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Rural areas all over the world often lacking affordable broadband Internet connectivity. High CAPEX and especially OPEX due to vast and sparsely populated areas often present an uneconomical environment for deploying traditional wireless carrier equipment. Particularly in emerging and developing countries the lack of well-trained personnel requires inherent self-managed networks. To address these issues, we have developed a carrier-grade heterogeneous Back-haul architecture which may be deployed to extend, complement or even replace traditional operator equipment. Our Wireless Back-Haul (WiBACK) network technology extends the Back-haul coverage by building on cost-effective equipment and provides highly automated self-management features still allowing for effective QoS-provisioning. Due to the limited capacity of Wireless Networks compared to cable or fiber networks, it is important to optimally utilize the wireless links and, hence, to configure them properly to match the characteristics of the wireless channel. This link calibration includes selecting the best-suited Modulation and Coding Scheme (MCS), Transmission (TX)-power and other MAC parameters such as the acknowledgment timeout. In this paper, we present our WiBACK architecture and its suitability for deployments in rural regions. Moreover, we propose a link calibration algorithm for IEEE 802.11 links and its crucial architectural role.
SDN and WMN evolved to be sophisticated technologies used in a variety of applications. However, a combined approach called wmSDN has not been widely addressed in the research community. Our idea in this field consists of WiFi-based point-to-point links managed by the OpenFlow protocol. We investigate two different issues regarding this idea. First, which WiFi operational mode is suitable in an OpenFlow managed broadcast domain? Second, does the performance decrease compared with other routing or switching principles? Therefore, we set up a real-world testbed and a suitable simulation environment. Unlike previous work, we show that it is possible to use WiFi links without conducting MAC address rewriting at each hop by utilizing the 4-address-mode.
Rural areas often lack affordable broadband Internet connectivity, mainly due to the CAPEX and especially the OPEX of traditional wireless carrier equipment, the vast and sparsely populated areas and, notably, the lack of trained personal. Addressing these issues we have developed a self-managed heterogeneous Wireless Back-Haul (WiBACK) architecture which may be deployed to complement or even replace traditional operator equipment. To optimally utilize fixed wireless point-to-point connectivity, its configuration is to be adjusted properly to the characteristics of the wireless channel. Due to lack of trained personal, time constraints during rapid temporary deployments or run-time network reconfigurations, this task must be automated. Some technologies already provide built-in ranging mechanisms, while others require external, often manual configuration. Such mechanisms should optimally exploit the individual PHY and MAC configuration options. The resulting link properties, such as capacity and latency, are utilized to optimally allocate resources for QoS-aware Pipes. Accordingly, in this paper, we present the AI Radio CalibrateLink primitive, discuss its crucial architectural role in separating spectrum from capacity management and present evaluation results of our resource model for IEEE 802.11a links.
Exemplarische Untersuchungen zum Potenzial von LTE zur Breitbandversorgung ländlicher Regionen
(2010)
Anhand von Funkfeldmessungen in mehreren ausgewählten Orten im Hochsauerlandkreis wird die Frage diskutiert, welchen Beitrag der Aufbau eines LTE-Netzes zur Breitbandversorgung von bisher unterversorgten Gebieten im ländlichen Raum liefern kann - und dies unter Verwendung bestehender GSM-Basisstationsstandorte und dem Frequenzbereich der Digitalen Dividende. Für verschiedene Szenarien werden Empfangspegelstatistiken mit geforderten Empfängerempfindlichkeiten verglichen, Statistiken zur zu erwartenden Datenraten abgeleitet und Netzkapazitäten abgeschätzt. Dabei zeigt sich, dass i. A. sowohl der Empfangspegel als auch die Netzkapazität ausreichen, um mittels LTE eine genügende Zahl von Anschlüssen mit einer Downlink-Datenrate von mindestens 1 Mbit/s in den untersuchten Ortschaften bereit zu stellen. Hohe Versorgungsgrade mit Datenraten von 50 Mbit/s sind jedoch nicht zu erwarten. Durch eine Außeninstallation der Endgeräteantennen lassen sich auch bei 2600 MHz nahezu optimale Empfangsbedingungen erzielen. Insofern scheint ein Mischbetrieb mit Frequenzen im 800- und im 2600-MHz-Bereich geeignet, die Netzkapazität auch im ländlichen Raum zu erhöhen.
