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.

We propose a simulation framework developed in Simulink for analyzing the performance of code dissemination in wireless sensor networks. The complete solution relies on a three-layer network stack where the LMAC, FixTree and RMD protocols operate in conjunction. For performance evaluation, we use in our simulations the radio link quality model derived from previous field trials. In this way, we can study the impact of real network conditions (e.g. fluctuating link quality, changing neighborhood) on the higher layer protocols and thus verify our design choices in non-idealized circumstances.

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.

Multi-channel communication protocols in wireless networks usually assume perfect orthogonality between wireless channels or consider only the use of interference-free channels. The first approach may overestimate the performance whereas the second approach may fail to utilize the spectrum efficiently. Therefore, a more realistic approach would be the careful use of interfering channels by controlling the interference at an acceptable level. We present a methodology to estimate the packet error rate (PER) due to inter-channel interference in a wireless network. The methodology experimentally characterizes the multi-channel interference and analytically estimates it based on the observations from the experiments. Furthermore, the analytical estimation is used in simulations to derive estimates of the capacity in larger networks. Simulation results show that the achievable network capacity, which is defined as the number of simultaneous transmissions, significantly increases with realistic interfering channels compared with the use of only orthogonal channels. When we consider the same number of channels, the achievable capacity with realistic interfering channels can be close to the capacity of idealistic orthogonal channels. This shows that overlapping channels which constitute a much smaller band, provides more efficient use of the spectrum. Finally, we explore the correctness of channel orthogonality and show why this assumption may fail in a practical setting.

The current literature on multi-channel protocols in wireless networks mostly assume perfect orthogonality among different channels. However, channel orthogonality depends on factors like transceiver characteristics, transmission power, distance between transmitters, etc. In this paper we investigate the impact of channel orthogonality on the network capacity by simulations. We explore the difference in capacity of the orthogonal hannels and interfering channels. We use an interference model which is based on extensive measurements on an example radio platform. Simulation results show that the achievable overall network capacity with realistic interfering channels can be close to the capacity ofidealistic orthogonal channels depending how much the re-ceiver is prone to the adjacent channel interference. This is an important implication since the careful use of interfering channels can provide better utilization of the spectrum.

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

We have investigated the radio interference behavior of a multi-channel WSN system with a typical radio platform. We have analyzed the results in terms of throughput and throughput per-channel spacing. The experimental results show that we can adjust the channel spacing with respect to the level of tolerated interference according to the application requirements. This gives us the possibility of simultaneous usage of as many as channels possible according to the permitted interference.

Our Multi Processor System on Chip (MPSoC) template provides processing tiles that are connected via a network on chip. A processing tile contains a processing unit and a Scratch Pad Memory (SPM). This paper presents the Omphale tool that performs the first step in mapping a job, represented by a task graph, to such an MPSoC, given the SPM sizes as constraints. Furthermore a memory tile is introduced. The result of Omphale is a Cyclo Static DataFlow (CSDF) model and a task graph where tasks communicate via sliding windows that are located in circular buffers. The CSDF model is used to determine the size of the buffers and the communication pattern of the data. A buffer must fit in the SPM of the processing unit that is reading from it, such that low latency access is realized with a minimized number of stall cycles. If a task and its buffer exceed the size of the SPM, the task is examined for additional parallelism or the circular buffer is partly located in a memory tile. This results in an extended task graph that satisfies the SPM size constraints.

In modern multiprocessor systems, processors can be stalled by inter-task communication when reading from a remote buffer. This paper presents a solution for the inter-task communication, that has a minimal impact on the performance of the system, hides the inter-task communication latency without requiring additional hardware. The solution applies to jobs, represented as task graphs, where the tasks are nested loop programs. Buffers are allocated in scratch-pad memories of the consuming tasks to provide low latency read access. For the nested loop programs, minimal buffer sizes can be determined to cover all possible communication patterns. The added computational complexity is low, as the solution adds only a few operations to the nested loop programs.

This paper describes an algorithm to determine the performance of real-time systems with tasks using stochastic processing times. Such an algorithm can be used for guaranteeing Quality of Service of periodic tasks with soft real-time constraints. We use a discrete distribution model of processing times instead of worst case times like in hard real-time systems. Such a model gives a more realistic view on the actual requirements of the system. The presented algorithm works for all deterministic scheduling systems, which makes it more general than existing 6algorithms and allows us to compare performance between these systems. To demonstrate our method, we make a comparison between the performance of the well known scheduling algorithms Earliest Deadline First and Rate Monotonic. We show that the complexity of our method can compete with other algorithms that work for a wide range of schedulers.

With the growing popularity of Wireless Sensor Networks (WSNs), the demand increases to perform time critical operations within such networks. A WSN is composed of sensor nodes, which contain a radio, ports for multiple sensors and a microcontroller. These sensor nodes have to provide a wide range of functionality as long as possible, while they use their scarce energy from a battery.

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.

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.

Virtual channel reservation is a simple approach for providing guaranteed throughput services in a virtual channel network-on-chip. However, its performance is limited by the number of virtual channels per physical channels. In this paper we explore the limits of the approach and investigate how these limits depend on the routing algorithm, the traffic locality, the network topology and the network size. The results show the the approach can be applied in a network of size 10-by-10 nodes 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.

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

RTnet is a distributed real-time network protocol for fully-connected local area networks with a broadcast capability. It supports streaming real-time and non-realtime traffic and on-the-fly addition and removal of network nodes. This paper presents a formal analysis of RTnet using the model checker Uppaal. Besides normal protocol behaviour, the analysis focuses on the fault-handling properties of RTnet, in particular recovery after packet loss. Both qualitative and quantitative properties are presented, together with the verification results and conclusions about the robustness of RTnet.

This paper presents measurements of radio interference using "ambient munode" sensor nodes. By varying distances and frequencies we get a measure of the interference caused by transmissions on adjacent bands. Our observations show that adjacent spectrum interference influences the data delivery, considerably. Channels should be separated in the spatial or in the frequency domains if interference is to be avoided. In addition, the distance to simultaneous transmitters and the number of simultaneous transmissions are highly correlated with channel spacing. Therefore, channel spacing can be adjusted according to spatial distances so that multiple concurrent transmissions can be performed without interference. We also give proposals for further investigation on the usage of this correlation that are relevant to the design of future multi-channel protocols

We describe a self-organizing, clustering protocol for band- width resource management in Wireless Sensor Networks. The proposed protocol allows the sensor nodes to communicate by a time-slotted, sched- uled MAC algorithm. When the nodes are densely deployed, i.e., the connectivity is very high, the MAC algorithm may not provide access for all of the nodes due to the limited number of time-slots, consequently the network capacity degrades. To overcome this drawback, we extend the time-slotted MAC algorithm by clustering the nodes into di®erent frequency domains while they can use the same time domain. The idea is basically to multiplex the time domain with the frequency domain. As a result, the number of nodes that are granted access to the wireless medium is increased by the number of frequency channels available. By using simulations, we evaluate the performance of the protocol. The results reveal that frequency multiplexing has the e®ect of increasing the capacity up to 100%.

In this paper we study the timing behaviour of streaming applications running on a multiprocessor architecture. Dependencies are derived between the application throughput and the timing characteristics of the processors and communication. Four different processor organizations that strongly influenced the results are considered and compared.