Number Of Access Points Research Articles

Speed variation during peak and off-peak hours on urban arterials in Shanghai

Increased speed variation on urban arterials is associated with reductions in both operational performance and safety. Traffic flow, mean speed, traffic control parameters and geometric design features are known to affect speed variation. An exploratory study of the relationships among these variables could provide a foundation for improving the operational and safety performance of urban arterials, however, such a study has been hampered by problems in measuring speeds. The measurement of speed has traditionally been accomplished using spot speed collection methods such as radar, laser and loop detectors. These methods can cover only limited locations, and consequently are not able to capture speed distributions along an entire network, or even throughout any single road segment. In Shanghai, it is possible to acquire the speed distribution of any roadway segment, over any period of interest, by capturing data from Shanghai’s 50,000+ taxis equipped with Global Positional Systems (GPS). These data, hereafter called Floating Car Data, were used to calculate mean speed and speed variation on 234 road segments from eight urban arterials in downtown Shanghai. Hierarchical models with random variables were developed to account for spatial correlations among segments within each arterial and heterogeneities among arterials. Considering that traffic demand changes throughout the day, AM peak, Noon off-peak, and PM peak hours were studied separately. Results showed that increases in number of lanes and number of access points, the presence of bus stops and increases in mean speed were all associated with increased speed variation, and that increases in traffic volume and traffic signal green times were associated with reduced speed variation. These findings can be used by engineers to minimize speed differences during the road network planning stage and continuing through the traffic management phase.

AP@home: The Artificial Pancreas Is Now at Home.

In the past years the development of an artificial pancreas (AP) has made great progress and many activities are ongoing in this area of research. The major step forward made in the last years was moving the evaluation of AP systems from highly controlled experimental conditions to daily life conditions at the home of patients with diabetes; this was also the aim of the European Union-funded AP@home project. Over a time period of 5 years a series of clinical studies were performed that culminated in 2 "final studies" during which an AP system was used by patients in their home environment for 2 or 3 months without supervision by a physician, living their normal lives. Two different versions of the AP system developed within this project were evaluated. A significant improvement in glycated hemoglobin was observed during closed-loop conditions despite the fact that during the control period the patients used the best currently available therapeutic option. In addition, a "single-port AP system" was developed within the project that combines continuous glucose monitoring and insulin infusion at a single tissue site. By using such a combined device the patients not only have to carry one less device around, the number of access points through the skin is also reduced from 2 to 1. In summary, close cooperation of 12 European partners, both academic centers and industry, enabled the development and evaluation of AP systems under daily life conditions. The next step is to develop these into products in cooperation with commercial partners.

Safety modeling of urban arterials in Shanghai, China

Traffic safety on urban arterials is influenced by several key variables including geometric design features, land use, traffic volume, and travel speeds. This paper is an exploratory study of the relationship of these variables to safety. It uses a comparatively new method of measuring speeds by extracting GPS data from taxis operating on Shanghai’s urban network. This GPS derived speed data, hereafter called Floating Car Data (FCD) was used to calculate average speeds during peak and off-peak hours, and was acquired from samples of 15,000+ taxis traveling on 176 segments over 18 major arterials in central Shanghai. Geometric design features of these arterials and surrounding land use characteristics were obtained by field investigation, and crash data was obtained from police reports. Bayesian inference using four different models, Poisson-lognormal (PLN), PLN with Maximum Likelihood priors (PLN-ML), hierarchical PLN (HPLN), and HPLN with Maximum Likelihood priors (HPLN-ML), was used to estimate crash frequencies. Results showed the HPLN-ML models had the best goodness-of-fit and efficiency, and models with ML priors yielded estimates with the lowest standard errors. Crash frequencies increased with increases in traffic volume. Higher average speeds were associated with higher crash frequencies during peak periods, but not during off-peak periods. Several geometric design features including average segment length of arterial, number of lanes, presence of non-motorized lanes, number of access points, and commercial land use, were positively related to crash frequencies.

