Günther Liebl

Deadline-aware scheduling for wireless video streaming

We present a new algorithm for deadline-aware scheduling of video streams over a wireless shared channel, which only requires the computation of a single metric per user and transmission slot. By incorporating side information about the video stream structure and the future channel behavior in the scheduling algorithm, our approach outperforms existing solutions by slowing down the transmission of streams to users with favorite channel conditions until their deadline is approaching. Hence, in overload situations, the quality of the bad users is significantly increased, while good users are almost unaffected. As a consequence, this leads to a fairer distribution of the achievable video quality among all users.

Adaptive video streaming over a mobile network with TCP-friendly rate control

This paper investigates the performance of TCP-Friendly Rate Control (TFRC) to control the transmission rate of scalable video streams when used in a mobile network. The streams are encoded using the Scalable Video Coding (SVC) extension of the H.264/AVC standard. Adding or removing the layers is decided based on the TFRC during varying channel conditions of the mobile network. We conduct simulations in various realistic use cases, evaluate and compare the performance with and without TFRC-based adaptation. The results show significant improvements in terms of lower loss rate, delay, required buffer size and less playback interruption.

Advancedwireless Multiuser Video Streaming using the Scalable Video Coding Extensions of H.264/MPEG4-AVC

We propose a dynamic sharing of radio resources in a wireless multiuser system by combining a flexible video coding scheme, namely the currently developed scalable video coding (SVC) extension of H.264/AVC with appropriate radio link buffer management for multiuser streaming services. The paper introduces the components of the proposed system and the used cross-layer interface. Simulation results verify the benefits of our approach

Retransmission strategies for MBMS over GERAN

In this work, reliable retransmission strategies, including point-to-point (p-t-p), point-to-multipoint (p-t-M) and point-to-multipoint incremental redundancy (p-t-M-IR) are studied with special focus on their applicability to multimedia broadcast and multicast services (MBMS) over GERAN. By employing a binary OR multiple access channel (BORMAC) model, analytical expressions for the system throughput, the residual RLC/MAC block loss rate, and the residual IP-packet loss rate are derived for all investigated schemes. Furthermore, a simple NACK oriented feedback policy, which allows the utilization of a resource efficient feedback channel in cellular environments is presented. It is shown that the p-t-M-IR scheme outperforms both the p-t-p and the p-t-M retransmission scheme significantly in terms of system throughput, residual loss RLC/MAC block loss rate, as well as residual IP-packet loss rate. The throughput reduction of the p-t-M-IR scheme with increasing number of mobiles in the serving area is significantly less than with other ARQ schemes.

Flexible outer Reed-Solomon coding on RLC layer for MBMS over GERAN

In this work, we present the multimedia broadcast multicast services (MBMS) framework for GSMEDGE radio access network (GERAN). Flexible outer Reed-Solomon coding is introduced in the GERAN MBMS environment. Performance estimations are presented. These performance estimations are used to compare the flexible RS coding scheme with simple repetition schemes. It is shown that at a target C/I of 7.5 dB and a maximum throughput of 40 kbit/s can be supported. Applying the flexible Reed-Solomon coding we also show that, e.g. for a C/I of 15 dB, even more than 90 kbit/s can be supported by MBMS.

Optimized H.264/AVC-based bit stream switching for mobile video streaming

We show the suitability of H.264/MPEG-4 AVC extended profile for wireless video streaming applications. In particular, we exploit the advanced bit stream switching capabilities using SP/SI pictures defined in the H.264/MPEG-4 AVC standard. For both types of switching pictures, optimized encoders are developed. We introduce a framework for dynamic switching and frame scheduling. For this purpose we define an appropriate abstract representation for media encoded for video streaming, as well as for the characteristics of wireless variable bit rate channels. The achievable performance gains over H.264/MPEG-4 AVC with constant bit rate (CBR) encoding are shown for wireless video streaming over enhanced GPRS (EGPRS).

Performance Evaluation on Dual-Cell HSDPA Operation

This paper presents a quantitative performance analysis of the Dual-Cell High-Speed Downlink Packet Access (DC-HSDPA) operation focused on the gain achieved by pooling the radio resources of two carriers in the same base station and enabling a collaborative operation (joint-scheduling) on the lower radio layers. One main target for the evolution of 3G mobile communication is to provide the possibility of significantly higher end-user data rates compared to what is achieved with the first releases of the 3G standards. This also refers to higher data rates over the entire cell area including users at the cell edge. 3GPP standards body has significantly enhanced the peak user throughput as part of Release-7 with features as MIMO and Higher Order Modulation (HOM) (1) and this has helped to improve the average user throughput to some extent. However, the rapid increase in mobile data usage calls for additional enablers to provide enhanced user experience throughout the cell, especially in the outer area of the cell coverage.

Optimized H. 264-Based Bitstream Switching for Wireless Video Streaming

In this work we show the suitability of H.264/AVC extended profile for wireless video streaming applications. In particular, we exploit the advanced bitstream switching capabilities of H.264/AVC using SP/SI pictures. Optimized encoders for switching pictures are proposed. Finally, a framework for dynamic switching and frame scheduling is proposed and the performance is shown for H.264/AVC video streaming over EGPRS

On practical crosslayer aspects in 3GPP video services

In this work we introduce 3GPP video services and discuss both the concept of service provision and Quality-of-Service (QoS) achievement. 3GPP video services are supported by many different QoS tools, which are applied depending on network conditions and service constraints. Despite the fact that the 3GPP QoS concept does not encourage complex cross-layer design, it is nevertheless possible to improve the performance of 3GPP video services tremendously by using the appropriate combination of tools. Three examples in the area of multimedia telephony and multimedia broadcast are provided, which support this statement.

Priority-based multiplexing of IP-streams onto shared cellular links

We present a new resource allocation strategy that allows efficient mapping of variable-rate IP-streams onto shared cellular links, while minimizing the overall bandwidth consumption and still meeting the individual quality-of-service constraints. It is based on the general principle of class-based queuing, with several modifications to adapt it to the specific characteristics of wireless links. Compared to other simpler solutions that do not support any prioritization of data streams, it yields significant performance improvements in terms of guaranteed bandwidth per user/service and fairness among competing streams, as is shown for a GSM-GPRS system.