Method and system for analyzing the aggregate downlink interference of DTC system to IMT users

Abstract

The present invention discloses a method and system for analyzing the aggregate downlink interference of a DTC system to an IMT user. The method comprises the following steps: step 1: obtaining a probability distribution function of the off-axis angle of a randomly pointing beam of a satellite to an interfered IMT user at any protection distance; step 2: mapping to obtain a probability distribution function of the logarithmic value of the interference gain of the satellite beam to the interfered IMT user; step 3: mapping the probability distribution function of the logarithmic value of the interference gain to a probability distribution function of the linear value of the interference gain; step 4: abstracting the interference gain of the satellite beam to the interfered IMT user as channel fading; step 5: calculating and outputting the aggregate interference distribution of the DTC system to the interfered IMT system user, and adjusting the downlink interference compensation strategy between the satellite and the IMT user based on the analysis results. The present invention can obtain interference analysis results that are more in line with reality, thereby improving the reliability of the communication link of the mobile phone directly connected to the satellite system and ensuring the signal coverage quality.

Description

Technical Field

[0001] The present invention relates to the field of wireless communications, and in particular to a method and system for analyzing downlink aggregate interference of a DTC system to an IMT user. Background Art

[0002] Satellite communications are considered a crucial means of reaching remote areas, oceans, mountainous areas, and other areas with limited connectivity. They also play a vital role in emergency rescue, military aerospace, and other fields. Currently, satellite communications systems are increasingly integrating with terrestrial communications systems to achieve ubiquitous coverage across the air, space, land, and sea in the future 6G (6th Generation Mobile Communication Technology) mobile communications system. Direct-to-cell (DTC) technology has made significant progress in recent years, enabling it to provide basic communications services to commercial devices, improving global communications coverage and access, and becoming a key technology in satellite-ground integration.

[0003] When large-scale satellite systems with steerable beams, used for direct mobile phone connections to satellites, interfere with the downlinks of terrestrial IMT user terminals, traditional time-stepping simulation methods are inefficient and the interference mechanisms are unclear. Interference from satellite downlinks to mobile phones can reduce the received signal-to-interference-and-noise ratio (SINR), leading to increased bit error rates, decreased data rates, and even link interruptions. Therefore, to maintain the reliability of direct mobile phone connection satellite systems and ensure coverage quality, downlink interference analysis between satellite communication systems and terrestrial IMT (International Mobile Telecommunications) systems in spectrum sharing scenarios is necessary. This is particularly important for evaluating and optimizing frequency interference when NTN (Non-Terrestrial Networks) and TN (Terrestrial Networks) coexist. Summary of the Invention

[0004] The technical problem to be solved by the embodiments of the present invention is to provide a method and system for analyzing the downlink aggregate interference of a DTC system to an IMT user, so as to improve the reliability of the communication link of a mobile phone directly connected to a satellite system.

[0005] To solve the above technical problems, an embodiment of the present invention proposes a method for analyzing the aggregate downlink interference of a DTC system to an IMT user, comprising:

[0006] Step 1: Obtain the probability distribution function of the off-axis angle of the satellite's randomly pointing beam to the interfered IMT user at any protection distance;

[0007] Step 2: Map and obtain the probability distribution function of the logarithm of the interference gain of the satellite beam to the interfered IMT user;

[0008] Step 3: Map the probability distribution function of the logarithmic value of the interference gain to the probability distribution function of the linear value of the interference gain;

[0009] Step 4: Based on the probability distribution function of the linear value of the interference gain, the interference gain of the satellite beam to the interfered IMT user is abstracted into channel fading;

[0010] Step 5: Calculate and output the aggregate interference distribution of the DTC system to the interfered IMT system users, and adjust the downlink interference compensation strategy between the satellite and the IMT users based on the analysis results.

[0011] Accordingly, an embodiment of the present invention further provides a system for analyzing downlink aggregate interference of a DTC system to an IMT user, including:

[0012] Off-axis angle unit: obtains the probability distribution function of the off-axis angle of the satellite's randomly pointing beam to the interfered IMT user at any protection distance;

[0013] Logarithmic unit: maps the probability distribution function of the logarithmic value of the interference gain of the satellite beam to the interfered IMT user;

[0014] Linear value unit: maps the probability distribution function of the logarithmic value of the interference gain to the probability distribution function of the linear value of the interference gain;

[0015] Abstraction unit: Based on the probability distribution function of the linear value of the interference gain, the interference gain of the satellite beam to the interfered IMT user is abstracted into channel fading;

[0016] Output unit: Calculates and outputs the aggregate interference distribution of the DTC system to the interfered IMT system users, and adjusts the downlink interference compensation strategy between the satellite and the IMT users based on the analysis results.

