CN115102607B - Low-rail navigation enhanced signal transmission method based on broadband CDMA communication system - Google Patents
Low-rail navigation enhanced signal transmission method based on broadband CDMA communication system Download PDFInfo
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Abstract
The invention discloses a low-orbit navigation enhancement signal transmission method based on a wideband code division multiple access communication system, belonging to the field of satellite navigation enhancement. In the invention, navigation enhancement information to be transmitted adopts fixed format framing, and pilot frequency components and data components carrying enhancement information adopt different orthogonal address codes for code division multiplexing; the satellite allocates a channel for the LePT signal and transmits resource position information of the LePT channel in the BCCH channel; the navigation fusion terminal monitors the P-CCPCH channel and obtains LePT signal channel information; the navigation fusion terminal receives data transmitted in the LePT signal data component and extracts security authentication information; and after the safety authentication is successful, the position and ephemeris information of the low orbit satellite are obtained by receiving the independent navigation information frame, and the ionosphere and troposphere correction information and the precise orbit and clock error information are obtained by receiving the navigation enhancement information frame. The invention can realize the enhancement of the basic service capability of the Beidou navigation system on the premise of not affecting the original communication function of the system.
Description
Technical Field
The invention relates to a low-orbit navigation enhancement signal transmission method based on a wideband code division multiple access communication system, belonging to the technical field of satellite navigation enhancement.
Background
GNSS systems have the ability to provide navigation, positioning and timing services worldwide, playing an increasing role in industry development. At present, the Beidou system is increasingly widely applied in various fields.
GNSS systems have the advantages of wide coverage, low deployment cost, etc., but they also have some inherent drawbacks:
(1) GNSS system constellations typically operate on medium-high orbit constellations, which result in satellites that are far from the terminal, severely path-loss, satellite navigation signal power levels below noise, and susceptible to interference and fraud.
(2) Because the signal strength is weaker, the positioning accuracy is insufficient only by the GNSS system, and the ground reference station is needed for assistance, the deployment cost of the satellite communication system is increased, and the cost advantage is weakened.
(3) The navigation speed is low, and the navigation terminal has low speed of searching navigation signals and resolving positions.
(4) The reliability is insufficient, the integrity level of the current GNSS system cannot meet the important field requirements related to life safety, and as the GNSS system is used in more fields, the requirements on the integrity are higher and higher.
The low orbit satellite has a series of advantages of low orbit high power, global coverage, rapid Doppler change, ground monitoring and antenna base and the like, and can provide a beneficial supplement for the traditional GNSS system. With the vigorous development of low-orbit satellite mobile communication and low-orbit navigation enhancement technology, the design of an enhancement system integrated with communication navigation based on a low-orbit constellation has raised an agenda.
Spread spectrum communication can remarkably enhance the anti-interference performance of signals, and Code Division Multiple Access (CDMA) technology is applied to partial low orbit satellite communication systems, and is a technology which is necessarily used in the next development of civil satellite communication. The signal spread by the spread spectrum code can be used for accurately measuring the pseudo range, and the low orbit satellite can use a wider frequency band for long-distance communication, and the communication and guide integrated system based on the WCDMA system is a GNSS navigation enhancement scheme with very strong feasibility.
The research of the navigation enhancement system based on the low orbit satellite communication system in China is still in a relatively primary stage, and the implementation of the navigation enhancement by the existing patent is mostly in a stage of determining a navigation fusion implementation step. For example, the patent with publication number CN106646563a, a low-orbit satellite-based enhanced navigation method, mainly uses the characteristic that the geometric position of a low-orbit satellite is greatly changed, and realizes the quick and high-precision calculation of pseudo range indirectly through geometric relationship, thereby realizing the effect of navigation enhancement. The patent with the application number 201811102234.1 discloses a method and a device for generating a communication navigation integrated fusion signal, which are based on an OFDMA system and are used for superposing CDMA positioning signals on the OFDMA signals to form the communication navigation integrated fusion signal, so that the performance of a navigation system and the positioning accuracy of indoor positioning are improved. However, to date, there has been no navigation enhancement signal transmission scheme specific to the low-rail wideband code division multiple access mobile communication system.
