Farzad Safaei

Managing latency and fairness in networked games

Fighting propagation delays in real-time interactive applications improves gameplay and fairness in networked games by trading off inconstencies and tuning decision points topology.

A Comparative Survey of VANET Clustering Techniques

A vehicular ad hoc network (VANET) is a mobile ad hoc network in which network nodes are vehicles—most commonly road vehicles. VANETs present a unique range of challenges and opportunities for routing protocols due to the semi-organized nature of vehicular movements subject to the constraints of road geometry and rules, and the obstacles which limit physical connectivity in urban environments. In particular, the problems of routing protocol reliability and scalability across large urban VANETs are currently the subject of intense research. Clustering can be used to improve routing scalability and reliability in VANETs, as it results in the distributed formation of hierarchical network structures by grouping vehicles together based on correlated spatial distribution and relative velocity. In addition to the benefits to routing, these groups can serve as the foundation for accident or congestion detection, information dissemination and entertainment applications. This paper explores the design choices made in the development of clustering algorithms targeted at VANETs. It presents a taxonomy of the techniques applied to solve the problems of cluster head election, cluster affiliation, and cluster management, and identifies new directions and recent trends in the design of these algorithms. Additionally, methodologies for validating clustering performance are reviewed, and a key shortcoming—the lack of realistic vehicular channel modeling—is identified. The importance of a rigorous and standardized performance evaluation regime utilizing realistic vehicular channel models is demonstrated.

Optimal assignment of distributed servers to virtual partitionsfor the provision of immersive voice communicationin massively multiplayer games

This paper investigates the assignment of audio mixing operations to a geographically distributed set of servers to provide an immersive voice communication environment for massively multi-player online games. The immersive voice communication service enables each avatar to hear a spatially accurate audio mix of the conversations in its hearing range. There are three primary delivery architectures for this service, namely, peer-to-peer, central server, and distributed servers. We focus on a distributed server architecture, which partitions the virtual world into regions or locales and then assigns the computation associated with the creation of audio scenes for all avatars in each locale to a server. Our aim is to find the optimal way to partition the virtual world into locales and then choose the locale servers in such a way that reduces the total delay perceived by all avatars. We have produced a mathematical formulation for the optimal partitioning and server assignment and developed a heuristics approach based on a graph algorithm. We have developed a simulation environment that creates both the physical world (geographic distribution of participants and the Internet topology model) and the virtual world (distribution of avatars based on different avatar aggregation behaviors). We have solved the problem exactly as well as using the heuristics for a range of simulated virtual and physical worlds. In many cases, the heuristics results were within 5% of the optimal. Our algorithms and simulation study will be of benefit to future immersive voice communication service providers in the design of a cost effective delivery architecture for this service.

Preparation and characterization of hybrid conducting polymer-carbon nanotube yarn

Hybrid polypyrrole (PPy)-multi walled carbon nanotube (MWNT) yarns were obtained by chemical and electrochemical polymerization of pyrrole on the surface and within the porous interior of twisted MWNT yarns. The material was characterized by scanning electron microscopy, electrochemical, mechanical and electrical measurements. It was found that the hybrid PPy-MWNT yarns possessed significantly higher mechanical strength (over 740 MPa) and Youngs modulus (over 54 GPa) than the pristine MWNT yarn. The hybrid yarns also exhibited substantially higher electrical conductivity (over 235 S cm(-1)) and their specific capacitance was found to be in excess of 60 F g(-1). Measurements of temperature dependence of electrical conductivity revealed semiconducting behaviour, with a large increase of band gap near 100 K. The collected low temperature data are in good agreement with a three-dimensional variable range hopping model (3D-VRH). The improved durability of the yarns is important for electrical applications. The composite yarns can be produced in commercial quantities and used for applications where the electrical conductivity and good mechanical properties are of primary importance.

