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- IEEE 802.11 (2)
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An increasing number of applications include real-time audio streaming over a communication network. Well-known examples are teleconferencing, tele-presentation, Internet Radio live streams and on-demand services. In cooperation with various broadcasters, GMD provides live and on-demand audio services over the Internet. Applications are based on commercial products as well as on own software developments. This paper describes some approaches to provide a real-time audio service over the Internet, discusses problems and experiences and presents an outlook for a streaming service in the future.
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.
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.
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.
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.
Rural areas all over the world often lack affordable broadband Internet connectivity. This is particularly, but not solely, true for developing and emerging countries. Also rural areas in western countries share similar problems of high capital expenditure (CAPEX) and especially operational expenditure (OPEX) due to vast and sparsely populated areas, which often present an uneconomical environment for deploying traditional wireless carrier equipment. To address these issues, we have developed a carrier-grade heterogeneous multi-radio back-haul architecture which may be deployed to extend, complement or even replace traditional operator equipment. Our Wireless Back-Haul (WiBACK) technology extends the back-haul coverage by building on cost-effective and low-power equipment while still allowing for effective Quality of Service (QoS)-provisioning. In this paper we first present a pilot scenario in Hennef-Theishohn, Germany, where the residents of a remote farm are provided with broadband Internet connectivity using a long-distance, multi-hop WiBACK network. We evaluate the QoS-related performance of this network and show that we can meet QoS demands one expects from a carrier-grade network even under heavy load conditions.
TV white spaces (TVWS), are seen as a key technology to enable the efficient use of scarce sub-GHz spectrum allowing for applications that may have a huge impact on internet penetration in rural parts of Africa. We first give an overview on TVWS, its use cases and highlight possible challenges against its uptake. Then we describe our carrier-grade wireless back-hauling solution (WiBACK) and discuss its capability for working with a geolocation database ensuring zero interference with licensed users.
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.
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.
Meshed wireless back-haul networks are seen as an affordable technology to bring Internet connectivity into rural and previously unconnected regions. To date, the main focus is to provide access to classical services such as theWWWor email. Access to such services requires the users to use a personal computer or a recent smart phone. Especially in developing regions, the prevailing end user device is a mobile phone. In order to connect mobile phones to an IP-based back-haul network, the network access points must provide a mobile phone air interface which is usually based on GSM or UMTS. In order to avoid dependence on a costly 3GPP infrastructure, we propose to deploy GSM or 3GPP nano cells in order to terminate the mobile phone protocols immediately at the mesh access points. Hence, the voice or data traffic can be carried over IP-based networks using open protocols such as SIP and RTP.
Providing Mobile Phone Access in Rural Areas via Heterogeneous Meshed Wireless Back-Haul Networks
(2011)
Wireless Mesh Networks (WMNs) are often seen as an affordable solution to bring Internet connectivity into rural and previously unconnected regions. To date, the main focus has been to provide access to classical services such as the WWW or email which requires the users to use a personal computer or a recent smart phone. In many developing regions, however, the prevailing end user device is a mobile phone. In order to connect mobile phones to an IP-based wireless back-haul networks, the network access points must provide a mobile phone air interface, compatible with GSM or UMTS specifications. Avoiding dependence on a costly mobile operator infrastructure, we propose to deploy GSM or 3GPP nano cells in order to terminate the mobile phone protocols immediately at the local network access points. Therefore, voice or data traffic can be carried over wireless back-haul networks using open protocols such as SIP and RTP. In this paper we present a meshed wireless back-haul network architecture whose access points have been equipped with GSM nano-cells. The voice packets generated by mobile phones are carried across the back-haul network in parallel to typical web or video traffic. We evaluate the QoS handling received by the voice calls across our multi-hop wireless testbed and show that our architecture can provide the resource isolation required to offer uninterrupted VoIP services in parallel to regular Internet traffic.
