José Augusto Miranda Nacif

Characterizing SopCast client behavior

Live streaming media applications are becoming more popular each day. Indeed, some important TV channels already broadcast their live content on the Internet. In such scenario, Peer-to-Peer (P2P) applications are very attractive as platforms to distribute live content to large client populations at low costs. A thorough understanding of how clients of such applications typically behave, particularly in terms of dynamic patterns, can provide useful insights into the design of more cost-effective and robust solutions. With the goal of extending the current knowledge of how clients of live streaming applications typically behave, this paper provides a detailed characterization of clients of SopCast, a currently very popular P2P live streaming application. We have analyzed a series of SopCast transmissions collected using PlanetLab. These transmissions are categorized into two different types, namely, major event live transmissions and regular (or non-event) live transmissions. Our main contributions are: (a) a detailed model of client behavior in P2P live streaming applications, (b) the characterization of all model components for two different types of transmissions in the SopCast application, (c) the identification of qualitative and quantitative similarities and differences in the typical client behavior across different transmissions, and (d) the determination of parameter values for the proposed client behavior model to support the design of realistic synthetic workload generators.

Efficient power management in real-time embedded systems

Power consumption became a crucial problem in the development of mobile devices, especially those that are communication intensive. In these devices, it is imperative to reduce the power consumption devoted to maintaining a communication link during data transmission/reception. The application of dynamic power management methodologies has contributed to the reduction of power consumption in general purpose computer systems. However, to further reduce power consumption in communication intensive real-time embedded devices, we have to consider the state of the computation and external events in addition to power management policies. In this paper we propose a model of an Extended Power State Machine (EPSM), where we adapt a Power State Machine to include the state of an embedded program in the power state machine formulation. This EPSM model is used to adapt the Quality of Service (QoS) in communication intensive devices to ensure low power consumption. In such development, a middleware layer fits in the systems architecture, being responsible for intercepting the data communication and implementing the EPSM. Also, a software tool was developed, allowing the Middleware Code to be generated based on the State Machine. A case study demonstrates the application of the proposed model to a real situation.

HydroNode: A low cost, energy efficient, multi purpose node for underwater sensor networks

The research of underwater sensor networks (UWSNs) is gaining attention due to its possible applications in many scenarios, such as ecosystem preservation, disaster prevention, oil and gas exploration and freshwater reservoirs management. The main elements of a UWSN are underwater sensor nodes (UWNs). In this paper we present HydroNode: a low cost, energy efficient, multipurpose underwater sensor node (UWN). Nowadays, to the best of our knowledge, there is no UWNs that is simultaneously low cost, low power, able to couple diverse types of sensors and educationally available. Thus, the objective of this paper is to fill this gap by describing the design of HydroNode, an underwater sensor node that fulfill all these requirements and can be used in various UWSNs applications. We used only commercial off-the-shelf components to build our underwater sensor node. Due to its multipurpose design, HydroNode can be used in different UWSNs, therefore aiding the research of UWSN system protocols, configurations and applications.

A Quantum-Dot Cellular Automata Processor Design

This paper describes the complete implementation of a robust SUBNEG (subtract and branch if negative) processor using quantum-dot cellular automata (QCA) technology. A processor is the basic unit in computer systems which is responsable for performing the basic arithmetic, logic, and input/output operations. QCA is a promising nanotechnology where components have nano size, ultra-low power consumption and could have a clock rate on terahertz rate. The architecture of our processor was inspired by the one used on the first carbon nanotube computer. We used this work as reference because both nanotechnology (the carbon nanotube and QCA) are promising and able to overcome the limits of current CMOS technology. Our work is the first implementation of a SUBNEG processor in QCA technology and, moreover, satisfies all constraints in order to make it robust. In a bottom-up approach, we first describe the building blocks that compose the QCA SUBNEG processor such as the ALU and the data and instruction memories. Next, we present the processor architecture. Lastly, we describe tests and performance evaluation of the QCA SUBNEG processor.

