Multiplex communications – Data flow congestion prevention or control
Reexamination Certificate
1996-12-19
2001-12-04
Olms, Douglas (Department: 2661)
Multiplex communications
Data flow congestion prevention or control
C455S001000, C370S236000
Reexamination Certificate
active
06327245
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
The invention relates to the field of wireless networks in which a large number of nodes communicate with a central computer. The invention relates more particularly to avoiding jamming in such a system.
B. Related Art
The aforementioned related applications describe The application relates to packet hopping networks in which messages are communicated wirelessly from a central computer to a network of nodes. The central computer has a weak transmitter and does not have the ability to communicate with all of the nodes. Accordingly, various nodes act as re-transmitters for retransmitting information to the others. Such networks are particularly useful for lighting control in a building.
In U.S. application Ser. No. 08/498,286, jamming was avoided by having a transmitting node slide its transmitting frequency with a relatively slow slide frequency. A receiving node would then slide its receiving frequency relatively quickly, to scan for transmitters. The receiving node would then temporarily freeze its receiving frequency upon crossing the frequency used by the transmitter. The receiver could then receive the message intended for it. Since transmission takes place at different frequencies, chances of being stuck at a frequency which is jammed was unlikely.
SUMMARY OF THE INVENTION
The object of the invention is to find an improved way to do jamming avoidance in large wireless networks.
This object is achieved through recognition that for many applications, especially lighting, the central computer only has to communicate with the nodes relatively rarely, for instance a few times a day. Accordingly, the central computer and all of the nodes can use a single channel. The channel need only be switched, albeit for all the nodes at once, in response to excessive use of the channel frequency by transmitters outside the current network.
A further aspect of the invention is a mechanism for getting all of the nodes to switch together to the new channel. In this aspect, commands are sent out substantially in advance of switching, i.e. via “time bomb”. The term “time bomb” will be defined below.
The invention has the advantage of substantially reducing the complexity and cost of the nodes.
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A.A. Bertossi et al, “Code Assignment for Hidden Terminal Interference Avoidance in Multihop Packet Radio Networks”, IEEE/ACM Transactions on Networking, vol. 3, No. 4, Aug. 1995, pp. 441-449.
Guida Frank
Melnik George
Satyanarayana Shrinagesh
Nguyen Brian
Olms Douglas
Philips Electronics North America Corporation
Slobod Jack D.
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