CN115102607A - Low-orbit navigation enhanced signal transmission method based on wideband code division multiple access communication system - Google Patents
Low-orbit navigation enhanced signal transmission method based on wideband code division multiple access 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, the navigation enhancement information to be transmitted adopts a fixed format to form frames, and the pilot frequency component and the data component carrying the enhancement information adopt different orthogonal address codes to carry out code division multiplexing; the satellite allocates channels for the LePT signals and sends the resource position information of the LePT channels in the BCCH channel; the navigation fusion terminal monitors a P-CCPCH channel and obtains LePT signal channel information; the navigation fusion terminal receives data transmitted in the LePT signal data component and extracts safety authentication information; after the safety certification 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 enhance the basic service capability of the Beidou navigation system on the premise of not influencing 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 globally, and are playing an increasingly important role in industry development. At present, the Beidou system is increasingly widely applied in various fields.
The GNSS system has the advantages of wide coverage range, low deployment cost and the like, but has some inherent defects:
(1) the GNSS system constellation generally operates on a medium-high orbit constellation, which causes the satellite to be far away from the terminal, the path loss to be serious, the power level of the satellite navigation signal to be lower than that of noise, and the satellite navigation signal is easy to be interfered and deceived.
(2) Because the signal intensity is weak, the positioning accuracy of the GNSS system is insufficient, and the GNSS system needs to be assisted by a ground reference station, so that the deployment cost of the satellite communication system is increased, and the cost advantage is weakened.
(3) The navigation speed is slow, and the navigation terminal has slow speed for searching the navigation signal and calculating the position.
(4) The reliability is not enough, the integrity level of the current GNSS system cannot meet the requirements of important fields related to life safety, and the requirements on the integrity are higher and higher as the GNSS system is used in more fields.
The low earth orbit satellite has a series of advantages of low orbit high power, global coverage, rapid Doppler change, ground monitoring space-based satellite and the like, and can provide beneficial supplement for the traditional GNSS system. With the vigorous development of low-earth-orbit satellite mobile communication and low-earth-orbit navigation enhancement technologies, the design of a communication and navigation integrated enhancement system based on a low-earth-orbit constellation has been proposed.
The spread spectrum communication can obviously enhance the anti-interference performance of signals, and a Code Division Multiple Access (CDMA) technology is applied to a part of low-orbit satellite communication systems and is a technology which is certainly used in the next development of civil satellite communication. Signals spread by using a spreading code can be used for accurately measuring pseudorange, low-orbit satellites can use a wider frequency band to carry out long-distance communication, and a communication integrated system based on a WCDMA (wideband code division multiple Access) system is a GNSS navigation enhancement scheme with high feasibility.
The research of the domestic low-earth-orbit satellite communication system-based navigation enhancement system is still in a relatively preliminary stage, and the realization of the navigation enhancement by the existing patents is mostly in a stage of determining a communication fusion realization step. For example, in the patent publication CN106646563A, "a low earth orbit satellite-based enhanced navigation method" mainly utilizes the characteristic that the geometric position of a low earth orbit satellite changes greatly, and realizes fast and high-precision calculation of pseudorange indirectly through a geometric relationship, thereby achieving the effect of navigation enhancement. The patent with application number 201811102234.1 discloses a method and a device for generating a communication and navigation integrated fusion signal, which provides a satellite navigation and communication integrated method based on an OFDMA system, wherein a CDMA positioning signal is superposed on an OFDMA signal to form a communication and navigation integrated fusion signal, and the performance of a navigation system and the positioning accuracy of indoor positioning are improved. However, up to now, there is no navigation enhancement signal transmission scheme specifically for the low-orbit wideband code division multiple access mobile communication system.
Disclosure of Invention
In view of this, the invention provides a low-orbit navigation enhanced signal transmission method based on a wideband code division multiple access communication system, and a satellite navigation enhanced lept (leo enhanced Positioning and timing) signal designed and transmitted based on the method can be used on a satellite communication system of a low-orbit WCDMA communication system with onboard processing capability, and can enhance the basic service capability of a Beidou navigation system on the premise of not influencing the original communication function of the system.
