CN104702558B - The phase noise elimination method of ofdm system - Google Patents
The phase noise elimination method of ofdm system Download PDFInfo
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- CN104702558B CN104702558B CN201310652815.3A CN201310652815A CN104702558B CN 104702558 B CN104702558 B CN 104702558B CN 201310652815 A CN201310652815 A CN 201310652815A CN 104702558 B CN104702558 B CN 104702558B
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Abstract
Present invention is disclosed a kind of removing method of ofdm system phase noise, and it is directed to a kind of ofdm system for having used specific APSK constellation mapping.The phase noise elimination method of the present invention estimates the common phase error CPE of ofdm system first, obtains CPE model, further eliminates CPE, obtain correcting each sub-carrier after CPE, in conjunction with the noise power of each subcarrier, phase noise coefficient F is calculated, finally eliminates phase noise.Technical scheme is employed, the characteristics of being mapped using specific APSK constellation, accurately, stably realizes the estimation and elimination to phase noise.
Description
Technical field
The present invention relates to a kind of demodulation method, more specifically to a kind of phase based on the mapping of specific APSK constellation point
Position noise cancellation method.
Background technology
OFDM technology is one kind of multi-carrier modulation.It is widely used in Modern Communication System.And phase is made an uproar
Sound can affect greatly to the receptivity of ofdm system.Phase noise is generally made by the various analog devices such as Up/Down Conversion
Into.Phase noise can cause the rotation of each sub-carrier phase, will also result in inter-sub-carrier interference.Therefore, phase noise and son
Inter-carrier interference, which is that demodulating system is required, to be solved the problems, such as, otherwise phase noise causes inter-sub-carrier interference, and between subcarrier
The orthogonality that can be destroyed between subcarrier is disturbed, so as to influence receptivity.
APSK is a kind of constellation mapping mode, and recently a kind of specific APSK is used to obtain shaping gain, so as to
Receptivity can be improved, still, the APSK constellation applied to ofdm system maps the problem of equally existing inter-sub-carrier interference.
The content of the invention
The purpose of the present invention aims to provide a kind of phase noise elimination method of ofdm system, to solve in the prior art
There is phase noise in ofdm system, the problem of influenceing receptivity.
According to above-mentioned purpose, implement the phase noise elimination method of the ofdm system of the present invention, include phase in receiving terminal
Noise estimating step, including：
Step 1, from the parameter H of ofdm systemi、YiAnd DiThe middle all or part of first specific numbers composition I of selectionB；
Wherein, DiRepresent determination point；HiAnd YiOne group of channel estimation in frequency domain vector H=that ofdm system receiver receives is represented respectively
[H0,H1..., HN-1]TWith frequency domain data vector Y=[Y0,Y1..., YN-1]TIn element, wherein N represent ofdm system son load
Ripple number；
Step 2, establish estimation equation group
Wherein, N'iRepresent the noise for setting up estimation equation group；FkRepresent phase noise coefficient F=[F-L, F-L+1...,
FL]TIn element, wherein L determine F length；
Step 3, calculate phase noise coefficient F.
Preferably, the first specific numbers meet following condition：
The frequency domain data vector X=[X of ofdm system transmitting0,X1..., XN-1]TA kind of middle member mapped using specific APSK
Plain XiSequence number, the specific APSK mappings include P × Q constellation point, and can use
To represent, whereinFor initial phase,
l0＜ l1＜ ... ＜ lP-1;
Amplitude is more than a predetermined threshold value T1DiSequence number；
Amplitude is less than a threshold value T2'sSequence number；Wherein, σi 2Represent one group of Frequency domain noise power estimate vector E=
[σ0 2, σ1 2..., σN-1 2]T.In element, wherein N represent ofdm system subcarrier number.
