CN101599942B - Method and device for receiving orthogonal frequency division multiplexing signal - Google Patents

Abstract

The invention discloses a method and a device for receiving an orthogonal frequency division multiplexing (OFDM) signal. The method comprises the following steps: firstly, after performing CP removal treatment, performing frequency shift on the OFDM signal so that the frequency of a taken out signal is distributed at two sides centering on a zero point; secondly, performing filtration and extraction on a time domain signal after the frequency shift so that the length of the time domain signal is M; and finally, performing DFT of an M point on the time domain signal of which the length is M, and taking a frequency domain signal out with the required length from M orthogonal sub-carriers obtained from the DFT according to the set frequency requirement of the signal required to be taken out. M is a minimum number which is equal to 2<n> and is more than or equal to NP so that M is far smaller than N compared with the DFT of an N point in the prior art, thus the method and the device reduce the data transfer amount and the calculation amount in the process of receiving the OFDM signal, improve the signal processing speed, and reduce the consumption of computing resources.

Description

A kind of method of reseptance of orthogonal frequency-division multiplex singal and device

Technical field

The present invention relates to orthogonal frequency division multiplexi, particularly a kind of method of reseptance of orthogonal frequency-division multiplex singal and device.

Background technology

OFDM (OFDM) technology is considered to realize a kind of very effective means of high speed data transfer.At present, the OFDM technology successfully has been applied in the technology such as digital audio broadcasting (DAB), digital video broadcasting (DVB) and WLAN (wireless local area network), and is considered to one of core technology the most attractive in the next generation mobile communication system.

The OFDM technology is a kind of multi-carrier transmission technology, and its main thought is: the channel total bandwidth is divided into the subcarrier of several quadratures, converts high-speed data signal to parallel low speed sub data flow, be modulated on each subcarrier and transmit.Compare with traditional multi-carrier transmission, OFDM can use more narrower orthogonal subcarrier to transmit.

In present OFDM technology, the ofdm signal method of reseptance of receiving terminal all is: the original ofdm signal that will receive earlier transforms to frequency domain by discrete Fourier transform (DFT) (DFT), take out the orthogonal sub-carriers of required number then at the frequency domain position of setting, promptly finish the ofdm signal receiving course, be met the frequency-region signal of setting frequency domain position and required orthogonal sub-carriers number.Physical Random Access Channel (PRACH) signal is a kind of special ofdm signal, when receiving the signal of the common existence of PRACH signal and conventional ofdm signal, the method of reseptance of prior art is that both are carried out DFT respectively, takes out required channel at the frequency domain position of setting again.Needing the length of the PRACH signal of acquisition is N _RA, needing the length of the conventional ofdm signal of acquisition is N.The method that receiving terminal obtains the PRACH signal is: taking-up length is N from the common signal that exists of PRACH signal and conventional ofdm signal that receives _RAOfdm signal, carry out N then _RAThe DFT of point transforms to frequency domain with it, and takes out required PRACH signal at the setting frequency domain position of agreement regulation.The method that receiving terminal obtains conventional ofdm signal is: taking out length from PRACH signal that receives and the signal that exists jointly is the ofdm signal of N, carry out the DFT that N is ordered then, it is transformed to frequency domain, and take out required conventional ofdm signal at the setting frequency domain position of agreement regulation.

5 kinds of forms of PRACH signal in standard 3GPPTS.36.211, have been stipulated, according to the regulation in the standard, N _RABe far longer than N, even can reach 12 times of N.Counting that DFT need handle when therefore obtaining the PRACH signal is to obtain required 12 times of counting of conventional ofdm signal, and operand is big, and this just causes the speed of signal processing when receiving ofdm signal slow, and expends a large amount of calculation resources.

In the prior art, the most frequently used ofdm signal receiving system is radio frequency remoto module and baseband processing unit (RRU+BBU) equipment.RRU+BBU equipment is made up of radio frequency remoto module (RRU) and baseband processing unit (BBU).For the ofdm signal that comprises Cyclic Prefix (CP), RRU goes CP to handle to it after receiving ofdm signal, will go the ofdm signal behind the CP to send BBU to then; In BBU, the ofdm signal behind the CP is carried out DFT, take out required channel at the frequency domain position of setting then, promptly obtain needed ofdm signal.For conventional ofdm signal, after past CP handled, it is little that RRU is sent to the ofdm signal data volume of BBU; And for the PRACH signal, because N _RABe 12 times of N, going CP to handle back RRU, to be sent to the data volume of PRACH signal of BBU very big, limited the processing speed of ofdm signal receiving course.And as previously described, the DFT operand among the BBU is big, and the speed of signal processing is slow, expends a large amount of calculation resources.

