CN100521554C - Frequency domain channel estimation method based on two-value full-pass sequence protection interval filling - Google Patents

Abstract

The invention is concerned with the space protection filling method of the training sequence for the single or multi-carrier wave radio communication system with multi-pathway interference. It is to achieve compatible of the single-single carrier wave modulating system of the BAP sequence and the PN sequence. The definition of the new training sequence is the Binary All Pass, BAP. Its average peak ratio closes to the least BAP sequence because its anti-dispersing Transformee de Fourier is the PN sequence. The BAP sequence is with invariableness frequency domain, like low average peak ratio and so on.

Description

Frequency domain channel estimation method based on the two-value full-pass sequence protection interval filling

Technical field

The invention belongs to digital information transmission technical field; be particularly related to OFDM (Orthogonal FrequencyDivision Multiplexing; OFDM) multicarrier system (Multi Carrier; MC) or single carrier (Single Carrier; SC) (Training Sequence, protection TS) is fill method at interval based on training sequence in the system.

Background technology

The problem that the current wireless communication technology mainly solves is how to improve transmission rate in limited bandwidth reliably.Single carrier and multicarrier modulation system are under multi-path channel, can produce frequency selective fading, be intersymbol interference (Inter SymbolInterference, ISI), to causing inter-block-interference (Inter Block Interference for the unit system for transmitting with the data block, IBI), shown in Fig. 1 .a.

A kind of method that anti-multipath is disturbed be between transmission data block, add protection at interval (Guard Interval, GI), shown in Fig. 1 .b.Usually protection length at interval is not less than the maximum multipath time-delay of channel, and then the data block between the protection does not at interval have inter-block-interference, shown in Fig. 1 .c.Can referring to (Z.Wang and G B.Giannakis, " Wireless multicarriercommunications-where fourier meets shannon, " IEEE Signal Processing Mag., vol.17, pp.29-48, May2000).For the system that does not have inter-block-interference,, can eliminate of the interference of protection interval to data block by protection Given information at interval; Method by channel estimating and channel equalization can be eliminated the intersymbol interference that exists within data block.Can be referring to (Witschnig H., Mayer, T., Petit M., Hutzelmann H., Springer A., Weigel R., The advantages of aunique word for synchronisation and channel estimation in a SC/FDE system Personal Mobile Communications Conference, 2003.5th European (Conf.Publ.No.492)22-25 April 2003 Page (s): 436-440).

Protection fill method at interval has multiple: Cyclic Prefix (Cyclic Prefix, CP), zero padding (Zero Padding, ZP) and pseudorandom or pseudo noise sequence (Pseudo Noise, PN).Referring to (Muquet B, Wang Z, Giannakis G.B, Courville M.de, and Duhamel P, Cyclic Prefixing or Zero Padding for Wireless Multicarrier Transmissions, IEEE Trans.on Communications, 2002,50 (12): 2136-2148) and national standard (GB 20600-2006, digital television ground broadcast transmission system frame structure, chnnel coding and modulation, 2006-08-18).Wherein PN sequence fill method is that (Training Sequence, TS) a kind of special case of fill method is shown in Fig. 1 .d for training sequence.The training sequence fill method can also be assisted in to anti-multipath and be carried out timing recovery, carrier wave recovery, frame synchronization (data block is synchronous), channel estimating and Noise Estimation etc., ensure the reliable transmission of wireless system, therefore in multicarrier and single-carrier system, be used widely.

The training sequence that protection is filled at interval can produce distortion under the situation that has noise and data to disturb, have a strong impact on the precision of channel estimation based on training sequence.The present invention proposes a kind of new protection based on training sequence fill method at interval, can improve under the white noise precision of channel estimation based on training sequence effectively.

Protection at interval fill method is irrelevant with the system modulation mode, therefore the system that can be used for single carrier and multicarrier and deposit based on the protection interval fill method of training sequence.The present invention further proposes the wireless communication system of compatible two classes protection interval fill method and compatible with single carrier wave multicarrier two class modulation systems, as shown in Figure 3.