In order to achieve the purpose, the invention adopts the technical scheme that:
a low orbit navigation enhanced 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, the initialization processes of authentication and network access are completed in a satellite network management center, and the speed and the position of the satellite communication terminal A are obtained according to navigation satellite signals; after 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 the standard of a WCDMA communication system, and then adopts different orthogonal address codes to perform code division multiplexing on a pilot frequency component and a data component carrying the enhancement information to form an LePT signal;
step 2: setting a sending period of the LePT signal, and broadcasting the LePT signal by using a fixed channel resource in the sending period;
and 3, step 3: the satellite allocates channels for the LePT signals, and sends the resource position information of the LePT channels in the BCCH channel, and the resource position information is borne on the P-CCPCH channel and is sent together with the WCDMA system information;
and 4, step 4: the navigation fusion terminal monitors the P-CCPCH channel and obtains the channel information of the LePT signal from the P-CCPCH channel, completes power estimation, frequency offset estimation and time synchronization through the common pilot signal and receives the LePT signal from the corresponding channel;
and 5: the navigation fusion terminal receives the data transmitted in the LePT signal data component, integrates the data, carries out integrity check, extracts safety authentication information for authentication, executes the step 6 if the authentication is safe, and stops signal processing if the authentication fails;
step 6: after the safety certification 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.
Furthermore, the frequency of the LePT signal conforms to the frequency structure division of a low-orbit 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 OVSF code as orthogonalization code to realize code division multiplexing; an integrity identifier is inserted into a frame structure of the LePT signal to mark the end of a section of information, and a receiving end confirms whether the complete signal is successfully received by checking the signal sequence identifier and the integrity identifier.
Further, the frames used in the data component of the LePT information are divided into three types: the three information frames are distinguished by a transmission format combination indicator and are broadcasted in a channel in a fixed time sequence and a fixed period; wherein:
the independent navigation information frame is used for assisting in completing independent positioning, and the broadcast content is orbit and clock error information of the satellite; the ground navigation fusion terminal receives basic navigation frame information and is matched with a LePT pilot signal component to realize pseudo-range measurement, and independent positioning or combined positioning with other GNSS systems is completed;
the safety certification information frame improves the navigation positioning performance from the positioning reliability angle; the low earth orbit satellite regularly sends safety certification information in a coverage area, and the terminal judges whether the signal is legal or not according to the information, so that the navigation enhancement service is carried out only by using the signal sent by the legal satellite, and the deception resistance is improved;
the navigation enhancement information frame carries satellite related information of the GNSS system, and adopts an SSR mode to represent navigation enhancement message information, so that the position resolving speed and the navigation precision of the navigation terminal are improved.
Further, the satellite low-orbit constellation directly allocates channel resources for the pilot component and the data component of the LePT signal in the CPICH channel and the S-CCPCH channel respectively, and broadcasts the LePT signal in the current coverage area.
The invention has the following advantages:
1) the invention can make full use of the characteristics of strong power and high moving speed of low-orbit satellite signals and can provide high-precision independent navigation service by using the pilot frequency component and the data component.
2) The invention can transmit navigation enhancement data to the terminal at a high speed, improve the navigation precision and the speed measurement precision of the Beidou system and realize navigation enhancement.
3) The method and the Beidou navigation signal are combined for resolving, so that the service range of the Beidou navigation system can be enlarged, and indoor navigation with sub-meter-level precision can be provided.
4) According to the method and the system, the safety authentication information is sent at regular time, and the navigation fusion terminal performs authentication through the authentication information, so that the navigation safety is improved, and the probability that the terminal is cheated is effectively reduced.
5) The adopted LePT (LEO enhanced Positioning and timing) signals can be used for a satellite communication system of a low-orbit WCDMA communication system with onboard processing capacity, so that the enhancement of the basic service capacity of the Beidou navigation system is realized, the navigation enhancement and the independent Positioning service can be provided under the conditions that the existing WCDMA low-orbit satellite communication system is not changed and the communication service quality is not influenced, and the effective supplement is provided for the existing GNSS system.
