CN1929466A - Orthogonal frequency division multiplexing modulating device and method based on superimposed pilot - Google Patents

Abstract

This invention discloses one cross frequency complex modulation device based on overlapped frequency, which comprises the following parts: OFDM modulation unit to receive data for OFDM modulation to get OFDM data signals; protection isolation plug unit to process plug zero operation on data signals to get OFDM characters; overlap unit to get guide frequency sequence to overlap OFDM characters and guide frequency sequence as certain power proportion, wherein the guide frequency comprises short and long codes; filter unit to output overlapped signals for fitter output base band.

Description

A kind of orthogonal frequency division multiplexing modulating device and method based on superimposed pilot

Technical field

The present invention relates to the digital TV Broadcasting Techniques field, particularly a kind of OFDM (OFDM) modulating device and method based on superimposed pilot.

Background technology

The OFDM modulation is the main modulation system of high-speed radio transmission, and it successfully has been applied in existing several digital television broadcasting system, and this comprises the DVB-T system in Europe, the ISDB-T system of Japan and the DMB-T system of China Tsing-Hua University development.With respect to traditional single-carrier system, the major advantage of ofdm system is that the computation complexity of modulation and demodulation is low, realize easily, and the modulation because The data walks abreast simultaneously, multicarrier system is fit to the transmission of high-speed data.

But in order to obtain good systematic function and spectrum efficiency, ofdm system needs synchronously accurate and channel estimating.The way of three kinds of above-mentioned digital television broadcasting systems is as follows:

(1) DVB-T and ISDB-T system all adopt in data flow and to insert one section known array, and these sequences are called pilot tone, and this pilot tone comprises two kinds of continuous pilot and scattered pilots, are used on frequency domain synchronously and estimate channel.The timing of DVB-T and ISDB-T system mainly depends on the Cyclic Prefix (CP) of OFDM symbol synchronously, determines the time synchronized point by the correlation of utilizing CP and data-signal.Yet the correlation of CP and data-signal is often poor under multipath channel, and this can cause regularly synchronous precision generally also poor.In addition, for channel estimating accurately, need to insert a large amount of pilot tones on frequency domain, have 11% running time-frequency resource to be used for pilot tone as the DVB-T system, this just greatly reduces the spectrum efficiency of system.

(2) main feature of DMB-T system be with the PN sequence replacing CP in the OFDM symbol, we are called the PN head.Because the PN head has good autocorrelation performance, receiver is synchronous as long as simple PN correlator just can obtain high-precision timing fast; Receiver can also be estimated the impulse response of multipath channel on time domain simultaneously, has so just avoided inserting a large amount of pilot tones in data, has improved the spectrum efficiency of system.But because PN head and channel have intimate equal lengths, estimate exactly that channel just needs to collect a large amount of PN heads, that is to say, wait for that receiving a plurality of OFDM symbols just might carry out channel estimating accurately.This not only causes very big processing delay, and Quick-Change channel also can increase channel estimation errors greatly under high-speed mobile environment.

At present, have a kind of OFDM modulator approach based on superimposed pilot (SiP), this method proposed as far back as 1999 and carried out research in theory, and the result shows that SiP can estimate channel faster and more accurately under high-speed mobile environment.But this method all is to consider to insert based on the OFDM prefix modulation system of CP, and the design to the PN sequence does not simultaneously have strict restriction yet, is not enough to embody the superiority of superimposed pilot.

Summary of the invention

In view of this, the object of the present invention is to provide a kind of orthogonal frequency division multiplexing modulating device and method, make it can be under the condition that does not influence spectrum efficiency, regularly synchronously accurately, reduce channel estimation error based on superimposed pilot.

A kind of orthogonal frequency division multiplexing modulating device based on superimposed pilot provided by the invention is achieved in that

A. modulation obtains the OFDM data-signal through OFDM with data, at the front or the increase protection interval, back of this OFDM data-signal, and protection filling zero at interval, obtain the OFDM symbol;

B. described OFDM symbol and the pilot frequency sequence that sets in advance are superposeed according to the certain power ratio on time domain;

Described pilot frequency sequence comprises short code and long code, wherein, short code and one protection equal in length at interval, the equal in length of long code and OFDM data-signal, and during stack, described short code is alignd with the protection interval, and long code is alignd with the OFDM data-signal;

C. obtain baseband transmit signals after the superposed signal that obtains among the step B being filtered by pulse shaping filter.

