CN101083515A - Channel estimation method and apparatus for OFDM of transmission diversity - Google Patents

Abstract

The invention provides an equipment and method for channel estimate of Orthogonal Frequency Division Multiplexing, which using the principle that the linear system doesn't change the response form for the complex exponent signal. Insert the complex exponent form in each frame of time domain's pilot frequency block data. Using the estimate technology and FFT processing obtain OFDM channel frequency range coefficient in a data frame. And stagger the position between each launch - receiving antenna link in the time. The pilot frequency data has the permanent enveloping characteristic in the time domain. The OFDM channel has good estimate precision by using average noise reduction processing. The entire channel installment also has low computation complexity.

Description

A kind of channel estimation methods of OFDM of transmit diversity and device

Technical field

The present invention relates to signal of communication processing method and device, particularly channel estimation methods and the device of a kind of OFDM of transmit diversity (OFDM).

Background technology

Need to provide the high speed data transfer ability in the future mobile communication system, OFDM can convert the frequency selectivity wireless channel to one group of parallel frequency flatness fading channel, make each subchannel can utilize simple single tap just can realize effective channel equalization, simultaneously, the bandwidth of each subchannel narrows down, make the duration of call sign elongated, use circulation prefix processing just can eliminate intersymbol interference.Therefore the OFDM technology has obtained increasingly extensive application in fields such as broadband wireless access WLAN and WiMAX, digital video transmission DVB-T and DMB DMB.

Diversity is a kind of effectively to the anti fading technology in radio communication, and the Space Time Coding technology of present development is implementation space, time and frequency diversity effectively, has very high code efficiency, and improves the reliability of whole transmission system.But decoding needs channel parameter information accurately when empty, estimate for the OFDM wireless transmission channel that has transmit diversity techniques, since estimate an antenna link between channel parameter in, can be subjected to simultaneously other transmit receive antenna links between interference, therefore signal to noise ratio is very low when estimating, is difficult to realize high-precision channel estimating.Usual way is when the frequency domain data of transmitting terminal is multiplexing, insert the pilot data of particular design at the diverse location of different antennae, the attenuation pilot data afterwards that each send-receive antenna link of process that makes receiving terminal receive is right can stagger on frequency domain mutually, thereby finish each antenna link between the estimation of channel parameter, can make emission time domain waveform peak-to-average power ratio be difficult to control but insert pilot tone, therefore select time domain pilot insertion technology to have than the better peak-to-average power ratio gain of pilot tone insertion technology at frequency domain.

Summary of the invention

The channel estimation methods of a kind of transmit diversity OFDM provided by the invention and device, be used for from the time domain pilot data block of receiving terminal estimate each emission, reception antenna link between the frequency domain channel parameter, keep having the peak-to-average power ratio of time domain emission preferably performance simultaneously.

In order to achieve the above object, the invention provides the channel estimation methods of a kind of transmit diversity OFDM, comprise following steps:

Step 1, the two-way modulating data of transmitting terminal is handled, obtained time domain valid data X _Di, (i=1,2);

Step 1.1, the two-way modulating data of transmitting terminal is gone here and there in serial-parallel conversion circuit and change;

Step 1.2, the data of step 1.1 output are carried out Space Time Coding handle in the Space Time Coding device;

Step 1.3, the two-way output signal of step 1.2 output is carried out N point IFFT (invert fast fourier transformation) computing respectively, obtain time domain valid data X _D1And X _D2Wherein, N represents the number of the subcarrier of OFDM data, and N point FFT is the mode that realizes the OFDM modulation technique;

Step 2, pilot data generation unit produce the needed time domain pilot data block of two transmit antennas vector simultaneously:

X _P=[exp (j*2 π * B*0* (0:1:L+K-1)/N) L exp (j*2 π * B*k* (0:1:L+K-1)/N) L] _{1 * b}, wherein, B is the subcarrier in frequency domain sampling interval of OFDM data, and L is the length of Cyclic Prefix, and b is that the time domain sample in the OFDM piece is counted, and K is average noise reduction length, and the value of K must satisfy (L+K) * B=b, and j represents complex signal $j=\sqrt{-1},$ N represents the number of OFDM data sub-carriers, and k represents natural number, and 0:1:L represents that excursion is from 0 to L, and step-length is 1;

Step 3, the time domain valid data X that respectively step 1 is obtained _D1And X _D2The time domain pilot data block vector X that obtains with step 2 _PSend into the pilot tone and the valid data time-domain multiplexed unit i of corresponding transmitting terminal separately, i=1,2, on time domain with X _PMultiplexing in the different time position of corresponding transmitting antenna, form corresponding Frame:

