CN101424734B - Method for reducing crystal vibration cost of GPS receiver - Google Patents
Method for reducing crystal vibration cost of GPS receiver Download PDFInfo
- Publication number
- CN101424734B CN101424734B CN2007101765975A CN200710176597A CN101424734B CN 101424734 B CN101424734 B CN 101424734B CN 2007101765975 A CN2007101765975 A CN 2007101765975A CN 200710176597 A CN200710176597 A CN 200710176597A CN 101424734 B CN101424734 B CN 101424734B
- Authority
- CN
- China
- Prior art keywords
- crystal oscillator
- time
- gps receiver
- frequency
- satellite
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Images
Abstract
The invention provides a method for reducing the crystal oscillation cost of a receiver of a global positioning system, which relates to the field of receiver design, such as a GPS system based on a global positioning system, in particular to the field that the design of a receiver chip is improved to reduce the dependence of the precision of an external crystal oscillator, and consequently, the cost of the crystal oscillator is reduced. The method calculates GPS satellite pseudo-random code transmitting time which is momently corresponding to two adjacent resolving synchronizing signals generated by hardware to calibrate the oscillation frequency of the crystal oscillator in a software mode, consequently, the radio frequency front-end sampling rate excursion caused by the frequency excursion of the crystal oscillator is modified by a noseband processing part, and the influence of GPS satellite capture by the excursion of a sampling rate is reduced. The invention uses the crystal oscillator with lower precision and low cost to solve the influence of the GPS satellite capture by the excursion of the sampling rate and is especially suitable for application occasions with low noise-signal ratio.
Description
Technical field
The present invention relates to receiver field, in particular for reducing the field of receiver crystal oscillator cost based on GPS (for example gps system).
Background technology
Global positioning satellite and navigational system, for example GPS (GPS) comprises one group of satellite constellation (the Navstar satellite is otherwise known as) that sends gps signal, this gps signal can be received the position that machine is used for confirming this receiver.Satellite orbit is arranged in a plurality of planes, so that any on earth position can both receive this kind signal from least four satellites.More typical situation is that most on earth places can both receive this kind signal from six above satellites.
The gps signal that each gps satellite transmitted all is a direct sequence expansion signal frequently.The signal of commercial use is relevant with standard setting service (SPS), and is referred to as the direct sequence two-phase spread signal of thick sign indicating number (C/A sign indicating number), under the carrier wave of 1575.42MHz, has the speed of per second 1.023 million chips.Pseudo noise (PN) sequence length is 1023 chips, corresponding to 1 millisecond time cycle.The PN sign indicating number that each satellites transmits is different (Gold sign indicating number) makes signal to send simultaneously from several satellites, and received simultaneously by a receiver, and is almost noiseless each other.Term " satellite asterisk " is relevant with this PN sign indicating number, can be in order to indicate different gps satellites.
The modulation signal of GPS is the combinational code of navigation message (the D sign indicating number is otherwise known as) and PN sign indicating number.The speed of navigation message is per second 50 bits.The base unit of D sign indicating number is the prime frame of one 1500 bit, and prime frame is divided into the subframe of 5 300 bits again.Wherein subframe one has comprised identification code, star kind data length of time, satellite clock corrected parameter information.Subframe two has comprised real-time gps satellite ephemeris (ephemeris) with subframe three, and ephemeris is the main content of current navigator fix information.Subframe four and subframe five have comprised the health status of 1-32 satellite, the almanac (alamanc) of UTC calibration information and ionospheric corrections parameter and 1-32 satellite.Almanac is the simplified subset of satellite ephemeris parameter.Broadcasted once in its per 12.5 minutes, the life-span is a week, can extend to 2 months.
One of main target of GPS receiver is to confirm the launch time of PN sign indicating number.Term " PN sign indicating number launch time " refers to that gps satellite PN sign indicating number is to the time from the gps satellite emission.This is through (each receives signal) local PN reference signal that produces being compared with the signal of reception and " slips " local reference is accomplished until aliging in time with the reception signal.Through being referred to as multiplying each other and integral process of " being correlated with ", these two signals are compared each other.When two signals were alignment in time, the result of output was maximum.Can make by this method receiver time and gps time synchronously on.
Be included in the navigation message, time-of-week (TOW) data that join with absolute time signal correction make the GPS receiver can be accurately and confirm local gps time reliably.The TOW data are transmitted by the time interval in 6 seconds by all satellites.The GPS receiver can use the absolute time signal to confirm the position exactly.Can obtain the difference of local zone time and gps time when having obtained customer location, thereby obtain accurate gps time.
The details of the data that gps signal comprised can find in ICD (Interface Control Document) ICD-GPS-200C; This document was formulated in 1993; Upgraded in 2003, publish by Rockwell Internation Corporation.