Channel Time Allocations and Handoff Management for Fair Throughput in Wireless Mesh Networks

In this paper, we study a wireless mesh network (WMN), where a number of access points (APs) form a wireless infrastructure and provide communications to the mobile stations (MSs). Different APs share the same frequency channel. We study how to provide fair long-term throughput for the MSs while efficiently utilizing the channel resources through effective handoff management and channel timeline allocations, where the channel time is allocated at two levels: first among the APs and then among the MSs. An optimization problem is first formulated and solved. The optimum solution is based on the assumption of having global information about the channel conditions of all the MSs and cannot be easily implemented in a practical WMN. Two distributed schemes are proposed by decoupling the handoff management and channel time allocations. The HO-CA scheme performs heuristic handoff decisions for the MSs based on their link gains to nearby APs and then optimizes the channel time allocations through an iterative process. The CA-HO scheme allocates the channel time to individual APs based on interfering relationship of the APs and then allows the MSs to make handoff decisions based on possible utilities from nearby APs. In both schemes, individual APs solve a local optimization problem to allocate channel time for their associated MSs. Numerical results indicate that both the proposed schemes can achieve very good fairness and that the HO-CA scheme achieves higher throughput.

Temporary Access Selection Technology in WIFI Networks

Currently, increasing numbers of access points (AP) are being deployed in enterprise offices, campuses and municipal downtowns for flexible Internet connectivity, but most of these access points are idle or redundant most of the time, which causes significant energy waste. Therefore, with respect to power conservation, applying energy efficient strategies in WIFI networks is strongly advocated. One feasible method is dynamically managing network resources, particularly APs, by powering devices on or off. However, when an AP is powered on, the device is initialized through a long boot time, during which period clients cannot be associated with it; therefore, the network performance would be greatly impacted. In this paper, based on a global view of an entire WLAN, we propose an AP selection technology, known as Temporary Access Selection (TAS). The criterion of TAS is a fusion metric consisting of two evaluation indexes which are based on throughput and battery life, respectively. TAS is both service and clients’ preference specific through balancing the data rate, battery life and packet size. TAS also works well independently in traditional WLANs in which no energy efficient strategy is deployed. Moreover, this paper demonstrates the feasibility and performance of TAS through experiments and simulations with Network Simulator version 3 (NS3).

Healthy Minds: Improving Access, Integration and Efficiency in Primary Mental Health Care

In early 2013, the North Coast NSW Medicare Local (NCML) initiated a process for redesign of the delivery of its mental health services, including the Access To Allied Psychological Services (ATAPS) Program. The Australian Primary Mental Health Care system has two key components: ATAPS and Better Access. Both are Commonwealth funded and accessed via General Practice. Healthy Minds aims to provide mental health services to some of the most vulnerable members of the North Coast NSW community who have complex social needs and who are less likely to visit a GP, or are less likely to recognise the need for help. Healthy Minds breaks historical separations and disconnections. It combines Better Access and ATAPS funding and co‐locates private providers within Community Service Organisations (CSOs) and public services to deliver psychological support. Healthy Minds improves access by: 1) Providing services within organisations which are already being accessed by vulnerable groups, reducing the need for further transport, or orientation to new services; 2) Providing a ‘soft’ entry to mental health services by delivering them within less stigmatising organisations, such as employment agencies, family support services or neighbourhood centres; and 3) Partnering with organisations who are able to assist vulnerable groups to access a GP in order to receive their initial referral (e.g. by providing transport, making appointment, issuing reminders) and are able to provide the same support to enhance attendance rates with the Private Practitioner. Healthy Minds improves integration by: 1) Placing Private Practitioners within CSOs, community and public health services which are meeting the social needs of the person, allowing for greater connection of the services, communication, and integration; and 2) Using ATAPS to fund Private Practitioners to attend Case Conferencing within those organisations. Some of the types of CSOs in which Private Practitioners have been co-located include employment agencies, women’s shelters, Aboriginal Medical Services, family support services, homelessness services, youth services, neighbourhood centres and disability services Healthy Minds improves value by: 1) Identifying clinical space with organisations which can be used by Private Practitioners free of charge, reducing overhead expenses; 2) Reducing the ATAPS remuneration to match the Better Access item numbers so that there is no disincentive to bulk-bill – allowing Better Access funding to be used when ATAPS funding is exhausted; 3) Minimising the travel costs to the consumer by providing services within a setting they are already World Congress on Integrated Care 2014, Sydney, November 23-26, 2014. International Journal of Integrated Care – Volume 14, 8 December – URN:NBN:NL:UI:10-1-116613– http://www.ijic.org/ accessing; and 4) Potentially reducing ‘Did Not Attends’ as clients are familiar with, and familiar to the organisations. Initial estimates and observations indicate that this approach has more than doubled the number of access points for psychological services across the North Coast of NSW. The six months to December 2013 has seen a 42% increase in the number of ATAPS sessions delivered, compared to the previous year. This has been accompanied with a 61% reduction in the average cost per session for the North Coast NSW Medicare Local.