Preferably, determination point DiFor D (Yi/Hi)。
Preferably, determination point DiFor D (Y'i/Hi)；Wherein, Y'i=gCPEYiI=0,1 ..., N-1;gCPERepresent common phase
Error,A (x) and Φ (x) represents the amplitude and phase of plural number；From
Frequency domain data vector X=[X0,X1..., XN-1]TThe middle all or part of second specific numbers composition set I of selectionA, second is special
Determine serial number frequency domain data vector X=[X0,X1..., XN-1]TThe middle element X mapped using the APSKiSequence number.
Preferably, threshold value T2ForWherein α is systemic presupposition value.
Preferably, performed using phase noise coefficient F and eliminate interference step, output eliminates the frequency domain data after interference
Y'', wherein
Technical scheme is employed, the characteristics of being mapped using specific APSK constellation, accurately, is stably realized
Estimation and elimination to phase noise.
Brief description of the drawings
In the present invention, identical reference represents identical feature all the time, wherein：
Fig. 1 is the flow chart that the present invention eliminates phase noise elimination method；
Fig. 2 is the APSK mapping graphs that the present invention is directed to；
Fig. 3 is the method flow diagram that phase noise is estimated in Fig. 1.
Embodiment
Technical scheme is further illustrated with reference to the accompanying drawings and examples.
The concept mentioned by the present invention is defined first, the present invention is applied to a kind of ofdm system, the ofdm system bag
Containing N number of subcarrier.Reference picture 1, input of the invention be one group of frequency domain data obtained by the receiver in the ofdm system to
Measure Y=[Y0,Y1..., YN-1]T, one group of channel estimation in frequency domain vector H=[H0,H1..., HN-1]TEstimate with one group of Frequency domain noise power
Count vectorial E=[σ0 2,σ1 2..., σN-1 2]T.Wherein, YiThe element in Y-direction amount is represented, corresponding to being f in frequency0+ i Δs f load
The data received on ripple, and Δ f is sub-carrier frequencies interval.Similarly, HiThe element in H vectors is represented, corresponding in frequency
Rate is foChannel coefficients on+i Δs f subcarrier, σi 2The element in E vectors is represented, corresponding to being f in frequencyo+ i Δs f
Noise power on carrier wave.
It could be theoretically argued that：
Wherein, X=[X0,X1..., XN-1]TIt is the frequency domain symbol that emitter is launched on the subcarrier that frequency is fo+i Δs f
Data vector, use XiRepresent the element in X vectors.NiFor noise, and F=[F-L, F-L+1..., FL]TFor phase noise coefficient,
Wherein FkRepresent the element in phase noise coefficient F vectors.L is the parameter that reception system realizes setting, to determine F's
Length, F length is 2L+1, if it is considered to L, which is 0, F, deteriorates to a scalar, that is, common phase error（CPE, common
phase error）.
The present invention is directed a kind of ofdm system with the mapping of specific APSK constellation, as shown in Fig. 2 the portion of X vectors
Divide or all employ a kind of specific APSK constellation mapping, this APSK constellation mapping meets following condition：The constellation point is reflected
Penetrating scheme includes P × Q constellation point, and available
l0＜ l1＜ ... ＜ lP-1To obtain all constellation points.Wherein, P represents the number of annulus on APSK constellation mapping graph, and Q represents every
The number put on individual annulus.
After above-mentioned APSK mappings are determined, all or part of second specific numbers composition set is selected from X vectors
IA, form set IAThe second specific numbers be X vectors in using above-mentioned APSK mapping element.For example, it is assumed that IA=1,3,
4 ... }, the element X in X vectors is represented1, X3, X4... employ this APSK mappings.
The method flow of the elimination phase noise of the present invention is as shown in figure 1, its general thought is：
Input the channel response-estimation CPE for data/each subcarrier that each subcarrier reception arrives, obtain CPE model-
Eliminate the noise power that CPE-obtain corrects each each subcarrier of sub-carrier-combinations after CPE, calculating phase noise coefficient
F-elimination phase noise.Illustrate above-mentioned thinking below by specific steps.
