Impact of cell load on 5GHz IEEE 802.11 WLAN

We have conducted an empirical study of the latest 5GHz IEEE 802.11 wireless LAN (WLAN) variants of 802.11n (5GHz) and 802.11ac (Wave 1), under different cell load conditions. We have considered typical configurations of both protocols on a Linux testbed. Under light load,there is no clear difference between 802.11n and 802.11ac in terms of performance and energy consumption. However, in some cases of high cell load, we have found that there may be a small advantage with 802.11ac. Overall, we conclude that there may be little benefit in upgrading from 802.11n (5GHz) to 802.11ac in its current offering, as the benefits may be too small.Postprin

PRACB: A Novel Channel Bonding Algorithm for Cognitive Radio Sensor Networks

Wireless sensor networks (WSNs) can utilize the unlicensed industrial, scientific and medical (ISM) band to communicate the sensed data. The ISM band has been already saturated due to overlaid deployment of WSNs. To solve this problem, WSNs have been powered up by cognitive radio (CR) capability. By using CR technique, WSNs can utilize the spectrum holes opportunistically. Channel bonding (CB) is a technique through which multiple contiguous channels can be combined to form a single wide band channel. By using channel bonding (CB) technique, CR based WSN nodes attempt to find and combine contiguous channels to avail larger bandwidth. In this paper, we show that probability of finding contiguous channels decreases with the increase in number of channels. Moreover, we propose two algorithms of primary radio (PR) activity based channel bonding schemes and compare with sample width algorithm (SWA). The simulation results show that our algorithm significantly avoids PR-CR harmful interference and CB in cognitive radio sensor networks (CRSNs) provides greater bandwidth to CR nodes

Розробка методу оцінювання ефективної швидкості передачі інформації на базі емпіричної моделі статистичного зв’язку основних параметрів безпровідного каналу стандарту 802.11

A method of estimating the effective data rate in channels of the Standard 802.11 was proposed. It provides for the measurement of the main energy parameter using the software and hardware of the subscriber device. This method is based on the empirical models of statistical relationships between the main parameters of the channel which are obtained on the basis of experimental studies using monitoring algorithms. The solutions obtained during the implementation of this method make it possible to take into account the maximum possible number of destabilizing factors and significantly reduce the time of assessment of the effective data rate. It should be noted that this method can be used for technical diagnostics of wireless networks of Standards 802.11x at the stages of network design and operation.It was established that when using the coefficient of energy efficiency, a significant error in the displacement of the points of intersection of the linear and logarithmic mathematical model occurs. This can lead to a discrepancy between the mathematical estimates of the effective data rate and real values. The statistical relationship gives a smaller error; however, it increases requirements for empirical studies to obtain the maximum possible reliability.One of the features of the proposed method is the reliability of assessment of the effective data rate. This reliability depends on three main factors: accuracy of assessing the results based on which the mathematical model was obtained; estimation of fluctuation intervals and characteristics of the Standard 802.11 equipment of different manufacturers. The last factor can be considered as a disadvantage that involves the creation of a database of parameters of the model of statistical relationship for different devices with correction coefficientsПредложен метод оценки эффективной скорости передачи информации в каналах стандарта 802.11, который предусматривает измерение основного энергетического параметра с помощью программно-аппаратных средств абонентского устройства. Основой такого метода являются эмпирические модели статистической связи между основными параметрами канала, полученные на основе экспериментальных исследований с применением алгоритмов мониторинга. Полученные при реализации данного метода решения позволяют учитывать максимально возможное количество дестабилизирующих факторов и значительно уменьшить время оценки эффективной скорости передачи информации. Следует отметить, что такой метод может использоваться для технической диагностики беспроводных сетей стандарта 802.11х на этапах проектирования и эксплуатации.Установлено, что, используя коэффициент энергетической эффективности, возникает значительная погрешность при смещении точек пересечения линейной и логарифмической математической модели. Это может приводить к отклонению математической оценки эффективной скорости передачи информации и реальных значений. Статистическая связь дает меньшую погрешность, но повышает требования к эмпирическим исследованиям для получения максимально-возможной достоверности.Одной из особенностей предложенного метода можно выделить достоверность оценки эффективной скорости передачи информации. Такая достоверность зависит от трех основных факторов: точность оценки результатов на основе которых получена математическая модель; оценка интервалов флуктуаций и характеристики оборудования стандарта 802.11 разных производителей. Последний фактор можно выделить как недостаток, предусматривающий создание базы данных параметров модели статистической связи для различных устройств с корректирующими коэффициентамиЗапропоновано метод оцінювання ефективної швидкості передачі інформації у каналах стандарту 802.11, який передбачає вимірювання основного енергетичного параметра за допомогою програмно-апаратних засобів абонентського пристрою. Основою такого методу є емпіричні моделі статистичного зв’язку між основними параметрами каналу, які отримано на основі експериментальних досліджень із застосуванням алгоритмів моніторингу. Отриманні при реалізації даного методу рішення дозволяють враховувати максимально-можливу кількість дестабілізуючих факторів та значно зменшити час оцінювання ефективної швидкості передачі інформації. Слід відзначити, що такий метод може використовуватись для технічної діагностики безпровідних мереж стандартів 802.11х на етапах проектування та експлуатації мереж.Встановлено, що використовуючи коефіцієнт енергетичної ефективності виникає значна похибка при зміщенні точок перетину лінійної та логарифмічної математичної моделі. Це може приводити до відхилення математичної оцінки ефективної швидкості передачі інформації та реальних значень. Статистичний зв’язок дає меншу похибку, але підвищує вимоги до емпіричних досліджень для отримання максимально-можливої достовірності.Однією із особливостей запропонованого методу, можна виділити достовірність оцінювання ефективної швидкості передачі інформації. Така достовірність залежить від трьох основних факторів: точність оцінювання результатів, на основі яких отримана математична модель; оцінювання інтервалів флуктуацій та характеристики обладнання стандарту 802.11 різних виробників. Останній фактор можна виділити як недолік, що передбачає створення бази даних параметрів моделі статистичного зв’язку для різних пристроїв із корегуючими коефіцієнтам

