A simple technique to estimate the position of a given mobile source inside a building is based o... more A simple technique to estimate the position of a given mobile source inside a building is based on the received signal strength. For this methodology to have a reasonable accuracy, radio visibility of the mobile by at least three access points is required. To reduce the number of the required access points and therefore, simplify the underlying coverage design problem, we propose a new scheme that takes into account the distribution of RF energy around the receiver. In other words, we assume that the receiver is equipped with a circular antenna with beamforming capability. In this way, the spatial spectrum of the received power can be measured by rotating the antenna beam around the 360-degree field of view. This spatial spectrum can be used by a single receiver as a mean for estimating the position of a mobile transmitter. In this paper, we investigate the feasibility of this methodology, and show the improvement achieved in the positioning accuracy.
A simple technique to estimate the position of a mobile node inside a building is based on the Re... more A simple technique to estimate the position of a mobile node inside a building is based on the Received Signal Strength (RSS). In previous publications, we investigated the effectiveness of using circular array antennas and beamforming in order to enable an access point to estimate the position of a mobile inside a building. We also discussed the feasibility of using model-based radio maps to reduce the need for extensive offline measurements. In this paper, a positioning algorithm based on the relative order of the received signal strengths is discussed. This algorithm in conjunction with the ray-tracing propagation model can have promising performance for indoor environments and essentially eliminates the needs for an extensive set of a priori measurement, training or intricate calibration.
A simple technique to estimate the position of a given mobile source inside a building is based o... more A simple technique to estimate the position of a given mobile source inside a building is based on the received signal strength. For this methodology to have a reasonable accuracy, radio visibility of the mobile by at least three access points is required. To reduce the number of the required access points and therefore simplify the underlying coverage design problem, we propose a novel scheme that takes into account the distribution of RF energy around the receiver. In other words, we assume that the receiver is equipped with a circular array antenna with beamforming capability. In this way, the spatial spectrum of the received power can be measured by electronically rotating the main lobe around the 360-degree field of view. This spatial spectrum can be used by a single receiver as a means for estimating the position of the mobile transmitter. In this paper, we investigate the feasibility of this methodology, and show the improvement achieved in the positioning accuracy.
A simple technique to estimate the position of a given mobile source inside a building is based o... more A simple technique to estimate the position of a given mobile source inside a building is based on the received signal strength. For this methodology to have a reasonable accuracy, radio visibility of the mobile node by at least three access points is required. To reduce the number of required access points and therefore, to simplify the underlying coverage design problem, a new scheme is presented that takes into account the distribution of RF energy around the receiver. In other words, it is assumed that the receiver is equipped with a circular antenna with beamforming capability. In this way, the spatial spectrum of the received power can be measured by rotating the antenna beam around the 360-degree field of view. This spatial spectrum can be used by the receiver as a means for estimating the position of a mobile transmitter. In this thesis, the feasibility of this methodology is investigated, and the improvement achieved in the positioning accuracy is shown. 3 4 Foremost, I would like to express my thanks to Kamran Sayrafian for his continuing support, interesting ideas and suggestions, his patient explanations and diverting lunch-time conversations.
A simple technique to estimate the position of a mobile node inside a building is based on the Re... more A simple technique to estimate the position of a mobile node inside a building is based on the Received Signal Strength (RSS). In a previous publication, we investigated the feasibility of using circular array antennas and beamforming in order to enable an access point to estimate the position of a mobile inside a building. The approach utilized the two dimensional information (i.e. RSS for various azimuth directions) that is captured in a priori measured radio map. Generating these radio maps is not only extremely laborintensive and time consuming but also sensitive to changes in the environment and possible source of interference. It would be interesting to find out if a deterministic propagation model such as ray tracing can be used to construct a radio map that effectively replaces the off-line manual measurements. In this paper, we investigate this issue and provide a novel positioning methodology that exhibits acceptable performance without the need for extensive set of measurements in the off-line mode. The performance for various parameters and building model accuracy will be presented and discussed.
Devices capable of connecting to multiple, overlapping networks simultaneously are becoming incre... more Devices capable of connecting to multiple, overlapping networks simultaneously are becoming increasingly common. For example, most laptops are equipped with LAN-and WLAN-interfaces, and smart phones can typically connect to both WLANs and 3G mobile networks. At the same time, streaming high-quality video is becoming increasingly popular. However, due to bandwidth limitations or the unreliable and unpredictable nature of some types of networks, streaming video can be subject to frequent periods of rebuffering and characterised by a low picture quality.
