A closed loop frequency offset adjustment method in a low earth orbit satellite scenario

Abstract

This invention discloses a closed-loop frequency offset adjustment method for low-Earth orbit satellite scenarios, belonging to the field of wireless communication technology. The satellite side always uses the carrier center as the anchor point for frequency offset feedback, and the satellite terminal always performs Doppler compensation according to the center frequency point of the PUSCH scheduling bandwidth. This method has low complexity, high frequency offset estimation accuracy, low degradation of PUSCH channel demodulation performance, and uplink closed-loop frequency offset maintenance function in low-Earth orbit satellite scenarios.

Description

Technical Field

[0001] This invention relates to the field of wireless communication, and in particular to a closed-loop frequency offset adjustment method in low-Earth orbit satellite scenarios. Background Technology

[0002] In low-Earth orbit (LEO) satellite communication systems, the rapid movement of satellites introduces the Doppler effect. The magnitude of the Doppler effect is determined by the relative speed of the satellites and the carrier frequency. Currently, broadband systems based on 5G technology are the main development direction for LEO satellite communication in China, characterized by large carrier bandwidth and high speed. 5G technology uses OFDM (Orthogonal Frequency Division Multiplexing) waveforms, which are highly sensitive to frequency offset. Frequency errors can disrupt the orthogonality between OFDM subcarriers, leading to a sharp deterioration in received signal quality. Furthermore, since the Doppler effect is frequency-dependent, a large carrier bandwidth results in inconsistent Doppler frequency shifts across different subcarriers; the larger the bandwidth, the greater the span of the Doppler frequency shift.

[0003] Low-Earth orbit (LEO) satellite terminals perform uplink transmission frequency pre-compensation based on their own GNSS (Global Navigation Satellite System) positioning and ephemeris information sent by the system. Due to errors in the positioning accuracy and ephemeris pre-compensation accuracy of the satellite terminal, residual frequency offsets will occur. These residual frequency offsets need to be estimated by the system side based on the uplink reference signal and fed back to the satellite terminal via MAC CE (MAC Control Element) adjustment commands, forming a closed-loop frequency offset adjustment mechanism. From a processing complexity perspective, satellite terminals generally perform Doppler pre-compensation based on the carrier center. However, due to the relatively wide carrier bandwidth, the residual Doppler frequency offset span between different subcarriers when the signal reaches the satellite can be quite large. This Doppler frequency offset span across different subcarriers will be referred to as inconsistent Doppler frequency offset in the following text.

[0004] Taking an orbital altitude of 1000km, an uplink carrier frequency of 30GHz, a carrier bandwidth of 400MHz, a subcarrier spacing of 120kHz, and a terminal operating elevation angle of 20° as an example, in the same scheduling time slot, the inconsistent Doppler frequency offset of the upper and lower edges of the carrier can vary between -3.84kHz and 3.84kHz, which will greatly degrade the demodulation performance.

[0005] Traditional terrestrial 5G relies on SRS (Sounding Reference Signal) for closed-loop frequency offset maintenance. While SRS can also be used in low-Earth orbit (LEO) satellite scenarios, the introduction of inconsistent Doppler frequency offset necessitates adaptive modifications to the frequency offset maintenance strategy. Satellite terminals perform frequency pre-compensation based on the carrier center. The estimated frequency offset varies depending on the SRS transmission location in different frequency domains; the base station's frequency offset estimate is based on the SRS transmission location as an anchor point, and changes in this anchor point will alter the estimated frequency offset. Furthermore, the system dynamically schedules the PUSCH (Physical Uplink Shared Channel) service channel, and the PUSCH frequency domain location also changes dynamically. Different frequency domain locations result in varying residual frequency offsets of the PUSCH signal reaching the satellite. These issues lead to abnormal closed-loop frequency offset adjustment in LEO satellite systems and degraded uplink PUSCH demodulation performance. Summary of the Invention

[0006] To address the aforementioned issues, this invention proposes a closed-loop frequency offset adjustment method for low-Earth orbit satellite scenarios. This method offers high frequency offset estimation feedback accuracy and can improve the demodulation performance of the uplink PUSCH channel.

