A non-terrestrial network synchronization method and system based on a bidirectional synchronization signal block

Abstract

The application provides a non-ground network synchronization method and system based on a bidirectional synchronization signal block, and relates to the technical field of wireless communication.The non-ground network synchronization method based on the bidirectional synchronization signal block specifically comprises the following steps: a satellite sends a first synchronization signal block at a preset downlink synchronization signal block resource position based on a satellite local clock, the first synchronization signal block occupies N continuous OFDM symbols in the time domain and M continuous subcarriers in the frequency domain, wherein M is a preset positive integer; and the synchronization signal block comprises a first primary synchronization signal, a second primary synchronization signal, an auxiliary synchronization signal and a physical broadcast channel.The system of the application does not depend on GNSS, synchronization is achieved through bidirectional SSB exchange, a ground terminal can complete time and frequency synchronization with the satellite without a GNSS receiver, and is suitable for scenarios where GNSS signals are unavailable, such as indoors, underground and electromagnetic interference environments.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, specifically to a synchronization method in a non-terrestrial network (NTN) communication system, and more particularly to a bidirectional synchronization method, system, and related equipment based on a novel synchronization signal block (SSB) that does not rely on a Global Navigation Satellite System (GNSS). Background Technology

[0002] Non-terrestrial networks (NTN) are a key technology introduced by 3GPP (3rd Generation Partnership Project) in the 5G NR (New Radio) standard. They are designed to provide wide-area coverage through satellites (including LEO, MEO, GEO, etc.) or high-altitude platforms (HAPS) to compensate for the insufficient coverage of terrestrial cellular networks in remote areas, oceans, and airspace. 3GPP Release 17 standardized NR NTN for the first time, and Release 18 further enhanced related functions. Synchronization is the foundation for terminal access to the network in NTN communication systems. User equipment (UE) needs to establish precise time and frequency synchronization with satellites in order to correctly send and receive data.

[0003] The limitations of existing synchronization technologies, and the synchronization and random access procedures of the NTN standard defined by 3GPP Rel-17 / 18 (based on TS 38.213 and TS 38.321), are as follows:

[0004] Step 1: Downlink synchronization; The UE detects the SSB (Synchronization Signal Block) transmitted by the satellite and obtains downlink timing synchronization and frequency offset estimation;

[0005] Step 2: GNSS positioning; The UE obtains its own geographical location (latitude, longitude, and altitude) through a GNSS receiver.

[0006] Step 3: TA Pre-compensation; The UE calculates the propagation delay and timing advance (TA) based on its GNSS location, satellite ephemeris, and common TA parameters. TA is used to compensate for the one-way propagation delay from the UE to the satellite, ensuring that the uplink signal arrives at the satellite aligned with the satellite's local frame.

[0007] Step 4: PRACH Transmission; The UE transmits a random access preamble on the selected PRACH (Physical Random Access Channel) time-frequency resource. The PRACH sequence uses the Zadoff-Chu sequence, designed to allow the base station / gNB to detect "which UE is requesting access";

[0008] Step 5: RAR reception; After the satellite detects PRACH, it sends a TA adjustment command in the Random Access Response (RAR), and the UE fine-tunes the uplink timing according to the TA command in the RAR;

[0009] Step 6: Uplink synchronization complete; the UE completes uplink synchronization and enters normal communication;

[0010] However, the above standard process has the following significant problems:

[0011] The first point concerns the strong dependence on GNSS. Steps 2 and 3 require the UE to have GNSS reception capability. Furthermore, in scenarios where GNSS signals are weak or unavailable (such as indoors, underground, urban canyons, electromagnetic interference environments, polar regions, etc.), the UE cannot obtain its own location and therefore cannot calculate the TA. According to Section 16.14.2.2 of 3GPP TS 38.300, "If the UE does not have a valid GNSS location and / or valid ephemeris and common TA parameters, the UE shall not transmit any signal (shall not transmit)." This means that a UE without GNSS cannot complete step 4 (PRACH transmission) in the standard NTN procedure, resulting in network access failure. From a standard perspective, 3GPP TS 38.300 §16.14.2.2 and TS 38.306 §16.14.2.1 explicitly state that the UE shall not transmit any signal when it lacks a valid GNSS location, ephemeris, and common TA parameters (shall not transmit). This prohibits PRACH transmission at the protocol level. From a technical perspective, PRACH is designed based on terrestrial network assumptions. Its guard time (GT) and cyclic prefix (CP) only cover the maximum round-trip delay difference within the cell (usually tens of microseconds). 3GPP Rel-17 introduced the extended PRACH format for NTN (TS 38.211 §6.3.3), extending the GT to about 6ms to cover LEO scenarios (one-way delay 1.7-6.7ms). However, for GEO satellites with a one-way propagation delay of about 120ms, even the extended format cannot cover it. Without GNSS-assisted TA pre-compensation, the PRACH preamble will significantly deviate from the preset detection window when it arrives at the satellite, resulting in only a portion of the PRACH sequence falling within the detection window. The detection probability is extremely low, and a large-scale sliding correlation search will introduce an extremely high false alarm rate. PRACH signals may fall into non-PRACH time-frequency resources, causing interference to other transmissions.

[0012] The second limitation is outdoor use; the GNSS-based solution inherently restricts the NTN terminal to use only in open outdoor environments, which contradicts NTN's vision of being connected anytime, anywhere.

[0013] Third, the synchronization accuracy is limited; for low-cost IoT terminals that do not have GNSS capabilities, existing solutions cannot provide an effective synchronization method.

[0014] The fourth issue is the asymmetry of one-way synchronization. Existing synchronization schemes mainly involve downlink synchronization from satellite to terminal (step 1), lacking an effective uplink synchronization feedback mechanism from terminal to satellite (steps 4-6 are only used for random access requests, not for synchronization status feedback), making it difficult to guarantee synchronization accuracy.

[0015] The existing SSB structure has limitations. The existing SSB structure defined in the 5G NR standard (3GPP TS 38.211) is as follows: it occupies 4 OFDM symbols in the time domain (symbol indices 0-3) and 240 consecutive subcarriers (20 resource blocks) in the frequency domain, where:

[0016] Symbol 0: Primary Synchronization Signal (PSS), occupying the middle 127 subcarriers;

[0017] Symbol 1: Physical Broadcast Channel (PBCH), which occupies all 240 subcarriers and contains PBCH data and its demodulation reference signal (DM-RS).

[0018] Symbol 2: The secondary synchronization signal (SSS) occupies 127 subcarriers in the middle, 48 subcarriers on each side for PBCH transmission, and 8 and 9 guard subcarriers respectively are set to zero;

[0019] Symbol 3: PBCH, occupying all 240 subcarriers;

[0020] In this standard SSB structure, there is only one PSS column (the PSS on one OFDM symbol), and the terminal can complete the task by detecting this single PSS column. Time and frequency are synchronized; however, in the NTN scenario, there is a huge propagation delay between the satellite and the ground terminal (about a few milliseconds for LEO satellites and about hundreds of milliseconds for GEO satellites) and Doppler frequency shift (up to tens of ppm for LEO satellites). The detection window provided by a single PSS is limited, and the detection performance is significantly reduced in low signal-to-noise ratio and high Doppler scenarios.

[0021] In summary, existing technologies lack a solution that can achieve efficient two-way synchronization between satellites and ground terminals without relying on GNSS, and in particular, lack a novel synchronization signal block structure to support it. Therefore, this invention proposes a non-terrestrial network synchronization method and system based on two-way synchronization signal blocks, thereby effectively... To resolve the aforementioned problems and difficulties. Summary of the Invention

[0022] To address the shortcomings of existing technologies, this invention provides a non-terrestrial network synchronization method and system based on bidirectional synchronization signal blocks, aiming to solve the following technical problems:

[0023] How to achieve synchronization between satellites and ground terminals in an NTN system without GNSS assistance;

[0024] How to design a new SSB structure that is more adaptable to the characteristics of NTN channels (large delay, Doppler, low signal-to-noise ratio).

