CN102123123A - Method for realizing integral frequency deviation estimation of receiver - Google Patents

Abstract

The invention discloses a method for realizing integral frequency deviation estimation of a receiver. The method comprises the following steps of: compensating decimal frequency deviation of a time domain training sequence in a received signal; extracting the time domain training sequence of the received signal according to a set extraction interval; extracting a local training sequence according to the same set interval; transforming the time domain training sequence which is subjected to time extraction into a frequency domain training sequence through FFT (Fast Fourier Transform) according to data length after the time extraction; multiplying the frequency domain training sequence by the extracted shift local training sequence to obtain a frequency domain multiplication result; and transforming the frequency domain multiplication result back to a time domain through IFFT (Inverse Fast Fourier Transform). Each peak value is determined for different shift values; and the shift value corresponding to the maximum peak value is an estimated integral frequency deviation value. By adopting the method, integral frequency deviation estimation can be quickly and accurately realized, and operation and hardware realization complexity in a frequency deviation estimation algorithm can be effectively reduced.

Description

A kind of whole frequency offset estimating implementation method of receiver

Technical field

The present invention relates to frequency offset estimating implementation method in a kind of communications field, relate in particular to a kind of whole frequency offset estimating implementation method of receiver.

Background technology

OFDM (Orthogonal Frequency Division Multiplexing OFDM) technology has been used the orthogonal property of frequency, in case its orthogonality goes to pot, the error rate of system sharply increases, and this also is a major defect of OFDM technology.The main cause that produces frequency deviation is exactly that radio circuit reception and transmitting terminal centre frequency do not match.If the transmitting terminal centre carrier frequency is f _t, the receiving terminal centre carrier frequency is f _r, then source data x (n) at transmitting terminal is:

At receiving terminal be

Then there is frequency deviation f in the data of receiving terminal after down-conversion as can be seen _r-f _tFrom above-mentioned row formula as can be seen, in time domain, the phase deviation that carrier wave frequency deviation caused is along with the increase of sampled point accumulates gradually, and equivalence is the linear phase skew.At frequency domain, disturb between average phase rotation that carrier wave frequency deviation causes and subcarrier, when frequency deviation was Δ f, frequency-region signal can be expressed as:

$Y\left(k\right)=X_k{H}_k\left\{\frac{\sin \mathrm{\π\Δf}}{N\sin (\mathrm{\π\Δf}/N)}\right\}{e}^{\mathrm{j\π\Δf}(N-1)/N}$

$+\underset{\underset{l\≠k}{l=-K}}{\overset{K}{\mathrm{\Σ}}}{X}_k{H}_k\left\{\frac{\sin \mathrm{\π\Δf}}{N\sin (\mathrm{\π}(l-k+\mathrm{\Δf})/N)}\right\}{e}^{\mathrm{j\π\Δf}(N-1)/N}{e}^{-\mathrm{j\π}(l-k)/N}$

$=Y^{\′}\left(k\right)+Y_{\mathrm{ICI}}\left(k\right)$

The signal that receives for frequency domain of Y (k) wherein, X _kBe the primary signal that sends, H _kBe the frequency domain response of k position of channel, N is a FFT length, and Y ' (k) and X _kLinear, Y _ICI(k) disturb between subcarrier.Along with the increase of carrier wave frequency deviation Δ f, function

Along with increase, disturb also along with increase between subcarrier.

In ofdm system, when carrier frequency offset takes place, partly be called integer frequency bias Δ f greater than the frequency deviation of subcarrier spacing _I, partly be called decimal frequency bias Δ f less than the frequency deviation of subcarrier spacing _fNeed the integer frequency bias Δ f that exists in the system of estimating in the OFDM receiver _IWith decimal frequency bias Δ f _f, by the frequency offset correction module data stream is proofreaied and correct then.

Because the system carrier frequency is higher, the subcarrier interbody spacer is less, small frequency deviation will cause the skew of several or dozens of carrier wave in the frequency domain after FFT (fast Fourier transform) modulation of OFDM symbol, so the frequency offset estimating of ofdm system will be divided into decimal frequency bias Δ f _fEstimate and integer frequency bias Δ f _IEstimate.Decimal frequency bias is estimated to utilize maximum likelihood method to finish usually.The integer frequency bias algorithm for estimating comprises that frequency domain puts in order the whole frequency deviation estimating method of the whole frequency deviation estimating method of frequency deviation estimating method, time domain, time-domain and frequency-domain combination.