Comparison of delivery architectures for immersive audio in crowded networked games

This paper examines appropriate network and server infrastructures for the provision of a realistic audio scene from the perspective of avatars in large-scale virtual environments. The audio scene of each avatar combines the voices and other sources of sound in the vicinity of the avatar, spatially placed, attenuated according to distance from the listener, and addition of sound effects to reflect the acoustic characteristics of the environment. We examine a range of delivery options including central-server, peer-to-peer with and without multicast, distributed proxies, distributed locale servers, and a hybrid model. We provide numerical results on the effect of different virtual world characteristics such as avatar density, hearing range, and correlation between the positions in the virtual and physical worlds. We compare delivery architectures based on a set of delay metrics aimed at measuring the interactive delay between avatars as well as accuracy of the scene. We make several recommendations on scalable implementation of such applications.

A survey on control separation techniques in multi-radio multi-channel MAC protocols

The rapid diminishing in the cost of commodity wireless hardware in recent years has prompted the use of multiple radios to improve the capacity of wireless networks. However, the research has shown that the improvement obtained from using multiple radios does not solely depend on the number of radios, but primarily on how these radios can be integrated in a constructive manner. A common way of integration multiple radios is to use a dedicated radio for control. To date, a number of multi-radio MAC protocol are employing a dedicated radio to control and coordinate the other radios, though the approaches are varied from one to another. In this paper, the control separation techniques in the multi-radio multi-channel MAC have been surveyed, and a classification of control separation techniques is provided. Moreover, this study points out the open research issues and intends to spark new interests and developments in this field.

DICE: Internet delivery of immersive voice communication for crowded virtual spaces

This paper develops a scalable system design for the creation, and delivery over the Internet, of a realistic voice communication service for crowded virtual spaces. Examples of crowded spaces include virtual market places or battlefields in online games. A realistic crowded audio scene including spatial rendering of the voices of surrounding avatars is impractical to deliver over the Internet in a peer-to-peer manner due to access bandwidth limitations and cost. A brute force server model, on the other hand, will face significant computational costs and scalability issues. This paper presents a novel server-based architecture for this service that performs simple operations in the servers (including weighted mixing of audio streams) to cope with access bandwidth restrictions of clients, and uses spatial audio rendering capabilities of the clients to reduce the computational load on the servers. This paper then examines the performance of two components of this architecture: angular clustering and grid summarization. The impact of two factors, namely a high density of avatars and realistic access bandwidth limitations, on the quality and accuracy of the audio scene is then evaluated using simulation results.

A real-time facial expression recognition system for online games

Multiplayer online games (MOGs) have become increasingly popular because of the opportunity they provide for collaboration, communication, and interaction. However, compared with ordinary human communication, MOG still has several limitations, especially in communication using facial expressions. Although detailed facial animation has already been achieved in a number of MOGs, players have to use text commands to control the expressions of avatars. In this paper, we propose an automatic expression recognition system that can be integrated into an MOG to control the facial expressions of avatars. To meet the specific requirements of such a system, a number of algorithms are studied, improved, and extended. In particular, Viola and Jones face-detection method is extended to detect small-scale key facial components; and fixed facial landmarks are used to reduce the computational load with little performance degradation in the recognition accuracy.

Fairness and playability in online multiplayer games

Playability and fairness are crucial elements of an enjoyable online game experience. The unavoidable propagation time introduced by the geographical distance between partici- pants can deteriorate the game responsiveness and playability. Also, differences in these delays can provide unfair advantages and/or disadvantages to different players. This paper explores the causal relationships between prop- agation time, inconsistencies, playability and fairness in on- line multiplayer games. It clearly defines causes of unfairness and introduces a theoretical quantification supported by an experimental technique to evaluate it in simulations. It also demonstrates through simulations the impact of changes in network architecture and topology on playability and fairness. I. INTRODUCTION

Provisioning overlay distribution networks

Future entertainment services are expected to be increasingly interactive, on demand and personalized. This paper aims to address the challenge of provisioning network and server resources to support the distribution of these services over the Internet. We propose the Overlay Distribution Network (ODN) as a cost-effective means to deliver these services. Because ODNs are created over shared network and server infrastructure, the provisioning problem becomes significantly complex. The paper formulates this problem as a joint resource provisioning and content replication optimization. The resulting formulation is proved to be NP-complete. We solved this problem with an efficient Lagrangian heuristic. Further, content clustering is employed to improve the heuristic run time. Initial results show that this is efficient. In some cases, clustering allows solutions with very similar quality to be achieved at a 20 times reduction in complexity.