A multi-satellite cooperative downlink transmission method and system based on single-terminal multi-data flow

Abstract

This invention discloses a multi-satellite cooperative downlink transmission method and system based on a single terminal and multiple data streams. This invention addresses scenarios where a single terminal simultaneously receives multiple independent data streams from multiple cooperating satellites on the same time-frequency resources. The method includes: a master node satellite determining the set of satellites participating in the cooperative downlink transmission, the corresponding data streams for each satellite, the DMRS configuration type, sparse frequency domain mapping parameters, antenna port indexes, and phase shift indexes, and distributing the configuration parameters to each auxiliary node satellite via inter-satellite links; each cooperating satellite generating DMRS pilots with sparse frequency domain density and adjustable phase shifts, and transmitting its respective data stream after completing delay and Doppler pre-compensation; the terminal obtaining the DMRS sequence parameters and port mapping relationships based on downlink control information, and performing joint channel estimation and reception processing on the multi-satellite composite received signals. This invention reduces pilot resource usage while ensuring the terminal can distinguish and estimate the channels of each satellite, and supports multi-satellite cooperative downlink transmission.

Description

Technical Field

[0001] This invention belongs to the field of satellite communication technology, specifically relating to a multi-satellite collaborative downlink transmission method and system based on a single terminal and multiple data streams. Background Technology

[0002] Low Earth Orbit (LEO) satellite multi-satellite cooperative transmission technology effectively utilizes the terminal's spatial degrees of freedom, achieving spatial division multiplexing and improving system spectral efficiency by transmitting independent data streams to the same terminal in parallel within the same time-frequency resources. In LEO satellite multi-satellite cooperative downlink transmission, delay and Doppler compensation at the satellite side can ensure that orthogonal pilot signals transmitted by multiple satellites are aligned at the receiver, meaning the arrival delay difference is less than one cyclic prefix (CP) period, thus satisfying the pilot orthogonality condition for multiple channels. Multi-antenna terminals use demodulation reference signals (DMRS) to estimate the channel with different satellites, and then perform spatial domain reception processing to separate and demodulate multiple data streams. This fully utilizes the terminal's spatial degrees of freedom, achieving spatial division multiplexing gain and significantly improving system spectral efficiency and transmission rate. In multi-satellite cooperative downlink scenarios with multiple data streams from a single terminal, high-precision channel estimation at the terminal side is crucial for reliable joint transmission, thus requiring efficient DMRS pilot design. However, the DMRS scheme used in the current 3GPP standard for the Physical Downlink Shared Channel (PDSCH) has the following limitations:

[0003] 1. High frequency domain pilot density: The satellite-to-ground link has strong line of sight (LoS) and frequency flatness. The existing pilot density is too high in the frequency domain, and more OFDM symbols are needed to expand the antenna port, resulting in large pilot overhead and reduced spectral efficiency.

[0004] 2. Not suitable for multi-satellite collaboration: The existing DMRS scheme mainly uses the pilot design framework of 3GPP NR PDSCH for downlink of single transmitter node. It can be used as a reference pilot framework in satellite-to-ground communication, but it does not consider the allocation of pilot resources, inter-satellite port mapping and inter-satellite signaling coordination in multi-satellite collaboration scenarios. It is difficult to directly apply to multi-satellite collaborative transmission systems for single terminal and multiple data streams. Summary of the Invention

[0005] Purpose of the invention: This invention aims to provide a multi-satellite cooperative downlink transmission method based on a single terminal and multiple data streams. It integrates pilot configuration and distribution, pilot generation and transmission, terminal reception and joint channel estimation, receiving beamforming and separation of multiple data streams in the multi-satellite cooperative downlink process, in order to solve the problems of high frequency domain density and lack of multi-satellite cooperative signaling mechanism in existing pilot schemes.

[0006] Technical solution: To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0007] In a first aspect, the present invention provides a multi-satellite cooperative downlink transmission method based on a single terminal and multiple data streams, applicable to scenarios where the same terminal simultaneously receives multiple independent data streams from multiple cooperative satellites on the same time-frequency resource. The method includes the following steps:

[0008] The master node satellite determines the set of satellites participating in the cooperative downlink, assigns data stream numbers, antenna port indices, and phase shift indices to each cooperative satellite, and determines the DMRS configuration type and frequency domain sparse spacing parameters based on the satellite-to-ground link delay spread estimation; the DMRS configuration type is an extended sparse frequency domain mapping type.

[0009] The master node satellite will send configuration parameters, including data stream number, DMRS configuration type, sparse frequency domain mapping parameters, antenna port index, and phase shift index, to each auxiliary node satellite via inter-satellite link;

[0010] Each cooperating satellite generates a DMRS pilot sequence with sparse frequency domain density and adjustable phase shift on the same time and frequency resources based on the received configuration parameters. After completing downlink delay and Doppler pre-compensation, it transmits the DMRS pilot and the corresponding data stream.

