Showing papers by "Xinyu Zhang published in 2014"

Does Full-Duplex Double the Capacity of Wireless Networks?

Abstract: Full-duplex has emerged as a new communication paradigm and is anticipated to double wireless capacity. Existing studies of full-duplex mainly focused on its PHY layer design, which enables bidirectional transmission between a single pair of nodes. In this paper, we establish an analytical framework to quantify the network-level capacity gain of full-duplex over halfduplex. Our analysis reveals that inter-link interference and spatial reuse substantially reduces full-duplex gain, rendering it well below 2 in common cases. More remarkably, the asymptotic gain approaches 1 when interference range approaches transmission range. Through a comparison between optimal halfand fullduplex MAC algorithms, we find that full-duplex’s gain is further reduced when it is applied to CSMA based wireless networks. Our analysis provides important guidelines for designing full-duplex networks. In particular, network-level mechanisms such as spatial reuse and asynchronous contention must be carefully addressed in full-duplex based protocols, in order to translate full-duplex’s PHY layer capacity gain into network throughput improvement.

Ubiquitous keyboard for small mobile devices: harnessing multipath fading for fine-grained keystroke localization

Abstract: A well-known bottleneck of contemporary mobile devices is the inefficient and error-prone touchscreen keyboard. In this paper, we propose UbiK, an alternative portable text-entry method that allows user to make keystrokes on conventional surfaces, e.g., wood desktop. UbiK enables text-input experience similar to that on a physical keyboard, but it only requires a keyboard outline printed on the surface or a piece of paper atop. The core idea is to leverage the microphone on a mobile device to accurately localize the keystrokes. To achieve fine-grained, centimeter scale granularity, UbiK extracts and optimizes the location-dependent multipath fading features from the audio signals, and takes advantage of the dual-microphone interface to improve signal diversity. We implement UbiK as an Android application. Our experiments demonstrate that UbiK is able to achieve above 95% of localization accuracy. Field trial involving first-time users shows that UbiK can significantly improve text-entry speed over current on-screen keyboards.

Leveraging directional antenna capabilities for fine-grained gesture recognition

Abstract: This paper presents a recognition scheme for fine-grain gestures. The scheme leverages directional antenna and short-range wireless propagation properties to recognize a vocabulary of action-oriented gestures from the American Sign Language. Since the scheme only relies on commonly available wireless features such as Received Signal Strength (RSS), signal phase differences, and frequency subband selection, it is readily deployable on commercial-off-the-shelf IEEE 802.11 devices. We have implemented the proposed scheme and evaluated it in two potential application scenarios: gesture-based electronic activation from wheelchair and gesture-based control of car infotainment system. The results show that the proposed scheme can correctly identify and classify up to 25 fine-grain gestures with an average accuracy of 92% for the first application scenario and 84% for the second scenario.

Scalable User Selection for MU-MIMO Networks

Abstract: In a multi-user MIMO (MU-MIMO) network, an AP with M antennas can only serve up to M users out of a large user population. The M users’ rates are inter-coupled and depend on their channel orthogonality. Substantial theoretical studies focused on selecting users to maximize capacity, but they require feedback of channel state information (CSI) from all users. The resulting overhead can easily overwhelm useful data in large scale networks. In this paper, we propose a scalable user selection mechanism called orthogonality probing based user selection (OPUS). OPUS only requires up to M rounds of CSI feedback. In each round, it employs a novel probing mechanism that enables a user to evaluate its orthogonality with existing users, and a distributed contention mechanism that singles out the best user to feedback its CSI. Software-radio based implementation and experimentation shows that OPUS significantly outperforms traditional user selection schemes in both throughput and fairness.

Autodirective audio capturing through a synchronized smartphone array

Abstract: High-quality, speaker-location-aware audio capturing has traditionally been realized using dedicated microphone arrays. But high cost and lack of portability prevents such systems from being widely adopted. Today's smartphones are relatively more convenient for audio recording, but the audio quality is much lower in noisy environment and speaker location cannot be readily obtained. In this paper, we design and implement Dia, which leverages smartphone cooperation to overcome the above limitations. Dia supports spontaneous setup, by allowing a group of users to rapidly assemble an array of smartphones to emulate a dedicated microphone array. It employs a novel framework to accurately synchronize the audio I/O clocks of the smartphones. The synchronized smartphone array further enables autodirective audio capturing, i.e., tracking the speaker's location, and beamforming the audio capturing towards the speaker to improve audio quality. We implement Dia on a testbed consisting of 8 Android phones. Our experiments demonstrate that Dia can synchronize the microphones of different smartphones with sample-level accuracy. It achieves high localization accuracy, and similar beamforming performance compared with a microphone array with perfect synchronization.

Semi-synchronous Channel Access for Full-Duplex Wireless Networks

Abstract: Full-duplex radios are often envisioned to double wireless link capacity. Substantial work has focused on redesigning the radio hardware to achieve this theoretical gain. From a network-protocol perspective, however, it remains an open problem how to exploit full-duplex radio, and how much gain it can achieve in practical multi-cell wireless LANs. In this paper, we propose FuMAC, a channel access protocol tailored for full-duplex radios to optimally exploit their unique capabilities. FuMAC addresses a unique trade off between PHY-layer full duplex transmission and MAC-level spatial reuse, through a semi synchronous channel access principle. Its design is enabled by a novel self-interference cancellation mechanism called Active Antenna Cancellation. We verify FuMAC using software-radio implementation combined with large scale simulation. The results demonstrate that conventional MAC protocols severely underutilize full-duplex's potential. In contrast, FuMAC can achieve more-than-doubled throughput gain over half-duplex wireless LANs and significantly outperform alternative full-duplex MAC designs, while maintaining a much higher level of fairness.

Demo: A paper keyboard for mobile devices

Abstract: A well-known bottleneck of contemporary mobile devices is the inefficient and error-prone touchscreen keyboard We have developed UbiK, an alternative portable text-entry method that allows user to type on a piece of paper, placed on solid surfaces like wood desktop UbiK leverages the microphones on a mobile device to accurately localize the keystrokes through fine-grained acoustic fingerprinting We have implemented UbiK as an Android application Our experiments demonstrate that UbiK is able to achieve above 95% of localization accuracy In this demonstration, we will show how Ubik works with an external paper keyboard (Figure 1) for a smartphone and a 7-inch tablet User participation will be welcome in this live demo