Scanning Latency Research Articles

<italic>C-SCAN</italic>: Wi-Fi Scan Offloading via Collocated Low-Power Radios

Wi-Fi channel scanning—the task of searching for available channels at a given location—is a fundamental feature to maintain always-available and high-quality wireless connectivity in today’s mobile devices. However, it is a challenging task to design an intelligent scanning algorithm that can discover available access points (APs) in a short time period, because the scanning station has no prior knowledge on the APs in its vicinity. Therefore, traditional scanning algorithms seek to discover available APs by scanning the full set of channels, including channels where no APs exist. This often induces unnecessary scanning latency and/or energy consumption. In this paper, we present a novel scheme, called C-SCAN , that exploits a low-power wireless personal area network interface, such as Bluetooth or ZigBee integrated into the device to offload Wi-Fi scanning overhead by suppressing unnecessary scanning of AP-free Wi-Fi channels. To this end, C-SCAN inspects channel information with a low-power Bluetooth radio and identifies which Wi-Fi channels are in use, prior to the actual channel scanning with a Wi-Fi interface. By excluding the channels determined to be empty, the Wi-Fi scanning manager can perform scanning only on available Wi-Fi channels. Thereby, a significant performance gain in terms of delay and energy is obtained. We implement a prototype of C-SCAN using a Bluetooth-compliant wireless transceiver and demonstrate its efficiency. Experimental results show that C-SCAN achieves high detection accuracy with low latency, even in dense Wi-Fi environments.

Stereo vision-based tracking of soft tissue motion with application to online ablation control in laser microsurgery

Recent research has revealed that image-based methods can enhance accuracy and safety in laser microsurgery. In this study, non-rigid tracking using surgical stereo imaging and its application to laser ablation is discussed. A recently developed motion estimation framework based on piecewise affine deformation modeling is extended by a mesh refinement step and considering texture information. This compensates for tracking inaccuracies potentially caused by inconsistent feature matches or drift. To facilitate online application of the method, computational load is reduced by concurrent processing and affine-invariant fusion of tracking and refinement results. The residual latency-dependent tracking error is further minimized by Kalman filter-based upsampling, considering a motion model in disparity space. Accuracy is assessed in laparoscopic, beating heart, and laryngeal sequences with challenging conditions, such as partial occlusions and significant deformation. Performance is compared with that of state-of-the-art methods. In addition, the online capability of the method is evaluated by tracking two motion patterns performed by a high-precision parallel-kinematic platform. Related experiments are discussed for tissue substitute and porcine soft tissue in order to compare performances in an ideal scenario and in a setup mimicking clinical conditions. Regarding the soft tissue trial, the tracking error can be significantly reduced from 0.72 mm to below 0.05 mm with mesh refinement. To demonstrate online laser path adaptation during ablation, the non-rigid tracking framework is integrated into a setup consisting of a surgical Er:YAG laser, a three-axis scanning unit, and a low-noise stereo camera. Regardless of the error source, such as laser-to-camera registration, camera calibration, image-based tracking, and scanning latency, the ablation root mean square error is kept below 0.21mm when the sample moves according to the aforementioned patterns. Final experiments regarding motion-compensated laser ablation of structurally deforming tissue highlight the potential of the method for vision-guided laser surgery.

IEEE 802.11 무선 랜에서 이웃 채널 정보에 기반한 점진적 채널 스캔 방법

IEEE 802.11 무선 랜에서 단말들은 자유롭게 이동할 수 있기 때문에 끊김 없는 서비스를 제공하기 위해 핸드오프가 중요하다. 무선 랜에서 핸드오프할 때 많은 채널에 대해 스캔을 수행하기 때문에 핸드오프 지연이 커져 실시간 서비스를 지원하는데 한계가 있다. 본 논문에서는 실시간 서비스를 위해 핸드오프 지연을 최소화하는 방법을 제안한다. 제안하는 방법에서, 무선 랜에 처음 접속하는 단말은 자신이 스캔한 채널 정보를 AP(Access Point)에게 전송한다. AP는 단말이 전송한 정보를 이용하여 서로 이웃하는 채널들의 정보를 테이블로 만들고 비콘 프레임을 통해 이 테이블을 단말들에게 전송한다. 단말들은 핸드오프를 진행할 때 전체 채널에 대해 스캔을 수행하지 않고 테이블에 있는 정보를 이용하여 일부 채널에 대해서만 스캔을 수행한다. 따라서 제안하는 방법은 핸드오프 지연을 줄일 수 있고 실시간 서비스를 지원할 수 있다. Handoff is a critical issue for seamless roaming in IEEE 802.11-based wireless networks. In order to provide real-time services, handoff mechanism must be provided. However, the IEEE 802.11 standard handoff is not appropriate to provide the services, because it is based on the full-scanning approach which spends too much time searching Access Point (AP). In this paper, we propose a new scheme, which can reduce the scanning latency. A station performs full-scanning operation for finding APs when it enters wireless networks for the first time. The station sends the scanned channel information to AP. AP maintains the neighbor channel table based on the information received from stations. A station performs the partial-scanning by using the table. Therefore, the proposed scheme can reduce the scanning latency.

