Phase-shift guard-space timestamp point for 5G/6G synchronization
A base station can cause a multitude of user devices in a network to be synchronized with the base station's clock using an ultra-lean low-complexity procedure in 5G or 6G. On a predetermined interval, the base station can transmit a timing signal in the guard-space of a predetermined resource element. The timing signal is a 180-degree phase reversal of the cyclic prefix centered in the guard-space. Each user device can receive the timing signal, determine how far the received timestamp point is from the middle of the guard-space (as viewed by the user device), and thereby determine a timing error between the user device clock and the base station clock, and correct the user device clock accordingly. In addition, the user device can average the timing adjustments over a number of instances, thereby determining a frequency offset if the average differs significantly from zero, and thereby adjust the clock frequency.
1. A method for a base station of a wireless network to provide synchronization signals, the method comprising:
a) transmitting a signal occupying a single symbol-time of a resource grid, the signal comprising a first guard-space portion followed by a second guard-space portion followed by a message portion;
b) wherein the message portion comprises a final region at an ending of the symbol-time, and a pre-final region immediately preceding the final region;
c) wherein the second guard-space portion is a copy of the signal in a final region of the message portion; and
d) wherein the first guard-space portion comprises a phase-shifted copy of the signal in the pre-final region of the message portion.
2. The method of claim 1 , wherein the message portion is transmitted according to 5G or 6G technology.
3. The method of claim 1 , wherein the phase-shifted copy of the signal in the pre-final region is phase-shifted by a multiple of 90 degrees relative to the signal in the pre-final region.
4. The method of claim 1 , wherein:
a) the signal occupies a particular subcarrier and a particular symbol-time of the resource grid during downlink-scheduled symbol-times; and
b) the particular subcarrier and the particular symbol-time are specified in a system information message.
5. The method of claim 4 , wherein:
a) the particular subcarrier is adjacent to a first subcarrier at a higher frequency and a second subcarrier at a lower frequency; and
b) zero power is transmitted, during the single symbol-time, in the first subcarrier and in the second subcarrier.
6. The method of claim 1 , wherein the signal comprises an OFDM (orthogonal frequency-division multiplexing) symbol comprising a sum of multiple subcarrier signals.
7. The method of claim 1 , wherein a duration of the first guard-space portion is equal to a duration of the second guard-space portion.
8. The method of claim 1 , further comprising:
a) constructing a reconstructed cyclic prefix by inverting a phase of the first guard-space portion and appending the second guard-space portion; and
b) performing signal processing on a signal comprising the reconstructed cyclic prefix concatenated with the message portion.
9. A method for a user device of a wireless network to receive synchronization signals, the method comprising:
a) receiving a signal occupying a single symbol-time of a resource grid, the signal comprising a first guard-space portion followed by a second guard-space portion followed by a message portion;
b) wherein the message portion comprises a final region at an ending of the symbol-time, and a pre-final region immediately preceding the final region;
c) comparing the signal in the second guard-space portion to the signal in the final region of the message portion;
d) comparing the signal in the first guard-space portion to the signal in the pre-final region, phase-shifted according to a predetermined phase shift;
e) determining, according to the comparing, a timestamp time corresponding to a boundary between the first guard-space portion and the second guard-space portion; and
f) adjusting a clock setting of the user device, according to the timestamp time, to bring the clock of the user device into agreement with a clock of a base station of the wireless network.
10. The method of claim 9 , wherein the predetermined phase shift is a non-zero multiple of 90 degrees.
11. The method of claim 9 , wherein the signal occupies a single subcarrier and a single symbol-time of the resource grid, the subcarrier and symbol-time specified by a system information message.
12. The method of claim 9 , wherein the signal comprises an OFDM (orthogonal frequency-division multiplexing) symbol comprising a sum of multiple subcarrier signals.
13. The method of claim 9 , further comprising:
a) calculating an error comprising:
i) a difference between the signal in the first guard-space portion and the signal in the pre-final region of the message portion phase-shifted according to the predetermined phase shift; plus
ii) a difference between the signal in the second guard-space portion and the signal in the final region of the message portion;
b) varying a time of a boundary between the first guard-space portion and the second guard-space portion; and
c) determining, according to the varying, a particular time of the boundary at which the error is minimized.
14. The method of claim 9 , wherein the adjusting the clock setting of the user device comprises:
a) determining a time error comprising a magnitude of a difference between the timestamp time and a midpoint of the guard-space;
b) when the timestamp time occurs earlier than the midpoint of the guard-space, adding the time error to the clock setting of the user device; and
c) when the timestamp time occurs later than the midpoint of the guard-space, subtracting the time error from the clock setting of the user device.
15. A method for a user device, of a wireless network comprising a base station, to adjust a clock frequency, the method comprising:
a) periodically receiving a guard-space timestamp point comprising a 180 degree phase reversal of a signal in a guard-space of a predetermined resource element;
b) upon receiving each timestamp point, determining a timing correction according to a time difference comprising a time of the timestamp point minus a time of a midpoint of the guard-space, and applying a time correction to a clock of the user device according to the time difference;
c) after receiving at least integer N timestamp points, determining an average of N time differences;
d) calculating a frequency offset comprising the average of N time differences, times a frequency of the clock of the user device, divided by an interval between the timestamp points; and
e) adjusting the frequency of the clock of the user device according to the frequency offset.
16. The method of claim 15 , wherein:
a) the interval between the timestamp points comprises an integer M of subframes; and
b) the integer M is specified by the base station in a system information message.
17. The method of claim 15 , further comprising:
a) when the average of N time differences is positive, reducing the frequency of the clock of the user device by the frequency offset; and
b) when the average of N time differences is negative, increasing the frequency of the clock of the user device by the frequency offset.
18. The method of claim 15 , further comprising, when a magnitude of the average of N time differences is below a predetermined threshold, declining to adjust the frequency of the clock of the user device.
19. The method of claim 15 , further comprising:
a) determining that the user device is in motion; and
b) transmitting a request message to the base station, requesting that the interval between the timestamp points be reduced.
20. The method of claim 15 , further comprising:
a) determining that the clock of the user device has a rate of drift above a predetermined threshold; and
b) transmitting a request message to the base station, requesting that the interval between the timestamp points be reduced.