Sidelink communications in cellular communication networks
According to an example aspect of the present invention, there is provided a method comprising, determining, by a network node, a timing offset (TO A ) of a first wireless link, determining, by the network node, a timing offset (TO B ) of a second wireless link, determining, by the network node, a timing offset (TO C ) of a third wireless link, calculating, by the network node, a timing calibration value of the first sidelink device using the timing offset (TO A ) of the first wireless link, the timing offset (TO B ) of the second wireless link and the timing offset (TO C ) of the third wireless link and transmitting, by the network node, at least the timing calibration value of the first sidelink device.
1 . A method, comprising:
determining, by a network node, a timing offset (TO A ) of a first wireless link, wherein the first wireless link comprises a link between a wireless network node and a first sidelink device, and the timing offset (TO A ) of the first wireless link is based on a calculated two-way delay of the first wireless link and a measured two-way delay of the first wireless link;
determining, by the network node, a timing offset (TO B ) of a second wireless link, wherein the second wireless link comprises a link between the wireless network node and a second sidelink device, and the timing offset (TO B ) of the second wireless link is based on a calculated two-way delay of the second wireless link and a measured two-way delay of the second wireless link;
determining, by the network node, a timing offset (TO C ) of a third wireless link, wherein the third wireless link comprises a link between the first sidelink device and the second sidelink device and the timing offset (TO C ) of the third wireless link is based on a calculated two-way delay of the third wireless link and a measured two-way delay of the third wireless link;
calculating, by the network node, a timing calibration value of the first sidelink device using the timing offset (TO A ) of the first wireless link, the timing offset (TO B ) of the second wireless link and the timing offset (TO C ) of the third wireless link; and
transmitting, by the network node, at least the timing calibration value of the first sidelink device, wherein the network node comprises a network node in a core network, and wherein the method further comprises:
prioritizing base stations based on timing calibration values of said base stations and transmitting to sidelink devices an ordered list of said base stations for initiating a timing calibration procedure; and/or
selecting a group of base stations based on timing calibration values of said group of base stations and transmitting information about the group to sidelink devices for clock alignment.
2 . The method according to claim 1 , wherein the network node comprises the wireless network node or a network node in a core network.
3 . The method according to claim 1 , wherein a timing offset is determined by subtracting a calculated two-way delay of a corresponding wireless link from a measured two-way delay of the corresponding wireless link.
4 . The method according to claim 1 , wherein the timing calibration value (SL1) of the first sidelink device is calculated as follows:
SL 1=½ TO C +½ TO A −½ TO B .
5 . The method according to claim 1 , wherein the timing calibration value (SL2) of the second sidelink device is calculated as follows:
SL 2=½ TO C +½ TO B −½ TO C .
6 . The method according to claim 1 , wherein the timing calibration value (NW) of the wireless network node is calculated as follows:
NW=TO A −SL 1.
7 . The method according to claim 1 , wherein the calculated two-way delay is two times a propagation delay between a transmitter and a receiver.
8 . The method according to claim 1 , wherein a measured two-way delay comprises a sum of two times a propagation delay between a transmitter and a receiver, a transmission and a reception delay at the transmitter, and a transmission and a reception delay at the receiver.
9 . The method according to claim 1 , wherein the calculated two-way delay is calculated based on a locations of a transmitter and a location of a receiver.
10 . The method according to claim 1 , further comprising:
detecting, before said determining steps, that there is a line-of-sight connection on the first wireless link, the second wireless link, and the third wireless link.
11 . The method according to claim 1 , wherein the network node comprises the wireless network node, and wherein the method further comprises:
transmitting the timing calibration value of the first sidelink device to the first sidelink device; and/or
transmitting the timing calibration value of the second sidelink device to the second sidelink device.
12 . The method according to claim 1 , further comprising:
calculating a timing calibration value of the wireless network node and a timing calibration value of the second sidelink device using the timing offset (TO A ) of the first wireless link, the timing offset (TO B ) of the second wireless link and the timing offset (TO C ) of the third wireless link.
13 . The method according to claim 1 , further comprising:
transmitting a request to the first sidelink device, to request the first sidelink device to measure the two-way delay of the third wireless link; and
receiving the measured two-way delay of the third wireless link from the first sidelink device.
14 . An apparatus, comprising:
at least one processing core; and
at least one memory including computer program code, the at least one memory and the computer program code being configured to, with the at least one processing core, cause the apparatus at least to:
determine a timing offset (TO A ) of a first wireless link, wherein the first wireless link comprises a link between a wireless network node and a first sidelink device, and the timing offset (TO A ) of the first wireless link is based on a calculated two-way delay of the first wireless link and a measured two-way delay of the first wireless link;
determine a timing offset (TO B ) of a second wireless link, wherein the second wireless link comprises a link between the wireless network node and a second sidelink device, and the timing offset (TO B ) of the second wireless link is based on a calculated two-way delay of the second wireless link and a measured two-way delay of the second wireless link;
determine a timing offset (TO C ) of a third wireless link, wherein the third wireless link comprises a link between the first sidelink device and the second sidelink device and the timing offset (TO C ) of the third wireless link is based on a calculated two-way delay of the third wireless link and a measured two-way delay of the third wireless link;
calculate a timing calibration value of the first sidelink device using the timing offset (TO A ) of the first wireless link, the timing offset (TO B ) of the second wireless link and the timing offset (TO C ) of the third wireless link; and
transmit at least the timing calibration value of the first sidelink device, wherein the apparatus comprises a network node in a core network, and wherein the apparatus is further caused to:
prioritize base stations based on timing calibration values of said base stations and transmitting to sidelink devices an ordered list of said base stations for initiating a timing calibration procedure; and/or
select a group of base stations based on timing calibration values of said group of base stations and transmitting information about the group to sidelink devices for clock alignment.