Bringing cross-layer MIMO to today's wireless LANs

Recent years have seen major innovations in cross-layer wireless designs. Despite demonstrating significant throughput gains, hardly any of these technologies have made it into real networks. Deploying cross-layer innovations requires adoption from Wi-Fi chip manufacturers. Yet, manufacturers hesitate to undertake major investments without a better understanding of how these designs interact with real networks and applications. This paper presents the first step towards breaking this stalemate, by enabling the adoption of cross-layer designs in today's networks with commodity Wi-Fi cards and actual applications. We present OpenRF, a cross-layer architecture for managing MIMO signal processing. OpenRF enables access points on the same channel to cancel their interference at each other's clients, while beamforming their signal to their own clients. OpenRF is self-configuring, so that network administrators need not understand MIMO or physical layer techniques. We patch the iwlwifi driver to support OpenRF on off-the-shelf Intel cards. We deploy OpenRF on a 20-node network, showing how it manages the complex interaction of cross-layer design with a real network stack, TCP, bursty traffic, and real applications. Our results demonstrate an average gain of 1.6x for TCP traffic and a significant reduction in response time for real-time applications, like remote desktop.National Science Foundation (U.S.

Learning Wi-Fi Performance

Accurate prediction of wireless network performance is important when performing link adaptation or resource allocation. However, the complexity of interference interactions at MAC and PHY layers, as well as the vast variety of possible wireless configurations make it notoriously hard to design explicit performance models. In this paper, we advocate an approach of “learning by observation” that can remove the need for designing explicit and complex performance models. We use machine-learning techniques to learn implicit performance models, from a limited number of real-world measurements. These models do not require to know the internal mechanics of interfering Wi-Fi links. Yet, our results show that they improve accuracy by at least 49% compared to measurement-seeded models based on SINR. To demonstrate that learned models can be useful in practice, we build a new algorithm that uses such a model as an oracle to jointly allocate spectrum and transmit power. Our algorithm is utility-optimal, distributed, and it produces efficient allocations that significantly improve performance and fairness

IEEE 802.11ac Performance Analysis and Measurement Tools

Wireless local area networks have witnessed a large growth over the course of the last decade which has led to increased data traffic and demand for higher speeds. One of the IEEE 802.11 standards family that was developed to offer very high throughput WLANs is IEEE 802.11ac. Theoretically, with the PHY and MAC enhancements embedded in this standard, it is expected to provide gigabit-per-second data rates. The WLAN standards in addition to other wireless technologies such as Bluetooth and ZigBee share the same unlicensed band, and the increase in the use of this band requires monitoring the wireless spectrum and addressing wireless coexistence problems via spectrum surveys which usually produce a large data volume, that requires advanced hardware capabilities to help overcome the challenges of storing, retrieving and processing the data. This thesis reports on the performance analysis of an IEEE 802.11ac network with respect to varied channel conditions such as SNR and SIR. Mathematical models of the relationship between the throughput, the delay of the network and SNR using interpolation, were provided. The results show that for good channel conditions i.e. high SNR, 802.11ac offers high throughput values. However, the throughput is highly affected by the interference level caused by other 802.11ac devices that share the same channel, as the throughput of the under-test network is directly proportional to the level of SIR. Moreover, this thesis details a measurement tool that implements a probabilistic efficient storage algorithm (PESA) proposed by Dr. Al-Kalaa with US FDA that could be used in deploying long-term spectrum surveys in the time-domain using LabVIEW. PESA algorithm is based on representing the dynamic range of a monitoring device by a Gaussian Mixture Model, establishing windows of activity and inactivity and mapping the windows to the Gaussian component with the largest responsibility for each window mean. The indexes of the Gaussian components are stored in addition to the count of samples in each window resulting in a significant storage volume reduction. The software was used to survey the 2.4 GHz band in a healthcare facility for 7 hours. The results show a reduction in the required storage size of approximately 98.8% while maintaining an accurate estimation of the channel utilization

Theoretical and experimental study of performance anomaly in multi-rate IEEE802.11ac wireless networks

