CN102833207A - Channel measuring method and channel measuring device applied to OFDM (Orthogonal Frequency Division Multiplexing) system - Google Patents

Abstract

The invention discloses a channel measuring method and a channel measuring device applied to an OFDM (Orthogonal Frequency Division Multiplexing) system. The effective channel measurement is completed by combining the characteristics of the OFDM system. The channel measuring method comprises the steps of a, carrying out FFT (Fast Fourier Transform) preprocessing on a pseudorandom sequence which is used for measuring, filling the processed sequence to an OFDM symbol of a specific location, and forming a complete time slot by the OFDM symbol and other OFDM symbols in the same time slot; b, converting the time slot into a time domain signal through processing procedures such as IFFT (Inverse Fast Fourier Transform) and parallel-to-serial transform of the OFDM system, carrying out radio frequency processing on the time domain signal, and then transmitting the time domain signal; and c, completing the synchronization by a receiving end and a transmitting end, completing the effective capture of a measuring signal in a corresponding time slot, detecting a correlation peak by adopting the method of sliding correlation detection, and using the correlation peak for researching the channel characteristics. According to the channel measuring method disclosed by the invention, the channel measurement of the OFDM system is realized, a transmitting device is not needed to be additionally introduced, the cost and the complexity of measuring are greatly reduced, and the interference on a business channel due to the measuring process is reduced at the same time.

Description

A kind of channel measuring method and device that is applied to ofdm system

Technical field

The present invention relates to the wireless mobile communications field, relate to a kind of channel measuring method and device that is applied to ofdm system.

Background technology

OFDM (Orthogonal Frequency Division Multiplexing abbreviates OFDM as) is a kind of multi-carrier modulation technology.OFDM is technological to be that a plurality of parallel rate data streams that frequency spectrum overlaps is sent with data stream modulates at a high speed, owing to the phenomenal growth of OFDM symbol period, has therefore improved the ability of OFDM symbol anti-multipath time delay; And, through adding protection at interval, can eliminate the intersymbol interference that multidiameter delay causes fully at OFDM symbol front end, simplified the equilibrium of receiving terminal; In addition, the OFDM technology has improved spectrum efficiency greatly owing to used the overlapping frequency spectrum of quadrature.The above-mentioned advantage of OFDM is widely used it in the new generation broadband wireless communication system.

The method of measurement of wireless channel mainly contains direct impulsive measurement, frequency domain channel is measured and spread spectrum slip measurement of correlation.Directly the performance of impulsive measurement receives to disturb with noise effect serious; The frequency domain channel measurement needs the sending and receiving end that precise time location and strict synchronism are arranged, and is not suitable for the measurement time varying channel; The band spectrum modulation characteristic of spread spectrum slip measurement of correlation method is can the filtering band logical to be disturbed, and can be to use method comparatively widely during multipath channel is measured through increasing the temporal resolution that the code check of measuring sequence improve multipath component.

The basic thought of spread spectrum slip coherent detection is to utilize the sharp-pointed autocorrelation performance of pseudo random sequence (PN sequence), reaches the purpose that detects each footpath signal amplitude of channel and time delay.When channel measurement, transmitting terminal sends the PN sequence, and through behind the channel, receiving terminal carries out related operation with signal that receives and local PN sequence (identical with the PN sequence that transmitting terminal sends).The local PN sequence that receiving terminal produces is slided, and when two PN sequence complete matchings, can obtain maximum correlation value, is the time delay of multipath component the time of delay that at this moment obtains.Because the time delay that different multipaths arrive is different, they reach maximal correlation in the different moment with local PN sequence respectively, so just can obtain the impulse response sample from the relevant result of receiving terminal slip, are used for the research of the characteristic of channel.

In the actual measurement process,, need specific transmitter to come the emission measurement signal if according to traditional spread spectrum slip relevant measurement method.But at special screnes such as railway, highway are along the line, it is bigger to be not easy to extra introducing transmitter or quantities, is difficult for carrying out.Under these scenes; For simplified measurement process as much as possible on the basis that guarantees the measuring-signal stable transfer; Can be through in existing communication system, adding required measuring-signal, and accomplish the extracting of measuring-signal at receiving terminal, thereby under the prerequisite of not extra increase transmitter; Utilize existing communication system, realize measurement the characteristic of channel.

