CN104702554B - Offset correction of carrier frequency method - Google Patents

Offset correction of carrier frequency method Download PDF

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Publication number
CN104702554B
CN104702554B CN201310661170.XA CN201310661170A CN104702554B CN 104702554 B CN104702554 B CN 104702554B CN 201310661170 A CN201310661170 A CN 201310661170A CN 104702554 B CN104702554 B CN 104702554B
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carrier frequency
value
oscillator
offset
bias estimation
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CN104702554A (en
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吴智湧
颜恺纬
张仲尧
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Realtek Semiconductor Corp
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Realtek Semiconductor Corp
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Abstract

The present invention proposes a kind of offset correction of carrier frequency method, and for correcting the carrier frequency shift of a receiver, the offset correction of carrier frequency method includes：Receive an at least Carrier frequency offset estimation value as caused by a digital carrier frequency bias estimation；A carrier frequency shift adjusted value is produced according to an at least Carrier frequency offset estimation value；And adjust an oscillator frequency of an oscillator of the receiver according to the carrier frequency shift adjusted value.

Description

Offset correction of carrier frequency method
Technical field
Disclosed herein embodiment be relevant to correction carrier frequency shift, espespecially one kind is applied in OFDM （Orthogonal Frequency Division Multiplexing,OFDM）The offset correction of carrier frequency side of receiver Method.
Background technology
In an OFDM communication system, such as the OFDM communication system 100 shown in Fig. 1, typically For, due to 102 and one receiving terminal of a transmitting terminal, 104 respective oscillator therein（It is not shown in the figures）Between there is frequency Difference, therefore a frequency mixer of receiving terminal 104（mixer）106 occur carrier frequency shift（Carrier Frequency Offset,CFO）The problem of；In addition, the analog-digital converter with regard to receiving terminal 104（Analog to Digital Converter,ADC）For 108, then sampling frequency deviation is had（Sample Cock Offset,SCO）The problem of.
Carrier frequency shift and sampling frequency deviation is destroy the main cause of system carrier orthogonality, in no correction or school In the case of positive deficiency, serious carrier-in-interference is often led to（Inter Carrier Interference,ICI）, therefore, such as The correction that carrier frequency shift is where carried out in OFDM receiver is actually crucial.Currently for the solution of above mentioned problem Mode is to utilize phase-locked loop（Phase Lock Loop,PLL）The correction of carrier frequency shift is completed to help, such as Fig. 2 institutes Show, its operation principles of phase-locked loop 200 are first with a phase detector（Phase Detector,PD）202 to find out one defeated Enter the phase difference between signal and a local clock pulse, further obtain a difference on the frequency, Yi Jijing via mathematical operation Cross loop filter 204 and then adjust a voltage-controlled oscillator according to the difference on the frequency（Voltage-Controlled Oscillator,VCO）206 output clock pulses and then the frequency for changing local oscillator, reach the school of carrier frequency shift Just or follow the trail of, however, implementation is generally carried out in phase-locked loop in an analog fashion, the difficulty not only designed is higher, and easily by process drift Influence, while expend more chip area.
In addition, the known known practice separately has the mode for only relying on digital signal processing to carry out implementor, specifically, It is not utilize analog circuit or radio circuit to correct, but merely by base band（Base band,BB）Digital circuit Make Carrier frequency offset estimation, and make the compensation of carrier frequency shift by way of signal processing, and then eliminate carrier-in-interference Influence.In general, except estimating with pilot tone signal (Pilot signal) in addition to compensation, can be based in the signal to carrier wave Frequency and sampling frequency are constantly followed the trail of（CFO tracking&SCO tracking）, allow and estimate or compensate not accurate enough The problem of caused influence minimize.However, though it is relatively simple to make the correction of carrier frequency shift using base-band digital circuit, It is likely that producing problems with, one is the DC terms wave filter after frequency mixer（DC Notch Filter）It is possible to meeting So that being influenceed thus to be filtered toward the close signal of direct current by carrier frequency shift, lead to not reduce.Secondly to work as When carrier frequency shift is more serious, it is possible to can be because leading code sign（preamble symbol）Detecting or decoding error, make The Carrier frequency offset estimation ability for obtaining digital circuit declines to a great extent.