In a word, adopt existing ofdm signal method of reseptance and device, the signal transmitted data amount is big and operand is big, causes the processing speed of ofdm signal receiving course slow, expends a large amount of calculation resources.

Summary of the invention

In view of this, main purpose of the present invention is to provide a kind of method of reseptance of ofdm signal, adopts this method can reduce to transmit data volume and amount of calculation when receiving ofdm signal.

Another object of the present invention is to provide a kind of receiving system of ofdm signal, adopt this device can when receiving ofdm signal, reduce to transmit data volume and amount of calculation.

For achieving the above object, technical scheme of the present invention specifically is achieved in that

The invention discloses a kind of method of reseptance of orthogonal frequency division multiplex OFDM signal, may further comprise the steps:

A, be that the ofdm signal of N carries out frequency displacement to length, make the frequency of the signal of required taking-up wherein in the filter range of filter, wherein N is the original ofdm signal length that receives;

B, be that the ofdm signal of N carries out filtering to the length after the frequency displacement;

C, be that the ofdm signal of N extracts to filtered length, extraction yield is L=N/M, obtains the time-domain signal that length is M, and wherein M equals 2 ⁿAnd more than or equal to N _PMinimum number, n is a positive integer, N _PThe orthogonal sub-carriers number of the frequency-region signal that takes out for needs, N＞M＞N _P

D, be that the time-domain signal of M carries out the discrete Fourier transform (DFT) DFT that M is ordered to length, obtain comprising the frequency-region signal of M orthogonal sub-carriers, the setting frequency domain position according to the signal of required taking-up takes out N from the frequency-region signal that comprises M orthogonal sub-carriers _PThe frequency-region signal of individual orthogonal sub-carriers.

Further comprise before the described steps A:

Go cyclic prefix CP to handle to the ofdm signal that receives, obtain the ofdm signal that length is N.

The frequency shift amount of the described frequency displacement of steps A is k=N ₀/ 2-k ₀-N _p/ 2, N wherein ₀Be effective subcarrier number, k ₀Frequency domain original position for the orthogonal sub-carriers of the ofdm signal of required taking-up.

The described low-pass filtering that is filtered into of step B adopts wave digital lowpass filter, and the frequency response of described wave digital lowpass filter is $H\left(e^{\mathrm{j\&omega;}}\right)=\left\{\begin{array}{cc}\sqrt{L}& 0\&le;\left|\mathrm{\&omega;}\right|\&le;\frac{N^{\&prime;}}{N}\mathrm{\&pi;}\\ 0& \end{array}\right.,$ Wherein N ' is N _pAn and integer between the M.

The method of the described extraction of step C extracts M point altogether for being to extract the locational point of integral multiple that is positioned at extraction yield L in the ofdm signal of N in length.

The invention also discloses a kind of receiving system of orthogonal frequency division multiplex OFDM signal, this device comprises:

Frequency shift unit is that the ofdm signal of N carries out frequency displacement to length, makes the frequency of the signal of required taking-up wherein in the filter range of filter, and the signal after the frequency displacement is outputed to filter unit, and wherein N is the original ofdm signal length that receives;

Filter unit, the signal after the frequency displacement of reception frequency shift unit output carries out filtering and filtered signal is outputed to extracting unit it;

Extracting unit, the filtered signal of the unit output of accepting filter also extracts it, and extraction yield is L=N/M, obtains time-domain signal that length is M and it is outputed to discrete Fourier transform (DFT) DFT unit, and wherein M equals 2 ⁿAnd more than or equal to N _PMinimum number, n is a positive integer, N _PThe orthogonal sub-carriers number of the frequency-region signal that takes out for needs, N＞M＞N _P

The DFT unit, the length that receives extracting unit output is the time-domain signal of M and it is carried out the DFT that M is ordered, obtain comprising the frequency-region signal of M orthogonal sub-carriers, the setting frequency domain position according to the signal of required taking-up takes out N from the frequency-region signal that comprises M orthogonal sub-carriers _PThe frequency-region signal of individual orthogonal sub-carriers.