Yet, in ofdm communication system, adopted orthogonal frequency division multiplexi, become the subchannel of some quadratures, high-speed data signal to be converted into parallel low speed sub data flow channel distribution and on each subchannel, transmit.In the ofdm communication system of reality; General through the conversion of FFT conversion realization data-signal from the time domain sequences to the frequency domain sequence; Transmit and directly to carry the time domain sequences of measuring-signal, so can't directly carry out channel measurement with spread spectrum slip measurement of correlation method.

Summary of the invention

Deficiency to prior art; The purpose of this invention is to provide a kind of time domain measurement scheme to ofdm communication system; Be applicable to extra introducing transmitter comparatively difficulty or the higher scene of cost; Effectively utilize existing ofdm communication system, under the prerequisite that does not increase transmitter, accomplish channel measurement, obtain channel information.

For achieving the above object, the present invention proposes a kind of processing method of in ofdm system transmits, inserting the time domain measurement sequence information and based on the testing apparatus of this method.The time domain measurement sequence that is used for channel measurement can be regarded as a kind of special bursty traffic, and the OFDM symbol of assigned address does not influence the transmission of normal flow in the complete filler timeslot, and a kind of possible situation is as shown in Figure 1.The present invention comprises following content:

Time domain measurement scheme to ofdm communication system is following:

A. the PN sequence that is used to measure is carried out the FFT preliminary treatment, the sequence after handling is filled to the OFDM symbol of assigned address, the OFDM symbol occupied with the ofdm system data flow separates in time, and constitutes complete time slot with other OFDM symbols with time slot;

B. pass through the handling processes such as IFFT conversion, parallel serial conversion, insertion Cyclic Prefix, digital to analog conversion of ofdm system, be converted into time-domain signal, carry out radio frequency processing and emission;

C. receiving terminal and transmitting terminal are accomplished clock synchronization, in corresponding time slot, accomplish effective extracting of measuring-signal, and detect relevant peaks through the method for slip coherent detection, are used for the research of the characteristic of channel.

The PN sequence that is used to measure adopts the Gold sequence of brachymemma.If the Gold sequence of brachymemma is a (n), a (n) is carried out basic 2-FFT conversion, can time domain sequences a (n) be transformed to frequency domain sequence A (k), the expression formula of a (n) being carried out the FFT conversion is:

$\left(n\right)\underset{n=0}{\overset{N-1}{\mathrm{\Σ}}}\left(n\right)e^{-j2\mathrm{\π}\frac{\mathrm{kn}}{N}}=A\left(k\right)$ k＝0，1，…，N-1

The process of filling the OFDM symbol with data flow is identical, and A (k) is filled to earlier in the OFDM symbol of appointment, carries out basic 2-IFFT conversion then.In a time slot, the OFDM character position that A (k) is corresponding is fixed.The expression formula of A (k) being carried out the IFFT conversion is:

$\mathrm{IFFT}\left[A\left(k\right)\right]N=\frac{1}{N}\underset{k=0}{\overset{N-1}{\mathrm{\Σ}}}A\left(k\right)e^{j2\mathrm{\π}\frac{\mathrm{kn}}{N}}=a\left(n\right)$ n＝0，1，…，N-1

Can find out from above-mentioned formula; The measuring-signal that comprises in the last transmission signal partly is exactly the brachymemma Gold sequence that is produced; This section sequence is to send continuously in sending signal; Therefore only need confirm this section sequence position and extract at receiving terminal, handling process such as it is relevant just can to slide.

The handling process of transmitting terminal is done following some explanation:

Inserting the FFT preprocessing process that increases before the brachymemma Gold sequence; Count corresponding with the IFFT process in the ofdm communication system; Can guarantee like this after the influence that balances out IFFT; The signal that outputs to radio-frequency front-end is identical with FFT preliminary treatment sequence before, for being used for the time domain sequences of channel measurement.

For the original data stream of ofdm communication system, still according to the original flow processing of system.

The handling process of receiving terminal is done following some explanation:

Receiving terminal can adopt universal measurement equipment such as VSA, need not possess functions such as demodulation in the ofdm system, FFT conversion.The major function of receiving terminal is the time synchronized of completion and transmitting terminal; And carry out the processing of radio-frequency front-end; Downconvert to intermediate frequency to signal, in corresponding time slot, carry out data and grasp, and the data that grasp are stored; Later stage realizes that through software it is relevant with the slip of local sequence, obtains the channel impulse response sample.