Step S1：Common phase error CPE (common phase error) is estimated first.If function A (x) and Φ (x)
Plural an amplitude and phase, i.e. x=A (x) e are calculated respectivelyjΦ(x)So CPE is estimated as
Step S2：CPE is eliminated, obtains Y 'i=gCPEYiI=0,1 ..., N-1.
, in some cases, can be by Y' as another embodiment of the inventioniApprox think to be equal to YiPair, i.e.,
In step S1'sFor, it is believed that gCPE=1.Now, the present invention is utilized
Phase noise elimination method to eliminate phase noise when, step S1 and step S2 can be skipped, directly since step S3, this
Y' in the case of kind in step S3iUse YiInstead of.
Step S3：As shown in figure 3, estimation phase noise coefficient F.
Step S3.1：Decision function D (x) D are defined firstiRepresent decision function D (x) value, i.e. determination point so that D
(x) it is constellation point nearest with X Euclidean distance in constellation mapping scheme.
Step S3.2：The estimation phase noise coefficient F first step is the parameter H from ofdm systemi、YiAnd DiMiddle selection institute
By or a part of first specific numbers form IB.If gCPE≠ 1, then DiFor D (Y 'i/Hi)And if gCPE=1, now DiIt is exactly D
(Yi/Hi).The collection for defining the sequence number for the subcarrier being selected is combined into IB, and form set IBThe first specific numbers meet with
Lower condition：
1. employ the X for the APSK constellation point mapping for meeting condition as described aboveiSequence number.
2. meet D (Y 'i/Hi) or D (Yi/Hi) amplitude be more than a threshold value T1DiSequence number（In other words it is Y'i/Hi
Or Yi/HiSequence number）, the threshold value is previously set for system.
Meet that the APSK constellation point of condition as described above is mapped with following features：More the point of outer ring is not more in constellation point
Easily judge by accident into other points in same circle.Therefore, more than threshold value T1Point and be less than threshold value T1Point form outer layer and internal layer
It is higher to carry out accuracy of estimation for two parts, the only point from outer layer.Therefore threshold value T1Bigger, the accuracy of judgement is bigger, but
Used point is also fewer, otherwise that judges by accident may increase, but point used is then more.
3. meet that amplitude is less than a threshold value T2'sSequence number, the threshold value can be system be previously set or
It is calculated according to H and E, is, for example,Wherein α is previously set by system.
Step S3.3：The second step for estimating phase noise coefficient F is according to equation group
To estimate F, wherein N 'iIt is so that the noise that the formula is set up.Estimate
The method of meter can obtain to make N 'iThe minimum F of mean power or other, can use various ripe algorithms, it is of the invention right
This is not construed as limiting.
For gCPE≠ 1 situation, the D in above formulaiFor D (Y'i/Hi), above-mentioned equation group can be equivalent to：
For gCPE=1 situation, the D in above formulaiFor D (Yi/Hi), above-mentioned equation group can be equivalent to：
Step S4：Subcarrier interference is finally eliminated, is exported
Such scheme is illustrated below by one embodiment.
Assuming that one group of frequency-region signal received by the present invention is Y=[Y0, Y1..., Y2047]T, obtained channel response estimates
It is calculated as H=[H0,H1,…H2047]T.Frequency domain symbol x=[X of transmitting0, X1..., X2047]TIn, serial number 0 to 171 and serial number
The frequency domain symbol launched on 1877 to 2047 subcarrier is 0, and remaining frequency domain symbol is obtained according to the constellation mapping shown in Fig. 2
Arrive.Wherein P=8, Q=32l0To l7Respectively 0.2639,0.4750,0.6333,0.7916,0.9499,
1.1346 1.3457 and 1.6360.
Step S1：First with sequence number in lAY in={ 172,173 ..., 1876 }iWith HiEstimate gCPE。
Step S2：Pass through Y'i=gCPEYiY ' is calculated in i=0,1 ..., N-1i。
Step S3：Estimate phase noise coefficient F
Step S3.1：Define decision function D (x)
Step S3.2：Next I is selected by following requirementB：
1.XiEmploy the APSK constellation point mapping shown in Fig. 2, i.e. 172≤i≤1876.
