Search results for "WLAN"
showing 10 items of 52 documents
Temporal Fairness Provisioning in Multi-Rate Contention-Based 802.11e WLANs
2005
The IEEE 802.11e extensions for QoS support in WLAN define the transmission opportunity (TXOP) concept, in order to limit the channel holding times of the contending stations in the presence of delay-sensitive traffic. We evaluate the use of TXOP for a different purpose: "temporal fairness" provisioning among stations employing different data rates. We show that the equalization of the channel access times allows each station to obtain its throughput basically (1) proportional to its transmission rate, and (2) independent of the transmitted frame length. This also improves the aggregate throughput of the overall WLAN. For a given TXOP limit, i.e., a granted channel access time, a station is…
Learning from Errors: Detecting ZigBee Interference in WiFi Networks
2014
In this work we show how to detect ZigBee interference on commodity WiFi cards by monitoring the reception errors, such as synchronization errors, invalid header formats, too long frames, etc., caused by ZigBee transmissions. Indeed, in presence of non-WiFi modulated signals, the occurrence of these types of errors follows statistics that can be easily recognized. Moreover, the duration of the error bursts depends on the transmission interval of the interference source, while the error spacing depends on the receiver implementation. On the basis of these considerations, we propose the adoption of hidden Markov chains for characterizing the behavior of WiFi receivers in presence of controlle…
Side Effects of Ambient Noise Immunity Techniques on Outdoor IEEE 802.11 Deployments
2008
A very common conclusion of many experimental studies about IEEE 802.11 outdoor network deployments is that their poor performance results derive from the unfavorable interference and multi-path signals in which the WLAN-cards are required to operate. Goal of this paper is to show that this condition does not always hold, and unexpected and inaccurated PHY layer implementations can be a primary cause of packet losses. With the support of extensive measurement campaigns led in our campus, we provide the performance evidence that IEEE 802.11 outdoor performance impairments are strongly affected by proprietary interference mitigation techniques that adaptively adjust the WLAN-card receiver sen…
Fenoskandijas ledus vairoga Zemgales loba subglaciālās reljefa sistēmas un dinamika
2015
Pētījums ir veikts par Fenoskandijas ledus vairoga Zemgales loba subglaciālajām reljefa formām un ledāja dinamiku Viduslatvijas zemienē un Ziemeļlietuvas līdzenumos, akcentējot drumlinu, lielizmēra glaciālo lineamentu, rievoto morēnu un ledājūdeņu straumju lineāro veidojumu morfoloģiju, telpisko sakārtojumu, iekšējo uzbūvi un veidošanās apstākļu kopsakarību ar ledāja–gultnes mijiedarbības zonas termālo apstākļu laiktelpiskajām izmaiņām. Balstoties uz lielmēroga topogrāfisko karšu un augstas izšķirtspējas reljefa modeļu analīzi, kartētas subglaciālās reljefa formas un iegūti to morfometriskie parametri. Lauka pētījumos ir iegūti oriģināli, ģeotelpiski precīzi piesaistīti dati par subglaciālo…
Gnaphalio uliginosi-eleocharitetum acicularis Passarge 1999, new plant community in Poland
2017
Zbiorniki wodne są bardzo cennymi miejscami florystycznymi w Polsce. Wśród nich najważniejsze dla zachowania różnorodności biologicznej flory są stawy rybne. Długookresowy proces oddziaływania ludzkiego na tego typu siedliska powodował zakłócenia w ich równowadze biologicznej. Zmiany w systemie wodnym, rozwój przemysłowy i chemizacja rolnictwa, zwłaszcza w okresie ostatnich dwóch stuleci, doprowadziły do zaniku wielu gatunków roślin oraz zbiorowisk roślinnych. Zespół Gnaphalio uliginosi-Eleocharitetum acicularis Passarge 1999 z klasy Isoëto-Nanojuncetea Br.-Bl. et Tx. 1943, po raz pierwszy został opisany w Niemczech. Rośnie na piaszczystych lub mulistych brzegach rzek, starorzeczach i w sta…
HERPETOFAUNA DI HUTAN DATARAN RENDAH HAYA, MAMBERAMO, PAPUA
2008
<p><em>During about 19 days field work survey (7-25 February 2008) on the Haya lowland forest area, Mamberamo Papua. Eksploration is the methods used in this study. Reptiles and amphibians were collected by hand on the night and day in several type of habitat (plains, swamp, oxbowlake, stream, creeks and hills). The result showed that 48 species of herpetofauna (21 species frogs, 19 species of lizard, six species of snakes and one species of turtles and crocodile) were found.</em></p>
Radio frequency fingerprinting for outdoor user equipment localization
2017
The recent advancements in cellular mobile technology and smart phone usage have opened opportunities for researchers and commercial companies to develop ubiquitous low cost localization systems. Radio frequency (RF) fingerprinting is a popular positioning technique which uses radio signal strength (RSS) values from already existing infrastructures to provide satisfactory user positioning accuracy in indoor and densely built outdoor urban areas where Global Navigation Satellite System (GNSS) signal is poor and hard to reach. However a major requirement for the RF fingerprinting to maintain good localization accuracy is the collection and updating of large training database. The Minimization…