Receiving terminal need not handled the data that grasp in real time, but it is relevant in the later stage data that grasp and known local Gold sequence to be slided, and detects relevant peaks, to obtain channel impulse response.

The means for channel measurement that is applied to ofdm system that the embodiment of the invention is used comprises:

Sending module is used to generate required Gold sequence, and it is done basic 2-FFT conversion, is filled in the OFDM symbol, after ovennodulation and radio frequency processing, launches;

Receiver module, major function are the time synchronized of completion and transmitting terminal, and carry out the processing of radio-frequency front-end, downconvert to signal and can handle intermediate frequency, after the intermediate frequency filtering it are sampled and the store sampled result;

Processing module, the particular time-slot fetched measuring-signal from the intermediate-freuqncy signal after the sampling to this signal relevant treatment of sliding, obtains the result and is used for later stage characteristic of channel research.

Description of drawings

Fig. 1 is a filling sketch map of measuring sequence in the OFDM symbol;

A kind of system block diagram that is applied to the channel measuring method of ofdm system that Fig. 2 provides for the embodiment of the invention;

Fig. 3 is the generative process sketch map of Gold sequence;

Fig. 4 is the autocorrelogram of brachymemma Gold sequence;

Fig. 5 utilizes ofdm system to carry out the analogous diagram as a result of channel measurement;

The means for channel measurement structural representation that is used to realize being applied to ofdm system that Fig. 6 provides for the embodiment of the invention.

Embodiment

To combine accompanying drawing and specific embodiment that the present invention is done further explain below.

Transmitting-receiving two-end is set up synchronously, is to utilize ofdm system to accomplish the necessary condition of channel measurement.Can guarantee that synchronously receiver finds the position of inserting the Gold sequence in transmitting exactly, and in an OFDM symbol, accomplish effective extracting of data.Consider the influence of synchronous precision, the time of can the proper extension data grasping is so that adopt the method for slip relevant search relevant peaks to seek the Gold sequence that is used for channel measurement in the later stage.

Shown in Fig. 2 communication system block diagram, transmitting terminal produces the Gold truncated sequence that is used to measure.The Gold sequence is a kind of pseudo random sequence that is gone out by m sequential derivation, is to be made up of preferably displacement mould two being added of m sequence, has the anti-forge random property that is similar to the m sequence, often be applied in the Modern Communication System, and be a kind of pseudo random sequence commonly used.As shown in Figure 3; At first produce two m sequences that length is identical respectively through two shift registers; These two sequences satisfy preferred right requirement; Then these two sequences are carried out mould two and add the Gold sequence that promptly obtains an equal length, the shift register among Fig. 3 is 31, and the m sequence length that therefore generates is 2 ³¹-1, corresponding Gold sequence length also is 2 ³¹-1.The short sequence of one section Len req of intercepting continuously from this segment length's sequence is as measuring sequence.The multi-carrier modulation part of the transceiver of current ofdm system has mainly adopted basic 2-FFT/IFFT module, and therefore in the present invention, the length of truncated sequence is chosen for 2 integral number power, so that carry out basic 2-FFT conversion process.Here the intercepting code length is that a string code word of 1024 is as measuring sequence.The Gold sequence of this section brachymemma still has good autocorrelation.

Fig. 4 is the autocorrelation performance figure of the brachymemma Gold sequence of code length 1024, in the slip correlated process, when sequence alignment, reaches maximum related value, promptly detects relevant peaks, and when sequence was not alignd, correlation was very little, can regard noise as.Therefore can use this sequence to carry out channel measurement according to the channel measurement principle of introducing before.

According to shown in Figure 2, after brachymemma Gold sequence generates, need carry out preliminary treatment to it, be filled to the OFDM symbol of assigned address then.At first sequence is done 1024 basic 2-FFT conversion; According to the FFT principle; Can obtain one 1024 frequency domain sequence,, be filled into the sequence after the conversion in the OFDM symbol of appointment afterwards according to structure shown in Figure 1; The position of this symbol in whole transmitting sequence time slot fixed, with the complete time slot of the common formation of other OFDM symbols with time slot.

According to OFDM digital modulation principle; Each OFDM symbol in the above-mentioned time slot need carry out the process that relates in the OFDM modulated processs such as IFFT processing, parallel serial conversion respectively; In inserting Cyclic Prefix (CP) process; Last several sample values of each OFDM symbol are copied to the sequence front end, form prefix, the length of Cyclic Prefix should be greater than the maximum additional time delay of channel to be measured.

