Deutsche Telekom

About: Deutsche Telekom is a company organization based out in Welwyn Garden City, United Kingdom. It is known for research contribution in the topics: Telecommunications network & Signal. The organization has 3473 authors who have published 5208 publications receiving 65429 citations. The organization is also known as: DTAG & German Telecom.

A statistical simulation model for the directional mobile radio channel and its configuration

Abstract: Currently new base station concepts are under investigation that take advantage of the directionality of the mobile radio channel either by utilizing antenna beam diversity or adaptive array reception techniques. Unfortunately, the Gaussian (wide sense) stationary uncorrelated scattering (GWSSUS) simulation concept which is most wide-spread adopted in fading simulators neglects any directional anisotropy of the propagation mechanism. In this paper a directional channel simulation model is introduced which is an extension to GWSSUS. Due to its relatively low structural complexity, this directional Gaussian scattering (DGS) concept is applicable not only to soft- but also to hardware fading simulators. The most important advantage of the DGS simulator is that it can easily be configured to match the properties of real-world propagation scenarios. This is achieved based on the information available from echo estimation, a method which recently was introduced for configuring statistical GWSSUS channel models directly from the results of wide-band channel sounding.

Photonic highway switches based on ring resonators used as frequency-selective components.

Abstract: A new concept for a highway switch, which can be used to connect different optical wavelength division multiplexing data highways for data exchange, is proposed and the system relevant properties are outlined. For the required add–drop filter elements we used ring resonators. Typical characteristics of channel bandwidth, channel spacing, free spectral range, amplification, and cross-talk behavior of a highway switch with double-cavity ring resonators are basically examined and to some extent compared with solutions that were obtained with standard single-ring resonators. A signal flow chart transformation for evaluating filter transfer functions is presented.

Enhanced video streaming to mobile clients

Abstract: A system for enabling streaming video to a mobile client includes a plurality of fixed node peers linked to the mobile client via one or more networks as well as a video source linked to fixed node peers and configured to provide streaming video data representing a video presentation to each of the fixed node peers. A decoder assembly associated with each of the fixed node peers is configured to decode the streaming video data and to transcode a portion of the decoded streaming video data for transmission to the mobile client. A video substream manager and interleaver on the mobile client is provided for receiving the transcoded output of the decoder assemblies of the fixed node peers and reconstructing the video presentation on a screen of the mobile client.

Optimum caching versus LRU and LFU: Comparison and combined limited look-ahead strategies

Abstract: We compare web caching strategies based on the least recently used (LRU) and the least frequently used (LFU) replacement principles with optimum caching according to Belady's algorithm. The achievable hit rates of the strategies are shown to improve with the exploited knowledge about the request pattern while the computation effort is also increasing. The results give an overview of performance tradeoffs in the whole relevant range for web caching with Zipf request pattern. In a second part, we study a combined approach of the optimum strategy for a limited look-ahead with LRU, LFU or other non-predictive methods. We evaluate the hit rate gain depending on the extent of the look-ahead for request traces and for the independent reference model (IRM) via simulation and derive an analytic confirmation of the observed behaviour. It is shown that caching for video streaming can benefit from the proposed look-ahead technique, when replacement decisions can be partly revised due to new requests being encountered during long lasting content updates.

A survey of adaptive services to cope with dynamics in wireless self-organizing networks

Abstract: In this article, we consider different types of wireless networks that benefit from and, in certain cases, require self-organization. Taking mobile ad hoc, wireless sensor, wireless mesh, and delay-tolerant networks as examples of wireless self-organizing networks (WSONs), we identify that the common challenges these networks face are mainly due to lack of centralized management, device heterogeneity, unreliable wireless communication, mobility, resource constraints, or the need to support different traffic types. In this context, we survey several adaptive services proposed to handle these challenges. In particular, we group the adaptive services as core services and network-level services. By categorizing different types of services that handle adaptation and the types of adaptations, we intend to provide useful design guidelines for achieving self-organizing behavior in network protocols. Finally, we discuss open research problems to encourage the design of novel protocols for WSONs.