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 & Terminal (electronics). The organization has 3473 authors who have published 5208 publications receiving 65429 citations. The organization is also known as: DTAG & German Telecom.

On Dependent Bit Allocation for Multiview Image Coding With Depth-Image-Based Rendering

Abstract: The encoding of both texture and depth maps of multiview images, captured by a set of spatially correlated cameras, is important for any 3-D visual communication system based on depth-image-based rendering (DIBR). In this paper, we address the problem of efficient bit allocation among texture and depth maps of multiview images. More specifically, suppose we are given a coding tool to encode texture and depth maps at the encoder and a view-synthesis tool to construct intermediate views at the decoder using neighboring encoded texture and depth maps. Our goal is to determine how to best select captured views for encoding and distribute available bits among texture and depth maps of selected coded views, such that the visual distortion of desired constructed views is minimized. First, in order to obtain at the encoder a low complexity estimate of the visual quality of a large number of desired synthesized views, we derive a cubic distortion model based on basic DIBR properties, whose parameters are obtained using only a small number of viewpoint samples. Then, we demonstrate that the optimal selection of coded views and quantization levels for corresponding texture and depth maps is equivalent to the shortest path in a specially constructed 3-D trellis. Finally, we show that, using the assumptions of monotonicity in the predictor's quantization level and distance, suboptimal solutions can be efficiently pruned from the feasible space during solution search. Experiments show that our proposed efficient selection of coded views and quantization levels for corresponding texture and depth maps outperforms an alternative scheme using constant quantization levels for all maps (commonly used in video standard implementations) by up to 1.5 dB. Moreover, the complexity of our scheme can be reduced by at least 80% over the full solution search.

Spatio-temporal radio channel characteristics in urban macrocells

Abstract: The performance assessment of new mobile radio base station (BS) transceiver concepts with adaptive intelligent antennas requires realistic directional radio channel models. An appropriate model is derived from the results of an extensive uplink sounding campaign performed at 1.9 GHz in a urban macrocell within the city of Frankfurt. In the experiments the wideband sounder RUSK XL was applied for synthetic aperture reception. The directional multipath propagation is characterised by means of delays, directions of arrival (DOA) at the BS antenna array and mean powers of the multipath components. The coupled delay-DOA-power information is determined by an adaptation of the 2-D unitary ESPRIT algorithm. It can be used directly to configure fading simulators for multiple antenna reception which reflect real-world small-area radio channel properties in simulations at the link level. Additionally, probability distribution functions for excess delays, DOAs and mean powers are derived from the measurement results. They are useful for consideration of directional propagation effects in investigations of the cellular system behaviour.

Exhausting battery statistics: understanding the energy demands on mobile handsets

Abstract: Despite the advances in battery technologies, mobile phones still suffer from severe energy limitations. Modern handsets are rich devices that can support multitasking thanks to their high processing power and provide a wide range of resources such as sensors and network interfaces with different energy demands. There have been multiple attempts to characterise those energy demands; both to save or to allocate energy to the applications on the handset. However, there is still little understanding on how the interdependencies between resources (interdependencies caused by the applications and users' behaviour) affect the battery life. In this paper, we demonstrate the necessity of considering all those dynamics in order to characterise the energy demands of the system accurately. These results indicate that simple algorithmic and rule-based scheduling techniques [7] are not the most appropriate way of managing the resources since their usage can be affected by contextual factors, making necessary to find customised solutions that consider each user's behaviour and handset features.

System support for accessing and switching among multiple wireless interfaces on mobile devices

Abstract: A client-based system (100) for use in a mobile client device (110) in communication with a remote server device (102) provides for dynamically switching among multiple wireless interfaces on the mobile client device (110). The system includes a first interface (113) for communicating over a cellular network (115), a second interface (114) for communicating over a WiFi network (116), and a computer-readable medium (112) within the mobile client device (110), having thereon computer-executable instructions for switching one or more connection-oriented sessions from one of the first and second interfaces to the other based on a selection policy selected from an energy saving selection policy, an offload selection policy, and a performance selection policy.

Rateless Coding with Feedback

Abstract: The erasure resilience of rateless codes, such as Luby-Transform (LT) codes, makes them particularly suitable to a wide variety of loss-prone wireless and sensor network applications, ranging from digital video broadcast to software updates. Yet, traditional rateless codes usually make no use of a feedback communication channel, a feature available in many wireless settings. As such, we generalize LT codes to situations where receiver(s) provide feedback to the broadcaster. Our approach, referred to as Shifted LT (SLT) code, modifies the robust soliton distribution of LT codes at the broadcaster, based on the number of input symbols already decoded at the receivers. While implementing this modification entails little change to the LT encoder and decoder, we show both analytically and through real experiments, that it achieves significant savings in communication complexity, memory usage, and overall energy consumption. Furthermore, we show that significant savings can be even achieved with a low number of feedback messages (on the order of the square root of the total number of input symbols) transmitted at a uniform rate. The practical benefits of Shifted LT codes are demonstrated through the implementation of a real over-the-air programming application for sensor networks, based on the Deluge protocol.