is further cancelled down to the noise floor in the subsequent digital domain.

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%.