7025134
Communication speed selection for embedded systems with networked voltage-scalable processors
High-speed serial network interfaces are gaining wide use in connecting multiple processors and peripherals in modern embedded systems, thanks to their size advantage and power efficiency. Many such interfaces also support multiple data rates, and this ability is opening a new dimension in the power/performance trade-offs between communication and computation on voltage scalable embedded processors. To minimize energy consumption in these networked architectures, designers must not only perform functional partitioning but also carefully balance the speeds between communication and computation, which compete for time and energy. Minimizing communication power without considering computation may actually lead to higher energy consumption at the system level due to elongated on-time as well as lost opportunities for dynamic voltage scaling on the processors. We propose a speed selection methodology for globally optimizing the energy consumption in embedded networked architectures. We formulate a multi-dimensional optimization problem by modeling communication dependencies between processors and their timing budgets. This enables engineers to systematically solve the problem of optimal speed selection for global energy reduction. We demonstrate the effectiveness of our speed selection approach with an image processing application mapped onto a multi-processor architecture with a multi-speed Ethernet.
1037858
Power-Aware Task Motion for Enhancing Dynamic Range of Embedded Systems with Renewable Energy Sources
In this paper we propose a novel scheduling framework for a dynamic real-time environment that experiences power consumption constraints. This framework is capable of dynamically adjusting the voltage/ speed of the system, such that no task in the system misses its deadline and the total energy savings of the system are maximized. 
 
Each task in the system consumes a certain amount of energy, which depends on a speed chosen for execution. The process of selecting speeds for execution while maximizing the energy savings of the system requires the exploration of a large number of combinations, which is too time consuming to be computed on-line. Thus, we propose an integrated heuristic methodology which executes an optimization procedure and an approximate greedy algorithm in a low computation time. This scheme allows the scheduler to handle power-aware real-time tasks with low cost while maximizing the use of the available resources and without jeopardizing the temporal constraints of the system. Simulation results show that our heuristic methodology achieves a performance with near-optimal results.
2364475
Combined functional partitioning and communication speed selection for networked voltage-scalable processors
This paper presents a new technique for global energy optimization through coordinated functional partitioning and speed selection for embedded processors interconnected by a high-speed serial bus. Many such serial interfaces are capable of operating at multiple speeds and can open up a new dimension of trade-offs to complement today's CPU-centric voltage scaling techniques for processors. We propose a multi-dimensional dynamic programming formulation for energy-optimal functional partitioning with CPU/communication speed selection for a class of data-regular applications under performance constraints. We demonstrate the effectiveness of our optimization techniques with an image processing application mapped onto a multi-processor architecture with a multi-speed Ethernet.
6169415
The Color-Degree Matrix and the Number of Multicolored Trees in Star Decompositions
In a previous paper we investigated the problem of counting the number of multicolored spanning trees in biclique decompositions. In particular for acyclic decompositions we found the minimum and maximum numbers of multicolored trees. We now introduce the color-degree matrix C and show that the number of multicolored trees is bounded below by the determinant of C with a row deleted. In fact, we obtain equality for acyclic decompositions and for star decompositions. Unfortunately, for arbitrary decompositions the ratio of this determinant to the actual number of trees can approach zero. We find that star decompositions on n vertices are in one to one correspondence with tournaments on n ? 1 vertices. This allows us to determine that the minimum number of multicolored trees among all star decompositions of Kn is (n ? 1)! and the average number is ((n + 1)/2)n ? 2. We bound the maximum number of multicolored trees between this average and ?n2/4?(n ? 1)/2 ? ?(n ? 2)2/4?(n ? 1)/2.
15656771
On optimal communication cost for gathering correlated data through wireless sensor networks
In many energy-constrained wireless sensor networks, nodes cooperatively forward correlated sensed data to data sinks. In order to reduce the communication cost (e.g.overall energy) used for data collection, previous works have focused on specific coding schemes, such as Slepian-Wolf Code or Explicit Entropy Code. However, the minimum communication cost under arbitrary coding/routing schemes has not yet been characterized. In this paper, we consider the problem of minimizing the total communication cost of a wireless sensor network with a single sink. We prove that the minimum communication cost can be achieved using Slepian-Wolf Code and Commodity Flow Routing when the link communication cost is a convex function of link data rate. Furthermore, we find it useful to introduce a new metric distance entropy, a generalization of entropy, to characterize the data collection limit of networked sources. When the energy consumption is proportional to the link data rate (e.g.normally in 802.11), we show that distance entropy provides a lower bound of the communication cost and can be achieved by using a specific rate SWC and shortest path routing. Theoretically, achieving optimality may require global knowledge of the data correlation structure, which may not be available in practice. Therefore, we propose a simple, hierarchical scheme that primarily exploits data correlation between local neighboring nodes. We show that for several correlation structures and topologies, the communication cost achieved by this scheme is within a constant factor of the distance entropy, i.e., it is asymptotically optimal. Finally, we simulate our algorithm using radar reffectivity data as well as traces from Gaussian Markov Fields (GMF). As the network size goes large, for the radar data, we find our algorithm saves two thirds of the communication cost compared to a non-coding approach; as for the GMF data, our algorithm converges to a constant factor (1 .5_1.8) the distance entropy.
269541
TinyGALS: a programming model for event-driven embedded systems
Networked embedded systems such as wireless sensor networks are usually designed to be event-driven so that they are reactive and power efficient. Programming embedded systems with multiple reactive tasks is difficult due to the complex nature of managing the concurrency of execution threads and consistency of shared states. This paper describes a globally asynchronous and locally synchronous model (TinyGALS) for programming event-driven embedded systems. Software components are composed locally through synchronous method calls to form modules, and asynchronous message passing is used between modules to separate the flow of control. In addition, a guarded yet synchronous model (TinyGUYS) is designed to allow thread-safe sharing of global state by multiple modules without explicitly passing messages. This programming model is structured such that all asynchronous message passing code and module triggering mechanisms can be automatically generted from a high-level specification. We have implemented the programming model and code generation facilities on a wireless sensor network platform known as the Berkeley motes. As an example, we have redesigned a multi-hop ad hoc communication protocol using the TinyGALS model.
35455221
A characterization of pancyclic complements of line graphs
Abstract We characterize graphs G such that the complements of their line graphs are pancyclic.
6152126
QoS-aware dynamic service composition in ambient intelligence environments
Due to the large success of wireless networks and handheld devices, the ambient intelligence (AmI) paradigm is becoming a reality. One of the most challenging objectives to achieve in AmI environments is to enable a user to perform a task by composing on the fly networked services available at a specific time and place. Towards this goal, we propose a solution based on semantic Web services, and we show how service capabilities described as conversations can be integrated to perform a user task that is also described as a conversation, further meeting the QoS requirements of the user task. Experimental results show that the runtime overhead of our algorithm is reasonable, and further, that QoS-awareness improves its performance.