In the steps A data being modulated the step that obtains the OFDM data-signal through OFDM comprises:

A1, data-signal is carried out serial/parallel conversion;

A2, will carry out inverse-Fourier transform through the parallel data-signal after the serial/parallel conversion;

A3, will be that serial signal obtains the OFDM data-signal through the conversion of signals behind the inverse-Fourier transform.

Protection is expanded greater than the maximum delay of channel at interval in the steps A.

Described long code and short code are to utilize diverse ways to produce, or produce one group of sequence with method of the same race, and this sequence length equals long and short sequence sum, then by the length separated into two parts, respectively as long code and short code.

Short code and long code satisfy auto-correlation and their cross correlation,

When short code is a ₀, a ₁..., a _S-1, and length is s and long code b ₀, b ₁..., b _L-1, when length is L, describedly satisfies desirable autocorrelation performance and be:

${\mathrm{\Σ}}_{n=0}^{s-1}{a}_n{a}_{(n+l)\mathrm{mod}s}=\mathrm{\δ}\left[l\right],l=\mathrm{0,1,2},...s-1$

${\mathrm{\Σ}}_{n=0}^{L-1}{b}_n{b}_{(n+l)\mathrm{mod}L}=\mathrm{\δ}\left[l\right],l=\mathrm{0,1,2},...L-1$

δ [0]=1 wherein, when l ≠ 0, δ [l]=0;

As short code a ₀, a ₁..., a _S-1With long code b ₀, b ₁..., b _L-1The time, describedly satisfy their cross correlation and be:

${\mathrm{\Σ}}_{n=0}^{s-1}{a}_n{b}_{(n+l)\mathrm{mod}L}=0,l=\mathrm{0,1},...,L-1.$

Among the step B according to the certain power ratio be: the average power of pilot tone accounts for and comprises 10%～30% of pilot tone and the total transmitting power of data-signal power.

The signal amplitude of short code and long code is identical or different; And have at the length sign indicating number under the situation of different amplitudes, the short code amplitude is greater than the amplitude of long code.

A kind of orthogonal frequency division multiplexing modulating device based on superimposed pilot provided by the invention is achieved in that

OFDM modulating unit (101), the data that are used for receiving carry out the OFDM modulation and obtain the OFDM data-signal;

The OFDM data-signal that protection zero insertion unit, interval (102) is used for that OFDM modulating unit 100 is obtained carries out the zero insertion operation and obtains the OFDM symbol;

Superpositing unit (103) is used to obtain pilot frequency sequence, the OFDM symbol of zero insertion unit, the interval of self-shield in the future 102 and the pilot frequency sequence that obtains and superposes according to the certain power ratio, described pilot frequency sequence comprises short code and long code, wherein, short code and protection equal in length at interval, the equal in length of long code and OFDM data-signal; During stack, described short code is alignd at interval with protection, and long code is alignd with the OFDM data-signal;

Shaping filter unit (104) carries out filtering output baseband transmit signals to the signal through stack.

Described pilot frequency sequence given in advance is kept in the superpositing unit (103), or has in the physical entity of communication interface with superpositing unit (103).

Described short code and long code satisfy auto-correlation and their cross correlation;

When short code is a ₀, a ₁..., a _S-1, and length is s and long code b ₀, b ₁..., b _L-1, when length is L, describedly satisfies desirable autocorrelation performance and be:

${\mathrm{\Σ}}_{n=0}^{s-1}{a}_n{a}_{(n+l)\mathrm{mod}s}=\mathrm{\δ}\left[l\right],l=\mathrm{0,1,2},...s-1$

${\mathrm{\Σ}}_{n=0}^{L-1}{b}_n{b}_{(n+l)\mathrm{mod}L}=\mathrm{\δ}\left[l\right],l=\mathrm{0,1,2},...L-1$

δ [0]=1 wherein, when l ≠ 0, δ [l]=0;

As short code a ₀, a ₁..., a _S-1With long code b ₀, b ₁..., b _L-1The time, describedly satisfy their cross correlation and be:

${\mathrm{\Σ}}_{n=0}^{s-1}{a}_n{b}_{(n+l)\mathrm{mod}L}=0,l=\mathrm{0,1},...,L-1.$

Described certain power ratio is: the average power of pilot tone accounts for and comprises 10%～30% of pilot tone and the total transmitting power of data-signal power.

