Kyungwhoon Cheun

Millimeter-wave beamforming as an enabling technology for 5G cellular communications: theoretical feasibility and prototype results

The ever growing traffic explosion in mobile communications has recently drawn increased attention to the large amount of underutilized spectrum in the millimeter-wave frequency bands as a potentially viable solution for achieving tens to hundreds of times more capacity compared to current 4G cellular networks. Historically, mmWave bands were ruled out for cellular usage mainly due to concerns regarding short-range and non-line-of-sight coverage issues. In this article, we present recent results from channel measurement campaigns and the development of advanced algorithms and a prototype, which clearly demonstrate that the mmWave band may indeed be a worthy candidate for next generation (5G) cellular systems. The results of channel measurements carried out in both the United States and Korea are summarized along with the actual free space propagation measurements in an anechoic chamber. Then a novel hybrid beamforming scheme and its link- and system-level simulation results are presented. Finally, recent results from our mmWave prototyping efforts along with indoor and outdoor test results are described to assert the feasibility of mmWave bands for cellular usage.

Mobile's millimeter-wave makeover

People in real estate joke that there are only three things that matter in the business of buying and selling property: location, location, location. The same could be said for radio spectrum. The frequencies used for cellular communications have acquired the status of waterfront lots-highly coveted and woefully scarce. And like beach-home buyers in a bidding war, mobile operators must constantly jockey for these prime parcels, sometimes shelling out as much as tens of billions of dollars for just a small sliver of the electromagnetic pie.

Frequency and Quadrature-Amplitude Modulation for Downlink Cellular OFDMA Networks

The distribution of the intercell interference (ICI) in conventional cellular networks employing orthogonal frequency-division multiple-access (OFDMA) with quadrature-amplitude modulation (QAM) tends to approach a Gaussian distribution when all available subcarriers in each cell are fully loaded. Recently, it has been also shown that the worst-case distribution of the ICI as additive noise in wireless networks with respect to the channel capacity is Gaussian. Thus, the channel capacity in cellular networks is expected to be further enhanced when the ICI could be designed properly so that it has a non-Gaussian distribution. This observation motivates us to propose, in this paper, a downlink cellular OFDMA network employing a modulation scheme called frequency and QAM (FQAM). We also derive maximum-likelihood metrics for the binary or non-binary error-correcting codes employed in the proposed network and propose their practical sub-optimal versions. Numerical results demonstrate that the distribution of the ICI in the proposed network deviates far from the Gaussian distribution. As a result, the transmission rates for the cell-edge users in the proposed network are significantly improved. In addition, the measurement results using practically implemented FQAM-based OFDMA systems verify that the transmission rates for the cell-edge users can dramatically increase, compared with the conventional QAM-based OFDMA network.

Feasibility of Mobile Cellular Communications at Millimeter Wave Frequency

High data rate at high mobile speed will still be an essential requirement for the future 5G mobile cellular system. High frequency bands above 6xa0GHz are particularly promising for the 5G system because of large signal bandwidths such high frequencies can offer. By using high gain beamforming antennas, the problem of high propagation loss at high frequencies can be overcome. However, the use of beamforming antennas at such high frequencies requires a significant change in the design of a cellular system. In particular, it requires a significant change in key functions such as cell search, random access, measurement of beams for fast beam adaptation, and various physical control and data channels. In this paper, we propose a new radio frame structure for the future mobile cellular communications system at millimeter wave frequency that addresses such challenges. A testbed was built at Samsung Electronics, Korea, based on the proposed frame structure at 28xa0GHz with bandwidth of 800xa0MHz. It attained the downlink (DL) data rate of 7.5xa0Gbps by delivering four streams of 64 QAM data with code rate of 3/4 to two mobile stations (MSs) located in a close distance to the base station antennas at fixed positions. It also achieved the DL data rate of 1.2xa0Gbps by delivering single stream of 16 QAM data with code rate of 3/4 to an MS moving at 110xa0km/h in a single cell of up to 800xa0m in a line-of-sight environment. Finally, it implemented handover and achieved an average handover interruption time of 21xa0ms in a three-cell environment, and demonstrated feasibility of mobile cellular communications at millimeter wave frequency.