[0011] The terminal obtains the DMRS configuration type, sparse frequency domain mapping parameters, antenna port index and phase shift index, the correspondence between antenna ports and cooperating satellites, and DMRS base sequence generation parameters based on the downlink control information sent by the master node satellite. It receives composite pilot signals sent by multiple cooperating satellites and performs joint channel estimation based on the DMRS base sequence and port mapping relationship in the downlink control information sent by the master node satellite to obtain the downlink channel information from each cooperating satellite to the terminal.

[0012] The terminal performs receive beamforming and multi-data stream separation based on the joint channel estimation results, and demodulates and receives multiple independent data streams transmitted by each cooperating satellite.

[0013] Furthermore, the single-terminal multiple data stream refers to the same terminal simultaneously receiving at least two independent downlink data streams transmitted by different cooperating satellites within the same time-frequency resource block; the master node satellite allocates different antenna port indices and phase shift indices to each cooperating satellite according to the number of independent downlink data streams, so that a one-to-one correspondence is formed between the antenna ports, cooperating satellites and data streams.

[0014] Furthermore, the frequency domain sparse spacing parameter is determined based on the comparison result between the maximum delay spread of the satellite-to-ground link and a preset threshold; when the maximum delay spread does not exceed the first threshold, the second sparse spacing type is selected; when the maximum delay spread is higher than the first threshold but does not exceed the second threshold, the first sparse spacing type is selected, wherein the second sparse spacing is greater than the first sparse spacing.

[0015] Furthermore, the frequency domain sparse spacing parameter is represented by the DMRS frequency domain group step parameter, the first... The position of the DMRS group in the frequency domain is determined by the starting subcarrier index, the frequency domain group step parameters, the local position offset function within the group, and the port offset corresponding to the antenna port.

[0016] Furthermore, all cooperating satellites share the same DMRS base sequence, the first... The DMRS pilot symbols corresponding to each antenna port are derived from the DMRS base sequence and phase shift index. The phase rotation factor is obtained by multiplying the determined phase rotation factors, which are used to distinguish different antenna ports on the same resource unit; different antenna ports use different phase shift indices. This ensures that the corresponding DMRS pilot sequence can be separated at the terminal side.

[0017] Furthermore, the phase rotation factor can take the form of a linear phase that varies with the subcarrier index. Different antenna ports correspond to different phase shift indices. The inner product of the DMRS pilot sequences of different antenna ports is zero or approximately zero. The autocorrelation of the DMRS pilot sequence inside each antenna port is zero or approximately zero at non-zero shifts.

[0018] Furthermore, the phase shift index is uniformly allocated by the master node satellite and sent to each auxiliary node satellite through the inter-satellite link; in a multi-satellite collaborative scenario with multiple data streams on a single terminal, one antenna port corresponds to one downlink data stream of a collaborative satellite.

[0019] Furthermore, the terminal obtains the DMRS base sequence, antenna port index, and phase shift index by: the master node satellite sending the DMRS configuration type and port mapping information to the terminal via downlink control signaling, and sending the same set of configuration parameters to each auxiliary node satellite via inter-satellite links, so that the known DMRS sequence parameters used for channel estimation on the terminal side are consistent with the parameters used for pilot generation on the satellite side.

[0020] Furthermore, the joint channel estimation employs least squares estimation or minimum mean square error estimation, and the received beamforming employs zero-forcing or minimum mean square error spatial filtering based on the estimated channel matrix to complete multi-data stream separation and demodulation reception.

[0021] Secondly, the present invention provides a multi-satellite cooperative downlink transmission system based on a single terminal and multiple data streams, used to implement the multi-satellite cooperative downlink transmission method based on a single terminal and multiple data streams described in the first aspect. The system includes a master node satellite, at least one auxiliary node satellite, and a target terminal, wherein:

[0022] The master node satellite is used to determine the set of satellites participating in the cooperative downlink, assign data stream numbers, antenna port indices, and phase shift indices to each cooperative satellite, and determine the DMRS configuration type and frequency domain sparse spacing parameters based on the satellite-to-ground link delay spread estimation; send the configuration parameters to each auxiliary node satellite via the inter-satellite link; and send the corresponding DMRS configuration type, sparse frequency domain mapping parameters, antenna port indices and phase shift indices, the correspondence between antenna ports and cooperative satellites, and DMRS base sequence generation parameters to the terminal via downlink control signaling.

[0023] The auxiliary node satellite is used to generate a DMRS pilot sequence with sparse frequency domain density and adjustable phase shift on the same time and frequency resources as the master node satellite according to the received configuration parameters. After completing downlink delay and Doppler pre-compensation, it transmits the DMRS pilot and corresponding data stream on the same time and frequency resources as the master node satellite.

[0024] The target terminal is used to receive composite pilot signals sent by multiple cooperating satellites according to downlink control information sent by the master node satellite, perform joint channel estimation, and perform receive beamforming and multi-data stream separation according to the joint channel estimation results, and demodulate and receive multiple independent data streams sent by each cooperating satellite.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0026] 1. Low pilot resource consumption: In this invention, the master node satellite determines the DMRS configuration type and frequency domain sparse spacing parameters based on the satellite-to-ground link delay spread estimation. The DMRS configuration type is an extended sparse frequency domain mapping type. By increasing the DMRS pilot subcarrier spacing according to the characteristics of strong line-of-sight between satellite and ground and low delay extended channel, the number of DMRS resource units within the same bandwidth is reduced, thereby reducing pilot overhead and releasing more time and frequency resources for service data transmission.

