NAVDAT system coverage calculation method and system

Abstract

The invention belongs to the field of marine safety communication, and particularly relates to an NAVDAT system coverage area calculation method and system, and the method comprises the steps: obtaining the relation between the coverage area and the field intensity under different conductivities and relative dielectric constants of different regions as first data; acquiring field intensity change data and seasonal field intensity change data of different regions to obtain second data; acquiring third data influencing the field intensity; according to the first data, the second data and the third data, obtaining a relation curve of the signal field intensity and the coverage area of the corresponding terrain; calculating to obtain a mixed path ground wave transmission curve based on a mixed path propagation algorithm and a coverage range corresponding to the relation curve and signal field intensity data, obtaining a signal-to-noise ratio corresponding to a given bit error rate based on the relevance between the signal-to-noise ratio and the bit error rate under M-QAM modulation, calculating noise field intensity based on bandwidth and frequency, and obtaining a signal-to-noise ratio corresponding to the given bit error rate. Obtaining the signal field intensity under a given bit error rate condition through the noise field intensity and the signal-to-noise ratio; and the coverage range of the NAVDAT system can be obtained through the obtained signal field intensity lookup graph.

Description

Technical Field

[0001] The invention belongs to the field of maritime safety communications, and in particular relates to a NAVDAT system coverage calculation method and system. Background Art

[0002] The NAVDAT system is a medium frequency radio communication system used for maritime safety communication services. It operates in the 500kHz frequency band and uses digital transmission technology to provide a shore-to-ship broadcast link. The NAVDAT coverage simulation algorithm can be applied to NAVDAT base station layout analysis and optimization of maritime safety communication coverage to ensure that maritime safety information can be conveyed to ships in a timely and accurate manner.

[0003] The existing NAVDAT coverage calculation is mainly based on the method in ITU-R P368 ground wave propagation curves for frequencies between 10 kHz and 30 MHz. The algorithm is a curve relationship between field strength and coverage. ITU-R P368 describes in detail how to determine the field strength of ground waves through these curves under given ground characteristics, such as Figure 2~Figure 8 shown.

[0004] However, the propagation curves provided by Recommendation ITU-R P368 have low applicability and low accuracy. This is because these propagation curves are calculated under a series of assumptions, including a smooth and uniform spherical ground, an exponential decrease in the tropospheric refractive index with height, and the fact that both the transmitting and receiving antennas are very close to the ground (the maximum height that can be used is , σ is conductivity, λ is wavelength). These curves are only used for propagation prediction of uniform paths. In addition, the Recommendation also gives the limitation of the use of these curves, that is, they should generally only be used to determine the field strength when the amplitude of ionospheric reflection is known to be negligible, and are not suitable for the situation where the receiving antenna is located far above the earth's surface. In addition, the Recommendation only provides transmission curves suitable for frequencies between 10kHz and 30 MHz in a single environment. Summary of the invention

[0005] The present invention is proposed based on the above-mentioned requirements of the prior art. The technical problem to be solved by the present invention is to provide a method and system for calculating the coverage of a NAVDAT system to improve the accuracy of the result.

[0006] In order to solve the above problems, the technical solution provided by the present invention includes: A NAVDAT coverage calculation method is provided, comprising: obtaining a relationship between coverage and field strength under different conductivity and relative dielectric constant in different regions as first data; obtaining field strength change data and seasonal field strength change data in different regions; obtaining second data according to the field strength change data and seasonal field strength change data of different terrains, wherein the third data represents seasonal change information of field strength in different terrains; obtaining third data affecting the field strength, wherein the third data includes transmission loss data of antenna height and transmission distance; obtaining a relationship curve between signal field strength and coverage of terrain corresponding to the second data according to the first data, the second data and the third data; calculating the field strength of a hybrid path composed of terrain segment S1 and terrain segment S2 based on a hybrid path propagation algorithm and the coverage and signal field strength data corresponding to the relationship curve, and obtaining a hybrid path ground wave transmission curve, which is expressed as: ,in, , E T =E2(d2)-E1(d2)+E1(d1+d2), according to the relationship curve between signal field strength and coverage range, we can obtain the field strength value E1(d1) of terrain segment S1 at distance d1, the field strength value E1(d2) of terrain segment S1 at distance d2, the field strength value E1(d1+d2) of terrain segment S1 at distances d1 and d2, the field strength value E2(d1) of terrain segment S2 at distance d1, and the field strength value E2(d2) of terrain segment S2 at distance d2. ), the field strength value E2(d1+d2) of terrain segment S2 at the distances d1 and d2; based on the correlation between the signal-to-noise ratio and the bit error rate under the M-QAM modulation format, the signal-to-noise ratio corresponding to a given bit error rate is obtained, the noise field strength is calculated based on the bandwidth and frequency, and the signal field strength under a given bit error rate condition is obtained through the noise field strength and the signal-to-noise ratio; using the correspondence between the field strength and the coverage range in the hybrid path ground wave transmission curve, the coverage range of the NAVDAT system can be obtained by looking up the obtained signal field strength map.

