A self-organizing node and a sensor network with self-organizing nodes

A node for use in a sensor network together with at least one other node, each node having at least one antenna element configured to be used as an antenna element in an array antenna, the node comprising:

• an internal clock;
• a transceiver circuitry configured to transmit and receive signals over at least a first communication channel and a second communication channel with non-equal speed of propagation, over the at least one antenna element;
• and
• a processor;
• wherein the node is configured to identify if a reset signal has been received over the first communication channel, and
• when the reset signal has been identified, the node is further configured to
• a) adjust the internal clock based on the reset signal, transmit an acknowledgement signal in response to the received reset signal, and initiate an acknowledgement process, or
• when the reset signal has not been identified, the node is further configured to
• b) transmit the reset signal over the first communication channel and receive a response signal in response to the transmitted reset signal from the at least one other node, and
• b1) if the response signal is an acknowledgement signal, the node is configured to initiate an acknowledgement process, or
• b2) if the response signal is a non-acknowledgement signal, the node is configured to adjust the internal clock based on the received non-acknowledgement signal and initiate the acknowledgement process;
• and
• wherein, to perform the acknowledgement process, the node is further configured to
• c) determine a distance to the at least one other node by measuring a travelling time for a signal over the second communication channel, exchange distance information with the at least one other node, and fine tune the internal clock of each node based on the distance information when transmitting over the first communication channel.

A method in a node for determining distance between nodes in a sensor network comprising a plurality of nodes, each node having at least one antenna element configured to be used as an antenna element in an array antenna, a unique identity, and the nodes being located at an arbitrary distance from each other, wherein each node comprises a processor, a memory, an internal clock, and a transceiver circuitry configured to transmit and receive signals over at least a first communication channel and a second communication channel with non-equal speed of propagation over the at least one antenna element, the method comprising:

• identifying if a reset signal has been received over the first communication channel;
• and
• when the reset signal has been identified, adjusting the internal clock based on the reset signal, transmitting an acknowledgement signal in response to the received reset signal, and initiating an acknowledgement process, or
• when the reset signal has not been identified, transmitting the reset signal over the first communication channel and receiving a response signal in response to the transmitted reset signal from at least one of the plurality of nodes;
• and
• i) if the response signal is an acknowledgement signal, initiating the acknowledgement process, or
• ii) if the response signal is a non-acknowledgement signal, adjusting the internal clock based on the received non-acknowledgement signal and initiating the acknowledgement process;
• wherein the acknowledgement process involves,
• determining a distance to one of the plurality of nodes by measuring a travelling time for a signal over the second communication channel;
• exchanging distance information with one of the plurality of nodes;
• and
• fine tuning the internal clock of each node based on the distance information when transmitting over the first communication channel.