[0025] How to achieve mutual synchronization between satellite and ground terminal through bidirectional SSB search and transmission;

[0026] How to enable ground terminals to track and adjust their clocks based on satellite time references.

[0027] To achieve the above objectives, the present invention provides the following technical solution:

[0028] A non-terrestrial network synchronization method based on bidirectional synchronization signal blocks, the method specifically includes the following steps:

[0029] The satellite uses its local clock as a reference and transmits a first synchronization signal block at a preset downlink synchronization signal block resource location. This first synchronization signal block occupies N consecutive OFDM symbols in the time domain and M consecutive subcarriers in the frequency domain. M is a preset positive integer; the synchronization signal block includes a first main synchronization signal, a second main synchronization signal, an auxiliary synchronization signal, and a physical broadcast channel;

[0030] The ground terminal detects the first synchronization signal block within a preset search window, obtains downlink timing synchronization, and establishes local frame timing with reference to the arrival time of the first synchronization signal block.

[0031] The ground terminal transmits a second synchronization signal block at an uplink synchronization signal block resource location that is offset by a preset value K relative to the downlink frame timing, based on local frame timing. The structure of the second synchronization signal block is the same as that of the first synchronization signal block.

[0032] The satellite detects the second synchronization signal block within a preset uplink search window, records the arrival time, and calculates the round-trip propagation delay by subtracting the preset value K from the time difference between the first time the satellite sends the first synchronization signal block and the second time it receives the second synchronization signal block.

[0033] The satellite transmits the round-trip propagation delay or the one-way propagation delay obtained based on the round-trip propagation delay to the ground terminal;

[0034] The ground terminal calibrates the uplink transmission timing based on the received one-way propagation delay to complete two-way synchronization;

[0035] The second synchronization signal block uses the same physical cell identifier as the first synchronization signal block to generate the first primary synchronization signal sequence, the second primary synchronization signal sequence, and the secondary synchronization signal sequence. The physical broadcast channel of the second synchronization signal block carries the terminal information block instead of the primary information block.

[0036] Furthermore, the first synchronization signal block and / or the second synchronization signal block occupy 5 consecutive OFDM symbols in the time domain, i.e., symbol indices 0, 1, 2, 3, and 4, and occupy 240 consecutive subcarriers in the frequency domain, with subcarrier indices from 0 to 239. Their time-frequency resource mapping relationship is as follows:

[0037] Symbol index 0 is the first OFDM symbol, carrying the first main synchronization signal, and occupies subcarriers 56 to 182 in the frequency domain. Subcarriers 0-55 and 183-239 are set to zero as guard bands.

[0038] Symbol index 1 is the second OFDM symbol, carrying the first physical broadcast channel, occupying subcarriers 0 to 239, and containing the main information block data encoded by polar code and the first set of demodulation reference signals;

[0039] Symbol index 2 is the third OFDM symbol, carrying the auxiliary synchronization signal and the second physical broadcast channel extension data. The auxiliary synchronization signal occupies subcarriers 56 to 182 in the frequency domain. Subcarriers 0-47 and 192-239 carry the second physical broadcast channel extension data. Subcarriers 48-55 and 183-191 are set to zero as guard bands for the auxiliary synchronization signal.

[0040] Symbol index 3 is the fourth OFDM symbol, carrying the second main synchronization signal, occupying subcarriers 56 to 182 in the frequency domain, with subcarriers 0-55 and 183-239 set to zero as guard bands;

[0041] Symbol index 4 is the fifth OFDM symbol, carrying the second physical broadcast channel, occupying subcarriers 0 to 239, and containing the remaining data of the main information block after polar code encoding and the second set of demodulation reference signals.

[0042] Furthermore, PSS-1 and PSS-2 are generated from the same or different pseudo-random sequences. When generated from different sequences, the PSS-2 sequence is a cyclically shifted version of the PSS-1 sequence, with a cyclic shift offset of [missing value]. It is a preset integer, which is implicitly indicated by system information or determined according to pre-configured rules.

[0043] Furthermore, the step of the ground terminal detecting the first synchronization signal block includes:

[0044] By performing sliding cross-correlation between the locally generated first PSS sequence and the received signal, the first correlation peak is detected, and the first candidate timing position and the first PSS identifier are obtained.

[0045] The preset time interval between the first PSS and the second PSS is superimposed at the first candidate timing position. A second PSS correlation test was performed to verify the existence of a second correlation peak.

[0046] If and only if the first correlation peak is detected at the first candidate timing position and in When the second correlation peak is detected after the interval, it is determined that a valid synchronization signal block has been detected, and the coarse timing synchronization point and coarse frequency offset estimate are recorded.

[0047] Based on the coarse synchronization result of the double-peak verification, the received signal is subjected to fine correlation detection of the second PSS by using the preset time interval between the first PSS and the second PSS to obtain the fine timing synchronization point and the fine frequency offset estimate.

[0048] Based on the precise synchronization results, the SSS sequence is detected to obtain the physical cell identifier;

[0049] Demodulate the PBCH to obtain the satellite's system frame number and NTN-SSB time index from the main information block.

[0050] Furthermore, the calculation method for the precise frequency offset estimate is as follows:

[0051]

[0052] in For coarse timing position, For precise timing position, The time interval between PSS-1 and PSS-2 This represents the baseband sample value of the received signal.

[0053] Furthermore, the step of the ground terminal calibrating the uplink transmission timing based on the received one-way propagation delay includes:

[0054] The ground terminal records the arrival time of the first synchronization signal block. ,by It serves as the reference origin for downlink frame timing and does not undergo absolute time alignment.

[0055] One-way propagation delay of ground terminal receiving satellite feedback ,in , The time when the satellite sends the first synchronization signal block. The time when the satellite receives the second synchronization signal block. This is the preset time offset;

[0056] Ground terminal with As a local time reference aligned with the satellite clock, the frequency and phase of the voltage-controlled oscillator are adjusted to lock the local clock to the satellite clock.

[0057] Furthermore, the method also includes synchronization maintenance and clock tracking steps:

[0058] The ground terminal continuously receives and detects the first synchronization signal block periodically transmitted by the satellite, and uses the joint correlation results of the first PSS and the second PSS to track the timing offset and frequency offset in real time.

[0059] Utilization ratio The integral controller adjusts the control voltage of the local voltage-controlled oscillator based on timing and frequency offsets to maintain continuous tracking of the satellite clock.

[0060] Furthermore, after the satellite detects the second synchronization signal block sent by the ground terminal, if the detected arrival time deviation exceeds a preset threshold, the uplink transmission time of the ground terminal is adjusted by a timed advance command.

[0061] A synchronization signal block is used in a non-terrestrial network communication system. The synchronization signal block occupies 5 consecutive OFDM symbols in the time domain, with symbol indices of 0, 1, 2, 3, and 4, and occupies 240 consecutive subcarriers in the frequency domain, with subcarrier indices from 0 to 239. Its time-frequency resource mapping relationship is as follows:

[0062] Symbol index 0 carries the first main synchronization signal and occupies subcarriers 56 to 182 in the frequency domain. The remaining subcarriers are set to zero as guard bands.

[0063] Symbol index 1 carries the first physical broadcast channel, occupying all 240 subcarriers, and contains the main information block data and demodulation reference signal;

[0064] Symbol index 2 carries the auxiliary synchronization signal and physical broadcast channel extended data, wherein the auxiliary synchronization signal occupies subcarriers 56 to 182 in the frequency domain, subcarriers 0-47 and 192-239 carry physical broadcast channel extended data, and subcarriers 48-55 and 183-191 are set to zero as guard bands;

[0065] Symbol index 3 carries the second main synchronization signal, occupying subcarriers 56 to 182 in the frequency domain, while the remaining subcarriers are set to zero as a guard band.