Further comprise in the described device:

Go to the cyclic prefix CP unit, receive ofdm signal and remove the CP of its original position, obtain the ofdm signal that length is N.

The frequency shift amount of described frequency shift unit is k=N ₀/ 2-k ₀-N _p/ 2, N wherein ₀Be effective subcarrier number, k ₀Frequency domain original position for the orthogonal sub-carriers of the ofdm signal of required taking-up;

Or,

Described filter unit carries out low-pass filtering, adopts wave digital lowpass filter, and the frequency response of described wave digital lowpass filter is $H\left(e^{\mathrm{j\&omega;}}\right)=\left\{\begin{array}{cc}\sqrt{L}& 0\&le;\left|\mathrm{\&omega;}\right|\&le;\frac{N^{\&prime;}}{N}\mathrm{\&pi;}\\ 0& \end{array}\right.,$ Wherein N ' is N _pAn and integer between the M;

Or,

Described extracting unit is to extract the locational point of integral multiple that is positioned at extraction yield L in the ofdm signal of N in length, extracts M point altogether.

Described frequency shift unit, filter unit, extracting unit and DFT unit are arranged in baseband processing unit BBU.

The described cyclic prefix CP unit that goes is arranged in radio frequency remoto module RRU.

As seen from the above technical solutions, the method and apparatus that ofdm signal of the present invention receives, after going the CP processing, earlier ofdm signal is carried out frequency displacement, make that the frequency of signal of required taking-up is is that the both sides at center distribute with the zero point, then the time-domain signal after the frequency displacement is carried out filtering and extraction, make that this time-domain signal length is M, be that the time-domain signal of M carries out the DFT that M is ordered to length at last, according to the setpoint frequency requirement of the signal of required taking-up, from M the orthogonal sub-carriers that DFT obtains, take out the frequency-region signal of Len req.Because M equals 2 ⁿAnd more than or equal to N _PMinimum number, 2 ⁿIndex n be positive integer, so compare with the N DFT of ordering in the prior art, M is far smaller than N, thereby the present invention reduced data conveying capacity and amount of calculation in the ofdm signal receiving course, has improved processing speed, has reduced expending of calculation resources.

Description of drawings

Fig. 1 is the flow chart of the method for reseptance of preferred embodiment ofdm signal of the present invention.

Fig. 2 is the structure chart of the receiving system of preferred embodiment ofdm signal of the present invention.

Embodiment

For making purpose of the present invention, technical scheme and advantage clearer, below with reference to the accompanying drawing embodiment that develops simultaneously, the present invention is described in more detail.

The method and apparatus that ofdm signal of the present invention receives, after going the CP processing, earlier ofdm signal is carried out frequency displacement, make that the frequency of signal of required taking-up is is that the both sides at center distribute with the zero point, then the time-domain signal after the frequency displacement is carried out filtering and extraction, make that this time-domain signal length is M, be that the time-domain signal of M carries out the DFT that M is ordered to length at last, according to the setpoint frequency requirement of the signal of required taking-up, from M the orthogonal sub-carriers that DFT obtains, take out the frequency-region signal of Len req.

Fig. 1 is the flow chart of the ofdm signal method of reseptance of a preferred embodiment of the present invention.The purpose of this ofdm signal method of reseptance is to be to take out the ofdm signal of N to be positioned at the frequency domain position of setting and to comprise N from length _pThe frequency-region signal of individual orthogonal sub-carriers.As shown in Figure 1, the concrete steps of ofdm signal method of reseptance of the present invention are as follows.

Step 101: this step goes CP to handle with of the prior art identical to the ofdm signal that receives, and obtaining length is the ofdm signal s (t) of N.Because most ofdm signal all disturbs between interference and subcarrier between original position insertion CP is in order to erasure signal, so at first remove the CP that is positioned at its original position when receiving ofdm signal.If what receive is the ofdm signal that does not insert CP, then needn't carry out this step, directly enter step 102.