Therefore, a kind of novel offset correction of carrier frequency mode is needed in this field badly, to reduce cost and fault rate.
The content of the invention
An object of the present invention is to provide a kind of apply in the carrier frequency shift school of OFDM receiver Correction method, it is above-mentioned to solve the problems, such as.
According to disclosed herein an embodiment, disclose a kind of offset correction of carrier frequency method, one connect for correcting The carrier frequency shift of receipts machine, the offset correction of carrier frequency method include：Receive by a digital carrier frequency bias estimation A caused at least Carrier frequency offset estimation value；A carrier frequency is produced according to an at least Carrier frequency offset estimation value Rate offsets adjusted value；And according to the carrier frequency shift adjusted value come adjust an oscillator of an oscillator of the receiver frequency Rate.
According to disclosed herein another embodiment, disclose a kind of machine-readable medium, a program code stored, when this When program code is performed by a processor, the program code can cause the step below the computing device to correct a reception The carrier frequency shift of machine：Receive an at least Carrier frequency offset estimation as caused by a digital carrier frequency bias estimation Value；A carrier frequency shift adjusted value is produced according to an at least Carrier frequency offset estimation value；And according to the carrier frequency Rate offsets adjusted value to adjust an oscillator frequency of an oscillator of the receiver.
Compared to known technology, proposed by the invention applies in the carrier frequency shift school of OFDM receiver Correction method, can significantly decrease the complexity of analog circuit, and strengthen the calibration capability of simple less digit correction method.
Brief description of the drawings
Fig. 1 is the schematic diagram of known OFDM communication system.
Fig. 2 is the schematic diagram of known phase-locked loop.
Fig. 3 is the flow chart of the embodiment of offset correction of carrier frequency method of the present invention.
Fig. 4 is showing for the embodiment for the machine-readable medium that the present invention is applied to offset correction of carrier frequency according to the present invention It is intended to.
Wherein, description of reference numerals is as follows：
100 OFDM communication systems
102 transmitting terminals
104 receiving terminals
106 frequency mixers
108 analog-digital converters
200 phase-locked loops
202 phase detectors
204 loop filters
206 voltage-controlled oscillators
S300~S320 steps
400 computer systems
402 processors
404 machine-readable mediums
Embodiment
Some vocabulary has been used among specification and following claims to censure specific component.Art Middle those of ordinary skill is, it is to be appreciated that manufacturer may call same component with different nouns.This specification and after Continuous claims are come not in a manner of the difference of title is used as and distinguishes component with the difference of component functionally Criterion as differentiation.It is an open use in the "comprising" of specification in the whole text and follow-up claim mentioned in Language, therefore " include but be not limited to " should be construed to.In addition, " coupling " one word is directly and indirectly electrically to connect comprising any herein Take over section.Therefore, if the first device of described in the text one is coupled to a second device, representing the first device directly can electrically connect The second device is connected to, or is electrically connected indirectly to the second device by other devices or connection means.
Digital carrier frequency calculations of offset circuit in receiver known in Main Basiss of the present invention is based on digital carrier frequency Carrier frequency offset estimation value caused by bias estimation, to produce carrier frequency shift adjusted value, wherein the digital carrier frequency Rate bias estimation can be the known general practice, for example, the digital carrier frequency bias estimation characteristic is not utilize simulation Circuit or radio circuit make to estimate, but merely by base band（Base band,BB）Digital circuit makees carrier frequency shift Estimation, its estimation principle can be defined by system specifications, or designer is realized using other algorithm.It is and of the invention It is characterised by that the carrier frequency shift adjusted value caused by the digital carrier frequency bias estimation is handled, goes forward side by side Signal after one step will treat is fed back to analog circuit to adjust the vibration of the source of the clock pulses signal of the front end of receiver Device frequency, rather than digital baseband circuit only in the rear end of receiver compensate.Describe in detail as follows.