Drawings
FIG. 1 is a schematic diagram of a multiplexing method of LePT signals;
FIG. 2 is a schematic diagram of a signal structure of a LePT signal;
FIG. 3 is a diagram of a frame structure of a data component signal in a LePT signal;
FIG. 4 is a diagram illustrating an encoding process for a data component signal in a LePT signal;
fig. 5 is a flowchart of a method for transmitting an enhanced low-track navigation signal according to an embodiment of the present invention.
Detailed Description
The present invention will be described in further detail below with reference to specific embodiments and the attached drawings.
A low orbit navigation enhanced 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 enhanced functions. As shown in fig. 5, the method specifically includes the following steps:
step 1: the satellite communication terminal A is started, initialization processes such as authentication and network access are completed in a satellite network management center, and 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 standard of a WCDMA communication system, and then 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 an LePT signal.
Step 2: a longer period of time is set as a transmission period of the LePT signal during which the LePT signal is broadcast using fixed channel resources. The time length can be determined by the busy degree of the current low-orbit satellite communication network, when the communication service is busy, the vacant channel resources in the CPICH channel and the S-CCPCH channel are less, the LePT sending period is shorter, and the communication service requirement is met by more frequent resource reallocation. When the communication service is not busy, a stable channel is easy to be opened up in the CPICH channel and the S-CCPCH channel for the use of the LePT signal, the sending period of the LePT signal is longer, and the LePT signal can be sent according to the allocation for a long time after one-time resource allocation.
And step 3: the satellite allocates channels for the LePT signals, and sends the resource location information of the LePT channels in the BCCH channel, and the information is carried on the P-CCPCH channel and is sent together with the WCDMA system information. The navigation fusion terminal does not need to establish connection with a low-orbit constellation, and can acquire the channel information of the LePT signal at the current time only by receiving a P-CCPCH broadcast channel.
And 4, step 4: the navigation fusion terminal monitors the P-CCPCH channel and obtains the channel information of the LePT signal from the P-CCPCH channel, completes power estimation, frequency offset estimation and time synchronization through the common pilot signal, and receives the LePT signal from the corresponding channel.
And 5: and the navigation fusion terminal receives the data transmitted in the LePT signal data component, integrates the data, checks the integrity of the data, and particularly extracts the safety 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 safety certification is successful, the position of the low-orbit satellite and ephemeris information are obtained 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. Through multiple pseudo-range measurements or combined solution with GNSS system signals, the navigation terminal can realize independent navigation or enhanced navigation.
And 7: by receiving the navigation enhancement information frame, the terminal obtains ionosphere and troposphere correction information and precise orbit and clock error information. The ground terminal can greatly enhance the resolving speed and the positioning precision of the GNSS system signal according to the information, realize the navigation enhancement of the GNSS system and improve the usability of the GNSS terminal. The high-power LePT pilot frequency component (compared with GNSS signals) is combined for joint positioning, so that indoor positioning can be realized, and the navigation precision is improved to a sub-meter level.
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 that modulates 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 sent on the common pilot channel (CPICH). In order not to affect the reception of the common pilot signal by the terminal, the pilot component of the LePT signal is transmitted with a lower power. The pilot component is spread with a long spreading code orthogonal to the common pilot channel distinct code to achieve higher spreading gain. The length of the spread spectrum code used by the signal is integral multiple of the spread spectrum code used by the common pilot channel signal in the WCDMA system, so that high-precision pseudo-range measurement is realized.
2) Designing a data signal: the chip rate of the data signal is fixed and the symbol rate is derived from the fixed chip rate and different spreading factors. In order to realize the transmission of the navigation enhancement information, different types of navigation enhancement information are framed, a corresponding frame structure is 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 the system resource has surplus, a special S-CCPCH channel can be configured to transmit the signals, and if the surplus does not exist, the signals are sent on the S-CCPCH channel carrying a Forward Access Channel (FACH).
