CN102355633A - Clock calibration method based on FM (Frequency Modulation) radio data system - Google Patents
Clock calibration method based on FM (Frequency Modulation) radio data system Download PDFInfo
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Abstract
The invention relates to a clock calibration method based on an FM (Frequency Modulation) radio data system, which belongs to the field of wireless telecommunication. Each node of a distributed network is in the coverage area of the same FM base station. The method comprises the following steps that: 1) an FM receiving chip is arranged on each node; 2) RDS (Radio Data System) radio data is sent to each node by the FM base station; 3) the FM receiving chip of each node receives and analyzes the RDS radio data in calibration so as to generate an RDS pulse signal; and 4) a local clock is calibrated by each node according to the frequency of the RDS pulse signal so as to realize the time synchronization of each node. The RDS pulse frequency is used as the intermediate frequency to calibrate the local clock of the nodes, reduce communication between the nodes, and save bandwidth and energy consumption, so clock deflection is eliminated, and the effect of clock calibration is achieved.
Description
Technical field
The present invention relates to a kind of clock correcting method, relate in particular to a kind of sensor network clock correcting method, belong to wireless communication field based on the FM radio data system based on the FM radio data system.
Background technology
Sensor network (Wireless Sensor Network; WSN) be a kind of typical distributed system; Each node all possesses certain calculating, storage and communication capacity in this network; But because the ability to work of individual node is lower, most sensor network is used all needs the node cooperation of a plurality of even the whole network could accomplish a certain task.In this case; Clock can be accomplished the prerequisite of cooperation synchronously often smoothly between node; For example monitor (AlbertoCerpa in the application in the animal life habit; JeremyElson; DeborahEstrin; LewisGirod; MichaelHamilton; AndJerryZhao.Habitatmonitoring:Applicationdriverforwirel esscommunicationstechnology.InProceedingsofthe2001ACMSIG COMMWorkshoponDataCommunicationsinLatinAmericaandtheCari bbean; April2001.) need depend on direction and the speed that animal positional information calculation animal that a plurality of nodes successively observe is moved; If the time of these nodes is inconsistent; The error of calculation of will pushing the speed, even can cause the erroneous judgement of the direction of motion.
Cause the main cause of internodal asynchronism(-nization) to derive from the crystal oscillator (Crystal Oscillator) that is used for timing on the node; Abbreviate crystal oscillator as; The crystal oscillator frequency of different nodes is deviation slightly; For example the clock drift of the crystal oscillator of the last equipment of typical sensor node platform Telosb is positive and negative 30 to 50ppm (ppm is part per million); That is to say; Two different crystal oscillators are under extreme case, and its clock frequency is only poor up to 100ppm, promptly differ 100us each second.In addition; For certain specific crystal oscillator; Its frequency drift is relevant with environmental factor; According to work (Christoph Lenzen; Philipp Sommer, Roger Wattenhofer, Optimal Clock Synchronization in Networks; Sensys 2009) result that records, its frequency drift of the crystal oscillator of 5MHz changes about 1ppm for per 5 degrees centigrade on the Mica2 node.For above-mentioned reasons, even the time of different nodes initially is being consistent, also can differ more and more far away as time passes.
The proposition of the clock synchronization protocol in the sensor network is just in the inconsistent problem that solves clock between node under this condition; According to the implementation of different clocks synchronous protocol, existing work can be divided into: message based time synchronized and based on the time synchronized of overall signal.The former is recorded in the time in clock source in the message, and the mode in sensor network inside through multi-hop is distributed to the synchronous node of needs with clock information, and its representative has RBS and FTSP; The latter is then by certain external global clock signal, and each node is according to global clock signal adjustment local zone time in the network, and its representative has the clock synchronization protocol based on GPS or power line.Often exist in the realization of above-mentioned two kinds of methods than big-difference; Usually do not rely on external condition in the former realization; The sensor network only operation between the dependency network interior nodes is accomplished whole synchronizing process, and the latter relies on outside source, so often equip special hardware on the node.
In the existing clock synchronization protocol, it is synchronous that message based clock synchronization protocol dependence control messages is accomplished global clock at the inundation of the whole network, the node energy that this process consumption is a large amount of, and take rare communication bandwidth.Thereby and can greatly reduce inter-node communication conserve bandwidth and energy consumption based on the clock synchronization of overall signal, therefore this method has caused researcher's extensive concern in recent years, but there is remarkable defective in existing protocol.For example, the GPS module need consume lot of energy, and can only not have out of doors under the environment of blocking and use; The clock signal that WWVB etc. broadcast on a large scale also only is applicable to the zone that outdoor signal intensity is high; Clock synchronization protocol based on power line can only cover power line zone on every side, therefore only is applicable to around indoor or the power transmission line.