Disclosure of Invention
In view of this, the present invention provides a low-orbit navigation enhancement signal transmission method based on a wideband code division multiple access communication system, and the satellite navigation enhancement LePT (LEO enhanced Positioning and Timing) signal designed and transmitted based on the method can be used in a satellite communication system with a satellite processing capability and a basic service capability of a Beidou navigation system can be enhanced without affecting the original communication function of the system.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
a low-rail navigation enhancement signal transmission method based on a wideband code division multiple access communication system comprises the following steps:
step 1: after the satellite communication terminal A is started, finishing an authentication and network access initialization process in a satellite network management center, and acquiring the speed and the position of the satellite communication terminal A according to navigation satellite signals; after the initialization is completed, the satellite communication terminal A initiates a communication request to a satellite network management center; the navigation enhancement information to be transmitted adopts fixed format framing to be compatible with WCDMA communication system standard, and then adopts different orthogonal address codes to carry out code division multiplexing on pilot frequency components and data components bearing the enhancement information to form LePT signals;
step 2: setting a transmission period of the LePT signal, and broadcasting the LePT signal by using fixed channel resources in the transmission period;
step 3: the satellite allocates a channel for the LePT signal and transmits resource position information of the LePT channel in the BCCH channel, wherein the resource position information is carried on the P-CCPCH channel and is transmitted together with WCDMA system information;
step 4: the navigation fusion terminal monitors the P-CCPCH channel and obtains LePT signal channel information from the P-CCPCH channel, and completes power estimation, frequency offset estimation and time synchronization through a common pilot signal, and receives the LePT signal from a corresponding channel;
step 5: the navigation fusion terminal receives the data transmitted in the LePT signal data component, integrates the data, performs integrity check, extracts security authentication information for authentication, executes step 6 if the authentication is secure, and stops signal processing if the authentication fails;
step 6: and after the safety authentication is successful, the position and ephemeris information of the low orbit satellite are obtained by receiving the independent navigation information frame, and the ionosphere and troposphere correction information and the precise orbit and clock error information are obtained by receiving the navigation enhancement information frame.
Further, the frequency of the LePT signal accords with the frequency structure division of the low-rail broadband code division multiplexing system, and the frequency division multiplexing system is supported; the data component signal of the LePT signal adopts a time division multiplexing system; the LePT signal uses the OVSF code as orthogonalization code to realize code division multiplexing; the integrity identifier is inserted into the frame structure of the LePT signal to mark the end of a piece of information, and the receiving end confirms whether the complete signal is successfully received by checking the signal sequence identifier and the integrity identifier.
Further, frames used in the data component of LePT information are divided into three types: the method comprises the steps of distinguishing an independent navigation information frame, a safety authentication information frame and a navigation enhancement information frame according to transmission format combination indicators, and broadcasting in a channel according to fixed time sequence and fixed period; wherein:
the independent navigation information frame is used for assisting in completing independent positioning, and broadcasting information is the orbit and clock error information of the satellite; the ground lead fusion terminal receives basic navigation frame information and cooperates with the LePT pilot signal component to realize pseudo-range measurement, so as to complete independent positioning or combined positioning with other GNSS systems;
the safety authentication information frame improves the navigation positioning performance from the positioning reliability; the low orbit satellite sends the security authentication information in the coverage area at regular time, the terminal judges whether the signal is legal according to the information, thus the navigation enhancement service is carried out by using the signal sent by the legal satellite only, and the fraud resistance is improved;
the navigation enhancement information frame carries satellite related information of the GNSS system, and represents navigation enhancement text information in an SSR mode, so that the position resolving speed and the navigation accuracy of the navigation terminal are improved.
Further, the satellite low orbit constellation allocates channel resources for pilot frequency component and data component of LePT signal respectively directly on CPICH channel and S-CCPCH channel, and broadcasts LePT signal in current coverage area.
The invention has the following advantages:
1) The invention can fully utilize the characteristics of strong signal power and high moving speed of the low-orbit satellite, and can provide high-precision independent navigation service by utilizing the pilot frequency component and the data component.