At receiving terminal; Accomplish after the clock synchronization; Measuring-signal is extracted in the position of the measurement sequence of filling according to transmitting terminal from receive signal; Again this section measuring-signal is done relevant treatment, concrete operations are: at first remove the cyclic prefix portion branch and obtain useful information, do circulation slip relevant treatment with the local brachymemma Gold sequence identical with transmitting terminal and this measurement sequence that produces then.Receive the influence of multipath channel, the slip correlated results can obtain a plurality of peak values.As shown in Figure 5; Each peak value is represented a footpath in the channel impulse response; Its amplitude square be the gain in this footpath; The time difference in each bar footpath and first footpath is the relative time delay in this footpath, and the multi-path resolved rate of this mode measurement result is influenced by the sample rate f s of transmitter multi-carrier modulation module mainly, promptly multi-path resolved rate Δ τ=2/f _s

The embodiment of the invention also provides realization to be applied to the device of the channel measuring method of ofdm system, and as shown in Figure 6, this device comprises transmitter module, receiver module and processing module.

Sending module is used to generate required Gold sequence, then it is done basic 2-FFT conversion, is filled in the OFDM symbol, does the signal modulation afterwards, radio frequency processing and emission;

Receiver module, major function are synchronous with the transmitting terminal deadline, and carry out the processing of radio-frequency front-end, downconvert to signal and can handle intermediate frequency, after the intermediate frequency filtering it are sampled and the store sampled result;

Processing module, the particular time-slot fetched measuring-signal from the intermediate-freuqncy signal after the sampling to this signal relevant treatment of sliding, obtains the result and is used for later stage characteristic of channel research.

The sending module of said apparatus comprises that sequence generates submodule, signal modulation submodule and radio frequency submodule.

Sequence generates submodule, is used for generating the Gold sequence that is filled to the OFDM symbol, and this section sequence is carried out basic 2-FFT conversion;

Signal modulation submodule; Be filled to Gold sequence in the OFDM symbol through basic 2-FFT conversion; Simultaneously the data normal filling of needs transmission to other OFDM symbols; This group OFDM symbol is carried out basic 2-IFFT conversion, parallel serial conversion, insertion Cyclic Prefix and digital-to-analogue conversion, generate the intermediate-freuqncy signal of emission in advance;

The radio frequency submodule carries out up-conversion and power amplification to modulated signal, accomplishes the emission of modulation signal.

When receiving signal, the receiver module of said apparatus comprises that clock synchronization submodule and signal receive submodule.

The clock synchronization submodule is used to realize the clock synchronization of receiving terminal and transmitting terminal, thereby can confirm the time slot position of measuring-signal in whole reception signal;

Signal receives submodule, after clock synchronization, downconverts to intermediate frequency, intermediate frequency filtering to received signal except that denoising, carries out analog-to-digital conversion and store sampled result to the intermediate-freuqncy signal of filtering output.

After obtaining to remove the reception signal of noise, carry out handled to obtain channel impulse response to this signal, the processing module of this device comprises that information extraction submodule, local sequence generate submodule and slip relevant sub-module.

The information extraction submodule, the time slot position that the measuring-signal of confirming according to clock synchronization belongs to, the particular time-slot fetched from the intermediate-freuqncy signal after the sampling is measured sequence, extracts the length of length for the Gold sequence of generation;

Local sequence generates submodule, generates the brachymemma Gold sequence identical with transmitting terminal, is used for that to do slip relevant with the measurement sequence that receives;

Slip relevant sub-module, the measurement sequence that generates Gold sequence that submodule generates and extraction with the local sequence coherent detection relevant peaks of sliding obtains the result and is used for the subsequent communication channel characteristic research.

Obviously, those skilled in the art can change with modification the present invention and not break away from the spirit and scope of the present invention.If change of the present invention and modification are belonged within the scope of claim of the present invention and equivalent technologies thereof, then the present invention also be intended to comprise these change and modification interior.