[0027] 2. Supports multi-satellite collaborative downlink: This invention enables the master node satellite to uniformly allocate antenna port indexes and phase shift indexes, and distributes unified DMRS configuration parameters to each auxiliary node satellite through inter-satellite links, so that each cooperating satellite can generate distinguishable pilot sequences on the same time and frequency resources, which facilitates the terminal to complete joint channel estimation.

[0028] 3. Facilitates compatibility with existing systems: This invention extends the sparse frequency domain mapping type on the basis of the existing DMRS configuration framework and reuses downlink control signaling and inter-satellite signaling to transmit relevant parameters, which is conducive to deployment in existing satellite communication systems. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the actual implementation process of multi-satellite collaborative downlink for single-terminal multi-data-stream systems.

[0030] Figure 2 This is a schematic diagram of a multi-satellite collaborative downlink transmission system based on a single terminal and multiple data streams.

[0031] Figure 3 This is a schematic diagram of the sparse frequency domain density pilot design of the present invention. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. These embodiments are only used to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0033] like Figure 1 As shown in the figure, this embodiment of the invention proposes a multi-satellite cooperative downlink transmission method based on a single terminal and multiple data streams. First, the master node satellite completes the selection of cooperative satellites and the configuration of pilot parameters. Second, the master node satellite completes the distribution of pilot parameters through inter-satellite links and downlink control signaling. Then, each cooperative satellite generates sparse DMRS pilots with adjustable phase shifts and sends the corresponding data streams. Finally, the terminal completes joint channel estimation, receive beamforming, and demodulation of multiple data streams.

[0034] Specifically, the multi-satellite cooperative downlink transmission method based on a single terminal and multiple data streams is applicable to scenarios where the same terminal receives multiple independent data streams from multiple cooperative satellites on the same time-frequency resource. Here, "single terminal" refers to a receiving terminal with only one target terminal, and "multiple data streams" refers to the target terminal simultaneously receiving multiple independent data streams from multiple cooperative satellites in the same time-frequency resource block. It should be noted that the number of data streams is no greater than the spatial separation dimension supported by the terminal. The method includes the following implementation steps:

[0035] Step 1: The master node satellite determines the set of satellites participating in the coordination based on the coordination scheduling results, assigns data stream numbers, antenna port indices and phase shift indices to each coordinating satellite, and determines the DMRS configuration type and frequency domain sparse spacing parameters based on the time delay spread estimation results of the satellite-to-ground link; wherein the DMRS configuration type is an extended sparse frequency domain mapping type.

[0036] Step 2: The master node satellite sends configuration parameters, including data stream number, DMRS configuration type, sparse frequency domain mapping parameters, antenna port index, and phase shift index, to each auxiliary node satellite via the inter-satellite link. It also sends the corresponding DMRS configuration type, sparse frequency domain mapping parameters, antenna port index and phase shift index, the correspondence between antenna ports and cooperative satellites, and DMRS base sequence generation parameters to the terminal via downlink control signaling, so that the pilot generation parameters on the satellite side are consistent with the known parameters on the terminal side.

[0037] Step 3: Each cooperating satellite generates a DMRS pilot sequence with sparse frequency domain density and adjustable phase shift on the same time-frequency resources based on the received configuration parameters. After completing downlink delay and Doppler pre-compensation, it transmits the DMRS pilot and corresponding data stream. Specifically, this includes:

[0038] Step 3.1: Each cooperating satellite performs DMRS mapping at the predetermined OFDM symbol position according to the DMRS type issued by the master node satellite; for strong line-of-sight satellite-to-ground links with small delay spread and large coherence bandwidth, the spacing between adjacent DMRS pilot subcarriers is increased to reduce pilot resource occupation; for scenarios with relatively strong frequency selectivity, a smaller sparse spacing is adopted.

[0039] Step 3.2: Based on sharing the same DMRS base sequence, each cooperating satellite applies different phase rotation factors to the DMRS pilot symbols mapped to the same resource unit according to the assigned antenna port index and phase shift index, so as to distinguish data streams from different satellites at the terminal side; the phase shift index is uniformly allocated by the master node satellite.

[0040] Step 3.3: Each cooperating satellite generates a DMRS pilot signal according to a unified configuration and carries its corresponding data stream. After completing time delay pre-compensation and Doppler pre-compensation, it sends downlink signals to the target terminal using the same time and frequency resources.

[0041] Step 4: Obtain the DMRS configuration type, sparse frequency domain mapping parameters, antenna port index and phase shift index, the correspondence between antenna ports and cooperating satellites, and DMRS base sequence generation parameters from the downlink control information sent by the master node satellite. Receive composite pilot signals sent by multiple cooperating satellites and perform joint channel estimation based on the DMRS base sequence and port mapping relationship in the downlink control information sent by the master node satellite to obtain the downlink channel information from each cooperating satellite to the terminal.

