D-07S-05

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

Deliverables

• 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

Prior Art

• 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). It says:

3.2.5.2 Independent Access [to several channels without reserving one channel/radio for control information]

A more complex control scheme for channel negotiation can allow simultaneous access to different channels by using multiple transceivers. This can increase the channel utilization. Although this scheme seems to be more practical and profitable, practical aspect and feasibility need to be examined in detail [28].

and

As discussed in Section 3.2.5, even though independent access seems to be practical and beneficial, this is beyond our current scope and remains a topic for future research.

That's what I would like to do :-)

Key Ideas / Project Execution Plan

• 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

Project Log

• getting an overview / reading papers

TODO

• what kind of distributed channel assignment algorithms exist
• how do these work in case we have a world view (proactive protocol)