Most GPS products does not use atomic clock as the internal oscillator reference source, and is to use the crystal oscillator of relative low price from the consideration of cost.These crystal oscillators have comprised that frequency stability is 10
-8About temperature compensation crystal oscillator (TCXO) and frequency stability 10
-9About but much expensive constant-temperature crystal oscillator (OCXO).The precision of crystal oscillator is one of main restricting factor of decision receiver performance.Outstanding influence is because crystal oscillator floats frequently, driven by crystal oscillator at radio-frequency front-end, and the sampling rate that analog intermediate frequency is converted to the analog to digital converter ADC of digital intermediate frequency is not a fixed value, but drifts about along with the drift of crystal oscillator frequency.And the bandwidth of code tracking loop is very little, usually several hertz of magnitudes.Under many circumstances, the drift of ADC sampling rate has exceeded the bandwidth of sign indicating number ring, makes the code tracking loop cisco unity malfunction, and then can't follow the tracks of gps satellite.Particularly under the situation of low signal-to-noise ratio, receiver need increase signal and add up the time to improve signal to noise ratio (S/N ratio), and equivalence has increased the skew of sampling rate like this, makes that the situation of code tracking loop cisco unity malfunction is particularly outstanding under the situation of low signal-to-noise ratio.Sampling rate skew can exert an influence to carrier tracking loop equally, but this influence can equivalence becomes the Doppler frequency deviation of satellite-signal, in the process of frequency pulling, is eliminated.Thereby the sampling rate skew can be ignored the influence of carrier wave ring.Most of commercial GPS receivers all are to address this problem through the precision that improves crystal oscillator.The crystal oscillator cost increase that these class methods are brought is quite obvious.At present, the price of high-precision TCXO can be compared with the price of GPS baseband processing chip itself mutually, and OCXO is also more expensive than GPS Base-Band Processing core especially.Along with the further reduction of GPS baseband processing chip price, and, can predict the cost quite great proportion that the crystal oscillator cost will account for the GPS receiver module to the further raising of crystal oscillator accuracy requirement.
For solving this difficult problem, a kind of sign indicating number ring scheme of the two poles of the earth is employed.This scheme was used for slightly catching of sign indicating number with a bigger sign indicating number ring of bandwidth before this, got into the narrower second level sign indicating number ring tracking of bandwidth immediately in case catch.This scheme has proposed other a kind of thinking for addressing the above problem, but hardware configuration is complicated, and power consumption increases, and can't reduce owing to crystal oscillator floats other precision influence that brings frequently.
Also have some schemes to be transformed into analog quantity and directly crystal oscillator is compensated the precision with the raising crystal oscillator, but such scenario-frame is complicated, needs custom-made crystal oscillator and compensating circuit thereof, and can only use TCXO, can not use OCXO through gps time.Simultaneously because real-Time Compensation makes that the frequency between twice calibration is unstable.The other scheme uses the synthetic DDS of numerical frequency to realize frequency output, solves frequency problem of unstable between twice calibration.But still based on the crystal oscillator of DDS, this scenario-frame is complicated simultaneously for its frequency stability, needs complicated encoding control circuit between GPS baseband processing chip and the DDS.Cost is high.All these schemes all are to have increased suitable adjunct circuit in commercial GPS timing chip periphery, complex structure, and cost is high.
Summary of the invention
The object of the invention provides and a kind ofly can effectively reduce the dependence of GPS receiver to the external crystal-controlled oscillation precision, and then reduces the method for crystal oscillator cost.
The present invention is through calculating the corresponding constantly gps satellite PN sign indicating number launch time of two adjacent Tick signals that is produced by hardware, with the form calibration crystal oscillator oscillation frequency of software.And then, partly revise the radio-frequency front-end sampling rate skew that causes by the crystal oscillator frequency deviation in Base-Band Processing, reduce the sampling rate skew to catching the influence of gps satellite.Concrete grammar is in receiver Base-Band Processing part the crystal oscillator oscillation frequency to be carried out soft alignment.Said soft alignment is to utilize gps satellite PN sign indicating number launch time crystal oscillator to be carried out soft alignment.
Adopt the hardware configuration form of catching passage use carrier tracking loop and code tracking loop combination of the receiver Base-Band Processing part of the inventive method.Wherein said sign indicating number ring is followed the tracks of and has been comprised a yardage word control generator.Said yardage word control generator has comprised a sampling rate register, realizes the change to yardage word control generator reference frequency through the value of revising this sampling rate register.The change of said sign indicating number NCO reference frequency has been revised and has been reduced ADC sampling rate skew in the radio-frequency front-end that the crystal oscillator frequency deviation causes, and then has reduced the influence of sampling rate skew to code tracking loop.
Said soft alignment process to crystal oscillator may further comprise the steps:
The Pseudo-Random Noise Code launch time of the corresponding GPS satellite of synchronization point is resolved in calculating, and with its storage;
Read stored previous and resolve the Pseudo-Random Noise Code launch time of the corresponding GPS satellite of synchronization point;
Calculate one and resolve the corresponding absolute time of synchronous signal cycle;
Calculate the corresponding absolute time of clock period that crystal oscillator drives, and then revise the crystal oscillator oscillation frequency; Wherein, Revising the crystal oscillator oscillation frequency comprises: the absolute time that has obtained to resolve synchronous signal cycle; Known again and resolved the corresponding clock number of synchronous signal cycle, promptly can calculate the actual frequency of crystal oscillator, and then can calculate the actual sample rate of radio-frequency front-end by the crystal oscillator driving; Further, the correction sampling rate that calculates is write the sign indicating number NCO register of hardware, waits for suitable opportunity and upgrade a yard NCO.
Further, the hardware configuration of catching passage use carrier tracking loop and code tracking loop combination of the receiver Base-Band Processing of said soft alignment method part.
Further, said code tracking loop has comprised a yardage word control generator.Said yardage word control generator has comprised a sampling rate register, realizes the change to yardage word control generator reference frequency through the value of revising said sampling rate register.
