# US 11,910,339 B2 · Methods and systems for uplink time synchronization in non-terrestrial networks based communication

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- Number: US 11,910,339 B2
- Document ID: US11910339B2
- Status: Granted
- Kind: B2
- Application number: 17/451,952
- Filed: 2021-10-22
- Published: 2022-04-28
- Granted: 2024-02-20
- Earliest claimed: 2020-10-23
- Assignees: Centre of Excellence in Wireless Technology; Indian Institute of Technology Madras (Iit Madras)
- Applicants: Centre of Excellence in Wireless Technology; Indian Institute of Technology Madras (IIT Madras)
- Inventors: Abhijeet Abhimanyu Masal; Priyanka Dey; Sunil Kaimalettu; Jeniston Deviraj Klutto Milleth; Bhaskar Ramamurthi
- Web page: https://patentgrep.com/patent/US11910339B2

## CPC

- H04W 56/001: {Synchronization between nodes}
- G01S 19/38: Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
- G01S 19/46: the supplementary measurement being of a radio-wave signal type
- H04B 7/18513: {Transmission in a satellite or space-based system}
- H04L 5/0048: {Allocation of pilot signals, i.e. of signals known to the receiver (allocation of control signalling H04L5/0053; use of control signalling H04L5/0091)}
- H04W 56/0045: {compensating for timing error by altering transmission time}
- H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72)
- G01S: RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A system and a method for performing uplink (UL) time synchronization in non-terrestrial networks (NTN) include Performing Downlink (DL) synchronization SSB signals. At least one information is received by a UE 102 from an NTN BS 104. A location information of a satellite is obtained using the at least one information received by the UE 102. Location of the UE 102 is estimated using one of GNSS receiver of the UE 102 and by processing at least one reference signal received by the UE 102 from multiple NTN-BS 104, using at least one multilateration technique and RTK. Timing Advance (TA) estimate is determined using the location of the satellite and location of the UE 102. TA applied is determined using the TA estimate and TA margin. PRACH is transmitted based on the TA applied and an information related to the TA applied is reported to the NTN-BS 104. Residual TA is estimated using the reported information related to the TA applied and the detected PRACH. The residual TA is indicated to the UE 102 for subsequent UL transmissions, in order to achieve the UL time synchronization in the NTN based communication network.

## Claims

### Claim 1

A method for performing Uplink (UL) time synchronization in a Non-Terrestrial Network (NTN) based communication network, the method comprising:
performing Downlink (DL) synchronization using Synchronization Signal Block (SSB) signals;
receiving, by a UE (102), at least one information from an NTN Base Station (BS) (104);
obtaining a location information of a satellite using the at least one information received by the UE (102);
estimating the location of the UE (102) using one of Global Navigation Satellite System (GNSS) receiver of the UE (102) and by processing at least one reference signal received by the UE (102) from multiple NTN BS (104), using at least one multilateration technique and Real-Time Kinematic (RTK);
determining Timing Advance (TA) estimate using the location of the satellite and location of the UE (102);
determining TA applied using the TA estimate and TA margin, wherein the TA margin is a value ranging from zero to a step size value (TAstep);
transmitting, by the UE (102), a Physical Random Access Channel (PRACH) based on the TA applied;
reporting, by the UE (102), an information related to the TA applied to the NTN-BS (104);
estimating, by the NTN-BS (104), residual TA using the reported information related to the TA applied and the detected PRACH and
indicating the residual TA to the UE (102) for subsequent UL transmissions, thereby achieving the UL time synchronization in the NTN based communication network.

### Claim 2 (depends on 1)

The method as claimed in claim 1, wherein the at least one information received from the NTN BS (104) comprises at least one of the satellite ephemeris, location coordinates, velocity magnitude and vector, clock timing reference, source of reference, minimum and maximum TA per beam or cell, TA margin, step size, rate of change of satellite location co-ordinates, satellite velocity vector with reference co-ordinates, rate of change of minimum TA, rate of change of maximum TA, feeder link delay including BS-satellite-gateway (SAT-GW) delay, and rate of change of feeder link delay.

### Claim 3 (depends on 2)

The method as claimed in claim 2, wherein the at least one information is signalled by the NTN-BS (104) over at least one of the broadcast channel and UE specific control channel.

### Claim 4 (depends on 1)

The method as claimed in claim 1, wherein the TA applied is determined as a difference between the TA estimate and the TA margin.

### Claim 5 (depends on 1)

The method as claimed in claim 1, comprising quantizing the TA estimate based on a at least one of the predefined step size (TAstep) and minimum TA signalled to the UE (102).

### Claim 6 (depends on 5)

The method as claimed in claim 5, wherein the minimum TA is the minimum timing advance from the NTN-BS (104) to the Earth's surface within its footprint.

### Claim 7 (depends on 5)

The method as claimed in claim 5, comprising the predefined TAstep configured as one of a cyclic prefix duration (Tcp) associated to a possible PRACH configuration and step size provided in the broadcast information.

### Claim 8 (depends on 7)

The method as claimed in claim 7, wherein one of the possible PRACH configuration is configured PRACH configuration.

### Claim 9 (depends on 1)

The method as claimed in claim 1, wherein the information related to the TA applied is reported to the NTN-BS (104) as a number of step size.

### Claim 10 (depends on 9)

The method as claimed in claim 9, wherein the number of step size is determined as a factor of the TA estimate and the TAstep.

### Claim 11 (depends on 1)

The method as claimed in claim 1, wherein the information related to the TA applied is updated based on a relative velocity of the satellite with the UE (102), determined using at least one of the rate of change of satellite location co-ordinates, satellite velocity vector with reference co-ordinates, rate of change of minimum TA, rate of change of maximum TA, and rate of change of feeder link delay.

### Claim 12

A system for performing Uplink (UL) time synchronization in a Non-Terrestrial Network (NTN) based communication network, the system comprising:
a processor; and
a memory connected with the processor, wherein the memory comprises programmed instructions for allowing the processor to:
perform Downlink (DL) synchronization using Synchronization Signal Block (SSB) signals;
receive, by a UE (102), at least one information from an NTN-Base Station (BS) (104);
obtain a location information of a satellite using the at least one information received by the UE;
estimate the location of the UE (102) using one of Global Navigation Satellite System (GNSS) receiver of the UE (102) and by processing at least one reference signal received by the UE (102) from multiple NTN-BS (104), using at least one multilateration technique and Real-Time Kinematic (RTK);
determine Timing Advance (TA) estimate using the location of the satellite and location of the UE (102);
determine TA applied using the TA estimate and TA margin, wherein the TA margin is a value ranging from zero to a step size value (TAstep);
transmit, by the UE (102), a Physical Random Access Channel (PRACH) based on the TA applied;
report, by the UE (102), an information related to the TA applied to the NTN-BS (104);
estimate, by the NTN-BS (104), the residual TA using the reported information related to the TA applied (104) and the detected PRACH; and
indicate the residual TA to the UE (102) for subsequent UL transmissions, thereby achieving the UL time synchronization in the NTN based communication network.