2) The invention can transmit navigation enhancement data to the terminal at high speed, improves the navigation precision and the speed measurement precision of the Beidou system, and realizes navigation enhancement.
3) The invention can improve the service range of the Beidou navigation system by carrying out joint calculation with the Beidou navigation signals, and can provide indoor navigation with sub-meter precision.
4) According to the invention, the security authentication information is sent at regular time, and the lead fusion terminal authenticates through the authentication information, so that the navigation security is improved, and the probability of cheating the terminal is effectively reduced.
5) The LePT (LEO enhanced Positioning and Timing) signal adopted by the invention can be used for a satellite communication system of a low-orbit WCDMA communication system with on-board processing capability, so that the basic service capability of the Beidou navigation system is enhanced, navigation enhancement and independent positioning service can be provided under the conditions of not changing the existing WCDMA low-orbit satellite communication system and not affecting the communication service quality, and effective supplement is provided for the existing GNSS system.
Drawings
FIG. 1 is a schematic diagram of a multiplexing scheme of LePT signals;
FIG. 2 is a schematic diagram of the signal structure of the LePT signal;
FIG. 3 is a schematic diagram of a frame structure of a data component signal in the LePT signal;
FIG. 4 is a schematic diagram of the encoding process of the data component signal in the LePT signal;
fig. 5 is a flowchart of a low-rail navigation enhancement signal transmission method according to an embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to specific embodiments and figures.
A low-rail navigation enhancement signal transmission method based on a wideband code division multiple access communication system designs a LePT signal and a service flow compatible with a WCDMA air interface, and is beneficial to realizing independent positioning and navigation enhancement functions. As shown in fig. 5, the method specifically comprises the following steps:
step 1: the satellite communication terminal A is started, the initialization processes of authentication, network access and the like are completed in the satellite network management center, and meanwhile, the speed and the position of the satellite communication terminal A are obtained according to navigation satellite signals. After the initialization is completed, the terminal A initiates a communication request to a network management center; the enhanced information is framed in a fixed format to be compatible with the WCDMA communication system standard, and the pilot frequency component and the data component carrying the enhanced information are subjected to code division multiplexing by adopting different orthogonal address codes to form the LePT signal.
Step 2: a long period of time is set as a transmission period of the LePT signal, and the LePT signal is broadcast using a fixed channel resource in the period. The time length can be determined by the busyness of the current low-orbit satellite communication network, when the communication service is busy, the spare channel resources in the CPICH channel and the S-CCPCH channel are less, the LePT sending period is shorter, and the communication service requirement needs to be met through more frequent resource reallocation. When the communication service is not busy, a stable channel is easily opened up in the CPICH channel and the S-CCPCH channel for the LePT signal to use, the LePT signal has a longer transmission period at the moment, and the LePT signal can be transmitted according to the allocation for a long time after one time of resource allocation.
Step 3: the satellite allocates a channel for the LePT signal and transmits resource location information of the LePT channel in the BCCH channel, which is carried on the P-CCPCH channel and transmitted together with WCDMA system information. The navigation fusion terminal does not need to establish connection with the low-orbit constellation, and can know the channel information of the LePT signal at the current time only by receiving the P-CCPCH broadcast channel.
Step 4: the navigation fusion terminal monitors the P-CCPCH channel and obtains LePT signal channel information from the P-CCPCH channel, and the navigation fusion terminal completes power estimation, frequency offset estimation and time synchronization through a common pilot signal and receives the LePT signal from a corresponding channel.
Step 5: the navigation fusion terminal receives the data transmitted in the LePT signal data component, integrates the data, performs integrity check, and particularly extracts the security authentication information for authentication. If the authentication is safe, the signal is used for further processing, and if the authentication fails, the signal processing is stopped.
Step 6: after the security authentication is successful, the navigation terminal can obtain the position and ephemeris information of the low orbit satellite by receiving the independent navigation information frame, and the navigation terminal can complete pseudo-range measurement through the information and the LePT pilot frequency component. The navigation terminal can realize independent navigation or enhanced navigation through multiple pseudo-range measurement or combined calculation with GNSS system signals.