[0007] Preferably, the third data includes the first factor formed by the influence of different types of antennas on the field strength value, the antenna gain of the antenna in the transmission direction, the RF feeder loss of the shore station, and the transmission loss due to the antenna height and the transmission distance.

[0008] Preferably, the first factor can be expressed as: , where P t is the transmitting power of the antenna, in W.

[0009] Preferably, the RF feeder loss L1 of the shore station can be expressed as: L1=β× l 1, among which, l 1 is the unit length of the RF feeder line.

[0010] Preferably, the antenna height and transmission distance versus transmission loss are expressed as: , , , , , where h r is the height of the receiving antenna, h t is the height of the transmitting antenna, d is the distance between antennas, in meters; λ is the wavelength, in meters, and the operating wavelength λ of the NAVDAT communication system is 600 meters.

[0011] Preferably, the relationship curve between the signal strength and the coverage range is expressed as: , where E is the field strength value obtained from the diagram in ITU-R 368, , is the field strength difference caused by the antenna power, i.e. the first factor, G is the gain of the antenna in the transmission direction, in dB, is the seasonal variation factor, L1 is the shore station RF feeder loss, unit is dB, and L2 is the impact of environmental factors on the transmission loss of the antenna, unit is dB.

[0012] Preferably, under the M-QAM encoding mode, the bit error rate p b The relationship with the signal-to-noise ratio is:

[0013] Wherein, M is the number of different modulation symbols and the size of the modulation constellation, erfc is the Gaussian error function, and the signal-to-noise ratio corresponding to a given bit error rate is obtained by looking up the table.

[0014] Preferably, the noise field strength can be expressed as: Among them, E n is the noise field strength in bandwidth b, B=10logb, in dB; F a is the noise level; the signal field strength can be expressed as: .

[0015] A calculation system for the coverage of a NAVDAT system is also provided, comprising: a first data acquisition module, which acquires the relationship between the coverage and the field strength under different conductivity and relative dielectric constant in different regions as the first data; a seasonal change module, which acquires the field strength change data and seasonal field strength change data of different regions; second data is obtained according to the field strength change data and seasonal field strength change data of different terrains, and the second data represents the seasonal change information of the field strength of different terrains; an antenna feature module, which acquires third data affecting the field strength, and the third data includes the transmission loss data of the antenna height and the transmission distance; a signal field strength calculation module, which acquires the relationship curve between the signal field strength and the coverage of the terrain corresponding to the second data according to the first data, the second data and the third data; a hybrid path calculation module, which calculates the field strength of the hybrid path composed of the terrain segment S1 and the terrain segment S2 based on the propagation algorithm of the hybrid path and the coverage and signal field strength data corresponding to the relationship curve, and obtains the hybrid path ground wave transmission curve, which is expressed as: ,in, , E T =E2(d2)-E1(d2)+E1(d1+d2), according to the relationship curve between signal field strength and coverage range, we can obtain the field strength value E1(d1) of terrain segment S1 at distance d1, the field strength value E1(d2) of terrain segment S1 at distance d2, the field strength value E1(d1+d2) of terrain segment S1 at distances d1 and d2, the field strength value E2(d1) of terrain segment S2 at distance d1, the field strength value E2(d2) of terrain segment S2 at distance d2, and the field strength value E1(d1+d2) of terrain segment S2 at distance The field strength value E2(d1+d2) at the points d1 and d2 is obtained; the signal-to-noise ratio calculation module can obtain the signal-to-noise ratio corresponding to a given bit error rate based on the correlation between the signal-to-noise ratio and the bit error rate under the M-QAM modulation format; the noise field strength calculation module calculates the noise field strength based on the bandwidth and frequency; the coverage range calculation module obtains the signal field strength under a given bit error rate condition through the noise field strength and the signal-to-noise ratio, and uses the correspondence between the field strength and the coverage range in the mixed path ground wave transmission curve to obtain the coverage range of the NAVDAT system by looking up the map.

