Games played by multiple users, each using a wireless terminal (e.g., PDA), have tremendous revenue potential for next generation wireless systems. However, the next generation of wireless systems (such as UMTS and other 3G systems) alone will not be able to provide the tight delay bounds required by these multi--player games. We develop a system architecture that enables high--quality games among multiple wireless users and at the same time enables network service providers and game service providers to charge for the gaming service. Our architecture relies on wireless vertical communication conducted over UMTS to register (authenticate) the users at the commencement of a game and to report scores at the end of the game. During the game the players exchange information over wireless horizontal communication conducted over wireless LANs. Our architecture is particularly well suited for games that have o#--line software distribution, but require a registration (authentication) each time the game is played. In this paper we describe our system architecture, which involves a UMTS--based Wireless Overlay Communication System (WOCS), and give the protocol for game initiation and score submissions. We also outline business cases for our system architecture and discuss the network provider's perspective.

Many studies show that the wireless network interface (WNI) accounts for a significant part of the power consumed by mobile terminals. Thus, putting the WNI into sleep when it is idle is an effective technique to save power. To support streaming applications, existing techniques cannot put the WNI into sleep due to strict delay requirements. In this paper, we present a novel power-aware and QoS-aware service model over wireless networks. In the proposed model, mobile terminals use proxies to buffer data so that the WNIs can sleep for a long time period. To achieve power-aware communication while satisfying the delay requirement of each flow, a scheduling scheme, called prioritybased bulk scheduling (PBS), is designed to decide which flow should be served at which time. Through analysis, we prove that the PBS service model can provide delay assurance and achieve power efficiency. We use Audio-on-Demand and Web access as case studies to evaluate the performance of the PBS service model. Experimental results show that PBS achieves excellent QoS provision for each flow and significantly reduces the power consumption.

The emerging applications for 3G and 4G wireless systems typically require highly heterogeneous and time-varying quality of service from the underlying protocol layers. The wireless links, however, provide only an unreliable communication channel that suffers from temporal outages. As a consequence, protocol mechanisms are needed, that based on the unreliable wireless links provide the different service qualities required by the emerging applications. In this paper we identify the emerging IP based applications for 3G and 4G wireless systems and categorize their QoS requirements. We discuss the wireless access mechanisms that show promise of being the basis for supporting these applications. We than propose a set of protocol mechanisms, that based on the discussed wireless access mechanisms, provide the required QoS for the different application categories.

We study the capacity, i.e., the number of customers per cell, and the quality of service for streaming video in the uplink direction of a cellular Code Division Multiple Access (CDMA)--based wireless system. We advocate the use of TCP as the transport layer protocol for streaming video in a Multi--Code CDMA (MC--CDMA) wireless system. Our approach is to stabilize the TCP-- throughput for video transmissions over the wireless links by employing a recently developed Simultaneous MAC Packet Transmission (SMPT ) approach. Our extensive simulations indicate that employing SMPT significantly improves both the video quality and the capacity when streaming video over TCP.

Reducing the power consumption of the wireless network interface (WNI) is an effective way to prolong the battery lifetime of the mobile terminal. It takes some time for the WNI to transit from the power-saving mode to the active mode. This transition delay and the error-prone wireless link bring many challenges for designing power-aware and QoS-aware service models. In this paper, we present a novel power-conserving service model for streaming applications over wireless networks. At the base station side, a new scheduling algorithm, called rate-based bulk scheduling (RBS), is designed to decide which flow should be served at which time. The mobile terminal relies on a proxy to buffer data so that the WNI can sleep for a long time period to save power. To deal with channel errors, a novel adaptive technique is presented to adjust the sleep time of the WNI according to the channel condition. Through analysis, we prove that RBS can provide delay guarantee and it is more power efficient than other rate-based fair queuing algorithms.

