Huai-Rong Shao

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.

WiFi-based indoor positioning

Recently, several indoor localization solutions based on WiFi, Bluetooth, and UWB have been proposed. Due to the limitation and complexity of the indoor environment, the solution to achieve a low-cost and accurate positioning system remains open. This article presents a WiFibased positioning technique that can improve the localization performance from the bottleneck in ToA/AoA. Unlike the traditional approaches, our proposed mechanism relaxes the need for wide signal bandwidth and large numbers of antennas by utilizing the transmission of multiple predefined messages while maintaining high-accuracy performance. The overall system structure is demonstrated by showing localization performance with respect to different numbers of messages used in 20/40 MHz bandwidth WiFi APs. Simulation results show that our WiFi-based positioning approach can achieve 1 m accuracy without any hardware change in commercial WiFi products, which is much better than the conventional solutions from both academia and industry concerning the trade-off of cost and system complexity.

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.

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.

Enhanced Power Saving in Next Generation Wireless LANs

Battery powered handheld devices need to operate for extended periods of time, and thus require to be energy conserving. This paper evaluates the performance of a new power saving scheme, called PSMP (power save multiple poll), developed for the upcoming IEEE 802.11n WLANs. Using both analysis and simulations, we investigate the benefits of using PSMP in a wireless LAN having multiple voice-over-IP (VoIP) clients. To boost the reliability of a PSMP sequence, we propose a new recovery scheme, which we call PSMP recovery. Our results show that the PSMP recovery scheme significantly improves the efficiency of the original PSMP sequence.

MAC-enabling technologies for high-throughput wireless LAN

Wireless LAN systems play an important role in todays CE applications. However, due to various MAC/PHY overheads, the throughput is severely degraded. In this paper, we discuss sev- eral MAC techniques that can improve wireless transmission effi- ciency and reliability. These techniques include frame aggrega- tion, block acknowledgment, and retransmission schemes. Using analysis and simulation, we evaluate their efficiency and through- put performance. We also discuss how these MAC techniques can meet the throughput and QoS requirements of high-quality multi- media transmission applications.

Progressive Transmission of Uncompressed Video over mmW Wireless

In this paper we propose a new progressive rate adaptation scheme for uncompressed video over millimeter wave wireless (mmW) in which the video data rate can be adapted to any rate smoothly and with minimal video quality degradation. Two major steps: 1. Progressive pixel differential transformation (PPDT) in which difference values of pixels are compressed and transmitted in a new systematic way for progressive rate adaptation. 2. Progressive pixel dropping (PPDP) in which pixels at different positions are evenly dropped in a new systematic way for progressive rate adaptation if the data rate is still too high to fit into the available channel bandwidth after the first step. Simulation results show that our proposed rate adaptation scheme can achieve at least 20 dB quality improvement in PSNR (Peak Signal to noise ratio) than the conventional rate adaptation schemes.

Improved Delayed ACK for TCP over Multi-Hop Wireless Networks

TCP performance in contention-based multi-hop wireless networks is shaped by two main factors, which are unlike the wired network case. First, the maximum throughput for a given topology and flow pattern is reached for a specific congestion window. This window is very difficult to detect under dynamically changing network traffic. Second, the excessive control traffic consumes channel bandwidth more severely than in the wired case. Our analysis and simulations show that the smaller TCP ACK packets consume channel resource comparable to the much longer TCP DATA packets, over high-speed connections. Motivated by this observation, we propose a new approach to improve TCP performance by further lowering the number of control packets compared with the known methods. Extensive simulations show that our strategy improves the TCP throughput up to 205% compared with the regular TCP. Although our simulation is based on 802.11, the same idea works in other networks using a contention-based MAC design.

A New Beacon Mechanism for 60 GHz Wireless Communication Networks

This paper proposes a new beacon mechanism for 60 GHz wireless communication networks that can greatly reduce beacon overhead caused by omni-directional transmission. Short common beacon with low-rate omni-directional transmission and individual beacon with high-rate directional transmission are combined to carry all required information in the conventional beacon. A short common beacon may only include part of the physical layer preamble, or preamble with physical layer header or plus MAC header to reduce the beacon transmission time. Numerical analysis verified that the proposed beacon scheme can improve MAC efficiency significantly.