[0017] The present invention has the following beneficial effects: It proposes a downlink interference analysis model for a DTC system with a protection distance constraint to an IMT system, and provides a complete lumped interference analysis derivation method based on the Poisson Point Process (PPP) and Binomial Point Process (BPP). This addresses the lack of interference modeling and analysis research for the emerging mobile phone direct satellite connection application system. Furthermore, it innovatively incorporates the random pointing model of the satellite beam and proposes a mapping method based on the actual satellite antenna pattern function, ultimately obtaining a probability distribution function for the interference gain of the interfered IMT user. This allows the analysis of random geometry to be extended to satellite systems with steerable beams. By incorporating random geometry methods, the present invention achieves efficient interference analysis in the proposed scenario. Compared with existing methods, the overall system interference analysis can produce more realistic interference analysis results, thereby improving the reliability of the communication link of the mobile phone direct satellite connection system and ensuring signal coverage quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural diagram of an interference scenario applied in an embodiment of the present invention.

[0019] Figure 2 Schematic diagram of a mathematical model for calculating the average number of satellites within a spherical cap according to an embodiment of the present invention.

[0020] Figure 3 2 is a schematic diagram of error analysis of different satellite density calculation methods according to an embodiment of the present invention.

[0021] Figure 4 It is a schematic diagram of plane modeling of a protection distance scenario according to an embodiment of the present invention.

[0022] Figure 5 This is an embodiment of the present invention Solution diagram.

[0023] Figure 6 This is a simulation verification diagram of the random directivity gain derivation according to an embodiment of the present invention.

[0024] Figure 7 1 is a diagram of the derivation and verification of PPP-URPM / SRPM under different numbers of orbital shell satellites according to an embodiment of the present invention, wherein (a) is based on PPP-URPM and (b) is based on PPP-SRPM.

[0025] Figure 8 This is a diagram of the derivation and verification of BPP-URPM under different numbers of orbital shell satellites in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] It should be noted that, unless there is a conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention is further described in detail below with reference to the drawings and specific embodiments.

[0027] In the embodiments of the present invention, if there are directional indications (such as up, down, left, right, front, back, etc.), they are only used to explain the relative position relationship and movement status of the various components under a specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0028] In addition, the terms "first," "second," and so on, used in this disclosure are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features being referred to. Therefore, features specified as "first" or "second" may explicitly or implicitly include at least one of these features.

[0029] The present invention is applied to the downlink interference scenario of a low-orbit DTC system with steerable beams on an IMT system user. The method for analyzing the downlink aggregate interference of a DTC system on an IMT user in an embodiment of the present invention includes steps 1 to 5.

[0030] Step 1: Obtain the probability distribution function of the off-axis angle of the satellite's randomly pointing beam to the interfered IMT user at any protection distance.

[0031] Step 2: Map and obtain the probability distribution function of the logarithm of the interference gain of the satellite beam to the interfered IMT user.

[0032] Step 3: Map the probability distribution function of the logarithmic value of the interference gain to the probability distribution function of the linear value of the interference gain.

[0033] Step 4: Based on the probability distribution function of the linear value of the interference gain, the interference gain of the satellite beam to the interfered IMT user is abstracted as channel fading.

[0034] Step 5: Calculate and output the aggregate interference distribution of the DTC system to the interfered IMT system users, and adjust the downlink interference compensation strategy between the satellite and the IMT users based on the analysis results.

