Sidelink Doppler Correction for Optimal Mobile Communications in 5G/6G
Direct communication between vehicles or other mobile wireless users is permitted in 5G and 6G, but the problem of Doppler frequency offsets remains unsolved. Now, methods are provided by which the mobile devices can exchange their geometrical parameters location, speed, and travel direction-in an initial message, thereby providing sufficient information for each user to calculate the net frequency shift according to the relative (vectorial) motions of the two wireless devices. Thereafter, they can both use the corrected frequency for optimal communication performance. Optionally, the initial message may be transmitted using “slow” transmission parameters, configured to enable User-2 to demodulate despite the frequency shift. Multiple versions and methods are included.
1 . A method for mobile wireless user devices to compensate for Doppler frequency shifts, the method comprising:
a) determining, by a first mobile wireless user device (“User-1”), a location, a speed, and a travel direction of User-1;
b) transmitting or broadcasting, by User-1, a first message indicating the location, speed, and travel direction of User-1;
c) receiving, by User-1, a second message from a second mobile wireless user device (“User-2”), the second message indicating a location, speed, and travel direction of User-2; and
d) calculating, by User-1, a Doppler frequency shift (“Δf”) according to a relative motion of User-2 relative to User-1.
2 . The method of claim 1 , wherein the first message is transmitted according to 5G or 6G technology.
3 . The method of claim 1 , wherein the first message is transmitted or broadcasted, by User-1, at a predetermined sidelink frequency (“f o ”) allocated for communications between mobile wireless user devices.
4 . The method of claim 3 , wherein the second message is transmitted, by User-2, at a transmission frequency that is received, by User-1, at the predetermined sidelink frequency f o .
5 . The method of claim 3 , further comprising:
a) calculating, by User-1, a Doppler-corrected transmission frequency (“f c ”) comprising the Doppler frequency shift Δf added to, or subtracted from, the predetermined sidelink frequency f o , according to the relative motion of User-2 relative to User-1.
6 . The method of claim 5 , wherein:
a) the Doppler-corrected transmission frequency f c is configured to be received, by User-2, Doppler shifted to the predetermined sidelink frequency f o .
7 . The method of claim 5 , further comprising:
a) transmitting, by User-1, to User-2, a third message transmitted at the Doppler-corrected transmission frequency f c .
8 . The method of claim 5 , further comprising:
a) periodically determining, by User-1, updated values of the location, speed, and direction of User-1;
b) periodically calculating, by User-1, updated values of the location, speed, and direction of User-2; and
c) periodically calculating, by User-1, an updated value of the Doppler frequency shift Δf.
9 . The method of claim 5 , wherein:
a) the first message is transmitted or broadcasted, by User-1, according to a slow transmission protocol and the third message is transmitted, by User-1, according to a fast transmission protocol, wherein the fast transmission protocol comprises a higher data rate or information density than the slow transmission protocol.
10 . A method for a first wireless user device (“User-1”) to communicate with a second wireless user device (“User-2”), the method comprising:
a) transmitting or broadcasting, by User-1, a first message indicating a location, a speed, a travel direction of User-1, and a wireless address or identification of User-1;
b) wherein the first message is transmitted or broadcasted at a predetermined sidelink frequency (“f o ”) allocated for communications directly between user devices; and wherein
c) the first message is transmitted or broadcasted according to parameters (“slow” parameters) configured to enable User-2 to receive and demodulate the first message, notwithstanding a Doppler frequency shift caused by a relative motion of User-2 relative to User-1.
11 . The method of claim 10 , further comprising:
a) receiving, by User-1, a second message, transmitted by User-2;
b) wherein the second message is transmitted at the predetermined sidelink frequency f o ;
c) the second message is received, by User-1, at a reception frequency different from the predetermined sidelink frequency, according to the Doppler frequency shift; and
d) the second message indicates a location, a speed, and a travel direction of User-2.
12 . The method of claim 11 , further comprising:
a) after receiving the second message, adjusting, by User-1, an adjusted reception frequency comprising the Doppler frequency shift added to or subtracted from the predetermined sidelink frequency f o ; and
b) receiving subsequent messages from User-2 at the adjusted reception frequency.
13 . The method of claim 12 , further comprising:
a) transmitting, by User-1, a third message to User-2, wherein the third message is transmitted at the predetermined sidelink frequency f o ; and
b) wherein the third message is transmitted according to further parameters (“fast” parameters) comprising a higher data rate or information density than the slow parameters.
14 . The method of claim 11 , further comprising:
a) after receiving the second message, changing, by User-1, the travel direction and/or speed of User-1; and
b) transmitting a correction message, by User-1 to User-2, wherein the correction message indicates an updated or changed location, speed, and travel direction of User-1;
c) wherein the correction message is transmitted at the predetermined sidelink frequency f o .
15 . The method of claim 14 , wherein:
a) the correction message is transmitted according to the slow parameters.
16 . The method of claim 10 wherein either:
a) User-1 is a mobile wireless user device and User-2 is a stationary wireless user device; or
b) User-2 is a mobile wireless user device and User-1 is a stationary wireless user device, or
c) User-1 is a mobile wireless user device and User-2 is a mobile wireless user device.
17 . A method for a first mobile wireless user device (“User-1”) to communicate with a second mobile wireless user device (“User-2”), the method comprising:
a) receiving, by User-1, a first message transmitted by User-2, wherein the first message indicates a location, a speed, and a travel direction of User-2, and wherein the first message is transmitted on a predetermined sidelink frequency (“f o ”) allocated for sidelink communications;
b) determining, by User-1, a location, a speed, and a travel direction of User-1;
c) calculating, by User-1, a relative motion of User-2 relative to User-1 by comparing the location, speed, and travel direction of User-2 with the location, speed, and travel direction of User-1; and
d) calculating, by User-1, a Doppler frequency shift Δf, relative to the predetermined sidelink frequency f o , according to the relative motion of User-2 relative to User-1.
18 . The method of claim 17 wherein:
a) the first message further comprises a “carrier field” comprising an interval of unmodulated signal transmitted at the predetermined sidelink frequency f o .
19 . The method of claim 17 , further comprising:
a) transmitting, by User-1, a second message to User-2, at a Doppler-corrected frequency comprising the predetermined sidelink frequency f o increased or decreased by the Doppler frequency shift Δf, according to the relative motion of User-2 relative to User-1;
b) wherein the second message indicates the location, speed, and travel direction of User-1.
20 . The method of claim 17 , further comprising:
a) calculating, and continuing to calculate, an updated relative location of
User-2 relative to User-1 according to the location, speed, and travel direction of User-2 as indicated in the first message, and according to updated determinations, by User-1, of the location, speed, and travel direction of User-1;
b) calculating, and continuing to calculate, updated values of the Doppler frequency shift Δf according to the updated locations, speeds, and travel directions of User-1 and User-2; and
c) transmitting, by User-1, to User-2, a third message at a Doppler-corrected frequency comprising the predetermined sidelink frequency f o plus or minus the updated Doppler frequency shift Δf.