Philip Perry

User perception of adapting video quality

In general, video quality adaptation and video quality evaluation are distinct activities. Most adaptive delivery mechanisms for streaming multimedia content do not explicitly consider user-perceived quality when making adaptation decisions. Equally, video quality evaluation techniques are not designed to evaluate instantaneous quality where the quality is changing over time. We propose that an Optimal Adaptation Trajectory (OAT) through the set of possible encoding exists, and that it indicates how to adapt encoding quality in response to changes in network conditions in order to maximize user-perceived quality. The subjective and objective tests carried out to find such trajectories for a number of different MPEG-4 video clips are described. Experimental subjective testing results are presented that demonstrate the dynamic nature of user perception with adapting multimedia. The results demonstrate that adaptation using the OAT out-performs conventional adaptation strategies in which only a single aspect of the video quality is adapted. In contrast, the OAT provides a mechanism to adapt multiple aspects of the video quality thereby giving better user-perceived quality in both the short and long term.

Network selection decision in wireless heterogeneous networks

In future wireless and mobile environments it is likely that users will have access to multiple networks at the same time. Therefore there is a need to have mechanisms in place to decide which network is the most suitable for each user at each moment in time for every application that the user requires. We propose a user-centric solution where users choose the radio access network which meets their data transfer terms best. Naturally, each user wants timely quality data delivery at a low cost. In the radio environment data rates can never be guaranteed due to the unreliable nature of the radio links. The user network selection algorithm needs to predict the data rate on offer in each of the available networks and make the decision based on those predictions. This paper allows the user to select the network that will maximise the consumer surplus for non real-time data, while taking into account the delays

Adaptive VoIP playout scheduling: assessing user satisfaction

Delay and packet loss dramatically affect the quality of voice-over-IP (VoIP) calls and depend on the playout buffer scheme implemented at the receiver. The choice of playout algorithm cant be based on statistical metrics without considering the perceived end-to-end conversational speech quality. The authors present a method for evaluating various playout algorithms that extends the E-model concept by estimating user satisfaction from time-varying transmission impairments. This article evaluates several playout algorithms and shows a correspondence between the authors results and those obtained via statistical loss and delay metrics.

Objective and subjective evaluation of QOAS video streaming over broadband networks

This article presents objective and subjective testing results that assess the performance of the Quality-Oriented Adaptation Scheme (QOAS) when used for high quality multimedia streaming over local broadband IP networks. Results of objective tests using a QOAS simulation model show very efficient adaptation in terms of end-user perceived quality, loss rate, and bandwidth utilization, compared to existing adaptive streaming schemes such as LDA+, and TFRCP. Subjective tests confirm these results by showing high end-user perceived quality of the QOAS under various network conditions.

A new large-signal AlGaAs/GaAs HBT model including self-heating effects, with corresponding parameter-extraction procedure

Accurate modelling of the microwave large-signal characteristics of AlGaAs/GaAs Heterojunction Bipolar Transistors (HBTs) is extremely useful for microwave power applications of the device. This paper presents a new type of HBT large-signal model which is valid for dc, small-signal and large-signal ac modes of operation. The model may be used over a wide range of operating conditions and includes allowance for self-heating effects which are very important for HBTs. Through the use of several novel features, the proposed approach is differentiated from the traditional Ebers-Moll or Gummel-Poon BJT representations. The new model is accompanied by a very simple parameter extraction process requiring only a series of conventional dc and multi-bias point small-signal S-parameter measurements. Finally, the model is validated by independent power sweep measurements on HBTs from two different manufacturers. >

A Comparison-Based Study of Quality-Oriented Video on Demand

The Quality Oriented Adaptation Scheme (QOAS) is used for high bit-rate multimedia streaming in local broadband multi-service all-IP networks. It balances two opposing goals: providing high quality multimedia-based services to end-users, and increasing the infrastructure utilization and number of customers simultaneously served. Extensive objective testing results presented in this paper show that QOAS achieves high performance in terms of end-user perceived quality, loss rate, throughput, link utilization, and number of customers simultaneously served. These results were obtained even in highly loaded and variable delivery conditions caused by traffic of different types, sizes, and variation patterns. QOAS performance was assessed stand-alone and in comparison with other existing solutions, adaptive and non-adaptive

Optimum adaptation trajectories for streamed multimedia

Most adaptive delivery mechanisms for streaming multimedia content do not explicitly consider user-perceived quality when making adaptations. We propose that an optimal adaptation trajectory through the set of possible encodings exists and that it indicates how to adapt encoding quality in response to changes in network conditions to maximize user-perceived quality. Such an optimum adaptation trajectory can be used with any transmission adaptation policy. We describe the subjective tests we carried out to find such trajectories for a number of different MPEG-4 video clips and indicate how this knowledge could be used in the operation of a practical system.

A QoS based call admission control and resource allocation mechanism for LTE femtocell deployment

Current trends show a growing number of femtocell deployments, this in turn will lead to increased volumes of voice traffic being transmitted through fixed broadband access networks such as Digital Subscriber Line. In this paper the issue of maintaining call quality through the resource constraint expedited forwarding queue of DSLAMs is investigated. A quality based Call Admission Control and resource allocation mechanism is provided to avoid resource overloading and call quality degradation. The ITU-Ts E-Model is used for call quality monitoring and a message exchange interface between the mobile and fixed networks which allows dynamic adjustment to network resources is described and simulated. The results show that high voice call quality can be maintained.

An Evaluation of Parameterized Gradient Based Routing With QoE Monitoring for Multiple IPTV Providers

Future communication networks will be faced with increasing and variable traffic demand, due largely to various services introduced on the Internet. One particular service that will greatly impact resource management of future communication networks is IPTV, which aims to provide users with a multitude of multimedia services (e.g. HD and SD) for both live and on demand streaming. The impact of this will be higher, when we consider multiple IPTV services overlaid on the same network. In this paper we propose a resource management scheme for a network provider that supports multiple IPTV providers. The proposed solution incorporates a new distributed routing mechanism in the underlying network that incorporates QoE monitoring. Through this monitoring process, network providers are able to provide timely updates of quality of flows for each IPTV provider. Simulation work has been conducted to validate the efficiency of the proposed solution in comparison to standard approaches.

Profile-Based, Load-Independent Anomaly Detection and Analysis in Performance Regression Testing of Software Systems

Performance evaluation through regression testing is an important step in the software production process. It aims to make sure that the performance of new releases do not regress under a field-like load. The main outputs of regression tests are the metrics that represent the response time of various transactions as well as the resource utilization (CPU, disk I/Oand Network). In this paper, we propose to use a concept known as Transaction Profile, which can provide a detailed representation for the transaction in a load independent manner, to detect anomalies through performance test runs. The approach uses data readily available in performance regression tests and a queueing network model of the system under test to infer the Transactions Profiles. Our initial results show that the Transactions Profiles calculated from load regression test data uncover the performance impact of any update to the software. Therefore we conclude that using Transactions Profiles is an effective approach to allow testing teams to easily assure each new software release does not suffer performance regression.