[0035] The core interference scenario of the present invention is the aggregate downlink interference of the DTC system to the IMT system users. The most basic interference protection variable involved is the protection distance. On the side of the interfered IMT system, a mobile terminal is deployed on the surface of the earth. The terminal is equipped with an omnidirectional antenna to receive the downlink signal from the nearest base station. This basic configuration conforms to the general IMT system modeling method. On the side of the interfering DTC system, the interference distance of the satellite is defined. The shortest distance from the satellite coverage area to the interfered terminal. , any interference distance satisfies The satellites in the interference protection zone shall not operate at the same frequency as the interfered terminal. This forms an interference protection zone for the interfered terminal. Any interfering satellite in the protection zone will not cause interference to the terminal. Figure 1 The visible space outside the protection zone for the terminal is called the interference zone, and the satellites in this area will cause co-frequency interference to the terminal. Figure 1 Analysis shows that the size of the interference protection zone is related to the protection distance and the size of the satellite's sub-satellite coverage area. The user distribution of a DTC system is widespread and random, so the satellite uses a steerable beam within its coverage area and achieves quasi-random directionality based on a scheduling strategy. The above is the core scenario modeling method of the present invention. Within this model, further modeling is required for the network model, link model, and random pointing model of each system. This will be described in detail in subsequent embodiments.

[0036] The method of the present invention mainly includes two parts. The first part proposes an analytical method for calculating the probability distribution function of the interference gain of a satellite with a steerable beam to an interfered IMT user under arbitrary protection distance constraints: for the case where the satellite beam has random directivity, combined with the proposed random pointing analysis model, the probability distribution function of the off-axis angle of a single satellite's randomly pointing beam to the interfered IMT user under arbitrary protection distance is derived by mathematical methods. On this basis, according to the transformation rule of the probability density function, as long as the antenna pattern function of the satellite beam and the off-axis angle satisfy monotonicity, the probability distribution function of the logarithmic value of the interference gain of the satellite beam to the interfered IMT user can be mapped. Finally, according to the monotonic mapping relationship between the logarithmic value and the linear value, the probability distribution function of the logarithmic value of the interference gain is finally mapped to the probability distribution function of the linear value of the interference gain. Second, a Stochastic Geometry (SG) analysis method is proposed to calculate the aggregate downlink interference from the DTC system to the interfered IMT users under the proposed interference scenario model. Based on the probability distribution function of the satellite beam interference gain obtained in Analysis Method 1 (Part 1), the satellite beam interference gain to the interfered IMT users is abstracted as a channel fading. Finally, based on the proposed interference scenario model, two typical SG models, PPP and BPP, are used to propose SG calculation and analysis methods to analyze the distribution of the aggregate interference from the DTC system to the interfered IMT users.

[0037] The embodiments of the present invention are mainly divided into three parts. The first part specifically describes the interference scenario and the implementation of mathematical modeling of the present invention; the second part more specifically describes the derivation method of the probability distribution function of the interference gain of the satellite's random pointing beam on the interfered IMT user; the third part specifically explains the interference analysis method and implementation using two typical SG models, PPP and BPP, for the downlink aggregate interference of the DTC system to the IMT user under the proposed scenario model.

[0038] First, the mobile phone direct connection satellite system acts as the jammer, and the satellite operates at an altitude of On the orbital plane, the minimum service elevation angle is , the semi-geocentric angle of the corresponding satellite coverage area is calculated as:

[0039] (1)

[0040] in is the radius of the earth. , and its corresponding geocentric angle is , so the angle between the satellite in the interference area and the interfered terminal is The minimum and maximum values ​​are:

[0041] (2)

[0042] The smallest exist Figure 1 In this study, the distribution of satellites on the orbital height sphere is modeled as PPP and BPP respectively. For the satellite density parameter under the PPP model The prior art has disclosed (ITU. Analytical method for determining the statistics of interference between non-geostationary orbit fixed-satellite service systems and other non-geostationary-satellite orbit fixed-satellite service systems or geostationary-satellite orbit fixed-satellite service networks: Recommendation ITU-R S.1529-0[R]. ITU-R, 2001.) The satellite spatial probability density under:

[0043] (3)

[0044] in is the longitude variable, is a latitude variable. Therefore, the satellite density above any latitude whose absolute value is less than the inclination is calculated as:

[0045] (4)

[0046] in is the total number of satellites in the system.

[0047] Now take the center of the earth as the coordinate origin, for any target terminal latitude , and the angle between it and the center of the earth is The coordinates of the center of the visible spherical cap ring As shown in formula (5), represent No. Axis coordinates ( The overall model is as follows. Figure 2 shown.

