Asynchronous dynamic network discovery for low power systems
View Patent ↗An ad hoc method is provided for synchronizing a wireless network. The method involves broadcasting a first signal including a join message from a first node (FN). The method also involves saving a first timestamps in a memory device internal to the FN after broadcasting the first signal. The method further involves generating a signal including a join response message after receiving the first signal. The join response message is comprised of a second timestamp indicating a local time during which the first signal was received at the second node (SN). The method also includes the step of determining an initial time offset by computing a difference between the first timestamp and the second timestamp. The method further includes the steps of generating a request to send (RTS) message at the FN. The FN uses the initial time offset in conjunction with the RTS message to asynchronously communicate with the SN.
1. A method for synchronizing a wireless network, comprising:
defining a first epoch at a first node to include a first continually repeated timing cycle at said first node;
defining a second epoch at a second node to include a second continually repeated timing cycle at said second node;
broadcasting a first signal including a join message from said first node;
generating a first timestamp value representing a duration of time between a beginning of said first epoch and a time when said first signal including said join message is broadcasted;
saving said first timestamp in a memory device internal to said first node;
generating at said second node a second signal including a join response message after receiving said first signal, said join response message comprising a second timestamp selected to be a value representing a duration of time between a beginning of said second epoch and a time when said first signal is received at said second node;
determining an initial time offset by computing a difference between said first timestamp and said second timestamp;
using said initial time offset, exclusive of any additional timing information received from said second node, to determine a time period associated with an active portion of a receiver duty cycle at said second node, and to synchronize a timing of a subsequent communication between said first node and said second node; and
selectively transmitting said subsequent communication from said first node to said second node exclusively during said active portion of said receiver duty cycle;
wherein said active portion of a receiver duty cycle begins at a time determined by the beginning of said first epoch at said first node, plus an increment defined by said initial time offset.
2. The method according to claim 1 , further comprising operating said first node and said second node so that said first epoch and said second epoch are asynchronous.
3. The method according to claim 1 , wherein said time offset represents a difference in a start time of said first epoch and said second epoch.
4. The method according to claim 1 , further comprising selectively activating an RF receiver in at least said second node in accordance with a predetermined duty cycle to cause said RF receiver activation during a period of time that is less than a duration of said second epoch.
5. The method according to claim 4 , further comprising generating at least one request to send (RTS) message at said first node to initiate a data communication with said second node, and generating a time stamp when each said RTS message is transmitted to said second node, said time stamp representing a duration of time from a beginning of said first epoch to a time when said RTS message is transmitted.
6. The method according to claim 5 , further comprising generating at least one clear to send (CTS) message at said second node to acknowledge said RTS message, said CTS message including a time stamp identifying when said RTS message was received at said second node relative to a beginning of said second epoch.
7. The method according to claim 6 , further comprising processing said CTS message at said first node to update said value of said initial time offset to obtain an updated time offset value.
8. The method according to claim 7 , further comprising selectively communicating a data message from said first node to said second node exclusively during a time corresponding to said RF receiver predetermined duty cycle.
9. A method for synchronizing a wireless network, comprising:
defining a first epoch at a first node to include a first continually repeated timing cycle at said first node;
defining a second epoch at a second node to include a second continually repeated timing cycle at said second node;
broadcasting a first signal including a join message from said first node;
generating a first timestamp in a memory device corresponding to a broadcast time of said first signal, said first timestamp selected to be a value representing a duration of time between a beginning of said first epoch and a time when said first signal is broadcasted;
generating at said second node a second signal including a join response message after receiving said first signal, said join response message comprising a second timestamp selected to be a value representing a duration of time between a beginning of said second epoch and a time when said first signal is received at said second node;
determining a time offset by computing a difference between said first timestamp and said second timestamp;
using said time offset at said first node, exclusive of any additional timing information received from said second node, to determine a time period associated with an active portion of an RF receiver duty cycle at said second node, to synchronize a timing of a subsequent communication between said first node and said second node;
selectively transmitting said subsequent communication from said first node to said second node exclusively during said active portion of said RF receiver duty cycle.
10. The method according to claim 9 , further comprising selecting said active portion of said RF receiver duty cycle to be less than an entire duration of said second epoch.
11. The method according to claim 9 , further comprising operating said first node and said second node asynchronously so that said first epoch and said second epoch are not synchronized.
12. The method according to claim 9 , wherein said time offset represents a difference in a start time of said first epoch and said second epoch.
13. The method according to claim 10 , further comprising periodically updating said time offset value.
14. The method according to claim 13 , further comprising using a request to send (RTS) message, and a clear to send (CTS) message to update said time offset value.
15. The method according to claim 14 , further comprising generating an RTS time stamp for transmission of said RTS message, and a CTS time stamp for receipt of said RTS message.
16. The method according to claim 15 , further comprising calculating an updated value of said time offset using said RTS time stamp and said CTS time stamp.
17. The method according to claim 9 , wherein said active portion of a receiver duty cycle begins at a time determined by the beginning of said first epoch at said first node, plus an increment defined by said initial time offset.