阅读说明：本技术 一种gps-l1c或bds-b1c频点卫星导航接收机冷启动方法 (Cold start method of GPS-L1C or BDS-B1C frequency point satellite navigation receiver ) 是由 张静 李晓 高敏 黄喆 郭欣 于 2019-09-27 设计创作，主要内容包括：本发明涉及一种GPS-L1C或BDS-B1C频点卫星导航接收机冷启动方法,属于卫星导航技术领域。该方法对GPS-L1C频点和BDS-B1C频点的导频分量和数据分量进行联合跟踪解调,利用导频分量的子码相位,结合其导航电文结构设计特点,使用拼接相邻电文帧策略,可有效减少卫星导航接收机收集完整星历的时间,大大缩短了卫星导航接收机GPS-L1C频点和BDS-B1C频点的冷启动时间。(The invention relates to a cold start method of a GPS-L1C or BDS-B1C frequency point satellite navigation receiver, belonging to the technical field of satellite navigation. The method carries out joint tracking demodulation on the pilot frequency component and the data component of the GPS-L1C frequency point and the BDS-B1C frequency point, utilizes the sub-code phase of the pilot frequency component, combines the structural design characteristics of navigation messages thereof, and uses the strategy of splicing adjacent message frames, thereby effectively reducing the time of a satellite navigation receiver for collecting complete ephemeris and greatly shortening the cold start time of the GPS-L1C frequency point and the BDS-B1C frequency point of the satellite navigation receiver.)

1. A cold start method of a GPS-L1C or BDS-B1C frequency point satellite navigation receiver is characterized by comprising the following steps:

(1) carrying out signal acquisition, tracking and bit synchronization processing on the pilot frequency component of the GPS-L1C or BDS-B1C frequency point signal, carrying out data demodulation on the pilot frequency component and the data component after realizing the bit synchronization of the pilot frequency component, and entering the step (2);

(2) storing pilot frequency subcode bits obtained by demodulating the pilot frequency component into a pilot frequency subcode buffer area, storing navigation message bits obtained by demodulating the data component into the navigation message buffer area, meanwhile, simultaneously counting the received navigation message bits, searching N bits in front of a satellite subcode sequence in the pilot frequency subcode buffer area, recording a received message count value at the current moment as a received message count value M1 at the matching moment once detecting that continuous N bits in the pilot frequency subcode buffer area are matched with the N bits in front of the satellite subcode sequence, and entering the step (3), otherwise, continuously executing the step (2);

(3) based on the unchanged content of a second subframe in adjacent navigation message frames, a principle of obtaining a complete second subframe by adopting a frame splicing method of adjacent frames is adopted, the number M2 of messages to be received which completely collect a first subframe and the second subframe is calculated according to a received message count value M1 at the matching moment, then pilot frequency subcode bits obtained by demodulating a pilot frequency component are continuously stored in a pilot frequency subcode buffer area, navigation message bits obtained by demodulating a data component are stored in a navigation message buffer area until the complete first subframe and the second subframe are completely collected until the messages to be received are completely collected, and the step (4) is carried out;

(4) splicing the navigation messages received in the navigation message buffer area into a complete navigation message frame according to whether the pilot frequency subcodes are turned over and the phase positions of the received pilot frequency subcodes;

(5) and performing de-interleaving processing on the spliced navigation message frame to obtain navigation message data, decoding the original message according to the message formatting format to obtain ephemeris parameters, and completing positioning calculation by using the ephemeris parameters.

2. The cold start method of the GPS-L1C or BDS-B1C frequency point satellite navigation receiver of claim 1, wherein the matching means that the two sequences are completely the same or the first sequence and the second sequence are completely the same in reverse.