The signal amplitude of short code and long code is identical or different; And have at the length sign indicating number under the situation of different amplitudes, the short code amplitude is greater than the amplitude of long code.

OFDM modulating unit (101) comprising:

Serial (201) is used for sending to anti-fast Fourier transform unit (202) to receiving after data-signal carries out serial/parallel conversion;

Anti-fast Fourier transform unit (202), be used for receive carry out inverse-Fourier transform through the parallel data-signal after the serial/parallel conversion after, export parallel/serial converting unit (203) to;

Parallel/serial converting unit (203) is used for exporting to protection zero insertion unit (102) at interval with after being serial signal through the conversion of signals behind the inverse-Fourier transform.

OFDM modulator approach provided by the invention; in the protection at interval of OFDM symbol, fill out 0; superpose on time domain in certain power ratio and continuous, periodic pilot tone then, at last through being used to limit the pulse shaping filter filtering of band to obtain baseband transmit signals.Continuous pilot is made of the continuation of one section special P N sequence period: the PN sequence has the cycle of an OFDM symbol lengths, and the PN sequence of one-period comprises long code and short code, and short code length equals to protect gap length, and long code length equals data length signal.At additive process, short code and protection alignment at interval, long code and data-signal alignment.

For this new O FDM modulation signal, receiver can be undertaken fast synchronously by short code, because short code is not subjected to the interference of OFDM symbol, so synchronized result is accurately.Need to carry out channel estimating synchronously.In order accurately to estimate channel, receiver can intercept the signal of one or several OFDM symbol lengths, carries out the channel estimating of time domain then with the PN sequence in one or several cycles.Channel estimated accuracy depends on the signal length that is intercepted.Therefore, the baseband transmit signals that generates of the present invention helps that receiver is realized fast synchronously and channel estimating accurately.And owing to protection fills 0 at interval, therefore the pilot frequency sequence of stack will not be subjected to the interference of OFDM symbol, and then can improve the speed and the precision of synchronous and channel estimating greatly.

Description of drawings

Fig. 1 is from the present invention is based on the OFDM modulating device structural representation of SiP.

Fig. 2 is for realizing the schematic flow sheet of the inventive method;

Fig. 3 is the signal structure of preceding OFDM symbol of pulse shaping filter and pilot frequency sequence, and wherein ZP is added in the data-signal front.

Fig. 4 is the signal structure of preceding OFDM symbol of pulse shaping filter and pilot frequency sequence, and wherein ZP is added in the data-signal back.

Fig. 5 generates schematic diagram for length/short code.

Embodiment

Core concept of the present invention is: on the basis of superimposed pilot, replace traditional slotting CP mode with zero insertion (ZP); Pilot tone is made up of periodic PN sequence, and the PN sequence is made of long code and short code, and the length of long code short code and signal stacked system all have certain limitation, makes the synchronous and channel estimating of receiver timing rapidly and accurately.

Referring to shown in Figure 1, realize the inventive system comprises OFDM modulating unit 101, zero insertion (ZP) unit 102, superpositing unit 103, shaping filter unit 104.Wherein, OFDM modulating unit 101, the data that are used for receiving are carried out the OFDM modulation and are obtained the OFDM data-signal; The OFDM data-signal that zero insertion unit, protection interval 102 is used for that OFDM modulating unit 101 is obtained carries out the zero insertion operation and obtains the OFDM symbol; Superpositing unit 103 is used to obtain pilot frequency sequence, the OFDM symbol of zero insertion unit, the interval of self-shield in the future 102 and the pilot frequency sequence that obtains and superposes according to the certain power ratio, described pilot frequency sequence comprises short code and long code, wherein, short code and protection equal in length at interval, the equal in length of long code and OFDM symbol; During stack, described short code is alignd long code and OFDM symbol aligned at interval with protection; The 104 pairs of signals through stack in shaping filter unit carry out filtering output baseband transmit signals.