[0066] Symbol index 4 carries the second physical broadcast channel, occupying all 240 subcarriers, and contains the remaining data of the main information block and the demodulation reference signal;

[0067] The first primary synchronization signal and the second primary synchronization signal are generated from the same or different pseudo-random sequences.

[0068] A non-terrestrial network synchronization system based on bidirectional synchronization signal blocks includes satellite nodes configured to periodically transmit a first synchronization signal block based on a satellite local clock, and to detect a second synchronization signal block at a pre-configured time-frequency resource location;

[0069] At least one ground terminal is configured to detect the first synchronization signal block, establish local frame timing with reference to the arrival time of the first synchronization signal block, send the second synchronization signal block based on the local frame timing, and calibrate the local clock after receiving the one-way propagation delay fed back by the satellite.

[0070] The first synchronization signal block and the second synchronization signal block occupy time domains A number of consecutive OFDM symbols occupy a certain number of positions in the frequency domain. A series of subcarriers, , The value is a preset positive integer; each synchronization signal block contains two main synchronization signal sequences, one auxiliary synchronization signal sequence, and physical broadcast channel data;

[0071] The ground terminal uses the same physical cell identifier as the first synchronization signal block to generate the first primary synchronization signal sequence, the second primary synchronization signal sequence, and the secondary synchronization signal sequence of the second synchronization signal block, and the physical broadcast channel of the second synchronization signal block carries the terminal information block instead of the primary information block.

[0072] A computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method or system as described in any one of claims 1 to 10.

[0073] This invention provides a non-terrestrial network synchronization method and system based on bidirectional synchronization signal blocks. It has the following beneficial effects:

[0074] This invention provides a non-terrestrial network synchronization method and system based on bidirectional synchronization signal blocks. It does not rely on GNSS and achieves synchronization through bidirectional SSB exchange. Ground terminals can achieve time and frequency synchronization with satellites without GNSS receivers. It is suitable for scenarios where GNSS signals are unavailable, such as indoor, underground, and electromagnetic interference environments.

[0075] This invention provides a non-terrestrial network synchronization method and system based on bidirectional synchronization signal blocks. The dual-PSS design improves detection performance and reliability. The NTN-SSB contains two columns of PSS (PSS-1 and PSS-2). Compared to the single-column PSS in existing 5G NR, the dual-PSS design provides…

[0076] Bimodal validation reduces false alarms: During time-domain sliding correlation, PSS-1 and PSS-2 at intervals Two correlated peaks are generated at this point. The receiver performs dual-peak joint detection (both intervals must be detected simultaneously). peak (Determining a valid SSB), the false alarm probability is reduced from that of the single PSS scheme. Reduce to , reduce by approximately This represents an order-of-magnitude improvement, significantly enhancing detection reliability at low signal-to-noise ratios.

[0077] Detection performance improvement: The detection probability of dual PSS joint detection in AWGN channel is improved by about 4.5dB compared with single PSS (the detection probability increases from 72% to 95% when SNR=-12dB), and the detection gain is about 3.8dB in Rician fading channel (K-factor=5dB);

[0078] Improved frequency offset estimation accuracy: Utilizing the known time interval between PSS-1 and PSS-2 Achieving CFO estimation at SCS=30kHz (Type B), The CFO estimation accuracy improved from ±0.5ppm per PSS to ±0.12ppm (approximately a 4-fold improvement); at SCS=120kHz (Type C), The accuracy of CFO estimation has been improved from ±2.0ppm to ±0.5ppm;

[0079] Anti-interference capability: Through the hierarchical detection strategy of dual PSS (single-peak candidate → dual-peak verification → fine synchronization), when one PSS symbol is affected by narrowband interference, synchronization can still be completed by relying on the other PSS, improving the anti-interference capability by about 6dB.

[0080] This invention provides a non-terrestrial network synchronization method and system based on bidirectional synchronization signal blocks. Through bidirectional SSB transmission between satellite and ground terminal, the ground terminal can continuously adjust its local clock based on the satellite clock, forming a closed-loop tracking mechanism. The synchronization accuracy is significantly better than that of a one-way synchronization scheme.

[0081] This invention provides a non-terrestrial network synchronization method and system based on bidirectional synchronization signal blocks, which does not require multiple satellites for positioning or ground reference stations for assistance; a single satellite can complete synchronization with the ground terminal.

[0082] This invention provides a non-terrestrial network synchronization method and system based on bidirectional synchronization signal blocks (SSBs). SSBs replace PRACHs to solve the problem of GNSS-free access: In standard NTN, GNSS-free terminals are completely unable to send PRACHs (due to the inability to pre-compensate TAs, causing the signal to deviate from the detection window). This invention uses uplink SSBs to replace PRACHs, utilizing the dual PSS+SSS+PBCH structure of SSBs to provide satellites with richer timing and identification information, breaking through the fundamental limitations of PRACHs in GNSS-free scenarios, and realizing synchronization and access for GNSS-free terminals.

[0083] This invention provides a non-terrestrial network synchronization method and system based on bidirectional synchronization signal blocks. The NTN-SSB structure proposed in this invention is appropriately extended while maintaining compatibility with the existing 5G NR frame structure, and can be implemented on existing hardware platforms through software upgrades.

[0084] This invention provides a non-terrestrial network synchronization method and system based on bidirectional synchronization signal blocks. For scenarios where multiple terminals in the same cell may simultaneously send uplink SSBs, this invention avoids conflicts through the following mechanism.

[0085] Temporal randomization: Before sending uplink SSB, each terminal independently selects a random backoff time within a preset random backoff window to reduce the probability of multiple terminals sending at the same time.

[0086] Frequency domain differentiation: Satellites allocate different subcarrier offsets or frequency domain resource blocks to different terminals, so that the uplink SSBs of different terminals are staggered in the frequency domain;

[0087] Terminal identification: Although terminals within the same cell use the same PCI to generate PSS and SSS, the UIB carried in the PBCH of each terminal contains a unique terminal identifier. The satellite distinguishes different terminals by demodulating the PBCH.

[0088] Scheduling and control: After initial synchronization is completed, the satellite allocates dedicated uplink SSB transmission time slots to each terminal through downlink signaling to achieve time division multiple access. Attached Figure Description

[0089] Figure 1 This is a schematic diagram of the NTN-SSB time-frequency resource mapping structure of the present invention;

[0090] Figure 2 This is a diagram of the NTN synchronization system architecture based on bidirectional SSB of the present invention;

[0091] Figure 3 This is an overall flowchart of the synchronization method of the present invention;

[0092] Figure 4 This is a flowchart of the dual PSS joint detection process of the present invention;

[0093] Figure 5 This is a block diagram of the synchronous maintenance and clock tracking closed-loop control of the present invention.