3. The cold start method of a GPS-L1C or BDS-B1C frequency point satellite navigation receiver of claim 1, wherein the method for judging whether the pilot frequency subcode is overturned is as follows:

when a first sequence formed by continuous N bits in a pilot frequency subcode buffer area is detected to be matched with a second sequence formed by the first N bits of a satellite subcode sequence, the two sequences are completely the same, and the pilot frequency subcode is not turned over; the first sequence and the second sequence are completely the same in inversion, and the pilot frequency subcodes are reversed.

4. The cold start method for the GPS-L1C or BDS-B1C frequency point satellite navigation receiver of claim 1, wherein N is less than or equal to the length M0 of the first sub-frame of the navigation message.

5. The cold start method for the GPS-L1C or BDS-B1C frequency point satellite navigation receiver of claim 4, wherein said N is not lower than 30.

6. The cold start method of the GPS-L1C or BDS-B1C frequency point satellite navigation receiver of claim 1, wherein the minimum number of messages to be received M2 is calculated as:

when N ≦ M1< L- (M0-N), M2 ═ L-M1;

when M1 is more than or equal to L- (M0-N), M2 is M0-N;

wherein, L is the total length of one frame of navigation message.

7. The cold start method of the GPS-L1C or BDS-B1C frequency point satellite navigation receiver of claim 6, wherein the specific method of the step (4) of splicing is as follows:

when M1 is equal to N, splicing is not needed, and the message in the message buffer area is a complete frame of navigation message;

when N < M1< L- (M0-N), splicing the front M1-N bit message in the message buffer to the rear L- (M1-N) bit message to finish splicing;

when M1 is more than or equal to L- (M0-N), splicing the front L-M0 bit message in the message buffer to the rear M0 bit message is completed.

8. The cold start method of GPS-L1C or BDS-B1C frequency point satellite navigation receiver as claimed in claim 1, wherein said pilot sub-code buffer and message buffer store messages in a shifting manner, and the length of the buffers is the total length L of one frame of navigation message.

9. The cold start method of a GPS-L1C or BDS-B1C frequency point satellite navigation receiver as claimed in claim 1, wherein said step (2) searches the first N bits of the satellite subcode sequence by means of fixed window matching.

10. The cold-start method of a GPS-L1C or BDS-B1C frequency point satellite navigation receiver according to claim 1, wherein the step (1) first captures a pilot component signal to obtain the estimated values of the doppler frequency and the code phase of the pilot component signal, then further detects and confirms the doppler frequency and the code phase obtained by the capture to realize the phase locking and the bit synchronization of the pilot component, and finally completes the data demodulation of the pilot component and the data component by using the orthogonality of the phases of the pilot component and the data component.

Technical Field

The invention relates to a cold start method of a GPS-L1C or BDS-B1C frequency point satellite navigation receiver, belonging to the technical field of satellite navigation.

Background

The cold start time is the time from power-on starting to outputting the first effective positioning result of the receiver under the condition of no external assistance, and is a key performance index of the satellite navigation receiver. The cold start time comprises the time for acquiring and tracking satellite signals, the time for collecting the full ephemeris and the navigation solution time, wherein the full ephemeris collection time accounts for the greatest proportion, so that the cold start time of the receiver can be effectively shortened by reducing the full ephemeris collection time.

The duration of one frame of non-GEO satellite navigation signals of a GPS-L1C/A frequency point and a BDS-B1 frequency point is 6s, complete three frames need to be continuously received, complete ephemeris can be collected, and the longest time is 30 s. The one-frame time length of satellite navigation signals of a modern GPS-L1C frequency point and a BDS-B1C frequency point is 18s, if a complete frame must be received from beginning to end according to a traditional design idea, the longest time required is 36s, and the complete ephemeris collection time is increased on the contrary, so that the cold start time is shortened by researching a method for reducing the complete ephemeris collection time by combining the text design characteristics of the receiver and fully utilizing the structural advantages of the receiver, and the performance of the receiver is improved.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: the method overcomes the defects of the prior art, and provides a cold start method of a GPS-L1C or BDS-B1C frequency point satellite navigation receiver, so that the time for collecting complete ephemeris is shortened, and the quick cold start is realized.