Described pilot frequency sequence is kept in the superpositing unit 103, or has in the physical entity of communication interface with superpositing unit 103.The average power of pilot tone accounts for and comprises 10%～30% of pilot tone and the total transmitting power of data-signal power.And the signal amplitude of short code and long code is identical or different; And have at the length sign indicating number under the situation of different amplitudes, the short code amplitude is greater than the amplitude of long code.

OFDM modulating unit 101 comprises serial 201, anti-fast Fourier transform unit 202, parallel/serial converting unit 203, wherein, serial 201 is used for sending to anti-fast Fourier transform unit 202 to receiving after data-signal carries out serial/parallel conversion; Anti-fast Fourier transform unit 202, be used for receive carry out inverse-Fourier transform through the parallel data-signal after the serial/parallel conversion after, export parallel/serial converting unit 203 to; Parallel/serial converting unit 203 is used for exporting to protection zero insertion unit 102 at interval with after being serial signal through the conversion of signals behind the inverse-Fourier transform.

Referring to shown in Figure 2, based on modulated structure shown in Figure 1, the present invention realizes that the method for modulating may further comprise the steps:

Step 201: modulation obtains the OFDM data-signal to a string data through OFDM earlier.

The process of OFDM modulation comprises: serial/parallel conversion, IFFT modulation and parallel/serial conversion.In order to realize quick inverse-Fourier transform, the progression of IFFT generally equals N=2 ⁿSo the length of data-signal equals N.

Step 202: the data-signal front that obtains in step 201 or back increase protection at interval, and in protection at interval zero insertion (ZP), obtain the OFDM symbol.Protection length at interval is greater than the maximum delay expansion of channel, can avoid the interference between the OFDM symbol that multipath causes like this.

Step 203: will increase the OFDM symbol at protection interval and pilot frequency sequence given in advance and on time domain, superpose.Described pilot frequency sequence comprises short code and long code, wherein, and short code and protection equal in length at interval, the equal in length of long code and OFDM symbol; During stack, described short code is alignd long code and OFDM symbol aligned at interval with protection;

The overlaying structure of OFDM symbol and PN sequence can be according to the OFDM symbol of different structure and is different.Referring to shown in Figure 3, if the OFDM symbol is to increase ZP before the OFDM data, so the PN sequence be short code preceding, long code after.Otherwise, if the symbol of OFDM is to increase ZP after the data of OFDM, so the PN sequence be short code after, long code is preceding, and short code and ZP alignment, long code and OFDM alignment of data, but concrete parameter is shown in Figure 4.It should be explicitly made clear at this point, short code must with at interval alignment of protection so that receiving terminal can utilize short code to carry out is synchronous fast.

Pilot frequency sequence can be expanded by one section PN sequence period and constitute.The PN sequence has following characteristics:

(1) cycle of PN sequence equals the length of an OFDM data-signal;

(2) the PN sequence of one-period comprises short code and long code two parts;

(3) short code length equals to protect gap length, and long code length equals data length signal N.

Suppose that protection is 2 of data-signal at interval ^-mDoubly, as 1/4,1/8,1/16 times etc., N.2 protection length at interval just equal so ^-m=2 ^N-mTherefore the length of the long and short sign indicating number of PN sequence just is respectively 2 ⁿWith 2 ^N-m

(4) long and short sign indicating number should have desirable autocorrelation performance and their cross correlation in theory.

Certainly, also can adopt the m sequence to generate length/short code, Fig. 5 is that the length/short code based on the m sequence generates schematic diagram.

As everyone knows, the m sequence can be used Fibonacci molded lines feedback shift register (LinearFeedback Shift Register, LFSR) realization.For example one degree of freedom is that 10 generator polynomial is:

X ¹⁰+X ⁷+1

Utilize following formula just can generate the m sequence of length for 210-1=1023, the phase place of this sequence can notice that initial value can not be 0 entirely by adjusting the initial value decision of LFSR.In order to obtain length/short code that length is 2 index side, also need mend 0 in m sequence front (perhaps back), make that 0 and 1 number equates that resulting sequence is known as balance m sequence in the calling sequence.Then, with balance m sequence do BPSK mapping just obtain value+1, length/short code of-1}.The mapping method of BPSK is: bit 0 becomes 1, and bit 1 becomes-1.At last, length/short code is carried out the amplitude adjustment: if the amplitude of length/short code is identical, so directly export value+1, length/short code of-1}; Otherwise, to length/short code difference multiplication by constants A _LongAnd A _Short, this constant requires to satisfy:

$\frac{s.A_{\mathrm{long}}^2+L.A_{\mathrm{short}}^2}{s+L}=P_{\mathrm{pilot}}$

P wherein _PilotIt is given pilot average transmitting power.Obviously following formula has infinite many groups about A _LongAnd A _ShortSeparate.Because short code will not be subjected to the interference of data-signal in the received signal, help fast synchronously, therefore two constants also will satisfy A _Short〉=A _LongThe adjusted sequence of amplitude is exactly a pilot frequency sequence, and its final and data-signal superposes in the certain power ratio.

In addition, in additive process, the average power P of pilot tone _PilotWith the data-signal power P _DataRequirement has fixing proportionate relationship.In general, pilot power P _PilotShared total transmitting power (P _Pilot+ P _Data) ratio between 10%～30%, obtain easily fast and accurately synchronously and channel estimating, otherwise cause easily bigger synchronously and channel estimation errors.

Step 204: the signal after the stack is by the band external leakage of signal, particularly PN sequence beyond the forming filter filtering regulation frequency spectrum, output baseband transmit signals.

Typical forming filter adopts roll-off cosine waveform (Raised cosine roll-off pulse) or root cosine waveform (Root raised cosine roll-off pulse).Except limit band function, forming filter should have big as far as possible bandwidth, and the bandwidth that can use with assurance OFDM data-signal is bigger.Can select for use the root cosine waveform of rolloff-factor between 0.03～0.2 proper in the engineering construction.

For this new O FDM modulation signal, receiver can be undertaken fast synchronously by short code, because short code is not subjected to the interference of OFDM symbol, so synchronized result is accurately.Need to carry out channel estimating synchronously.In order accurately to estimate channel, receiver can intercept the signal of one or several OFDM symbol lengths, carries out the channel estimating of time domain then with the PN sequence in one or several cycles.Promptly use the PN sequencal estimation of one-period, just can obtain the precision of channel estimation higher than DMB-T system.

Claims (13)

1, a kind of orthogonal frequency-division complex modulation method based on superimposed pilot is characterized in that, this method may further comprise the steps:

A. modulation obtains the OFDM data-signal through OFDM with data, at the front or the increase protection interval, back of this OFDM data-signal, and protection filling zero at interval, obtain the OFDM symbol;

B. described OFDM symbol and the pilot frequency sequence that sets in advance are superposeed on time domain;

Described pilot frequency sequence comprises short code and long code, wherein, short code and one protection equal in length at interval, the equal in length of long code and OFDM data-signal, and during stack, described short code is alignd with the protection interval, and long code is alignd with the OFDM data-signal;

C. obtain baseband transmit signals after the superposed signal that obtains among the step B being filtered by pulse shaping filter.

2, method according to claim 1 is characterized in that, in the steps A data is modulated the step that obtains the OFDM data-signal through OFDM and comprises:

A1, data-signal is carried out serial/parallel conversion;

A2, will carry out inverse-Fourier transform through the parallel data-signal after the serial/parallel conversion;

A3, will be that serial signal obtains the OFDM data-signal through the conversion of signals behind the inverse-Fourier transform.

3, method according to claim 1 is characterized in that, protection is expanded greater than the maximum delay of channel at interval in the steps A.

4, method according to claim 1 is characterized in that, described long code and short code are to utilize diverse ways to produce, or produce one group of sequence with method of the same race, this sequence length equals long and short sequence sum, then by the length separated into two parts, respectively as long code and short code.

5, method according to claim 1 is characterized in that, short code and long code satisfy auto-correlation and their cross correlation,

When short code is a ₀, a ₁..., a _S-1, and length is s and long code b ₀, b ₁..., b _L-1, when length is L, describedly satisfies desirable autocorrelation performance and be:

${\mathrm{\Σ}}_{n=0}^{s-1}{a}_n{a}_{(n+l)\mathrm{mod}s}=\mathrm{\δ}\left[l\right],l=\mathrm{0,1,2},...s-1$

${\mathrm{\Σ}}_{n=0}^{L-1}{b}_n{b}_{(n+l)\mathrm{mod}L}=\mathrm{\δ}\left[l\right],l=\mathrm{0,1,2}...L-1$