[0042] Step 5: The terminal performs receive beamforming and multi-data stream separation based on the joint channel estimation results, and demodulates and receives the multiple independent data streams sent by each cooperating satellite.

[0043] In the above steps, the inter-satellite signaling transmission process takes place before the satellite actually transmits the DMRS pilot signal. It is used to complete the pilot type selection, port index allocation, phase shift index allocation, and transmission timing coordination, thereby ensuring that multiple satellites form a distinguishable pilot structure on the terminal side.

[0044] In practical applications, the frequency domain sparse spacing parameter is determined based on the comparison result between the maximum delay spread of the satellite-to-ground link and a preset threshold; when the maximum delay spread does not exceed the first threshold, the second sparse spacing type is selected; when the maximum delay spread is higher than the first threshold but does not exceed the second threshold, the first sparse spacing type is selected, wherein the second sparse spacing is greater than the first sparse spacing.

[0045] The frequency domain sparse spacing parameter is represented by the DMRS frequency domain group step parameter. The position of the DMRS group in the frequency domain is determined by the starting subcarrier index, the frequency domain group step parameters, the local position offset function within the group, and the port offset corresponding to the antenna port.

[0046] In this embodiment, the extended sparse frequency domain mapping types are denoted as Type3 and Type4. The main difference between Type3 and Type4 lies in the different frequency domain sparse intervals. The former is suitable for relatively conservative sparse configurations, while the latter is suitable for scenarios with stronger line-of-sight and smaller latency spread. Both only change the mapping position of DMRS in the frequency domain, without changing the principle of constructing pilot orthogonality based on phase shift index. Therefore, this invention realizes a closed-loop design for pilot configuration, transmission, and reception processing in multi-satellite collaborative downlink through the implementation process of sparse frequency domain mapping, phase shift index differentiation, inter-satellite signaling distribution, and terminal joint estimation.

[0047] In some optional implementations, the cooperating satellites share the same DMRS base sequence, the first... The DMRS pilot symbols corresponding to each antenna port are derived from the DMRS base sequence and phase shift index. The phase rotation factor is obtained by multiplying the determined phase rotation factors, which are used to distinguish different antenna ports on the same resource unit; different antenna ports use different phase shift indices. This ensures that the corresponding DMRS pilot sequence can be separated at the terminal side.

[0048] The phase rotation factor can take the form of a linear phase that varies with the subcarrier index. Different antenna ports correspond to different phase shift indices, and the inner product of the DMRS pilot sequences of different antenna ports is zero or approximately zero. The autocorrelation of the DMRS pilot sequence within each antenna port is zero or approximately zero at non-zero shifts. The terminal separates the composite pilots according to the known phase shift index and port mapping relationship. The above phase shift construction can draw on the idea of ​​code division orthogonal pilots, and the improvement of this invention lies in its use with sparse frequency domain mapping, multi-satellite cooperative port allocation, and inter-satellite signaling linkage.

[0049] In practical implementation, the phase shift index is uniformly allocated by the master node satellite and sent to each auxiliary node satellite through the inter-satellite link; in the multi-satellite collaborative scenario with multiple data streams on a single terminal, one antenna port corresponds to one downlink data stream of a collaborative satellite.

[0050] In some optional implementations, the terminal obtains the DMRS base sequence, antenna port index, and phase shift index by: the master node satellite sending the DMRS configuration type and port mapping information to the terminal via downlink control signaling, and sending the same set of configuration parameters to each auxiliary node satellite via inter-satellite links, so that the known DMRS sequence parameters used for channel estimation on the terminal side are consistent with the parameters used for pilot generation on the satellite side.

[0051] In some optional implementations, the joint channel estimation employs least squares estimation or minimum mean square error estimation, and the receive beamforming employs zero-forcing or minimum mean square error spatial filtering based on the estimated channel matrix to complete multi-data stream separation and demodulation reception.

[0052] The proposed pilot design and inter-satellite signaling design will be explained in detail below with specific scenarios. Figure 2 This is a schematic diagram of a multi-satellite collaborative downlink transmission system based on a single terminal and multiple data streams. Figure 2 The angular parameters (azimuth) shown in the diagram are as follows. and pitch angle It is used to characterize the relative geometric relationship between the cooperating satellite and the target terminal, and can be used for cooperating satellite selection, beam pointing determination, and calculation of time delay and Doppler pre-compensation parameters.