Further, the said synchronizing signal of resolving is produced by the synchronizing signal maker that resolves of hardware.
Further, the said synchronizing signal maker that resolves is to be driven by crystal oscillator, and to resolve the corresponding clock number that is driven by crystal oscillator of synchronous signal cycle be known.
Further, the said length of the resolving synchronous signal cycle register that resolves the synchronizing signal maker through modification changes.
Further, the said synchronous signal cycle that resolves of new calculating is carried out fault-tolerant processing,, wait for next time and calculating if the synchronous signal cycle value of resolving that calculates surpasses threshold value then gives up.Said computation process is to resolve in the synchronous signal cycle at one to accomplish.
Further, said calculating GPS satellite Pseudo-Random Noise Code process launch time comprises:
Resolve the synchronizing signal rising edge and come temporarily, hardware latchs a yard NCO, sign indicating number counter, millisecond counter and bit counter;
Time-of-week information in the navigation message of demodulation GPS satellite;
Make up each time register and time-of-week information, calculate Pseudo-Random Noise Code launch time.
Further, said calculating Pseudo-Random Noise Code need have at least a satellite to realize frame synchronization launch time.When having accomplished frame synchronization, use a highest satellite of the relative receiver of the satellite elevation angle to calculate Pseudo-Random Noise Code launch time more than a satellite.
Further, the affirmation of said frame synchronization need meet the following conditions simultaneously:
Find continuous three sub-frame synchronous codes;
Each subframe verification is passed through;
The frame number of each subframe is in the interval of [1～5];
The time-of-week that adjacent sub-frame demodulates (TOW) time phase difference 300 bits.
Utilize frequency stability lower but cheaply crystal oscillator can solve sampling rate skew influence to catching, particularly in the application scenario of low signal-to-noise ratio.This invents the existing receiver basic boom of change useless, can be transplanted to easily on the existing receiver product.This invention need not calibrated crystal oscillator with example, in hardware, has simplified system design greatly, has reduced cost, and it is little to possess hardware spending simultaneously, and extensibility is strong, the reliability advantages of higher.One embodiment of the present of invention can improve 2 one magnitude equivalently with the performance that ordinary temp compensates crystal oscillator (thousand price＜5 of 20PPM yuan/every).
Description of drawings
Fig. 1 is the general structured flowchart of GPS receiver;
Fig. 2 is the flow process of the GPS receiver positioning calculation of a preferred embodiment of the present invention;
Fig. 3 be a preferred embodiment of the present invention catch the channel architecture block diagram;
Fig. 4 is the synoptic diagram of GPS text synchronous code;
Fig. 5 is the structural representation of GPS text hand-over word;
Fig. 6 is the structured flowchart of the hardware time register of a preferred embodiment of the present invention;
Fig. 7 be a preferred embodiment of the present invention crystal oscillator is carried out the FB(flow block) of soft alignment.
Embodiment
For making the object of the invention, technical scheme and advantage clearer, below in conjunction with specific embodiment, and with reference to accompanying drawing, to further explain of the present invention.
For simplicity, gps time (GPST) when all referring to gps system among the present invention.During constantly gps system of the PN sign indicating number that term " PN sign indicating number launch time " is defined as the emission of certain gps satellite.For simplicity, all refer to PN sign indicating number launch time " launch time " among the present invention.
Fig. 1 has described the general structure of GPS receiver, and the present invention is based on also that similar structures realizes, some embodiment of the present invention have used structure shown in the figure.Whole GPS receiver is made up of radio-frequency front-end 102, Base-Band Processing 103, application layer 104, gps antenna 101 and external crystal-controlled oscillation 113 parts in the frame of broken lines shown in the figure.The GPS radio frequency rf signal receives the laggard radio frequency front end of going into by gps antenna, at first amplifies through pre-low-noise amplifier 105, is down-converted to analog intermediate frequency IF by low-converter 106 then.And then, convert digital intermediate frequency into through analog to digital converter ADC 107 and transfer to Base-Band Processing and partly make Base-Band Processing.After wherein the output of analog to digital converter ADC is controlled through automatic gain control AGC108, feed back to the gain of low-converter with the stable simulation intermediate frequency.And the reference frequency of low-converter is generated by frequency synthesizer 109.And analog to digital converter ADC and frequency synthesizer are all driven by external crystal-controlled oscillation 113.The frequency drift of external crystal-controlled oscillation has directly determined the sampling rate to analog intermediate frequency.