Summary of the invention
To the deficiency of existing work, the present invention proposes a kind of distributed network clock correcting method based on the FM radio data system, and each node of said distributed network is in the coverage of same FM base station, and its step comprises:
1) the FM receiving chip is set on each node;
2) the RDS broadcast data is sent to each node in the FM base station;
3) the FM receiving chip of each node receives and resolves the RDS broadcast data when calibration, generates the RDS pulse signal;
4) each node is realized the time synchronized of each node according to RDS pulse signal frequency calibration local clock.
Each node of described method is calibrated local clock according to the skewed clock α of the local clock frequency of RDS pulse signal frequency and this node.
Each node of described clock correcting method is periodically calibrated local clock.
Described clock correcting method each time the calibration process of local clock comprise calibration constantly with calibration cycle two parts, the said calibration moment is to certain RDS hardware interrupts that should node; The receiving chip of the FM receiving terminal of this node is in resting state in calibration cycle.
When described clock correcting method is calibrated in startup first, set clock deflection α
0Initial value, skewed clock α
0Be the ratio of RDS clock frequency and this node crystal oscillator rated frequency, sleep cycle is T first
0
Further, when the i time this node local clock of calibration,, be calculated as follows the skewed clock α that calibrates for this i time
1:
x
i=c
n(i)-c
n(i-1), c
n(i) be the present node clock periodicity, start node periodicity c is set
n(0)=0i-1 is a preceding periodicity;
α
I-1Be previous skewed clock, FM chip dormancy time was T after calculating was accomplished.
Skewed clock when initial is an estimated value, T
0Be selected from 10～30 seconds; T sets according to required precision, and T is selected from 10～60 minutes.
Described distributed network system (DNS) is a sensor network, and each node is a sensor network nodes, can form network through wireless communication interface between each node.
The present invention is primarily aimed at this process of Frequency Synchronization, based on the FM radio data system RDS pulse is calibrated the node local clock as intermediate frequency, reduces inter-node communication, conserve bandwidth and energy consumption, thus eliminate different internodal skewed clocks.
The FM radio data system
Traditional FM broadcasting only comprises analog audio information, and for more subsidiary digital informations in transmission of audio, industrial quarters has been formulated radio data system (Radio Data System) agreement, is called for short RDS.Subsidiary a spot of digital information when the RDS agreement is supported in broadcast audio information, like FM base station title, broadcast program introduction etc., initial RDS standard was formulated in 1984, supported these agreements by the end of having a large amount of base stations so far.
In RDS broadcasting, digital information is with continuous bit stream form broadcasting, and the form of satisfied regulation.According to the RDS standard, the least unit of bit stream is called RDS piece (Block), and a RDS piece comprises 26 Bit datas, and per 4 RDS pieces are formed a RDS group (Group).Because each RDS piece is big or small identical; Therefore FM receiving terminal (promptly supporting the broadcast receiver chip of a RDS decoding) RDS piece of every decoding required time is identical; This time is about 21.894 milliseconds; It (is hardware interrupts that RDS piece of the every decoding of FM receiving terminal generally then produces a pulse signal; Be used to read the RDS block message); So when the FM receiving terminal continues decoding RDS piece, just can produce periodic pulse signal, as shown in Figure 1.Distributed network model and clock synchronization process
The distributed network model that the present invention was suitable for as shown in Figure 2.Comprise a plurality of network nodes in the network, each node has local clock, and this clock carries crystal oscillator by plate usually and produces, and the local clock frequency on for example existing Telosb platform and the Mica2 platform is respectively 32.768KHz and 5MHz.Can form network through short-range wireless communications interfaces between node, among Fig. 2 between node link be illustrated by the broken lines.The FM base station can cover most city and neighboring area (comprising indoor and outdoors), next power consumption 100 of normal conditions, and the FM base station coverage distance of 000W reaches 150km, and high energy reaches about 240km under the situation that does not have interference signal.Therefore, the present invention supposes that all nodes all are in the coverage of same FM base station, puts aside that different nodes are in a plurality of base station ranges.In fact, the network size of current application is often less than the coverage (radius 150～240km) of a base station.
