Open Access

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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].