Chiu Ngo

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.

Green operation of multi-band wireless LAN in 60 GHz and 2.4/5 GHz

IEEE 802.11ad Task Group is currently defining a standard for multi-gigabits per second data rate WLAN connections in the 60 GHz band with a target completion date of 2012. The 802.11n, which operates in 2.4/5 GHz band, guarantees data rate of at least 108 Mbps and coverage of about 50 meters, with a maximum data rate of 600Mbps over relatively short distances. In comparison, 60 GHz band can support multi-gigabit data-rates (up to 6 Gbps), but the typical coverage is limited to around 10 meters due to significantly higher propagation loss. Therefore, the two wireless bands provide widely different, yet complementary, characteristics in terms of range and throughput. However, there is a greater need for an efficient multi-band operation that enables selecting the optimum interface based on the communicating stations physical proximity and multi-band channel conditions. In this paper, we present techniques that facilitate green multi-band IEEE 802.11ad for portable devices. We performed a detailed simulation study and the results indicate that the proposed techniques reduce energy consumption of the multi-band Wi-Fi devices as they are at least 40% more power efficient.

MAC enhancements for downlink multi-user MIMO transmission in next generation WLAN

For the first time in the WLAN technology, multi-user downlink transmission will be made possible by the upcoming IEEE standard, 802.11ac. In this paper, we will report its current status, focusing on the MAC modifications and enhancements that are necessary to support the unique feature of downlink multi-user MIMO transmission. In particular, the technique of enhancing Transmit Opportunity (TXOP) for downlink MU-MIMO transmission and the revised backoff procedures for secondary ACs will be introduced and discussed. The performance of the proposed mechanisms is evaluated using simulations. The proposed TXOP Sharing mechanism has been accepted in the 802.11ac draft specification and is currently under letter ballot in the IEEE 802.11 WG.

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.

Multi-user support in next generation wireless LAN

For the first time in the WLAN technology, multi-user downlink transmission will be made possible by the upcoming IEEE standard, 802.11ac. In this paper, we will report its current status, focusing on the MAC modifications and enhancements that are necessary to support the unique feature of downlink multi-user MIMO transmission. Specifically, the technique of TXOP sharing and its related issues and solutions will be discussed and illustrated.

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.

Supporting Uncompressed HD Video Streaming without Retransmissions over 60GHz Wireless Networks

Uncompressed HD (high-definition) video delivery over wireless personal area networks (WPANs) is a challenging problem because of the limited bandwidth and variations in channel. The most straight forward technique to recover from channel errors is to retransmit corrupted packets. However, retransmissions introduce significant delay/jitter and require additional bandwidth. Therefore, retransmissions may be unsuitable for uncompressed video streaming. In this paper, we develop, simulate, and evaluate an millimeter- wave (mmWave) system for supporting uncompressed video streams up to 3-Gbps without any retransmissions. New features of the mmWave system incorporates: (i) UEP (unequal error protection) where different video bits (MSBs and LSBs) are protected differently, (ii) a multiple-CRC to determine whether MSB or/and LSB portions are in error, (iii) RS code swapping (RSS), an error concealment scheme which can conceal some errors in video pixels. Simulations using real uncompressed HD images indicate that the proposed mmWave system can maintain good average PSNR (peak-signal-to-noise-ratio) under poor channel conditions, achieving what is generally accepted as a good picture quality with PSNR values greater than 40 dB. Moreover, the proposed system results in less fluctuating PSNR values.

Adaptive Multi-beam Transmission of Uncompressed Video over 60GHz Wireless Systems

Millimeter wave (mmWave) technology provides possibility to replace uncompressed high-definition video cables (such as HDMI, DVI, or DisplayPort) with wireless links. However, it is very challenging to meet the strict quality of service (QoS) requirements from uncompressed video streaming applications since 60 GHz wireless signals can be easily blocked by human body and other obstacles. In this paper, we first discuss the specific technical challenges in mmWave system to support long-time stable video streaming. Then, we propose a new adaptive multi-beam transmission solution in which pixel partitioning, switched multi- beam transmission, and fast video format adaptation are key techniques to solve the raised technical problems. Initial performance evaluation shows that our approach can achieve high- quality video streaming performance.