Step 102: carry out frequency displacement to removing the ofdm signal s (t) behind the CP, obtain signal y (t).

OFDM uses orthogonal subcarrier to transmit, and therefore requires transmission signals to satisfy accurate frequency domain position, and this just causes total length is the frequency domain position that the ofdm signal s (t) of N has setting.And in the subsequent step of ofdm signal method of reseptance of the present invention, therefore the frequency of signal that requires required taking-up need carry out frequency displacement to it earlier obtaining signal s (t) afterwards in the filter range of filter.To adopt low pass filter is example, with k ₀The frequency domain original position of orthogonal sub-carriers of representing the ofdm signal of required taking-up is represented frequency shift amount that s (t) is carried out frequency displacement, then k=N with k ₀/ 2-k ₀-N _p/ 2.N wherein ₀Be effective sub-carrier number, effectively subcarrier is that the length stipulated in the standard is the ofdm signal of N allows use in total bandwidth subcarrier.N _pBe the occupied sub-carrier number of the signal of required taking-up.Behind time-domain signal s (t) the frequency displacement k that receives, obtain signal y (t), that is:

y(t)＝s(t)e ^(j2πnk)/N

Step 103: adopt specially designed digital filter that the time-domain signal y (t) that step 102 obtains is carried out low-pass filtering, output time-domain signal v (t).

This step can adopt the logical or low-pass filtering of band, is example with the low-pass filtering, designs a wave digital lowpass filter, requires its technical indicator to be: frequency response $0\&le;\left|\mathrm{\&omega;}\right|\&le;\frac{N^{\&prime;}}{N}\mathrm{\&pi;}$ Between be

$\frac{N^{\&prime;}}{N}\mathrm{\&pi;}<\left|\mathrm{\&omega;}\right|\&le;\mathrm{\&pi;}$ Between be 0.Wherein, N ' is N _pAn integer between＜N '＜M; M equals 2 ⁿAnd more than or equal to N _PMinimum number, 2 ⁿIndex n be positive integer; L=N/M.Because the signal of required taking-up has the protection frequency band, so the passband of the filter of requirement design is steady; And as long as the signal that guarantees required taking-up in the passband of filter, the transition band width of filter and other signal in the stopband just can not influence the signal of required taking-up, so be not strict with the transition band width and the stopband of filter.For this reason, the frequency response with low pass filter is designed to:

$H\left(e^{\mathrm{j\&omega;}}\right)=\left\{\begin{array}{cc}\sqrt{L}& 0\&le;\left|\mathrm{\&omega;}\right|\&le;\frac{N^{\&prime;}}{N}\mathrm{\&pi;}\\ 0& \end{array}\right.$

The low pass filter that satisfies above-mentioned requirements is a lot, all can adopt.Be example with one 2 rank Butterworth filter only, the transfer function of filter is herein:

b＝[0.0035 0.0069 0.0035]

a＝[1.0000 -1.8268 0.8407]

$H\left(z\right)=\frac{B\left(z\right)}{A\left(z\right)}=\frac{b\left(1\right)+b\left(2\right)z^{-1}+b\left(3\right)z^{-2}}{1+a\left(2\right)z^{-1}+a\left(3\right)z^{-2}}=\frac{0.0035+{0.0069z}^{-1}+{0.0035z}^{-2}}{1-{1.8268z}^{-1}+{0.8407z}^{-2}}$

Then adopt above-mentioned 2 rank Butterworth LPF, its output v (t) with the pass of input y (t) is:

v(t)-1.8268v(t-1)+0.8407v(t-2)＝0.0035y(t)+0.0069y(t-1)+0.0035y(t-2)

Step 104: the time-domain signal v (t) that step 103 is obtained extracts, and obtaining length is the time-domain signal z (t) of M.

The time-domain signal v (t) that obtains after the low-pass filtering is extracted, and its extraction yield is L, L=N/M.Can adopt several different methods to finish extraction, one of them the simplest method is to be to extract the locational point of integral multiple that is positioned at extraction yield L in the ofdm signal of N in length, extracts M point altogether, that is:

Only be example with the method, other method that can finish extraction all can adopt herein, only need satisfy extraction yield L=N/M and get final product.

