P.G. Jansen’s research while affiliated with University of Twente and other places

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.

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.

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.

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.

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.

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

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 algorithms 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.

In modern multiprocessor systems, proces-sors can be stalled by inter-task communication when read-ing from a remote buffer. This paper presents a solution for the inter-task communication, that has a minimal im-pact on the performance of the system, hides the inter-task communication latency without requiring additional hard-ware. 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.

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.

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