Gps signal is converted into and is changed over to Base-Band Processing behind the digital medium-frequency signal and partly handle.Base-Band Processing part is caught passage 110 by some passages, and the tracing channel 111 of some passages is formed with embedded microprocessor 112.Catch passage in order to the gps satellite in the search visual field, confirm each visible satellite, and carrier doppler that transmits and PN sign indicating number code phase.Tracing channel 111 is used to follow the tracks of the satellite that captures, and synchronous with it, so that calculate the launch time of PN sign indicating number, demodulates navigation message simultaneously in order to the location.Said bit synchronous and the frame synchronization of comprising synchronously.The number of catching passage and tracing channel can require to change flexibly according to performance, cost, power consumption etc.A preferred embodiment of the present invention has used 12 to catch passage and 12 tracing channel.Another preferred embodiment of the present invention has used 32 to catch passage and 12 tracing channel.SiRFII has used the passage of catching of as many as 1920 for chip.Embedded microprocessor 112 is used to control each catches and tracing channel, accomplishes the demodulation text simultaneously, calculates the time of arrival of PN sign indicating number, and then resolve work such as receiver location, speed and time.Crystal oscillator frequency soft alignment process of the present invention is also accomplished in this embedding declines processing.Whole Base-Band Processing part also is to utilize external crystal-controlled oscillation 113 as frequency reference.Crystal oscillator can use temperature compensating crystal oscillator TCXO or the higher temperature control crystal oscillator OCXO of precision, if even have the specific (special) requirements can the high atomic clock of service precision, but along with the raising of accuracy requirement, the cost of crystal oscillator also is close to the increase of index percent.Because radio-frequency front-end and Base-Band Processing have been used same crystal oscillator, also make when reducing cost through the Base-Band Processing part to the crystal oscillator soft alignment, and then reduce the crystal oscillator frequency deviation and possibility is provided the influence of radio frequency front-end sampling rate.
Base-Band Processing partly calculates to be exported to application layer 104 by various port after the information such as position, speed and current time of receiver and does further to use.The basic structure of application layer is a user interface 114, can also on its basis, do various expansions.Base-Band Processing also is diversified to the interface shape of application layer partly.One embodiment of the present of invention use the NMEA0183 standard of industrywide standard through the output of RS232 interface.An alternative embodiment of the invention provide meet NMEA0183 agreement time code in, also provide from customized binary message form, quantity of information is bigger, data volume is littler.An alternative embodiment of the invention has also used interfaces such as RS485, CAN bus and Ethernet to realize adapting to the demand of different application environment except that using RS232 as the standard interface.Application layer has comprised electronic chart usually, and driving planning waits the typical application in the GIS category.
Usually, radio-frequency front-end shown in the figure and Base-Band Processing are packaged into an independently chip separately.But also there is plurality of applications that two parts are packaged together and becomes the SIP system.And more product of the future unites two into one two parts and forms single S OC chip.The present invention is suitable for the GPS receiver chip of above-mentioned form.
Fig. 2 has described a preferred embodiment GPS receiver of the present invention and has realized the flow process of location.The calculating that is used for the various parameters of crystal oscillator soft alignment all need be merged in this flow process.This process finishes until calculating receiver location 206 from 201 beginnings of receiver power-up initializing, has accomplished one-time positioning and has resolved, and begins new round computation process immediately.This process is to be triggered by the Tick signal rising edge that the Tick maker generates.The Tick maker is driven by crystal oscillator, and the interval of twice Tick signal is strict precisely only relevant with the frequency accuracy of crystal oscillator.Usually get into trapped state 202 after receiver powers on, search is to confirm satellite, the carrier frequency of visible satellite and the code phase of PN sign indicating number in the sight line.Search to carrier frequency under this state is coarse, usually hundreds of hertz magnitude.Get into frequency pulling state 203 afterwards, to differing several hertz magnitude, carry out bit synchronous simultaneously to local frequency pulling with the satellite carrier frequency.After accomplishing frequency pulling, receiver gets into tracking mode 204, accomplishes frame synchronization, promptly can get into demodulation text state 205, and the text demodulation of modulating on the carrier wave is come out to be used for 206 times calculating of the state that the resolves receiver location subsequently.
What Fig. 3 described is the channel architecture of catching of a preferred embodiment of the present invention.In this part corresponding diagram 1 110.This structure has certain representativeness, and at present a lot of products have all used similar structure.This catches the combination that passage comes down to adjustable carrier tracking loop and PN code tracking loop, also is called as the auxiliary carrier wave ring of sign indicating number ring.Used correlator as the carrier frequency of coupling receiving satellite signal and the means of PN sign indicating number code phase in this structure.In other application examples, can use additive methods such as matched filter, FFT power Spectral Estimation, FFT circular correlation.But the citation form of carrier tracking loop and the combination of PN code tracking loop all is similar.After digital medium-frequency signal 301 is obtained by radio-frequency front-end shown in Figure 1 102, get into and catch passage and be divided into homophase (I road) and quadrature (Q road) two-way mutually, the cosine component and the sinusoidal component that reappear carrier wave 303 with this locality respectively multiply each other 302.Further, the correlator 304 that gets into separately carries out related operation.Here, correlator also can be by a tenth of the twelve Earthly Branches own wave filter, FFT power Spectral Estimation, FFT circular correlation etc. other can mate the frequency of receiving satellite signal and the method for PN sign indicating number replaces.The reference quantity of its related operation is by this locality reproduction pseudo-code 305; And the result of related operation (perhaps similar matching operation process) transfers to detecting device 310 detections, synthesizes the output frequency of (carrier wave NCO) 309 through synthetic (sign indicating number NCO) 307 of the numerical frequency of corresponding algorithm controls PN sign indicating number and carrier frequency.Sign indicating number NCO has comprised a sampling rate register among the present invention, can realize the change to sign indicating number NCO reference frequency through the value of revising this sampling rate register.Code generator 306 is driven by sign indicating number NCO, supplies with the correlator computing in order to the PN sign indicating number that generates local reproduction.The output frequency of sign indicating number NCO has directly influenced the speed of this locality reproduction PN sign indicating number of code generator generation.Like this, correlator, detecting device, sign indicating number NCO, code generator have formed a sign indicating number ring.Simultaneously detecting device has been controlled the output frequency of carrier wave NCO, through sin/cos mapping 308, square wave converted to sinusoidal wavely becomes the local carrier wave that reappears with cosine waveform, and then entering multiplier and digital medium-frequency signal carries out multiplying.Like this, multiplier, correlator, detecting device, carrier wave NCO, a carrier wave ring of Sin/Cos mapping formation.