Step 7: by receiving the navigation enhancement information frame, the terminal obtains ionosphere and troposphere correction information and precision orbit and clock error information. The ground terminal can greatly enhance the resolving speed and the positioning precision of the GNSS system signals according to the information, realize the navigation enhancement of the GNSS system and improve the availability of the GNSS terminal. Combining the high power LePT pilot component (compared to GNSS signals) for joint positioning can achieve indoor positioning and increase navigation accuracy to sub-meter levels.
As shown in fig. 4, the design of the LePT signal is divided into two parts:
(1) Signal design
1) Pilot signal design: the signal is a BPSK signal modulating a long spreading code, and carries no other information except the spreading code. The pilot signal chip rate is lower than the chip rate of the data signal. The pilot component is transmitted on a common pilot channel (CPICH). The pilot component of the LePT signal is transmitted with lower power so as not to affect the reception of the common pilot signal by the terminal. The pilot component is spread with a long spreading code orthogonal to the common pilot channel distinguishing code to obtain a higher spreading gain. The length of the spreading code used by the signal is an integer multiple of the spreading code used by the common pilot channel signal in the WCDMA system, thereby realizing high-precision pseudo-range measurement.
2) Data signal design: the chip rate of the data signal is fixed and the symbol rate is derived from the fixed chip rate and the different spreading factors. In order to realize the transmission of the navigation enhancement information, different kinds of navigation enhancement information are framed, corresponding frame structures are adopted to transmit on an auxiliary common control physical channel (S-CCPCH), and the functions of the navigation enhancement information are marked in a mode of a Transport Format Combination Identifier (TFCI). When there is a surplus in system resources, a special S-CCPCH channel can be configured to transmit the signals, and if there is no surplus, the signals are sent on the S-CCPCH channel carrying a Forward Access Channel (FACH).
The position information, ephemeris information, ionosphere, troposphere correction information, GNSS system precise orbit and clock error information of the current time are transmitted to a Radio Access Network (RAN) formed by a low orbit satellite constellation at fixed time by a Core Network (CN) formed by ground gateway stations and are stored by the satellite constellation. The data component encoding process of the LePT signal is similar to the encoding process of paging information in WCDMA protocol: firstly, a data service module on a satellite transmits navigation enhancement information to be transmitted to a radio link layer control protocol entity (RLC), and the RLC divides the information into information segments and transmits the information segments to an MAC-b entity of an MAC sub-layer for further processing. The first part of the transmission block is processed by Cyclic Redundancy Check (CRC), CRC information is added, and then tail bits are added. And carrying out 1/2 convolution coding on the data block to obtain a data block with doubled length, and finally using rate matching to form transmission data with required length and mapping the transmission data into the S-CCPCH physical channel wireless frame time slot.
The LePT data component signal adopts a single time slot frame length of 20 bits, and is composed of a 2bit Transmission Format Combination Indicator (TFCI), 12bit data, a 1bit integrity identifier and a 5bit signal sequence identifier. The 2bit TFCI is used for distinguishing the type of the carried data; the integrity mark is used for marking the end of one piece of information, if the information carried by one time slot is the last section in the whole piece of information, the integrity mark is 1, and the bit is 0 under the other conditions; the signal sequence identity is used to mark the position of the piece of information in a 600bit length data block. The receiving end can confirm whether the complete signal is successfully received by checking the signal sequence identifier and the integrity identifier.
(2) Information frame design
The frames used in the LePT data component are divided into three types: independent navigation information frame, safety authentication information frame and navigation enhancement information frame. The three signals are distinguished by a Transport Format Combination Indicator (TFCI) and broadcast in the channel with a fixed timing and a fixed period.
The independent navigation information frame is used for assisting in completing independent positioning, and the main broadcast content is the orbit and clock error information of the satellite. The ground lead fusion terminal receives the basic navigation frame information and can realize pseudo-range measurement by matching with the LePT pilot signal component, thereby completing independent positioning or combined positioning with other GNSS systems.