Fig. 3 is refer to, Fig. 3 is according to carrier frequency shift of the present invention（Carrier Frequency Offset,CFO）School The flow chart of one embodiment of correction method.Offset correction of carrier frequency method 3 can be applied to an OFDM （Orthogonal Frequency Division Multiplexing,OFDM）Receiver.Offset correction of carrier frequency method 3 To estimate according to a carrier frequency shift caused by the carrier frequency shift counting circuit in the OFDM receiver One control capacitance Crystal_cap of evaluation CFO_est and the oscillator in OFDM receiver list A frequency offset △ corresponding to the capacitance of positionFWith a frequency shift (FS) direction, to calculate a carrier frequency shift adjusted value CFO （That is an electric capacity adjustment amount △ of the oscillatorcap）.In step s 302, in order to reduce excessive adjustment and exclude extreme Situation, the extremum in Carrier frequency offset estimation value CFO_est all within a specific time period T can be excluded, and to surplus Under Carrier frequency offset estimation value CFO_est be averaged.For example, can be by carrier frequency all within a specific time period T Maximum and minimum value in bias estimation value CFO_est are excluded, and remaining Carrier frequency offset estimation value CFO_est is entered Row is average, removes extremum mean carrier frequency bias estimation value CFO_ave_without_maxmin to obtain one, and will go to pole End value mean carrier frequency bias estimation value CFO_ave_without_maxmin is as the mean carrier within specific time period T Frequency offset estimate f CFO_ave.It should be noted that because the direction of skew may be fast or partially slow, therefore average carry Frequency offset estimate CFO_ave be probably on the occasion of or negative value.
Next, in step s 304, the mean carrier frequency bias estimation value after taking absolute value can be judged | CFO_ave| Whether a critical value Φ is less thanCFOAnd one flag blsFreeze whether be equal to it is correct（True）, if so, being then directly entered step S320；If it is not, it can then enter step S306 and calculate an electric capacity adjustment amount △cap=ceil ((| CFO_ave|- ΦCFO)/△ F), wherein ceil ((| CFO_ave|- ΦCFO)/△F) be to (| CFO_ave|- ΦCFO)/△FUnimpeded access is carried out to integer Computing.Next in step S308, △ can be judgedcapWhether it is less than or equal to 0, if so, then entering in step S310, and sentences Determine critical value ΦCFOFor one first critical value TmaxAnd flag blsFreeze is set to True；If step S308 judges △capNot Less than or equal to 0, then into step S312.
In step S312, it can judge whether mean carrier frequency bias estimation value CFO_ave is more than or equal to 0, if so, then Into step S314, and set the control capacitance Crystal_cap of the oscillator in the OFDM receiver= Crystal_cap+△cap, step S318 is directly entered afterwards.If otherwise judge that CFO_ave more than or equal to 0, then can not enter Enter step S316, and set the control capacitance Crystal_cap of the oscillator in the OFDM receiver= Crystal_cap-△cap, step S318 is likewise entered afterwards.In step S318, critical value Φ is judgedCFOIt is critical for one second Value TminAnd flag blsFreeze is set to mistake（False）.
Mean carrier frequency bias estimation value after taking absolute value | CFO_ave| exceeds the first critical value TmaxAfterwards, just Continue to update the carrier frequency shift adjusted value according to mean carrier frequency bias estimation value caused by follow-up specific time period, To correct the oscillator of the OFDM receiver, reached until follow-up mean carrier frequency bias estimation value is reduced to To the second critical value TminUntill.That is, compared herein using sluggish（hysteresis comparison）Principle exclude to put down Equal Carrier frequency offset estimation value CFO_ave is within the scope of one（Second critical value TminWith the first critical value TmaxBetween）'s Unstability.
