Pierre G. Jansen

MC-LMAC: A multi-channel MAC protocol for wireless sensor networks

In traditional wireless sensor network (WSN) applications, energy efficiency may be considered to be the most important concern whereas utilizing bandwidth and maximizing throughput are of secondary importance. However, recent applications, such as structural health monitoring, require high amounts of data to be collected at a faster rate. We present a multi-channel MAC protocol, MC-LMAC, designed with the objective of maximizing the throughput of WSNs by coordinating transmissions over multiple frequency channels. MC-LMAC takes advantage of interference and contention-free parallel transmissions on different channels. It is based on scheduled access which eases the coordination of nodes, dynamically switching their interfaces between channels and makes the protocol operate effectively with no collisions during peak traffic. Time is slotted and each node is assigned the control over a time slot to transmit on a particular channel. We analyze the performance of MC-LMAC with extensive simulations in Glomosim. MC-LMAC exhibits significant bandwidth utilization and high throughput while ensuring an energy-efficient operation. Moreover, MC-LMAC outperforms the contention-based multi-channel MMSN protocol, a cluster-based channel assignment method, and the single-channel CSMA in terms of data delivery ratio and throughput for high data rate, moderate-size networks of 100 nodes at different densities.

Efficient computation of buffer capacities for multi-rate real-time systems with back-pressure

A key step in the design of multi-rate real-time systems is the determination of buffer capacities. In our multi-processor system, we apply back-pressure as caused by bounded buffers in order to control jitter. This requires the derivation of buffer capacities that both satisfy the temporal constraints as well as constraints on the buffer capacity. Existing exact solutions suffer from the computational complexity associated with the required conversion from a multi-rate dataflow graph to a single-rate dataflow graph. In this paper we present an algorithm, with linear computational complexity, that does not require this conversion and that determines close to minimal buffer capacities. The algorithm is applied to an MP3 play-back application that is mapped on our network based multi-processor system.

A virtual channel network-on-chip for GT and BE traffic

This paper presents an on-chip network for a runtime reconfigurable system-on-chip. The network uses packet-switching with virtual channels. It can provide guaranteed services as well as best effort services. The guaranteed services are based on virtual channel allocation, in contrast to other on-chip networks where guarantees are provided by time-division multiplexing. The network is particularly suitable for systems in which the traffic is dominated by streams. We model the data traffic in the system and simulate the behaviour of the network with this model. The results show that the network is capable of handling the system traffic and can provide the required guarantees

Multi-channel support for dense wireless sensor networking

Currently, most wireless sensor network applications assume the presence of single-channel Medium Access Control (MAC) protocols. When sensor nodes are densely deployed, single-channel MAC protocols may be inadequate due to the higher demand for the limited bandwidth. To overcome this drawback, we propose multiple channel support for improving the performance. Our method allows the nodes to utilize new frequency channels which results in the significant increase on the number of nodes that are granted access to the wireless medium. The method requires only one half-duplex transceiver per node, which is capable of sending and receiving over distinguished frequency channels. Simulation results show that, method successfully utilizes multiple channels and increases the performance proportional to the number of available frequencies for an example single-channel MAC protocol, LMAC.

Efficient Computation of Buffer Capacities for Cyclo-Static Real-Time Systems with Back-Pressure

This paper describes a conservative approximation algorithm that derives close to minimal buffer capacities for an application described as a cyclo-static dataflow graph. The resulting buffer capacities satisfy constraints on the maximum buffer capacities and end-to-end throughput and latency constraints. Furthermore we show that the effects of run-time arbitration can be included in the response times of dataflow actors. We show that modelling an MP3 playback application as a cyclo-static dataflow graph instead of a multi-rate dataflow graph results in buffer capacities that are reduced up to 39%. Furthermore, the algorithm is applied to a real-life car-radio application, in which two independent streams are processed

Service discovery at home

Service discovery is a fairly new field that kicked off since the advent of ubiquitous computing and has been found essential in the making of intelligent networks by implementing automated discovery and remote control between devices. This paper provides an overview and comparison of several prominent service discovery mechanisms currently available. It also introduces the at home anywhere service discovery protocol (SDP@HA) design which improves on the current state of the art by accommodating resource lean devices, implementing a dynamic leader election for a central cataloguing device and embedding robustness to the service discovery architecture as an important criterion.

Providing QoS Guarantees in a NoC by Virtual Channel Reservation

We propose an approach for providing Quality-of-Service guarantees in a virtual channel Network-on-Chip. The approach is based on virtual channel reservation - routes with guaranteed lower throughput bound are reserved over the virtual channels. The performance of such an approach is limited by a number of factors: number of virtual channel in the network, number of requested routes, traffic locality etc. We test the performance of the proposed approach for variety of traffic conditions. We investigate the influence of three system parameters - routing algorithm, network topology and communication locality - on the performance limits of the approach. The results are derived by simulations using a streaming traffic model. The results show the approach is feasible for a network of size 10-by-10 with four virtual channels per physical channel. The traffic locality has strong influence on the performance limits of the approach and can also help in reducing the communication energy cost by 50% to 70%. The type of the routing algorithm does not practically influence the performance limits.

An algorithm for generating node disjoint routes in Kautz digraphs

The authors focus on a particular class of interconnection networks: Kautz networks. These networks have nice properties: a network with degree d and N=d/sup k/+d/sup k-1/ nodes (for any cardinal d, k>0), has a diameter of at most /sup d/log N, the degree d is fixed and independent of the network size. The network is fault-tolerant and the connectivity is d. There is a straightforward mapping from standard computation graphs such as a linear array, a ring and a tree to a Kautz network. The network allows for a simple routing algorithm, even when nodes or links are faulty. There exists d node disjoint paths between any pair of vertices. The paper presents an algorithm to generate these node disjoint routes. The routes are delivered with increasing length and are free of loops. It proves that these routes are node disjoint and as short as possible.<<ETX>>

Communication between nested loop programs via circular buffers in an embedded multiprocessor system

Multimedia applications, executed by embedded multiprocessor systems, can in some cases be represented as task graphs, with the tasks containing nested loop programs. The nested loop programs communicate via arrays and can be executed on different processors. Typically an array can be communicated via a circular buffer with a capacity smaller than the array. For such buffers, the communicating nested loop programs have to synchronize and a sufficient buffer capacity needs to be computed. In a circular buffer we use a write and a read window to support rereading, out-of-order reading or writing, and skipping of locations. A cyclo static dataflow model is derived from the application and used to compute buffer capacities that guarantee deadlock free execution. Our case-study applies circular buffers in a Digital Audio Broadcasting channel decoder application, where the frequency deinterleaver reads according to a non-affine pseudo-random function. For this application, buffer capacities are calculated that guarantee deadlock free execution.

Clockwise: a mixed-media file system

This paper presents Clockwise, a mixed-media file system. The primary goal of Clockwise is to provide a storage architecture that supports the storage and retrieval of best-effort and real-time file system data. Clockwise provides an abstraction called a dynamic partition that groups lists of related (large) blocks on one or more disks. Dynamic partitions can grow and shrink in size and reading or writing of dynamic partitions can be scheduled explicitly. With respect to scheduling, Clockwise uses a novel strategy to pre-calculate schedule slack time and it schedules best-effort requests before queued real-time requests in this slack time.