Target RSU Selection with Low Scanning Latency in WiMAX-enabled Vehicular Networks

WiMAX offers promising data rate, low deployment cost and support for Vehicular Networks (VNs). In VNs, vehicles have high mobility as they move from the coverage area of a Serving-RSU (S-RSU) to a Target-RSU (T-RSU). When moving from a S-RSU to another RSU, every vehicle should complete handover process. However, seamless handover is one of the major challenges in WiMaX while supporting real-time applications for VNs. Handover latency mainly results from the T-RSU selection and scanning of multiple channels. In this paper, we therefore propose an efficient network assisted handover scheme which attempts to reduce the T-RSU selection and scanning time of Mobile Stations (MSs) during the handover process. Our scheme allows a S-RSU to calculate the amount of time during which an MS can receive services from a forthcoming T-RSU based on its velocity and a coverage area of the T-RSU, which is defined as Coverage/Service Time. Later on, S-RSU uses this coverage time for the selection of the T-RSU. In addition, a serving RSU also aids an MS with channel information and estimated time to start scanning in order to get associated with its T-RSU. Thus, our scheme allows the MS to scan only one channel of the selected T-RSU. Using the NS-2 simulator, for evaluation, we compared our scheme with some existing solutions. The simulation results show that due to the pre-selection of a reliable T-RSU, our proposed scheme efficiently reduces the network overhead. Furthermore, aiding an MS with channel information of a T-RSU reduces overall scanning latency and increases the network throughput.

Editorial for Special Issue on “Advances on Vehicular Communication Systems”

Editorial: The joint efforts of academia and industry in the past years have led to the introduction of new on board applications and services. In addition, governments and standardization organizations have agreed upon a common set of standards (DSRC) specific to vehicle-tovehicle (V2V) and vehicle-to-infrastructure (V2I) communications. Combined with the cellular network infrastructure, they pave the way for a plethora of solutions empowered by vehicular communications. Among these solutions, we have emergency alerts, autonomous vehicles, infotainment, comfort services, cooperative road sensing and collaborative applications. Also, the integration between smartphones and vehicles has been addressed by many researchers, and a wide range of applications are already available, many more being expected. In terms of communication systems, mobility effects and channel conditions heavily affect the signal quality, introducing path-loss, fading, and received power fluctuations. Under such conditions, several issues remain open including message dissemination in congested environments, Quality of Service (QoS), efficient and adaptive routing, MAC layer enhancements, mobility prediction, efficient handovers, etc. For this special issue we have selected 6 high-quality papers among a total of 26 submissions. The first article, entitled “Implementation and Performance Evaluation of Distributed Autonomous Multi-Hop Vehicle-to-Vehicle Communications over TV White Space” by K. Tsukamoto et al., presents a two-layer control channel model able to establish the multi-hop network. In their proposal, the vehicles construct a swarm using location and direction information, while sharing route and channel information. The vehicles use GPS-driven oscillators for coarse synchronization, introducing a time margin to accommodate for the remaining drift. Simulation results show that the proposed idea is suitable for vehicular environments, providing efficient and stable V2V communication. The second article, entitled “Safety enhancement and Carbon Dioxide (CO2) reduction in VANETs” by A.F. Santamaria et al., discusses new approaches for road safety. In particular, the authors illustrate a novel cooperative architecture supporting both V2V and V2I connectivity. The idea, called SeAWave, takes advantage of the IEEE802.11p standard, enhancing it by adding useful messages to improve the vehicles’ active and passive safety systems based on information about the environment and road conditions. Simulations show good results for the proposed smart traffic management system. The third article, entitled “Target RSU Selection with Low Scanning Latency in WiMAX-enabled VANETs” by S.H. Ahmed et al., addresses the problem of handover management in VANETs, exploiting the potentialities of WiMAX services when users switch between C. T. Calafate (*) : P. Fazio Technical University of Valencia, Valencia, Spain e-mail: calafate@disca.upv.es

Group scanning scheme for fast target channel decision in seamless handover of wireless networks

AbstractIn wireless networks, when a mobile roaming station decides to initiate a handover, it should scan multiple channels operated by neighboring base stations (BSs) (or access points (APs)) in order to find an appropriate target base station before the actual handover. In some wireless networks, the active base station is able to provide a list of channels operated by neighboring base stations. However, some of these candidate channels may not be accessible to the mobile station (MS); nonetheless, the MS scans the candidate channels consecutively. For this reason, it may take a relatively long time for the MS to select an adequate target base station channel. This process can degrade the quality of service (QoS) during handovers. To shorten the scanning latency efficiently, in this paper we propose a cooperative channel scanning method whereby groups of MSs scan candidate channels using a dispersive schedule. They then share the scanning results amongst themselves, which results in a fast handover channel decision. To apply the proposed method to a real network environment, we present a group scanning architecture and detailed application scenarios appropriate for IEEE 802.16e worldwide interoperability for microwave access (WiMAX) networks. Numerical analyses and simulation results show that our proposed method achieves a shorter target channel scanning latency. Our method is thus more efficient in terms of scanning time and channel selection accuracy. Copyright © 2010 John Wiley & Sons, Ltd.

A neighbor caching mechanism for handoff in IEEE 802.11 wireless networks

Seamless handover in IEEE 802.11 for Quality of Service (QoS) demanding applications is one of the critical issues because of handover latency. In this paper, we propose the Neighbor Graph Cache (NGC) mechanism to reduce scanning latency while a mobile station tries to make a link-layer handover. The handoff latency can be greatly reduced through the NGC algorithm. We used OPNET modeler as the simulation tool. The simulation results show that the handover delay by NGC is 2.614 ms. It is less than 50 ms and able to meet the criteria of VoIP application.