Embedded Networking for High Data Rate Multi-Source Applications

1. Abstract

Because of the increasing demand for high speed sensor traffic on embedded platforms, there is a need to examine approaches for attaining high throughput without sacrificing the ability to sample sensor data at high speed.

The current protocols for networking on embedded devices focus on power consumption and attempt to leave the network hardware off for most of the time, giving them longer battery life at the expense of network speed.

The aim of the project would be to establish a protocol for high speed networking in star topology networks designed for small-scale sensor networks with a more theoretical look at other topologies.

Focus is on a multiple audio stream input to a PC from several embedded devices using a network protocol based round the IEEE 802.15.4 low-level protocol.

2. Introduction

With the advent of low cost, low power consumption small embedded platforms, interest has been growing in both the research community and in industry in large wireless sensor networks1, usually with low bandwidth requirements and long battery life.

This has led to a number of network protocols designed to give developers a low-power consumption, but highly reliable data transfer between motes and (usually) more powerful computers which do the heavyweight data processing.

This is a perfect solution for infrequent data reading on large networks, (such as weather monitoring, i.e. pressure, temperature, wind speed, etc.) but applications with high bandwidth requirements using these same protocols soon suffer from poor performance[2].

Thus, the aim of this project is to address this network protocol shortfall by re-examining the manner in which data is transmitted in a sensor network to allow for more bandwidth for high-rate sensing applications.

The rest of this proposal contains some background on the problem and attempts to rectify it, the project proposal itself, containing the aims and objectives for the project, and the methodology to be used during the project.

A program of work is also supplied, detailing the expected duration for each of the tasks in this project, along with a list of resources required to complete it.

Any research material used to formulate this proposal are listed at the end of this document.

3. Background

In most designs for embedded sensor networks, the IEEE 802.15.4 Medium Access Control (MAC) protocol is also used, which, in turn is usually used with the ZigBee high-level protocol to provide Low-Rate Wireless Personal Area Networks (LR-WPAN’s)[3].

This, while good for infrequent sensor readings in non real time applications does not allow for large payloads in its protocol, or, for that matter, even define a ‘large payload’ or how to handle them3.

At the other end of the scale, is the IEEE 802.11 standard for wireless communication, employed frequently in laptop computers and other similar specification mobile devices (PDAs, Ultra-Portable machines, etc.) which can deal with speeds of up to (and including) 54Mbit/s, which would, of course, be more than enough to send substantial amounts of sensor data, but the transceivers are high-drain, CPU-intensive components, making them unsuitable for small, low power, embedded devices2.

The uses for high speed embedded wireless are becoming increasingly clear, as designers and developers find new uses for small disposable networked devices. Notable situations in which high speed transfer is desirable could be in emergency and rescue operations, where fast deployment of a network to relay information or video feeds around a scene is required. Alternatively as an example of a less critical systems application, multi-source audio recording for video conferencing, with devices placed around the rooms giving full audio coverage, and (assuming that the devices know their relative locations) possibly spacial audio transmission, with the room being recreated audibly at the other conference location1.

4. The Proposed Project

4.1 – Aims and Objectives

The project will examine methods for achieving high speed data transfer on existing IEEE 802.15.4 compatible hardware using Intel iMote devices as the high-speed data acquisition platform.

The star network topology will be used for all of the design, implementation and testing phases, but grid and mesh networks will be briefly touched upon in theory only as these are beyond the scope of this project.

By using the star network topology, the focus of the project will be on the second example described in section 3, the multiple-source audio capture example, as audio input can have almost any sample speed, giving great flexibility for testing. However, location detection (adjacency calculations and triangulation) will be omitted, as they are beyond the scope of this project.

The CSMA and CSMA\CA methods will be examined and evaluated for their merits in this application and the IEEE 802.15.4 standard will be used for low-level control of the radio modules.

In conclusion; the following list concisely describes the aims of the project:

  • Assess the capability of the Intel iMote platform to sample at high rates while managing the network stack.
  • Assess the ability of the IEEE 802.15.4 standard to take large- payloads at high speeds in one to one networks.
  • Examine the networking methods available to retrieve multiple, high-speed data sources simultaneously.
  • Develop an API (if only a basic one) for high-speed communication for embedded devices to aid further development in this area.

4.1 – Methodology

The networking methods will be tested by sending a fixed amount of sample data through the network and the transfer rate calculated based on the transfer time.

Large numbers of packets should be sent as to adequately minimise any erroneous results, and make any problems very apparent.

The same sample data will be used on each network method, as to ensure that the results are comparable, and the same iMotes will be used in the network for each test.

The networks themselves will be constructed in such a manner that any environmental effects are negated. This will be done by ensuring that the iMotes are always well within their documented radio range of each other, and that each iMote can detect every other iMote (overlapping radio fields) as to not corrupt the data acquired.

5. Programme of Work

The required elements of this project can be broken down as follows:

  • Toolchain Setup – Gather required resources to get code compiling and running on the ‘motes’
  • Examine the supplied hardware in detail, especially the data acquisition and network components.
  • Investigate current strategies for high speed networking on embedded platforms in more detail, and determine which approach to pursue.
  • Design and implement basic data acquisition using the audio input on the motes and see what data input rate can be achieved. Use a direct link to a PC for analysis at this stage (no networking).
  • Assess weather TinyOS or another similar operating system is required, or if a simple monotasking application is sufficient, and if an OS is required, implement a toolchain to install it on the motes.
  • Design and implement a basic single mote network link to a PC to get a base-line measurement for how much data a single network channel can actually run at.
  • Design and implement a multi-mote network based on section to acquire more than one data stream simultaneously and experiment with protocols to achieve the highest data rate.
  • Design and implement a network API for subsequent developers to use for high-speed networking.
  • Finish Report

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