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WiFi-based Long Distance (WiLD) networks have emerged as a promising alternative approach for Internet in rural areas. However, the MAC layer, which is based on the IEEE802.11 standard, comprises contiguous stations in a cell and is spatially restricted to a few hundred meters at most. In this work, we summarize efforts by different researchers to use IEEE802.11 over long-distances. In addition, we introduce WiLDToken, our solution to optimizing the throughput and fairness and reducing the delay on WiLD links. Compared to previous alternative MAC layers protocols for WiLD, our focus is on optimizing a single link in a multi-radio multi-channel mesh. We implement our protocol in the ns-3 network simulator and show thatWiLDToken is superior to an adapted version of the Distributed Coordination Function (DCF) for different link distances. We find that the throughput on a single link is close to the physical data-rate without a major decrease over longer distances.
An Empirical Evaluation of the Received Signal Strength Indicator for fixed outdoor 802.11 links
(2015)
For the evaluation of the received signal strength indication (RSSI) a different methodology compared to previous publications is introduced in this paper by exploiting a spectral scan feature of recent Qualcomm Atheros WiFi NICs. This method is compared to driver reports and to an industrial grade spectrum analyzer. During the conducted outdoor experiments a decreased scattering of the RSSI compared to previous publications is observed. By applying well-known mathematical tests for normality it is possible to show that the RSSI does not follow a normal distribution in a line-of-sight outdoor environment. The evaluated spectral scan features offers additional possibilities to develop interference classifiers which is an important step for frequency allocation in long-distance 802.11 networks.
More and more devices will be connected to the internet [3]. Many devicesare part of the so-called Internet of Things (IoT) which contains many low-powerdevices often powered by a battery. These devices mainly communicate with the manufacturers back-end and deliver personal data and secrets like passwords.
WiFi-based Long Distance (WiLD) networks have emerged as a promising alternative technology approach for providing Internet in rural areas. An important factor in network planning of these wireless networks is estimating the path loss. In this work, we present various propagation models we found suitable for point-to-point (P2P) operation in the WiFi frequency bands. We conducted outdoor experiments with commercial offthe- shelf (COTS) hardware in our testbed made of 7 different long-distance links ranging from 450 m to 10.3 km and a mobile measurement station. We found that for short links with omni-directional antennas ground-reflection is a measurable phenomenon. For longer links, we show that either FSPL or the Longley-Rice model provides accurate results for certain links. We conclude that a good site survey is needed to exclude influences not included in the propagation models.
WiFi-based Long Distance (WiLD) networks have emerged as a promising alternative approach for Internet in rural areas. The main hardware components of these networks are commercial off-the-shelf WiFi radios and directional antennas. During our experiences with real-world WiLD networks, we encountered that interference among long-distance links is a major issue even with high gain directional antennas. In this work, we are providing an in-depth analysis of these interference effects by conducting simulations in ns-3. To closely match the real-world interference effects, we implemented a module to load radiation pattern of commonly used antennas. We analyze two different interference scenarios typically present as a part of larger networks. The results show that side-lobes of directional antennas significantly influence the throughput of long-distance WiFi links depending on the orientation. This work emphasizes that the usage of simple directional antenna models needs to be considered carefully.
More and more low-power wide-area networks (LPWANs) are being deployed and planning the gateway locations plays a significant role for the network range, performance and profitability. We choose LoRa as one LPWAN technology and evaluated the accuracy of the Received Signal Strength Indication (RSSI) of different chipsets in a laboratory environment. The results show the chipsets report significantly different RSSI. To estimate the range of a LPWAN beforehand, path loss models have been proposed. Compared to previous work, we evaluated the Longley-Rice Irregular Terrain Model which makes use of real-world elevation data to predict the path loss. To verify the results of that prediction, an extensive measurements campaign in a semi-urban area in Germany has been conducted. The results show that terrain data can increase the prediction accuracy.
