CN104702558A - Phase noise elimination method for OFDM system - Google Patents

Abstract

The present invention discloses a phase noise elimination method for an OFDM (Orthogonal Frequency Division Multiplexing) system, and aims at the OFDM system which uses specific APSK (Amplitude Phase Shift Keying) constellation mapping. In the phase noise elimination method of the present invention, firstly, a CPE (Common Phase Error) of the OFDM system is estimated for obtaining a CPE model; the CPE is further eliminated for obtaining each subcarrier symbol after the CPE is corrected; in combination with the noise power of each subcarrier, a phase noise coefficient F is computed and obtained; and finally, phase noise is eliminated. Through adoption of the technical scheme of the present invention, the characteristics of the specific APSK constellation mapping can be used for accurately and stably realizing estimation and elimination on the phase noise.

Description

The phase noise elimination method of ofdm system

Technical field

The present invention relates to a kind of demodulation method, more particularly, relate to a kind of phase noise elimination method mapped based on specific APSK constellation point.

Background technology

OFDM technology is the one of multi-carrier modulation.It is widely used in Modern Communication System.And phase noise can affect greatly the receptivity of ofdm system.Phase noise is caused by various analogue devices such as Up/Down Conversions usually.Phase noise can cause the rotation of each sub-carrier phase, also can cause inter-sub-carrier interference.Therefore, phase noise and inter-sub-carrier interference are the required problems solved of demodulating system, otherwise phase noise causes inter-sub-carrier interference, and inter-sub-carrier interference can destroy the orthogonality between subcarrier, thus affect receptivity.

APSK is a kind of constellation mapping mode, and a kind of specific APSK is used to obtain shaping gain recently, thus can improve receptivity, but the APSK constellation being applied to ofdm system maps the problem that there is inter-sub-carrier interference equally.

Summary of the invention

Object of the present invention aims to provide a kind of phase noise elimination method of ofdm system, solves ofdm system in prior art and there is phase noise, affect the problem of receptivity.

According to above-mentioned purpose, implement the phase noise elimination method of ofdm system of the present invention, comprise phase noise estimating step at receiving terminal, comprising:

Step one, from the parameter H of ofdm system _i, Y _iand D _imiddle selection all or a part of first specific numbers composition I _b; Wherein, D _irepresent determination point; H _iand Y _irepresent one group of channel estimation in frequency domain vector H=[H that ofdm system receiver receives respectively ₀, H ₁..., H _n-1] ^twith frequency domain data vector Y=[Y ₀, Y ₁..., Y _n-1] ^tin element, wherein N represents the subcarrier number of ofdm system;

Step 2, sets up estimate equation group $H_i{D}_i+{N^{,}}_i={\mathrm{\Σ}}_{k=-L}^L{F}_k{Y}_{i+k}i\∈I_B;$

Wherein, N' _irepresent and make estimate equation form vertical noise; F _krepresent phase noise coefficient F=[F _-L, F _-L+1..., F _l] ^tin element, wherein L determines the length of F;

Step 3, compute phase noise coefficient F.

Preferably, the first specific numbers meets the following conditions:

The frequency domain data vector X=[X that ofdm system is launched ₀, X ₁..., X _n-1] ^tthe element X that a kind of specific APSK of middle employing maps _isequence number, described specific APSK maps and comprises P × Q constellation point, and available represent, wherein for initial phase, l ₀< l ₁< ... < l _p-1;

Amplitude is greater than a predetermined threshold value T ₁d _isequence number;

Amplitude is less than a threshold value T ₂'s sequence number; Wherein, σ _i ²represent one group of Frequency domain noise power estimate vector E=[σ ₀ ², σ ₁ ²..., σ _n-1 ²] ^t.In element, wherein N represents the subcarrier number of ofdm system.

Preferably, determination point D _ifor D (Y _i/ H _i).

Preferably, determination point D _ifor D (Y' _i/ H _i); Wherein, Y' _i=g _cPEy _ii=0,1 ..., N-1; g _cPErepresent common phase error, a (x) and Φ (x) represents the phase and magnitude of plural number; From frequency domain data vector X=[X ₀, X ₁..., X _n-1] ^tmiddle selection all or a part of second specific numbers composition set I _a, the second specific numbers is frequency domain data vector X=[X ₀, X ₁..., X _n-1] ^tthe element X that the described APSK of middle employing maps _isequence number.

Preferably, threshold value T ₂for wherein α is systemic presupposition value.

