Ji-sung Oh

A 60 GHz wireless network for enabling uncompressed video communication

Uncompressed high-definition video streaming over wireless personal area networks is a challenging problem because of the high data rate requirement and channel variations. With the advances in RF technology and the huge bandwidth available worldwide in the 57-66 GHz millimeter-wave unlicensed spectrum, mmWave WPANs that can support multigigabit transmission are being developed. However, compared to low-frequency signals (2.4 or 5 GHz), mmWave signals are more fragile; indeed, the propagation losses are significantly higher. In this article we present an mmWave system for supporting uncompressed HD video up to 3 Gb/s. The system includes various efficient error protection and concealment schemes that exploit unequal error resilience properties of uncompressed video. Some of them have been adopted in the emerging 60 GHz WPAN standards such as WirelessHD, ECMA TC48, and IEEE 802.15.3c. Simulations using real uncompressed HD images indicate that the proposed mmWave system can maintain, under poor channel conditions, good average peak-signal-to-noise-ratio and low video quality metric scores.

Short Range Gigabit Wireless Communications Systems: Potentials, Challenges and Techniques

In this paper, we discuss multi-gigabits per second wireless networks in the 60GHz millimeter wave frequency band. Despite the large unlicensed bandwidth offered by the 60GHz frequency band, severe technical challenges exist towards making multi-Gbps a reality. We discuss the challenges in three different layers: PHY, MAC and the application layers. We also discuss some important technologies in overcoming these challenges, including antenna array beamforming, baseband modulation, data aggregation. The worldwide 60GHz regulatory and the ongoing standardization efforts are reviewed as well.

Multi-Stage Iterative Antenna Training for Millimeter Wave Communications

We study 60 GHz millimeter wave communication systems employing SVD based transmit precoding and receive combining, and propose a multi-stage iterative method in training the antenna coefficients. The antenna training is carried out in multiple stages one after another, while each stage features an iterative process based on the power iteration principle. Null space projection is used as an enabling step for iterative training in inner stages. The proposed training method is especially efficient for systems with a much smaller number of RF chains relative to the number of antennas on both transmitter and receiver sides.

A practical SDMA protocol for 60 GHz millimeter wave communications

We study spatial division multiple access in 60 GHz millimeter wave communications and focus on estimation of the optimal transmit beamforming vectors for stations and optimal receive beamforming vectors for the access point. An iterative antenna training protocol is developed, where the optimal transmit/ receive beamforming vectors are computed without explicit knowledge of the actual wireless channels. The proposed training method is especially attractive to systems with a much smaller number of RF chains relative to the number of antenna elements, thanks to its low training overhead.

Principles of IEEE 802.15.3c: Multi-Gigabit Millimeter-Wave Wireless PAN

Interests in millimeter-wave resulted in the forma- tion of Task Group 3c (TG3c) within IEEE 802.15 in 2005. It is currently developing a 60 GHz based alternative physical layer supporting PHY data rates of multi-giga bits per second (multi- Gbps) for the existing 802.15.3 Wireless Personal Area Net- work (WPAN) standard. In comparison to the baseline 802.15.3 standard, the unique features of 802.15.3c are: 1) Directional transmissions; 2) Aggregation and Block Ack for supporting multi-Gbps MAC-SAP rate (up to 5.7 Gbps); 3) Unequal Error Protections for enabling uncompressed video streaming. In this paper, we present principles of the key features of the current draft D08 (1). In addition, we conduct a detailed simulation study and the results indicate that the 802.15.3c can indeed support emerging applications such as gigabit file transfers and high definition uncompressed video streaming in a Wireless PAN. Index Terms—IEEE 802.15.3c, Wireless, WPAN, Gigabit, 60 GHz, millimeter-wave.

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.

DFT Structured Codebook Design with Finite Alphabet for High Speed Wireless Communication

A low-complexity numerical codebook construction method is presented in this paper for limited feedback transmit beamforming systems. The so-constructed codebook takes a DFT matrix structure and achieves equal amplitude beamforming all the time. The codebooks are designed such that the selected row indices mimic the behavior of a difference set which, when exists, is able to achieve codebook optimality. Finite alphabet constraint on the codebook is further studied, where scalar quantization is further applied.

A robust beamforming scheme with low power and complexity for IEEE 802.11n systems

Due to the extremely increased interference of multiple-input multiple-output systems, designing efficient transmit beamforming schemes is significant to degrade the interference. A novel beamforming scheme is addressed by incorporating a multiple hypothesis testing problem with the characteristics of the wireless channel. The proposed beamforming scheme is operated by the implicit beamforming protocol in the IEEE 802.11n standard. From the simulation results, it is confirmed that the proposed scheme has high SNR gain. The proposed beamforming scheme is implemented in Toshiba 40nm low power process and shows a gate count of only 33K and power consumption of 3.39mW. Field test results show that the maximum increase of the data rate with the proposed scheme is about 42 percent and the increase of coverage with the proposed scheme is 85 percent, while maintaining the robustness of incorrect channel state information.