Feature Adaptive Online Sequential Extreme Learning Machine for lifelong indoor localization

Wi-Fi-based indoor localization with high capability and feasibility needs to implement lifelong online learning mechanism. However, the characteristic of Wi-Fi is wide variability, which lies in not only the fluctuation of signal strength value, but also the increase or decrease in the number of access points (APs). The traditional algorithms are effective for signal fluctuation, but cannot handle the dimension-changing problem of features caused by increase and decrease in APs' number. To solve this problem, we propose a Feature Adaptive Online Sequential Extreme Learning Machine (FA-OSELM) algorithm. It can transfer the original model to a new one with a small number of data with new features, so as to make the new model suitable for the new feature dimension. The experiments show that the FA-OSELM can get higher accuracy with a small amount of new data, and it is an effective method to make lifelong indoor localization practical.

Recreational trails are an important cause of fragmentation in endangered urban forests: A case-study from Australia

Remnant urban forests are often popular sites for recreational activities such as hiking, biking and motorised recreation. This can result in the formation of extensive trail networks, fragmenting vegetation into patches separated by modified edge effects and ultimately contributing to the degradation of the ecosystem as a whole. Here we use a GIS approach to assess the extent and diversity of trail-based fragmentation across 17 remnants of endangered urban forest (total area 829ha, Tall Open Blackbutt Forest) in southeast Queensland, Australia. Fourteen different trail types totalling 46.1km were mapped with informal biking and hiking trails the most common (57%, 26.5km). More than 47ha (5.7%) of forest have been lost to trails and their edge effect, nearly equal to the area recently cleared for urban development. The degree of fragmentation in some remnants was in the same order of magnitude as found for some of the most popular nature-based recreation sites in the world. In localised areas, the fragmentation was particularly severe as a result of wide trails used by motorised recreation, but these trails were generally uncommon across the landscape (5%). Spatial regression revealed that the number of access points per remnant was positively correlated with the degree of fragmentation. We encourage more landscape-scale research into trail-based fragmentation due to its capacity to impact extensive areas of endangered ecosystems. Management should seek to minimise the creation of informal trails by hardening popular routes, instigating stakeholder collaboration and centralising visitor flow.

Scaling Wireless Uplink Capacity with Multi-User Beamforming

Due to the fact that the wireless spectrum is limited but the wireless demand can grow unlimited, how to improve the wireless capacity becomes one of the hot topics in wireless network field. In this paper, we focus on the scenario of busy wireless environment, and present a protocol with multiple user beamforming. The protocol enables a network to scale its uplink throughput with the number of access points. Theoretical and experimental results show that our protocol have higher uplink throughput compared with 802.11. Moreover, our protocol is the first method that shows that linear scaling of uplink throughput with the number of access points is possible.

