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.

Process for allocating frequencies to base stations of a mobile radiotelephone network.

Abstract: A process for allocating frequencies to base stations of a mobile radiotelephone network is based on input information which contains at least the number of frequencies required for each base station, the admissible frequencies in the mobile radiotelephone network and information on possible interference effects between the base stations in the event of similar and/or contiguous frequencies. The following steps are alternatively carried out: (a) a base station among the plurality of base stations to which not all available frequencies have yet been allocated is selected according to a first base station selection criterion and if required further base station selection criteria; (b) a frequency is selected according to a first frequency selection criterion and if required further frequency selection criteria; (c) the frequency selected during step (b) is identified as allocated to the base station selected during step (a).

Comparison of Subjective Quality Evaluation for HEVC Encoded Omnidirectional Videos at Different Bit-rates for UHD and FHD Resolution

Abstract: In this paper, we perform subjective quality evaluation studies for HEVC/H.265-encoded omnidirectional videos at different bit-rates for two different resolutions (FHD and UHD) on an Oculus Rift. Results of these tests provide insight into appropriate coding and resolution settings for given bitrate constraints, for example in an HTTP-based streaming (HAS) context. Subjective quality judgements were collected on a 5-point Absolute Category Rating (ACR) scale. Further, we collected head motion data during viewing and rating. Working towards the technical goal of subjective evaluation for different resolutions and bit-rates, we address aspects of how to conduct respective viewing tests, involving information from head-rotation tracking (yaw and pitch) and motion-sickness questionnaires. Quality adaptation (in terms of resolution and bit-rate) of omnidirectional videos is an important feature of media streaming. Its effect on subjective quality evaluations of 360° video has not been investigated so far. To utilize network and processing resources efficiently, limitations in the resolution of current Head Mounted Displays (HMDs), with typically 2160 x 1200 pixels per view, may be exploited. The subjective test results provide indications for boundaries between resolution and quantization scaling. To discuss the merits of the applied subjective test method, we compare simulator sickness scores along with behavioral data.

On the systematic measurement errors of correlative mobile radio channel sounders

Abstract: We show that measurements of time-varying mobile radio channels obtained with uncalibrated correlative channel sounders are affected by four different types of systematic errors (commutation, pulse-compression, aliasing, and misinterpretation error). We analyze these errors and provide upper error bounds that are formulated in terms of channel and sounder parameters. Based on these error bounds, we provide guidelines for a judicious choice of important sounder parameters. Computer simulations using a simple two-path channel illustrate our theoretical results. Finally, we show how our results can be used to assess the accuracy of measured channel data.

Field trials using coordinated multi-point transmission in the downlink

Abstract: We report on field trials using CoMP transmission in the downlink of a mobile radio network. Two new features enable over-the-air CoMP transmission from physically separated base stations and terminals. These are distributed synchronization and a fast virtual local area network. Using VLAN tags, terminals feed back the multi-cell channel state information to their serving bases where it is multiplexed with shared data. Both are multicast to other cooperative base stations over the backhaul. In our trials, two terminals are served in two overlapping cells and placed in specific indoor, outdoor-to-indoor and outdoor scenarios. We have realized both intra-site as well as inter-site CoMP. While outage is indeed a big problem at the cell edge with full frequency reuse, with CoMP it is not observed anymore. Average throughput gains by factors 4 to 22 are observed when using CoMP compared to interference-limited transmission while between 27 and 78% of the isolated cell throughput is measured in both cells simultaneously.

Location coding for mobile image retrieval

Abstract: For mobile image retrieval, efficient data transmission can be achieved by sending only the query features. Each query feature is composed of a descriptor and a location in the image. The former is used to find candidate matching images using a "bag-of-words" approach while the latter is used in a geometric consistency check to map features in the query image to corresponding features in the database image. We investigate how to compress the location information and how lossy compression affects the geometric consistency check. The location information is converted into a location histogram and a context-based arithmetic coding with location refinement method is then proposed to code the histogram. The effects of lossily compressing the location information are evaluated empirically in terms of the errors in corresponding features and the error of the estimated geometric transformation model. From our experiments, rates at ~5.1 bits per feature can achieve errors comparable to lossless coding. The proposed scheme achieves a 12.5x rate reduction compared to the floating point representation, and 2.8x rate reduction compared to a fixed point representation.