Preferably, utilize phase noise coefficient F to perform and eliminate interference step, export the frequency domain data Y'' eliminated after interference, wherein ${Y^{\&prime;\&prime;}}_i={\mathrm{\&Sigma;}}_{k=-L}^L{F}_k{Y}_{i+k}i=L,L+1,...,N-L-1.$

Have employed technical scheme of the present invention, the feature that specific APSK constellation maps can be utilized, accurately, stably realize the estimation to phase noise and elimination.

Accompanying drawing explanation

In the present invention, identical Reference numeral 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 graph that the present invention is directed to;

Fig. 3 is the method flow diagram estimating phase noise in Fig. 1.

Embodiment

Technical scheme of the present invention is further illustrated below in conjunction with drawings and Examples.

First define the concept mentioned by the present invention, the present invention is applied to a kind of ofdm system, and this ofdm system comprises N number of subcarrier.With reference to Fig. 1, input of the present invention is one group of frequency domain data vector Y=[Y that the receiver in this ofdm system obtains ₀, Y ₁..., Y _n-1] ^t, one group of channel estimation in frequency domain vector H=[H ₀, H ₁..., H _n-1] ^twith one group of Frequency domain noise power estimate vector E=[σ ₀ ², σ ₁ ²..., σ _n-1 ²] ^t.Wherein, Y _irepresent the element in Y-direction amount, corresponding in frequency is f ₀the data that the received over subcarriers of+i Δ f arrives, and Δ f is sub-carrier frequencies interval.Similarly, H _irepresent the element in H vector, corresponding in frequency is f _ochannel coefficients on the subcarrier of+i Δ f, σ _i ²represent the element in E vector, corresponding in frequency is f _onoise power on the subcarrier of+i Δ f.

Think in theory:

$H_i{X}_i+N_i=\underset{k=-L}{\overset{L}{\mathrm{\&Sigma;}}}{F}_k{Y}_{i+k}i=L,L+1,...,N-L-1$

Wherein, X=[X ₀, X ₁..., X _n-1] ^tbe transmitter be the frequency domain symbol data vector that the subcarrier of fo+i Δ f is launched in frequency, use X _irepresent the element in X vector.N _ifor noise, and F=[F _-L, F _-L+1..., F _l] ^tfor phase noise coefficient, wherein F _krepresent the element in phase noise coefficient F vector.L is the parameter that receiving system realizes setting, and in order to determine the length of F, the length of F is 2L+1, if think that L is that namely 0, F deteriorates to a scalar, that is common phase error (CPE, common phaseerror).

There is the present invention is directed a kind of the ofdm system that specific APSK constellation maps, as shown in Figure 2, a kind of specific APSK constellation that partly or entirely have employed of X vector maps, and this APSK constellation maps and meets following condition: this constellation point scheme comprises P × Q constellation point, and available l ₀< l ₁< ... < l _p-1obtain all constellation point.Wherein, P represents the number of annulus on APSK constellation mapping graph, and Q represents the number that each annulus is put.

After determining above-mentioned APSK mapping, from X vector, select all or a part of second specific numbers composition set I _a, form set I _athe second specific numbers be the element adopting above-mentioned APSK to map in X vector.Such as, I is supposed _a={ 1,3,4 ..., represent the element X in X vector ₁, X ₃, X ₄have employed this APSK to map.

As shown in Figure 1, its general thought is the method flow of elimination phase noise of the present invention:

Input the channel response-estimation CPE of data/each subcarrier that each subcarrier reception arrives, obtain the model-elimination CPE of CPE-the obtain each sub-carrier after correcting CPE-in conjunction with the noise power of each subcarrier, compute phase noise coefficient F-elimination phase noise.Below by concrete steps, above-mentioned thinking is described.

Step S1: first estimate common phase error CPE (common phase error).If function A (x) and Φ (x) calculate a plural phase and magnitude respectively, i.e. x=A (x) e ^{j Φ (x)}so CPE is estimated as

Step S2: eliminate CPE, obtain Y ' _i=g _cPEy _ii=0,1 ..., N-1.

As another embodiment of the invention, in some cases, can by Y' _ithink approx and equal Y _i, namely for step S1's , think g _cPE=1.Now, when utilizing phase noise elimination method of the present invention to eliminate phase noise, step S1 and step S2 can be skipped, directly from step S3, the Y' in this case in step S3 _iall use Y _ireplace.

Step S3: as shown in Figure 3, estimates phase noise coefficient F.

Step S3.1: first define decision function D (x) and use D _irepresent the value of decision function D (x), i.e. determination point, makes D (x) for constellation point nearest with the Euclidean distance of X in constellation mapping scheme.