The technical solution of the invention is as follows: a cold start method of a GPS-L1C or BDS-B1C frequency point satellite navigation receiver is realized by the following steps:

(1) carrying out signal acquisition, tracking and bit synchronization processing on the pilot frequency component of the GPS-L1C or BDS-B1C frequency point signal, carrying out data demodulation on the pilot frequency component and the data component after realizing the bit synchronization of the pilot frequency component, and entering the step (2);

(2) storing pilot frequency subcode bits obtained by demodulating the pilot frequency component into a pilot frequency subcode buffer area, storing navigation message bits obtained by demodulating the data component into the navigation message buffer area, meanwhile, simultaneously counting the received navigation message bits, searching N bits in front of a satellite subcode sequence in the pilot frequency subcode buffer area, recording a received message count value at the current moment as a received message count value M1 at the matching moment once detecting that continuous N bits in the pilot frequency subcode buffer area are matched with the N bits in front of the satellite subcode sequence, and entering the step (3), otherwise, continuously executing the step (2);

(3) based on the unchanged content of a second subframe in adjacent navigation message frames, a principle of obtaining a complete second subframe by adopting a frame splicing method of adjacent frames is adopted, the number M2 of messages to be received which completely collect a first subframe and the second subframe is calculated according to a received message count value M1 at the matching moment, then pilot frequency subcode bits obtained by demodulating a pilot frequency component are continuously stored in a pilot frequency subcode buffer area, navigation message bits obtained by demodulating a data component are stored in a navigation message buffer area until the complete first subframe and the second subframe are completely collected until the messages to be received are completely collected, and the step (4) is carried out;

(4) splicing the navigation messages received in the navigation message buffer area into a complete navigation message frame according to whether the pilot frequency subcodes are turned over and the phase positions of the received pilot frequency subcodes;

(5) and performing de-interleaving processing on the spliced navigation message frame to obtain navigation message data, decoding the original message according to the message formatting format to obtain ephemeris parameters, and completing positioning calculation by using the ephemeris parameters.

The matching means that the two sequences are identical or that the first sequence is inverted from the second sequence.

The method for judging whether the pilot frequency subcode is overturned comprises the following steps:

when a first sequence formed by continuous N bits in a pilot frequency subcode buffer area is detected to be matched with a second sequence formed by the first N bits of a satellite subcode sequence, the two sequences are completely the same, and the pilot frequency subcode is not turned over; the first sequence and the second sequence are completely the same in inversion, and the pilot frequency subcodes are reversed.

The N is less than or equal to the length M0 of the first sub-frame of the navigation message.

And N is not less than 30.

The calculation expression of the minimum number M2 of messages to be received is:

when N ≦ M1< L- (M0-N), M2 ═ L-M1;

when M1 is more than or equal to L- (M0-N), M2 is M0-N;

wherein, L is the total length of one frame of navigation message.

The splicing method in the step (4) comprises the following specific steps:

when M1 is equal to N, splicing is not needed, and the message in the message buffer area is a complete frame of navigation message;

when N < M1< L- (M0-N), splicing the front M1-N bit message in the message buffer to the rear L- (M1-N) bit message to finish splicing;

when M1 is more than or equal to L- (M0-N), splicing the front L-M0 bit message in the message buffer to the rear M0 bit message is completed.

The pilot frequency sub-code buffer area and the message buffer area store messages in a shifting mode, and the length of each buffer area is the total length L of one frame of navigation messages.

And (2) searching the first N bits of the satellite subcode sequence by adopting a fixed window matching mode.

The step (1) captures the pilot frequency component signal to obtain the estimation values of the Doppler frequency and the code phase of the pilot frequency component signal, then further detects and confirms the Doppler frequency and the code phase obtained by capturing to realize the phase locking and the bit synchronization of the pilot frequency component, and finally completes the data demodulation of the pilot frequency component and the data component by utilizing the orthogonality of the phase of the pilot frequency component and the data component.