In addition, also some particular steps in visual changes in demand Fig. 3 offset correction of carrier frequency method 3.For example, It can separately judge what specific time period T1 mean carrier frequency bias estimation value CFO_ave and previous specific time period T-1 were calculated Gap △ between mean carrier frequency bias estimation value CFO_ave-1CFO_aveWhether a critical values of anomalies is exceeded.That is, it is if flat Equal Carrier frequency offset estimation value CFO_ave occurs very big suddenly compared to mean carrier frequency bias estimation value CFO_ave-1 Change, then this mean carrier frequency bias estimation value CFO_ave is accidental exceptional value, it may be possible to which noise is some abnormal Situation caused by, therefore, this exceptional value is not just employed to produce electric capacity adjustment amount △cap, to avoid the adjustment of mistake from moving Make.If also, for example, △CFO_aveMore than a critical value ΦCFO_dif, then specific time period T1 offset correction of carrier frequency is terminated；So And if this situation continuously occurs, for example, the mean carrier frequency bias estimation that previous specific time period T-1 is calculated Difference between the mean carrier frequency bias estimation value CFO_ave-2 that value CFO_ave-1 and preceding two specific time periods T-2 are calculated Away from △CFO_ave-1More than critical value ΦCFO_dif, and △CFO_aveAlso greater than a critical value ΦCFO_dif, then may this be more violent Change the exception of non-category burst, but need the carrier frequency shift being adjusted, should be regarded as normal mean carrier frequency skew Estimate CFO_ave, and be employed to produce electric capacity adjustment amount △capIt is adjusted with the oscillator to the receiving terminal.
Referring to Fig. 4, Fig. 4 is the machine-readable medium that the present invention is applied to offset correction of carrier frequency according to the present invention The schematic diagram of one embodiment.Computer system 400 includes a processor 402 and a machine-readable medium 404, for example, meter Calculation machine system 400 can be a personal computer, and machine-readable medium 404 can any in personal computer have data The storage device of memory function, such as volatile memory, non-voltile memory, hard disk, CD.In the present embodiment, machine can Read to store a program code PROG in media 304, when program code PROG is loaded and performed by processor 402, program generation Code PROG can make processor 402 be directed at least Carrier frequency offset estimation value received from a digital carrier frequency bias estimation Producing a carrier frequency shift adjusted value, and a vibration of the receiver is adjusted according to the carrier frequency shift adjusted value One oscillator frequency of device, that is, perform the disclosed offset correction of carrier frequency method (step i.e. shown in Fig. 3 S300~S324).Because those skilled in the art with reference to the foregoing content for Time Series Analysis Method should be appreciated that processor 402 The Time-Series analysis operation that configuration processor code PROG is carried out, therefore further description is omitted herein.
The offset correction of carrier frequency method applied in OFDM receiver proposed by the invention, can be with base band Digital circuit is realized, also can be realized using software or firmware, and the result calculated is passed through into write-in to base-band digital The buffer of circuit, or analog circuit is directly fed back to control the frequency of oscillator, to reach correction carrier frequency shift Purpose.Compared to known technology, the complexity of analog circuit can be significantly decreased, and strengthens simple less digit correction method Calibration capability.
Presently preferred embodiments of the present invention is the foregoing is only, all equivalent changes done according to claims of the present invention are with repairing Decorations, it should all belong to the covering scope of the present invention.

Claims (7)

  1. A kind of 1. offset correction of carrier frequency method, for correcting the carrier frequency shift of a receiver, the carrier frequency shift Bearing calibration includes：
    Receive an at least Carrier frequency offset estimation value as caused by a digital carrier frequency bias estimation；
    A carrier frequency shift adjusted value is produced according to an at least Carrier frequency offset estimation value；And
    An oscillator frequency of an oscillator of the receiver is adjusted according to the carrier frequency shift adjusted value；
    The step of wherein according to the carrier frequency shift adjusted value to adjust the oscillator frequency of the oscillator of the receiver Carried out by one of following three kinds of modes：
    First way：According to an at least Carrier frequency offset estimation value and the unit of a control capacitance of the oscillator A frequency offset and a frequency shift (FS) direction corresponding to capacitance, to calculate the carrier frequency shift adjusted value；
    The second way：According to the digital carrier frequency bias estimation within a specific time period caused multiple carrier frequencies Bias estimation value calculates a mean carrier frequency bias estimation value；Judge whether the mean carrier frequency bias estimation value exceeds One critical value；And when the mean carrier frequency bias estimation value exceeds the critical value, then offset according to the mean carrier frequency Estimate produces the carrier frequency shift adjusted value；And
    The third mode：According to the digital carrier frequency bias estimation in a current period and each period in multiple preceding periods Within caused multiple Carrier frequency offset estimation values calculate the mean carrier frequency bias estimation value of the period, with Distinguish corresponding multiple mean carrier frequency bias estimation values with those preceding periods to the current period；When judging that this is current Whether the difference between mean carrier frequency bias estimation value in section and those preceding periods corresponding to wantonly two continuous time Beyond a critical value；And if the current period and continuous multiple differences corresponding to those preceding periods are critical beyond this It is worth or without departing from the critical value, then produces the carrier frequency according to the mean carrier frequency bias estimation value of the current period Offset adjusted value.
