People Involved
- Evan Hart - Hardware / Project Oversite
- Constantine Mavromichalis - Battery Back-Up
- Cliff Murphy - Firmware / Software
- Alex Odom - Data Merging/Sharing Research
- Ben Sanders - Backwards Compatibility
- Curt Stein - Backwards Compatibility
Flash Demo of a MeshNetwork
What is a Mesh Network?
| Wireless ad-hoc network is a computer network in which the communication links are wireless. The network is ad hoc because each node is willing to forward data for other nodes, and so the determination of which nodes forward data is made dynamically based on the network connectivity. The decentralized nature of most wireless ad hoc networks makes them suitable for a variety of applications where central nodes cannot be relied on, and may improve the scalability of wireless ad-hoc networks compared to wireless managed networks. |
Definition from Wikipedia, Wireless ad-hoc network
Our MeshNetwork Goals and Uses:
The goal of the UI Vast WiFi Network is to create a mesh network between vehicles that provides real time tracking data to any connected wireless client. Primarily we are interested in sharing APRS position and telemetry data from the balloon. Our secondary goals are to provide tracking information on all nodes in the mesh network, and to distribute any onboard data that we retrieve from the balloon/cabsule's at the landing site. By modifying off-the-shelf hardware we can create high-power wireless nodes that help supply the UI VAST Network with important mission data for our GERTTS project. Our wireless mesh network helps nodes find a way to pass data even if the network layout changes such as when vehicles change order or spread far enough apart that the front and rear nodes can no longer communicate directly.
The Hardware:
To keep costs down, our wireless network is built around consumer 802.11 WiFi hardware. This is a common wireless network technology that allows high speed data transfer and mobile operation. Also support can be found in many laptop computers built today.
In order to provide high power yet cost effective network nodes, we selected the Linksys WRT54G router for use in our network. This router features two removable antennas and the ability to modify its programming instructions (or firmware). This adds support for external serial ports and a GPS receiver.
The removable antennas allow us to install high gain antennas to increase the communications range of the router, and the ability to change the programming instructions allows us to increase the amplifier output to produce a stronger radio signal that can travel further than it would otherwise. The serial ports allow us to add a GPS receiver for position information of the node and a TNC connected to a Ham radio receiver to receive remote APRS packets from both the balloon and potentially the other nodes.
The hardware modifications help to improve the strength of our WiFi connection which allows us to communicate further between wireless nodes. It helps the performance of the network by allowing network data to travel further and more reliably.
Our UI Vast WiFi Network currently uses vertical omni-directional antennas with the car's roof as its ground plane and the radio amplifier set to output about 84mW of power (vs the default 28mW).
The Linksys WRT-54G runs on a power source of 12 Volts and 0.5 Amps from it's external power connector. We need to have mobile batteries put in parallel with the power source for the router as a temporary back-up because it takes time for the router to be operational if the power from the bus should fail. Specifications on the mobile back-up battery can be found here: Linksys Mobile Battery
The Software:
The software and protocols for the UI Vast WiFi Mesh Network are still being determined.
Network Services:
A list of network services can be found on the UI VAST network page. This page will eventually include some excerpts from that page, but will not be a comprehensive list of available network services.
Network Performance:
Currently some basic network performance information can be found on the UI VAST network page. That information (bandwidth, performance through node hops, long-distance performance) will end up on this page once more comprehensive data can be collected on the network's performance characteristics. But network service performance (such as concurrent GPSD users) will be added to the UI VAST network page since the performance of network services doesn't depend on network performance.