FQAM : A modulation scheme for beyond 4G cellular wireless communication systems

We analyze the performance of bit interleaved coded modulation (BICM) and coded modulation (CM) systems with frequency and quadrature amplitude modulation (FQAM), which is a combination of frequency shift keying (FSK) and quadrature amplitude modulation (QAM). Numerical results show that for modest code rates in low signal-to-noise ratio regions, the normalized throughputs of FQAM based CM systems are close to the theoretical channel capacity limit compared to that of QAM and FSK based CM systems. Also, we analyze the performance of downlink cellular LTE systems using FQAM and compare it with that using QAM, especially for cell-edge users. Numerical results show that, unlike QAM, the statistical distribution of inter-cell interference (ICI) incurred with FQAM highly deviates from the Gaussian distribution and has a heavier tail. The results also show that due to the non-Gaussian nature of the ICI incurred with FQAM, the transmission rate of a cell-edge user using FQAM is significantly higher than that using QAM.

Holistic Design Considerations for Environmentally Adaptive 60 GHz Beamforming Technology

Proliferation of all forms of smart devices has driven the demand for high-data-rate Wi-Fi in recent years. Utilizing wide bandwidth in high frequency is the most efficient way of guaranteeing the explosive data demands. In spite of the notable advancements of RF technologies at millimeter wave, the relatively high propagation loss remains problematic. The authors present efficient beamforming technology to mitigate this challenge. In this article, we first discuss the principles and major applications of beamforming technology. Afterward, we present the challenges for optimizing the efficiency of beamforming as well as the solutions to tackle them by proposing enhanced algorithms and advanced design architectures based on our hands-on experience and knowledge. Lastly, experimental results are discussed to deduce insight and vision of future Wi-Fi.

60 GHz Wireless Communication for Future Wi-Fi

Abstract The 60xa0GHz Wi-Fi based on the IEEE s802.11ad standard has been attractive for recent years due to the high potential of the large bandwidth in 60xa0GHz unlicensed band allowing the multi-gigabit data transfer. However, the commercialization 60xa0GHz Wi-Fi is still not widely spread yet, mainly due to the high limitation of coverage as well as the lack of diverse applications. In the letter, we developed a novel technical beamforming system as a total radio solution across a wide range of holistic antenna and radio-frequency (RF) circuits design and cross-layer algorithm design to realize atmospheric beamforming coverage. To solve these challenges in the 60xa0GHz communications, our design and implementation are considered in all major layers, and the experimental results are presented to deduce insight and vision of future Wi-Fi.

Low-Complexity Decoding of Block Turbo Codes Based on the Chase Algorithm

Block turbo codes (BTCs) are constructed by serially concatenating linear block codes and iteratively decoded by letting each component code be decoded in two stages. The Chase algorithm is employed in the first stage to make a list of candidate codewords by generating a fixed number of test sequences (TSs) and algebraically decoding them, regardless of the signal-to-noise ratio or the iteration number. In the second stage, the extrinsic information is generated for iterative decoding. In this letter, we propose a low-complexity decoding algorithm for BTCs. The proposed algorithm first checks whether an algebraic hard-decision decoder outputs a codeword for a given decoder input vector, and then adaptively applies one of the two estimation rules. Based on these two rules, the number of TSs in the proposed algorithm can be made monotonically decreasing with iterations. Numerical results demonstrate that the proposed algorithm has much lower computational complexity with a negligible performance loss, compared with the conventional decoding scheme based on the Chase algorithm.

A modulation technique for active interference design under downlink cellular OFDMA networks

In cellular systems, the interference has been the most critical issue that practically limits the performance of overall networks. Furthermore, the distribution of the inter-cell interference (ICI) in conventional cellular networks employing orthogonal frequency-division multiple-access (OFDMA) with quadrature amplitude modulation (QAM) tends to approach a Gaussian distribution, which is known to be the worst-case distribution of the ICI as additive noise resulting in poor channel capacity. Thus, a dramatic enhancement of the channel capacity for the cellular network is expected when the ICI could be designed properly so that it has a non-Gaussian distribution. In this context, a cellular OFDMA system with a novel modulation scheme, frequency and quadrature-amplitude modulation (FQAM), is proposed in this paper. The statistical distribution of the ICI is shown to deviate far from the Gaussian distribution for the proposed FQAM-based system. Accordingly, it is shown that the non-Gaussian distribution of the ICI incurred with FQAM results in significantly improved transmission rates for the cell-edge users. Also, from the measurement results using practically implemented FQAM-based OFDMA systems, it is verified that the transmission rate for the cell-edge users could be increased significantly over the conventional QAM-based OFDMA system.