[0016] Compared with the prior art, the present invention takes into account the factors that affect the coverage effect of the NAVDAT shore-based system as much as possible, and at the same time determines the association between the factors and the corresponding results, so as to ensure the accuracy of the NAVDAT coverage model. At the same time, during the construction of the NAVDAT system, comprehensive analysis and planning are carried out to ensure the construction quality and effect of the system. Based on the limited deployment resources of my country's existing medium and high frequency coastal radio stations, and considering the feasibility of site selection, the present invention proposes the overall scientific layout of NAVDAT stations. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the embodiments of this specification. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0018] Figure 1 A flowchart of a method for calculating coverage of a NAVDAT system in an embodiment of the present invention; Figure 2 It is a schematic diagram of the ground wave transmission curve in an environment where the seawater has a low salinity conductivity of 1s / m and a relative dielectric constant of 80; Figure 3 It is a schematic diagram of the ground wave transmission curve in an environment where the average conductivity of seawater salinity is 5s / m and the relative dielectric constant is 70; Figure 4 The conductivity of wet ground on land is 10 -2 s / m, schematic diagram of ground wave transmission curve in an environment with a relative dielectric constant of 70; Figure 5 The conductivity of the ground on land is 3×10 -3 s / m, schematic diagram of ground wave transmission curve in an environment with a relative dielectric constant of 22; Figure 6 For medium dry ground on land, the conductivity is 10 -3 s / m, schematic diagram of ground wave transmission curve in an environment with a relative dielectric constant of 15; Figure 7 The conductivity of dry ground on land is 3×10 -4 s / m, schematic diagram of ground wave transmission curve in an environment with a relative dielectric constant of 7; Figure 8 For dry land, the ground conductivity is 10 -4 s / m, schematic diagram of ground wave transmission curve in an environment with a relative dielectric constant of 3; Fig. 9 It is a schematic diagram of three-stage mixing paths; Fig.10 Function diagrams for 4-QAM, 16-QAM, 64-QAM, and 256-QAM encoding methods; Fig.11 The figure is a connection structure diagram of a NAVDAT system coverage calculation system in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the term "connected" should be understood in a broad sense, for example, it can be a fixed connection, or a detachable connection, or an integral connection, which can be a mechanical connection, or an electrical connection, which can be a direct connection, or can be indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0021] The terms "top", "bottom", "above", "lower", and "on" used throughout the description are relative to the relative positions of components of a device, such as the relative positions of the top and bottom substrates within a device. It is understood that devices are multifunctional regardless of their orientation in space.

[0022] To facilitate understanding of the embodiments of the present invention, specific embodiments will be further explained below in conjunction with the accompanying drawings. The embodiments do not constitute a limitation on the embodiments of the present invention.

[0023] Example 1 This embodiment provides a method for calculating the coverage of a NAVDAT system. Figure 1-Figure 10 shown.

[0024] The calculation method of the NAVDAT system coverage is as follows: Figure 1 As shown, including: The relationship between the coverage area and the field strength under different electrical conductivities and relative dielectric constants in different regions is obtained as the first data.

[0025] The field strength variation data and seasonal field strength variation data of different regions are obtained; and second data are obtained according to the field strength variation data and seasonal field strength variation data of different terrains, wherein the second data represents the variation information of the field strength of different terrains with the seasons.

[0026] The NAVDAT shore-based system operates at 500kHz, mainly using ground wave propagation. Determining the various factors that affect its coverage is the basis for studying the coverage range algorithm model. There are many factors that affect the coverage of the NAVDAT shore-based system, which will interfere with the coverage to varying degrees. Different interference factors have different degrees of influence on the results, and it is necessary to determine their relationship with the results. Determining the relationship between various influencing factors and coverage is the premise for the accuracy of the NAVDAT coverage range model.

[0027] The propagation curves given in Recommendation ITU-R P.368 do not reflect seasonal changes, but in order to improve the accuracy of the results and take the impact of different seasons into account, the propagation curves and coverage need to be corrected.

[0028] For example, in Eastern Europe, where the average temperature in January is -10°C, the signal strength of the ground wave will change with the seasonal temperature. For medium-frequency communications in mid-latitudes, continental climates, and densely forested areas, the average seasonal variation range of the link ground wave strength is 10-18dB within a maximum range of about 100 kilometers. In large cities (10dB) or when passing through cities (up to 15dB). The maximum value of the link strength variation range occurs in rural areas (15-18dB). Other regions with similar climate and natural conditions may produce similar results.

[0029] Based on the field strength changes measured in the Eastern European region, the field strength changes of the link when passing through different regions can be summarized, as shown in Table 1.

[0030] Table 1 Field strength variation when the link passes through different regions (z) Forest area In large cities Traveling through large cities Rural areas Field strength change (dB) 10-18 10 15 15-18 In other geographical areas, the average range of seasonal variation depends on the temperature in January. This is because the variation of links with similar soil / vegetation conditions can only be distinguished by the average temperature in January. Taking into account the differences in climatic conditions in different geographical areas, an approximate assessment of the seasonal variation of field strength is made in proportion to the temperature range. Based on the field strength variation values ​​when the link passes through different areas and the average temperature in January. For example, for a link laid in a city with an average temperature of +4°C in January, the field strength range is about 10×(4 / 13) ≈ 3 dB, calculated based on the data in Table 1.

