CN101945078A - Frequency deviation estimation method based on noise subspace - Google Patents

Abstract

The invention discloses a frequency deviation estimation method based on the noise subspace, which comprises the steps of: calculating a phase angle rotational component caused by the frequency deviation according to a received time domain signal; averaging and normalizing the phase angle rotational component to obtain a corresponding fine frequency deviation estimation value; carrying out fine frequency deviation correction on the sequence of the received time domain signal; compensating the corrected time domain signal with an Epsilon phase; carrying out N-point Discrete Fourier Transform on the compensated signal; removing symbols modulated on a subcarrier; carrying out M-point Inverse Discrete Fourier Transform to obtain a time domain signal with the length M; computing the sum of the modulus squares of G values at the head of the time domain signal with the length M and M to G values at the end of the time domain signal with the length M and calculating the minimum ratio of the modulus squares to provide the estimated value of a coarse frequency deviation; and adding the estimated coarse frequency deviation value with the fine frequency deviation value to obtain the total frequency deviation estimation value. The invention is suitable for various block transmitting systems, including OFDM, with cyclic prefixes, and has the advantages of speediness, reliability, light load, wide capture range, high estimation precision, low complexity for implementation and like.

Description

Frequency deviation estimating method based on noise subspace

Technical field

The present invention relates to a kind of frequency synchronization method that is applied to OFDM (OFDM) system that belongs to mobile communication simultaneous techniques field, be specifically related to a kind of fast and reliable, duty ratio is less, capture range is big, estimated accuracy is high, implementation complexity is low frequency deviation estimating method based on noise subspace.

Background technology

Frequency Synchronization is the prerequisite of mobile communication system energy proper communication.In order to support high-speed data service, future mobile communication system will be the system of broadband, many (sending and receiving) antenna, and OFDM is the important candidate scheme of future mobile communication system.For following mobile radio telecommunications, the difference of transmitting-receiving two-end crystal oscillator exerts an influence to carrier frequency, and it is offset, thereby destroys the orthogonality between the subcarrier in the ofdm system.Compare with single-carrier system, ofdm system is more responsive to carrier wave frequency deviation, how to reduce between subcarrier and to disturb the influence of ICI to systematic function, is one of the prerequisite that can be used widely of ofdm system.Traditional frequency synchronization method all or based on frequency domain training sequence or based on time-domain training sequence comes carrier wave frequency deviation is estimated that they all have such-and-such shortcoming: be not suitable for packet data transmission, load too high, capture range is little, estimated performance is undesirable, computation complexity is high.

Summary of the invention

Goal of the invention:, the invention provides a kind of fast and reliable, duty ratio is less, capture range is big, estimated accuracy is high, implementation complexity is low frequency deviation estimating method based on noise subspace in order to overcome the deficiencies in the prior art.

Technical scheme: to achieve these goals, the frequency deviation estimating method based on noise subspace of the present invention may further comprise the steps:

1), the time-domain signal to receiving, according to P that it comprised identical subsequence, calculate the phase angle rotational component that causes owing to frequency deviation;

2), above-mentioned phase angle rotational component is done mean deviation normalization and can obtain corresponding thin frequency offset estimating value;

3), the time-domain signal sequence that receives is made thin frequency offset correction;

4), the time-domain signal after proofreading and correct is carried out the compensation that phase place is ε;

5), the signal after the compensation is the discrete Fourier transform (DFT) DFT that N is ordered;

6), remove the symbol of modulating on the subcarrier;

7), be the inverse discrete fourier transform IDFT that M is ordered, obtain the time-domain signal that length is M;

8), the mould of M-G value of G value of the stem of this time-domain signal and afterbody square is sued for peace respectively, and calculate its ratio

9), minimum Provided the estimated value of thick frequency deviation;

10), the thick frequency deviation value that will estimate and thin frequency deviation value addition, obtain total frequency offset estimating value;

Wherein, ε is the thick frequency deviation value chosen in advance, for-N/2 between the N/2 and do not comprise-integer of N/2; N is the sub-carrier number of ofdm system; P is a subsequence number identical in the training symbol, and M is the sub-carrier number that training sequence takies; G is the length of Cyclic Prefix; Usually, G is greater than the maximum delay expansion of wireless multipath fading channel, and P=N/M.

As preferably, in the described step 4) time-domain signal after proofreading and correct being carried out phase place is that the specific implementation method of the compensation of ε is: i sampling to time-domain signal be multiply by

Beneficial effect: the frequency deviation estimating method based on noise subspace of the present invention, can be used to comprise the various block transmission systems that Cyclic Prefix is arranged of OFDM, this method compared with prior art has the following advantages:

1) by introducing the notion of noise subspace, can enlarge the estimation range of thick frequency deviation, improve the precision of estimating, and estimate the impulse response of channel simultaneously; 2) Fourier just/inverse transformation exists implementation structure and algorithm efficiently fast, this method by adopt a large amount of Fouriers just/inverse transformation, can the mitigation system implementation complexity.