  2. 2. offset correction of carrier frequency method according to claim 1, the wherein receiver are an OFDM receiver.
  3. 3. offset correction of carrier frequency method according to claim 1, when adjusting this according to the carrier frequency shift adjusted value When the step of oscillator frequency of the oscillator of receiver is carried out by the first way, wherein according to the carrier frequency Skew adjusted value includes to adjust the step of the oscillator frequency of the oscillator of the receiver：
    The control capacitance of the oscillator is adjusted according to the carrier frequency shift adjusted value.
  4. 4. offset correction of carrier frequency method according to claim 3, wherein being adjusted according to the carrier frequency shift adjusted value The step of control capacitance of the oscillator, includes：
    According to the digital carrier frequency bias estimation within a specific time period caused multiple Carrier frequency offset estimation values To calculate a mean carrier frequency bias estimation value；
    Judge the mean carrier frequency bias estimation value absolute value whether be less than a threshold value and one judgement flag bit whether To allow；
    When the absolute value of the mean carrier frequency bias estimation value is not allow not less than the threshold value or the judgement flag bit, An electric capacity adjustment amount of the control capacitance is calculated according to following formula：
    △cap=ceil ((| CFO_ave |-ΦCFO)/△F)
    Wherein △capFor the electric capacity adjustment amount, CFO_ave is the mean carrier frequency bias estimation value, ΦCFOFor the threshold value, △FFor the frequency offset；
    The control capacitance is adjusted according to the electric capacity adjustment amount.
  5. 5. offset correction of carrier frequency method according to claim 4, wherein adjusting the control electric capacity according to the electric capacity adjustment amount The step of value, includes：
    Judge whether the electric capacity adjustment amount is less than or equal to zero；
    When the electric capacity adjustment amount is more than zero and the mean carrier frequency bias estimation value is more than or equal to zero, the control electric capacity Value increases the electric capacity adjustment amount；
    When the electric capacity adjustment amount is more than zero and the mean carrier frequency bias estimation value is less than zero, the control capacitance is reduced The electric capacity adjustment amount.
  6. 6. offset correction of carrier frequency method according to claim 1, when adjusting this according to the carrier frequency shift adjusted value When the step of oscillator frequency of the oscillator of receiver is carried out by the second way, wherein judging the carrier frequency The step of whether bias estimation value exceeds the critical value has additionally comprised：
    After the mean carrier frequency bias estimation value exceeds the critical value, continue to put down according to caused by follow-up specific time period Equal Carrier frequency offset estimation value updates the carrier frequency shift adjusted value, until averagely being carried caused by follow-up specific time period Frequency offset estimate is reduced to untill reaching another critical value.
  7. 7. offset correction of carrier frequency method according to claim 1, when adjusting this according to the carrier frequency shift adjusted value When the step of oscillator frequency of the oscillator of receiver is carried out by the second way, wherein according to the digital carrier Frequency offset estimation within the specific time period caused by those Carrier frequency offset estimation values come calculate the mean carrier frequency The step of rate bias estimation value, includes：
    Select from those Carrier frequency offset estimation values the Carrier frequency offset estimation value of a part, the wherein part Carrier frequency offset estimation value does not include a maximum of those Carrier frequency offset estimation values and at least one of a minimum value； And
    The Carrier frequency offset estimation value a part of according to this calculates the mean carrier frequency bias estimation value.
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CN109120568B (en) 2018-08-31 2020-04-03 北京邮电大学 Clustering-based frequency offset determining and eliminating method and device and electronic equipment

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