[0031] Table 2 Field intensity changes under different January temperatures Average temperature in January in the Northern Hemisphere (℃) 4 0 -10 -16 Corresponding field strength difference range u (dB) 4 8 13 15 The second data is obtained based on the field intensity changes in different regions and the corresponding field intensity changes under different weather conditions, and is expressed as:

[0032] Third data affecting the field strength is obtained, where the third data includes transmission loss data due to antenna height and transmission distance.

[0033] The coverage calculation of the NAVDAT shore-based system can refer to the actual experience of existing NAVTEX stations. NAVTEX is a medium-frequency maritime digital broadcasting system that can broadcast maritime safety information and other service information on 500kHz. By measuring and analyzing the signal coverage of NAVTEX, the signal propagation characteristics in the actual environment can be obtained, providing a reference for the coverage calculation of NAVDAT. Terrain and weather have an important influence on the propagation of radio signals. Both terrain factors and weather factors affect the conductivity of the ground, air and water. Equipment factors include the gain, power, loss, etc. of the transmitting station.

[0034] The propagation curve in Recommendation ITU-R P.368 uses a short vertical monopole with a transmission power of 1 kW as the radiating unit. However, in reality, the transmission power of the NAVDAT antenna is not necessarily 1 kW. In addition, there are factors such as antenna gain, feeder loss, and antenna height, which will affect the propagation curve. Therefore, the influence of antenna factors should also be considered and the propagation curve and coverage range should be corrected. The specific corrections include: The third data of the influence of antenna factors on field strength includes the first factor formed by the influence of different types of antennas on the field strength value, the antenna gain G of the antenna in the transmission direction, the RF feeder loss L1 of the shore station, and the transmission loss L2 of the antenna height and transmission distance.

[0035] For the first factor: The conclusion given in the ground wave transmission curves between 10kHz and 30MHz in Recommendation ITU-R-368 is that the radiating unit is a short vertical monopole located on a fully conductive flat ground, and the field strength value when the radiated power is 1 kW does not take into account the impact of different types of antennas on the field strength value. Therefore, when calculating the field strength at different distances, the difference between the antenna transmission power and the standard 1kW should be added. The first factor can be expressed as:

[0036] Where P t is the transmitting power of the antenna, in W.

[0037] For antenna gain: In addition to calculating the effect of the antenna transmission power on the field strength, the antenna gain G in the transmission direction should also be added when calculating the field strength, in dB.

[0038] For the shore station RF feeder loss: The shore station RF feeder loss refers to the energy loss introduced by the feeder wire, cable, and waveguide. It is related to the conductor impedance, dielectric loss, radiation loss, etc. The shore station RF feeder loss L1 can be expressed as is the RF feeder line loss per unit length, in dB / m, set as input parameter, l 1 is the unit length of the RF feeder, in m, and is specifically expressed as follows: L1=β× l 1 For the transmission loss of antenna height and transmission distance: The concept of radio link transmission loss in Recommendation ITU-R P.341-7 gives that when the antenna is installed on or near the ground, that is, h<λ, h is the antenna height, and λ is the wavelength. Especially at frequencies below 30 MHz, the free space value of the antenna radiation resistance changes due to the ground. Therefore, the power flux density of the receiving antenna depends on the height of the transmitting antenna, and the effective capture area of ​​the receiving antenna depends on the height of the antenna above the ground.

[0039] By considering the plane perfectly conducting surface h t and h r The transmission loss between two vertical lossless short dipoles at two heights gives an idea of ​​the effect of the environment on the operation of a pair of antennas (forming a basic circuit). The distance between the antennas is very large compared to the wavelength λ of the NAVDAT system.

[0040]

[0041]

[0042]

[0043]

[0044]

[0045] Among them, h r is the height of the receiving antenna, h t is the height of the transmitting antenna, d is the distance between the antennas, in meters, λ is the wavelength, in meters, and the operating wavelength λ of the NAVDAT communication system is 600 meters.

[0046] A relationship curve between the signal field strength and the coverage range of the terrain corresponding to the second data is obtained according to the second data and the third data.

[0047] The field strength in the ITU-R 368 intermediate frequency ground wave transmission algorithm is E, with the unit of dBμV / m. When calculating the field strength, the influence of seasonal changes, antenna differences, antenna height and transmission distance should be considered. The relationship curve between the signal field strength and the coverage range that characterizes the corresponding relationship between the field strength and the distance is:

[0048] Where E is the field strength value obtained from the diagram in ITU-R 368. , is the field strength difference caused by the antenna power, i.e. the first factor. G is the gain of the antenna in the transmission direction, in dB. is a seasonal variation factor. L1 is the RF feeder loss of the shore station, in dB, and L2 is the effect of environmental factors on the transmission loss of the antenna, in dB.

[0049] The field strength of the hybrid path composed of the terrain segment S1 and the terrain segment S2 is calculated based on the propagation algorithm of the hybrid path and the coverage range and signal field strength data corresponding to the relationship curve to obtain the hybrid path ground wave transmission curve.