The position information, the ephemeris information, the ionosphere, the troposphere correction information, the GNSS system precise orbit and the clock error information of the current time are transmitted to a Radio Access Network (RAN) consisting of a low-orbit satellite constellation by a Core Network (CN) consisting of ground gateway stations at regular time and are stored by the satellite constellation. The data component encoding process for the LePT signal is similar to the encoding process for paging messages in the 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 sublayer for further processing. The transport block first performs Cyclic Redundancy Check (CRC) coding, adding CRC information, and then adding tail bits. 1/2 convolution coding is carried out on the data block to obtain a data block with the length being doubled, and finally, transmission data with the required length is formed by using rate matching and is mapped to a wireless frame time slot of an S-CCPCH physical channel.
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 2-bit Transmission Format Combination Indicator (TFCI), 12-bit data, a 1-bit integrity identifier and a 5-bit signal sequence identifier. The TFCI with 2 bits is used for distinguishing the type of the carried data; the integrity mark is used for marking the end of a section of information, if the information carried by a time slot is the last section of the whole section of information, the integrity mark is 1, and the bit is 0 under the other conditions; the signal sequence identifier is used to mark the position of the segment of information in a 600bit length block of data. 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: an independent navigation information frame, a safety certification information frame and a navigation enhancement information frame. These 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 orbit and clock error information of the satellite. And the ground communication and navigation 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 joint positioning with other GNSS systems.
The safety authentication information frame improves the navigation positioning performance from the positioning reliability angle. The low earth orbit satellite regularly sends the safety certification information in the coverage area, the terminal judges whether the signal is legal according to the information, and only the signal sent by the legal satellite is used for navigation enhancement service, so that the deception resistance is improved.
The navigation enhancement information frame carries the related information of the GNSS system satellite, and the navigation enhancement information is broadcasted to the terminal by utilizing the advantage of high speed of low-orbit satellite signals, so that the position resolving speed and the navigation precision of the navigation terminal are improved. The navigation information adopts an SSR (State space presentation) mode to represent navigation enhancement message information, and the navigation enhancement message information conforms to RTCM STANDARD 10403.2 standards. The information carried in the navigation enhancement signal can be resolved without error by a navigation terminal that supports the RTCM STANDARD 10403.2 compliant standard.
In the frame structure design, the function can be expanded by increasing the type of the Transport Format Combination Indicator (TFCI), and more functions can be provided.
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 pseudorange measurement. The data component is used to transmit navigation enhancement information.
The signal structure diagram of the LePT signal is shown in fig. 2. In this example, the low earth orbit satellite system uses the WCDMA system for communication. Assuming that the LePT signal data component is transmitted over a frequency band having a center frequency of 1.9GHz, the chip rate is 3.84Mcps, and the symbol rate is obtained from a fixed chip rate and different spreading factors. The spreading factor on the downlink used to convey the LePT data component ranges from 128 to 512, so the modulation symbol rate varies from 7.5kbps to 30 kbps. The shortest duration of the data component signal is 10 ms, the chip length is fixed to 38400chips, the symbol length is 300-75 bits unequal, and the longer data component signal is subjected to integral multiple expansion on the basis of the chip length and the symbol length.
The pilot component of the LePT signal is transmitted on the common pilot channel (CPICH), which assumes navigation and secondary synchronization functions and is BPSK modulated. In order to meet the compatibility requirement with the Beidou system, the pilot frequency component uses Gold codes with the period of 10230 for spreading, the sending period is 1.67ms, and the code rate is 3.069 Mcps. The pilot component has a symbol rate of 300bps and transmits an all 0 signal. The pilot component is secondary coded using a Neumann-Hoffman code, with each NH code symbol corresponding to 1bit0 data. The NH code period is 16.7ms, and the code length is 10 bits. To avoid affecting the common pilot channel function, the LePT pilot channel power is 1/10 times the common pilot signal power. The signal is a continuous transmission signal, and is broadcast in a satellite coverage area for a long time.