In pilot tone and valid data time-domain multiplexed unit 1, first data block of each frame of Frame is inserted time domain pilot data block vector X _P, second data block of each frame inserts zero, and all data blocks in back are all directly inserted valid data X _D1

In pilot tone and valid data time-domain multiplexed unit 2, second data block of each frame of Frame inserted time domain pilot data block vector X _P, first data block of each frame inserts zero, and all data blocks in back are all directly inserted valid data X _D2

The two paths of data frame of step 4, correspondence that step 3 is obtained adds circulation prefix processing, a back L data that are about to each OFDM Frame copy to the front of each Frame, after forming enough protections at interval, the two paths of data that obtains is launched from different transmitting antennas respectively;

Step 5, the signal of receiving on the receiving terminal antenna is gone circulation prefix processing, the front L of each symbol of the signal that is about to receive data are removed;

Step 6, the data that step 5 is obtained are sent into pilot tone and data demultiplexing unit and are carried out demultiplexing and handle, insertion position according to pilot tone in the step 3 and valid data separates pilot data and the valid data that receive, and obtains corresponding pilot data Y between each corresponding emission, the reception antenna link _Pi(i=1,2) and valid data Y _D, to valid data Y _DCarrying out N point FFT frequency domain interpolation handles;

Step 7, with pilot data Y _P1And Y _P2Send into time domain least square channel estimating apparatus, obtain the channel frequency domain parameter on all OFDM sub-carrier positions

Step 7.1, least-squares estimation unit at first estimate the channel frequency domain parameter of initial OFDM subcarrier sample position ${\hat{H}}_{\mathrm{Pi}}^{\′}={X_P}^H{Y}_{\mathrm{Pi}},(i=\mathrm{1,2}),$ X _pBe the reference pilot data block vector that obtains in the step 2, H representative carrying out conjugate transpose computing;

Step 7.2, losing dirty noise reduction processing unit will

The front L value of every group of L+K channel estimation value lose;

Step 7.3, lose dirty noise reduction processing unit to every group

The K of a back estimated value averages noise reduction process, obtains corresponding channel frequency domain parameter on each sampling subcarrier

Step 7.4, IFFT circuit utilize IFFT to incite somebody to action

Transform to time domain, obtain

Step 7.5, tap coefficient acquiring unit are right according to the tap watt level

Sort, select L wherein maximum tap coefficient then, find L important time domain tap parameter

Step 7.6, FFT frequency domain interpolation circuit are to this L important time domain tap

After filling N-L individual zero, carry out N point FFT frequency domain interpolation and handle, obtain the channel frequency domain parameter on all OFDM sub-carrier positions

Step 8, will handle the valid data Y that obtains through pilot tone and valid data demultiplexing unit _DWith the channel frequency domain parameter of estimating to obtain

Decoding is handled when carrying out sky in the decoder when sky;

Step 9, the data that step 8 is obtained are carried out in parallel-to-serial converter and are gone here and there conversion, recover and the corresponding modulating data of transmitting terminal.

The present invention also provides the channel estimating apparatus of a kind of transmit diversity OFDM, comprises least-squares estimation unit that circuit successively connects, loses dirty noise reduction processing unit, IFFT circuit, tap coefficient acquiring unit and FFT frequency domain interpolation circuit;

Described least-squares estimation unit is mainly used in from receiving pilot blocks vector Y _Pi, the initial least square channel evaluation data on the sub-carrier positions that obtains in (i=1,2) sampling ${\hat{H}}_{\mathrm{Pi}}^{\′}={X_P}^H{Y}_{\mathrm{Pi}},(i=\mathrm{1,2});$

Describedly lose dirty noise reduction processing unit, be used for from initial least square channel evaluation data

In a front L data of L+K data estimator of every group of channel are lost, the back K data to every group of channel average noise reduction process then;

Described IFFT circuit, be used for

Transform to time domain, obtain

Described tap coefficient acquiring unit is used for N tap data from time domain

In find L important tap coefficient

Just earlier right

Arrange according to watt level, select L wherein maximum tap coefficient then

Described FFT frequency domain interpolation circuit is used for L important time domain tap

Carry out the processing of N point FFT frequency domain interpolation after filling N-L individual zero, obtain the channel frequency domain parameter on all OFDM sub-carrier positions

The present invention utilizes linear system complex exponential signal to be had the principle of invariance of response forms, in each frame structure of time domain, insert the pilot data piece of complex exponential form, and handle at the simple least-squares estimation technology of receiving terminal utilization and FFT and to obtain an OFDM channel frequency coefficient in the Frame, in time each is launched simultaneously a reception antenna link between pilot data piece insertion position stagger, the pilot data of being invented has permanent envelope trait in time domain, average noise reduction process makes the OFDM channel estimating of transmit diversity of the present invention have good estimated accuracy, and the realization of whole channel estimating apparatus also has lower computation complexity.

