Decentralized Channel Management in Scalable Multihop Spread Spectrum Packet Networks
This thesis addresses the problems of managing the transmissions of stations in a
spread-spectrum packet radio network so that the system can remain e ective when
scaled to millions of nodes concentrated in a metropolitan area. The principal difficulty in scaling a system of packet radio stations is interference from other stations in
the system. Interference comes both from nearby stations and from distant stations.
Each nearby interfering station is a particular problem, because a signal received from
it may be as strong as or stronger than the desired signal from some other station.
Far interfering stations are not individually a problem, since each of their signals
will be weaker, but the combined e ect may be the dominant source of interference.
The thesis begins with an analysis of propagation and interference models. The
overall noise level in the system (mainly caused by the many distant stations) is then
analyzed, and found to remain manageable even as the system scales to billions of
nodes. A scheme for designing a scalable packet radio network is then presented.
Included is a method of scheduling packet transmissions to avoid collisions (caused
by interference from nearby stations) without the need for global coordination or
synchronization. Simulations of a system of one thousand stations are used to verify
and illustrate the methods used.
A method of choosing routes (minimum-energy routes) is demonstrated in simulation to produce a fully connected and functional network for one hundred and one
thousand randomly placed stations. Unfortunately, congestion as the system scales is
unavoidable if the tra c is not limited to some degree of locality. If tra c is limited
to a few hops, then for a large system the techniques presented in this thesis are
superior to ideal time division multiplexing of a clear channel.
Audio from ARRL and TAPR 1998 Digital Communications Conference
Packet Radio Networks with Millions or Billions of Stations