[0048] (5)

[0049] The radius of this visible spherical cap is , so for any latitude within the spherical cap latitude , the corresponding longitude span within the spherical cap is:

[0050] (6)

[0051] Furthermore, the average density of satellites in the spherical cap can be calculated according to equations (4) and (6):

[0052] (7)

[0053] Since only the interference occurrence area needs to be analyzed, the average density of satellites in the interference occurrence area is:

[0054] (8)

[0055] To verify the calculation accuracy of formula (8), a track with an inclination of 60° is designed. Walker constellation, the difference between the calculated satellite density and the actual satellite density at each latitude is simulated and analyzed, and the approximate calculation method in the existing technology (ElSawy H, Sultan-Salem A, Alouini MS, et al. Modeling and analysis of cellular networks using stochastic geometry: A tutorial[J]. IEEE CommunicationsSurveys & Tutorials, 2016, 19(1): 167-203.) is used as a comparison. Figure 3 The results show that Equation (8) has a very good approximation to the satellite density under the actual constellation. This is because Equation (8) accurately considers the satellite probability density integral on the orbital shell in the interference occurrence area.

[0056] The ground mobile terminal acts as the interfered communication node, configures an omnidirectional antenna, and establishes a link with the ground base station closest to it. The ground base station is modeled using two-dimensional PPP. The density of the base station per unit area is For the PPP model, at any distance from the mobile terminal Within the range, the point process intensity of the base station Calculated as Therefore, the distance between the terminal and the base station is Less than or equal to The probability of The probability that there is a base station within the range:

[0057] (9)

[0058] Further derivation of the cumulative distribution function can be obtained about the chain distance The probability distribution of is:

[0059] (10)

[0060] For the downlink from the base station to the terminal, the base station transmit power is , the base station antenna gain is , the path loss index is , channel fading , the terminal omnidirectional antenna receives with unity gain, so the signal strength of the interfered link is described as:

[0061] (11)

[0062] For the satellite-to-ground downlink, the satellite transmit power , the antenna peak gain is (Unit: dBi), beamwidth is calculated according to formula (12) (unit: degree):

[0063] (12)

[0064] The gain of the satellite beam to the interfered terminal is affected by the randomness of the satellite pointing and is Correlated random variables, using Description: The satellite antenna gain is shown in equation (13), unit: dBi.

[0065] (13)

[0066] in is the beam off-axis angle (unit: degree), = 1.5 times the half beamwidth (unit: degree). For simplicity, the far sidelobe level of the antenna is ignored. ,Since the core of scenario analysis is interference, simplification of weak interference gain is not expected to have a significant ,impact on the final analysis results.

[0067] In terms of satellite-to-ground link loss, considering the free space loss, the angle between the satellite and the center of the earth of the disturbed terminal is The path loss from the satellite to the terminal is:

[0068] (14)

[0069] in is the speed of light, take , is the signal carrier frequency, in Hz.

[0070] Based on the above, the interference signal strength of the satellite to the terminal is:

[0071] (15)

[0072] It is necessary to consider the influence of random directivity of satellite beam in the study and note that the random directivity gain of beam to the interfered terminal is different at different interference distances. The premise for obtaining the beam interference gain distribution is to obtain the probability distribution of the satellite beam's off-axis angle to the interfered terminal and map it to the gain distribution based on the actual antenna pattern function. Since the calculation of the off-axis angle is quite complicated on the spherical model, the analytical model under the protection distance condition is approximately simplified to the plane case, such as Figure 4 As shown in the figure, the sub-satellite point is modeled as the origin of the coordinate system, the direction from the sub-satellite point to the disturbed terminal is the X axis, and the direction to the satellite is the Z axis. The satellite coordinate vector , under-satellite coverage area radius , terminal coordinate vector For a satellite beam, the pointing center passes through the azimuth angle in the xOy plane. and the distance from the origin Expressed as .

[0073] The above technical details provide a specific system modeling approach, including a mathematical model for analyzing satellite random directivity. The following section analyzes the specific derivation of the probability distribution function for the interference gain of a satellite beam on an interfered IMT user, which is Technical Section 2.

[0074] First, for the case where the satellite beam is uniformly distributed in the sub-satellite coverage area, this model is called URPM (Uniform Random Pointing Model). and centrifugal radius The joint probability density of is:

[0075] (16)

[0076] Direction vector from satellite to beam center , the direction vector from the satellite to the disturbed terminal , so the cosine of the beam off-axis angle is:

[0077] (17)

[0078] in , .