[0053] 1. Pilot design

[0054] The core contradiction of DMRS lies in this: on the one hand, DMRS does not transmit effective data, and the more resources it consumes, the lower the data transmission efficiency; on the other hand, the denser the DMRS network, the more accurate the channel estimation, the better the receiver performance, and the more DMRS ports there are, the more users or data streams can be served simultaneously. For example... Figure 3 As shown, Configuration Type 1 and Type 2 are two reference configuration types defined by existing 3GPP protocols, which can serve as a reference basis for satellite-to-ground downlink pilot design. Type 1 has a wider frequency domain distribution and higher channel estimation accuracy in environments with richer multipath propagation, but supports relatively fewer concurrent data streams; Type 2 has more concentrated resources and improves port capacity through denser code division multiplexing. 3GPP specification 38.211 stipulates that DMRS sequences are mapped to resource elements according to the following formula, with frequency domain subcarrier indexes... satisfy

[0055] (1)

[0056] in For DMRS frequency domain group index, For local indexing of the frequency domain within the group, This is a port-dependent offset, generated by the antenna port. Refer to table (38.211, Table 7.4.1.1.2-1) to determine that for Type 1, For Type 2, According to the formula The frequency domain location of the pilot signals under existing Configuration Type 1 and Type 2 can be determined. For Type 1, take... , , Substitution Equation 1 yields This represents all even-numbered subcarriers within the physical resource block, with a density of... For Type 2, take , , Substitution Equation 2 yields This constitutes two sets of consecutive dual subcarriers ( and ), density is To describe the two types of sparse frequency domain mapping proposed in this invention, Type 3 and Type 4, the formula will be... Rewritten as a parameterized expression, for , No. Group, No. The DMRS subcarrier index of each antenna port is

[0057] (2)

[0058] in Indicates the starting subcarrier index of the DMRS frequency domain mapping. Indicates the connection with the antenna port The corresponding frequency domain offset, Indicates Type The frequency domain group step parameters, Indicates Type The intra-group offset function, Indicates Type This is the set of position indexes within the group, and all subsequent configuration types are expanded within this unified framework. Therefore, the parameter values ​​for Type 1 and Type 2 can be summarized in the following table:

[0059] Table 1. Parameter Values ​​for Type 1 and Type 2

[0060]

[0061] In multi-satellite collaborative scenarios, satellite-to-ground wireless channels typically propagate primarily using Loss of Path (LoS), with weak multipath components and minimal delay spread. Therefore, this invention increases the spacing between adjacent DMRS pilot subcarriers based on existing mapping concepts to construct two sparse frequency domain mapping types: Type 3 and Type 4. Type 3 corresponds to the first sparse interval, and Type 4 corresponds to the second sparse interval, with the second sparse interval being larger than the first. Essentially, this changes the frequency domain position occupied by the DMRS while maintaining the DMRS base sequence and port differentiation mechanism unchanged. Based on this, two new configuration types are designed, satisfying equation (2).

[0062] (3)

[0063] For Type 3, , No. Group, No. The DMRS subcarrier index of each antenna port can be represented as:

[0064] (4)

[0065] Type 3 continues the intra-group local structure of Configuration Type 1, that is, two frequency domain positions are still retained within the same group, with an interval of 2 subcarrier spacing units; the difference from the existing denser configuration is that the inter-group step parameter is increased. This increases the distance between adjacent groups in the frequency domain, thereby reducing the proportion of DMRS resources. If we take... , , Substituting into equation (4) yields

[0066] (5)

[0067] The total is Compared to Type 1, the number of subcarriers is reduced from 18 to 6 within 3 physical resource blocks, resulting in a decrease in resource element (RE) overhead. .

[0068] Compared to Type 3, Type 4 further improves sparsity, reserving only a single position within a group, and further reducing port capacity in exchange for maximum sparsity. , its first Group, No. The DMRS subcarrier index of each antenna port can be represented as:

[0069] (6)

[0070] Type 4 no longer retains the intra-group two-position structure, but instead maps only one frequency domain position per group. Therefore, the sparsity of Type 4 is achieved by two parts: the number of intra-group positions is reduced from two to one, and the inter-group step size is further increased. To make Type 4 more sparse than Type 3, the following should be satisfied: If we take , , Substituting into equation (6) yields

[0071] (7)

[0072] That is, each physical resource block occupies only one subcarrier, resulting in a decrease in overhead compared to Type 1. Therefore, the parameters can be summarized in the following table:

[0073] Table 2 Parameter value table for Type 1 to Type 4

[0074]

[0075] To ensure that the DMRS after sparse mapping still reflects the frequency domain changes of the channel, further analysis of the actual frequency domain sampling interval under different mapping types is needed. Let the system subcarrier interval be... Starting from equation (2), for two adjacent groups and The difference between the frequency domain positions can be obtained

[0076] (8)

[0077] Therefore, the actual frequency interval between two adjacent DMRS sets is: Considering the maximum delay spread of the strong line-of-sight channel between satellite and ground, it is... The corresponding coherent bandwidth is denoted as To ensure that the pilot signals after sparse mapping can still reflect changes in the channel frequency domain, the following conditions should be met: .

[0078] It should be particularly pointed out that, Figure 3 The sparsity of the intermediate frequency (IF) can be adjusted according to different deployment scenarios. Specifically, it can be based on the maximum latency spread of the satellite-to-ground link. The pilot spacing parameter is selected based on the coherent bandwidth estimate or a preset scenario threshold; when the time delay spread is small and the channel frequency selectivity is weak, a sparser Type 4 is selected; when the time delay spread is relatively large, a more conservative Type 3 is selected. In one possible implementation, the sparse mapping type can be selected according to the following rules: when... When the channel is sufficiently flat, select Type 4; when At that time, Type 4 was already too sparse, so Type 3 was chosen; among them, and A latency extension threshold pre-set according to business reliability requirements. This indicates that Type 3 may also be too sparse, requiring a switch back to a denser pilot configuration, or an increase in the number of pilot symbols and a reduction in the pilot step size. Compared to Configuration Type 1 and Type 2, this invention reduces time-frequency resource overhead by decreasing the proportion of pilot REs.

