Synchronization apparatus and method

Patent metadata

Field	Value
Publication number	US-9577702-B2
Application number	US-201514849304-A
Country	US
Kind code	B2
Filing date	Sep 9, 2015
Priority date	Sep 30, 2014
Publication date	Feb 21, 2017
Grant date	Feb 21, 2017

Abstract

A system and a method for time synchronization on a wireless network, based on the exchange of Chirp Spread Spectrum information. Time signals are broadcast from a master ( 40 ) to a plurality of slave devices ( 101, 102, 103 ). The modulation used includes a compensation of offsets in the master's system clock by symbol-wide frequency shifts that is particularly precise, fine and simple to implement. The system and method of the invention are particularly suitable for synchronizing a telecommunication cell network.

First claim

The invention claimed is:

1. A system comprising at least a timing slave device and a timing master device, wherein each timing slave device includes or has access to a time reference, wherein the timing master comprises or has access to a master time reference, wherein said timing master device and said timing slave device are operatively arranged for transmitting and receiving radio signals, characterized in that the timing master is operatively arranged for transmitting time signals to said slave device said time signals comprising a plurality of frequency chirps encoding an absolute time information derived from the time reference of the timing master, for time-stamping the time signals received from the timing master by the timing slave device and for synchronizing its time reference with the time reference of the timing master based on the time stamps, on a propagation time to the timing master, and on said frequency chirps.

2. The system of claim 1 , wherein said devices have a ranging mode, allowing to determine the propagation time between the slave device and the timing master device.

3. The system of claim 1 , whereby the timing master has a system clock and is operatively arranged to compensate an offset between the system clock and the master time reference by shifting the frequency of each chirp by an amount based on said offset and on a frequency slope of the chirp.

4. The system of claim 1 , wherein, in the ranging mode, the at least one timing slave is arranged to send a ranging request to the timing master, wherein the timing master is arranged to reply with a ranging reply comprising frequency chirps whose frequencies and phases are aligned with the time reference of the timing slave device.

5. The system of claim 4 , wherein the ranging request comprises an authentication of the timing slave device, and the timing master is arranged for replying only to ranging requests coming from authorized timing slave devices.

6. The system of claim 2 , wherein the ranging is initiated by the slave, or wherein the ranging is initiated by the master who transmits the resulting propagation time to the slave.

7. The system of claim 1 , wherein the time signals are broadcast signal, receivable and capable of being processed by a plurality of timing slave devices.

8. The system of claim 1 , wherein said timing master is arranged for sending a plurality of time signals according to a predetermined sequence.

9. The system of claim 8 , wherein said sequence is a periodic sequence or a pseudorandom sequence.

10. The system of claim 6 , wherein the timing slave devices are arranged to calibrate their time references based on the timestamps of the received time signals.

11. The system of claim 1 , wherein the slaves are arranged to average several time signals.

12. The system of claim 1 , wherein one or more of said ranging requests, ranging reply and time signals are transmitted through a diversity of antennas at a transmitter and/or at a receiver side, or through a diversity of frequencies.

13. The system of claim 1 , wherein the master timing device and the slave timing devices are part of a cellular telephone network.

14. A method of synchronizing time across a wireless radio link comprising broadcasting by a master device a plurality of time signals comprising a plurality of frequency chirps according to a predetermined time sequence, on said radio link, receiving and time stamping said time signals on said radio link by one or more slave devices, characterized in that an absolute time information is encoded in the plurality of frequency chirps.

15. The method of claim 14 , wherein the frequency chirps are compensated to account for an offset relative to a master time reference by shifting the frequency of each chirp by an amount based on said offset and on a frequency slope of the chirp.

16. The method of claim 13 , including calibrating a time reference of said timing slave device based on the time stamps of the received time signals.

17. The method of claim 13 , comprising obtaining a propagation time from the master device to the one or more slave devices by exchanging chirp-encoded ranging messages between them.

Assignees

• Semtech Corp

Inventors

• Seller Olivier Bernard Andre

Classifications

• H04B1/69 Primary

  Spread spectrum techniques · CPC title

• H04L7/033

  using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop · CPC title

• H04W56/0035

  detecting errors in frequency or phase · CPC title

• H04B2001/6912

  using chirp · CPC title

• H04J3/0667

  Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays (arrangements for monitoring round trip delays in packet switching networks H04L43/0864) · CPC title