Wolfgang Karner

Traffic Analysis and Modeling for World of Warcraft

The popularity of MMOGs (massively multiplayer online games) has grown fast. This new type of online games uses a different type of protocol and has other limitations to delay and packet loss than the classical well established games like FPSs (first person shooters). This paper focuses on the traffic patterns generated by a MMOG named WoW (World of Warcraft). We analyzed IP layer information like packet size and rate from network traces and user level information like session durations. Finally we present a simple synthetic traffic generator for WoW traffic clients.

Link Error Prediction in Wireless Communication Systems with Quality Based Power Control

The quality of end-to-end services over wireless communication networks highly depends on the error characteristics of the wireless links. By utilizing the link error characteristics for optimizing the higher layer protocols in a so called cross-layer approach, high quality improvements can be achieved, especially when considering the predictability of errors. In this document it is shown that wireless communication systems with quality based power control mechanisms entail such predictive nature of the link error characteristics. A method for obtaining estimated values of future link error probabilities in the UMTS (universal mobile telecommunications system) DCH (Dedicated CHannel) as an example is presented in this document. Furthermore, it is shown that various well-known and often used error models based on Markov chains are not capable of representing the predictive nature of the channel, whereas a two-state alternating Weibull renewal process describes the characteristics properly.

Content-aware scheduling for video streaming over HSDPA networks

In this article we propose the implementation of a content-aware cross-layer optimization for video streaming in HSDPA networks. The video packets are marked at the IP layer based on the impact on the quality of experience at the application layer. In the core network these packets are mapped onto multiple logical paths with different quality of service accordingly to their marking. The proposed approach complies with the 3GPP releases newer than R99. It has been tested with an HSDPA system level simulator and H-264 video traces. The results of simulations show that the proposed content aware scheduling delivers over 1 dB Y-PSNR improvement compared to the standard round robin.

Cross-Layer Detection of Visual Impairments in H.264/AVC Video Sequences streamed over UMTS Networks

Incorrectly received packets in low-rate video sequences result in the loss of considerably large picture areas that have to be concealed. The performance of error concealment decreases with the size of the interpolated picture area. The incorrectly received packets may still contain some correct information that can be exploited at the decoder. In this work we propose the utilization of information from the link layer of UMTS (universal mobile telecommunications System) at the application layer for better pre-localization of errors in the bitstream domain. Syntax check together with the detection of impairments in the pixel domain decide which part of the incorrectly received packets will be concealed. We evaluate the results using error traces from the live UMTS network and H.264/AVC (advanced video coding) encoded video stream. Apart from reduced complexity facilitated by the cross-layer approach, the proposed method gains 1.09 dBs of Y-PSNR compared to a slice rejection mechanism.

Indoor Coverage Prediction and Optimization for UMTS Macro Cells

As most of the time mobile devices are used inside buildings, it is of particular interest for mobile network operators to cover indoor areas with their services. In order to reach satisfying indoor coverage without having too much extra costs for e.g. additional cell sites, optimum network planning has to be performed with the aid of coverage prediction by using propagation models. In this work we compare eight empirical and one deterministic model (ray tracing) by their usability and general validity for predicting the indoor coverage in UMTS macro cells. Furthermore, the accuracy of the models is shown via a comparison to measurements inside an office building in a live UMTS network in the city center of Vienna, Austria. It was found that despite the high effort for the usage, the deterministic model could not reach higher accuracy than the empirical models. Additionally, in this work we investigate improvements of the indoor coverage in UMTS macro cells by optimizing various base station antenna parameters.

Error Prediction Based Redundancy Control for Robust Transmission of Video Over Wireless Links

The loss of UDP/IP packets has a high impact on the quality of the low-rate video streaming, since one UDP/IP packet typically represents a considerable part of a picture, which is discarded and concealed if an error was detected by a UDP checksum. In this work we propose a method that allows for the utilization of error-free parts of such UDP packets. The detection of errors is facilitated by the use of CRC (cyclic redundancy check) information of the smaller link layer packets. Resynchronization of the variable length code at the beginning of the link layer packets is provided by using side information. To keep the additional rate small and to have low distortion at the same time, we propose sending the side information depending on the prediction of the channel quality. Experimental results show a considerable improvement in video quality at the receiver.

Modeling E-Mail Traffic for 3G Mobile Networks

Traffic models are to provision the increasing load of packet switched traffic in mobile 3G networks. However, most traffic models were designed to fit the need of low delay wired connections. In this paper we propose a new traffic model for POP3 e-mail traffic generation in 3G mobile networks scenarios. The model is based on traces which were extracted in a live 3G network of a mobile operator. The main improvement of the model is the explicit modeling of the login process that takes place between the client and the server. We implemented the model in the network simulation tool ns-2 and based on this we simulated various scenarios to visualize the impact of a leading initialisation phase in high RTT environments. The results proof that the extension can reproduce the effect from the login in a more precise way. Finally a comparison between the measured and the simulated service footprints were compared. The new model performs better than common models in this scenario.

The Impact of Link Error Modeling on the Quality of Streamed Video in Wireless Networks

The influence of channel error characteristics on higher layer protocols or methods which are considering or even exploiting the error statistics is significant especially in wireless networks where fading and interference effects result in error pattern correlation properties (error bursts). In this work we are analysing the impact of the channel properties directly on the quality of streamed video. We are focusing on the quality of transmitted H.264/AVC video streaming over UMTS DCH (Dedicated Channel) and compare the quality of the streamed video simulated over measured link error traces (the measurements performed in a live UMTS network) to simulations with a memoryless channel and to models with enhanced error characteristics. The results show that appropriate modeling of the link layer error characteristics is very important but it can also be concluded that the error correlation properties of the link- or the network-layer model do not have an impact on the quality of the video stream as long as the resulting IP packet error probability remains unchanged.

A measurement based model for UMTS DL DCH dynamic bearer type switching

3GPP specifications allow to change the physical resources allocated to the users dynamically to optimize the radio resource utilization in UMTS. Network operators can make use of this optimization feature by properly adjusting dynamic bearer type switching in their networks. In this paper we show an analysis of the dynamic bearer type switching based on measurements in a live UMTS network in the city center of Vienna, Austria. Particularly, we present the usage probability and the runlength distribution of the three different radio access bearers which are used for transmission over the UMTS DCH (dedicated channel) packet switched (PS) domain in DL (down link), namely 384 kbit/s, 128 kbit/s and 64 kbit/s bearer. For the performance evaluation of applications, system level simulators are used, where the lower layers are usually represented via stochastic models. Following the measured statistics we develop a model capable of properly describing the dynamic switching between the mentioned bearers. Furthermore, we show that a four-state Markov model with its geometrically distributed runlengths does not provide sufficient accuracy. We achieve an enhancement by using a four-state renewal process with Weibull distributed runlengths as presented in this document.

Analysis of video streaming with SP and SI frames in UMTS mobile networks

In this paper we discuss possible benefits of transmitting SI frames as an error resilience tool in UMTS video streaming. SP and SI frames can be used to stop temporal error propagation, as an alternative to the regular insertion of I frames. Since their application relays on feedback information from the mobile equipment, different delay scenarios have been investigated. The performed transmission simulations show enhancement of the rate-distortion behaviour when using SP and SI frames with reduced feedback times. The error traces were measured at transport block level in a live UMTS mobile network.