JP3693440B2 - GPS receiver - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a GPS receiver capable of ensuring the continuity of positioning work when navigation data sent from a GPS satellite is once locked off and shortening the time until reframe synchronization.
[0002]
[Prior art]
A GPS receiver used for precision positioning or the like includes a DSP (digital signal processor) that demodulates a consumer C / A code among radio waves transmitted from a plurality of GPS satellites by an SS spreading method.
[0003]
This DSP is configured with multiple channels so that it can despread radio waves and demodulate data, and simultaneously process multiple satellite radio waves, and it captures all available satellites while minimizing positioning errors. Select the combination of satellites to be used, and perform positioning using the navigation data sent from each satellite.
[0004]
By the way, as shown in FIG. 1, the format of the navigation message sent from the satellite includes message data for 1 to 10 words with 30 bits as one word.
[0005]
At the beginning of the first word, preamble data (data unique to each satellite) is assigned 8 bits, and the last 6 bits are assigned to parity bits as error correction codes.
[0006]
The second word has a Z count first, followed by data, and the last 6 bits are assigned to the parity bit. Hereinafter, 6 bits of parity bits are provided at the end of each word.
[0007]
And if the GPS receiver succeeds in the synchronization supplement by despreading and the radio wave is locked on, the signal sent at the transfer rate of 50 bps starts to be captured from the random position of each word. Cannot be used as data, but can be used as data only by first detecting the head of word 1 from the signal.
[0008]
In this case, the detection of the head depends on the preamble data, and can be determined by a combination of 8-bit patterns of 1, 0, 1, 0. By judging the value, the head can be detected, and after that, it can be automatically judged by the application built in the receiver according to the format how many bits to what bits are needed. Can execute a positioning determination operation using a required bit location.
[0009]
As a method for determining the frame synchronization, a preamble pattern built in the receiver and an actual number are detected from a sequence of 1, 0, 1, 0,... Detected after the radio wave is locked on. If the preamble message matches, the next Z count is taken out with this as the head candidate, the sequence is repeated again, and if the next word 1 preamble matches and the Z count is +1, the frame is synchronized. Judgment is made, and thereafter, the navigation data is synchronized and tracked so as not to lose sight of the navigation data.
[0010]
However, such conventional GPS receivers have technical problems described below.
[0011]
[Problems to be solved by the invention]
In other words, GPS satellite signals are inherently very weak signals, so the power level is likely to decrease in the shadow of a shielding part or in satellites with a low elevation angle. It is easy to end.
[0012]
Once locked off, all the obtained data is cleared and the same operation is repeated when the lock is turned on again.Therefore, it takes a long time to re-lock, which is an obstacle to continuous positioning. It was.
[0013]
That is, the data transfer rate from the satellite is 50 bps, and the time taken to capture a message of all 10 words is 30 bits per word. For example, data after the preamble data (after time A in FIG. 1) Is reproduced, 30 × 10 × 1/50 = 6 sec is necessary, and this is repeated again. When searching whether or not the Z count is +1, the maximum time required for the search is
6 × 2 + (30 + 9) × 1/50 = 12.78 sec. It will take 12.78 sec, including the playback time after the lock-off. During this time, measurement will be impossible and the continuity of positioning will be lost. become.
[0014]
The present invention solves the above problems, and an object of the present invention is to provide a GPS receiver capable of performing reframe synchronization in a short time.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, the present invention locks on a signal from a GPS satellite by using the SS communication method, reads navigation data for a predetermined word at a predetermined transfer speed, and reads the first word of each navigation data. Search the preamble data, read the navigation data again with the data as the head, and check the frame synchronization by detecting the state where the value of the Z counter in the second word is incremented by 1 in each navigation data. Thereafter, in the GPS receiver that is configured to perform frame synchronization, the bit frame information at the time when the receiver is locked off is stored, and during the re-search / tracking of the receiver, the virtual contents are stored based on the stored contents. Virtual tracking means for performing an operation of tracking the target navigation data at the same transfer speed as the transfer speed, As a result of the tracking, the radio wave is turned on, and when the actual data is reproduced and the actual data for one word is obtained, the parity is matched. Then, it is characterized by re-frame synchronization.
That is, according to the present invention, the last 6 bits of data of each word are allocated to the parity, and the same as the parity calculated from the 29th and 30th bits of the previous word and the 1st to 24th bits. It is focused on what is in.