Communication between a pair of nodes in the network may get disrupted due to failures of links/nodes resulting in zero effective bandwidth between them during the recovery period. It has been observed that such disruptions are not too uncommon and may last from tens of seconds to minutes. Even an occasional such disruption can drastically degrade the viewing experience of a participant in a video streaming session particularly when a sequence of frames central to the story are lost during the disruption. The conventional approach of prefetching video frames and patching lost ones with retransmissions is not always viable when disruptions are localized and experienced only by a few among many receivers. Error spreading approaches that distribute the losses across the video work well only when the disruptions are quite short. As a better alternative, we propose a disruption-tolerant content-aware video streaming approach that combines the techniques of content summarization and error spreading to enhance viewers experience even when the disruptions are long. We introduce the notion of “substitutable content summary frames ” and provide a method to select these frames and also their transmission order to mitigate the impact of a disruption. In the event of a disruption, the already received summary frames are played by the client during disruption and near normal playback is resumed after the disruption. We evaluate our approach and demonstrate that it provides acceptable viewing experience with minimal startup latency and client buffer.

The intricate dependency of networking protocols upon the performance of the wireless channel motivates the investigation of network channel approximations for fading channels. Wireless networking protocols are increasingly being designed and evaluated with the assistance of networking simulators. While evaluating networking protocols such as medium access control, routing, and reliable transport, the network channel model, and its associated capacity, will drastically impact the achievable network throughput. Researcher relying upon simulation results must therefore use extreme caution to ensure the use of similar channel models when performing protocol comparisons. Some channel approximations have been created to mimic the behavior of a fading environment, however there exists little to no justification for these channel approximations. This dissertation addresses the need for a computationally efficient fading channel approximation for use in network simulations. A rigorous flat fading channel model was developed for use in accuracy measurements of channel approximations. The iii

We propose a cross--layer design for the real--time streaming of prerecorded video with prefetching to clients in wireless CDMA networks. Our design exploits the recently discovered temporal correlation structure of the multiple access interference (MAI) which enables accurate prediction of the MAI levels. Based on the MAI prediction, we optimize the transmissions of the video traffic so as to make judicious use of the radio resources and therefore to achieve small video playback starvation probabilities. A key component of our transmission control is the Join--the--Shortest--Queue (JSQ) scheduling, which selects the client with the smallest prefetched reserve for transmission (provided that the client's predicted MAI is low). Our simulation results indicate that in typical scenarios, the starvation probabilities using our cross--layer design with the MAI prediction, are at least one order of magnitude smaller than of the conventional JSQ protocol with link probing at the link/MAC layer.

New challenging deployment scenarios are accommodating portable devices with limited and heterogeneous capabilities that roam among wireless access localities during service provisioning with session continuity requirements, such as in multimedia streaming. The paper proposes an original two-level buffering strategy to maintain streaming continuity independently of client roaming at provision time. In particular, it focuses on a specific component of the proposed support infrastructure, i.e., the pure Java buffering component, which has shown to outperform the standard Java Media Framework in both streaming initialization time and imposed overhead.

Multimedia information services in mobile environments are becoming more and more important with the proliferation of 3G technologies. Media streaming, in particular, is a promising technology for providing services such as news clips, live sports, and hot movies on the fly. To avoid service interruption when the users keep moving, proper data management strategies must be employed. We propose a new headlight prefetching technique for the streaming access points to deal with the uncertainty of client movement and the requirement of seamless service hand-off. For each mobile client, we maintain a virtual fan-shaped prefetching zone along the direction of movement similar to the headlight of a moving vehicle. The overlapping area and the accumulated virtual illuminance of the headlight zone on a particular cell determines the degree and volume of prefetching to be made by the streaming access point of that cell. Headlight prefetching solves the issues of identifying the streaming access points responsible for prefetching, the timing and the amount of data to prefetch in a single mechanism which is simple and effective. Simulation results demonstrate that our techniques can significantly decrease streaming disruptions, reduce bandwidth consumption, increase cache utilization and improve service response time.