Showing papers by "Xinyu Zhang published in 2013"
14 Apr 2013
TL;DR: Gap Sense (GSense) is introduced, a novel mechanism that can coordinate heterogeneous devices without modifying their PHYlayer modulation schemes or spectrum widths and is shown to deliver coordination information with close to 100% accuracy within practical SNR regions.
Abstract: Coordination of co-located wireless devices is a fundamental function/requirement for reducing interference. However, different devices cannot directly coordinate with one another as they often use incompatible modulation schemes. Even for the same type (e.g., WiFi) of devices, their coordination is infeasible when neighboring transmitters adopt different spectrum widths. Such an incompatibility between heterogeneous devices may severely degrade the network performance. In this paper, we introduce Gap Sense (GSense), a novel mechanism that can coordinate heterogeneous devices without modifying their PHYlayer modulation schemes or spectrum widths. GSense prepends legacy packets with a customized preamble, which piggy-backs information to enhance inter-device coordination. The preamble leverages the quiet period between signal pulses to convey such information, and can be detected by neighboring nodes even when they have incompatible PHY layers. We have implemented and evaluated GSense on a software radio platform, demonstrating its significance and utility in three popular protocols. GSense is shown to deliver coordination information with close to 100% accuracy within practical SNR regions. It can also reduce the energy consumption by around 44%, and the collision rate by more than 88% in networks of heterogeneous transmitters and receivers.
133 citations
TL;DR: This work proposes a novel mechanism, called cooperative carrier signaling (CCS), that exploits the inherent cooperation among ZigBee nodes to harmonize their coexistence with WiFi WLANs, and reduces collision between ZigBee and WiFi by 50% for most cases, and by up to 90% in the presence of a high-level interference, all at negligible WiFi performance loss.
Abstract: The unlicensed ISM spectrum is getting crowded by wireless local area network (WLAN) and wireless personal area network (WPAN) users and devices. Spectrum sharing within the same network of devices can be arbitrated by existing MAC protocols, but the coexistence between WPAN and WLAN (e.g., ZigBee and WiFi) remains a challenging problem. The traditional MAC protocols are ineffective in dealing with the disparate transmit-power levels, asynchronous time-slots, and incompatible PHY layers of such heterogeneous networks. Recent measurement studies have shown moderate-to-high WiFi traffic to severely impair the performance of coexisting ZigBee. We propose a novel mechanism, called cooperative carrier signaling (CCS), that exploits the inherent cooperation among ZigBee nodes to harmonize their coexistence with WiFi WLANs. CCS employs a separate ZigBee node to emit a carrier signal (busy tone) concurrently with the desired ZigBee's data transmission, thereby enhancing the ZigBee's visibility to WiFi. It employs an innovative way to concurrently schedule a busy tone and a data transmission without causing interference between them. We have implemented and evaluated CCS on the TinyOS/MICAz and GNURadio/USRP platforms. Our extensive experimental evaluation has shown that CCS reduces collision between ZigBee and WiFi by 50% for most cases, and by up to 90% in the presence of a high-level interference, all at negligible WiFi performance loss.
102 citations
30 Sep 2013
TL;DR: Adaptive Feedback Compression meets challenges using a novel cross-layer adaptation metric, a metric extracted from 802.11 packet preambles, and uses it to guide the selection of compression intensity, so as to balance the tradeoff between overhead reduction and capacity loss.
Abstract: MIMO beamforming technology can scale wireless data rate proportionally with the number of antennas. However, the overhead induced by receivers' CSI (channel state information) feedback scales at a higher rate. In this paper, we address this fundamental tradeoff with Adaptive Feedback Compression (AFC). AFC quantizes or compresses CSI from 3 dimensions --- time, frequency and numerical values, and adapts the intensity of compression according to channel profile. This simple principle faces many practical challenges, e.g., a huge search space for adaption, estimation or prediction of the impact of compression on network throughput, and the coupling of different users in multi-user MIMO networks. AFC meets these challenges using a novel cross-layer adaptation metric, a metric extracted from 802.11 packet preambles, and uses it to guide the selection of compression intensity, so as to balance the tradeoff between overhead reduction and capacity loss (due to compression). We have implemented AFC on a software radio testbed. Our experiments show that AFC can outperform alternative approaches in a variety of radio environments.
