Using wireless mesh networks for Early Warning Systems

Assigned to: Jens Nachtigall

Advisor: Kai Köhne

Expected Submission: December 2007

Problem Statement

Early Warning Systems needs real-time communication (the reactive DSR protocol cannot achieve this)
using cheap COTS hardware (no or very limited access to the MAC layer, but it is fine to switch channels every x secs)
802.11b offers 3 non-overlapping channels, 802.11a even 12
make use of these multiple channels by means of ("virtual") multiradio nodes like the WRAPBoards without excluding the common single radio nodes, i.e. utilise multiple radios (channels) whenever possible whithout requiring a node to have several radios

Distributed channel assignment algorithm
based on a proactive routing protocol (allows world view)
using unmodified standard 801.11 MAC (only interacting with the MAC by switching the channel of one the available interfaces from time to time)
increase throughput (to retrieve data, e.g. MiniSeed) and decrease latency (for EWS) by using non-overlapping channels, i.e. a node can receive and transmit at the same time by having its to wifi interfaces at different channels

several attempts to make use of the non-overlapping channels by proposing a different MAC layer (however, for COTS you usually do not have access to the MAC):
- Comparison of Multi-Channel MAC Protocols
- Multi-channel MAC with Dynamic Channel Selection for Ad Hoc Networks
Dissertation A Proactive Routing Protocol for Multi-Channel Wireless Ad-hoc Networks by Unghee Lee (requires two radios at every node; one is used for control/routing information only and the other one for data/ack only)

proactive protocols have a "world view" of the network. This is nice because routes to nodes do not have to be found out on demand prior to sending data (which is slow) (the routing protocol could also not only flood link state information but also other information every node with a certain hop distance (adjustable by TTL) should know like GPS coordinates of all nodes
the idea is to piggyback channel assignment information with the HELLO or TOPOLOGY CONTROL (TC) messages of http://olsr.org and to have a distributed channel assign algorithm taking into account joining/leaving/movement of nodes
both radios are used for data and control (routing) messages, no need to reserve one radio for control messages only
2 (or more) single radio nodes that are connected by an ethernet cable can form a "virtual multi-radio node