Wherein, the whole frequency deviation estimating method of time-domain and frequency-domain combination transforms to frequency domain based on time-domain training sequence by FFT, and the frequency domain operation result returns time domain by IFFT (inverse fast Fourier transform) operation transform again, obtains whole frequency offset estimation result.Compare with other whole frequency offset estimating algorithms, the estimating speed of this algorithm is fast, the precision height, and still, owing to wherein used FFT and IFFT computing, algorithm operation quantity is also relatively large.

Summary of the invention

The object of the invention provides a kind of whole frequency offset estimating implementation method of receiver, can realize whole fast and accurately frequency offset estimating, can reduce operand and hardware implementation complexity in the frequency offset estimating algorithm simultaneously.

A kind of whole frequency offset estimating implementation method of receiver comprises following content:

(1) fractional part of frequency offset of time-domain training sequence in the compensation received signal;

(2) extract by setting extraction interval time-domain training sequence to received signal;

(3) by identical setting at interval, local training sequence is extracted;

(4), be transformed to frequency domain training sequence by the time-domain training sequence of FFT conversion after with decimation in time according to the data length behind the decimation in time;

(5) the displacement this locality training sequence with frequency domain training sequence and after extracting multiplies each other, and obtains the frequency domain multiplied result;

(6) through the IFFT conversion, time domain is returned in the conversion of frequency domain multiplied result, for different shift values, determine peak value separately, the shift value of peak-peak correspondence is estimated whole frequency deviation value.

The whole frequency offset estimating implementation method of a kind of receiver provided by the present invention all extracts receiving sequence and local sequence, has shortened the data length of FFT and IFFT conversion, has both reduced the implementation complexity of the two, has reduced the transform operation amount again.Whole fast and accurately frequency offset estimating be can realize, operand and hardware implementation complexity in the frequency offset estimating algorithm reduced simultaneously.

Description of drawings

The basic flow sheet of the whole frequency offset estimating implementation method of a kind of receiver of Fig. 1

Specific embodiments

Be described in detail below in conjunction with 1 pair of content of the present invention of accompanying drawing:

(1) fractional part of frequency offset of time-domain training sequence in the compensation received signal.

If time-domain training sequence length is N, the Domain Synchronous training sequence is expressed as r _I(k), k=0 wherein, 1 ..., N, then the time-domain training sequence after the fractional part of frequency offset compensation is shown below: r _I(k)=r (k) e ^{-j2 π ε fk}, k=0,1 ..., N, ε are the fractional part of frequency offset that estimates, and f is the synchronizing signal carrier spacing, and N is the length of time-domain training sequence.

(2) according to the interval S that sets, and S is the integer greater than zero.Time-domain training sequence to received signal extracts.Time-domain training sequence after the extraction is:

r _S(n)＝r _I(S*n)，n＝0，1，2...，N/S

(3) according to setting S at interval, local training sequence is extracted.If local training sequence is expressed as sync (k), k=0,1 ..., N, the local training sequence after then extracting is:

sync _S(n)＝sync(S*n)，n＝0，1，2...，N/S

(4),, the time-domain training sequence behind the decimation in time is transformed to frequency domain training sequence by the FFT conversion according to the data length behind the decimation in time.

R _S(n)＝FFT(r _S(n)，)n＝0，1，2...，N/S

(5) the local training sequence after the extraction of frequency domain training sequence and different displacements is multiplied each other, obtain the frequency domain multiplied result.

prod(n)＝R _S(n)*sync _S(n-shift)n＝0，1，2...，N/S

Wherein, shift is a shift value.

(6) by the IFFT conversion, time domain is returned in the conversion of frequency domain multiplied result:

R _T(n)＝IFFT(prod(n))n＝0，1，2...，N/S

For different shift values, seek peak value separately.The shift value of peak-peak correspondence is estimated whole frequency deviation.

Claims (2)

1. the whole frequency offset estimating implementation method of a receiver comprises following steps:

(1) fractional part of frequency offset of time-domain training sequence in the compensation received signal;

(2) extract by setting extraction interval time-domain training sequence to received signal;

(3) by identical setting at interval, local training sequence is extracted;

(4), be transformed to frequency domain training sequence by the time-domain training sequence of FFT conversion after with decimation in time according to the data length behind the decimation in time;

(5) the local training sequence of displacement after frequency domain training sequence and the extraction multiplies each other, and obtains the frequency domain multiplied result;

(6) through the IFFT conversion, time domain is returned in the conversion of frequency domain multiplied result, for different shift values, determine peak value separately, the shift value of peak-peak correspondence is estimated whole frequency deviation value.

2. the whole frequency offset estimating implementation method of a kind of receiver as claimed in claim 1 is characterized in that described setting extraction is spaced apart the integer greater than zero.

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