The safety authentication information frame improves the navigation positioning performance from the positioning reliability. The low orbit satellite sends the security authentication information in the coverage area at regular time, the terminal judges whether the signal is legal according to the information, and the navigation enhancement service is carried out by using only the signal sent by the legal satellite, so that the fraud resistance is improved.
The navigation enhancement information frames carry the satellite related information of the GNSS system, the navigation enhancement information is broadcast to the terminal by utilizing the advantage of high speed of the low-orbit satellite signals, and the position resolving speed and the navigation precision of the navigation terminal are improved. The navigation information adopts SSR (state space representation) mode to represent navigation enhancement text information, which accords with RTCM STANDARD 10403.2 standard. The information carried in the navigation enhancement signal can be solved without error by a navigation terminal supporting the RTCM STANDARD 10403.2 standard.
In the frame structure design, the function expansion can be performed by adding the type of Transport Format Combination Indicator (TFCI), providing more functions.
As shown in fig. 1, the LePT signal is composed of two parts, a navigation component and a data component. The navigation component is responsible for completing independent navigation and synchronous work and can be used for Doppler frequency offset estimation and precise pseudo-range measurement. The data component is used to transmit navigation enhancement information.
The signal structure of the LePT signal is shown in fig. 2. In this example, the low-orbit satellite system uses the WCDMA system for communication. Let's assume that the data component of the LePT signal is transmitted in a frequency band having a center frequency of 1.9GHz and a chip rate of 3.84Mcps, the symbol rate being derived from a fixed chip rate and different spreading factors. The spreading factor on the downlink for conveying the LePT data component ranges from 128 to 512, so the modulation symbol rate varies from 7.5kbps to 30kbps. The shortest duration of the data component signal is 10 ms, the chip length is fixed at 38400chips, the symbol length is 300bit-75bit unequal, and the longer data component signal is subjected to integral multiple expansion based on the shortest duration.
The pilot component in the LePT signal is sent on a common pilot channel (CPICH), which performs navigation and secondary synchronization functions using BPSK modulation. In order to meet the compatibility requirement of the Beidou system, the pilot frequency component uses Gold codes with the period of 10230 to spread spectrum, the transmission period is 1.67ms, and the code rate is 3.069Mcps. The symbol rate of the pilot component is 300bps and an all 0 signal is transmitted. The pilot component is twice encoded using Neumann-Hoffman codes, with each NH code symbol corresponding to 1bit0 data. The NH code period is 16.7ms and the code length is 10 bits. In order to avoid affecting the common pilot channel function, the LePT pilot channel power is 1/10 of the common pilot signal power. The signal is a continuous transmission signal, and is broadcast in satellite coverage for a long time.
The LePT signal data component consists of information frames of different types, the information frames are transmitted on an S-CCPCH channel by adopting a corresponding frame structure, the functions of the LePT signal data component are marked by a mode of a Transport Format Combination Identifier (TFCI), and frames used in the LePT data component are divided into three types: independent navigation information frame, safety authentication information frame and navigation enhancement information frame. When there is surplus in system resource, a special S-CCPCH channel can be configured to transmit the signal, if there is no surplus, the signal is multiplexed on the S-CCPCH channel carrying Forward Access Channel (FACH) by code division multiplexing mode to be transmitted.
The data signal format is shown in fig. 3, and the length of a single time slot frame adopted by the LePT data component signal is 20 bits, and the LePT data component signal is composed of a 2bit Transmission Format Combination Indicator (TFCI), 12bit data, a 1bit integrity identifier and a 5bit signal sequence identifier. The 2bit TFCI is used for distinguishing the type of the carried data; the integrity mark is used for marking the end of one piece of information, if the information carried by one time slot is the last section in the whole piece of information, the integrity mark is 1, and the bit is 0 under the other conditions; the signal sequence identity is used to mark the position of the piece of information in a 600bit length data block. The receiving end can confirm whether the complete signal is successfully received by checking the signal sequence identifier and the integrity identifier.