The LePT signal data component is composed of different kinds of information frames, corresponding frame structures are adopted to transmit on an S-CCPCH channel, the functions of the LePT signal data component are marked in a Transmission Format Combination Identifier (TFCI) mode, and the frames used in the LePT data component are divided into three types: an independent navigation information frame, a safety certification information frame and a navigation enhancement information frame. When the system resource has surplus, a special S-CCPCH channel can be configured to transmit the signals, if the surplus does not exist, the signals are multiplexed on the S-CCPCH channel carrying a Forward Access Channel (FACH) in a code division multiplexing mode to be transmitted.
The data signal format is as shown in fig. 3, the length of a single timeslot frame adopted by the LePT data component signal is 20 bits, and the LePT data component signal is composed of a 2-bit Transport Format Combination Indicator (TFCI), 12-bit data, a 1-bit integrity flag and a 5-bit signal sequence flag. The TFCI with 2 bits is used for distinguishing the type of the carried data; the integrity mark is used for marking the end of a section of information, if the information carried by a time slot is the last section of the whole section of information, the integrity mark is 1, and the bit is 0 under the other conditions; the signal sequence identifier is used to mark the position of the segment of information in a 600bit length block of data. 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 piggyback content and the functions are different. The independent navigation information frame is used for assisting in completing independent positioning, and the main broadcast content is orbit and clock error information of the satellite. And the ground navigation 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 angle. The low earth orbit satellite regularly sends the safety certification information in the coverage area, the terminal judges whether the signal is legal according to the information, and only the signal sent by the legal satellite is used for navigation enhancement service, so that the deception resistance is improved. The navigation enhancement information frame carries the related information of the GNSS system satellite, and the navigation enhancement information is broadcasted to the terminal by utilizing the advantage of high speed of low-orbit satellite signals, so that the position resolving speed and the navigation precision of the navigation terminal are improved. The navigation information adopts an SSR (State space presentation) mode to represent navigation enhancement message information, and accords with RTCM STANDARD 10403.2 standard. The information carried in the navigation enhancement signal can be resolved without error by a navigation terminal that supports the RTCM STANDARD 10403.2 compliant standard.
The navigation enhancement service flow based on the LePT signal is as follows:
the position information, the ephemeris information, the ionosphere, the troposphere correction information, the GNSS system precise orbit and the clock error information of the current time are transmitted to a Radio Access Network (RAN) consisting of a low-orbit satellite constellation by a Core Network (CN) consisting of ground gateway stations at regular time and are stored by the satellite constellation. The data component encoding process for the LePT signal is similar to the encoding process for paging messages in the 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 sublayer for further processing. The transmission block with the length of 240 bits is firstly processed by Cyclic Redundancy Check (CRC) coding, 16 bits of CRC information is added, and then 8 bits of tail bits are added. At the moment, the length of the data block is 264bit, 1/2 convolutional coding is carried out on the data block to obtain the data block with the length of 528bit, and finally, the transmission data with the length of 600bit is formed by using rate matching and is divided into 30 parts which are mapped into the radio frame time slot of the S-CCPCH physical channel.
The satellite sets a longer time period as a sending period of the LePT signal according to the busy degree of the current communication service, and the LePT signal uses fixed channel resources to broadcast in the period.
The low earth orbit satellite sends the resource position information of the LePT channel in the BCCH channel, and the information is carried on the P-CCPCH channel and is sent together with the WCDMA system information.
The navigation fusion terminal monitors the P-CCPCH channel and obtains the channel information of the LePT signal from the P-CCPCH channel, completes power estimation, frequency offset estimation and time synchronization through the common pilot frequency signal, and receives the LePT signal from the S-CCPCH channel.
And the navigation fusion terminal receives the data transmitted in the LePT signal data component, integrates the data, checks the integrity of the data, and particularly extracts the safety 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 safety certification is successful, the position of the low orbit satellite and the ephemeris information are obtained by receiving the independent navigation information frame, and the navigation terminal can complete the pseudo-range measurement through the information and the LePT pilot frequency component. The terminal can realize independent navigation or enhanced navigation by measuring pseudo-range for multiple times or jointly resolving with GNSS system signals.
