Method for measuring time of arrival of signals in a communications network
View Patent ↗A method for measuring the Time Of Arrival of signals in a communications network is provided. A transmitter emits a beacon that is a digital message of known content, followed by timing information. The message is preceded by a pseudo-random binary phase-shift keying (BPSK) modulated sequence that allows the receiver to synchronize on the received signal using the autocorrelation method. During the synchronization process, are computed the approximated Time Of Arrival (TOA) and approximated frequency difference between the local oscillator and the received signal. The content of the beacon message is then used for correcting the approximated TOA and the frequency differences, providing results of very high precision of TOA. The timing information that follows the beacon is used for network clock synchronization and for computing the distances between network nodes.
1. A method of communication of a message within an ad hoc network comprising:
transmitting a beacon from a first node, wherein the beacon comprises a digital message of a known content;
receiving the digital message at a second node;
synchronizing at the second node on the received digital message using an autocorrelation method, wherein the synchronizing step comprises:
computing an approximated time of arrival,
computing an approximated frequency difference between a local oscillator and the received digital message; and
correcting the approximated time of arrival and the frequency difference.
2. A method of operation of a node within a wireless network comprising:
receiving a digital message from a neighbor node;
recording a time of arrival of the received digital message; and
correcting the time arrival of the received digital message, wherein the correcting of the time of arrival comprises computing one or more relative corrections selected from a group comprising relative speeds of nodes, relative differences of oscillators' frequencies, and virtual ranges between nodes.
3. A method of operation of a node within a wireless network as claimed in claim 2 , wherein the receiving step comprises receiving the digital message including a timing message, wherein the timing message comprises:
a message preamble,
a beacon message, and
a timing information.
4. A method of operation of a node within a wireless network as claimed in claim 3 , wherein the message preamble comprises a pseudo random code pn sequence in binary phase-shift keying modulation, and further wherein the correcting step comprises:
synchronizing a receiver to the digital message signal,
identifying an approximated time of arrival, and
identifying an approximated frequency difference.
5. A method of operation of a node within a wireless network as claimed in claim 3 , wherein the beacon message comprises:
a sequence of (I,Q) samples modulated in amplitude and phase according with one or more defined functions.
6. A method of operation of a node within a wireless network as claimed in claim 3 , wherein the timing information comprises:
a list of neighbor nodes from which one or more messages have been received, along with the Time Of Arrival, the measured frequency shift and the measured frequency drift of each received message.
7. A method of operation of a node within a wireless network as claimed in claim 6 , wherein the timing information further comprises:
a time, according to a local clock, when a message was transmitted.
8. A node within an ad hoc wireless communication network comprising:
a transceiver for communicating one or more messages with one or more other nodes within the ad hoc wireless communication network using quadrature amplitude modulation;
a clock register for determining a current time;
a memory for storing one or more time of arrival calculations and one or more algorithms;
a local oscillator; and
a time of arrival calculator coupled to the transceiver, the clock register, the local oscillator, and the memory for determining a time of arrival of one or more received messages,
wherein the time of arrival calculator uses the stored one or more algorithms to:
synchronize a received digital message using an autocorrelation message including:
retrieving a time of arrival from the clock register,
computing an approximated frequency difference between the local oscillator and the received digital message, and
correcting the approximated time of arrival and the frequency difference.
9. A node within an ad hoc wireless communication network as claimed in claim 8 , wherein the correcting comprises computing one or more relative corrections selected from a group comprising relative speeds of nodes, relative differences of oscillators' frequencies, and virtual ranges between nodes.
10. A node within an ad hoc wireless as claimed in claim 8 , wherein the received digital message comprises a timing message, and further wherein the timing message comprises:
a message preamble,
a beacon message, and
a timing information.
11. A node within an ad hoc wireless as claimed in claim 10 , wherein the message preamble comprises a pseudo random code pn sequence in binary phase-shift keying modulation, and further wherein the correcting comprises:
synchronizing a receiver to the digital message signal,
identifying an approximated time of arrival, and
identifying an approximated frequency difference.
12. A node within an ad hoc wireless as claimed in claim 10 , wherein the beacon message comprises:
a sequence of (I,Q) samples modulated in amplitude and phase according with one or more defined functions.
13. A node within an ad hoc wireless as claimed in claim 10 , wherein the timing information comprises:
a list of neighbor nodes from which one or more messages have been received, along with the Time Of Arrival, the measured frequency shift and the measured frequency drift of each received message.
14. A node within an ad hoc wireless as claimed in claim 10 , wherein the timing information further comprises:
a time, according to a local clock, when a message was transmitted.