IEEE 802.11 wireless local area networks (WLANs) are shared networks, which use contention-based distributed coordination function (DCF) to share access to wireless medium among numerous wireless stations. The performance of the distributed coordination function mechanism mostly depends on the network load, number of wireless nodes and their data rates. The throughput unfairness, also known as performance anomaly is inherent in the very nature of mixed data rate Wi-Fi networks using the distributed coordination function. This unfairness exhibits itself through the fact that slow clients consume more airtime to transfer a given amount of data, leaving less airtime for fast clients. In this paper, we comprehensively examine the performance anomaly in multi-rate wireless networks using three approaches: experimental measurement, analytical modelling and simulation in Network Simulator v.3 (NS3). The results of our practical experiments benchmarking the throughput of a multi-rate 802.11ac wireless network clearly shows that even the recent wireless standards still suffer from airtime consumption unfairness. It was shown that even a single low-data rate station can decrease the throughput of high-data rate stations by 3–6 times. The simulation and analytical modelling confirm this finding with considerably high accuracy. Most of the theoretical models evaluating performance anomaly in Wi-Fi networks suggest that all stations get the same throughput independently of the used data rate. However, experimental and simulation results have demonstrated that despite a significant performance degradation high-speed stations still outperform stations with lower data rates once the difference between data rates becomes more significant. This is due to the better efficiency of the TCP protocol working over a fast wireless connection. It is also noteworthy that the throughput achieved by a station when it monopolistically uses the wireless media is considerably less than 50 % of its data rate due to significant overheads even in most recent Wi-Fi technologies. Mitigating performance anomaly in mixed-data rate WLANs requires a holistic approach that combines frame aggregation/fragmentation and adaption of data rates, contention window and other link-layer parameters

Tiheiden Wi-Fi verkkojen optimointi Markov-ketjumallien ja simuloidun jäähdytyksen avulla

Currently, the demand for wireless communication capacity is rising rapidly due to challenging applications such as video streaming and the emerging Internet of things. In meeting these ambitious requirements, the most important factor is predicted to be network densification, which refers to increasing the geographical density of simultaneously communicating devices. A natural choice for implementing dense networks is the wireless local area network technology Wi-Fi, characterized by being cheap and easy to deploy. Network density aggravates the harmful effects of interference and causes scarcity of free transmission bandwidth. To counter this, dense networks need radio resource management algorithms. This thesis presents a Wi-Fi radio resource management algorithm, which jointly optimizes access point channels, user association and transmission power. It estimates future throughput using a continuous time Markov chain based model, and finds solutions maximizing this estimate via a discrete search metaheuristic called simulated annealing. The algorithm is validated through a wide range of simulations where for instance network density is varied. The algorithm is found to be highly versatile, yielding good performance in all scenarios. Moreover, the general design approach places few restrictions on further algorithm improvement and extension. Markov chain modeling, although accurate in an idealized setting, turns out to be inaccurate with real-world Wi-Fi, with a simpler model offering similar accuracy but lighter computational load.Nykyisin vaatimukset langattoman tiedonsiirron kapasiteetille ovat voimakkaassa kasvussa johtuen haastavista sovelluksista kuten videon suoratoistosta ja tulossa olevasta esineiden Internetistä. Näiden vaatimusten täyttämiseksi tärkein keino on langattomien tiedonsiirtoverkkojen tihentäminen, mikä tarkoittaa yht’aikaa samalla maantieteellisellä alueella kommunikoivien laitteiden määrän kasvattamista. Luonnollinen valinta tiheiden verkkojen toteuttamiseen on langattomien lähiverkkojen teknologia Wi-Fi, jonka etuja ovat edullisuus ja asennuksen helppous. Langattoman verkon tiheys lisää haitallista interferenssiä ja aikaansaa pulaa vapaista lähetystaajuuksista. Näiden ongelmien ratkaisemiseksi tarvitaan radioresurssien hallinta-algoritmeja. Tässä työssä suunnitellaan Wi-Fiä varten radioresurssien hallinta-algoritmi, joka optimoi samanaikaisesti tukiasemien kanavia, käyttäjien allokaatiota tukiasemille sekä lähetystehoja. Se estimoi tulevia tiedonsiirtonopeuksia jatkuvan ajan Markov-ketjuihin pohjautuvan mallin avulla ja löytää tämän estimaatin maksimoivia ratkaisuja hyödyntämällä diskreettiä hakumenetelmää nimeltä simuloitu jäähdytys. Algoritmi validoidaan käyttäen monipuolista joukkoa simulaatioita, jossa vaihtelee esimerkiksi verkon tiheys. Algoritmi osoittautuu erittäin monipuoliseksi, sillä sen suorituskyky on hyvä kaikissa simulaatioskenaarioissa. Käytetyn lähestymistavan etuna on myös se, että se asettaa varsin vähän rajoituksia algoritmin jatkokehitykselle. Markov-ketjumallit osoittautuvat todellisen Wi-Fin tapauksessa epätarkoiksi, vaikka ne idealisoidussa ympäristössä ovatkin tarkkoja. Käy ilmi, että yksinkertaisemmalla mallilla saadaan vastaava tarkkuus, mutta laskentatehoa tarvitaan vähemmän