In this work we propose an efficient resource allocation algorithm for OFDMA based wireless systems supporting heterogeneous traffic. The proposed algorithm provides proportionally fairness to data users and short term rate guarantees to real-time users. Based on the QoS requirements, buffer occupancy and channel conditions, we propose a scheme for rate requirement determination for delay constrained sessions. Then we formulate and solve the proportional fair rate allocation problem subject to those rate requirements and power/bandwidth constraints. Simulations results show that the proposed algorithm provides significant improvement with respect to the benchmark algorithm.

In this paper, we propose an enhancement to the existing IEEE 802.11 distributed coordination function (DCF) MAC to improve channel spatial reuse efficiency, and thus improve overall network data throughput. Our modification, named the location enhanced DCF (LED) for IEEE 802.11, incorporates location information in DCF frame exchange sequences so that stations sharing the communication channel are able to make better interference predictions and blocking assessments. Utilizing an underlying physical layer design that supports frame capture, the LED enhanced interference estimation can increase overall network data throughput by permitting more concurrent transmissions. In this paper we also analytically study the potential performance enhancement of the LED over the original IEEE 802.11 DCF. The results are verified using the ns-2 simulator, which shows that up to 35% of DCF blocking decisions are unnecessary and our LED method can achieve up to 22% more throughput than the original DCF.

We present a framework for agreements in pervasive environments called the Universal Pervasive Transaction Framework (UPTF) for parties transacting in wireless insecure environments using mobile devices. We discuss one type of such agreement with commercial interest, namely mobile payments from a payer to a payee. We have implemented two complete systems for purchasing and payment with mobile devices utilizing UPTF. The first introduces a special purpose, new mobile device called the Universal Pervasive Transaction Device (UPTD) and the second utilizes J2ME-capable mobile phones.

The Task Computing framework is designed to operate in dynamic ubiquitous environments in which a mobile computing user dynamically discovers the current set of available semantically defined services. Task Computing allows the end-user to easily and seamlessly integrate and manipulate services found on their own computer, the nearby devices and relevant remote web services. The user can create, execute and monitor complex tasks resulting from compositions of these services. In this paper, how Task Computing addresses some issues in mobile and ubiquitous multimedia applications and some of the multimedia related semantic services currently implemented in this framework are described.

Cooperative modulation techniques can reduce the energy requirements for the long haul transmission of data from localized sensor networks. This saving is vital in extending the battery life of power limited sensor nodes communicating over a time-limited channel. Several transmission methods, including a novel scheme that conveys information via node selection, are analyzed. The energy cost in local communications needed to support the cooperative long haul link is determined and used to make comparisons between the techniques.

This paper discusses ongoing research on automatically configurable distributed control systems. We are investigating the use of networks of relatively small controllers that contain intelligence and communication capabilities to perform factory automation. These systems are expected to be more robust, adaptable and flexible than conventional designs. To achieve these benefits, fundamental changes in the underlying control system architecture are needed. The system architecture is divided into two portions: the control infrastructure and the control algorithms. Requirements for the control infrastructure are described that implement basic services to support distributed control, including the ability for a new control node to announce its presence and capabilities to the system without disrupting ongoing activities. The control algorithms for this system must be designed with certain properties: autonomy and cooperativeness; that are able to respond to changes in the physical plant and its usage. A laboratory for studying autoconjigurable control systems is under development using prototype distributed controllers on a CAN-based network. Two experiments are described that demonstrate autoconfiguration capability. The potential applications and the future directions of this research are discussed.

A recovery protocol for distributed systems using the time warp control mechanism is described. The proposed protocol is fault tolerant to multiple process failures. Time warp is an optimistic execution technique in which synchronization is achieved using rollback. The recovery protocol exploits the redundancy already available to implement process rollback in the time warp mechanism. Thus, the protocol has little additional bookkeeping overhead, which contrasts with many other recovery protocols.>

A recovery procedure for distributed systems using the time warp control mechanism is described. Time warp is an optimistic execution technique in which synchronization is achieved using rollback. The recovery procedure is a protocol that exploits the redundancy already available to implement process rollback in the time warp mechanism. Thus, the recovery protocol has little additional bookkeeping overhead, unlike many other recovery procedures. An informal proof of the correctness of the recovery procedure for a single process failure is presented. The protocol is extended so that it becomes resilient to multiple process failures.>

Given a collection of distributed programs and the modules they use, the module allocation problem is to determine an assignment of modules to processors that minimizes the total execution cost of the programs. Standard approaches to this problem are based on solving either a network flow problem or a constrained 0-1 integer programming problem.

In this paper we analyze the performance of two predominant ring architectures: the slotted ring and the token-controlled ring. First we describe each of the networks. Then we discuss the simulation models that we developed for them, being careful to point out the assumptions that were made about the networks and their operating environment. Finally we describe the experiments that were run using the simulation models and present their results.