Description of drawings

Fig. 1 is the flow chart of the channel estimation methods of a kind of transmit diversity OFDM provided by the invention;

Fig. 2 is the pilot tone of channel estimation methods of a kind of transmit diversity OFDM provided by the invention and the frame structure schematic diagram of valid data time-domain multiplexed unit 1;

Fig. 3 is the pilot tone of channel estimation methods of a kind of transmit diversity OFDM provided by the invention and the frame structure schematic diagram of valid data time-domain multiplexed unit 2;

Fig. 4 is the structural representation of the channel estimating apparatus of a kind of transmit diversity OFDM provided by the invention.

Embodiment

Following according to Fig. 1～Fig. 4, specify better embodiment of the present invention:

As shown in Figure 1, the invention provides the channel estimation methods of a kind of transmit diversity OFDM, comprise following steps:

Step 1, the two-way modulating data of transmitting terminal is handled, obtained time domain valid data X _Di, (i=1,2);

Step 1.1, the two-way modulating data of transmitting terminal is gone here and there in serial-parallel conversion circuit and change;

Step 1.2, the data of step 1.1 output are carried out Space Time Coding handle in the Space Time Coding device;

Step 1.3, the two-way output signal of step 1.2 output is carried out N point IFFT (invert fast fourier transformation) computing respectively, obtain time domain valid data X _D1And X _D2

Step 2, pilot data generation unit produce the needed time domain pilot data sequence of two transmit antennas simultaneously:

X _P＝[exp(j*2π*B*0*(0:1:L+K-1)/N)L?exp(j*2π*B*k*(0:1:L+K-1)/N)L] _1×b

, wherein, B is the subcarrier in frequency domain sampling interval of OFDM data, and L is the length of Cyclic Prefix, and b is that the time domain sample in the OFDM piece is counted, and K is average noise reduction length, and the value of K must satisfy (L+K) * B=b, and j represents complex signal $j=\sqrt{-1},$ N represents the number of OFDM data sub-carriers, and k represents natural number, and 0:1:L represents that excursion is from 0 to L, and step-length is 1;

Step 3, respectively with time domain valid data X _D1And X _D2With time domain pilot data X _PSend into the pilot tone and the valid data time-domain multiplexed unit i of corresponding transmitting terminal separately, (i=1,2), on time domain with X _PMultiplexing in the different time position of corresponding transmitting antenna, form corresponding Frame;

A time domain data frame is made up of several data blocks, and each data block comprises several OFDM symbols, and these quantity can be set according to actual service conditions, and the number of data points in each data block is b;

As shown in Figure 2, in pilot tone and the valid data time-domain multiplexed unit 1, first data block of each frame of Frame is inserted pilot data piece X _P, for second emission, reception antenna link between channel estimating separate, second data block of each frame inserts zero, all data blocks in back are all directly inserted valid data X _D1

As shown in Figure 3, in pilot tone and the valid data time-domain multiplexed unit 2, second data block of each frame of Frame inserted pilot data piece X _P, for first emission, reception antenna link between channel estimating separate, it is zero that first data block of each frame is inserted, all data blocks in back are all directly inserted valid data X _D2

The two paths of data frame of step 4, correspondence that step 3 is obtained adds circulation prefix processing, a back L data that are about to each OFDM Frame copy to the front of each Frame, after forming enough protections at interval, the two paths of data that obtains is launched from different transmitting antennas respectively;

Step 5, the signal of receiving on the receiving terminal antenna is gone circulation prefix processing;

Step 6, the data that step 5 is obtained are sent into pilot tone and data demultiplexing unit and are carried out demultiplexing and handle, and obtain corresponding pilot data Y between each corresponding emission, the reception antenna link _Pi(i=1,2) and valid data Y _D, to valid data Y _DCarrying out N point FFT frequency domain interpolation handles;

Step 7, with pilot data Y _P1And Y _P2, send into time domain least square channel estimating apparatus, obtain the channel frequency domain parameter on all OFDM sub-carrier positions

Step 7.1, least-squares estimation unit 101 at first estimate the channel frequency domain parameter of initial OFDM subcarrier sample position ${\hat{H}}_{\mathrm{Pi}}^{\′}={X_P}^H{Y}_{\mathrm{Pi}},(i=\mathrm{1,2})$ , X _pBe reference pilot data block vector, H representative carrying out conjugate transpose computing;