Description of drawings

Fig. 1 is the block diagram of the frequency deviation estimating method based on noise subspace of the present invention;

Fig. 2 is the implement device structural representation of the frequency deviation estimating method based on noise subspace of the present invention.

Embodiment

Below in conjunction with accompanying drawing the present invention is done further explanation.

As shown in Figure 2, the implement device of the frequency deviation estimating method based on noise subspace of the present invention comprises multiplication adding up device, multiplier, phase angle calculation element, fast fourier transformation apparatus, phase compensation and demodulating equipment, inverse fast fourier transform device, squaring device, indoor minimum value searcher and adder.

Suppose that a number of sub carrier wave that ofdm system comprised is N, the length of Cyclic Prefix is G.Training symbol is made up of two sections identical subsequences, takies the even bit subcarrier on frequency domain.At this moment, M=N/2, P=2.The training sequence that receives is delivered to parallel multiplication, multiplier module, phase angle computing module successively, utilize the structure of subsequence, obtain corresponding thin frequency deviation (fractional part of frequency offset) estimated value, and training sequence is carried out phasing.(N/2, N/2] select the preset value of integer ε in the scope successively as thick frequency deviation (integer frequency offset), compensate once more proofreading and correct the back signal, and estimate the time domain impulse response of channel.The ratio of calculating noise subspace and signal subspace power is determined the estimated value of integer frequency offset by the ratio of minimum.At last, with thick, thin frequency offset estimating value addition, export total frequency offset estimating value.

Specific algorithm is described below:

At first received signal is imported that multiplication adds up, multiplication and phase angle calculation element estimate fractional part of frequency offset, promptly

${\widehat{\mathrm{\υ}}}_f=\frac{1}{\mathrm{\π}}\mathrm{angle}\left\{\frac{1}{M}\underset{n=0}{\overset{M-1}{\mathrm{\Σ}}}{r}^{*}\left(n\right)r(n+M)\right\}$ [formula one]

Wherein, signal r (n), and n=0,1 ..., the training sequence behind the removal Cyclic Prefix that N} represents to receive; Angle{} represents to get the phase angle operation.Then, utilize the thin frequency deviation of estimating to proofread and correct to received signal

$\hat{r}\left(n\right)=r\left(n\right)e^{-j\frac{2\mathrm{\π}{\widehat{\mathrm{\υ}}}_f(G+n)}{N}},n=\mathrm{0,1},...,N-1$ [formula two]

(N/2, N/2] the interior preset value of selecting integer ε as integer frequency offset of scope, carry out phase compensation to the time-domain signal after proofreading and correct:

[formula three]

Burst after the phase compensation be multiply by the DFT matrixing to frequency domain, get rid of modulation symbol then after, multiply by the IDFT matrixing again to time domain.

When ε was even number, this process can be expressed as:

${\hat{h}}^{\mathrm{\ϵ}}={[{\hat{h}}_0^{\mathrm{\ϵ}},...,{\hat{h}}_{M-1}^{\mathrm{\ϵ}}]}^T={F_1}^{-1}{X}^{-1}{F}_2{\stackrel{\‾}{r}}^{\mathrm{\ϵ}}$ [formula four]

Here, F ₂Be the matrix of a M * N, the element of the capable q row of its p is:

${\left[F_2\right]}_{p,q}=e^{-j\frac{4\mathrm{\π}(p-1)(q-1)}{N}}$ [formula five]

F ₁Be the matrix of a M * M, the element of the capable q row of its p is:

${\left[F_1\right]}_{p,q}=e^{-j\frac{2\mathrm{\π}(p-1)(q-1)}{M}}$ [formula six]

X is the diagonal matrix of a M * M, and its diagonal element is the known training sequence of receiving terminal.

When ε was odd number, this process can be expressed as:

${\hat{h}}^{\mathrm{\ϵ}}={[{\hat{h}}_0^{\mathrm{\ϵ}},...,{\hat{h}}_{M-1}^{\mathrm{\ϵ}}]}^T={F_1}^{-1}{X}^{-1}{F}_3{\stackrel{\‾}{r}}^{\mathrm{\ϵ}}$ [formula seven]

Here, F ₃Be the matrix of a M * N, the element of the capable q row of its p is:

${\left[F_3\right]}_{p,q}=e^{-j\frac{2\mathrm{\π}[2(p-1)-1](q-1)}{N}}$ [formula eight]

With the sequence that obtains

Be sent to quadratic sum adder unit ratio calculated

${\mathrm{\ρ}}_{\mathrm{\ϵ}}=\frac{\underset{i=G}{\overset{M-1}{\mathrm{\Σ}}}{\left|{\hat{h}}_i^{\mathrm{\ϵ}}\right|}^2}{\underset{i=0}{\overset{G-1}{\mathrm{\Σ}}}{\left|{\hat{h}}_i^{\mathrm{\ϵ}}\right|}^2}$ [formula nine]

