Seok Ho Won

Inter-Cell Interference Coordination/Avoidance for Frequency Reuse by Resource Scheduling in an OFDM-Based Cellular System

This paper proposes and evaluates a new method for mitigating inter-cell interference. We show that the proposed method results in a minor degradation of block error rate under low traffic loading but results in significant improvements for high traffic loads. We also propose and compare two options for resource re-allocation following allocation conflicts: immediate (synchronous) re-allocation and round-robin re-allocation. Simulation results indicates that round-robin reallocation results in good BLER performance when the traffic load is high.

Capacity enhancement by using optimum step sizes of controlling target SIR in a CDMA system

This paper describes the capacity improvement by an algorithm controlling the base stations receiving target SIR (signal-to-interference ratio) to maintain a pre-set FER (frame error rate). It is shown that the presented algorithm has a lower mean for the actual SIR received at the antenna than the existing method which applies the fixed target SIR needed for the worst case to every user and every time instant. It is also shown that the capacity of the system can be further increased by applying the optimum step sizes in the algorithm.

Physical layer implementation and evaluation of multiple input multiple output - orthogonal frequency division multiplexing (MIMO-OFDM) system

In this paper, we introduce a physical layer implementation and some test results for the multiple input multiple output - orthogonal frequency division multiplexing (MIMO-OFDM) fast prototype system for the fourth generation mobile communication. The system has the key features of antenna diversity maximizing and fading-robustness with the preamble/pilots and frame structures, which are suitable for channel estimation, timing, and frequency synchronization and unbiased signal-to-noise-plus-interference ratio estimation. These features are verified by the analysis and evaluation test results got from the implemented MIMO-OFDM system.

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.

Channel estimation methods adequate to space time transmit diversity receiver in the W-CDMA IMT-2000 system

This paper presents some channel estimation methods adequate for the space time transmit diversity (STTD) receiver that coherently demodulates signals from each path of two transmit antennas. The STTD mode receiver estimates the channel information of each antenna path from the received common pilot channel (CPICH) signals with known orthogonal patterns transmitted by two antennas at the base station. The conventional channel estimation methods using a pilot filter result in serious inter-antenna interference caused by imperfect orthogonal processing of signals between the two antennas. Another drawback is the inter-symbol interference caused by lack of orthogonality between two symbols Which is the basic premise of the STTD decoding algorithm. This paper analyzes the effects of the inter-symbol interference and proposes some robust channel estimation methods to reduce the effects of the inter-symbol interference; This paper also compares the performance of the proposed channel estimation methods in various fading channel environments through the effective signal to interference ratio (SIR) and the bit error rate (BER).

A Robust AMC that Guarantees Packet Error Rate and its Evaluation under a Handover Scenario in OFDM-Based Evolved UTRA Downlink

This paper proposes and evaluates a new AMC method to improve throughput and guarantee a constant packet error rate in an OFDM-based evolved UTRA (E-UTRA) downlink. Simulation results show that the proposed method has a better throughput than conventional methods in most overall wireless environments, including the handover region where the cell edge effect is problematic, and thus, the method increases the handover success rate in the given handover scenario. Further evaluation of the method using various cell loading factors verify that the method resists against the interferences that occur more in high cell loadings and also in the handover region.

Development of 5G CHAMPION testbeds for 5G services at the 2018 Winter Olympic Games

This paper describes the first available 5G testbeds as designed by 5G CHAMPION, a collaborative research project undertaken by over twenty consortium members and targeting the provision of 5G services at the 2018 Winter Olympics in Korea. In order to provide 5G services such as augmented reality (AR), virtual reality (VR), high quality, interactive multi-player video games, the testbeds shall fulfill the challenging requirements such as ultra-high data rates, ultra-reliable low latency, and mass connectivity. To meet such requirements, revolutionary testbed architectures are proposed, designed to be flexible, cost- and energy-efficient, through adopting state-of-art multi-radio access technologies (RAT) in client devices and in the network. The testbeds will also provide mmWave wireless backhaul, an interoperable and seamless connection between two different access networks located in Europe and on the site of the Korean Winter Olympic Games.

Virtual antenna mapping MIMO techniques in a massive MIMO test-bed for backward compatible LTE mobile systems

This paper proposes a virtual antenna mapping method for backward compatible massive or large-scale antenna multiple input multiple output (MIMO) base stations that provide communication services for legacy user equipment (UE) that can recognize only two or four base station antennas. The proposed method adopts and improves the omnidirectional beamforming that has been pioneered in previous works with proposing new method of determining antenna array coefficients through shifting the discrete Fourier transform (DFT) basis vectors for Zadoff-Chu (ZC) sequences. In the proposed method, the number of the parameters to be optimized is only two although the number of transmit antennas is hundreds or more (e.g., 500 antennas was proved in the paper as an example). Moreover, with the independent properties of the shifted versions of ZC sequences, this paper proves the fact that the coefficient vectors consisting virtual transmit antennas are independent when the channel gains work as the coefficients of them. This characteristic gives diversity with the pre-codes because two pre-code vectors must independent which means their linear combination with the non-zero channel gains or coefficients cannot be zero. The computer simulation results provide four important findings; the most important is that the actual number of virtually mapped physical antennas is inversely proportional to the transmit power per antenna.

An omnidirectional beamforming technique for massive MIMO systems

Alongside highly sharp beamforming, omnidirectional beamforming (OBF) is important technique for a practical system to make beacons or broadcast channels. Therefore, many methods have been proposed to find optimum transmission antenna coefficients to steer omnidirectional beams efficiently. These conventional optimization methods are simple and efficient. However, for massive multiple input multiple output (MIMO) systems, as the number of variables or transmission antenna coefficients to optimize increases, the computation complexity increases exponentially and eventually it is impossible to compute. To solve this problem, we redefine system model by approximation and variable substitution processes to use Fourier transform for analysis. By using these processes, we find new OBF method that is simple and tolerable to the errors inevitably occurred in the processes. Even for the massive MIMO system with hundreds of transmission antennas, the proposed method has only two optimization variables while the conventional methods try to compute hundreds of optimization variables. Moreover we find the values of these two optimization variables asymptotically approaches constant as the number of transmission antennas increases. Therefore, our accomplishment contributes to future analysis for ideal massive MIMO system.

Backward compatible MIMO techniques in a massive MIMO test-bed for long term evolution (LTE) mobile systems

This paper proposes a virtual antenna mapping method for backward compatible massive or large-scale antenna multiple input multiple output (MIMO) base stations that provide communication services for legacy user equipment (UE) that can recognize only two or four base station antennas. The proposed method adopts and improves the omnidirectional beamforming that has been pioneered in previous works. The computer simulation results provide four important findings; the most important is that the actual number of virtually mapped physical antennas is inversely proportional to the transmit power per antenna.