Methods and apparatuses for receiver (Rx)—transmitter (Tx) round trip time estimation

An apparatus, comprising:

• at least one processor;
• and
• at least one non-transitory memory storing instructions that, when executed with the at least one processor, cause the apparatus at least to:
• receive, at a network element, a signal from another network element and record a time of receipt (t1) of the signal;
• predict, by the network element, a transmit time based on allocated resources, applied difference between downlink to uplink transmission timing, and internal errors at the network element;
• estimate Rx-Tx measurement based on a difference between the time of receipt and the predicted transmit time;
• transmit the estimated Rx-Tx measurement to said another network element on a shared channel;
• calculate a difference in estimated Rx-Tx measurements and track a delta Rx-Tx measurement;
• transmit, when a change in the estimated Rx-Tx measurements is above a range and threshold of the delta Rx-Tx measurement, the difference or delta in the estimated Rx-Tx measurement to said another network element;
• transmit an intra-symbol offset on the shared channel to said another network element;
• measure an actual value of Rx-Tx based on actual transmission of the shared channel;
• determine whether there is an error between the actual Rx-Tx measurement and the estimated Rx-Tx measurement;
• and
• transmit, when there is an error, a correction of the error to said another network element,
• wherein the signal comprises one of a reference signal, positioning reference signal (PRS), primary synchronization signal (PSS), secondary synchronization signal (SSS), channel state information reference signal (CSI-RS), demodulation reference signal (DM-RS), or sidelink signal, and
• wherein the transmitting comprises transmitting a difference or delta in the estimated Rx-Tx measurement and transmitting an intra-symbol offset using a reference signal.