Step S3.2: estimate that the first step of phase noise coefficient F is the parameter H from ofdm system _i, Y _iand D _imiddle selection all or a part of first specific numbers composition I _b.If g _cPE≠ 1, then D _ifor D (Y ' _i/ Hi ₎if, and g _cPE=1, now D _ibe exactly D (Y _i/ H _i).Defining by the set of the sequence number of the subcarrier selected is I _b, and form set I _bthe first specific numbers meet the following conditions:

1. have employed the X of the APSK constellation point mapping meeting condition as described above _isequence number.

2. meet D (Y ' _i/ H _i) or D (Y _i/ H _i) amplitude be greater than a threshold value T ₁d _isequence number (be in other words Y' _i/ H _ior Y _i/ H _isequence number), this threshold value is that system sets in advance.

The APSK constellation point meeting condition as described above is mapped with following features: in constellation point, more the point of outer ring is more not easy other points of judging by accident in same circle.Therefore, threshold value T is greater than ₁point be less than threshold value T ₁point define outer and internal layer two parts, only select outer field point to carry out accuracy of estimation higher.Therefore threshold value T ₁larger, the accuracy of judgement is larger, but the point used is also fewer, on the contrary may the increasing of erroneous judgement, and but point used is then more.

3. meet amplitude and be less than a threshold value T ₂'s sequence number, this threshold value can set in advance for system, also can be to calculate according to H and E, such as, be wherein α is set in advance by system.

Step S3.3: the second step of estimation phase noise coefficient F is according to equation group

estimate F, wherein N ' _iit is the noise that this formula is set up.The method estimated can be obtain to make N ' _ithe minimum F of average power or other, can use various ripe algorithm, the present invention is not construed as limiting this.

For g _cPEthe situation of ≠ 1, the D in above formula _ifor D (Y' _i/ H _i), above-mentioned equation group can be equivalent to:

$H_{i}D({Y^{\&prime;}}_i/H_i)+{N^{,}}_i=\underset{k=-L}{\overset{L}{\mathrm{\&Sigma;}}}{F}_k{Y}_{i+k}i\&Element;I_B$

For g _cPEthe situation of=1, the D in above formula _ifor D (Y _i/ H _i), above-mentioned equation group can be equivalent to:

$H_{i}D(Y_i/H_i)+{N^{,}}_i={\mathrm{\&Sigma;}}_{k=-L}^L{F}_k{Y}_{i+k}i\&Element;I_B$

Step S4: finally eliminate subcarrier interference, exports

${Y^{\&prime;\&prime;}}_i={\mathrm{\&Sigma;}}_{k=-L}^L{F}_k{Y}_{i+k}i=L,L+1,...,N-L-1.$

Such scheme is illustrated below by an embodiment.

Suppose that one group of frequency-region signal received by the present invention is Y=[Y ₀, Y ₁..., Y ₂₀₄₇] ^t, the channel response obtained is estimated as H=[H ₀, H ₁... H ₂₀₄₇] ^t.Frequency domain symbol x=[the X launched ₀, X ₁..., X ₂₀₄₇] ^tin, sequence number is 0 to 171 is that on the subcarrier of 1877 to 2047, the frequency domain symbol launched is 0 with sequence number, and remaining frequency domain symbol obtains according to the constellation mapping shown in Fig. 2.Wherein P=8, Q=32 l ₀to l ₇be respectively 0.2639,0.4750,0.6333,0.7916,0.9499,1.1346,1.3457 and 1.6360.

Step S1: first utilize sequence number at l _a=172,173 ..., 1876 } in Y _iwith H _iestimate g _cPE.

Step S2: pass through Y' _i=g _cPEy _ii=0,1 ..., N-1 calculates Y ' _i.

Step S3: estimate phase noise coefficient F

Step S3.1: definition decision function D (x)

Step S3.2: next select I by following requirement _b:

1.X _ihave employed the APSK constellation point shown in Fig. 2 to map, i.e. 172≤i≤1876.

2.D (Y ' _i/ H _i) amplitude be greater than 1.6, namely D (Y ' _i/ H _i) be the point of outmost turns in Fig. 2.

3. amplitude be less than threshold value α=2.