Compared with the prior art, the invention has the beneficial effects that:

(1) by utilizing the subcode phase of the pilot frequency component and combining the structural design characteristics of the navigation messages of the GPS-L1C frequency point and the BDS-B1C frequency point, the method and the device can effectively reduce the time of the satellite navigation receiver for collecting the complete ephemeris by using the strategy of splicing the adjacent message frames, reduce 18s to the maximum extent and greatly shorten the cold start time of the GPS-L1C frequency point and the BDS-B1C frequency point of the satellite navigation receiver.

(2) The invention directly determines the signal turning condition of the navigation message by using the phase turning state when the pilot frequency component subcodes are matched, thereby improving the phase turning judgment efficiency.

(3) The invention guides the capture and tracking of the data component through the capture and tracking of the pilot frequency component, thereby greatly saving the resource of signal processing and accelerating the capture and tracking processing speed of the data component.

Drawings

FIG. 1 is a frame structure of navigation messages before interleaving after encoding of a GPS-L1C frequency point and a BDS-B1C frequency point in the invention;

FIG. 2 is a flow chart of a cold start method of a satellite navigation receiver according to the present invention;

FIG. 3 is a schematic diagram of the storage of the pilot sub-code buffer and the text buffer used in the present invention;

FIG. 4 is a schematic view of a message receiving and splicing process scenario 1 of the present invention;

fig. 5 is a schematic diagram of the message receiving and splicing process case 2 of the present invention.

Detailed Description

The invention is described in further detail below with reference to the following figures and specific examples:

the central frequency point of the satellite navigation signal of the GPS-L1C frequency point and the BDS-B1C frequency point is 1575.42MHz, and comprises a pilot frequency component and a data component, wherein the phases of the pilot frequency component and the data component are orthogonal. Wherein:

(1) and modulating a sub-code in the pilot frequency component, wherein the length of the sub-code is 1800 bits, the period of the sub-code is 18s, and the sub-code sequence of each satellite is known and repeated.

(2) And modulating navigation messages in the data component, wherein the length of each frame of messages is 1800 bits, the broadcasting period is 18s, the frame structure of the messages before being interleaved after coding is shown in figure 1, each message frame comprises 3 subframes with different lengths, the first subframe fixedly broadcasts satellite numbers and hourly second counts, the second subframe fixedly broadcasts basic navigation information such as satellite clock parameters and ephemeris parameters, and the third subframe broadcasts changed data block information based on page types. Message data required by the receiver for completing positioning calculation after cold start are extracted from a first subframe and a second subframe, wherein the first subframe of each message frame is different and cannot be spliced between adjacent frames; and except the ephemeris updating time, the second sub-frame in the adjacent frames is the same and can be spliced between the adjacent frames. (note: the text received by the receiver is formed by interleaving the second sub-frame and the third sub-frame according to the convention in the interface control file based on the frame structure shown in fig. 1.)

(3) The sub-code period in the pilot component is equal to the navigation message frame period in the data component and remains synchronized, i.e. the start times are strictly aligned.

According to the design of the GPS-L1C frequency point and BDS-B1C frequency point navigation message structures, the navigation messages in the data component are spliced according to the sub-code phase of the tracking demodulation of the pilot frequency component, and the time for collecting the complete ephemeris can be effectively reduced. Therefore, the invention designs a method for shortening the time for collecting the complete ephemeris by splicing the adjacent text frames so as to shorten the cold start time of the GPS-L1C frequency point and the BDS-B1C frequency point of the satellite navigation receiver, and the specific implementation flow chart is shown in FIG. 2.