Step 105: the time-domain signal z (t) to step 104 output carries out the DFT that M order, obtains comprising the frequency-region signal zc (n) of M orthogonal sub-carriers, and according to the signal frequency-domain position of required taking-up, taking-up N from signal zc (n) _PThe frequency-region signal of individual orthogonal sub-carriers.

Frequency-region signal zc (n) is:

zc(n)＝DFT(z(n)，M)

Wherein, the M that counts of IDFT equals 2 ⁿAnd more than or equal to N _PMinimum number.

Adopt ofdm signal method of reseptance of the present invention embodiment illustrated in fig. 1, need corresponding ofdm signal receiving system, the composition structure of this device as shown in Figure 2.

Referring to Fig. 2, ofdm signal receiving system of the present invention comprises frequency shift unit 202, filter unit 203, extracting unit 204 and DFT unit 205, and can also comprise CP unit 201 before frequency shift unit 202.

Go the 201 pairs of ofdm signals that receive in CP unit to go CP to handle, obtaining total length is the ofdm signal s (t) of N, and it is outputed to frequency shift unit 202.Frequency shift unit 202 receives the signal s (t) that goes 201 outputs of CP unit, and it is carried out the frequency displacement that frequency shift amount is k, obtains time-domain signal y (t), and it is outputed to filter unit 203.Frequency shift amount k=N ₀/ 2-k ₀-N _p/ 2, N wherein ₀Be effective sub-carrier number, effectively subcarrier is that the length stipulated in the standard is the ofdm signal of N allows use in total bandwidth subcarrier.N _pBe the occupied sub-carrier number of the signal of required taking-up.k ₀Frequency domain original position for the orthogonal sub-carriers of the ofdm signal of required taking-up.Filter unit 203 can adopt the logical or low pass filter of band, is example with the low-pass filtering, adopts specially designed wave digital lowpass filter, receive the signal y (t) of frequency shift unit 202 outputs, it is carried out low-pass filtering, obtain time-domain signal v (t), and it is outputed to extracting unit 204.The accept filter time-domain signal v (t) of unit 203 output of extracting unit 204, and it is carried out the extraction that extraction yield is L=N/M obtains length and is the signal z (t) of M and it is outputed to DFT unit 205.Wherein M equals 2 ⁿAnd more than or equal to N _PMinimum number, 2 ⁿIndex n be positive integer.Extracting unit 204 can adopt several different methods to finish extraction, and one of them the simplest method is to be to extract the locational point of integral multiple that is positioned at extraction yield L in the ofdm signal of N in length, extracts M point altogether, that is:

DFT unit 205 receives the time-domain signal z (t) of extracting unit 204 outputs, and it is carried out the DFT that M is ordered, and obtains comprising the frequency-region signal zc (n) of M orthogonal sub-carriers.According to the signal frequency-domain position of required taking-up, can from signal zc (n), take out N _PThe frequency-region signal of individual orthogonal sub-carriers.

In filter unit 203, with the technical index design of the wave digital lowpass filter that adopts be: frequency response exists $0\&le;\left|\mathrm{\&omega;}\right|\&le;\frac{N^{\&prime;}}{N}\mathrm{\&pi;}$ Between be

$\frac{N^{\&prime;}}{N}\mathrm{\&pi;}<\left|\mathrm{\&omega;}\right|\&le;\mathrm{\&pi;}$ Between be 0.Wherein, N ' is N _pAn integer between＜N '＜M.Require the passband of wave digital lowpass filter steady, require not strict transition band width and stopband.The frequency response of wave digital lowpass filter is designed to: $H\left(e^{\mathrm{j\&omega;}}\right)=\left\{\begin{array}{cc}\sqrt{L}& 0\&le;\left|\mathrm{\&omega;}\right|\&le;\frac{N^{\&prime;}}{N}\mathrm{\&pi;}\\ 0& \end{array}\right..$ The wave digital lowpass filter that satisfies above-mentioned requirements is a lot, all can adopt.With one 2 rank Butterworth filter is example, and its transfer function is:

b＝[0.0035 0.0069 0.0035]

a＝[1.0000 -1.8268 0.8407]