[0007] The specific technical solution adopted is as follows:

[0008] A closed-loop frequency offset adjustment method for low-Earth orbit satellite scenarios includes the following steps:

[0009] Step 1: The satellite terminal performs initial downlink synchronization based on its own GNSS positioning and preset ephemeris.

[0010] Step 2: After downlink synchronization, the satellite terminal obtains the ephemeris information broadcast by the system side. Based on the ephemeris information and GNSS positioning, the satellite terminal calculates the initial uplink frequency offset. And perform initial uplink frequency offset pre-compensation, and send PRACH (Physical Random Access Channel) sequence;

[0011] Step 3: After receiving the PRACH sequence, the satellite estimates the corresponding frequency offset value. , frequency offset value Feedback is sent to the satellite terminal via MSG2;

[0012] Step 4: After receiving MSG2, the satellite terminal transmits the frequency offset value fed back from the satellite side. Carrier center frequency offset compensation value calculated by ephemeris The uplink transmission frequency offset is obtained by adding the two values; the uplink frequency is adjusted by the uplink transmission frequency offset to complete the initial uplink frequency synchronization.

[0013] Step 5: After the RRC (Radio Resource Control) connection is established, the satellite terminal sends the corresponding SRS signal based on the SRS configuration on the base station side.

[0014] Step 6: The satellite side performs frequency offset estimation based on SRS to obtain the SRS center frequency offset. And estimate the slope of frequency offset between different subcarriers based on the SRS signal. The frequency offset value of the uplink carrier center is derived. ;

[0015] Step 7, the satellite side will use the frequency offset value derived in Step 6. Feedback is sent to the satellite terminal via MAC CE;

[0016] Step 8: After receiving the MAC CE, the satellite terminal calculates the frequency offset value based on the feedback from the satellite side. And the carrier center frequency offset compensation value calculated from the ephemeris. The satellite terminal obtains the transmission frequency corresponding to the uplink carrier center and adjusts the uplink transmission frequency to that frequency.

[0017] Step 9: The satellite terminal obtains the center subcarrier frequency of the scheduling signal bandwidth based on the PUSCH scheduling frequency domain position. The satellite terminal's PUSCH transmission frequency is based on the PUSCH scheduling signal bandwidth and the center subcarrier frequency. With the center frequency of the uplink carrier The uplink transmission frequency is adjusted using a ratio.

[0018] The beneficial effects of adopting the above-mentioned optimized technical solution are as follows:

[0019] This invention differs from the closed-loop frequency offset adjustment strategy of terrestrial mobile communication systems. It can support inconsistent Doppler frequency offset under large bandwidth. The satellite side always uses the carrier center as the anchor point for frequency offset feedback, and the terminal always performs Doppler compensation according to the center frequency point of the PUSCH scheduling bandwidth. It has low complexity, high frequency offset estimation accuracy, and low degradation of PUSCH channel demodulation performance. It can realize the uplink closed-loop frequency offset maintenance function in low-orbit satellite scenarios. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the uplink inconsistent Doppler frequency offset proposed in this invention;

[0021] Figure 2 This is a schematic diagram of Doppler frequency offset feedback with the carrier center as the anchor point proposed in this invention;

[0022] Figure 3This is a schematic diagram of the Doppler frequency offset pre-compensation proposed in this invention, using the PUSCH scheduling bandwidth center as the basis. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings.

[0024] like Figure 1 , Figure 2 and Figure 3 As shown in the figure, this embodiment provides a closed-loop frequency offset adjustment method for low-Earth orbit satellite scenarios, which includes the following steps:

[0025] Step 1: The satellite terminal performs downlink initial synchronization based on its own GNSS positioning and preset ephemeris.

[0026] Step 2: After downlink synchronization, the satellite terminal can obtain the accurate ephemeris information broadcast by the system side. Based on the broadcast ephemeris information and GNSS positioning, the satellite terminal calculates the initial uplink transmission frequency offset. Using uplink frequency offset Perform initial uplink frequency offset pre-compensation and send the PRACH sequence.