With today's widespread deployment of wireless technologies, it is often the case that a single c... more With today's widespread deployment of wireless technologies, it is often the case that a single communication device can select from a variety of access networks. At the same time, there is an ongoing trend towards integration of multiple network interfaces into end-hosts, such as cell phones with HSDPA, Bluetooth and WLAN. By using multiple Internet connections concurrently, network applications can benefit from aggregated bandwidth and increased fault tolerance. However, the heterogeneity of wireless environments introduce challenges with respect to implementation, deployment, and protocol compatibility. Variable link characteristics cause reordering when sending IP packets of the same flow over multiple paths. This paper introduces a multilink proxy that is able to transparently stripe traffic destined for multihomed clients. Operating on the network layer, the proxy uses path monitoring statistics to adapt to changes in throughput and latency. Experimental results obtained from a proof-of-concept implementation verify that our approach is able to fully aggregate the throughput of heterogeneous downlink streams, even if the path characteristics change over time. In addition, our novel method of equalizing delays by buffering packets on the proxy significantly reduces IP packet reordering and the buffer requirements of clients.
The increasing speed and coverage of wireless widearea networks (WWAN) has made technologies such... more The increasing speed and coverage of wireless widearea networks (WWAN) has made technologies such as GPRS, UMTS, or HSDPA a popular way to access the Internet for both mobile and stationary users. However, depending on the scenario, WWAN can suffer from severe IP packet loss due to corruption, which is mistaken by TCP as an indication of path congestion. This paper presents an approach to solve the loss differentiation problem for the widespread scenario of wireless networks being used as access networks to the Internet. Our solution allows TCP to distinguish between congestion and corruption loss and to properly react to both phenomena. Loss differentiation is achieved by placing an assisting agent on the WWAN's base station, which replies a TCP sender in the wired Internet with a new type of acknowledgement. Without harming TCP's end-toend semantics, these acknowledgements provide feedback about congestion on the wired path and corruption on the wireless path and support the sender in taking remedial action. Results from simulations indicate that our proposed corruption recovery algorithm significantly improves the TCP goodput. In addition, excessive RTO growth and pauses in the TCP flow that result from repeated packet corruption are considerably reduced.
A well known challenge with mobile video streaming is fluctuating bandwidth. As the client device... more A well known challenge with mobile video streaming is fluctuating bandwidth. As the client devices move in and out of network coverage areas, the users may experience varying signal strengths, competition for the available resources and periods of network outage. These conditions have a significant effect on video quality.
The explosive deployment of wired and wireless communication infrastructure has recently enabled ... more The explosive deployment of wired and wireless communication infrastructure has recently enabled many novel applications and sparked new research problems. One of the unsolved issues in today's Internet -the main topic of this thesis -is the goal of increasing data transfer speeds of end hosts by aggregating and simultaneously using multiple network interfaces. This objective is most interesting when the Internet is accessible through several, relatively slow and variable (typically wireless) networks, which are unable to single-handedly provide the required data rate for resource-intensive applications, such as bulk file transfers and high-definition multimedia streaming.
Video streaming ranks among the most popular services offered through the Internet today. At the ... more Video streaming ranks among the most popular services offered through the Internet today. At the same time, accessing the Internet over public WiFi and 3G networks has become part of our everyday lives. However, streaming video in wireless environments is often subject to frequent periods of rebuffering and characterized by low picture quality. In particular, achieving smooth and quality-adaptive streaming of live video poses a big challenge in mobile scenarios.
This informative paper describes the harsh environment in which sensor networks operate, explains... more This informative paper describes the harsh environment in which sensor networks operate, explains challenges of routing in sensor networks and provides an overview of existing approaches of multi-hop routing.
Networked devices often come equipped with multiple network interfaces, and bandwidth aggregation... more Networked devices often come equipped with multiple network interfaces, and bandwidth aggregation is one of the many possible benefits of using multiple interfaces simultaneously. Real-world networks introduce several challenges that have often been ignored by related work on bandwidth aggregation. The challenges include limited connectivity due to NAT-boxes, link heterogeneity and link variability.
Devices capable of connecting to multiple, overlapping networks simultaneously is becoming increa... more Devices capable of connecting to multiple, overlapping networks simultaneously is becoming increasingly common. For example, most laptops are equipped with LAN-and WLAN-interface, and smart phones can typically connect to both WLANs and 3G mobile networks. At the same time, streaming high-quality video is becoming increasingly popular. However, due to bandwidth limitations or the unreliable and unpredictable nature of some types of networks, streaming video can be subject to frequent periods of rebuffering and characterized by a low picture quality.