$H\left(z\right)=\frac{B\left(z\right)}{A\left(z\right)}=\frac{b\left(1\right)+b\left(2\right)z^{-1}+b\left(3\right)z^{-2}}{1+a\left(2\right)z^{-1}+a\left(3\right)z^{-2}}=\frac{0.0035+{0.0069z}^{-1}+{0.0035z}^{-2}}{1-{1.8268z}^{-1}+{0.8407z}^{-2}}$

Then adopt this 2 rank Butterworth LPF, its output v (t) with the pass of input y (t) is:

v(t)-1.8268v(t-1)+0.8407v(t-2)＝0.0035y(t)+0.0069y(t-1)+0.0035y(t-2)

Compared with prior art, ofdm signal method of reseptance of the present invention has reduced amount of calculation.The DFT that prior art adopts N to order, needed multiplication computation amount is

And the multiplication computation amount of filtering of the present invention is (2a+1) * N, and wherein a is the exponent number of the filter that step 104 adopted, and the amount of calculation of the IDFT that M is ordered is very little, can ignore.For example, system bandwidth 20M, the PRACH signal of the form of stipulating among the standard 3GPPTS.36.211 1, the points N of DFT=24576, then adopting the required multiplication computation amount of prior art is 179220, and adopt ofdm signal method of reseptance of the present invention, and the second-order low-pass filter multiplication computation amount is 122835, amount of calculation has reduced 31%.

When adopting RRU+BBU equipment to receive ofdm signal, will go CP unit 201, frequency shift unit 202, filter unit 203 and extracting unit 204 to place RRU; For DFT unit 205, same as the prior art, will place BBU in DFT unit 205, different is, the BBU of prior art carries out the DFT that N is ordered, and DFT of the present invention unit 205 only carries out the DFT that M is ordered, and can take out desired signal., need in the prior art to transmit the ofdm signal that length is N, and adopt method of reseptance of the present invention and device in the data that BBU transmits at RRU, only needing to transmit length is the ofdm signal of M, because M equals 2 ⁿAnd more than or equal to N _PMinimum number, so the present invention has significantly reduced the data conveying capacity of RRU to BBU.

As seen from the above-described embodiment, the method and apparatus that adopts ofdm signal of the present invention to receive, after going the CP processing, earlier ofdm signal is carried out frequency displacement, make that the frequency of signal of required taking-up is is that the both sides at center distribute with the zero point, then the time-domain signal after the frequency displacement is carried out low-pass filtering and extraction, make that this time-domain signal length is M, be that the time-domain signal of M carries out the DFT that M is ordered to length at last, according to the setpoint frequency requirement of the signal of required taking-up, from M the orthogonal sub-carriers that DFT obtains, take out the frequency-region signal of Len req.Because M equals 2 ⁿAnd more than or equal to N _PMinimum number, 2 ⁿIndex n be positive integer, so compare with the N DFT of ordering in the prior art, M is far smaller than N, has reduced data conveying capacity and amount of calculation in the ofdm signal receiving course, has improved conversion speed, has reduced expending of calculation resources.

In a word, the above is preferred embodiment of the present invention only, is not to be used to limit protection scope of the present invention.Within the spirit and principles in the present invention all, any modification of being done, be equal to replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (9)

1. the method for reseptance of an orthogonal frequency division multiplex OFDM signal is characterized in that, may further comprise the steps:

A, be that the ofdm signal of N carries out frequency displacement to length, make the frequency of the signal of required taking-up wherein in the filter range of filter, wherein N is the original ofdm signal length that receives;

B, be that the ofdm signal of N carries out filtering to the length after the frequency displacement;

C, be that the ofdm signal of N extracts to filtered length, extraction yield is L=N/M, obtains the time-domain signal that length is M, and wherein M equals 2 ⁿAnd more than or equal to N _PMinimum number, n is a positive integer, N _PThe orthogonal sub-carriers number of the frequency-region signal that takes out for needs, N＞M＞N _P

D, be that the time-domain signal of M carries out the discrete Fourier transform (DFT) DFT that M is ordered to length, obtain comprising the frequency-region signal of M orthogonal sub-carriers, the setting frequency domain position according to the signal of required taking-up takes out N from the frequency-region signal that comprises M orthogonal sub-carriers _PThe frequency-region signal of individual orthogonal sub-carriers;

Wherein, the described low-pass filtering that is filtered into of step B adopts wave digital lowpass filter, and the frequency response of described wave digital lowpass filter is $H\left(e^{\mathrm{j\&omega;}}\right)=\left\{\begin{array}{cc}\sqrt{L}& 0\&le;\left|\mathrm{\&omega;}\right|\&le;\frac{N^{\&prime;}}{N}\mathrm{\&pi;},\\ 0& \end{array}\right.$ Wherein N ' is N _pAn and integer between the M.