Usually, the carrier tracking loop of catching passage has hundreds of hertz bandwidth, to realize the traction to the frequency offset in the search rate step-length.Therefore, the skew of the sampling rate of radio-frequency front-end can be left in the basket to the influence of carrier wave ring.But code tracking loop is owing to be used to calculate PN sign indicating number launch time, is designed to narrow bandwidth usually, and a typical bandwidth is several hertz of magnitudes.Excessive bandwidth can be brought the reduction of bearing accuracy, thereby each big GPS receiver chip manufacturer does not use the code tracking loop of wide bandwidth.Because the smaller bandwidth of code tracking loop, the influence that the deviation of radio-frequency front-end analog to digital converter sampling rate is brought just can not be left in the basket.All the more so under the situation of low signal-to-noise ratio, during low signal-to-noise ratio, need to increase the time of adding up to improve signal to noise ratio (S/N ratio), if at this moment the deviation of sampling rate arrives to a certain degree, catch and possibly can't carry out fully.
Fig. 4 describes the synoptic diagram of GPS text synchronous code.Synchronous code (preamble) the 403rd, the preceding 8 bits of remote measurement word (telemery word, abbreviation TLW) 401, just the first eight bit of each subframe.Utilize this synchronous code can achieve frame synchronous.This synchronous code possibly or be " 01110100 " for " 10001011 " according to last two the indicated polarity 402 of last subframe.In case confirm to find this synchronous code, promptly can confirm the beginning of a sub-frame.TLM also has one 16 reservation position and one 6 check bit in addition.Concrete structural information and checking algorithm can find detailed description in the ICD-GPS-200C document.
In fact navigation message data stream itself possibly contain similar " 10001011 " or " 01110100 " data segment.So the present invention uses following combination verification criterion will miss synchronous probability and drops to low-down level:
1) finds continuous three sub-frame synchronous codes;
2) each subframe verification is passed through;
3) frame number of each subframe is in the interval of [1:5];
4) TOW time phase difference 300 bits that demodulate of adjacent sub-frame.
Fig. 5 describes the structural representation of GPS text hand-over word.Hand-over word (Hand Over Word, abbreviation HOW) is right after after the remote measurement word.1 to 17 of hand-over word is a time-of-week (Time of Week, abbreviation TOW) 502, be from every Saturdays/start at during midnight zero Sunday time counting, the resolution of TOW is 6 seconds.The 18th 503 expression, after self-information was injected, the satellite momentum moment unloading phenomenon of whether rolling was indicated for satellite for the 19th 504 synchronously, and whether the unlabeled data frame time is consistent with the subcode clock time.The 20th～23 505 is subframe numbers.Last six 507 is check bit.More detailed hand-over word structural information and checking algorithm can find in the ICD-GPS-200C document.
Fig. 6 has described the structured flowchart of the hardware time register of a preferred embodiment of the present invention.Be the prerequisite that realizes the location clearing launch time of calculating satellite PN sign indicating number, also be among the present invention in order to the essential condition of the parameter of calculating the soft alignment crystal oscillator, thereby most important.Digital intermediate frequency 601 gets into the sign indicating number ring among the figure.Structure is consistent with the sign indicating number ring structure shown in Fig. 3, is made up of correlator 602, embedded microprocessor 604, C/A code generator 603, sign indicating number NCO 605.Just realized the function of detecting device with flush bonding processor.Sign indicating number NC0605 in the frame of broken lines, sign indicating number counter 606, millisecond counter 607, bit counter 608 is closed the title time register.Wherein sign indicating number NCO has characterized code phase, and the sign indicating number counter has characterized the relative number of chip of C/A sign indicating number, and millisecond counter has characterized a millisecond number that navigation message bit is interior, and bit counter has characterized the bit number of navigation message.These counters are initialised when achieve frame is synchronous and give initial value.Especially, sign indicating number NCO realizes increasing a process when carrying out related operation.The process of its frame synchronization details in Fig. 4.And sign indicating number counter, millisecond counter, bit counter rely on the carry of previous counter to increase 1 separately.The Tick maker is driven by external crystal-controlled oscillation, and is every at a distance from fixing Tick signal of system clock number generation.The time interval of this signal is strict accurate and known, and is only relevant with the frequency of external crystal-controlled oscillation.One embodiment of the present of invention use 0.3s as the Tick signal period, and an alternative embodiment of the invention is used 0.15s.The Tick signal period is short more, and is high more to the precision of crystal oscillator calibration, but the length of Tick signal period also receives the restriction of the arithmetic capability and the power consumption of baseband processing chip.All time registers latch when the Tick signal comes, to guarantee not receive the influence of software query counter delay.Can obtain the launch time of second following precision in the combination of these time registers.And need obtain the launch time of second above precision through separating the TOW conversion.This process details in Fig. 5.