δ [0]=1 wherein, when l ≠ 0, δ [l]=0;

As short code a ₀, a ₁..., a _S-1With long code b ₀, b ₁..., b _L-1The time, describedly satisfy their cross correlation and be:

${\mathrm{\Σ}}_{n=0}^{s-1}{a}_n{b}_{(n+l)\mathrm{mod}L=0},l=\mathrm{0,1},...,L-1.$

6, method according to claim 1 is characterized in that, described OFDM symbol of step B and the pilot frequency sequence that sets in advance superpose according to the certain power ratio on time domain;

According to the certain power ratio be: the average power of pilot tone accounts for and comprises 10%～30% of pilot tone and the total transmitting power of data-signal power.

7, method according to claim 1 is characterized in that, the signal amplitude of short code and long code is identical or different; And have at the length sign indicating number under the situation of different amplitudes, the short code amplitude is greater than the amplitude of long code.

8, a kind of orthogonal frequency division multiplexing modulating device based on superimposed pilot is characterized in that, this device comprises:

The data that OFDM modulating unit (101) is used for receiving are carried out the OFDM modulation and are obtained the OFDM data-signal;

Protection zero insertion unit, interval (102) is used for that the OFDM data-signal that OFDM modulating unit (101) obtains is carried out the zero insertion operation and obtains the OFDM symbol;

Superpositing unit (103) is used to obtain the OFDM symbol of pilot frequency sequence, the zero insertion unit, interval of self-shield in the future (102) and the pilot frequency sequence that obtains superposes according to the certain power ratio, described pilot frequency sequence comprises short code and long code, wherein, short code and protection equal in length at interval, the equal in length of long code and OFDM data-signal; During stack, described short code is alignd at interval with protection, and long code is alignd with the OFDM data-signal;

Shaping filter unit (104) carries out filtering output baseband transmit signals to the signal through stack.

9, device according to claim 8 is characterized in that, described pilot frequency sequence given in advance is kept in the superpositing unit (103), or has in the physical entity of communication interface with superpositing unit (103).

10, device according to claim 8 is characterized in that, described short code and long code satisfy auto-correlation and their cross correlation;

When short code is a ₀, a ₁..., a _S-1, and length is s and long code b ₀, b ₁..., b _L-1, when length is L, describedly satisfies desirable autocorrelation performance and be:

${\mathrm{\Σ}}_{n=0}^{s-1}{a}_n{a}_{(n+l)\mathrm{mod}s}=\mathrm{\δ}\left[l\right],l=\mathrm{0,1,2},...s-1$

${\mathrm{\Σ}}_{n=0}^{L-1}{b}_n{b}_{(n+l)\mathrm{mod}L}=\mathrm{\δ}\left[l\right],l=\mathrm{0,1,2},...L-1$

δ [0]=1 wherein, when l ≠ 0, δ [l]=0;

As short code a ₀, a ₁..., a _S-1With long code b ₀, b ₁..., b _L-1The time, describedly satisfy their cross correlation and be:

${\mathrm{\Σ}}_{n=0}^{s-1}{a}_n{b}_{(n+l)\mathrm{mod}L}=0,l=\mathrm{0,1},...,L-1.$

11, device according to claim 8 is characterized in that, described OFDM symbol and the pilot frequency sequence that sets in advance superpose according to the certain power ratio on time domain;

Described certain power ratio is: described certain power ratio is: the average power of pilot tone accounts for and comprises 10%～30% of pilot tone and the total transmitting power of data-signal power.

12, device according to claim 8 is characterized in that, the signal amplitude of short code and long code is identical or different; And have at the length sign indicating number under the situation of different amplitudes, the short code amplitude is greater than the amplitude of long code.

13, device according to claim 8 is characterized in that, OFDM modulating unit (101) comprising:

Serial (201) is used for sending to anti-fast Fourier transform unit (202) to receiving after data-signal carries out serial/parallel conversion;

Anti-fast Fourier transform unit (202), be used for receive carry out inverse-Fourier transform through the parallel data-signal after the serial/parallel conversion after, export parallel/serial converting unit (203) to;

Parallel/serial converting unit (203) is used for exporting to protection zero insertion unit (102) at interval with after being serial signal through the conversion of signals behind the inverse-Fourier transform.

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