As shown in FIG. 2, the method for shortening the cold start time of the GPS-L1C frequency point and the BDS-B1C frequency point of the satellite navigation receiver in the invention is realized by the following steps:

(1) carrying out signal acquisition, tracking and bit synchronization processing on the signal pilot frequency component, carrying out data demodulation on the pilot frequency component and the data component after realizing the bit synchronization of the pilot frequency component, and entering the step (2);

because the pilot frequency component and the data component have a fixed phase relationship, in order to save hardware resources, a pilot frequency component signal can be captured first to obtain estimated values of the Doppler frequency and the code phase of the pilot frequency component signal, then the Doppler frequency and the code phase obtained by capture are further detected and confirmed to realize pilot frequency component phase locking and bit synchronization, and finally data demodulation of the pilot frequency component and the data component is completed simultaneously by utilizing orthogonality of the pilot frequency component and the data component phase.

(2) Storing pilot frequency subcode bits obtained by demodulating the pilot frequency component into a pilot frequency subcode buffer area, storing navigation message bits obtained by demodulating the data component into the navigation message buffer area, meanwhile, counting the received navigation message bits, searching N bits in front of a satellite subcode sequence in the pilot frequency subcode buffer area in a fixed window matching mode, recording a received message count value at the current moment as a received message count value M1 at the matching moment once detecting that continuous N bits in the pilot frequency subcode buffer area are matched with the N bits in front of the satellite subcode sequence, and entering the step (3), otherwise, continuing to execute the step (2);

the N needs to meet the requirements of high efficiency and high reliability, if the N cannot be too long, the calculated amount is large, the efficiency is affected, if the N cannot be too short, the calculated amount is large, otherwise misjudgment is easily caused, and as an optimal scheme, the value range of the N is not less than 30 and is not higher than the length M0 of the first sub-frame of the navigation message.

The matching means that the two sequences are identical or that the first sequence is inverted from the second sequence.

The pilot frequency sub-code buffer area and the message buffer area store messages in a shifting mode, and the length of the buffer areas is the total length of the navigation messages.

(3) Based on the unchanged content of a second subframe in adjacent navigation message frames, a principle of obtaining a complete second subframe by adopting a frame splicing method of adjacent frames is adopted, the number M2 of messages to be received which completely collect a first subframe and the second subframe is calculated according to a received message count value M1 at the matching moment, then pilot frequency subcode bits obtained by demodulating a pilot frequency component are continuously stored in a pilot frequency subcode buffer area, navigation message bits obtained by demodulating a data component are stored in a navigation message buffer area until the complete first subframe and the second subframe are completely collected until the messages to be received are completely collected, and the step (4) is carried out;

the calculation expression of the minimum message number M2 to be received of the completely collected first subframe and second subframe is as follows:

when N ≦ M1< L- (M0-N), M2 ═ L-M1;

when M1 is more than or equal to L- (M0-N), M2 is M0-N;

wherein, L is the total length of one frame of navigation message.

(4) Splicing the navigation messages received in the navigation message buffer area into a complete navigation message frame according to whether the pilot frequency subcodes are turned over and the phase positions of the received pilot frequency subcodes;

the method for judging whether the pilot frequency subcode is overturned comprises the following steps:

when a first sequence formed by continuous N bits in a pilot frequency subcode buffer area is detected to be matched with a second sequence formed by the first N bits of a satellite subcode sequence, the two sequences are completely the same, and the pilot frequency subcode is not turned over; the first sequence and the second sequence are completely the same in inversion, and the pilot frequency subcodes are reversed.

The specific splicing method comprises the following steps:

when M1 is equal to N, splicing is not needed, and the message in the message buffer area is a complete frame of navigation message;

when N < M1<1800- (M0-N), splicing the front M1-N bit message in the message buffer to the rear 1800- (M1-N) bit message to finish splicing;

when M1 is more than or equal to 1800- (M0-N), splicing the front 1800-M0 bit message in the message buffer to the rear M0 bit message is completed.

(5) And performing de-interleaving processing on the spliced navigation message frame to obtain navigation message data, decoding the original message according to the message formatting format to obtain ephemeris parameters, and completing positioning calculation by using the ephemeris parameters.