[0079] Adjustable phase-shifted pilots achieve orthogonal multiplexing of multiple pilot sequences by applying a known phase rotation to pilot symbols on the same RE, thus increasing the multiplexing degree of pilot sequences. Assume the number of DMRS pilot symbols on an OFDM symbol is... , No. The pilot signal corresponding to each antenna port is determined by the DMRS base sequence and the phase rotation factor corresponding to that antenna port. The above phase rotation construction can draw on the existing code division orthogonal pilot expression method, while the improvement of this invention is that it is used for sparse frequency domain mapping, port allocation and inter-satellite signaling coordination in multi-satellite cooperative scenarios.

[0080] (9)

[0081] in, The base sequence is (e.g., the Zadoff-Chu sequence). The phase rotation factor introduces a linear phase in the frequency domain to achieve code division orthogonality. Indicates the antenna port index. In this embodiment, each antenna port corresponds one-to-one with the cooperating satellite and the corresponding data stream, with a corresponding phase shift index.

[0082] Different antenna ports (cooperative satellites) The sequence inner product (cross-correlation) between them is zero or approximately zero, thus enabling the terminal to distinguish DMRS pilots from different satellites using known port indices and phase shift indices.

[0083] (10)

[0084] in To indicate conjugation, the base sequence (such as the Zadoff-Chu sequence) satisfies (Constant Modulus), the third row of the equation uses the formula for the summation of finite geometric series. When hour, Each term is 1, and the sum equals 1. ;when hour, It is an integer, because For any integer All are true (complex index) (with a period), we can obtain .

[0085] The autocorrelation of the sequence within each antenna port is zero or low at non-zero shifts, which helps the terminal suppress inter-pilot interference during joint channel estimation.

[0086] (11)

[0087] in Indicates conjugate. This is the autocorrelation shift. Because... It is an integer. and Only difference multiples of ,and (multiple indexes) (for a period), therefore we have Consider a base sequence that is an ideal autocorrelation sequence, satisfying... , For impulse functions, only when The value is 1 for the time and 0 for the rest.

[0088] For each antenna port, the master node satellite pre-assigns a corresponding phase shift index. It is then transmitted to the corresponding cooperating satellite via inter-satellite links; each cooperating satellite generates an adjustable phase-shift pilot based on the assigned phase-shift index.

[0089] (12)

[0090] It should be noted that the number of ports in equations (9) to (12) is used to describe the pilot configuration of different antenna ports and does not limit the number of cooperating satellites that the system can support. By uniformly allocating phase shift indexes and port indexes to the master node satellite, multi-satellite transmission can be supported on the same resources, achieving efficient reuse of time and frequency resources. The terminal obtains the DMRS base sequence from the downlink control information. and ports Corresponding phase shift index Joint channel estimation can be performed using least squares or least mean square error methods, thereby achieving spatial filtering and data stream separation. In one specific implementation, the terminal uses the received base sequence... and antenna port Corresponding phase shift index Known DMRS sequences can be obtained.

[0091] (13)

[0092] in This refers to the total number of satellites participating in the coordinated downlink. After multiple cooperating satellites transmit pilot signals on the same DMRS resource unit, the terminal... The composite pilot signal received by each receiving antenna is

[0093] (14)

[0094] in For the first One collaborative satellite to the terminal Downlink channel of each receiving antenna For noise. The received pilot signals within a DMRS resource cell are written in matrix form to obtain...

[0095] (15)

[0096] in The pilot matrix consists of known DMRS sequences for each port. The terminal can be obtained using least squares estimation.

[0097] (16)

[0098] When the DMRS sequences at each port are orthogonal or approximately orthogonal, there is , No. One collaborative satellite to the terminal The channel estimate for each receiving antenna can be expressed as:

[0099] (17)

[0100] After performing the above estimation on all receiving antennas, the terminal obtains the multi-satellite joint channel matrix. .in, The Column corresponding to the first The downlink channels from each cooperating satellite to each receiving antenna of the terminal. The terminal further identifies each column of channels as the downlink channel information of the corresponding cooperating satellite according to the correspondence between the antenna ports and the cooperating satellites.

[0101] Compared to single-satellite multi-data-stream transmission, in this embodiment, the composite pilot signal received by the terminal is independently transmitted by multiple spatially separated cooperating satellites, each corresponding to a different satellite-to-ground propagation link. The terminal does not estimate the composite pilot signal as a single pilot signal. Instead, it utilizes the DMRS base sequence, antenna port index, phase shift index, and the correspondence between antenna ports and cooperating satellites transmitted by the master node satellite to perform joint estimation and port-level separation of the composite pilot signal, thereby obtaining the channel information from each cooperating satellite to the terminal. Subsequently, the terminal performs zero-forcing or minimum mean square error reception filtering based on the multi-satellite joint channel matrix to achieve the separation and demodulation of multiple independent data streams.