Fig. 7 has explained the FB(flow block) that crystal oscillator is carried out soft alignment.Prerequisite of the present invention is to have at least a satellite to be in tracking mode.This situation to the overwhelming majority is real.If current time is in tracking mode more than a satellite, then choose the highest satellite in the relative receiver elevation angle, to reduce the influence of ionosphere to launch time.Whether system's detection hardware Tick maker after initialization 701 exports Tick signal 702.If the Tick rising edge arrives, then once calculate PN sign indicating number launch time and crystal oscillator is carried out the soft alignment process; If the Tick rising edge does not arrive, then continue to wait for.In other words, twice pair of Tick cycle that is spaced apart that crystal oscillator is implemented soft alignment.One embodiment of the present of invention use 0.3s as Tick signal slot (Tick time), and an alternative embodiment of the invention is used 0.15s.The Tick signal is to be generated by the Tick maker of hardware, so frequency precisely and only relevant with the degree of stability of crystal oscillator.The length of Tick signal period can change through the register of revising the Tick maker.When the Tick signal comes, hardware latchs a series of time counter 703.These time registers comprise: sign indicating number NCO, sign indicating number counter, millisecond counter, bit counter.The structure and the operational process of these registers are described in detail in Fig. 6.Further, demodulate TOW information 704 in the navigation message.The value of assembly time register and the temporal information of TOW can calculate Tick constantly corresponding PN sign indicating number launch time 705, with being about to its storage, are used for the calculating of next cycle.Further, read the last corresponding PN sign indicating number transmitting time 706 of a Tick cycle of storage.The absolute time of this time and gps system differs the propagation delay of an electromagnetic wave from satellite to reception; But because in the short period interval; This propagation delay is almost constant, is the absolute time under the coordinate system so the difference of the PN sign indicating number launch time that can think that two Tick calculate constantly is exactly a gps system.In other words, utilize the corresponding PN sign indicating number of Tick time that calculates promptly can calculate the absolute time 707 of Tick sigtnal interval correspondence launch time.
Further, the Tick signal period that calculates is carried out fault-tolerant processing 708.The Tick cyclical theory upper deviation that calculates only depends on crystal oscillator, and its error amount should be very little, promptly abandons if the calculated value deviation surpasses a threshold value, waits for next time and calculating.Obtained the absolute time in Tick cycle, known the clock number that the Tick cycle is corresponding again, promptly can calculate the actual frequency 709 of crystal oscillator, and then can calculate the actual sample rate 710 of radio-frequency front-end by the crystal oscillator driving.Further, the correction sampling rate that calculates is write the sign indicating number NCO register 711 of hardware, waits for suitable opportunity and upgrade a yard NCO712.Upgraded sign indicating number NCO; Be equal to and revised the analog to digital converter sampling rate skew that reduces in the radio-frequency front-end that the crystal oscillator frequency deviation causes analog intermediate frequency is transformed into digital intermediate frequency; And then reduced the influence of sampling rate skew to code tracking loop, and do not have the sampling rate of direct modification radio-frequency front-end.Through such calibration, system reduces the requirement of crystal oscillator greatly.The precision equivalence of the cheap temperature compensating crystal oscillator (TXCO) of one embodiment of the present of invention 20PPM has improved 2 one magnitude.This scheme need not done any feedback and compensation to crystal oscillator simultaneously, has reduced the complexity and the cost of system, has improved reliability, and adaptability is strong, can be widely used for the improvement of existing system.Do not have mimic channel that crystal oscillator is fed back in real time in addition, guaranteed the frequency stability between twice calibration.
Although method and apparatus of the present invention is described with reference to gps satellite, should be appreciated that these principles are equally applicable to adopt the positioning system of the combination of pseudo-satelite (pseudolites) or satellite and pseudo-satelite.Pseudo-satelite is a kind of transmitter based on ground, and it is propagated and is modulated at L frequency range PN sign indicating number (similar with gps signal) on the ripple signal, and normally synchronous with gps time.Each transmitter can be endowed the PN sign indicating number of a uniqueness, thereby allows to be discerned by remote receiver.Pseudo-satelite is used under such situation, that is, and and from the gps signal of orbiter disappearance, like tunnel, mine, buildings or other closed area and obviously block.Here employed term " satellite " comprises the equivalence of pseudo-satelite or pseudo-satelite, and employed here term gps signal comprises the signal from the similar GPS of pseudo-satelite or pseudo-satelite equivalence.
In the discussion in front, the present invention describes with reference to american global positioning system (GPS).Yet, should be appreciated that these methods are equally applicable to similar global position system, like Muscovite GLONASS (Glonass) system, the Big Dipper 1 and the Big Dipper 2 systems of Galileo (Galileo) system in Europe and China.Employed term " GPS " also comprises some global position systems like this, like Muscovite GLONASS (Glonass) system, and the Big Dipper 1 and the Big Dipper 2 systems of Galileo (Galileo) system in Europe and China.Term " gps signal " comprises the signal from other global position systems.
In the preceding text, the method for the crystal oscillator cost that reduces the GPS reception has been described.Although the present invention describes with reference to specific embodiment, clearly, those of ordinary skill in the art under the situation of invention scope that non-migration claims are limited and spirit, can also do various modifications and change to these embodiment.Therefore, instructions and accompanying drawing are descriptive, rather than determinate.
The above; Be merely the embodiment among the present invention, but protection scope of the present invention is not limited thereto, anyly is familiar with this technological people in the technical scope that the present invention disclosed; The conversion that can expect easily or replacement all should be encompassed in of the present invention comprising within the scope.Therefore, protection scope of the present invention should be as the criterion with the protection domain of claims.