Step 7.2, losing dirty noise reduction processing unit 102 will

The front L value of every group of L+K channel estimation value lose;

Step 7.3, lose 102 pairs every group of dirty noise reduction processing unit

The K of a back estimated value averages noise reduction process, obtains corresponding channel frequency domain parameter on each sampling subcarrier

Step 7.4, IFFT circuit 103 utilize IFFT to incite somebody to action Transform to time domain, obtain

Step 7.5, tap coefficient acquiring unit 104 are right according to the tap watt level

Sort, L wherein maximum tap coefficient selected in the back, finds L important time domain tap parameter

Step 7.6, FFT frequency domain interpolation circuit 105 are to this L important time domain tap

After filling N-L individual zero, carry out N point FFT frequency domain interpolation and handle, obtain the channel frequency domain parameter on all OFDM sub-carrier positions

Step 8, will handle the valid data Y that obtains through pilot tone and valid data demultiplexing unit _DWith the channel frequency domain parameter of estimating to obtain

Decoding is handled when carrying out sky in the decoder when sky;

Step 9, the data that step 8 is obtained are carried out in parallel-to-serial converter and are gone here and there conversion, recover and the corresponding modulating data of transmitting terminal.

As shown in Figure 4, the present invention also provides the channel estimating apparatus of a kind of transmit diversity OFDM, comprises least-squares estimation unit 101 that circuit successively connects, loses dirty noise reduction processing unit 102, IFFT circuit 103, tap coefficient acquiring unit 104 and FFT frequency domain interpolation circuit 105;

Described least-squares estimation unit 101 is mainly used in from receiving pilot blocks vector Y _Pi, the initial least square channel evaluation data on the sub-carrier positions that obtains in (i=1,2) sampling ${\hat{H}}_{\mathrm{Pi}}^{\′}={H_P}^H{Y}_{\mathrm{Pi}},(i=\mathrm{1,2});$

Describedly lose dirty noise reduction processing unit 102, be used for from initial least square channel evaluation data By a front L data of L+K data estimator of every group of channel are lost, the back K data to every group of channel average noise reduction process then;

Described IFFT circuit 103, be used for

Transform to time domain, obtain

Described tap coefficient acquiring unit 104 is used for N tap data from time domain

In find L important tap coefficient

Just earlier right

Arrange according to watt level, select L wherein maximum tap coefficient then

Described FFT frequency domain interpolation circuit 105 is used for L important time domain tap

Carry out the processing of N point FFT frequency domain interpolation after filling N-L individual zero, obtain the channel frequency domain parameter on all OFDM sub-carrier positions

The present invention utilizes linear system complex exponential signal to be had the principle of invariance of response forms, in each frame structure of time domain, insert the pilot data piece of complex exponential form, and handle at the simple least-squares estimation technology of receiving terminal utilization and FFT and to obtain an OFDM channel frequency coefficient in the Frame, in time each is launched simultaneously a reception antenna link between pilot data piece insertion position stagger, the pilot data of being invented has permanent envelope trait in time domain, average noise reduction process makes the OFDM channel estimating of transmit diversity of the present invention have good estimated accuracy, and the realization of whole channel estimating apparatus also has lower computation complexity.

Claims (6)

1. the channel estimation methods of a transmit diversity OFDM is characterized in that, comprises following steps:

Step 1, the two-way modulating data of transmitting terminal is handled, obtained time domain valid data X _Di, i=1,2;

Step 2, pilot data generation unit produce the needed time domain pilot data block of two transmit antennas vector simultaneously:

X _P=[exp (j*2 π * B*0* (0: 1: L+K-1)/N) L exp (j*2 π * B*k* (0: 1: L+K-1)/N) L] _{1 * b}, wherein, B is the subcarrier in frequency domain sampling interval of OFDM data, and L is the length of Cyclic Prefix, and b is that the time domain sample in the OFDM piece is counted, and K is average noise reduction length, and the value of K must satisfy (L+K) * B=b, and j represents complex signal $j=\sqrt{-1},$ N represents the number of OFDM data sub-carriers, and k represents natural number, 0: 1: L represents that excursion is from 0 to L, and step-length is 1;

Step 3, the time domain valid data X that respectively step 1 is obtained _D1And X _D2The time domain pilot data X that obtains with step 2 _PSend into the pilot tone and the valid data time-domain multiplexed unit i of corresponding transmitting terminal separately, i=1,2; On time domain with X _PMultiplexing in the different time position of corresponding transmitting antenna, form corresponding Frame;