Existing clock synchronizing method (like RBS or FTSP) is divided into two parts with the clock synchronization process: to the time with synchronously.So-called to the time be exactly sometime, make the local zone time of each node reach instantaneous unanimity, promptly eliminate instantaneous time deviation; And be the frequency unanimity that keeps the local zone time of each node synchronously.In sensor network, message based time synchronization protocol mainly pay close attention to the time process, the raising time to the time precision.For example, among the FTSP author propose operation RBS reaches on the Mica platform single step to the time mean accuracy be 29.1 delicate, and operation FTSP only is 1.48 delicate.The target of synchronizing process is to make the nodal clock frequency consistent, can introduce the notion of skewed clock for this reason, if the clock frequency of two nodes is respectively f
AAnd f
B, then the skewed clock between them does
This shows that if the frequency of two clocks is consistent, skewed clock is 1 so.Clock frequency is extremely important in practical application synchronously between node, even it is consistent to reach the node initial time of Frequency Synchronization, differing as time passes also can be increasing.
Clock correcting method based on the FM radio data system
The target of clock alignment is under different nodal clock physical frequencies condition of different, to make their logical frequency consistent.Wherein the logical timer frequency is meant physical frequencies is carried out the result that certain conversion obtains, two node A and B for example, and their phy clock frequency is respectively f
A=10MHz and f
B=5MHz is so with f
AObtain a logical timer identical divided by 2 with the B clock frequency.In distributed network, the clock frequency of different nodes is different, but does not know the relation between the frequency each other between them, therefore need utilize a kind of intermediate frequency to carry out transition.A and Node B is still an example, if there is a signal of intermediate frequency of 2MHz C, then A and B are frequency frequency frequency clock skew and C 5 and 2.5, respectively, then let
and
you get the same frequency as two logical clock.It should be noted that this calibration just provides a kind of approach for different nodal clock conversions, can't cause the decline of clock accuracy.With the event detection is example, supposes that still the start-up time of node A and B is consistent, starts 1 second of back constantly if incident occurs in so, and node A and the B node time that detects incident is respectively 10 * 10 so
6With 5 * 10
6, time precision still with the frequency dependence of node hardware clock, and the logical timer of two nodes is 2 * 10 can get outgoing event and take place through calibration the time
6Thereby A and B are judged as same incident with testing result.
Basic ideas of the present invention are that the recurrent pulses (as shown in Figure 1) that will be produced by RDS are regarded a kind of external clock signal as, are called RDS clock note and make cr, calibrate nodal clock with the RDS clock as a kind of middle transition.If the local clock of each node can both be identical with RDS clock speed in the network, then be equivalent to and eliminate internodal skewed clock.For example its frequency of the crystal oscillator of 32.768KHz is 32.768KHz and cycle to be the inverse 1/32768 second of frequency.Describe the periodic calibration method that the present invention proposes below in detail.
As shown in Figure 3, dash area is represented calibration and blank parts is represented calibration cycle, corresponding certain RDS hardware interrupts of the moment of each calibration among the figure.The FM receiving chip is in resting state in calibration cycle, thereby can save a large amount of energy consumptions; In calibration constantly, the FM receiving chip starts back reception signal and produces pulse signal (as shown in Figure 1).In order to describe this calibration process in detail, we isolate one of them elementary cell, promptly by the i-1 time calibration back to the i time calibration completion this section period, all the other processes can and the like.It should be noted that node calibration can be regarded as accomplishes in a flash, so calibration elapsed time not itself.Suppose to be respectively c at the nodal clock of the i-1 time and the i time calibration
n(i-1) and c
n(i), then make x
i=c
n(i)-c
n(i-1), its physical significance is illustrated in the periodicity of the i time calibration cycle interior nodes clock experience.Similarly, make n
i=c
r(i)-c
r(i-1), promptly be illustrated in the periodicity of the i time interior RDS clock experience of calibration cycle.Definition RDS clock and nodal clock deflection are α=f
r/ f
n, f wherein
rAnd f
nThe frequency of representing RDS clock and nodal clock respectively, so α representes the skewed clock of two clocks.According to these definition, can draw that the relation between the RDS clock and nodal clock is between calibrating for the i-1 time to the i time:
n
i=α
iX
i+ Δ
i(formula 1)