[0050] Recommendation ITU-R 368 proposes an algorithm that can be used to determine propagation on mixed paths (non-uniform smooth roads): such a path may consist of terrain segments S1, S2, S3, etc. with lengths d1, d2, d3 and conductivity and dielectric constants σ1, σ2, σ3, etc. The three terrain segments are as follows: Fig. 9 shown.

[0051] The method assumes that field strength E is available for different types of terrain in the respective uniform terrain sections S1, S2, S3, etc., and that these curves are all for the same source T, for example determined by a given inverse distance curve. The value for any other source can eventually be calculated.

[0052] The transmission of the NAVDAT system usually goes through the ground-sea process, so the field strength under the mixed path needs to be considered. In addition, the NAVDAT system requires a two-stage mixed path calculation method, so the Millington three-stage method needs to be corrected.

[0053] For a given frequency, according to the relationship curve between signal field strength and coverage range, the field strength value E1(d1) of terrain segment S1 at distance d1, the field strength value E1(d2) of terrain segment S1 at distance d2, the field strength value E1(d1+d2) of terrain segment S1 at distances d1 and d2, the field strength value E2(d1) of terrain segment S2 at distance d1, the field strength value E2(d2) of terrain segment S2 at distance d2, and the field strength value E2(d1+d2) of terrain segment S2 at distances d1 and d2 are obtained by looking up the table, and the unit is dB(V / m). Among them, terrain segment S1 and terrain segment S2 correspond to two different relationship curves between signal field strength and coverage range. For example, terrain segment S1 represents dry land on land, and terrain segment S2 represents seawater. d1 and d2 represent different transmission distances respectively. For example, d1 represents 10 nautical miles on land, and d2 represents 20 nautical miles in the ocean. E1(d2) is the field strength at 20 nautical miles in the curve of signal field strength versus coverage range corresponding to dry land, and E2(d1) is the field strength at 10 nautical miles in the curve of signal field strength versus coverage range corresponding to the ocean.

[0054] The coordinate values ​​of the boundary between land and sea are stored in the database. If the station is built on land, the distance on land is obtained by the distance from the station location to the boundary, and the distance on land is obtained by the distance from the boundary to the receiving location.

[0055] Calculate E R Field strength:

[0056] E T Field strength calculation: E T =E2(d2)-E1(d2)+E1(d1+d2) The required field strength E for the mixed path is X for:

[0057] When calculating the field strength value in a specific direction, if the station location is known, the length of the land segment can be known. Therefore, the mixed path ground wave transmission curve diagram in this direction can be calculated based on the length of the land segment and the land and sea ground wave transmission curve diagrams. The transmission curve diagram corresponds to the relationship between the field strength and distance on the mixed path.

[0058] Based on the correlation between the signal-to-noise ratio and the bit error rate under the M-QAM modulation format, the signal-to-noise ratio corresponding to a given bit error rate is obtained, the noise field strength is calculated based on the bandwidth and frequency, and the signal field strength under a given bit error rate condition is obtained through the noise field strength and the signal-to-noise ratio.

[0059] Under M-QAM coding mode, the bit error rate pb The relationship with the signal-to-noise ratio is:

[0060] Where M is the number of different modulation symbols and the size of the modulation constellation, and erfc is the Gaussian error function. The function diagrams of 4-QAM, 16-QAM, 64-QAM, 256-QAM and other coding methods are shown in Fig.10 As shown. Given the bit error rate is 0.1, 10 -5 , 10 -9 The signal-to-noise ratio SINR in the following cases.

[0061] Compared with the NAVTEX system, the bandwidth of the NAVDAT system has increased, and the frequency range of signals that the system can transmit has become wider, which increases the amount of information that the system can process. However, as the bandwidth increases, the system will also receive more noise in the frequency range, resulting in a corresponding increase in the noise level. When the signal-to-noise ratio decreases, the sensitivity of the receiver may be affected, resulting in the inability to receive weaker signals, which reduces the radio transmission range. Therefore, compared with NAVTEX, NAVDAT will bring about problems such as increased noise, reduced signal-to-noise ratio, and limited transmission range after the bandwidth increases. However, the current model in Recommendation ITU-R P.368 has not yet considered the impact of bandwidth changes on the transmission curve and coverage. Therefore, the impact of bandwidth on the transmission range should also be considered, and the propagation curve and coverage should be corrected.

[0062] Bandwidth refers to the frequency range in which a signal or channel can be transmitted, that is, the width of the frequency band occupied by the signal. The bandwidth of the NAVDAT system is 10KHz, while the bandwidth of the NAVTEX system is 170Hz. The amplitude of the noise is often proportional to the bandwidth of the system. When the bandwidth of the system increases, the amplitude of the noise will also increase accordingly. These noises will be more obvious in a wider bandwidth.