[0079] because It's about function, and the joint probability density function of the two variables is known, so The probability density function of can be calculated. The analysis and calculation results are as follows. Assume the reference value ,when When:

[0080] (18)

[0081] when When:

[0082] (19)

[0083] in and is a random variable describing the coordinate position of the satellite beam in the area covered by the satellite. is the distance between the satellite beam center and the sub-satellite point, is the azimuth of the beam center; Z θFor random variables 、 A random variable that describes the cosine value of the off-axis angle of the satellite beam to the victim terminal (z is the characteristic of Z θ distributed function variables); is the angle between the satellite in the interference area and the interfered IMT user terminal, is the radius of the earth; F() is the cumulative distribution function, is the radius of the satellite coverage area, h is the altitude of the satellite's orbit, π is the circumference of a circle, and d is the integral sign. To satisfy The minimum distance from the subsatellite point among all beams with the value of , which is located on the X axis of the scene, is obtained by Figure 5 The geometric relationships shown are calculated and solved.

[0084] about Although the cumulative distribution function of is expressed piecewise, the entire function is continuous on the domain of definition and can be obtained by taking the derivative of the cumulative distribution function. The probability density function of . Since the distribution expression is complex and not closed, only the important results in the derivation process are given:

[0085] (20)

[0086] in The derivative of Figure 5 Obtained After obtaining the probability distribution of the satellite beam off-axis angle cosine value, the probability distribution of the off-axis angle cosine value is mapped to the probability distribution of the off-axis angle according to the probability density function transformation rule, and then mapped to the probability distribution of the beam gain logarithm according to the antenna pattern function. Finally, the probability distribution of the linear value of the random pointing beam gain is obtained according to the conversion relationship between the logarithm and the linear value, which is recorded as .

[0087] In order to verify the correctness of the derivation, a numerical method is used to compare the complex analytical results with the simulation under Monte Carlo. The results are as follows: Figure 6 This verification curve is obtained under the conditions of a satellite orbit altitude of 600 km, a minimum service elevation angle of 40°, a protection distance of 270 km, and a beam peak gain of 35 dBi.

[0088] The distribution of the interference gain of a satellite beam to a victim terminal under the uniform random pointing model is complex and non-closed-form, so a simplified mathematical model of the random pointing gain is necessary. Note that when the off-axis angle of the satellite beam to the terminal follows a uniform distribution within the domain of definition, a simple expression for the random pointing gain can be obtained. This distribution model is called the Simplified Random Pointing Model (SRPM). Subsequent simulations show that the interference distribution curves obtained under the SRPM are quite close to those obtained under the URPM.

[0089] For height , the minimum service elevation angle is The satellite field of view angle corresponding to the satellite coverage area for:

[0090] (twenty one)

[0091] Since the off-axis angle of the satellite beam to the disturbed terminal obeys a uniform distribution within the definition domain, the probability density function of the beam off-axis angle is:

[0092] (twenty two)

[0093] in The value range of is:

[0094] (twenty three)

[0095] Based on the probability distribution of the off-axis angle, the probability distribution of the logarithmic gain value is given by the reference REC-1528 antenna pattern function. In order to make the expression easy to handle, the antenna gain is expressed by a unique function:

[0096] (twenty four)

[0097] This gain function covers the vast majority of off-axis angles in the antenna pattern function. It only overestimates the actual gain in very low-probability off-axis angle events (less than 1.5 times the half-beamwidth), which may lead to relatively pessimistic analytical results on a smaller statistical scale. According to equations (22) and (24), the probability density function of the logarithm of the beam gain is:

[0098] (25)

[0099] in, is the probability distribution function of the logarithmic gain, is the random variable of the logarithmic value of the interference gain, Y is usually 1.5 times the satellite half beam width, G mLs is the peak gain of the satellite antenna, which is generally -6.75dB.

[0100] According to the conversion relationship between logarithmic value and linear value, the probability density function of the gain linear value is obtained as follows:

[0101] (26)

[0102] The lower and upper bounds of the domain of the distribution function are calculated as:

[0103] (27)

[0104] The above is a method for deriving the probability distribution function of beam interference gain. The following content proposes a method for deriving the distribution expression of the aggregate downlink interference of the DTC system to IMT users based on PPP and BPP, which is the third technical part.