[0094] In the picture:

[0095] 101. PSS-1 (First Primary Synchronization Signal, located at symbol 0, subcarriers 56-182); 102. PBCH-1 (First Physical Broadcast Channel, located at symbol 1, subcarriers 0-239); 103. SSS (Secondary Synchronization Signal, located at symbol 2, subcarriers 56-182); 104. PSS-2 (Second Primary Synchronization Signal, located at symbol 3, subcarriers 56-182); 105. PBCH-2 (Second Physical Broadcast Channel, located at symbol 4, subcarriers 0-239); 201. Satellite Node (Space Segment Node in NTN); 202. Ground Terminal (User Segment Equipment in NTN); 203. Downlink NTN-SSB Link (SSB transmission from satellite to ground terminal) 204. Uplink NTN-SSB Link (SSB transmission link from ground terminal to satellite); 205. Onboard Clock (high-stability clock source for satellite); 206. Ground Terminal Clock (local clock of ground terminal, object to be synchronized); 201-214. Synchronization Method Steps (numbers of each sub-step of the synchronization method, including downlink SSB transmission, PSS detection, SSS detection, PBCH demodulation, uplink SSB transmission, RTT calculation, delay feedback, timing calibration, synchronization maintenance and TA adjustment); 401-406. Dual PSS Detection Steps (numbers of each sub-step of dual PSS joint detection); 501-507. Clock Tracking Loop Components (numbers of each component in the closed-loop clock tracking system). Detailed Implementation

[0096] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0097] Example 1:

[0098] like Figure 1-5 As shown, embodiments of the present invention A novel synchronization signal block (NTN-SSB) structure suitable for NTN systems is proposed, such as... Figure 1 As shown, NTN-SSB (100) occupies 5 consecutive OFDM symbols in the time domain (symbol indices 0 to 4) and 240 consecutive subcarriers in the frequency domain (subcarrier indices 0 to 239), forming a total of one The time-frequency resource grid is shown in Table 1, which gives the detailed time-frequency resource mapping relationship of each signal in the NTN-SSB.

[0099] Table 1 NTN-SSB Time-Frequency Resource Mapping Table

[0100] PSS-1 (First Master Synchronization Signal) 0 56-182 127 101 PBCH-1 (First Physical Broadcast Channel) 1 0-239 240 102 SSS (Secondary Synchronization Signal) 2 56-182 127 103 PBCH-Edge_L (Left Edge PBCH) 2 0-47 48 102a PBCH-Edge_R (Right Edge PBCH) 2 192-239 48 102b Guard_L (Left Side Protective Strip) 2 48-55 8 - Guard_R (Right Side Protective Strip) 2 183-191 9 - PSS-2 (Second Master Synchronization Signal) 3 56-182 127 104 PBCH-2 (Second Physical Broadcast Channel) 4 0-239 240 105

[0101] 1.1 First Master Synchronization Signal (PSS-1);

[0102] like Figure 1 As shown in reference numeral 101, PSS-1 is located at symbol index 0, occupying subcarriers 56 to 182 (a total of 127 subcarriers) in the frequency domain. Subcarriers 0-55 and 183-239 are set to zero as guard bands. The PSS-1 sequence is a BPSK modulated m-sequence of length 127, numbered within the physical layer cell identifier group. The specific generation method follows the PSS sequence generation formula defined in Section 7.4.2.2 of 3GPP TS 38.211:

[0103]

[0104]

[0105] in, Generate a sequence of primitive polynomials for the sequence m. ;

[0106] The time interval between PSS-1 and PSS-2 ,in Depending on the currently configured subcarrier spacing (SCS), let SCS = ,but ,in This is the duration of the cyclic prefix. hour, , ;exist hour, ;exist hour, ;

[0107] 1.2 First Physical Broadcast Channel (PBCH-1);

[0108] like Figure 1 As shown in reference numeral 102, PBCH-1 is located at symbol index 1 and occupies all 240 subcarriers. PBCH-1 carries a portion of the encoded Master Information Block (MIB) data and the demodulation reference signal (DM-RS). PBCH-1 and PBCH-2 jointly transmit the complete MIB information, which is encoded using Polar Code and mapped onto resource units after QPSK modulation.

[0109] 1.3 Auxiliary Synchronization Signal (SSS);

[0110] like Figure 1 As shown in reference numeral 103, the SSS is located at symbol index 2, occupying subcarriers 56 to 182 (a total of 127 subcarriers) in the frequency domain. Subcarriers 0-47 and 192-239 carry PBCH edge data (PBCH-Edge_L and PBCH-Edge_R), while subcarriers 48-55 and 183-191 are set to zero as guard bands. The SSS sequence is a BPSK modulation sequence of length 127, numbered by the physical layer cell identifier group. It was decided to work with PSS to determine a complete community identifier. ;

[0111] 1.4 Second Master Synchronization Signal (PSS-2);

[0112] like Figure 1 As shown in reference numeral 104, PSS-2 is located at symbol index 3, occupying subcarriers 56 to 182 in the frequency domain (a total of 127 subcarriers). Subcarriers 0-55 and 183-239 are set to zero as guard bands.

[0113] There are two optional modes for generating PSS-2 sequences;

[0114] Mode A (Same Sequence Mode): The PSS-2 sequence is exactly the same as the PSS-1 sequence. In this case, since PSS-1 and PSS-2 transmit the same content, the receiver can use the correlation results of the two symbols to perform incoherent merging, thereby improving the detection signal-to-noise ratio;

[0115] Mode B (Different Sequence Modes): The PSS-2 sequence is a preset cyclically shifted version of the PSS-1 sequence, that is:

[0116]

[0117] in This is the preset cyclic shift offset. The cyclic shift amount of PSS-2 is implicitly indicated by system information or determined by pre-configured rules, and may carry a small amount of additional auxiliary information bits;

[0118] Preferably, mode A is used in this embodiment to maximize detection performance;

[0119] 1.5 Second Physical Broadcast Channel (PBCH-2);

[0120] like Figure 1 As shown in reference numeral 105, PBCH-2 is located at symbol index 4 and occupies all 240 subcarriers. PBCH-2 carries the remaining portion of the encoded MIB data and DM-RS;

[0121] PBCH-1 and PBCH-2 together constitute a complete PBCH transport block, with a total of 864 bits after encoding (432 QPSK modulation symbols). After scrambling, rate matching, and polar code encoding, the data are mapped onto the resource elements (REs) of PBCH-1 and PBCH-2.

[0122] Table 2 PBCH Transport Block Content Structure

[0123] System Frame Number (SFN) High 8 bits 8 The high 8 bits of the wireless frame number The lower 2 bits of the system frame number (SFN) 2 The lower 2 bits of the wireless frame number (implicitly carried through scrambling) Half-frame bit 1 Indicates whether the SSB is located in the first or second half of the 10ms frame. NTN-SSB Time Index 3-6 Depending on the $L_{\max}$ configuration, this identifies the location of the SSB within the burst set. Subcarrier Offset (ssb) 4-5 Frequency offset between SSB and Point A SIB1 subcarrier spacing 1 Indicates the SCS used for SIB1 transmission SIB1 Configuration Information 8 SIB1 time-frequency scheduling information Satellite clock reference 32-64 When using UTC reference time or GPS, it is optional to carry a GNSS indicator. Common TA parameter indication 8-16 Beam-level Common Timing Advance Parameter Index Reserved bits variable Future expansion use CRC 24 24-bit Cyclic Redundancy Check

[0124] The total effective payload of the MIB carried by the PBCH (excluding CRC) is encoded by polar code to generate coded bits. After rate matching, scrambling and QPSK modulation, it is mapped to PBCH-1 (symbol 1, 432 REs), PBCH-2 (symbol 4, 432 REs) and the PBCH edge region of symbol 2 (96 REs), for a total of 960 REs, including 144 DM-RS REs and 816 data REs.

[0125] 1.6 Periodic and Burst Set Configuration of NTN-SSB;

[0126] The NTN-SSB transmission cycle can be configured as follows: One of 5, 10, 20, 40, 80, 160 ms. Preferably, the default period for the initial access phase is 20 ms. Within an NTN-SSB burst set, a maximum of [number missing] bursts can be formed. One NTN-SSB, Depends on the frequency band and SCS configuration;

[0127] FR1 Sub-6GHz

[0128] FR2 (millimeter wave):

[0129] Each NTN-SSB's time-domain location in its burst set is uniquely identified by the NTN-SSB time index, which is implicit in the cyclic shift of the PSS-2 (when using mode B) or indicated by an explicit bit in the PBCH.