Quantifying Interference in WiLD Networks using Topography Data and Realistic Antenna Patterns
(2019)
Avoiding possible interference is a key aspect to maximize the performance in Wi-Fi based Long Distance networks. In this paper we quantify self-induced interference based on data derived from our testbed and match the findings against simulations. By enhancing current simulation models with two key elements we significantly reduce the deviation between testbed and simulation: the usage of detailed antenna patterns compared to the cone model and propagation modeling enhanced by license-free topography data. Based on the gathered data we discuss several possible optimization approaches such as physical separation of local radios, tuning the sensitivity of the transmitter and using centralized compared to distributed channel assignment algorithms. While our testbed is based on 5 GHz Wi-Fi, we briefly discuss the possible impact of our results to other frequency bands.
Quantifying the spectrum occupancy in an outdoor 5 GHz WiFi network with directional antennas
(2018)
WiFi-based Long Distance networks are seen as a promising alternative for bringing broadband connectivity to rural areas. A key factor for the profitability of these networks is using license free bands. This work quantifies the current spectrum occupancy in our testbed, which covers rural and urban areas alike. The data mining is conducted on the same WiFi card and in parallel with an operational network. The presented evaluations reveal tendencies for various aspects: occupancy compared to population density, occupancy fluctuations, (joint)-vacant channels, the mean channel vacant duration, different approaches to model/forecast occupancy, and correlations among related interfaces.
Real-World Performance of current Mesh Protocols in a small-scale Dual-Radio Multi-Link Environment
(2017)
Two key questions motivated the work in this paper: What is the impact of different usage schemes for multiple channels in a dual-radio Wireless Mesh Network (WMN), and what is the impact of some popular WMN routing protocols on its performance. These two questions were evaluated in a small and simple real-world scenario. A major concern was reproducibility of the results. We show that it is beneficial to use both radios on different frequencies in a fully meshed environment with four routers. The routing protocols Babel, B.A.T.M.A.N. V, BMX7 and OLSRv2 recognize a saturated channel and prefer the other one. We show that in our scenario all of the protocols perform equally well since the protocol overhead is comparably low not influencing the overall performance of the network.
This paper describes the security mechanisms of several wireless building automation technologies, namely ZigBee, EnOcean, ZWave, KNX, FS20, and Home-Matic. It is shown that none of the technologies provides the necessary measure ofsecurity that should be expected in building automation systems. One of the conclusions drawn is that software embedded in systems that are build for a lifetime of twenty years or more needs to be updatable.
Verschiedene intelligente Heimautomatisierungsgeräte wie Lampen, Schlösser und Thermostate verbreiten sich rasant im privaten Umfeld. Ein typisches Kommunikationsprotokoll für diese Geräteklasse ist Bluetooth Low Energy (BLE). In dieser Arbeit wird eine strukturierte Sicherheitsanalyse für BLE vorgestellt. Die beschriebene Vorgehensweise kategorisiert bekannte Angriffsvektoren und beschreibt einen möglichen Aufbau für eine Analyse. Im Zuge dieser Arbeit wurden einige sicherheitsrelevante Probleme aufgedeckt, die es Angreifern ermöglichen die Geräte vollständig zu übernehmen. Es zeigte sich, dass im Standard vorgesehene Sicherheitsfunktionen wie Verschlüsselung und Integritätsprüfungen häufig gar nicht oder fehlerhaft implementiert sind.
The combination of Software-Defined Networking (SDN) and Wireless Mesh Network (WMN) is challenging due to the different natures of both concepts. SDN describes networks with homogeneous, static and centralized controlled topologies. In contrast, a WMN is characterized by a dynamic and distributed network control, and adds new challenges with respect to time-critical operation. However, SDN and WMN are both associated with decreasing the operational costs for communication networks which is especially beneficial for internet provisioning in rural areas. This work surveys the current status for Software-Defined Wireless Mesh Networking. Besides a general overview in the domain of wireless SDN, this work focuses especially on different identified aspects: representing and controlling wireless interfaces, control-plane connection and topology discovery, modulation and coding, routing and load-balancing and client handling. A complete overview of surveyed solutions, open issues and new research directions is provided with regard to each aspect.