[0063] The signal-to-noise ratio (SNR) is the ratio of signal power to noise power and is an important indicator of signal quality. The higher the SNR, the better the signal quality during transmission, the less noise interference, and the more stable the signal can be transmitted to a longer distance, thereby expanding the coverage range. During signal transmission, as the distance increases, the signal strength will gradually weaken, and the noise interference will also increase. When the SNR drops to a certain level, the signal will not be effectively received, resulting in limited coverage.

[0064] The bandwidth of the NAVDAT system is about 60 times that of the NAVTEX system. When the bandwidth increases, the noise power increases more significantly while the signal power remains unchanged, resulting in a decrease in the signal-to-noise ratio. This will reduce the quality of the output signal and make it difficult to accurately extract the useful signal from the noise, thus affecting the transmission quality and coverage.

[0065] The relationship between noise field strength, bandwidth and frequency is given in the radio noise of Recommendation ITU-R P.372-16. For a short vertical monopole antenna on an ideal conductor ground, the noise field strength can be expressed as:

[0066] Among them, E n is the noise field strength in bandwidth b, B=10logb, in dB; F a It is the noise level in dB, which can be obtained by . In this project, the value at a frequency of 500KHz is taken as the atmospheric noise that exceeds 99.5% of the time.

[0067] By using the corresponding relationship between field strength and coverage range in the hybrid path ground wave transmission curve, the coverage range of the marine digital broadcasting system can be obtained by checking the obtained signal field strength map.

[0068] Therefore, the signal strength under a given bit error rate can be obtained from the noise strength and signal-to-noise ratio. The signal strength can be expressed as:

[0069] In summary, although Recommendation ITU-R P.368 provides a basic transmission curve model covering the medium frequency range (10kHz to 30MHz) for the field of ground wave propagation, this model has a high reference value in terms of theoretical framework and prediction method. However, when it is actually applied to a specific communication system such as NAVDAT, the model is not fully adapted to the system characteristics and needs to be modified and optimized in a targeted manner. The NAVDAT system may face mixed propagation paths, seasonal changes, more complex antenna configurations, wider bandwidth requirements, and variable ocean conditions, all of which may have a significant impact on the ground wave propagation characteristics, and the model in Recommendation ITU-R P.368 does not reflect these challenges in the actual operating environment. Therefore, in order to more accurately predict the transmission performance of the NAVDAT system and optimize its performance in practical applications, it is necessary to make necessary modifications and extensions based on the basic model of Recommendation ITU-R P.368 and the specific characteristics of the NAVDAT system.

[0070] Example 2 This embodiment provides a system for calculating the coverage of a NAVDAT system, such as Fig.11 shown.

[0071] The NAVDAT system covers computing systems including: The first data acquisition module acquires the relationship between the coverage and the field strength under different electrical conductivities and relative dielectric constants in different regions as the first data.

[0072] The seasonal change module obtains field strength change data and seasonal field strength change data of different regions; obtains second data based on the field strength change data and seasonal field strength change data of different terrains, and the second data represents the change information of field strength of different terrains with seasons.

[0073] The antenna characteristic module obtains third data that affects the field strength, wherein the third data includes transmission loss data of antenna height and transmission distance; and obtains a relationship curve between the signal field strength and coverage range of the terrain corresponding to the second data based on the first data, the second data and the third data.

[0074] For the first factor: The conclusion given in the ground wave transmission curves between 10kHz and 30MHz in Recommendation ITU-R-368 is that the radiating unit is a short vertical monopole located on a fully conductive flat ground, and the field strength value when the radiated power is 1 kW does not take into account the impact of different types of antennas on the field strength value. Therefore, when calculating the field strength at different distances, the difference between the antenna transmission power and the standard 1kW should be added. The first factor can be expressed as:

[0075] Where P t is the transmitting power of the antenna, in W.

[0076] For antenna gain: In addition to calculating the effect of the antenna transmission power on the field strength, the antenna gain G in the transmission direction should also be added when calculating the field strength, in dB.

[0077] For the shore station RF feeder loss: The shore station RF feeder loss refers to the energy loss introduced by the feeder wire, cable, and waveguide, which is related to the conductor impedance, dielectric loss, radiation loss, etc. The shore station RF feeder loss L1 can be expressed as is the RF feeder line loss per unit length, in dB / m, set as input parameter, l 1 is the unit length of the RF feeder, in m, and is specifically expressed as follows: L1=β× l 1 For the transmission loss of antenna height and transmission distance: The concept of radio link transmission loss in Recommendation ITU-R P.341-7 gives that when the antenna is installed on or near the ground, that is, h<λ, h is the antenna height, and λ is the wavelength. Especially at frequencies below 30 MHz, the free space value of the antenna radiation resistance changes due to the ground. Therefore, the power flux density of the receiving antenna depends on the height of the transmitting antenna, and the effective capture area of ​​the receiving antenna depends on the height of the antenna above the ground.