Handover Strategies in Beacon-Enabled Mobile Sensor Network

IEEE 802.15.4 has become the de facto standard in many areas of wireless sensor network (WSN) such as body area networks, industrial automation, and healthcare domains. In many WSN applications, the sensor nodes could be mobile, and indoor communications are limited in terms of signal propagation. Therefore, a large number of access points need to be deployed to cover large areas. To maintain the sensor connectivity, sensor node should frequently change the serving access point by performing a mechanism known as a handover. We observed that the amount of time required for the association process is the key reason IEEE 802.15.4 is unable to handle the mobility. In this paper, we show what is required for node mobility support and propose three strategies for the support. First, the proactive algorithm is developed to anticipate the future link breakage. Second, a new greedy scanning technique is presented, which prevents nodes from scanning multiple channels. Third, the coordinator selection algorithm is developed which chooses the best coordinator that gives the longest connectivity time reducing the handover frequency. Experimental results have verified that our schemes work well in the mobile sensor network environment.

Performance Analysis of Multi-Source Multi-Relay with Multiple Antennas Cooperative Networks with Best Relay Selection

In this paper we analyze the system performance of multi-source multi-relay with multiple antennas cooperative networks. We present an amplify and forward (AF) multiple-input multiple-output relay scenario, where finite number of sources communicate with single destination via multiple relay access points equipped with finite number of antennas. In this network a relay selection scheme is adopted, where the best relay is chosen using the instantaneous channel state information (CSI). Maximal ration combiner (MRC) and maximal ratio transmitter (MRT) are used at the relay to obtain maximum achievable received signal-to-noise ratio (SNR). We derive closed-form and analytical bound expressions for the outage probability and symbol error rate (SER) with joint multiple-sources and cooperative diversity. Further high SNR asymptotic analysis on the outage probability and average SER are performed to characterize the diversity gain. Then, the analytical expressions are validated with Monte Carlo simulations. The results reveal that the diversity gain is determined by the number of the sources, the number of access points in the system and the number of the antennas in each access point. ©2014 Engineering and Technology Publishing.

Using Authorities to Improve Subject Searches

Authority files have played an important role in improving the quality of indexing and subject cataloging. Although authorities can significantly improve searching by increasing the number of access points, they are rarely an integral part of the information retrieval process, particularly end-users’ searches. A retrieval prototype, searchFAST, was developed to test the feasibility of using an authority file as an index to bibliographic records. searchFAST uses Faceted Application of Subject Terminology (FAST) as an index to OCLC's WorldCat.org bibliographic database. The searchFAST prototype complements, rather than replaces, existing WorldCat.org access. The bibliographic file is searched indirectly; first the authority file is searched to identify appropriate subject headings, then the headings are used to retrieve the matching bibliographic records. The prototype demonstrates the effectiveness and practicality of using an authority file as an index. Searching the authority file leverages authority control work by increasing the number of access points while supporting a simple interface designed for end-users.

A Simple Method for Determining an Optimal Number of Access Points in Distributed WLAN Networks

In large wireless installations based on WLAN systems, mechanisms governing their operation other than just those related to the radio coverage may play a crucial role in the customer experienced quality of service (EoS). In particular, two factors have been identified as having a particular impact on the final efficiency of the distributed WLAN network. The first one is the IEEE 802.11x protocol overhead (assisted with the choice of the preamble length) which is largely dependent on the kind of WLAN standard used – ‘b/g’, ‘a’ or ‘n’. The other factor is the MAC protocol scheme, the CSMA/CA, developed for the IEEE 802.11x family, identical for all its sub-standards. A simple formula has been developed that accounts for both these aspects and provides an easy-to-implement method allowing deployment of the minimum number of access points as a function of the expected number of users, assuring a guaranteed effective throughput per user at optimal utilization of the total available capacity. DOI: http://dx.doi.org/10.5755/j01.eee.19.9.5658