[0102] 2. Inter-satellite signaling design

[0103] The current DMRS configuration signaling settings in PDSCH are as follows:

[0104]

[0105] The `dmrs-Type` indicates the DMRS configuration type used for the downlink, which determines the frequency domain mapping method. For the Type 3 and Type 4 sparse frequency domain mapping types proposed in this invention, configuration can be performed at the enumeration value extension position of this signaling. The difference between Type 3 and Type 4 lies in the different frequency domain sparse intervals: Type 3 is used for relatively conservative sparse configurations, while Type 4 is used for scenarios with stronger line-of-sight and smaller delay spread. The impact of both on the aforementioned adjustable phase-shift pilot design is only reflected in the different frequency domain positions of the DMRS; it does not affect the designed mechanism for port differentiation and pilot orthogonal multiplexing through phase-shift indexing. In a multi-satellite collaborative scenario, the master node satellite first sends Radio Resource Control (RRC) signaling to the auxiliary node satellite via inter-satellite links. The RRC signaling includes at least the DMRS configuration type, sparse frequency domain mapping parameters, antenna port index, and phase shift index. After parsing the signaling, the auxiliary node satellite generates DMRS pilots that are distinguishable from those of the master node satellite. Subsequently, each collaborative satellite transmits pilots on agreed time-frequency resources, and the terminal completes joint channel estimation, receiver beamforming, and multi-data stream reception based on the pre-received downlink control information.

[0106] Based on the same inventive concept, embodiments of the present invention provide a multi-satellite cooperative downlink transmission system based on a single terminal and multiple data streams, used to implement the multi-satellite cooperative downlink transmission method based on a single terminal and multiple data streams described in any of the foregoing examples. The system includes a master node satellite, at least one auxiliary node satellite, and a target terminal, wherein: the master node satellite is used to determine the set of satellites participating in the cooperative downlink, assign data stream numbers, antenna port indices, and phase shift indices to each cooperative satellite, and simultaneously determine the DMRS configuration type and frequency domain sparse spacing parameters based on the satellite-to-ground link delay spread estimation; send the configuration parameters to each auxiliary node satellite via inter-satellite links; and send the corresponding DMRS configuration type, sparse frequency domain mapping parameters, and antenna port index to the terminal via downlink control signaling. The system includes: line port index and phase shift index, the correspondence between antenna ports and cooperating satellites, and DMRS base sequence generation parameters; the auxiliary node satellite, which generates a DMRS pilot sequence with sparse frequency domain density and adjustable phase shift on the same time-frequency resources as the master node satellite according to the received configuration parameters, and transmits the DMRS pilot and corresponding data stream on the same time-frequency resources as the master node satellite after completing downlink delay and Doppler pre-compensation; and the target terminal, which receives composite pilot signals transmitted by multiple cooperating satellites according to downlink control information sent by the master node satellite, performs joint channel estimation, and performs receive beamforming and multi-data stream separation according to the joint channel estimation results, and demodulates and receives multiple independent data streams transmitted by each cooperating satellite.

[0107] The specific implementation of the satellite and terminal in the system is described in the foregoing method embodiments and will not be repeated here. Any aspects not detailed in this invention are well-known techniques to those skilled in the art.

Claims

1. A multi-satellite cooperative downlink transmission method based on single-terminal multi-data stream, characterized in that, The method, applicable to scenarios where a single terminal simultaneously receives multiple independent data streams from multiple cooperating satellites on the same time-frequency resource, includes the following steps: The master node satellite determines the set of satellites participating in the cooperative downlink, assigns data stream numbers, antenna port indices, and phase shift indices to each cooperative satellite, and determines the DMRS configuration type and frequency domain sparse spacing parameters based on the satellite-to-ground link delay spread estimation; the DMRS configuration type is an extended sparse frequency domain mapping type. The master node satellite will send configuration parameters, including data stream number, DMRS configuration type, sparse frequency domain mapping parameters, antenna port index, and phase shift index, to each auxiliary node satellite via inter-satellite link; and send the corresponding DMRS configuration type, sparse frequency domain mapping parameters, antenna port index and phase shift index, the correspondence between antenna ports and cooperative satellites, and DMRS base sequence generation parameters to the terminal via downlink control signaling. Each cooperating satellite generates a DMRS pilot sequence with sparse frequency domain density and adjustable phase shift on the same time and frequency resources based on the received configuration parameters. After completing downlink delay and Doppler pre-compensation, it transmits the DMRS pilot and the corresponding data stream. The terminal obtains the DMRS configuration type, sparse frequency domain mapping parameters, antenna port index and phase shift index, the correspondence between antenna ports and cooperating satellites, and DMRS base sequence generation parameters based on the downlink control information sent by the master node satellite. It receives composite pilot signals sent by multiple cooperating satellites and performs joint channel estimation based on the DMRS base sequence and port mapping relationship in the downlink control information sent by the master node satellite to obtain the downlink channel information from each cooperating satellite to the terminal. The terminal performs receive beamforming and multi-data stream separation based on the joint channel estimation results, and demodulates and receives multiple independent data streams transmitted by each cooperating satellite.

