Methods and systems for uplink time synchronization in non-terrestrial networks based communication

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.