Claims (13)
1. a method that reduces GPS receiver crystal oscillator cost is characterized in that, in receiver Base-Band Processing part the crystal oscillator oscillation frequency is carried out soft alignment, and said method is specific as follows:
The Pseudo-Random Noise Code launch time of the corresponding GPS satellite of synchronization point is resolved in calculating, and with its storage;
Read stored previous and resolve the Pseudo-Random Noise Code launch time of the corresponding GPS satellite of synchronization point;
Calculate one and resolve the corresponding absolute time of synchronous signal cycle;
Calculate the corresponding absolute time of clock period that crystal oscillator drives, and then revise the crystal oscillator oscillation frequency;
Wherein, Revising the crystal oscillator oscillation frequency comprises: the absolute time that has obtained to resolve synchronous signal cycle; Known again and resolved the corresponding clock number of synchronous signal cycle, promptly can calculate the actual frequency of crystal oscillator, and then can calculate the actual sample rate of radio-frequency front-end by the crystal oscillator driving; Further, the correction sampling rate that calculates is write the sign indicating number NCO register of hardware, waits for suitable opportunity and upgrade a yard NCO.
2. the method for reduction GPS receiver crystal oscillator cost according to claim 1 is characterized in that, the hardware configuration of catching passage use carrier tracking loop and code tracking loop combination of the receiver Base-Band Processing part of said soft alignment method.
3. want the method for 2 described reduction GPS receiver crystal oscillator costs according to right, it is characterized in that said code tracking loop has comprised a yardage word control generator.
4. want the method for 3 described reduction GPS receiver crystal oscillator costs according to right; It is characterized in that; Said yardage word control generator has comprised a sampling rate register, realizes the change to yardage word control generator reference frequency through the value of revising said sampling rate register.
5. the method for reduction GPS receiver crystal oscillator cost according to claim 1 is characterized in that, the said synchronizing signal of resolving is produced by the synchronizing signal maker that resolves of hardware.
6. the method for reduction GPS receiver crystal oscillator cost according to claim 1 is characterized in that, resolve the synchronizing signal maker and be by crystal oscillator to drive, and to resolve the corresponding clock number that is driven by crystal oscillator of synchronous signal cycle is known.
7. the method that reduction GPS receiver crystal oscillator cost according to claim 1 is stated is characterized in that, the register that the said length of resolving synchronous signal cycle is resolved the synchronizing signal maker through modification changes.
8. the method for reduction GPS receiver crystal oscillator cost according to claim 1; Its characteristic also is; The said synchronous signal cycle that resolves to new calculating carries out fault-tolerant processing, if the synchronous signal cycle value of resolving that calculates surpasses threshold value then gives up, waits for next time and calculating.
9. the method for reduction GPS receiver crystal oscillator cost according to claim 1, its characteristic are that also said computation process is to resolve in the synchronous signal cycle at one to accomplish.
10. the method for reduction GPS receiver crystal oscillator cost according to claim 1 is characterized in that, said calculating GPS satellite Pseudo-Random Noise Code process launch time comprises:
Resolve the synchronizing signal rising edge and come temporarily, hardware latchs a yard NCO, sign indicating number counter, millisecond counter and bit counter;
Time-of-week information in the navigation message of demodulation GPS satellite;
Make up each time register and time-of-week information, calculate Pseudo-Random Noise Code launch time.
11. the method for reduction GPS receiver crystal oscillator cost according to claim 10, its characteristic are that also said calculating Pseudo-Random Noise Code need have at least a satellite to realize frame synchronization launch time.
12. the method for reduction GPS receiver crystal oscillator cost according to claim 10; Its characteristic also is; In said calculating Pseudo-Random Noise Code process launch time; When having accomplished frame synchronization, use a highest satellite of the relative receiver of the satellite elevation angle to calculate Pseudo-Random Noise Code launch time more than a satellite.
