JPH10186015A - Gps receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain a second frame synchronization in a short time by locking-on ratio waves after the second search tracking of a receiver at the time of lock- off, and implementing the second frame synchronization if parity coincides when the actual data for one work are acquired. SOLUTION: A CPU implements second frame synchronization at the time of lock-off. Counters virtually repeat the same process as that before lock-off. When the lock-off period exceeds the period set on a time-out counter 16, values of the counters are cleared, and a frames synchronization process is made in the normal process mode because errors against actual data are generated when the period after lock-off becomes long. When it is judged that no time-over occurs, a parity check is made after one word is acquired. If parity coincides, the second frame synchronization is implemented. Frame synchronization is completed with two words at maximum in 1.2sec.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a GPS which can secure continuity of positioning operation when navigation data sent from a GPS satellite is once locked off, and shorten the time until re-frame synchronization. Regarding the receiver.

[0002]

2. Description of the Related Art In a GPS receiver used for precision positioning or the like, a DS for demodulating a consumer C / A code in radio waves transmitted from a plurality of GPS satellites by an SS spreading method.
P (digital signal processor) is provided.

This DSP is configured with multiple channels so that it can despread radio waves and demodulate data, and simultaneously process a plurality of satellite radio waves. A combination of satellites with the smallest error is selected, and positioning is performed using navigation data sent from each satellite.

The format of a navigation message sent from a satellite is, as shown in FIG.
It contains 1 to 10 words of message data, with 0 bit as one word.

At the beginning of the first word, preamble data (data unique to each satellite) is 8 bits,
The last six bits are assigned to parity bits as error correction codes.

The second word has a Z count first, followed by data, and the last six bits are assigned to parity bits. Hereinafter, six parity bits are provided at the end of each word. .

[0007] Then, in the state where the GPS receiver succeeds in synchronization acquisition by despreading and locks on the radio wave, 50b
Since a signal transmitted at a transfer rate of ps is started to be captured from a random position of each word, it cannot be used as data as it is, and the head of word 1 is first detected from the signal. It can be used as data for the first time.

In this case, the head detection depends on the preamble data and can be determined by a combination of 8-bit 1, 0, 1, 0... Patterns which are codes specific to the satellite. By judging the value of the Z counter, the head can be detected, and thereafter, the bit number and the bit number of the required data can be automatically determined by an application built in the receiver according to the format. Therefore, the positioning determination operation using the required bit locations can be executed thereafter.

As a method for determining the frame synchronization, there are two methods:
When the preamble pattern included in the receiver matches the actual preamble message from the sequence of 0, 1, 0,..., The next Z count is taken out as a candidate for the head, and the sequence is again calculated. If the preamble of the next word 1 coincides with the next preamble and the Z count is +1, it is determined that the frame has been synchronized. Thereafter, the navigation data is synchronously tracked so that the navigation data is not lost.

However, such a conventional GPS receiver has the following technical problems.

[0011]

That is, since the GPS satellite signal is originally a very weak signal, the power level tends to decrease in a shadow of a shielding part or in a satellite having a low elevation angle. Lock-off is likely to occur due to some of these obstacles.

When the lock is once turned off, all the obtained data are cleared, and the same operation is repeated when the lock is turned on again, so that the time until the relock is long, and the obstacle to the continuous positioning is obstructed. Had become.

That is, the data transfer rate from the satellite is 50 bps, and the time required to capture all 10-word messages is 30 bits per word. Therefore, for example, after the preamble data (after the time point A in FIG. 1) Assuming that the data is reproduced in ()), 30 × 10 × 1/50 = 6
sec, and this is repeated again, and +
When searching for 1 or not, the maximum time required for the search is 6 × 2 + (30 + 9) × 1/50 = 12.78 sec
It takes time c, including the time of playback after the lock-off, during this time it is completely unmeasurable,
Positioning continuity will be lost.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a GPS receiver capable of performing re-frame synchronization in a short time.