[0078] By considering the plane perfectly conducting surface h t and h r The transmission loss between two vertical lossless short dipoles at two heights gives the effect of the environment on the operation of a pair of antennas (forming a basic circuit). The distance between the antennas is very small compared to the wavelength λ of the NAVDAT system.

[0079]

[0080]

[0081]

[0082]

[0083]

[0084] Among them, h r is the height of the receiving antenna, h t is the height of the transmitting antenna, d is the distance between the antennas, in meters, λ is the wavelength, in meters, and the operating wavelength λ of the NAVDAT communication system is 600 meters.

[0085] The signal strength calculation module obtains the second data output by the weather change module and the third data output by the antenna characteristic module, and obtains the relationship curve between the signal strength and the coverage range through the second data and the third data, which is expressed as: , where E is the field strength value obtained from the map in ITU-R 368, which is the first data. is the field strength difference caused by the antenna power, i.e. the first factor. G is the gain of the antenna in the transmission direction, in dB. is a seasonal variation factor. L1 is the RF feeder loss of the shore station, in dB, and L2 is the effect of environmental factors on the transmission loss of the antenna, in dB.

[0086] The hybrid path calculation module calculates the field strength of the hybrid path composed of the terrain segment S1 and the terrain segment S2 based on the hybrid path propagation algorithm and the coverage range and signal field strength data corresponding to the relationship curve, and obtains the hybrid path ground wave transmission curve, which is expressed as: ,in, , E T=E2(d2)-E1(d2)+E1(d1+d2), according to the relationship curve between signal field strength and coverage range, we can obtain the field strength value E1(d1) of terrain segment S1 at distance d1, the field strength value E1(d2) of terrain segment S1 at distance d2, the field strength value E1(d1+d2) of terrain segment S1 at distances d1 and d2, the field strength value E2(d1) of terrain segment S2 at distance d1, the field strength value E2(d2) of terrain segment S2 at distance d2, and the field strength value E2(d1+d2) of terrain segment S2 at distances d1 and d2.

[0087] The signal-to-noise ratio calculation module can obtain the signal-to-noise ratio corresponding to a given bit error rate based on the correlation between the signal-to-noise ratio and the bit error rate under the M-QAM modulation format. p b The relationship with the signal-to-noise ratio is:

[0088] Where M is the number of different modulation symbols and the size of the modulation constellation, and erfc is the Gaussian error function. The function diagrams of 4-QAM, 16-QAM, 64-QAM, 256-QAM and other coding methods are shown in Fig.10 As shown. Given the bit error rate is 0.1, 10 -5 , 10 -9 The signal-to-noise ratio SINR in the following cases.

[0089] Noise field strength calculation module, based on the relationship between bandwidth and frequency, for a short vertical monopole antenna on an ideal conductor ground, the noise field strength can be expressed as:

[0090] Among them, E n is the noise field strength in bandwidth b, B=10logb, in dB; F a It is the noise level in dB, which can be obtained by . In this project, the value at a frequency of 500KHz is taken as the atmospheric noise that exceeds 99.5% of the time.

[0091] The coverage range calculation module obtains the signal field strength under a given bit error rate condition through noise field strength and signal-to-noise ratio. The corresponding relationship between field strength and coverage range in the mixed path ground wave transmission curve is used to obtain the coverage range of the NAVDAT system by checking the map.

[0092] The signal strength can be expressed as:

[0093] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for calculating the coverage of a NAVDAT system, characterized in that: include: Obtaining the relationship between coverage and field strength under different electrical conductivities and relative dielectric constants in different regions as first data; Acquire field intensity variation data and seasonal field intensity variation data of different regions; obtain second data according to the field intensity variation data and seasonal field intensity variation data of different terrains, wherein the second data represents seasonal variation information of field intensity of different terrains; Acquire third data affecting the field strength, wherein the third data includes transmission loss data of antenna height and transmission distance; obtain a new relationship curve between the signal field strength and the coverage range of the terrain corresponding to the second data according to the first data, the second data and the third data; Based on the propagation algorithm of the hybrid path and the coverage and signal field strength data corresponding to the relationship curve, the field strength of the hybrid path composed of the terrain segment S1 and the terrain segment S2 is calculated to obtain the hybrid path ground wave transmission curve, which is expressed as: in, , E T =E2(d2)-E1(d2)+E1(d1+d2), according to the relationship curve between signal field strength and coverage range, the field strength value E1(d1) of terrain segment S1 at distance d1, the field strength value E1(d2) of terrain segment S1 at distance d2, the field strength value E1(d1+d2) of terrain segment S1 at distances d1 and d2, the field strength value E2(d1) of terrain segment S2 at distance d1, the field strength value E2(d2) of terrain segment S2 at distance d2, and the field strength value E2(d1+d2) of terrain segment S2 at distances d1 and d2 are obtained by looking up the table; Based on the correlation between the signal-to-noise ratio and the bit error rate under the M-QAM modulation format, the signal-to-noise ratio corresponding to a given bit error rate is obtained, the noise field strength is calculated based on the bandwidth and frequency, and the signal field strength under a given bit error rate condition is obtained through the noise field strength and the signal-to-noise ratio; By using the corresponding relationship between field strength and coverage range in the hybrid path ground wave transmission curve, the coverage range of the NAVDAT system can be obtained by checking the obtained signal field strength map.