[0130] Example 2:

[0131] refer to Figure 2 and Figure 3 This embodiment provides a bidirectional synchronization method based on the NTN-SSB described in Embodiment 1, including the following steps:

[0132] 2.1 Downlink synchronization phase (satellite → ground terminal);

[0133] Step 201: The satellite uses its own highly stable onboard clock as a time reference and transmits downlink NTN-SSB according to a preset period and the location of NTN-SSB time-frequency resources. The satellite's onboard clock preferably uses a chip-scale atomic clock (CSAC) or a higher-precision rubidium atomic clock, with frequency stability superior to... On the order of / s;

[0134] Step 202: After the ground terminal powers on, it performs a full-band search within the pre-configured frequency band, using a synchronization raster as the step size. For each candidate frequency point, the ground terminal performs PSS-1 detection within the possible transmission window of the NTN-SSB;

[0135] The specific process of PSS-1 testing is as follows:

[0136] The ground terminal samples the received time-domain signal at a preset sampling rate to obtain the digital baseband signal. ;

[0137] Use locally generated PSS-1 sequences (three possible) (Generated separately) and the received signal are subjected to sliding cross-correlation.

[0138] ;

[0139] in The sequence is a local PSS-1 sequence, and L is the correlation window length.

[0140] when Exceeding the preset first detection threshold Record the candidate coarse timing position. and corresponding ;

[0141] Simultaneously, the coarse frequency offset estimate is calculated based on the phase information of the PSS-1 correlation peak. ;

[0142] refer to Figure 4 The specific process for bimodal verification is as follows:

[0143] Step 202A (Double Peak Verification): Since the NTN-SSB of this invention contains two PSS columns (PSS-1 and PSS-2), after detecting the candidate peak of PSS-1, the ground terminal utilizes the known time interval between PSS-1 and PSS-2. ( (one OFDM symbol), in Perform PSS-2 correlation detection near the location to verify the existence of a second correlation peak.

[0144] If and only if in A PSS-1 related peak was detected at the location and in The location also detected a related peak value of PSS-2 (the peak value exceeded the preset second threshold). Only when this condition is met is a valid NTN-SSB detected. At this point, a record is made.

[0145]

[0146] ;

[0147] Otherwise, if only a single PSS-1 related peak exists and not in If the corresponding PSS-2 peak value is found after the interval, the current candidate is determined to be a false alarm due to noise, and the search continues.

[0148] This bimodal verification mechanism significantly reduces the false alarm probability: in the single PSS scheme, noise spikes exceed the threshold. The probability is In the dual PSS scheme of this invention, two intervals are required. The probability that all noise spikes exceed the threshold simultaneously is (in (This represents the false alarm probability of PSS-2), resulting in an overall decrease in false alarm probability of approximately [missing information]. Order of magnitude. Furthermore, bimodal verification can also combat single-peak interference scenarios (such as narrowband interference affecting only one PSS symbol), improving the robustness of synchronization signals in NTN scenarios.

[0149] Step 203: After the dual-peak verification is passed, the ground terminal... PSS-2 precision correlation detection was performed nearby to obtain the precise timing position. :

[0150] ;

[0151] in To fine-tune the search range, W is the width of the search window (preferably W is half the length of a CP). Using the joint correlation results of PSS-1 and PSS-2, the precise frequency offset estimate is calculated.

[0152] ;

[0153] Compared to the single-column PSS scheme, based on The range of dual PSS frequency offset estimation is reduced. The estimation accuracy is improved by the same factor, but the actual accuracy is increased by the same factor. For example, in Under configuration, The estimation accuracy is improved by about 3 times.

[0154] Step 204: Based on the fine synchronization result, the ground terminal at symbol index 2 (relative to...) SSS is detected on the offset. The ground terminal generates local SSS candidate sequences (corresponding to 336 types). ), and perform correlation detection with the received signal at the SSS resource location to determine ;

[0155] ;

[0156] in The frequency domain value of the received signal on the SSS subcarrier. Frequency domain representation of the local SSS sequence

[0157] According to PSS detection and SSS detection obtained Calculate the complete physical cell identifier

[0158] ;

[0159] Step 205: The ground terminal demodulates the PBCH on symbol indices 1 and 4 (and the edge subcarriers of symbol index 2). The demodulation process includes...

[0160] Channel estimation using PBCH DM-RS

[0161] Equalization and demodulation were performed on PBCH-1 and PBCH-2 respectively.

[0162] Combine the demodulated soft bits of PBCH-1 and PBCH-2 for polar code decoding.

[0163] Extract MIB information from the decoding results

[0164] The MIB contains the following NTN synchronization key information.

[0165] System Frame Number (SFN) is 10 bits.

[0166] NTN-SSB Time Index: [Retrieved] Configuration used to determine the position of NTN-SSB within a half-frame.

[0167] Satellite clock reference: Includes the satellite's Coordinated Universal Time (UTC) reference time or GPS time reference time.

[0168] NTN-SSB Subcarrier Offset (SSB-SubcarrierOffset): Indicates the frequency offset between the NTN-SSB and the common resource block grid.

[0169] SIB1 configuration information: used for scheduling and demodulation of subsequent system information block 1;

[0170] 2.2 Uplink synchronization phase (round-trip delay measurement);

[0171] Step 206: The ground terminal determines the uplink NTN-SSB transmission time based on the downlink frame timing established in step 205. Since the ground terminal cannot yet know the one-way propagation delay at this point... The specific value is not based on the satellite's absolute time, so the clock is adjusted according to the received satellite NTN-SSB time. As the reference origin for local frame timing

[0172] The ground terminal determines the uplink NTN-SSB transmission time based on the offset K (K is a positive integer, in OFDM symbols or time slots) indicated in the system pre-configuration or PBCH.

[0173] ;

[0174] in The time unit (depending on the SCS configuration, such as the duration of an OFDM symbol or a time slot). The offset K must be designed to ensure that the ground terminal has sufficient processing time for PSS detection, SSS detection, PBCH demodulation, and uplink SSB generation. Specifically, the minimum value of K should satisfy...

[0175] ;

[0176] in The time required for joint detection of PSS-1 and PSS-2 For PBCH decoding time, For the uplink NTN-SSB generation time, For symbols or time slot duration, This indicates rounding up. Preferably, K is 2. Eight time slots (corresponding to approximately 1.4~5.7ms at SCS=15kHz) are used to balance processing time and synchronization setup speed.

[0177] The local clock voltage-controlled oscillator (VCXO) of the ground terminal is frequency-locked with reference to the received signal carrier frequency in the initial stage, and the clock phase is temporarily based on... Based on

[0178] Step 207: Ground terminal transmits NTN-SSB data at the uplink time. Send the uplink NTN-SSB. The time-frequency structure of the uplink NTN-SSB is the same as that of the downlink NTN-SSB, but the content is different.

[0179] PSS and SSS: The ground terminal generates PSS and SSS sequences using the same Physical Cell Identifier (PCI) as the received downlink NTN-SSB. Since the satellite knows the PCI of its own transmitted downlink NTN-SSB, it can directly use the same PCI to generate a local reference sequence when searching for uplink NTN-SSBs, eliminating the need for blind detection of 336 possible PSSBs. The availability of candidates significantly reduces the complexity of uplink search and shortens satellite detection time.

[0180] PBCH: The PBCH of the uplink NTN-SSB does not carry the MIB, but instead carries the UE Information Block (UIB), which contains the identification information, capability indication, and status information of the ground terminal.

[0181] The uplink NTN-SSB transmission period can be configured to be an integer multiple of the downlink NTN-SSB period (e.g., 2 times, 4 times) to reduce unnecessary uplink overhead.

[0182] Step 208: The satellite detects the uplink NTN-SSB transmitted by the ground terminal within the pre-configured uplink NTN-SSB search window. The satellite detection process is similar to the downlink detection process of the ground terminal, including...