[0027] Step 3: After receiving the PRACH sequence, the satellite estimates the corresponding frequency offset value. The frequency offset value is obtained through MSG2. Feedback is sent to the satellite terminal.

[0028] Step 4: After receiving MSG2 (a random access confirmation message sent from the base station to the satellite terminal in the mobile communication network to confirm the satellite terminal's random access request), the satellite terminal, based on the frequency offset value fed back from the satellite side... And the carrier center frequency offset compensation value calculated by ephemeris ,according to Perform uplink frequency adjustment to complete initial uplink frequency synchronization.

[0029] Step 5: After the RRC connection is established, the satellite terminal sends the corresponding SRS signal based on the SRS configuration on the base station side.

[0030] Step 6: The satellite side performs frequency offset estimation based on SRS to obtain the SRS center frequency offset. And estimate the slope of frequency offset between different subcarriers based on the SRS signal. Thus, the frequency offset of the carrier center can be derived. .

[0031] Step 7, the satellite side will adjust the frequency offset Feedback is sent to the satellite terminal via MAC CE.

[0032] Step 8: After receiving the MAC CE, the satellite terminal calculates the frequency offset value based on the feedback from the satellite side. And the carrier center frequency offset compensation value calculated from the ephemeris. Obtain the transmission frequency corresponding to the uplink carrier center. + + At the same time, the satellite terminal will adjust its uplink transmission frequency to that frequency.

[0033] Step 9: The satellite terminal obtains the center subcarrier frequency of the scheduling signal bandwidth based on the PUSCH scheduling frequency domain position. Let the frequency of the entire uplink carrier center be . The satellite terminal will then follow the frequency offset. + + Compensation sent via PUSCH The frequency offset pre-compensation value for PUSCH transmission time is calculated based on broadcast ephemeris and GNSS positioning;

[0034] Based on the SRS scheduling cycle, steps 6 to 9 are executed repeatedly to continuously adjust the uplink closed-loop frequency.

Claims

1. A closed-loop frequency offset adjustment method for low-Earth orbit satellite scenarios, characterized in that, The process includes the following: Step 1: The satellite terminal performs initial downlink synchronization based on its own GNSS positioning and preset ephemeris. Step 2: After downlink synchronization, the satellite terminal obtains the ephemeris information broadcast by the system side. Based on the ephemeris information and GNSS positioning, the satellite terminal calculates the initial uplink frequency offset. And perform initial uplink frequency offset pre-compensation, and send the PRACH sequence; Step 3: After receiving the PRACH sequence, the satellite estimates the corresponding frequency offset value. , frequency offset value Feedback is sent to the satellite terminal via MSG2; Step 4: After receiving MSG2, the satellite terminal transmits the frequency offset value fed back from the satellite side. Carrier center frequency offset compensation value calculated by ephemeris The uplink transmission frequency offset is obtained by adding the two values; the uplink frequency is adjusted by the uplink transmission frequency offset to complete the initial uplink frequency synchronization. Step 5: After the RRC connection is established, the satellite terminal sends the corresponding SRS signal based on the SRS configuration on the base station side; Step 6: The satellite side performs frequency offset estimation based on SRS to obtain the SRS center frequency offset. And estimate the slope of frequency offset between different subcarriers based on the SRS signal. The frequency offset value of the uplink carrier center is derived. ; Step 7, the satellite side will use the frequency offset value derived in Step 6. Feedback is sent to the satellite terminal via MAC CE; Step 8: After receiving the MAC CE, the satellite terminal calculates the frequency offset value based on the feedback from the satellite side. And the carrier center frequency offset compensation value calculated from the ephemeris. The satellite terminal obtains the transmission frequency corresponding to the uplink carrier center and adjusts the uplink transmission frequency to that frequency. Step 9: The satellite terminal obtains the center subcarrier frequency of the scheduling signal bandwidth based on the PUSCH scheduling frequency domain position. The satellite terminal's PUSCH transmission frequency is based on the PUSCH scheduling signal bandwidth and the center subcarrier frequency. With the center frequency of the uplink carrier The uplink transmission frequency is adjusted using a ratio.

Images