In pilot tone and valid data time-domain multiplexed unit 1, first data block of each frame of Frame is inserted time domain pilot data block vector X _P, second data block of each frame inserts zero, and all data blocks in back are all directly inserted valid data X _D1

In pilot tone and valid data time-domain multiplexed unit 2, second data block of each frame of Frame inserted time domain pilot data block vector X _P, first data block of each frame inserts zero, and all data blocks in back are all directly inserted valid data K _D2

The two paths of data frame of step 4, correspondence that step 3 is obtained adds circulation prefix processing, a back L data that are about to each OFDM Frame copy to the front of each Frame, after forming enough protections at interval, the two paths of data that obtains is launched from different transmitting antennas respectively;

Step 5, the signal of receiving on the receiving terminal antenna is gone circulation prefix processing, the front L of each symbol of the signal that is about to receive data are removed;

Step 6, the data that step 5 is obtained are sent into pilot tone and data demultiplexing unit and are carried out demultiplexing and handle, insertion position according to pilot tone in the step 3 and valid data separates pilot data and the valid data that receive, and obtains corresponding pilot data Y between each corresponding emission, the reception antenna link _Pi, i=1,2 and valid data Y _D, to valid data Y _DCarrying out N point FFT frequency domain interpolation handles;

Step 7, with pilot data Y _P1And Y _P2Send into time domain least square channel estimating apparatus, obtain the channel frequency domain parameter on all OFDM sub-carrier positions

Step 8, will handle the valid data Y that obtains through pilot tone and valid data demultiplexing unit _DWith the channel frequency domain parameter of estimating to obtain

Decoding is handled when carrying out sky in the decoder when sky;

Step 9, the data that step 8 is obtained are carried out in parallel-to-serial converter and are gone here and there conversion, recover and the corresponding modulating data of transmitting terminal.

2. the channel estimation methods of transmit diversity OFDM as claimed in claim 1 is characterized in that, described step 1 comprises following steps:

Step 1.1, the two-way modulating data of transmitting terminal is gone here and there in serial-parallel conversion circuit and change;

Step 1.2, the data of step 1.1 output are carried out Space Time Coding handle in the Space Time Coding device;

Step 1.3, the two-way output signal of step 1.2 output is carried out the computing of N point, inverse fast Fourier transform respectively, obtain time domain valid data X _D1And X _D2

3. the channel estimation methods of transmit diversity OFDM as claimed in claim 1 is characterized in that, in the described step 2: the value of K satisfies (L+K) * B=b.

4. the channel estimation methods of transmit diversity OFDM as claimed in claim 1 is characterized in that, in the described step 3, the forming process of Frame is:

In pilot tone and valid data time-domain multiplexed unit 1, first data block of each frame of Frame is inserted time domain pilot data block vector X _P, second data block of each frame inserts zero, and all data blocks in back are all directly inserted valid data X _D1

In pilot tone and valid data time-domain multiplexed unit 2, second data block of each frame of Frame inserted time domain pilot data block vector X _P, first data block of each frame inserts zero, and all data blocks in back are all directly inserted valid data X _D2

5. the channel estimation methods of transmit diversity OFDM as claimed in claim 1 is characterized in that, described step 7 comprises following steps:

Step 7.1, first least-squares estimation unit (101) estimate the channel frequency domain parameter of initial OFDM subcarrier sample position earlier ${\hat{H}}_{\mathrm{Pi}}^{\′}={X_P}^H{Y}_{\mathrm{Pi}},$ I=1,2, X _pBe the reference pilot data block vector that step 2 obtains, H representative carrying out conjugate transpose computing;

Step 7.2, will lose dirty noise reduction processing unit (102)

The front L value of every group of L+K channel estimation value lose;

Step 7.3, lose dirty noise reduction processing unit (102) to every group

The K of a back estimated value averages noise reduction process, obtains corresponding channel frequency domain parameter on each sampling subcarrier

Step 7.4, IFFT circuit (103) utilize IFFT to incite somebody to action

Transform to time domain, obtain

Step 7.5, tap coefficient acquiring unit (104) are right according to the tap watt level

Sort, select L wherein maximum tap coefficient then, find L important time domain tap parameter

Step 7.6, FFT frequency domain interpolation circuit (105) are to this L important time domain tap

After filling N-L individual zero, carry out N point FFT frequency domain interpolation and handle, obtain the channel frequency domain parameter on all OFDM sub-carrier positions

6. the channel estimating apparatus of a transmit diversity OFDM, it is characterized in that, comprise least-squares estimation unit (101) that circuit successively connects, lose dirty noise reduction processing unit (102), IFFT circuit (103), tap coefficient acquiring unit (104) and FFT frequency domain interpolation circuit (105).

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