[0183] PSS-1 detection → Coarse synchronization

[0184] PSS-2 detection → Precise synchronization

[0185] SSS detection → Confirm ground terminal identification

[0186] PBCH demodulation → Obtain the Terminal Information Block (UIB) content of the ground terminal, including identification information and status.

[0187] Satellite records the arrival time of uplink NTN-SSB. Since the satellite knows the time it will transmit downlink NTN-SSB. Given the known response offset K of the ground terminal, the satellite calculates the round-trip propagation delay accordingly.

[0188] ;

[0189] Under the symmetric link assumption, the one-way propagation delay is...

[0190] ;

[0191] Asymmetric link handling: When the uplink and downlink propagation delays are asymmetrical (e.g., satellites use transparent transponders resulting in different uplink and downlink frequency bands, or there are different atmospheric refraction effects in the uplink and downlink channels). It will introduce errors At this point, the satellite can correct its behavior in the following ways.

[0192] The satellite pre-calculates the uplink and downlink time delay differences based on ephemeris information and beam coverage geometry. and will As a system information broadcast Alternatively, the satellite can measure the change in RTT through multiple two-way SSB exchanges and use Kalman filtering to estimate the true one-way delay.

[0193] The corrected one-way delay is ;

[0194] Step 209: The satellite will calculate the one-way delay. Sending signaling to the ground terminal via downlink signaling. Signaling methods include, but are not limited to, any of the following:

[0195] Method 1: Carry through a dedicated field in the subsequent NTN-SSB PBCH

[0196] Method 2: Carry the command in advance via a timed advance message in the Random Access Response (RAR).

[0197] Method 3: Carry the timing advance command (TAC) in the MAC CE (Media Access Control Control Element). The step size and range of the TAC are adapted to the high latency characteristics of NTN (the step size is extended to N times that of conventional terrestrial networks).

[0198] 2.3 Uplink timing calibration

[0199] Step 210: The ground terminal receives the one-way delay feedback from the satellite in step 209. Based on this, the uplink timing is calibrated. Specifically, the ground terminal adjusts its local time base to [the specified value].

[0200] ;

[0201] The local time of the ground terminal, based on the satellite clock, equals the local time when the satellite SSB is received, plus the one-way propagation delay.

[0202] The voltage-controlled oscillator (VCO) at the ground terminal adjusts the phase and frequency based on the calculated time difference, locking the local clock to the satellite clock reference. At this point, the ground terminal obtains its first absolute time reference synchronized with the satellite.

[0203] 2.4 Synchronization and Clock Tracking Stage

[0204] refer to Figure 5 This stage achieves closed-loop clock tracking and synchronization maintenance.

[0205] Step 211: After completing initial synchronization and timing calibration, the ground terminal enters synchronization maintenance mode. In this mode, the ground terminal continuously receives downlink NTN-SSBs periodically transmitted by the satellite and uses dual PSSs for continuous timing and frequency tracking.

[0206] For the k-th received NTN-SSB, the ground terminal calculates the joint correlation peak position of PSS-1 and PSS-2. and frequency offset Reference value at initial synchronization and By comparison, timing drift and frequency drift are obtained.

[0207]

[0208]

[0209] The ground terminal uses the aforementioned drift amount to proportional The integral (PI) controller adjusts the control voltage of the local voltage-controlled oscillator to achieve continuous tracking of the local clock with the satellite clock.

[0210] Step 212: When the ground terminal detects continuous The correlation peak of the NTN-SSB is lower than the preset unlock threshold. If a synchronization loss occurs, the system will re-enter the initial search phase (step 202).

[0211] Step 213: Satellite-side synchronization maintenance. After receiving each uplink NTN-SSB, the satellite assesses the synchronization status of the ground terminal. The satellite can do this by re-measuring the RTT and calculating the delay change. ,like Exceeding the preset threshold The satellite sends a timing advance command via MAC CE to adjust the uplink transmission timing of the ground terminal. The ground terminal updates its local one-way delay estimate based on the received TAC. And adjust the uplink timing calibration value accordingly.

[0212] Step 214 (optional): After multiple bidirectional SSB exchanges are completed between the satellite and the ground terminal, weighted averaging or Kalman filtering can be used to process the measured RTT values ​​to obtain a more accurate one-way delay estimate. This improves synchronization accuracy.

[0213] Example 3: Closed-loop clock tracking system;

[0214] refer to Figure 5 This embodiment provides a clock tracking system for a ground terminal, including:

[0215] Receiver module: Used to receive downlink NTN-SSB signals transmitted by the satellite and record the signal arrival time;

[0216] PSS Joint Correlation Detection Module: Used to perform joint correlation detection of PSS-1 and PSS-2 on the received signal, and output timing offset and frequency offset estimates;

[0217] Frame timing establishment module: Establishes local frame timing based on the joint detection results of PSS-1 and PSS-2, using the arrival time of the first NTN-SSB. Generate a local frame counter using the local time reference origin;

[0218] Uplink SSB generation module: Based on local frame timing, it generates uplink NTN-SSB at the uplink resource position with an offset of preset value K;

[0219] One-way delay receiving module: Receives the one-way propagation delay fed back by the satellite. , used to calibrate the local time base;

[0220] Loop filter module: A second-order digital phase-locked loop (DPLL) that smooths the timing and frequency offset estimates, including a proportional branch (coefficient). ) and a product branch (coefficient) );

[0221] Proportion The output of the integral controller is:

[0222]

[0223] in This refers to the timing error or frequency offset error of the k-th detection. This is the proportionality coefficient. This is the integral coefficient. Based on the satellite motion characteristics in the NTN scenario, and The preferred configuration is as follows:

[0224] LEO (600-1200km) 7.5-7.8km / s 0.35 0.08 15Hz MEO (8000km) 3.0-3.5km / s 0.25 0.05 10Hz GEO (35786km) ~0km / s 0.15 0.02 5Hz

[0225] LEO scenarios involve satellites moving at high speeds with large time delay variations, requiring significant... and For rapid tracking; in GEO scenarios, satellites are relatively stationary, requiring smaller... and To obtain a more stable clock output. Integral coefficient The value of must satisfy To ensure loop stability;

[0226] Voltage-controlled oscillator (VCXO) module: Adjusts the output frequency and phase of the local clock according to the control voltage output by the loop filter, so that the local clock is locked to the satellite clock reference;

[0227] Timing advance compensation module: based on one-way delay Timing drift of the loop filter output Calculate the uplink transmission timing pre-compensation value, which is used for timing advance of subsequent uplink channels.

[0228] Example 4: Adaptation to different NTN scenarios;

[0229] The NTN-SSB and synchronization method of the present invention can be flexibly adapted to NTN scenarios with different orbital altitudes and different subcarrier spacing (SCS) configurations. Table 3 gives the key time parameters corresponding to the three NTN-SSB types.