Claims (9)

1. a channel measuring method that is applied to ofdm system is characterized in that, said channel measuring method comprises:

A. the pseudo random sequence that is used to measure is carried out the FFT preliminary treatment; Sequence after handling is filled to the OFDM symbol of assigned address; The OFDM symbol occupied with the ofdm system data flow separates in time, and constitutes complete time slot with other OFDM symbols with time slot;

B. pass through the handling processes such as IFFT conversion, parallel serial conversion, insertion Cyclic Prefix, digital to analog conversion of ofdm system, be converted into time-domain signal, carry out radio frequency processing and emission;

C. receiving terminal and transmitting terminal are accomplished clock synchronization, in corresponding time slot, accomplish effective extracting of measuring-signal, and detect relevant peaks through the method for slip coherent detection, are used for the research of the characteristic of channel.

2. according to the described channel measuring method that is applied to ofdm system of claim 1; It is characterized in that the described pseudo random sequence of step a is one section brachymemma Gold sequence, has good autocorrelation; Sequence length is 2 integral number power, can realize the complete filling of OFDM symbol.

3. according to the described channel measuring method that is applied to ofdm system of claim 1, it is characterized in that the described sequence fill method of step a is: time domain sequences is done basic 2-FFT conversion, be filled to the sequence after handling the OFDM symbol of assigned address.

4. according to the described method of claim 3; It is characterized in that; Sequence in the described assigned address OFDM symbol can intactly be reduced into the time domain sequences that is used to measure through basic 2-IFFT conversion, and its time-domain position is always fixing time slot position, does not influence the transfer of data of ofdm communication system.

5. according to the described channel measuring method that is applied to ofdm system of claim 1; It is characterized in that; Do not need independent emission measurement signal in the measuring process, need not extra introducing emitter, only need in the transmission signal of former ofdm system, to insert one section and measure sequence; Can not impact normal data transfer, whole measuring process can not brought interference to Traffic Channel yet; The sequence insertion position that receiving terminal is set according to transmitting terminal is accomplished the extraction of measuring-signal and is done subsequent treatment.

6. a means for channel measurement that is applied to ofdm system is characterized in that, described means for channel measurement comprises:

Sending module is used to generate required Gold sequence, and it is done basic 2-FFT conversion, is filled in the OFDM symbol, does the signal modulation afterwards, radio frequency processing and emission;

Receiver module, major function are to accomplish synchronously with transmitting terminal, and carry out the processing of radio-frequency front-end, downconvert to signal and can handle intermediate frequency, after the intermediate frequency filtering it are sampled and the store sampled result;

Processing module, the particular time-slot fetched measuring-signal from the intermediate-freuqncy signal after the sampling to this signal relevant treatment of sliding, obtains the result and is used for later stage characteristic of channel research.

7. according to the described means for channel measurement that is applied to ofdm system of claim 6, it is characterized in that said sending module comprises:

Sequence generates submodule, is used for generating the Gold sequence that is filled to the OFDM symbol, and this section sequence is carried out basic 2-FFT conversion;

Signal modulation submodule; Be filled to Gold sequence in the OFDM symbol through basic 2-FFT conversion; Simultaneously the data normal filling of needs transmission to other OFDM symbols; This group OFDM symbol is carried out basic 2-IFFT conversion, parallel serial conversion, insertion Cyclic Prefix and digital-to-analogue conversion, generate the intermediate-freuqncy signal of emission in advance;

The radio frequency submodule carries out up-conversion and power amplification to modulated signal, accomplishes the emission of modulation signal.

8. according to the described means for channel measurement that is applied to ofdm system of claim 6, it is characterized in that said receiver module comprises:

The clock synchronization submodule is used to realize the clock synchronization of receiving terminal and transmitting terminal, thereby can confirm the time slot position of measuring-signal in whole reception signal;

Signal receives submodule, after clock synchronization, downconverts to intermediate frequency, intermediate frequency filtering to received signal except that denoising, carries out analog-to-digital conversion and store sampled result to the intermediate-freuqncy signal of filtering output.

9. according to the described means for channel measurement that is applied to ofdm system of claim 6, it is characterized in that described processing module comprises:

The information extraction submodule, the time slot position that the measuring-signal of confirming according to clock synchronization belongs to, the particular time-slot fetched from the intermediate-freuqncy signal after the sampling is measured sequence, extracts the length of length for the Gold sequence of insertion;

Local sequence generates submodule, generates the brachymemma Gold sequence identical with transmitting terminal, is used for that to do slip relevant with the measurement sequence that receives;

Slip relevant sub-module, the measurement sequence that generates Gold sequence that submodule generates and extraction with the local sequence coherent detection relevant peaks of sliding obtains the result and is used for the subsequent communication channel characteristic research.

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