By receiving the navigation enhancement information frame, the terminal obtains ionosphere and troposphere correction information and precise orbit and clock error information. The ground terminal can greatly enhance the resolving speed and the positioning precision of the GNSS system signal according to the information, realize the navigation enhancement of the GNSS system and improve the usability of the GNSS terminal. The high-power LePT pilot frequency component (compared with GNSS signals) is combined for joint positioning, so that indoor positioning can be realized, and the navigation precision is improved to a sub-meter level.
In summary, the present invention provides a low-orbit navigation enhanced 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, it can be applied to a low-earth-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, reserve function expansion space and have certain function expansion capacity.
Claims (4)
1. A low orbit navigation enhanced 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, the initialization processes of authentication and network access are completed in a satellite network management center, and the speed and the position of the satellite communication terminal A are obtained according to navigation satellite signals; after 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 the standard of a WCDMA communication system, and then adopts different orthogonal address codes to perform code division multiplexing on a pilot frequency component and a data component carrying the enhancement information to form an LePT signal;
step 2: setting a sending period of the LePT signal, and broadcasting the LePT signal by using a fixed channel resource in the sending period;
and 3, step 3: the satellite allocates channels for the LePT signals, and sends the resource position information of the LePT channels in the BCCH channel, and the resource position information is borne on the P-CCPCH channel and is sent together with the WCDMA system information;
and 4, step 4: the navigation fusion terminal monitors the P-CCPCH channel and obtains the channel information of the LePT signal from the P-CCPCH channel, completes power estimation, frequency offset estimation and time synchronization through the common pilot frequency signal, and receives the LePT signal from the corresponding channel;
and 5: the navigation fusion terminal receives the data transmitted in the LePT signal data component, integrates the data, carries out integrity check, extracts safety authentication information for authentication, executes the step 6 if the authentication is safe, and stops signal processing if the authentication fails;
step 6: after the safety certification is successful, the position and ephemeris information of the low orbit satellite are obtained by receiving the independent navigation information frame, and the correction information of the ionosphere and the troposphere and the precision orbit and clock error information are obtained by receiving the navigation enhancement information frame.
2. The transmission method of low-orbit navigation enhanced signals based on the wideband code division multiple access communication system according to claim 1, wherein the frequency of the LePT signal conforms to the frequency structure division of the low-orbit 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 OVSF code as orthogonalization code to realize code division multiplexing; an integrity identifier is inserted into a frame structure of the LePT signal to mark the end of a section of information, and a receiving end confirms whether the complete signal is successfully received by checking the signal sequence identifier and the integrity identifier.
3. The transmission method of enhanced low-track navigation signals based on 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 three information frames are distinguished by a transmission format combination indicator and are broadcasted in a channel in a fixed time sequence and a fixed period; wherein:
the independent navigation information frame is used for assisting in completing independent positioning, and the broadcast content is orbit and clock error information of the satellite; the ground navigation fusion terminal receives basic navigation frame information and is matched with a LePT pilot signal component to realize pseudo-range measurement, and independent positioning or combined positioning with other GNSS systems is completed;
the safety authentication information frame improves the navigation positioning performance from the positioning reliability angle; the low earth orbit satellite regularly sends safety certification information in a coverage area, and the terminal judges whether the signal is legal or not according to the information, so that the navigation enhancement service is carried out only by using the signal sent by the legal satellite, and the deception resistance is improved;
the navigation enhancement information frame carries satellite related information of the GNSS system, and adopts an SSR mode to represent navigation enhancement message information, so that the position resolving speed and the navigation precision of the navigation terminal are improved.
4. The transmission method of low-orbit navigation enhancement signals based on the wideband code division multiple access communication system according to claim 1, wherein the satellite low-orbit constellation directly allocates channel resources for the pilot component and the data component of the LePT signal in the CPICH channel and the S-CCPCH channel, respectively, and broadcasts the LePT signal in the current coverage area.
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