[0015]

In order to achieve the above object, the present invention locks on a signal from a GPS satellite by the SS communication system, reads navigation data for a predetermined word at a predetermined transfer rate, The preamble data of the first word is searched for in each piece of navigation data, and the navigation data is read again starting from that data. As a result, the value of the Z counter in the second word of each piece of navigation data becomes +
In the GPS receiver which confirms the frame synchronization by detecting the state of “1” and thereafter performs the frame synchronization, the bit receiver stores the bit frame information at the time when the receiver is locked off. Virtual tracking means for performing an operation of tracking virtual navigation data at the same transfer rate as the transfer rate based on the stored contents during re-search / tracking of the receiver; and radio waves resulting from the re-search / tracking of the receiver. Means for comparing and checking the parity of the real data when the real data is reproduced and one word of real data is obtained. If the parities match, re-frame synchronization and It is characterized by doing. That is, according to the present invention, the last 6 bits of data of each word are assigned to the parity, and the same as the 29, 30 bits of the previous word and the parity calculated from the 1st to 24th bits are assigned. It focuses on the fact that it is included. Therefore, in the present invention, it is possible to determine whether or not the data is garbled by determining whether or not the parity of the measured value and the parity of the calculated value coincide with each other in a transfer time of up to two words. Reframe synchronization can be confirmed.

[0016]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

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 GPS receiver.

First, in FIG. 2, the GPS receiver according to the present invention converts a 1.5 GHz signal from the antenna 1 into an RF signal.
2, after digitization via IF3,
Input to SP4.

The signal input into the DSP 4 is superimposed on the signal having the same frequency as that of the carrier wave from the local oscillator 6 via the mixer 5 to supplement the signal synchronously.

Further, the C / A code 8 is superimposed via the second mixer 7 and the data obtained by synchronizing and supplementing the C / A code 8 are sequentially detected via the accumulator 10 and input to the CPU 9.

Inside the CPU 9, the C / A epoch data is stored in an epoch counter 11, as shown in FIG.
The bit counter 12, the word counter 13, the Z counter 14, and the subframe counter 15 in parallel therewith are counted while being sequentially carried.

Although the configuration of each of the above counters is the same as that of the conventional counter, a timeout counter 16 for C / A epoch data is added in the present invention. This is because if the time after the lock-off is long, an error with respect to the actual data appears, and a predetermined time passes after the lock-off, a time-over signal is generated, and the re-frame synchronization process described later is performed. It stops and performs normal processing.

The accumulator 10 is operated for 1 msec.
The integrated value is 5 by the accumulator 16 for 20 msec.
The data is reproduced into 0 bps data and stored in the 32-bit shift register 17.

In the above configuration, when the satellite is locked for the first time after the power is turned on, the DSP 4 detects 1, 0, 1, 0,...
If the preamble pattern built into the receiver matches the actual preamble message,
With this as the head candidate, take out the next Z count,
By flowing the sequence again, it is determined that frame synchronization has been achieved because the next preamble matches and the Z count is +1.
After that, the navigation data is tracked synchronously so as not to lose track of the navigation data.

From this state, once the lock is turned off, C
The PU 9 executes re-frame synchronization according to the processing procedure shown in FIG. First, in step A1, each counter virtually repeats the same processing as before lock-off.

On the other hand, when the lock-off time exceeds the time set in the time-out counter 16 as shown in step A2, the value of each counter is cleared in step A3, and the frame is cleared in the normal processing mode shown in step A4. Perform synchronous processing.

If it is determined in step A2 that the time is not over, when one word (30 bits of data) is obtained in step A5, a parity check is performed in step A6.

In the parity check, for example, in FIG. 1, even if data starts to be detected at the point B at the beginning of word 3, the last 6 bits of data in the next word 4 are allocated to the parity. Word 3 of 2
The unknowns X from the 1st to the 24th bit are given using the 9th and 30th bits, and it is assumed that the data match if the answer is the same. Therefore, at most two words, 1, 2,
The frame synchronization ends in sec.

[0029]

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 re-frame synchronization of the GPS receiver will be shorter than in the past. This is suitable for maintaining the continuity of the positioning because the time required for the positioning can be reduced.

[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 illustrating 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)

[Claims] 1. An SS communication system locks on a signal from a GPS satellite, reads navigation data for a predetermined word at a predetermined transfer rate, and searches for preamble data of the first word in each navigation data. The navigation data is read again with the data as the head, and as a result, the value of the Z counter in the second word of each navigation data is +
1. A GPS receiver which confirms frame synchronization by detecting the state of "1" and performs frame synchronization thereafter, stores bit frame information at the time when the receiver is locked off, and Virtual tracking means for performing an operation of tracking virtual navigation data at the same transfer rate as the transfer rate based on the stored content during the re-search tracking of the receiver; Means for comparing and checking the parity of the actual data when the data is reproduced and one word of actual data is obtained, and if the parities match, re-frame synchronization is performed. GPS receiver.