92 citations
30 Sep 2013
TL;DR: NEMOx organizes a network into practical-size clusters, each containing multiple distributed APs (dAPs) that opportunistically synchronize with each other for netMIMO downlink transmission for large-scale wireless networks.
Abstract: Network MIMO (netMIMO) has potential for significantly enhancing the capacity of wireless networks with tight coordination of access points (APs) to serve multiple users concurrently. Existing schemes realize netMIMO by integrating distributed APs into one ``giant'' MIMO but do not scale well owing to their global synchronization requirement and overhead in sharing data between APs. To remedy this limitation, we propose a novel system, NEMOx, that realizes netMIMO downlink transmission for large-scale wireless networks. NEMOx organizes a network into practical-size clusters, each containing multiple distributed APs (dAPs) that opportunistically synchronize with each other for netMIMO downlink transmission. Inter-cluster interference is managed with a decentralized channel-access algorithm, which is designed to balance between the dAPs' cooperation gain and spatial reuse---a unique tradeoff in netMIMO. Within each cluster, NEMOx optimizes the power budgeting among dAPs and the set of users to serve, ensuring fairness and effective cancellation of cross-talk interference. We have implemented and evaluated a prototype of NEMOx in a software radio testbed, demonstrating its throughput scalability and multiple folds of performance gain over current wireless LAN architecture and alternative netMIMO schemes.
76 citations
Patent•
31 Jan 2013TL;DR: In this paper, a plurality of remote antennas and access points are configured to adapt channel allocations to the remote antennas of the respective cluster based on a tracking of sums of collision loss probabilities.
Abstract: Systems and methods for system for channel access adaptation are disclosed. One system includes a plurality of remote antennas and a plurality of access points. The remote antennas transmit data to receivers and obtain channel state information. Additionally, each access point controls a different cluster of the remote antennas and receives the respective channel state information from the remote antennas of the cluster. Further, each access point is configured to, independently from other access points, adapt channel allocations to the remote antennas of the respective cluster based on a tracking of sums of collision loss probabilities. Each given sum is determined by the access point for a different given set of a plurality of sets of cooperating remote antennas in the respective cluster, where each constituent collision loss probability in the given sum is determined by the access point from a different interference clique to which the given set belongs.
11 citations
TL;DR: A new protocol called Chorus is proposed that improves the efficiency and scalability of broadcast service with a MAC/PHY layer that allows packet collisions, and validates Chorus's superior performance with respect to scalability, reliability, delay, etc., under a broad range of network scenarios.
Abstract: Conventional wireless broadcast protocols rely heavily on the 802.11-based CSMA/CA model, which avoids interference and collision by conservative scheduling of transmissions. While CSMA/CA is amenable to multiple concurrent unicasts, it tends to degrade broadcast performance significantly, especially in lossy and large-scale networks. In this paper, we propose a new protocol called Chorus that improves the efficiency and scalability of broadcast service with a MAC/PHY layer that allows packet collisions. Chorus is built upon the observation that packets carrying the same data can be effectively detected and decoded, even when they overlap with each other and have comparable signal strengths. It resolves collision using symbol-level interference cancellation, and then combines the resolved symbols to restore the packet. Such a collision-tolerant mechanism significantly improves the transmission diversity and spatial reuse in wireless broadcast. Chorus' MAC-layer cognitive sensing and scheduling scheme further facilitates the realization of such an advantage, resulting in an asymptotic broadcast delay that is proportional to the network radius. We evaluate Chorus' PHY-layer collision resolution mechanism with symbol-level simulation, and validate its network-level performance via ns-2, in comparison with a typical CSMA/CA-based broadcast protocol. Our evaluation validates Chorus's superior performance with respect to scalability, reliability, delay, etc., under a broad range of network scenarios (e.g., single/multiple broadcast sessions, static/mobile topologies).
11 citations