Because skewed clock changes in time, it is constant in a period of time that hypothesis is somebody's turn to do value when handling, so α in this formula
iBe illustrated in the skewed clock in the calibration cycle the i time.Δ
iThe noise that expression is introduced owing to the error on calculating or measuring, this noise satisfies Δ usually
i＜＜x
iTherefore in calculating, can ignore.So can be similar to by following formula and calculate skewed clock:
In the top formula, x
iCan on node, record, and owing to FM chip in calibration cycle is in resting state n
iCan't directly record, need estimate.The method of estimation is to utilize the skewed clock α that last one-period calculates
I-1, according to n
i≈ α
i-1x
iSo, because all corresponding RDS hardware interrupts n of the moment of each calibration
iBe integer, so n
iCan obtain through round, promptly
At known x
iAnd n
iSituation under, can calculate current skewed clock value α through formula (2)
iDefinition according to skewed clock can know, alpha reaction the ratio of RDS pulse frequency and nodal clock frequency, for the node of same network shown in Figure 2, because they receive same FM base station signal, so their RDS pulse frequency is identical.Can know the distributed calibration that to accomplish nodal clock through the RDS pulse as intermediate frequency according to the front discussion; In whole calibration process, need not carry out any communication between node; Therefore can not cause communication bandwidth and energy consumption; Reach the minimizing inter-node communication, the effect of conserve bandwidth and energy consumption.The operation principle of an elementary cell more than has been described, and whole calibration process is periodically to carry out, its reason is that the frequency of nodal clock is time dependent, therefore need calibrate repeatedly.
Description of drawings
Fig. 1 is a cyclic pulse signal sketch map of the present invention;
Fig. 2 is a network model sketch map of the present invention;
Fig. 3 is a periodically trimming process sketch map of the present invention;
Fig. 4 is clock alignment circulation process figure of the present invention.
Embodiment
Like Fig. 4, α when initial
0Estimated value under the desirable line, the theoretical value that generally can get skewed clock, the i.e. ratio of RDS clock frequency and crystal oscillator rated frequency.In addition, when system start-up, set start node time c
n(0)=0, the calibration steps of node is following so:
Step 1: node starts, and to set the start node clock be 0, sets initial skewed clock α
0Be theoretical value, sleep cycle is T
α(being represented by nodal clock) is with the dormancy of posterior nodal point FM chip;
Step 2: when nodal clock arrives dormancy time T first
0The time, the FM chip enable receives signal and produces the RDS pulse, is producing the moment record present node clock c of RDS pulse
n(i), the prediction node is at calibration RDS clock c constantly
r(i), calculate current skewed clock by front formula (2), shown in formula (3), FM chip dormancy time T after calculating is accomplished;
Step 3: when the time be in the calibration cycle (i * T, (i+1) * t] time, make that instantaneous nodal clock is t, so Dui Ying RDS clock is estimated as c
r(i)+α
i[t-c
n(i)], promptly estimated, utilize this estimated value can judge the time of the same incident that different nodes observe by current nodal clock with in the skewed clock value that last one-period calculates.After noticing this relation, if a plurality of node is all calibrated according to above-mentioned steps, because the RDS clock of arbitrary node maintenance is all approximate approaching with the speed of RDS pulse, the speed of so internodal RDS clock also is approximate approaching.For example, the RDS clock of node A and Node B maintenance is remembered work respectively
With
The RDS clock that both safeguard at a certain absolute moment t is respectively so
With
Order is c in the actual value of t moment RDS clock
r(t), order so
So
With
Between difference will be less than e
a+ e
b, according to the description of front can know because
With
All with c
rSo approximate e
a+ e
bAlso less.
The time of indication is all represented nodal clock in above-mentioned three steps, because the FM chip can't obtain the exact value of RDS clock when being in resting state.Therefore, in step 3, need estimate current RDS clock time according to the calculated value that step 2 obtains.Through this calibration process; The RDS clock of safeguarding on the node (through the calculating in the step 2 and the estimation in the step 3) keeps a kind of approximate corresponding relation with actual RDS pulse; Difference between the two is 0 in calibration constantly; And in calibration cycle, change in time and change; But, can not accumulate so can guarantee difference because calibration is periodic.Because the skewed clock when initial is an estimated value, so T
0Usually less (10～30 seconds) are excessive to prevent calibration error, and T can set (being generally 10～60 minutes) according to the requirement of precision, and the more little then precision of T is high more and energy consumption is big more.