[0105] For interference indicators SIR (Signal to Interference Ratio) and arbitrary thresholds , SIR is greater than The probability of the useful signal can be analyzed as In different The total probability formula that satisfies this condition is:

[0106] (28)

[0107] in SIR is the signal-to-interference ratio of the satellite system to the terminal aggregate interference, T is the threshold, S is the signal strength from the base station to the terminal, P describes the probability, r0 is the communication distance from the terminal to the base station, is the probability density function about r0, calculated as ,in is the deployment density of base stations per unit area; is the base station antenna gain, P bs is the base station transmission power, P sat is the satellite transmission power, is the included angle between satellite i in the satellite set and the terminal’s geocentric center, is the random pointing gain of the beam of satellite i in the satellite set to the terminal, is the satellite point process set, is the free space loss from satellite i to the terminal.

[0108] because It follows a logarithmic distribution with mean 1, so:

[0109] (29)

[0110] in , is the satellite point set, is the satellite point process space, The process applies the probability generation functional (PGFL) of PPP, . The general expression is:

[0111] (30)

[0112] in and The off-axis angle range is obtained by equation (23), which is substituted into the antenna pattern function and converted into a linear value. Since the satellite beam random pointing gain is not a closed form under the actual analytical method, only the expression under SRPM is given:

[0113] (31)

[0114] Figure 7 The correctness of the results derived in this section was verified using the Monte Carlo method under URPM and SRPM. The parameters for the satellite system are set to be 600 km orbital altitude, 30° minimum service elevation angle, 100 km protection distance, 30 dBi satellite antenna peak gain, and 20 dBW / 20 MHz transmit power. The ground-side base station spacing is 1200 m (converted to Approximately ), path loss index , the base station antenna gain is 18 dBi (the default main axis points to the user), and the transmission power is 16 dBW / 20 MHz. In addition, the signal frequency is selected as 2 GHz. It is noted that when the number of satellites is small, the CDF (Cumulative Distribution Function) does not converge to 1 significantly. The reason is that Equation (29) has already implied the probability that there is no satellite in the interference area, and the SIR is always greater than when there is no interfering satellite. .

[0115] For the BPP model, the number of satellites appearing in the orbital spherical point space is a fixed integer. Similar to PPP, the position of each satellite point is uniformly random and independent and identically distributed in the point space. Therefore, for any satellite, the probability of it appearing in the interference area is:

[0116] (32)

[0117] The corresponding probability of not appearing in the interference area for For the BPP model, formula (28) is also applicable, and formula (29) is changed to:

[0118] (33)

[0119] in The process is based on the independent and identical distribution of each point. Calculated as:

[0120] (34)

[0121] in Same as formula (30), It is the angle between the satellite and the center of the earth of the disturbed terminal under the condition that the satellite appears in the interference area. The probability distribution of is calculated by taking the derivative of the cumulative distribution function of the satellite in the interference region:

[0122] (35)

[0123] According to the above derivation, Figure 8 The correctness of the derivation results was verified by Monte Carlo. Figure 7 The simulation results are verified in the URPM model, so only the simulation results of the URPM analytical model are provided. The parameter selection is the same as that of PPP.

[0124] The system for analyzing downlink aggregate interference of a DTC system to an IMT user according to an embodiment of the present invention includes:

[0125] Off-axis angle unit: obtains the probability distribution function of the off-axis angle of the satellite's randomly pointing beam to the interfered IMT user at any protection distance;

[0126] Logarithmic unit: maps the probability distribution function of the logarithmic value of the interference gain of the satellite beam to the interfered IMT user;

[0127] Linear value unit: maps the probability distribution function of the logarithmic value of the interference gain to the probability distribution function of the linear value of the interference gain;

[0128] Abstraction unit: Based on the probability distribution function of the linear value of the interference gain, the interference gain of the satellite beam to the interfered IMT user is abstracted into channel fading;

[0129] Output unit: Calculates and outputs the aggregate interference distribution of the DTC system to the interfered IMT system users, and adjusts the downlink interference compensation strategy between the satellite and the IMT users based on the analysis results.