QoS Access Points Placement with Fault Tolerance in Wireless Local Area Networks

In this paper, we study the problem of enhancing the fault tolerance of IEEE 802.11 wireless local area networks in the design stage. We aim to settle proper number of access points (APs) and carefully locate them, such that the system can tolerate AP failures while guaranteeing QoS requirement. Given a set of clients (end-users), each client has a traffic demand for Internet access. The problem of our concern is to find out the minimal number of access points and proper location, such that the fault tolerance and QoS constraint are both satisfied. That is, when there is no AP failure, the actual traffic delivery ratio for each client shall exceed the threshold. When their happens that one AP failed, the clients it served can switch to other APs with reconfiguration of the system, while providing an acceptable bandwidth. We proposed a heuristic algorithm, firstly we place one AP in each candidate place and gradually decrease the APs until no more APs can be deleted, in each step we make fault tolerance checking. Our proposed method can effectively solve the problem of tolerating to access point failure in the design phase of wireless local area networks. Simulations are conducted to show the performance of our proposed method.

Development of a safety performance function for motorcycle accident fatalities on Malaysian primary roads

This study uses a generalized linear model approach, i.e. negative binomial regression, to develop a predictive model for motorcycle fatal accidents on Malaysian primary roads. For the modeling process, a huge data inventory has been carried out, integrating the road geometry features, fatal accident records and traffic censuses from 3 selected states for the past 3-year period. The results show that motorcycle fatalities per kilometer on primary roads are statistically significantly affected by the average daily number of motorcycles and the number of access points per kilometer. The model established for this study can also be regarded as the first motorcycle safety performance function in Malaysia and probably in Asia. Also noted in this study is the need to establish a proper and systematic road geometry and traffic census inventory in order to develop better accident prediction models for Malaysia in the future.

A Hybrid PSO-Fuzzy Model for Determining the Category of 85th Speed

The 85th speed of vehicles is one of the traffic engineering parameters used by road safety equipment designers. It is usually used for maintenance activities and designing of warning signs and road equipments. High measuring costs of speed data collection lead decision makers to define a methodology for determining the category of 85th speed using indirect parameters. In this research work, focusing on undivided intercity roads, a hybrid particle-swarm-optimization- (PSO-) fuzzy model has been developed to determine the category of 85th speed. In this model, geometric design parameters including roads' width and length characteristics and roadside land use are considered as input variables whereas the category of the 85th speed is output variable. A set of experimental data is used for evaluating the performance of the proposed model comparing to a well-known model of exponential regression. It is shown that the developed PSO-fuzzy model is capable of determining the category of 85th speed with an accuracy of 96%, while exponential regression can estimate that with up to 84% accuracy. Variable effectiveness procedure shows that the lane width has more direct effect on 85th speed than shoulder width and the number of access points. The percentage of forbidden overtaking is also found to have indirect effect on 85th speed.

Comparison of WiFi positioning on two mobile devices

Metropolitan WiFi positioning is widely used to complement GPS on mobile devices. WiFi positioning typically has very fast time-to-first-fix and can provide reliable location information when GPS signals are too weak for a position fix. Several commercial WiFi positioning systems have been developed in recent years and most newer model smart phones have the technology embedded. This study empirically determined the performance of WiFi positioning system on two different mobile devices. Skyhook's system, running on an iPhone and a laptop, was selected for this study. Field work was carried out in three cities at a total of 90 sites. The positional accuracy of WiFi positioning was found to be very similar on the two devices with no statistically significant difference between the two error distributions. This suggests that the replicability of WiFi positioning on different devices is high based on aggregate performance metrics. Median values for positional accuracy in the three study areas ranged from 43 to 92 m. These results are similar to earlier independent evaluations of Skyhook's system. The number of access points (APs) observed on the iPhone was consistently lower than that on the laptop. This lower number of APs, however, was not found to reduce positional accuracy. In general, no relationship was found between the number of APs and positional accuracy for either device, counter to earlier findings. The results indicate, however, that WiFi positioning can be achieved with a small number of APs (5–10), but that increased numbers of APs do not contribute to improved positional accuracy. Despite the agreement in aggregate performance metrics between the two devices, the replicability of WiFi positioning using Skyhook's system in terms of getting the same location by using two different devices at approximately the same place and time was relatively poor. Implications for location-based services on mobile devices are discussed.

