Wireless sensor transmission method and apparatus
Methods and apparatus are described for transmitting messages by sensors in a system, such as a home security system. The messages are deemed received only when a sensor receives both an acknowledgement and a response from a central controller, and retransmissions occur when either an acknowledgement or a response is not received.
1 . A method, performed by a wireless sensor for efficient message transmission by the wireless sensor, comprising:
using a public key received from the controller during a public key exchange with the controller to establish a shared secret;
determining, by a processor, an occurrence of an event in proximity to the wireless sensor via a signal received from a detector coupled to the processor, the event causing a change in a state of a barrier being monitored by the wireless sensor;
in response to determining that the event has occurred, using, by the processor, the shared secret to generate an encrypted frame, comprising an unencrypted, unique identification of the wireless sensor and an encrypted event identification that identifies the state of the barrier resulting from the event that has occurred;
transmitting, by the processor via a mesh-network transceiver coupled to the processor, the encrypted frame;
determining, by the processor, an occurrence of a further event in proximity to the wireless sensor via a further signal received from the detector coupled to the processor, the further event causing a subsequent change in a state of the barrier being monitored by the wireless sensor;
determining, by the processor via the mesh-network transceiver, whether a first message from a central controller in communication with the wireless sensor that the encrypted frame was received;
determining, by the processor via the mesh-network transceiver, whether a second message, transmitted separately from the first message, from the controller that the frame was decrypted successfully was received; and
in response to determining that the further event has occurred and only when both the first message and the second message have been determined to be received, using, by the processor, the shared secret to generate a further encrypted frame, comprising the unencrypted, unique identification of the wireless sensor and an encrypted event identification that identifies the subsequent state of the barrier resulting from the further event that has occurred.
2 . The method as recited in claim 1 , wherein the encrypted frame further comprises an unencrypted preamble, an unencrypted system identification, an unencrypted indication of a length of the encrypted frame, and an unencrypted checksum.