Real-Time Communication in Wireless Home Networks

This paper describes a medium access protocol for real-time communication in wireless networks. Medium access is controlled by a scheduler, which utilizes a pre-emptive earliest deadline first (PEDF) scheduling algorithm. The scheduler prevents collisions in the network, where normally only collisions are avoided. PEDF is the scheduler of choice, because it has excellent properties with respect to bandwidth utilization, dynamic behaviour and feasibily analysis. The scheduler can be deployed in managed networks, where it resides in the base station, as well as in peer to peer or ad hoc networks, were it is distributed over the stations. The protocol is simulated and an implementation based on IEEE 802.11b is realized

Characterization of multi-channel interference

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

Routing in Wireless Multimedia Home Networks

This paper describes an adapted version of the destination sequenced distance vector routing protocol (DSDV) which is suitable to calculate routes in a wireless real-time home network. The home network is based on a IEEE 802.11b ad hoc network and uses a scheduled token to enforce real-time behaviour to support multimedia streams. The multimedia network protocol works for both single-hop and multi-hop networks, however in the latter case special measures have to be taken to forward streams from node to node and to find routes. Existing routing protocols exhibit non-deterministic behaviour which may interfere with the correct streaming of multimedia. The proposed routing protocol does not rely on flooding, instead it piggy-backs the real-time token and behaves in a predictable manner. Simulation of the routing protocol shows that routes in the network are found in finite time

Communicating Personal Gadgets

This paper focuses on communication in personal area networks. A personal area networks (PAN) is characterized as an informal collection, or community, of connected small, lightweight, and resource-lean devices, or gadgets. Two basic concepts are visible in the development of PANs, the distributed and the centralized concept. The paper introduces a real-time communication protocol that is suitable for both concepts. The communication protocol can deal with several types of traffic: real-time or nonreal- time, bursty or isochronous, high or low bitrate. The protocol is undemanding in terms of resources, so even simple devices can participate in the network. The network is simulated and a prototype is realized

The communication processor of TUMULT-64

Tumult (Twente University MULTi-processor system) is a modular extendible multi-processor system designed and implemented at the Twente University of Technology in co-operation with Oce Nederland B.V. and the Dr. Neher Laboratories (Dutch PTT). Characteristics of the hardware are: MIMD type, distributed memory, message passing, high performance, real-time and fault tolerant. A distributed real-time operating system has been realized, consisting of a multi-tasking kernel per node, inter process communication via typed messages and a distributed file system. In this paper first a brief description of the system is given, after that the architecture of the communication processor will be discussed. Reduction of the communication overhead due to message passing will be emphasized.\ud \u

Real Time in a Real Operating System

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Flexible Scheduling in Multimedia Kernels: an Overview

Current Hard Real-Time (HRT) kernels have their timely behaviour guaranteed on the cost of a rather restrictive use of the available resources. This makes current HRT scheduling techniques inadequate for use in a multimedia environment where we can make a considerable profit by a better and more flexible use of the resources. We will show that we can improve the flexibility and efficiency of multimedia kernels. Therefore we introduce Real Time Transactions (RTT) with Deadline Inheritance policies for a small class of scheduling algorithms and we will evaluate these algorithms for use in a multimedia environmen

Implementing and Evaluating Jukebox Schedulers Using JukeTools

Scheduling jukebox resources is important to build efficient and flexible hierarchical storage systems. JukeTools is a toolbox that helps in the complex tasks of implementing and evaluating jukebox schedulers. It allows the fast development of jukebox schedulers. The schedulers can be tested in numerous environments, both real and simulated types. JukeTools helps the developer to easily detect errors in the schedules. Analyzer tools create detailed reports on the behavior and performance of any of the scheduler, and provide comparisons between different schedulers. This paper describes the functionality offered by JukeTools, with special emphasis on how the toolbox can be used to develop jukebox schedulers

Verifying the distributed real-time network protocol RTnet using Uppaal

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