TVWS에서 스펙트럼 에티켓 및 GA를 사용한 WRAN과 WLAN의 효율적 주파수 공유기법

PURPOSE: An efficient frequency sharing system of WRAN and WLAN using spectrum etiquette and genetic algorithm in TV white space and a method thereof are provided to reduce mutual interference according to co-existence of various heterogeneous communication devices like the WRAN and the WLAN. CONSTITUTION: An information acquisition unit (110) acquires information of WRAN and WLAN. An optimum resource allocation unit (120) allocates optimum frequency sub-band on the basis of the information collected from the information acquisition unit. A broadcasting unit (130) broadcasts the optimum frequency sub-band to each corresponding system. TV white space (TVWS) is idle frequency resource of TV broadcasting frequency band, and is frequency channel space which can be used without additional authorization. The information acquired by the information acquisition unit corresponds to setting state of a peripheral device, channel allocation state, installation position, access mode method and the number of access points (AP). [Reference numerals] (110) Information acquisition unit; (120) Optimum resource allocation unit; (121) First channel selection unit; (122) Second channel selection unit; (130) Broadcasting unit

A mobility model for studying wireless communication and the complexity of problems in the model

AbstractWireless communication has become omnipresent in the world and enables users to have an unprecedented ability to communicate any time and any place. In this article, we propose a mobility model for studying wireless communication. The model incorporates elements such as users, access points, and obstacles so that it faithfully mimics the real environment. Interesting problems that have practical applications are posed and solved. More specifically, we study the complexity of three problems in a grid. The source reachability problem (SRP) models a situation in which we want to determine whether two access points can communicate at a certain time in a mobile environment. When users are involved in this situation, we call this problem the user communication problem (UCP). We show that SRP can be solved in O(max{d,t}m2) time, where d is the number of obstacles, t is the time bound in the statement of the problem, and m is the number of access points; we show that UCP can be solved in O(max{d,t}m4) time. The third problem called the user communication, limited source access problem (UCLSAP) studies a situation where we want to determine whether two users can communicate uninterruptedly during the duration of the model while considering battery‐time limits of the access points. In contrast to the first two problems, we demonstrate that UCLSAP is intractable, unless P = NP. In conclusion, we briefly discuss the extension of our model to three dimensions and provide a list of open problems. © 2012 Wiley Periodicals, Inc. NETWORKS, 2012

Investigation of Travel Time Reliability in Work Zones with Private-Sector Data

The impact of work zones on mean travel time and travel time reliability has gained attention as agencies focus on performance measurement. Travel time reliability in work zones often has been difficult for agencies to quantify because of the time and expense required to collect travel time data. Several private-sector companies have begun to sell travel time data; this availability has created an opportunity to examine cost-effectively work zone impacts on travel time reliability on a broader basis. The Virginia Department of Transportation recently acquired probe vehicle-based travel time data for 2010 from a private-sector data provider. These data were used to calculate measures of travel time reliability at 15 work zones and to examine factors that affected travel time reliability. Travel time reliability was quantified with 95th percentile travel time, a buffer index, and a planning time index. The work zones experienced a statistically significant degradation across all measures of travel time reliability as compared with baseline conditions. Work zone mean buffer index, planning time index, and 95th percentile travel time rates were higher by 48%, 18%, and 16%, respectively. Although lane closures occurred during off-peak periods, work zones that involved lane closures experienced increases in their mean buffer index, planning time index, and 95th percentile travel time with rates of 67%, 23%, and 22%, respectively. Annual average daily traffic per lane and the number of access points per mile were found to have the most obvious relationships with declines in reliability at work zones.