2. The single- terminal multi-data stream based multi-satellite coordinated downlink transmission method of claim 1, wherein, The term "single terminal multiple data streams" refers to the simultaneous reception of at least two independent downlink data streams transmitted by different cooperating satellites within the same time-frequency resource block by the same terminal. The master node satellite assigns different antenna port indices and phase shift indices to each cooperating satellite according to the number of independent downlink data streams, so that a one-to-one correspondence is formed between the antenna ports, cooperating satellites, and data streams. 3.The single-antenna multi-data stream based multi-satellite coordinated downlink transmission method of claim 1, wherein, The frequency domain sparse spacing parameter is determined based on the comparison between the maximum delay spread of the satellite-to-ground link and a preset threshold; when the maximum delay spread does not exceed the first threshold, the second sparse spacing type is selected. When the maximum delay spread is higher than the first threshold but not higher than the second threshold, the first sparse interval type is selected, where the second sparse interval is greater than the first sparse interval.

4. The single- terminal multi-data stream based multi-satellite coordinated downlink transmission method of claim 1, wherein, The frequency domain sparse interval parameter is expressed by a DMRS frequency domain group step parameter, and the first The position of the group DMRS in the frequency domain is determined by a starting subcarrier index, a frequency domain group step parameter, a local position offset function in the group, and a port offset corresponding to the antenna port.

5. The single- terminal multi-data stream based multi-satellite coordinated downlink transmission method of claim 1, wherein, All cooperating satellites share the same DMRS base sequence, the first The DMRS pilot symbols corresponding to each antenna port are derived from the DMRS base sequence and phase shift index. The phase rotation factor is obtained by multiplying the determined phase rotation factors, which are used to distinguish different antenna ports on the same resource unit; different antenna ports use different phase shift indices. This ensures that the corresponding DMRS pilot sequence can be separated at the terminal side.

6. The method according to claim 5, wherein, The phase rotation factor can take the form of a linear phase that varies with the subcarrier index. Different antenna ports correspond to different phase shift indices. The inner product of the DMRS pilot sequences of different antenna ports is zero or approximately zero. The autocorrelation of the DMRS pilot sequence inside each antenna port is zero or approximately zero at non-zero shifts.

7. The single- terminal multi-data stream based multi-satellite coordinated downlink transmission method of claim 5, wherein, The phase shift index is uniformly allocated by the master node satellite and sent to each auxiliary node satellite through the inter-satellite link; in a multi-satellite collaborative scenario with multiple data streams on a single terminal, one antenna port corresponds to one downlink data stream of a collaborative satellite.

8. The single- terminal multi-data stream based multi-satellite coordinated downlink transmission method of claim 1, wherein, The terminal obtains the DMRS base sequence, antenna port index, and phase shift index by means of: the master node satellite sending the DMRS configuration type and port mapping information to the terminal through downlink control signaling, and sending the same set of configuration parameters to each auxiliary node satellite through inter-satellite links, so that the known DMRS sequence parameters used for channel estimation on the terminal side are consistent with the parameters used for pilot generation on the satellite side.

9. The single- terminal multi-data stream based multi-satellite coordinated downlink transmission method of claim 1, wherein, The joint channel estimation employs least squares estimation or minimum mean square error estimation, and the receive beamforming employs zero-forcing or minimum mean square error spatial filtering based on the estimated channel matrix to complete multi-data stream separation and demodulation reception.

10. A multi-satellite coordinated downlink transmission system based on single-terminal multi-data stream, configured to implement the multi-satellite coordinated downlink transmission method based on single-terminal multi-data stream according to any one of claims 1-9, characterized in that, It includes a master node satellite, at least one auxiliary node satellite, and a target terminal, wherein: The master node satellite is used to determine the set of satellites participating in the cooperative downlink, assign data stream numbers, antenna port indices, and phase shift indices to each cooperative satellite, and determine the DMRS configuration type and frequency domain sparse spacing parameters based on the satellite-to-ground link delay spread estimation; send the configuration parameters to each auxiliary node satellite via the inter-satellite link; and send the corresponding DMRS configuration type, sparse frequency domain mapping parameters, antenna port indices and phase shift indices, the correspondence between antenna ports and cooperative satellites, and DMRS base sequence generation parameters to the terminal via downlink control signaling. The auxiliary node satellite is used to generate a DMRS pilot sequence with sparse frequency domain density and adjustable phase shift on the same time and frequency resources as the master node satellite according to the received configuration parameters. After completing downlink delay and Doppler pre-compensation, it transmits the DMRS pilot and corresponding data stream on the same time and frequency resources as the master node satellite. The target terminal is used to receive composite pilot signals sent by multiple cooperating satellites according to downlink control information sent by the master node satellite, perform joint channel estimation, and perform receive beamforming and multi-data stream separation according to the joint channel estimation results, and demodulate and receive multiple independent data streams sent by each cooperating satellite.

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