Step S3.3: establish I _b={ i _{b, 0}, i _{b, 1}..., i _{b, M-1},

Now, right $H_{i}D({Y^{\&prime;}}_i/H_i)+{N^{,}}_i={\mathrm{\&Sigma;}}_{k=-L}^L{F}_k{Y}_{i+k}i\&Element;I_B$ Convert, a kind of expression way of equivalence can be obtained, that is:

PF=a+n, wherein:

$a={[H_{i_{b,0}}D\left(\frac{{Y^{\&prime;}}_{i_{b,0}}}{H_{i_{b,0}}}\right),...,H_{i_{b,M-1}}D\left(\frac{{Y^{\&prime;}}_{i_{b,M-1}}}{H_{i_{b,M-1}}}\right)]}^T$

$n={[{N^{\&prime;}}_{i_{b,0}},...,{N^{\&prime;}}_{i_{b,M-1}}]}^T$

L＝10。

Utilize minimum mean square error criterion, obtain F=(p ^hp) ^-1p ^ha.

Step S4: finally eliminate subcarrier interference and obtain

${Y^{\&prime;\&prime;}}_i={\mathrm{\&Sigma;}}_{k=-L}^L{F}_k{Y}_{i+k}i=L,L+1,...,N-L-1.$

Follow-up de-mapping method can according to Y " _iand H _icalculate the LLR of every bit information.

It will be understood to one skilled in the art that, above specification is only one or more execution modes in the numerous embodiment of the present invention, and not uses limitation of the invention.Any equalization for the above embodiment changes, modification and the equivalent technical scheme such as to substitute, as long as spirit according to the invention, all will drop in scope that claims of the present invention protect.

Claims (6)

1. a phase noise elimination method for ofdm system, comprises phase noise estimating step, it is characterized in that, described estimating step comprises:

Step one, from the parameter H of ofdm system _i, Y _iand D _imiddle selection all or a part of first specific numbers composition set I _b; Wherein, D _irepresent determination point; H _iand Y _irepresent one group of channel estimation in frequency domain vector H=[H that ofdm system receiver receives respectively ₀, H ₁..., H _n-1] ^twith frequency domain data vector Y=[Y ₀, Y ₁..., Y _n-1] ^tin element, wherein N represents the subcarrier number of ofdm system;

Step 2, sets up estimate equation group $H_i{D}_i+{N^{,}}_i={\mathrm{\&Sigma;}}_{k=-L}^L{F}_k{Y}_{i+k}i\&Element;I_B;$

Wherein, N' _irepresent and make estimate equation form vertical noise; F _krepresent phase noise coefficient F=[F _-L, F _-L+1..., F _l] ^tin element, wherein L determines the length of F;

Step 3, calculates described phase noise coefficient F.

2. the phase noise elimination method of ofdm system as claimed in claim 1, it is characterized in that, described first specific numbers meets the following conditions:

The frequency domain data vector X=[X that ofdm system is launched ₀, X ₁..., X _n-1] ^tthe element X that a kind of specific APSK of middle employing maps _isequence number, described specific APSK maps and comprises P × Q constellation point, and available represent, wherein for initial phase, l ₀< l ₁< ... < l _p-1;

Amplitude is greater than a predetermined threshold value T ₁d _isequence number;

Amplitude is less than a threshold value T ₂'s sequence number; Wherein, σ _i ²represent one group of Frequency domain noise power estimate vector E=[σ ₀ ², σ ₁ ²..., σ _n-1 ²] ^tin element, wherein N represents the subcarrier number of ofdm system.

3. the phase noise elimination method of ofdm system as claimed in claim 2, is characterized in that, described threshold value T ₂for wherein α is systemic presupposition value.

4. the phase noise elimination method of ofdm system as claimed in claim 2, is characterized in that, described determination point D _ifor D (Y _i/ H _i).

5. the phase noise elimination method of ofdm system as claimed in claim 2, is characterized in that, described determination point D _ifor D (Y' _i/ H _i); Wherein, Y' _i=g _cPEy _ii=0,1 ..., N-1; g _cPErepresent common phase error, a (x) and Φ (x) represents the phase and magnitude of plural number; From frequency domain data vector X=[X ₀, X ₁..., X _n-1] ^tmiddle selection all or a part of second specific numbers composition set I _a, described second specific numbers is frequency domain data vector X=[X ₀, X ₁..., X _n-1] ^tthe element X that the described APSK of middle employing maps _isequence number.

6. the phase noise elimination method of ofdm system as claimed in claim 5, is characterized in that, utilizes described phase noise coefficient F to perform and eliminates interference step, export the frequency domain data Y'' eliminated after interference, wherein ${Y^{\&prime;\&prime;}}_i={\mathrm{\&Sigma;}}_{k=-L}^L{F}_k{Y}_{i+k}i=L,L+1,...,N-L-1.$