System-level Dynamic Power Management Techniques for Communication Intensive Devices

Low-power devices require energy-aware design and dynamic power management techniques to reduce the power consumption. Communication intensive devices make the decision of shutting down idle components very difficult, especially in wireless communication. This paper presents a new system-level dynamic power management technique to reduce the power consumption of communication intensive sensor nodes in wireless sensor networks. It analyzes the application-level information to determine the need for communication and to selectively shutdown hardware components, specially the radio. The hybrid automata framework is used to dynamically change duty cycles, making the best trade-off between energy conservation and quality of service, according to the application requirements. Simulation results reveal that application-level information is crucial to reduce power consumption and to increase the sensor node lifetime

Exception handling in microprocessors using assertion libraries

In complex system-on-a-chip (SoC) designs, designers often need to add new features into an original processor core, such as to extend the exception handling mechanism to consider exceptions in the remaining portion of the SoC design. We present in this paper a scalable architecture that can be used to add complex exception handling mechanisms in processor cores and how it can be used to extend the fixed set of exceptions found in microprocessor cores. This mechanism is based on the use of assertion libraries linked by an assertion processor to incorporate these new functionalities.

HydroNode: an underwater sensor node prototype for monitoring hydroelectric reservoirs

The research of underwater sensor networks (UWSNs) is gaining attention due to its possible applications in many scenarios, such as ecosystem preservation, disaster prevention, oil and gas exploration and freshwater reservoirs management. The main elements of a UWSN are underwater sensor nodes (UWNs). In this paper we present HydroNode, an underwater sensor node prototype for monitoring hydroelectric reservoirs. The objective of this paper is to describe the design of HydroNode for Hydroelectric Reservoirs Monitoring. We only used commercial off-the-shelf components to build our underwater sensor node. Due to its multipurpose design, HydroNode can be used in different UWSNs, therefore aiding the research of UWSN system protocols, configurations and applications.

Efficient Allocation of Verification Resources using Revision History Information

Verifying large industrial designs is getting harder each day. The current verification methodologies are not able to guarantee bug free designs. Some recurrent questions during a design verification are: Which modules are most likely to contain undetected bugs? In which modules the verification team should concentrate their effort? This information is very useful, because it is better to start verifying the most bug-prone modules. In this work we present a novel approach to answer these questions. In order to identify these bug-prone modules, the revision history of the design is used. Using information of an academic experiment, we demonstrate that there is a close relationship between bugs/changes history and future bugs. Our results show that allocating modules for verification based on bugs/changes leaded to the coverage of 91.67% of future bugs, while random based strategy covered only 37.5% of the future bugs.

Autonomous Wireless Lake Monitoring

Underwater sensor networks (USNs) are an emerging research field, with applications ranging from military to environment monitoring. The authors present an innovative USN application: autonomous wireless lake monitoring. Such technology can be applied to monitor lakes, especially for limnology, where scientists determine water quality by measuring environmental variables such as temperature, pH, and dissolved oxygen. This application, which can collect and analyze those physical quantities in near real time, could help improve quality of life for humans and prevent ecodisasters.

Survey on the design of underwater sensor nodes

Underwater wireless sensor networks are networks composed of various underwater sensor nodes (USNs) that are able to communicate with each other. The vast majority of Earth’s surface is composed of water, which makes such networks a very interesting research topic and enables a variety of applications, i.e, from oil monitoring to real time water pollution control. The design of USNs is paramount to the network’s operation. In comparison to terrestrial wireless sensor nodes, USNs are more expensive, larger, and present greater energy consumption, due to the harsh conditions of the aquatic environment. This leads to different challenges that need to be addressed in the design of the node, including processing, communications, energy management, data sensing, and storage. This survey aids in the development of underwater sensor nodes, and underwater applications. We present a general architecture of USNs and discuss the basic functions that must be accomplished by each unit. We also present a comprehensive study of all elements that compose a sensor node, including microcontrollers, memories, sensors, and batteries. In doing so, we highlight which aspects should be of pivotal importance in the design of a USN and how they affect communication protocols and applications. We believe that this survey can facilitate and guide development of future UWSN applications and protocols.