[0130] As an implementation method, the off-axis angle unit adopts a uniform random pointing model or a simplified random pointing model to obtain a probability distribution function of the off-axis angle θ, and sets:

[0131] ;

[0132] The probability distribution function of the off-axis angle obtained using the uniform random pointing model is:

[0133] Set a baseline value ,when When:

[0134] ;

[0135] when When:

[0136] ;

[0137] in, and is a random variable describing the coordinate position of the satellite beam in the area covered by the satellite. is the distance between the satellite beam center and the sub-satellite point, is the azimuth of the beam center; Zθ is the random variable 、 A random variable, used to describe the cosine value of the off-axis angle of interference from the satellite beam to the victim terminal; , ; is the angle between the satellite in the interference area and the interfered IMT user terminal, is the radius of the earth; F() is the cumulative distribution function, To satisfy The minimum distance from the sub-satellite point among all beams with the value of is the radius of the satellite coverage area, h is the height of the satellite's orbit, and π is the pi;

[0138] The probability distribution function of the off-axis angle obtained using the simplified random pointing model is:

[0139] ;

[0140] in, The value range of is:

[0141] ;

[0142] in, is the satellite field of view angle corresponding to the satellite coverage area.

[0143] As an implementation method, the probability distribution function of the gain logarithm is:

[0144] ;

[0145] in, is the probability distribution function of the gain logarithm, g d is the logarithmic random variable of interference gain, Y is 1.5 times of the satellite half beam width, G m is the peak gain of the satellite antenna, Ls is -6.75dB.

[0146] As an implementation method, the probability distribution function of the linear value of the interference gain is for:

[0147] ;

[0148] As an implementation method, the output unit calculates the aggregate interference distribution according to the following formula:

[0149] ;

[0150] in , SIR is the signal-to-interference ratio of the satellite system to the terminal aggregate interference, T is the threshold, S is the signal strength from the base station to the terminal, P describes the probability, r0 is the communication distance from the terminal to the base station, is the probability density function about r0, calculated as ,in is the deployment density of base stations per unit area; is the base station antenna gain, P bs is the base station transmission power, P sat is the satellite transmission power, is the included angle between satellite i in the satellite set and the terminal’s geocentric center, is the random pointing gain of the beam of satellite i in the satellite set to the terminal, is the satellite point process set, is the free space loss from satellite i to the terminal.

[0151] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for analyzing the aggregate downlink interference of a DTC system to an IMT user, characterized in that: include: Step 1: Obtain the probability distribution function of the off-axis angle of the satellite's randomly pointing beam to the interfered IMT user at any protection distance; Step 2: Map and obtain the probability distribution function of the logarithm of the interference gain of the satellite beam to the interfered IMT user; Step 3: Map the probability distribution function of the logarithmic value of the interference gain to the probability distribution function of the linear value of the interference gain; Step 4: Based on the probability distribution function of the linear value of the interference gain, the interference gain of the satellite beam to the interfered IMT user is abstracted into channel fading; Step 5: Calculate and output the aggregate interference distribution of the DTC system to the interfered IMT system users, and adjust the downlink interference compensation strategy between the satellite and the IMT users based on the analysis results.

2. The method for analyzing the aggregate downlink interference of the DTC system to the IMT user according to claim 1, wherein: In step 1, a uniform random pointing model or a simplified random pointing model is used to obtain the probability distribution function of the off-axis angle θ, and let: ； The probability distribution function of the off-axis angle obtained using the uniform random pointing model is: Set a baseline value ,when When: ； when When: ； in, and is a random variable describing the coordinate position of the satellite beam in the area covered by the satellite. is the distance between the satellite beam center and the sub-satellite point, is the azimuth of the beam center; Z θ For random variables 、 A random variable, used to describe the cosine value of the off-axis angle of interference from the satellite beam to the victim terminal; , ; is the angle between the satellite in the interference area and the interfered IMT user terminal, is the radius of the earth; F() is the cumulative distribution function, To satisfy The minimum distance from the sub-satellite point among all beams with the value of is the radius of the satellite coverage area, h is the height of the satellite's orbit, and π is the circumference of a circle; The probability distribution function of the off-axis angle obtained using the simplified random pointing model is: ； in, The value range of is: ； in, is the satellite field of view angle corresponding to the satellite coverage area.

3. The method for analyzing the aggregate downlink interference of the DTC system to the IMT user according to claim 2, characterized in that: In step 2, the probability distribution function of the gain logarithm is: ； in, is the probability distribution function of the logarithmic gain, is the random variable of the logarithmic value of the interference gain, Y is 1.5 times the satellite half beam width, G m is the peak gain of the satellite antenna, Ls is -6.75dB.