2.D(Y′i/Hi) amplitude be more than 1.6, i.e. D (Y 'i/Hi) be Fig. 2 in outmost turns point.
3.Amplitude be less than threshold valueα=2.
Step S3.3：If IB={ iB, 0, iB, 1..., iB, M-1,
Now, it is rightConvert, a kind of table of equal value can be obtained
Up to mode, i.e.,：
PF=a+n, wherein：
L=10.
Using minimum mean square error criterion, F=(p are obtainedHp)-1PHa。
Step S4：Subcarrier interference is finally eliminated to obtain
Follow-up de-mapping method can be according to Y "iAnd HiCalculate the LLR per bit information.
It will be understood to one skilled in the art that the specification of the above is only one kind in the numerous embodiments of the present invention
Or several embodiments, and not use limitation of the invention.Any equivalent change for embodiment described above, modification with
And the technical scheme such as equivalent substitute, as long as meeting the spirit of the present invention, will all fall in claims of the present invention
In the range of protecting.
Claims (5)
1. a kind of phase noise elimination method of ofdm system, including phase noise estimating step, it is characterised in that the estimation
Step includes：
Step 1, from the parameter H of ofdm systemi、YiAnd DiThe middle all or part of first specific numbers composition set I of selectionB；Its
In, DiRepresent determination point；HiAnd YiOne group of channel estimation in frequency domain vector H=[H that ofdm system receiver receives is represented respectively0,
H1,…,HN-1]TWith frequency domain data vector Y=[Y0,Y1,…,YN-1]TIn element, wherein N represents the subcarrier of ofdm system
Number；
Step 2, establish estimation equation group
Wherein, N'iRepresent the noise for setting up estimation equation group；FkRepresent phase noise coefficient F=[F-L, F-L+1..., FL]TIn
Element, wherein L determine F length；
Step 3, the phase noise coefficient F is calculated,
Wherein, first specific numbers meet following condition：
The frequency domain data vector X=[X of ofdm system transmitting0,X1,…,XN-1]TA kind of middle element X mapped using specific APSKi
Sequence number, the specific APSK mappings include P × Q constellation point, and can use
To represent, whereinFor initial phase, l0
＜ l1＜ ... ＜ lP-1；
Amplitude is more than a predetermined threshold value T1DiSequence number；
Amplitude is less than a threshold value T2'sSequence number；Wherein, σi 2Represent one group of Frequency domain noise power estimate vector E=[σ0 2,
σ1 2..., σN-1 2]TIn element, wherein N represent ofdm system subcarrier number, wherein, P represent APSK constellation mapping graph on
The number of annulus, Q represent the number put on each annulus.
2. the phase noise elimination method of ofdm system as claimed in claim 1, it is characterised in that the threshold value T2ForWherein α is systemic presupposition value.
3. the phase noise elimination method of ofdm system as claimed in claim 1, it is characterised in that the determination point DiFor D
(Yi/Hi)。
4. the phase noise elimination method of ofdm system as claimed in claim 1, it is characterised in that the determination point DiFor D (Y'i/
Hi)；Wherein, Y 'i=gCPEYiI=0,1 ..., N-1；gCPECommon phase error is represented,
A (x) and Φ (x) represents the amplitude and phase of plural number；From frequency domain data vector X=[X0,X1,…,XN-1]TMiddle selection is all or one
The specific numbers composition set of part second IA, second specific numbers are frequency domain data vector X=[X0,X1,…,XN-1]TIn
The element X mapped using the APSKiSequence number.
5. the phase noise elimination method of ofdm system as claimed in claim 4, it is characterised in that utilize the phase noise
Coefficient F, which is performed, eliminates interference step, and output eliminates the frequency domain data Y " after interference,
Wherein
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