2. the method for reseptance of ofdm signal as claimed in claim 1 is characterized in that, further comprises before the described steps A:

Go cyclic prefix CP to handle to the ofdm signal that receives, obtain the ofdm signal that length is N.

3. the method for reseptance of ofdm signal as claimed in claim 1 or 2 is characterized in that, the frequency shift amount of the described frequency displacement of steps A is k=N ₀/ 2-k ₀-N _p/ 2, N wherein ₀Be effective subcarrier number, k ₀Frequency domain original position for the orthogonal sub-carriers of the ofdm signal of required taking-up.

4. the method for reseptance of ofdm signal as claimed in claim 1 or 2 is characterized in that, the method for the described extraction of step C extracts M point altogether for being to extract the locational point of integral multiple that is positioned at extraction yield L in the ofdm signal of N in length.

5. the receiving system of an orthogonal frequency division multiplex OFDM signal is characterized in that, this device comprises:

Frequency shift unit is that the ofdm signal of N carries out frequency displacement to length, makes the frequency of the signal of required taking-up wherein in the filter range of filter, and the signal after the frequency displacement is outputed to filter unit, and wherein N is the original ofdm signal length that receives;

Filter unit, the signal after the frequency displacement of reception frequency shift unit output carries out filtering and filtered signal is outputed to extracting unit it;

Extracting unit, the filtered signal of the unit output of accepting filter also extracts it, and extraction yield is L=N/M, obtains time-domain signal that length is M and it is outputed to discrete Fourier transform (DFT) DFT unit, and wherein M equals 2 ⁿAnd more than or equal to N _PMinimum number, n is a positive integer, N _PThe orthogonal sub-carriers number of the frequency-region signal that takes out for needs, N＞M＞N _P

The DFT unit, the length that receives extracting unit output is the time-domain signal of M and it is carried out the DFT that M is ordered, obtain comprising the frequency-region signal of M orthogonal sub-carriers, the setting frequency domain position according to the signal of required taking-up takes out N from the frequency-region signal that comprises M orthogonal sub-carriers _PThe frequency-region signal of individual orthogonal sub-carriers;

Wherein, described filter unit carries out low-pass filtering, adopts wave digital lowpass filter, and the frequency response of described wave digital lowpass filter is $H\left(e^{\mathrm{j\&omega;}}\right)=\left\{\begin{array}{cc}\sqrt{L}& 0\&le;\left|\mathrm{\&omega;}\right|\&le;\frac{N^{\&prime;}}{N}\mathrm{\&pi;},\\ 0& \end{array}\right.$ Wherein N ' is N _pAn and integer between the M.

6. the receiving system of ofdm signal as claimed in claim 5 is characterized in that, further comprises in the described device:

Go to the cyclic prefix CP unit, receive ofdm signal and remove the CP of its original position, obtain the ofdm signal that length is N.

7. as the receiving system of claim 5 or 6 described ofdm signals, it is characterized in that the frequency shift amount of described frequency shift unit is k=N ₀/ 2-k ₀-N _p/ 2, N wherein ₀Be effective subcarrier number, k ₀Frequency domain original position for the orthogonal sub-carriers of the ofdm signal of required taking-up;

Or,

Described extracting unit is to extract the locational point of integral multiple that is positioned at extraction yield L in the ofdm signal of N in length, extracts M point altogether.

8. as the receiving system of claim 5 or 6 described ofdm signals, it is characterized in that described frequency shift unit, filter unit, extracting unit and DFT unit are arranged in baseband processing unit BBU.

9. the receiving system of ofdm signal as claimed in claim 6 is characterized in that, the described cyclic prefix CP unit that goes is arranged in radio frequency remoto module RRU.

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