The three information frame formats are the same, but the piggybacked content and functionality are different. The independent navigation information frame is used for assisting in completing independent positioning, and the main broadcast content is the orbit and clock error information of the satellite. The ground lead fusion terminal receives the basic navigation frame information and can realize pseudo-range measurement by matching with the LePT pilot signal component, thereby completing independent positioning or combined positioning with other GNSS systems. The safety authentication information frame improves the navigation positioning performance from the positioning reliability. The low orbit satellite sends the security authentication information in the coverage area at regular time, the terminal judges whether the signal is legal according to the information, and the navigation enhancement service is carried out by using only the signal sent by the legal satellite, so that the fraud resistance is improved. The navigation enhancement information frames carry the satellite related information of the GNSS system, the navigation enhancement information is broadcast to the terminal by utilizing the advantage of high speed of the low-orbit satellite signals, and the position resolving speed and the navigation precision of the navigation terminal are improved. The navigation information adopts SSR (state space representation) mode to represent navigation enhancement text information, which accords with RTCM STANDARD 10403.2 standard. The information carried in the navigation enhancement signal can be solved without error by a navigation terminal supporting the RTCM STANDARD 10403.2 standard.
The navigation enhancement service flow based on the LePT signal is as follows:
the position information, ephemeris information, ionosphere, troposphere correction information, GNSS system precise orbit and clock error information of the current time are transmitted to a Radio Access Network (RAN) formed by a low orbit satellite constellation at fixed time by a Core Network (CN) formed by ground gateway stations and are stored by the satellite constellation. The data component encoding process of the LePT signal is similar to the encoding process of paging information in WCDMA protocol: firstly, a data service module on a satellite transmits navigation enhancement information to be transmitted to a radio link layer control protocol entity (RLC), and the RLC divides the information into information segments with the length of 240 bits and transmits the information segments to an MAC-b entity of an MAC sub-layer for further processing. A 240bit long transport block is first subjected to Cyclic Redundancy Check (CRC) encoding, adding 16bit CRC information, and then adding 8bit tail bits. At this time, the length of the data block is 264 bits, the data block is subjected to 1/2 convolution coding to obtain a data block with the length of 528 bits, and finally, the data block is subjected to rate matching to form transmission data with the length of 600 bits, and the transmission data is divided into 30 parts and mapped into S-CCPCH physical channel wireless frame time slots.
The satellite sets a long period of time as a transmission period of the LePT signal according to the busyness of the current communication service, and the LePT signal is broadcast using a fixed channel resource in the period.
The low orbit satellite transmits resource location information of the LePT channel in the BCCH channel, which is carried on the P-CCPCH channel and transmitted together with WCDMA system information.
The navigation fusion terminal monitors the P-CCPCH channel and obtains LePT signal channel information from the P-CCPCH channel, and performs power estimation, frequency offset estimation and time synchronization through a common pilot signal, and receives the LePT signal from the S-CCPCH channel.
The navigation fusion terminal receives the data transmitted in the LePT signal data component, integrates the data, performs integrity check, and particularly extracts the security authentication information for authentication. If the authentication is safe, the signal is used for further processing, and if the authentication fails, the signal processing is stopped.
After the security authentication is successful, the navigation terminal can obtain the position and ephemeris information of the low orbit satellite by receiving the independent navigation information frame, and the navigation terminal can complete pseudo-range measurement through the information and the LePT pilot frequency component. The terminal can realize independent navigation or enhanced navigation through multiple pseudo-range measurement or combined calculation with GNSS system signals.
By receiving the navigation enhancement information frame, the terminal obtains ionosphere and troposphere correction information and precision orbit and clock error information. The ground terminal can greatly enhance the resolving speed and the positioning precision of the GNSS system signals according to the information, realize the navigation enhancement of the GNSS system and improve the availability of the GNSS terminal. Combining the high power LePT pilot component (compared to GNSS signals) for joint positioning can achieve indoor positioning and increase navigation accuracy to sub-meter levels.
