PoCL-R : A Scalable Low Latency Distributed OpenCL Runtime

Offloading the most demanding parts of applications to an edge GPU server cluster to save power or improve the result quality is a solution that becomes increasingly realistic with new networking technologies. In order to make such a computing scheme feasible, an application programming layer that can provide both low latency and scalable utilization of remote heterogeneous computing resources is needed. To this end, we propose a latency-optimized scalable distributed heterogeneous computing runtime implementing the standard OpenCL API. In the proposed runtime, network-induced latency is reduced by means of peer-to-peer data transfers and event synchronization as well as a streamlined control protocol implementation. Further improvements can be obtained streaming of source data directly from the producer device to the compute cluster. Compute cluster scalability is improved by distributing the command and event processing responsibilities to remote compute servers. We also show how a simple optional dynamic content size buffer OpenCL extension can significantly speed up applications that utilize variable length data. For evaluation we present a smartphone-based augmented reality rendering case study which, using the runtime, receives 19× improvement in frames per second and 17× improvement in energy per frame when offloading parts of the rendering workload to a nearby GPU server. The remote kernel execution latency overhead of the runtime is only 60 ms on top of the network roundtrip time. The scalability on multi-server multi-GPU clusters is shown with a distributed large matrix multiplication application.acceptedVersionPeer reviewe

Cross-Layer Optimization of DVB-T2 System for Mobile Services

Mobile broadcast services have experienced a strong boost in recent years through the standardization of several mobile broadcast systems such as DVB-H, ATSC-M/H, DMB-T/H, and CMMB. However, steady need for higher quality services is projected to surpass the capabilities of the existing mobile broadcast systems. Consequently, work on new generations of mobile broadcast technology is starting under the umbrella of different industry consortia, such as DVB. In this paper, we address the question of how DVB-T2 transmission can be optimized for improved mobile broadcast reception. We investigate cross-layer optimization techniques with a focus on the transport of scalable video (SVC) streams over DVB-T2 Physical Layer Pipes (PLP). Throughout the paper, we propose different optimization options and verify their utility

Prediction and Transmission Optimization of Video Guaranteeing a Bounded Zapping-Delay in DVB-H

Zapping-delay is an important factor contributing to the quality-of-experience (QoE) of any multimedia service; the longer the zapping-delay, the worse is the QoE. Therefore, for a good QoE, it is necessary to bind zapping-delay within acceptable bounds. Coded video uses a motion compensated prediction structure that contributes to the zapping-delay. In DVB-H, zapping-delay is further increased because of the time-sliced burst transmission architecture. Hence, any attempt to bind zapping-delay must consider both the prediction structure of coded video, as well as the time-sliced transmission architecture of DVB-H. This paper analyzes prediction structure of video as binary relations generating a prediction graph. Reachability concepts of graph theory are then applied to construct binary valued indicator functions. These indicator functions inform about the reception, decoding, and play-out states of each access-unit in the video sequences. zapping-delay is studied by dissecting the components that it is composed off. Conditions for minimizing each of them individually, while the final zapping-delay does not exceed a known bound, is found. Emphasis is also laid on gradual quality enhancement after the display of the new program has started

Comparison of Error Protection Methods for Audio-Video Broadcast over DVB-H

<p/> <p>The paper discusses methods for robust audio-video broadcast over the digital video broadcasting-handheld (DVB-H) system. DVB-H includes a link-layer forward error correction (FEC) scheme known as multiprotocol encapsulation (MPE) FEC, which provides equal error protection (EEP) to the transmitted media streams. Several approaches for unequal error protection (UEP) have been proposed in the literature, and the applicability of some of them to DVB-H is analyzed in the paper. A link-layer UEP method based on priority segmentation of the media streams is chosen for more detailed analysis. According to the method, audio and the most important coded video pictures are protected by MPE-FEC more robustly compared to the remaining coded pictures. In order to compare EEP and UEP in a DVB-H environment, an error-prone DVB-H channel was simulated, audio-visual clips were sent through it, and a comprehensive subjective quality evaluation was conducted in a controlled laboratory environment. The results of the subjective evaluation revealed that the use of UEP improves the subjective quality of some test clips noticeably when the channel conditions were severe, while in other tested channel conditions and clips, UEP and EEP performed equally well.</p

Optimal channel changing delay for mobile TV over DVB-H

This paper provides an analysis on the optimal channel changing delay in DVB-H (Digital Video Broadcasting for Handhelds) channels for Mobile Television. DVB-H uses a time-sliced transmission scheme to reduce the power consumption used for radio reception in DVB-H receivers. Channel changing delay, i.e. changing from one audio-visual service to another, is increased due to the time slicing scheme in DVB-H. One of the significant factors in channel changing delay is the Decoder Refresh Delay. The Decoder Refresh Delay is the time from the start of video decoding to the start of correct output from decoder. This delay is minimized when a time-slice starts with a random access point picture such as an instantaneous decoding refresh (IDR) picture in H.264/AVC standard. In DVB-H, encapsulation into time-slices is performed independently from content encoding. At the time of encoding, the exact time-slice boundaries are typically unknown, and therefore it is impossible to align the location of IDR pictures to time-slice boundaries. The average decoder refresh delay can decrease by frequent IDR pictures in the bit stream. However, using very frequent IDR pictures drops the compression efficiency and the quality of compressed video dramatically. Another factor in channel changing delay is the delay required to compensate the variation in bit rate. In video streaming over DVB-H the improved quality and compression efficiency obtained by using variable bit rate should be exploited. Higher quality and compression performance can he provided by higher delay. Moreover, when changing channels, a delay is required until the start of the desired time-slice and a further delay is incurred to complete the reception of the entire time-slice. These delays depend on the time-slicing parameters that define the power saving percentage obtained as the result of the time-slice scheme. The lower the receiver power consumption, the higher delay is required. Therefore, there is a strong multilateral relationship between the quality of compressed video, the channel changing delay and the power consumption in the receiver. Simulations were conducted and based on the simulation results an optimal operating area is proposed