In the span of ε, by search unit, the searching minimum

${\widehat{\mathrm{\υ}}}_i=\underset{\mathrm{\ϵ}\∈(-N/2,N/2]}{\min }{\mathrm{\ρ}}_{\mathrm{\ϵ}}$ [formula ten]

Minimum ρ _εCorresponding phase place ε is the thick frequency deviation of estimation

Thin, the thick frequency offset estimating value that estimates is delivered to adder, and can to obtain total frequency offset estimating value as follows:

$\widehat{\mathrm{\υ}}={\widehat{\mathrm{\υ}}}_i+{\widehat{\mathrm{\υ}}}_f$ [formula 11]

According to above description, can obtain performing step following (as shown in Figure 1) based on the frequency deviation estimating method of noise subspace:

1), the time-domain signal to receiving, according to P that it comprised identical subsequence, calculate the phase angle rotational component that causes owing to frequency deviation;

2), above-mentioned phase angle rotational component is done mean deviation normalization and can obtain corresponding thin frequency offset estimating value;

3), the time-domain signal sequence that receives is made thin frequency offset correction;

4), the time-domain signal after proofreading and correct is carried out the compensation that phase place is ε;

5), the signal after the compensation is done discrete Fourier transform (DFT) (DFT) conversion that N is ordered;

6), remove the symbol of modulating on the subcarrier;

7), do inverse discrete fourier transform (IDFT) conversion that M is ordered, obtain the time-domain signal that length is M;

8), the mould of M-G value of G value of the stem of this time-domain signal and afterbody square is sued for peace respectively, and calculate its ratio

9), minimum

Provided the estimated value of thick frequency deviation;

10), the thick frequency deviation value that will estimate and thin frequency deviation value addition, obtain total frequency offset estimating value.

Wherein, ε is the thick frequency deviation value chosen in advance, for-N/2 between the N/2 and do not comprise-integer of N/2; N is the sub-carrier number of ofdm system; P is a subsequence number identical in the training symbol, and M is the sub-carrier number that training sequence takies; G is the length of Cyclic Prefix.Usually, G is greater than the maximum delay expansion of wireless multipath channel, and P=N/M.In the step 4) time-domain signal after proofreading and correct being carried out phase place is that the specific implementation method of the compensation of ε is: i sampling to time-domain signal be multiply by

Multiplication adding up device, multiplier and phase angle calculation element are finished the computing that comprises in the formula [], multiplier is finished thin frequency offset correction (formula [two]) and phase compensation (formula [three]) computing, discrete Fourier just/inverse transformation device and demodulating equipment finish the computing that comprises among formula [four], [five], [six], [seven] and [eight], the quadratic sum multiplier is finished formula [nine], and the minimum value searcher is finished the estimation (formula [ten]) of thick frequency deviation in the window.Adder is finished total frequency offset estimating computing (formula [11])

The above only is a preferred implementation of the present invention; be noted that for those skilled in the art; under the prerequisite that does not break away from the principle of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (2)

1. frequency deviation estimating method based on noise subspace is characterized in that this method may further comprise the steps:

1), the time-domain signal to receiving, according to P that it comprised identical subsequence, calculate the phase angle rotational component that causes owing to frequency deviation;

2), above-mentioned phase angle rotational component is done mean deviation normalization and can obtain corresponding thin frequency offset estimating value;

3), the time-domain signal sequence that receives is made thin frequency offset correction;

4), the time-domain signal after proofreading and correct is carried out the compensation that phase place is ε;

5), the signal after the compensation is the discrete Fourier transform (DFT) DFT that N is ordered;

6), remove the symbol of modulating on the subcarrier;

7), be the inverse discrete fourier transform IDFT that M is ordered, obtain the time-domain signal that length is M;

8), the mould of M-G value of G value of the stem of this time-domain signal and afterbody square is sued for peace respectively, and calculate its ratio

9), minimum

Provided the estimated value of thick frequency deviation;

10), the thick frequency deviation value that will estimate and thin frequency deviation value addition, obtain total frequency offset estimating value;

Wherein, ε is the thick frequency deviation value chosen in advance, for-N/2 between the N/2 and do not comprise-integer of N/2; N is the sub-carrier number of ofdm system; P is a subsequence number identical in the training symbol, and M is the sub-carrier number that training sequence takies; G is the length of Cyclic Prefix; Usually, G is greater than the maximum delay expansion of wireless multipath fading channel, and P=N/M.

2. the time synchronization method based on noise subspace according to claim 1 is characterized in that: in the described step 4) time-domain signal after proofreading and correct being carried out phase place is that the specific implementation method of the compensation of ε is: i sampling to time-domain signal be multiply by

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