2. The NAVDAT system coverage calculation method according to claim 1, characterized in that: The third data includes the first factor formed by the influence of different types of antennas on the field strength value, the antenna gain of the antenna in the transmission direction, the RF feeder loss of the shore station, and the transmission loss due to the antenna height and the transmission distance.

3. The NAVDAT system coverage calculation method according to claim 2, characterized in that: The first factor can be expressed as: , where P t is the transmitting power of the antenna, in W.

4. The NAVDAT system coverage calculation method according to claim 2, characterized in that: The RF feeder loss L1 of the shore station can be expressed as: L1 = β × l 1, among which, l 1 is the unit length of the RF feeder line.

5. The NAVDAT system coverage calculation method according to claim 2, characterized in that: The antenna height and transmission distance are expressed as follows: Among them, h r is the height of the receiving antenna, h t is the height of the transmitting antenna, d is the distance between antennas, in meters; λ is the wavelength, in meters. The operating wavelength λ of the NAVDAT communication system is 600 meters.

6. The NAVDAT system coverage calculation method according to claim 1, characterized in that: The relationship curve between the signal strength and the coverage range is expressed as: Where E is the field strength value obtained from the diagram in ITU-R 368, , is the field strength difference caused by the antenna power, i.e. the first factor, G is the gain of the antenna in the transmission direction, in dB, is the seasonal variation factor, L1 is the RF feeder loss of the shore station, in dB, and L2 is the impact of environmental factors on the transmission loss of the antenna, in dB.

7. The NAVDAT system coverage calculation method according to claim 1, characterized in that: Under M-QAM coding mode, the bit error rate p b The relationship with the signal-to-noise ratio is: Wherein, M is the number of different modulation symbols and the size of the modulation constellation, erfc is the Gaussian error function, and the signal-to-noise ratio corresponding to a given bit error rate is obtained by looking up the table.

8. The NAVDAT system coverage calculation method according to claim 1, characterized in that: The noise field strength can be expressed as: Among them, E n is the noise field strength in bandwidth b, B=10logb, in dB; F a is the noise level; The signal strength can be expressed as: .

9. A system for calculating the coverage of a NAVDAT system, characterized in that: include: A first data acquisition module acquires the relationship between the coverage and the field strength under different electrical conductivities and relative dielectric constants in different regions as first data; A seasonal variation module is used to obtain field strength variation data and seasonal field strength variation data of different regions; second data is obtained according to the field strength variation data and seasonal field strength variation data of different terrains, wherein the second data represents seasonal variation information of field strength of different terrains; The antenna characteristic module obtains third data affecting the field strength, wherein the third data includes transmission loss data of antenna height and transmission distance; A signal strength calculation module, which obtains a curve of the relationship between the signal strength and the coverage range of the terrain corresponding to the second data according to the first data, the second data and the third data; The hybrid path calculation module calculates the field strength of the hybrid path composed of the terrain segment S1 and the terrain segment S2 based on the hybrid path propagation algorithm and the coverage range and signal field strength data corresponding to the relationship curve, and obtains the hybrid path ground wave transmission curve, which is expressed as: ,in, , E T =E2(d2)-E1(d2)+E1(d1+d2), according to the relationship curve between signal field strength and coverage range, the field strength value E1(d1) of terrain segment S1 at distance d1, the field strength value E1(d2) of terrain segment S1 at distance d2, the field strength value E1(d1+d2) of terrain segment S1 at distances d1 and d2, the field strength value E2(d1) of terrain segment S2 at distance d1, the field strength value E2(d2) of terrain segment S2 at distance d2, and the field strength value E2(d1+d2) of terrain segment S2 at distances d1 and d2 are obtained by looking up the table; The signal-to-noise ratio calculation module can obtain the signal-to-noise ratio corresponding to a given bit error rate based on the correlation between the signal-to-noise ratio and the bit error rate under the M-QAM modulation format; Noise field strength calculation module, which calculates the noise field strength based on bandwidth and frequency; The coverage range calculation module obtains the signal field strength under a given bit error rate condition through noise field strength and signal-to-noise ratio. The corresponding relationship between field strength and coverage range in the mixed path ground wave transmission curve is used to obtain the coverage range of the NAVDAT system by checking the map.

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