13. the method for reduction GPS receiver crystal oscillator cost according to claim 12 is characterized in that the affirmation of said frame synchronization need meet the following conditions simultaneously:
Find continuous three sub-frame synchronous codes;
Each subframe verification is passed through;
The frame number of each subframe is in 1～5 interval;
The time-of-week that adjacent sub-frame demodulates differs 300 bits.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2007101765975A CN101424734B (en) | 2007-10-31 | 2007-10-31 | Method for reducing crystal vibration cost of GPS receiver |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN2007101765975A CN101424734B (en) | 2007-10-31 | 2007-10-31 | Method for reducing crystal vibration cost of GPS receiver |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN101424734A CN101424734A (en) | 2009-05-06 |
| CN101424734B true CN101424734B (en) | 2012-01-04 |
Family
ID=40615462
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN2007101765975A Active CN101424734B (en) | 2007-10-31 | 2007-10-31 | Method for reducing crystal vibration cost of GPS receiver |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN101424734B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102393526A (en) * | 2011-08-17 | 2012-03-28 | 东莞市泰斗微电子科技有限公司 | Method for correcting crystal oscillator frequency of satellite navigation receiving device and corresponding device |
| EP2924468A1 (en) * | 2014-03-28 | 2015-09-30 | The European Community, represented by the European Commission | Method and apparatus for processing radionavigation signals for atmospheric monitoring |
| CN104113371A (en) * | 2014-07-23 | 2014-10-22 | 成都天奥信息科技有限公司 | Transmit type satellite monitoring simulating device and working and application method |
| EP3331292B1 (en) * | 2015-08-27 | 2021-12-29 | Huawei Technologies Co., Ltd. | Method and device for indicating synchronous signal period |
| CN106896384B (en) * | 2015-12-18 | 2019-06-28 | 大唐半导体设计有限公司 | A kind of device of frequency search and the method for realizing frequency search |
| CN111256691A (en) * | 2020-02-17 | 2020-06-09 | 苏州芯智谷智能科技有限公司 | Networking hardware time reference establishing method based on GNSS/MEMS inertia combined chip |
| CN111586454B (en) * | 2020-05-21 | 2022-04-01 | 上海大因多媒体技术有限公司 | Large screen splicing synchronization method and system |
| CN114428473A (en) * | 2021-12-17 | 2022-05-03 | 北京无线电计量测试研究所 | Special servo control chip SIP system, test device and method for chip atomic clock |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5594453A (en) * | 1994-11-01 | 1997-01-14 | Trimble Navigation, Ltd | GPS receiver having a rapid acquisition of GPS satellite signals |
| CN1439897A (en) * | 2002-02-19 | 2003-09-03 | 伊莱德公司 | Software compensating crystal oscillator |
| CN1649287A (en) * | 2005-03-18 | 2005-08-03 | 北京北方烽火科技有限公司 | Digital phase-lock method for clock signal in radio-frequency Layuan module |
-
2007
- 2007-10-31 CN CN2007101765975A patent/CN101424734B/en active Active
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5594453A (en) * | 1994-11-01 | 1997-01-14 | Trimble Navigation, Ltd | GPS receiver having a rapid acquisition of GPS satellite signals |
| CN1439897A (en) * | 2002-02-19 | 2003-09-03 | 伊莱德公司 | Software compensating crystal oscillator |
| CN1649287A (en) * | 2005-03-18 | 2005-08-03 | 北京北方烽火科技有限公司 | Digital phase-lock method for clock signal in radio-frequency Layuan module |
Non-Patent Citations (2)
| Title |
|---|
| 寇艳红等.GPS接收机中晶振误差的模拟方法.《电子与信息学报》.2004,第26卷(第8期),1319-1323. * |
| 郭芳.用GPS秒信号锁定高频振荡器的方法研究.《时间频率学报》.2004,第27卷(第2期),94-101. * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN101424734A (en) | 2009-05-06 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN101424734B (en) | Method for reducing crystal vibration cost of GPS receiver | |
| CN101430372B (en) | Low-cost time service and synchronization method and equipment for global positioning system receiver | |
| CN100397094C (en) | Time determination in satellite positioning system receivers and methods therefor | |
| CN102272625B (en) | Local clock frequency calibration using low earth orbit (leo) satellites | |
| US6191731B1 (en) | GPS receiver having a fast time to first fix | |
| KR101000984B1 (en) | Method and apparatus for validating a position in a satellite positioning system using range-rate measurements | |
| CN101118281B (en) | Process for self-correcting local crystal oscillator frequency with GPS receiving machine | |
| US6614395B2 (en) | Self-calibrating electronic distance measurement instrument | |
| US20070268180A1 (en) | Fast time to first fix by calibration of a real time clock | |
| CN101424733B (en) | Defectively positioning method under signal temporal deletion condition of global positioning system | |
| CA2437340A1 (en) | Satellite-based positioning system receiver for weak signal operation | |
| CA2506700A1 (en) | Satellite-based positioning system improvement | |
| WO2007086894A2 (en) | Combining measurements and determining clock offsets | |
| CN101963669A (en) | Method and apparatus for weak data frame sync in a positioning system | |
| US8970431B2 (en) | Method and apparatus for weak data bit sync in a positioning system | |
| US11709278B2 (en) | Method and system for signal detection including positioning signals | |
| CN101755223A (en) | The navigator fix of no timing information | |
| CN101446635B (en) | Super low-power-consumption low-cost GPS chip framework for mobile facility | |
| Lim et al. | L1/L2CS GPS receiver implementation with fast acquisition scheme | |
| JP2009098099A (en) | Positioning device for mobile body | |
| CN103983989A (en) | Digital non-integer tracking loop for satellite positioning and navigation receiving system | |
| US6393291B1 (en) | Method and apparatus for deriving a high rate output in a GPS system | |
| EP3748401A1 (en) | System and method for position determination of a stationary gnss receiver using a distributed time signal | |
| KR20030013405A (en) | Satellite-based positioning system receiver for weak signal operation | |
| Marques Filho et al. | Real time estimation of GPS receiver clock offset by the Kalman filter |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| C06 | Publication | ||
| PB01 | Publication | ||
| C10 | Entry into substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| C14 | Grant of patent or utility model | ||
| GR01 | Patent grant | ||
| TR01 | Transfer of patent right |
Effective date of registration: 20180214 Address after: 100086 Beijing city Huairou District Yanqi Yanqi Economic Development Zone South four Street No. 25 Building No. 3 hospital No. 307 Patentee after: Beijing Zhongke micro Intellectual Property Service Co., Ltd. Address before: 100029 Beijing city Chaoyang District Beitucheng West Road No. 3 Patentee before: Institute of Microelectronics, Chinese Academy of Sciences |
|
| TR01 | Transfer of patent right |