Claims (10)
1. distributed network clock correcting method based on the FM radio data system, each node of said distributed network is in the coverage of same FM base station, and its step comprises:
1) the FM receiving chip is set on each node;
2) the RDS broadcast data is sent to each node in the FM base station;
3) the FM receiving chip of each node receives and resolves the RDS broadcast data when starting, and generates the RDS pulse signal;
4) each node is realized the time synchronized of each node according to RDS pulse signal frequency calibration local clock.
2. the method for claim 1 is characterized in that, each node is calibrated local clock according to the skewed clock α of the clock frequency of RDS pulse signal frequency and this node.
3. method as claimed in claim 1 or 2 is characterized in that each node is periodically calibrated local clock.
4. method as claimed in claim 3 is characterized in that, each time the calibration process of local clock comprise calibration constantly with calibration cycle two parts, the said calibration moment is to RDS hardware interrupts that should node; The receiving chip of the FM receiving terminal of this node is in resting state in calibration cycle.
5. method as claimed in claim 4 is characterized in that, first alignment settings skewed clock α
0Be the ratio of RDS clock frequency and this node crystal oscillator rated frequency, dormancy period is T first
0
6. method as claimed in claim 5 is characterized in that, when the i time this node local clock of calibration, is calculated as follows the skewed clock α of this i time calibration
i:
x
i=c
n(i)-c
n(i-1), c
n(i) be the present node clock periodicity, start node periodicity c
n(0)=0, i-1 is a preceding periodicity;
α
I-1Be previous skewed clock, the dormancy period of FM chip was T after calculating was accomplished.
7. method as claimed in claim 5 is characterized in that T
0Be selected from l0～30 second; T sets according to required precision.
8. method as claimed in claim 6 is characterized in that T is selected from 10～60 minutes.
9. the method for claim 1 is characterized in that, said distributed network system (DNS) is a sensor network, and each node is a sensor network nodes.
10. method as claimed in claim 9 is characterized in that, can form network through wireless communication interface between said each node.
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103298099A (en) * | 2012-03-04 | 2013-09-11 | 山东大学威海分校 | Time synchronizing method based on bimodal clock frequency estimation |
| CN104581928A (en) * | 2015-01-12 | 2015-04-29 | 浙江大学 | Time synchronization signal processing method based on FM broadcast signals |
| WO2017016321A1 (en) * | 2015-07-27 | 2017-02-02 | 深圳思凯微电子有限公司 | Digital frequency modulation broadcast based clock synchronization method and frequency modulation broadcast receiver |
| WO2019024064A1 (en) * | 2017-08-04 | 2019-02-07 | 深圳市汇顶科技股份有限公司 | Timing method, clock device and terminal device |
| CN114629582A (en) * | 2020-12-10 | 2022-06-14 | 深圳绿米联创科技有限公司 | Method, device and equipment for automatically calibrating local time of intelligent equipment and storage medium |
-
2011
- 2011-10-11 CN CN2011103070074A patent/CN102355633A/en active Pending
Non-Patent Citations (1)
| Title |
|---|
| LIQUN LI ET.AL: "Exploiting FM Radio Data System for Adaptive Clock Calibration in Sensor Networks", 《MOBISYS"11 》 * |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103298099A (en) * | 2012-03-04 | 2013-09-11 | 山东大学威海分校 | Time synchronizing method based on bimodal clock frequency estimation |
| CN104581928A (en) * | 2015-01-12 | 2015-04-29 | 浙江大学 | Time synchronization signal processing method based on FM broadcast signals |
| CN104581928B (en) * | 2015-01-12 | 2018-04-20 | 浙江大学 | A kind of method of the time synchronizing signal processing based on FM fm broadcast signals |
| WO2017016321A1 (en) * | 2015-07-27 | 2017-02-02 | 深圳思凯微电子有限公司 | Digital frequency modulation broadcast based clock synchronization method and frequency modulation broadcast receiver |
| WO2019024064A1 (en) * | 2017-08-04 | 2019-02-07 | 深圳市汇顶科技股份有限公司 | Timing method, clock device and terminal device |
| US10498524B2 (en) | 2017-08-04 | 2019-12-03 | Shenzhen GOODIX Technology Co., Ltd. | Timing method, clock device and terminal device |
| CN114629582A (en) * | 2020-12-10 | 2022-06-14 | 深圳绿米联创科技有限公司 | Method, device and equipment for automatically calibrating local time of intelligent equipment and storage medium |
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Application publication date: 20120215 |