JMM Abstracts 

Vol.5 No.4 December, 2009

Research Articles

Optimal Channel Selection for Real-Time Multimedia Uplink Transmissions in Ambulances (271-386)  
Ana Goulart, Wei Zhan, and Robert Arnold 
Through wireless internet access, ambulances take advantage of the widespread cellular coverage in rural and urban areas to transfer audio, video, and vital signs to the emergency room. In the current implementation adopted by the DREAMSTM ambulances, a designated channel is selected randomly. It is used to transmit high priority data, such as vital signs and audio. The remaining channels are used for video transmission. Whenever the communication system in the ambulance detects a certain threshold of packet losses in the designated channel, the communication system randomly switches the high priority data to another wireless channel. However, the designated channel selection process does not necessarily select the best available channel. The objective of this paper is to optimize this process through proportional-integral-derivative (PID) control and optimization with feedback. For each channel, an objective function is calculated. It includes a derivative term for fast response and an integration term for detection of small but consistent differences between channels, in addition to the proportional term. Using a causal real-time optimization algorithm, the maximum objective function is continuously selected.  Thus, the proposed optimal channel selection algorithm enables the ambulance’s communication system to intelligently shift the load to better quality channels without detailed information about the channels. The proposed algorithm combines key performance metrics (i.e., reliability and effective transmission rate), which can be calibrated with different weights. Using data from simulation and experiments in commercial cellular networks, we compare the performance of the ambulance with and without the algorithm to show dramatic improvements in the reliability and throughput of the ambulance’s uplink transmissions.

Situated Interaction and Cognition in the Wild, Wild World: Unleashing the Power of Users as Innovators (287-300)  
Hanna Risku, Eva Mayr ,and Michael Smuc 
Taking the user into account in the design of multimedia and mobile applications is now common and accepted. However, aside from the verbal recognition of the importance of the role of users and the implementation of usability and human factors, their consequences have not systematically changed product development and design practices. Usability research and testing play a minor role in comparison to technical possibilities, process management and economic considerations in the development phase. Therefore, we take a closer look at the user and the human cognitive and interactive capabilities according to today’s Cognitive Science approaches like Situated Cognition. What effect would it have if we took the Situated, Embodied Cognition view seriously? Would it really make a difference in design and development practices? And would it make a difference to the implementation of other cognitive approaches like the Symbol Manipulation (Information Processing) or Connectionist (Parallel Distributed Cognition) views that might play a background role in guiding professional practices? This paper draws parallels between the development of Cognitive Science and the fields of Human Computer Interaction and Usability and puts forward the claim that a serious consideration of current thinking and knowledge regarding the situatedness and embodiment of human cognition fundamentally changes our assumptions and actions regarding the role of schemes, situations, intentions and functions, tools and environments, and the role of cooperation in the design of mobile and multimedia applications.

Effective Video Streaming using Mesh P2P with MDC over MANETs (301-316)  
Nadian N. Qadri, Antonio Liotta, Muhammad Altaf, Martin Fleury,  
and Mohammed Ghanbari 
Peer-to-Peer (P2P) streaming and Mobile Ad hoc Networks (MANETs) have turned out to be two of the most active research areas for pervasive computing. These areas were developed independently of each other with the result that there is insufficient verification of whether the P2P distribution paradigm and specifically P2P real-time video streaming would work on MANETs. In this paper, we demonstrate that mesh-based P2P streaming together with Multiple Description Coding (MDC) over MANETs effectively provides real-time video streaming. MDC, a promising video coding technique, is emerging as an alternative way to improve video quality for both P2P over an internet and for MANET applications. This paper shows that mesh-based P2P when combined with MDC results in improvement in delivered video quality making it acceptable for ad hoc networks. For that purpose, the GloMoSim simulator was modified to support mesh-based P2P and MDC. This kind of video streaming will be useful for many ad hoc applications such as search and rescue applications, military applications, inter-vehicular communication, and video conferencing.

A Hierarchical Network Design Solution for Mobile IPv6 (317-332)  
Vilmos Simon, László Bokor, and Sandor Imre 
Over the past years a number of IP micro-mobility protocols have been proposed as an extension or complement of Mobile IP. Although the development of these protocols has generated considerable interest in industry and academia, none of them have been widely deployed. The main reason of this lack of real-life usage of micro-mobility proposals is that the RFCs or drafts of these protocols do not address the problems regarding the realization of the micro-mobility structures in detail during the procedures of network design. This shortage is true in case of Hierarchical Mobile IP as well (RFC 4140), which is one of the most significant micro-mobility solutions aiming to reduce the signaling delay and the number of signaling messages of Mobile IP. In order to provide guidelines for network designers we propose a new a hierarchical network design algorithm (HIENDA) based on the structure given by a Location Area planning algorithm, aligned with a MAP allocation algorithm in Hierarchical Mobile IPv6 to optimize the mobility management in Mobil IP networks. HIENDA considers the topology constraints, and takes the available mobility pattern and Access Router handover rate information as input, and finds a near optimal hierarchical structure for which the total signaling cost will be minimal. From the simulation results the conclusion could be drawn that HIENDA outperforms the other existing hierarchy optimizing solutions in the term of Location Update Cost, at the same time keeping the Packet Delivery Cost on a low level.

Analysis of Temporal Evolution of Social Networks (333-350)  
Khaled Mahdi, Maytham Safar and Hisham Farahat  
The article presents an analysis of dynamic social network where words, nodes and edges appear and disappear through time. We study a popular virtual social network in the internet, known as Paltalk. We analyze the exact and approximated cyclic entropy variation with time with the purpose to establish the robustness of the network. In addition, we study the effect of weighed links on the analysis of such graphs.

On Context-Sensitive Usability Evaluation in Mobile HCI (351-370)  
Karin A. Hummel, Thomas Grill, and Andrea Hess  
In usability evaluations, experiments are often conducted in closed laboratory situations to avoid disturbing influences. Due to non-realistic usage assumptions, this approach has important shortcomings when mobile Human Computer Interactions (m-HCIs) have to be evaluated. On the other hand, field studies allow to perform experiments close to real-world conditions, but potentially introduce influences caused by the environment, which have not been fully investigated so far.  With this work, we contribute to distinguishing application shortcomings from environmental disturbances which both potentially cause decreased user performance. Our approach is based on monitoring environmental conditions during the usability experiment, such as light, acceleration, sound, temperature, and humidity, and relating them to user actions. Therefore, a mobile context-framework has been developed based on a Wireless Sensor Network (WSN) carried together with a mobile PC. We present results of a small study (seven persons) in the lab which pointed at increased delays and error rates of user interactions under induced environmental disturbances. Hereby, we demonstrate the potential of environmental monitoring for understanding user performance. Additionally, we present novel results of a usability study carried out in the field where we tested 19 persons under varying environmental conditions. The results showed that error rate and delay are influenced by environmental parameters, but in a more complex way than expected a-priori.

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