[0230] Table 3 Time parameters of NTN-SSB under different SCS configurations

[0231] parameter NTN-SSB Type A NTN-SSB Type B NTN-SSB Type C Applicable SCS ($\Delta f$) 15kHz 30kHz 120kHz Applicable frequency band FR1 (Sub-6GHz) FR1 (Sub-6GHz) FR2 millimeter wave OFDM symbol length $T_{\text{sym}}$ 66.67μs 33.33μs 8.33μs The standard CP length is $T_{\text{CP}}$ (μs). 4.69μs 2.34μs 0.59μs Total symbol interval ($T_{\text{sym}}+T_{\text{CP}}$) 71.35μs 35.68μs 8.92μs Total duration of NTN-SSB (5 symbols) 356.77μs 178.39μs 44.58μs **Double PSS interval $\Delta T$ (3 symbols) ** **214.06μs** **107.03μs** **26.75μs** Maximum frequency offset estimation range ($\pm 1 / 2\Delta T$) ±2.34kHz ±4.67kHz ±18.69kHz Typical NTN-SSB transmission cycle 20ms 20ms 40ms Maximum number of SSBs in a burst set $L_{\max}$ 4 8 64

[0232] Scenario A - LEO satellite (orbital altitude 500-2000km);

[0233] Propagation delay: approximately 1.7-6.7 ms (one-way);

[0234] Doppler shift: up to ±48ppm (approximately ±20kHz @ 6GHz);

[0235] Recommended SCS configuration: 30kHz (Type B) or 120kHz (Type C);

[0236] Recommended NTN-SSB types: Type B (FR1), Type C (FR2);

[0237] NTN-SSB cycle: 20ms;

[0238] Double PSS interval :107.03μs (Type B) or 26.75μs (Type C);

[0239] Frequency offset estimation range: ±4.67kHz (Type B) or ±18.69kHz (Type C);

[0240] Analysis: For LEO scenarios, the biggest technical challenge is Doppler frequency shift. When using Type C (SCS=120kHz), the frequency offset estimation range of dual PSS is ±18.69kHz, which can cover the residual Doppler frequency shift of most LEO satellites (after coarse frequency offset correction). Dual PSS joint detection can achieve a detection gain of about 4.5dB compared with single PSS, significantly improving the synchronization probability under low elevation angle (low SNR) conditions.

[0241] Scene B - GEO satellite (orbital altitude 35786km);

[0242] Propagation delay: approximately 119-125ms (one-way);

[0243] Doppler shift: minimal (approximately ±0.1 ppm);

[0244] Recommended SCS configuration: 15kHz (Type A);

[0245] Recommended NTN-SSB type: Type A

[0246] NTN-SSB cycle: 40ms or 80ms;

[0247] Double PSS interval : 214.06μs;

[0248] Analysis: GEO scenarios have extremely high propagation delay but very low Doppler. Type A has the longest dual PSS interval (214μs), and using dual PSS for coherent accumulation can achieve the best noise suppression effect, with an SNR gain of about 3dB. In addition, the ground terminal can use the satellite UTC time carried in the PBCH to directly calibrate the local clock, which greatly shortens the initial synchronization time.

[0249] Scenario C - MEO satellites (orbital altitude 7000-25000km);

[0250] Propagation delay: approximately 24-85ms (one-way);

[0251] Doppler shift: moderate (approximately ±10-20 ppm);

[0252] Recommended SCS configuration: 15kHz (Type A) or 30kHz (Type B);

[0253] Recommended NTN-SSB type: Type A or Type B;

[0254] NTN-SSB cycle: 20ms or 40ms;

[0255] Analysis: The parameter characteristics of MEO scenarios are between those of LEO and GEO, and the NTN-SSB type can be flexibly selected based on the specific orbital altitude and terminal capabilities; it is recommended that Type B be preferred for medium and low orbits, and Type A be preferred for high orbits.

[0256] Example 5: Applications in multi-beam scenarios;

[0257] In a multi-beam satellite scenario, each beam corresponds to one NTN-SSB. The NTN-SSBs of different beams are transmitted sequentially within the NTN-SSB burst set using time division multiplexing (TDM) in the time domain. The time index of each beam's NTN-SSB uniquely identifies that beam.

[0258] By detecting the NTN-SSB of its own beam, the ground terminal can not only complete synchronization, but also obtain the identifier of its own beam through the NTN-SSB time index, and then associate the beam-specific common TA parameters for subsequent random access and uplink transmission.

[0259] Example 6: Performance simulation evaluation;

[0260] To verify the technical effectiveness of this invention, the performance of the NTN-SSB structure and bidirectional synchronization method was evaluated using the MATLAB simulation platform. The simulation parameters were set as follows:

[0261] Channel model: AWGN + Rician fading (K-factor = 5dB);

[0262] Frequency bands: n255 (L-band, 1.6GHz) and n256 (S-band, 2.2GHz);

[0263] SCS configuration: 15kHz (Type A) and 30kHz (Type B);

[0264] Doppler shift: ±20ppm for LEO scene, ±0.1ppm for GEO scene;

[0265] Terminal type: Low-cost IoT terminal (without GNSS module);

[0266] Table 4 Comparison of dual PSS detection performance (SCS=30kHz, Type B)

[0267] SNR=-15dB Detection probability 45% 78% +33% SNR=-12dB Detection probability 72% 95% +23% SNR=-10dB Detection probability 88% 99.2% +11.2% False alarm probability (SNR=-10dB) 1.2×10⁻³ <![CDATA[4.5×10⁻ 6 ]]> Reduced by approximately 2.5 orders of magnitude Frequency offset estimation RMSE ±0.48ppm ±0.11ppm 4.4 times improvement Regularly estimate RMSE ±0.32μs ±0.08μs Improved by 4 times

[0268] Table 5 Comparison of Synchronization Establishment Time

[0269] LEO Outdoor 2-5s (GNSS cold start) 0.8-1.5s This invention eliminates the need for GNSS cold start. LEO indoor Failure (no GNSS signal) 1.2-2.0s This invention can achieve synchronization indoors. GEO outdoor 2-5s (GNSS cold start) 1.0-1.8s Longer PSS intervals result in more robust detection. GEO indoor Failure (no GNSS signal) 1.5-2.5s The RTT is relatively large but it does not affect the establishment of synchronization.

[0270] Simulation conclusions:

[0271] Under low signal-to-noise ratio (SNR=-12dB) conditions, the detection probability of the dual PSS scheme reaches 95%, which meets the synchronization requirements of NTN weak coverage scenarios.

[0272] The dual-peak verification mechanism reduces the false alarm probability by about 2.5 orders of magnitude, significantly reducing the terminal's ineffective search power consumption;

[0273] The frequency offset estimation accuracy is improved by 4.4 times, enabling IoT terminals to maintain frequency synchronization even in Doppler scenarios;

[0274] Synchronization setup time is reduced by about 60% compared to GNSS schemes, and it is not limited by GNSS signal availability.

[0275] The following points should be noted in this article:

[0276] 1. The accompanying drawings of the embodiments disclosed herein only relate to the structure of the embodiment #imgpt239# of this disclosure, while the structure of #imgpt240# can be referred to in a general design.

[0277] 2. Where there is no conflict, the embodiments of this disclosure and the features in the embodiments can be combined with each other to obtain new embodiments.

[0278] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A non-terrestrial network synchronization method based on bidirectional synchronization signal blocks, characterized in that: The method specifically includes the following steps: The satellite uses its local clock as a reference and transmits a first synchronization signal block at a preset downlink synchronization signal block resource location. This first synchronization signal block occupies N consecutive OFDM symbols in the time domain and M consecutive subcarriers in the frequency domain. M is a preset positive integer; the synchronization signal block includes a first main synchronization signal, a second main synchronization signal, an auxiliary synchronization signal, and a physical broadcast channel; The ground terminal detects the first synchronization signal block within a preset search window, obtains downlink timing synchronization, and establishes local frame timing with reference to the arrival time of the first synchronization signal block. The ground terminal transmits a second synchronization signal block at an uplink synchronization signal block resource location that is offset by a preset value K relative to the downlink frame timing, based on local frame timing. The structure of the second synchronization signal block is the same as that of the first synchronization signal block. The satellite detects the second synchronization signal block within a preset uplink search window, records the arrival time, and calculates the round-trip propagation delay by subtracting the preset value K from the time difference between the first time the satellite sends the first synchronization signal block and the second time it receives the second synchronization signal block. The satellite transmits the round-trip propagation delay or the one-way propagation delay obtained based on the round-trip propagation delay to the ground terminal; The ground terminal calibrates the uplink transmission timing based on the received one-way propagation delay to complete two-way synchronization; The second synchronization signal block uses the same physical cell identifier as the first synchronization signal block to generate the first primary synchronization signal sequence, the second primary synchronization signal sequence, and the secondary synchronization signal sequence. The physical broadcast channel of the second synchronization signal block carries the terminal information block instead of the primary information block.