4. The method for analyzing the aggregate downlink interference of a DTC system to an IMT user according to claim 3, wherein: In step 3, the probability distribution function of the linear value of the interference gain is for: 。 5. The method for analyzing the aggregate downlink interference of the DTC system to the IMT user according to claim 4, characterized in that: In step 5, the aggregate interference distribution is calculated according to the following formula: ； in , SIR is the signal-to-interference ratio of the satellite system to the terminal aggregate interference, T is the threshold, S is the signal strength from the base station to the terminal, P describes the probability, r0 is the communication distance from the terminal to the base station, is the probability density function about r0, calculated as ,in is the deployment density of base stations per unit area; is the base station antenna gain, P bs is the base station transmission power, P sat is the satellite transmission power, is the included angle between satellite i in the satellite set and the terminal’s geocentric center, is the random pointing gain of the beam of satellite i in the satellite set to the terminal, is the satellite point process set, is the free space loss from satellite i to the terminal.

6. A system for analyzing the aggregate downlink interference of a DTC system to an IMT user, characterized in that: include: Off-axis angle unit: obtains the probability distribution function of the off-axis angle of the satellite's randomly pointing beam to the interfered IMT user at any protection distance; Logarithmic unit: maps the probability distribution function of the logarithmic value of the interference gain of the satellite beam to the interfered IMT user; Linear value unit: maps the probability distribution function of the logarithmic value of the interference gain to the probability distribution function of the linear value of the interference gain; Abstraction unit: Based on the probability distribution function of the linear value of the interference gain, the interference gain of the satellite beam to the interfered IMT user is abstracted into channel fading; Output unit: Calculates and outputs the aggregate interference distribution of the DTC system to the interfered IMT system users, and adjusts the downlink interference compensation strategy between the satellite and the IMT users based on the analysis results.

7. The system for analyzing downlink aggregate interference of a DTC system to an IMT user according to claim 6, wherein: The off-axis angle unit uses a uniform random pointing model or a simplified random pointing model to obtain the probability distribution function of the off-axis angle θ, and let: ； The probability distribution function of the off-axis angle obtained using the uniform random pointing model is: Set a baseline value ,when When: ； when When: ； in, and is a random variable describing the coordinate position of the satellite beam in the area covered by the satellite. is the distance between the satellite beam center and the sub-satellite point, is the azimuth of the beam center; Z θ For random variables 、 A random variable, used to describe the cosine value of the off-axis angle of interference from the satellite beam to the victim terminal; , ; is the angle between the satellite in the interference area and the interfered IMT user terminal, is the radius of the earth; F() is the cumulative distribution function, To satisfy The minimum distance from the sub-satellite point among all beams with the value of is the radius of the satellite coverage area, h is the height of the satellite's orbit, and π is the circumference of a circle; The probability distribution function of the off-axis angle obtained using the simplified random pointing model is: ； in, The value range of is: ； in, is the satellite field of view angle corresponding to the satellite coverage area.

8. The DTC system for analyzing downlink aggregate interference to IMT users according to claim 7, characterized in that: The probability distribution function of the gain logarithm is: ； in, is the probability distribution function of the logarithmic gain, is the random variable of the logarithmic value of the interference gain, Y is 1.5 times the satellite half beam width, G m is the peak gain of the satellite antenna, Ls is -6.75dB.

9. The system for analyzing downlink aggregate interference of a DTC system to an IMT user according to claim 8, wherein: Probability distribution function of the linear value of interference gain for: 。 10. The system for analyzing downlink aggregate interference of a DTC system to an IMT user according to claim 9, characterized in that: The output unit calculates the aggregate interference distribution according to the following formula: ； in , SIR is the signal-to-interference ratio of the satellite system to the terminal aggregate interference, T is the threshold, S is the signal strength from the base station to the terminal, P describes the probability, r0 is the communication distance from the terminal to the base station, is the probability density function about r0, calculated as ,in is the deployment density of base stations per unit area; is the base station antenna gain, P bs is the base station transmission power, P sat is the satellite transmission power, is the included angle between satellite i in the satellite set and the terminal’s geocentric center, is the random pointing gain of the beam of satellite i in the satellite set to the terminal, is the satellite point process set, is the free space loss from satellite i to the terminal.

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