Therefore, according to the present invention, it is possible to determine whether or not the data is garbled by checking whether or not the parity of the actually measured value and the calculated value coincides with each other in a transfer time of a maximum of 2 words. Reframe synchronization can be confirmed.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0017]
FIG. 2 is a block diagram showing a hardware configuration of a GPS receiver to which the present invention is applied, and FIG. 3 is a block diagram showing an internal configuration of a CPU of the hardware.
[0018]
First, in FIG. 2, the GPS receiver according to the present invention digitizes a 1.5 GHz signal from the antenna 1 via RF2 and IF3, and then inputs this signal to the DSP 4.
[0019]
The signal input in the DSP 4 is superposed with a frequency signal having the same carrier frequency as that of the local oscillator 6 via the mixer 5 for synchronization.
[0020]
Further, addition data sequentially detected by superimposing the C / A code 8 via the second mixer 7 and supplementing the synchronization via the accumulator 10 is also input to the CPU 9.
[0021]
In the CPU 9, as shown in FIG. 3, the C / A epoch data is counted while being sequentially carried by the epoch counter 11, the bit counter 12, the word counter 13, the Z counter 14 and the subframe counter 15 in parallel therewith. Is done.
[0022]
The configuration of each counter described above is the same as the conventional one, but in the present invention, a time-out counter 16 for C / A epoch data is added. This is because if the time after the lock-off is long, an error occurs with the actual data. A predetermined time elapses after the lock-off, a time-over signal is generated, and reframe synchronization processing described later is performed. It stops and performs normal processing.
[0023]
Further, 1 msec integrated value of the accumulator 10, by 20msec accumulator 1 7 Played 50bps data, stored in the 32-bit shift register 1 8.
[0024]
In the above configuration, when the first satellite is locked after the power is turned on, the DSP 4 detects the sequence of 1, 0, 1, 0,... When the preamble pattern built in the receiver matches the actual preamble message, the next Z count is taken out using this as the head candidate, and the next sequence is repeated, and the next preamble matches and the Z count is +1. Thus, it is determined that the frames are synchronized, and thereafter, the tracking is performed so that the navigation data is not lost.
[0025]
Once locked off from this state, the CPU 9 executes reframe synchronization according to the processing procedure shown in FIG. First, in step A1, each counter virtually repeats the same process as before the lock-off.
[0026]
On the other hand, as shown in step A2, when the lock-off time exceeds the time set in the timeout counter 16, the value of each counter is cleared in step A3, and frame synchronization processing is performed in the normal processing mode shown in step A4. Do.
[0027]
If it is determined in step A2 that the time is not over, when one word (30 bits of data) is acquired in step A5, a parity check is performed in step A6.
[0028]
The parity check, for example, in FIG. 1, also beginning to be detected is the data in the first and a B point in word 3, and 6-bit data of the last is assigned to a parity for the next word 4, the previous word The unknown number X from the 1st to the 24th bit is increased using the 29th and 30th bits of 3, and if the answers given are the same, the data match. Therefore, frame synchronization is completed in a maximum of 2 words and 1 second.
[0029]
【The invention's effect】
As described in detail above, in the GPS receiver according to the present invention, if the time from lock-off to re-lock is short, the time for reframe synchronization is shortened compared to the conventional case. Therefore, it is suitable for maintaining positioning continuity.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a format of each word of a navigation message of a GPS satellite.
FIG. 2 is a schematic block diagram showing a hardware configuration of a GPS receiver according to the present invention.
FIG. 3 is a block diagram showing an internal configuration of a CPU of the hardware.
FIG. 4 is a flowchart showing a processing procedure of the CPU at the time of lock-off.
[Explanation of symbols]
4 DSP
6 Local oscillator 8 C / A code 9 CPU
10 Accumulator

Claims (1)

Using the SS communication method, the signal from the GPS satellite is locked on, the navigation data for a predetermined word is read at a predetermined transfer speed, and the preamble data of the first word is retrieved from each navigation data. The GPS data is read again, and as a result, the frame synchronization is confirmed by detecting the state in which the value of the Z counter in the second word is incremented by 1 in each navigation data, and thereafter the frame synchronization is performed. In the receiver,
The bit frame information at the time when the receiver is locked off is stored, and the virtual navigation data is tracked at the same transfer speed as the transfer speed based on the stored contents during re-search and tracking of the receiver. A virtual tracking means to perform the action;
A means for comparing and checking the parity of the actual data when the actual data is reproduced as a result of the re-search and tracking of the receiver and the actual data for one word is obtained;
A GPS receiver, wherein if the parity matches, reframe synchronization is performed.

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