2. The non-terrestrial network synchronization method based on bidirectional synchronization signal blocks according to claim 1, characterized in that: The first synchronization signal block and / or the second synchronization signal block occupy 5 consecutive OFDM symbols in the time domain, i.e., symbol indices 0, 1, 2, 3, and 4, and occupy 240 consecutive subcarriers in the frequency domain, with subcarrier indices from 0 to 239. Their time-frequency resource mapping relationship is as follows: Symbol index 0 is the first OFDM symbol, carrying the first main synchronization signal, and occupies subcarriers 56 to 182 in the frequency domain. Subcarriers 0-55 and 183-239 are set to zero as guard bands. Symbol index 1 is the second OFDM symbol, carrying the first physical broadcast channel, occupying subcarriers 0 to 239, and containing the main information block data encoded by polar code and the first set of demodulation reference signals; Symbol index 2 is the third OFDM symbol, carrying the auxiliary synchronization signal and the second physical broadcast channel extension data. The auxiliary synchronization signal occupies subcarriers 56 to 182 in the frequency domain. Subcarriers 0-47 and 192-239 carry the second physical broadcast channel extension data. Subcarriers 48-55 and 183-191 are set to zero as guard bands for the auxiliary synchronization signal. Symbol index 3 is the fourth OFDM symbol, carrying the second main synchronization signal, occupying subcarriers 56 to 182 in the frequency domain, with subcarriers 0-55 and 183-239 set to zero as guard bands; Symbol index 4 is the fifth OFDM symbol, carrying the second physical broadcast channel, occupying subcarriers 0 to 239, and containing the remaining data of the main information block after polar code encoding and the second set of demodulation reference signals.

3. The non-terrestrial network synchronization method based on bidirectional synchronization signal blocks according to claim 2, characterized in that: The PSS-1 and PSS-2 are generated from the same or different pseudo-random sequences. When generated from different sequences, the PSS-2 sequence is a cyclically shifted version of the PSS-1 sequence, with a cyclic shift offset of [missing value]. It is a preset integer, which is implicitly indicated by system information or determined according to pre-configured rules.

4. The non-terrestrial network synchronization method based on bidirectional synchronization signal blocks according to claim 1, characterized in that: The steps for the ground terminal to detect the first synchronization signal block include: By performing sliding cross-correlation between the locally generated first PSS sequence and the received signal, the first correlation peak is detected, and the first candidate timing position and the first PSS identifier are obtained. The preset time interval between the first PSS and the second PSS is superimposed at the first candidate timing position. A second PSS correlation test was performed to verify the existence of a second correlation peak. If and only if the first correlation peak is detected at the first candidate timing position and in When the second correlation peak is detected after the interval, it is determined that a valid synchronization signal block has been detected, and the coarse timing synchronization point and coarse frequency offset estimate are recorded. Based on the coarse synchronization result of the double-peak verification, the received signal is subjected to fine correlation detection of the second PSS by using the preset time interval between the first PSS and the second PSS to obtain the fine timing synchronization point and the fine frequency offset estimate. Based on the precise synchronization results, the SSS sequence is detected to obtain the physical cell identifier; Demodulate the PBCH to obtain the satellite's system frame number and NTN-SSB time index from the main information block.

5. A non-terrestrial network synchronization method based on bidirectional synchronization signal blocks according to claim 4, characterized in that: The calculation method for the precise frequency offset estimate is as follows: in For coarse timing position, For precise timing position, The time interval between PSS-1 and PSS-2 This represents the baseband sample value of the received signal.

6. The non-terrestrial network synchronization method based on bidirectional synchronization signal blocks according to claim 1, characterized in that: The steps for the ground terminal to calibrate the uplink transmission timing based on the received one-way propagation delay include: The ground terminal records the arrival time of the first synchronization signal block. ,by It serves as the reference origin for downlink frame timing and does not undergo absolute time alignment. One-way propagation delay of ground terminal receiving satellite feedback ,in , The time when the satellite sends the first synchronization signal block. The time when the satellite receives the second synchronization signal block. This is the preset time offset; Ground terminal with As a local time reference aligned with the satellite clock, the frequency and phase of the voltage-controlled oscillator are adjusted to lock the local clock to the satellite clock.

7. The non-terrestrial network synchronization method based on bidirectional synchronization signal blocks according to claim 1, characterized in that: The method also includes synchronization maintenance and clock tracking steps: The ground terminal continuously receives and detects the first synchronization signal block periodically transmitted by the satellite, and uses the joint correlation results of the first PSS and the second PSS to track the timing offset and frequency offset in real time. Utilization ratio The integral controller adjusts the control voltage of the local voltage-controlled oscillator based on timing and frequency offsets to maintain continuous tracking of the satellite clock.

8. A non-terrestrial network synchronization method based on bidirectional synchronization signal blocks according to claim 1, characterized in that: After the satellite detects the second synchronization signal block sent by the ground terminal, if the detected arrival time deviation exceeds a preset threshold, the uplink transmission time of the ground terminal is adjusted by a timed advance command.

9. A synchronization signal block for use in a non-terrestrial network communication system, characterized in that: The synchronization signal block occupies 5 consecutive OFDM symbols in the time domain, with symbol indices of 0, 1, 2, 3, and 4, and occupies 240 consecutive subcarriers in the frequency domain, with subcarrier indices from 0 to 239. Its time-frequency resource mapping relationship is as follows: Symbol index 0 carries the first main synchronization signal and occupies subcarriers 56 to 182 in the frequency domain. The remaining subcarriers are set to zero as guard bands. Symbol index 1 carries the first physical broadcast channel, occupying all 240 subcarriers, and contains the main information block data and demodulation reference signal; Symbol index 2 carries the auxiliary synchronization signal and physical broadcast channel extended data, wherein the auxiliary synchronization signal occupies subcarriers 56 to 182 in the frequency domain, subcarriers 0-47 and 192-239 carry physical broadcast channel extended data, and subcarriers 48-55 and 183-191 are set to zero as guard bands; Symbol index 3 carries the second main synchronization signal, occupying subcarriers 56 to 182 in the frequency domain, while the remaining subcarriers are set to zero as a guard band. Symbol index 4 carries the second physical broadcast channel, occupying all 240 subcarriers, and contains the remaining data of the main information block and the demodulation reference signal; The first primary synchronization signal and the second primary synchronization signal are generated from the same or different pseudo-random sequences.

10. A non-terrestrial network synchronization system based on bidirectional synchronization signal blocks, characterized in that: It includes satellite nodes configured to periodically transmit a first synchronization signal block based on the satellite's local clock, and to detect a second synchronization signal block at a pre-configured time-frequency resource location; At least one ground terminal is configured to detect the first synchronization signal block, establish local frame timing with reference to the arrival time of the first synchronization signal block, send the second synchronization signal block based on the local frame timing, and calibrate the local clock after receiving the one-way propagation delay fed back by the satellite. The first synchronization signal block and the second synchronization signal block occupy time domains A number of consecutive OFDM symbols occupy a certain number of positions in the frequency domain. A series of subcarriers, , The value is a preset positive integer; each synchronization signal block contains two main synchronization signal sequences, one auxiliary synchronization signal sequence, and physical broadcast channel data; The ground terminal uses the same physical cell identifier as the first synchronization signal block to generate the first primary synchronization signal sequence, the second primary synchronization signal sequence, and the secondary synchronization signal sequence of the second synchronization signal block, and the physical broadcast channel of the second synchronization signal block carries the terminal information block instead of the primary information block.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, it implements the method or system as described in any one of claims 1 to 10.

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