In summary, the present invention proposes a low-rail navigation enhancement signal transmission method based on a wideband code division multiple access communication system, which adopts a specially designed LePT signal. Based on the LePT signal, the present invention can be applied to a low-orbit satellite communication system using the WCDMA system without affecting the communication service capability. In addition, the LePT signal can provide independent positioning, safety authentication and navigation enhancement functions, and a function expansion space is reserved, so that the LePT signal has a certain function expansion capability.
Claims (4)
1. A low-rail navigation enhancement signal transmission method based on a wideband code division multiple access communication system is characterized by comprising the following steps:
step 1: after the satellite communication terminal A is started, finishing an authentication and network access initialization process in a satellite network management center, and acquiring the speed and the position of the satellite communication terminal A according to navigation satellite signals; after the initialization is completed, the satellite communication terminal A initiates a communication request to a satellite network management center; the navigation enhancement information to be transmitted adopts fixed format framing to be compatible with WCDMA communication system standard, and then adopts different orthogonal address codes to carry out code division multiplexing on pilot frequency components and data components bearing the enhancement information to form LePT signals;
step 2: setting a transmission period of the LePT signal, and broadcasting the LePT signal by using fixed channel resources in the transmission period;
step 3: the satellite allocates a channel for the LePT signal and transmits resource position information of the LePT channel in the BCCH channel, wherein the resource position information is carried on the P-CCPCH channel and is transmitted together with WCDMA system information;
step 4: the navigation fusion terminal monitors the P-CCPCH channel and obtains LePT signal channel information from the P-CCPCH channel, and completes power estimation, frequency offset estimation and time synchronization through a common pilot signal, and receives the LePT signal from a corresponding channel;
step 5: the navigation fusion terminal receives the data transmitted in the LePT signal data component, integrates the data, performs integrity check, extracts security authentication information for authentication, executes step 6 if the authentication is secure, and stops signal processing if the authentication fails;
step 6: and after the safety authentication is successful, the position and ephemeris information of the low orbit satellite are obtained by receiving the independent navigation information frame, and the ionosphere and troposphere correction information and the precise orbit and clock error information are obtained by receiving the navigation enhancement information frame.
2. The low-rail navigation enhancement signal transmission method based on the wideband code division multiple access communication system according to claim 1, wherein the frequency of the LePT signal accords with the frequency structure division of a low-rail wideband code division multiplexing system and supports a frequency division multiplexing system; the data component signal of the LePT signal adopts a time division multiplexing system; the LePT signal uses the OVSF code as orthogonalization code to realize code division multiplexing; the integrity identifier is inserted into the frame structure of the LePT signal to mark the end of a piece of information, and the receiving end confirms whether the complete signal is successfully received by checking the signal sequence identifier and the integrity identifier.
3. The low-rail navigation enhancement signal transmission method based on the wideband code division multiple access communication system according to claim 2, wherein the frames used in the data component of the LePT information are divided into three types: the method comprises the steps of distinguishing an independent navigation information frame, a safety authentication information frame and a navigation enhancement information frame according to transmission format combination indicators, and broadcasting in a channel according to fixed time sequence and fixed period; wherein:
the independent navigation information frame is used for assisting in completing independent positioning, and broadcasting information is the orbit and clock error information of the satellite; the ground lead fusion terminal receives basic navigation frame information and cooperates with the LePT pilot signal component to realize pseudo-range measurement, so as to complete independent positioning or combined positioning with other GNSS systems;
the safety authentication information frame improves the navigation positioning performance from the positioning reliability; the low orbit satellite sends the security authentication information in the coverage area at regular time, the terminal judges whether the signal is legal according to the information, thus the navigation enhancement service is carried out by using the signal sent by the legal satellite only, and the fraud resistance is improved;
the navigation enhancement information frame carries satellite related information of the GNSS system, and represents navigation enhancement text information in an SSR mode, so that the position resolving speed and the navigation accuracy of the navigation terminal are improved.
4. The method for transmitting low-orbit navigation-enhanced signal based on wideband code division multiple access communication system as claimed in claim 1, wherein the satellite low-orbit constellation allocates channel resources for pilot component and data component of the LePT signal respectively directly on CPICH channel and S-CCPCH channel, and broadcasts the LePT signal in the current coverage area.
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