Today, mobile devices like laptops and cell phones often come equipped with multiple network inte... more Today, mobile devices like laptops and cell phones often come equipped with multiple network interfaces, enabling clients to simultaneously connect to independent access networks. Even though applications, such as multimedia streaming and video-on-demand delivery systems, could potentially benefit greatly from the aggregated bandwidth, implementation and standardization challenges have so far hindered the deployment of multilink solutions. Previously, we have explored the benefits of collaboratively using multiple Internet connections to progressively download and play back large multimedia files. In this paper, we present an improved version of our approach that utilizes HTTP's capability of request pipelining in combination with range retrieval requests. While, in our earlier work, the optimal choice of file segmentation size presented a tradeoff between throughput and startup latency, the enhanced solution is able to overcome this tradeoff. The use of very small segments no longer impairs the efficiency of throughput aggregation, which additionally makes our solution robust against link variances and agnostic to network heterogeneity.
Multimedia streaming is increasing in popularity and has become one of the dominating services on... more Multimedia streaming is increasing in popularity and has become one of the dominating services on the Internet today. Even though user devices are often equipped with multiple network interfaces and in reach of several access networks at the same time, media streams are normally communicated over only one of the available Internet connections. In this paper, we explore the challenges and potential benefits of using multiple access networks simultaneously. Exploiting HTTP's capability of handling requests for specific byte ranges of a file, we present the implementation of a lightweight, application-layer, on-demand streaming service that requires no changes to existing servers and infrastructure. Based on real-world experiments with a multihomed host, we investigate the potential performance gains of video-on-demand playout. We achieve a bandwidth aggregation efficiency of 90% when downloading over 3 heterogeneous access networks in parallel. In addition, we analyze the effect of file segmentation on the buffer requirements and the startup latency.
With the increasing deployment of wireless technologies, such as WLAN, HSDPA, and WiMAX, it is of... more With the increasing deployment of wireless technologies, such as WLAN, HSDPA, and WiMAX, it is often the case that simultaneous coverage of several access networks is available to a single user device. In addition, devices are also often equipped with multiple network interfaces. Thus, if we can exploit all available network interfaces at the same time, we can obtain advantages like the aggregation of bandwidth and increased fault tolerance. However, the heterogeneity and dynamics of the links also introduce challenges. Due to different link delays, sending packets of the same flow over multiple heterogeneous paths causes the reordering of packets. In this paper, we quantify the impact of network heterogeneity and the use of multiple links on IP packet reordering. We show with practical measurements, according to commonly used metrics, that packet reordering over multiple links exceeds the reordering caused by common connections in high-speed, wide-area networks. We also demonstrate that heterogeneity and reordering exceed the assumptions presented in related work. By using sufficiently large buffers, packet reordering can be avoided. However, for devices with high resource constraints, the workload of using large buffers is expensive. Sender-side solutions of dividing and scheduling a packet sequence over multiple links can reduce the buffer requirements at the receiver. Initial experiments with a static scheduler, that has knowledge of average link delay and throughput estimates, show that packet reordering can be reduced by only 38 % due to the dynamic heterogeneity of the two links.
Direction estimation inside buildings is a difficult and challenging task due to severe multipath ... more Direction estimation inside buildings is a difficult and challenging task due to severe multipath signal propagation. Numerous algorithms and techniques exist that provide high-resolution direction estimation under certain conditions and channel models; however, to our knowledge they all perform poorly at indoor environments. Here, we propose a technique that enables a receiver to achieve greater reliability in estimating source direction through some collaboration with the source. We assume that the receiver and the transmitter are synchronized and they are equipped with circular phased array antennas that have beamforming capability. If the transmitter-receiver pair always steer their main lobes into opposite directions, the spatial spectrum of the received power can be used as a mean for estimating the direction of the transmitting source. In this paper, we investigate the feasibility of this methodology, and show the achieved improvement.
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Papers by Dominik Kaspar
In this paper, we quantify the impact of network heterogeneity and the use of multiple links on IP packet reordering. We show with practical measurements, according to commonly used metrics, that packet reordering over multiple links exceeds the reordering caused by common connections in high-speed, wide-area networks. We also demonstrate that heterogeneity and reordering exceed the assumptions presented in related work. By using sufficiently large buffers, packet reordering can be avoided. However, for devices with high resource constraints, the workload of using large buffers is expensive. Sender-side solutions of dividing and scheduling a packet sequence over multiple links can reduce the buffer requirements at the receiver. Initial experiments with a static scheduler, that has knowledge of average link delay and throughput estimates, show that packet reordering can be reduced by only 38 % due to the dynamic heterogeneity of the two links.