Die Erfindung betrifft ein System (1) zum Ausrichten einer Richtfunkantenne (a1) auf eine weitere Richtfunkantenne (a2). Das System weist ein Positioniermittel (P) auf, welches an einem vom Ort der auszurichtenden Richtfunkantenne (a1) und vom Ort der weiteren Richtfunkantenne (a2) verschiedenen Ort positioniert ist, wobei der Ort des Positioniermittels (P) vom Ort der auszurichtenden Richtfunkantenne (a1) aus einsehbar ist. Erfindungsgemäß umfasst das System (1) ferner ein Berechnungsmittel (L), das ausgebildet ist, einen Ausrichtungsfehler (α) der auszurichtenden Richtfunkantenne (a1) zu bestimmen, wobei der Ausrichtungsfehler (α) einen Winkel angibt, der zwischen einer ersten virtuellen Geraden (g1), welche den Ort der auszurichtenden Antenne (a1) und den Ort der weiteren Richtfunkantenne (a2) beinhaltet, und einer zweiten virtuellen Geraden (g2), welche den Ort der auszurichtenden Antenne (a1) und den Ort des Positioniermittels (P) beinhaltet, liegt.
Evaluation and Optimization of IEEE802.11 multi-hop Backhaul Networks with Directional Antennas
(2020)
A major problem for rural areas is the inaccessibility to affordable broadband Internet connections. In these areas distances are large, and digging a cable into the ground is extremely expensive, considering the small number of potential customers at the end of that cable. This leads to a digital divide, where urban areas enjoy a high-quality service at low cost, while rural areas suffer from the reverse.
This work is dedicated to an alternative technical approach aiming to reduce the cost for Internet Service Provider in rural areas: WiFi-based Long Distance networks. A set of significant contributions of technology related aspects of WiFi-based Long Distance networks is described in three different fields: Propagation on long distance Wi-Fi links, MAC-layer scheduling and Interference modeling and Channel Assignment with directional antennas.
For each field, the author composes and discusses the state-of-the-art. Afterwards, the author derives research questions and tackles several open issues to develop these kinds of networks further towards a suitable technology for the backhaul segment.
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.
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.
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.
The lack of affordable broadband Internet connectivity in rural areas, especially in emerging regions, is seen as a major barrier for access to knowledge, education or government services. In order to reduce the costs of back-hauling in rural regions, often without access to a stable power grid, alternative solutions are required to provide high-bandwidth back-hauling at minimal power consumption to allow solar-powered operation. In this paper, we show that cost-effective low-power IEEE802.11n (MIMO) hardware together with a single cross-polarized antenna can be a viable solution to the problem. Our study shows that up to 200 Mbps of actual throughput can be achieved over distances larger than 10 km while the power consumption of a typical forwarding node is well below 10 Watts (http://wiback.org/repeater) - suitable for a cost-effective solar-powered operation. Through theoretical analysis and extensive measurements we show that such a low-cost setup can be used to establish reliable long-distance links providing high-bandwidth connectivity at low latencies and consequently providing the capacity demanded by today’s services - everywhere. Exploiting these findings we are in the process of extending existing fiber-based infrastructures in rural Africa with our Wireless Back-Haul (WiBACK) architecture.
With the growing potential of wireless backhaul technologies for outdoor environments and rising interest in unlicensed bands for broadband delivery, dynamic channel assignment and improved spectrum utilization is re-emerging as a research topic. In this paper we describe a centralized channel assignment optimization for our wireless backhaul architecture WiBACK. In order to efficiently utilize wireless channels in heterogeneous networks, we propose an improvement to the current frequency planning scheme using 802.11 as an example. The contributions in this paper can improve broadband access for emerging areas, often lacking required telecommunication infrastructure.
This work describes extensions to the well-known Distributed Coordination Function (DCF) model to account for IEEE802.11n point-to-point links. The developed extensions cover adaptions to the throughput and delay estimation for this type of link as well peculiarities of hardware and implementations within the Linux Kernel. Instead of using simulations, the approach was extensively verified on real-world deployments at various link distances. Additionally, trials were conducted to optimize the CWmin values and the number of retries to maximize throughput and minimize delay. The results of this work can be used to estimate the properties of long-distance 802.11 links beforehand, allowing the network to be planned more accurately.
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.
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.
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.
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.
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.
This work provides a short but technical introduction to the main building blocks of a blockchain. It argues that a blockchain is not a revolutionary technology but rather a clever combination of three fields: cryptography, decentralization and game theory. In addition, it summaries the differences between a public, private and federate blockchain model and the two prominent consensus mechanism Proof-of-Work (POW) and Proof-of-Stake (POS).
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.
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.
Rural areas often lack affordable broadband Internet connectivity, mainly due to the CAPEX and especially OPEX of traditional operator equipment [HEKN11]. This digital divide limits the access to knowledge, health care and other services for billions of people. Different approaches to close this gap were discussed in the last decade [SPNB08]. In most rural areas satellite bandwidth is expensive and cellular networks (3G,4G) as well as WiMAX suffer from the usually low population density making it hard to amortize the costs of a base station [SPNB08].