Summary of the invention

The objective of the invention is to propose a kind of new protection interval fill method and frequency domain channel estimation method, can be used for single carrier and multicarrier system based on training sequence.

The present invention defines a kind of novel training sequence, and promptly (Binary All Pass BAP), and proposes its searching method to two-value full-pass sequence.Two-value full-pass sequence is characterised in that its discrete Fourier transform (DFT) is a binary sequence, as the PN sequence; Peak-to-average force ratio can obtain from the anti-discrete Fourier transform (DFT) search of PN sequence near minimum two-value full-pass sequence.

The present invention proposes the frequency domain channel estimation method based on the two-value full-pass sequence protection interval filling, can be used for single carrier and multicarrier transmission systems based on data block.It is characterized in that with the protection interval of two-value full-pass sequence filling block transmission system, this method is to realize as follows successively, as shown in Figure 4 in digital integrated circuit or computer.

At transmitting terminal

Step (1) is according to given training sequence length N, 2 ^P-1≤ N＜2 ^p, a PN sequence length Np to be searched is proposed, Np=2 ^p-1, wherein p is a positive integer, and Ng generator polynomial and Np initial phase are correspondingly arranged, the number of PN sequence to be searched is Ng*Np, the minimum peak-to-average force ratio PARmin of initialization is a maximum, i.e. positive infinity, and the peak-to-average force ratio of defined nucleotide sequence is: the ratio of the peak power of sequence and average power;

Step (2), each PN sequence generator polynomial and each initial phase to obtaining in the step (1) generate a PN sequence;

Step (3) is got the anti-discrete Fourier transform (DFT) of top n sample calculation of PN sequence, obtains the two-value full-pass that length is N (Binary All Pass, BAP) sequence.The discrete Fourier transform (DFT) value of two-value full-pass sequence is+1 or-1;

Step (4), if the peak-to-average force ratio by definition calculating two-value full-pass sequence less than minimum peak-to-average force ratio PARmin, then upgrades PARmin, and writes down this two-value full-pass sequence and corresponding PN sequence, comprises PN generator polynomial and initial phase;

Step (5) finishes search after the PN sequence search for the treatment of all initial phases, all generator polynomials is finished, and obtains the two-value full-pass sequence of peak-to-average force ratio minimum;

Step (6) to single carrier and the multicarrier system based on data block, is filled protection at interval with two-value full-pass sequence;

Step (7), two-value full-pass sequence and data to be transmitted piece obtain base band output successively after framing and back-end processing; At receiving terminal

Step (1 ') obtains the circular convolution y (n) of two-value full-pass sequence x (n) and multipath channel impulse response h (n):

$y\left(n\right)=x\left(n\right)\⊗h\left(n\right)+v\left(n\right),$

Wherein, symbol

The computing of expression circular convolution, v (n) is circular convolution noise superimposed and data interference as a result;

Step (2 '): calculate two-value full-pass sequence x (n) and circular convolution discrete Fourier transform (DFT) Y (k)=DFT of y (n) (y (n)) as a result

X(k)＝DFT(x(n))

Wherein according to two-value full-pass sequence character, X (k) be+1, the binary sequence of-1};

Step (3 '): be calculated as follows estimated value H_est (k)=Y (k)/X (k) of the discrete Fourier transform (DFT) H (k) of multipath channel impulse response h (n)=+ Y (k) or-Y (k)

Obviously and since X (k) be+1, the binary sequence of-1}, the division arithmetic of channel estimating is very simple;

Step (4 '): the anti-discrete Fourier transform (DFT) of the H_est that calculation procedure (3 ') obtains (k), so that obtain the estimated value of multipath channel impulse response h (n)

h_est(n)＝IDFT(H_est(k))

At transmitting terminal, the two-value full-pass sequence that PN sequence and this PN sequence obtain through anti-discrete Fourier transform (DFT) enters the framing step after through a gating switch.At transmitting terminal, multi-carrier signal and single-carrier signal enter the framing step after through a gating switch.As shown in Figure 3.

The binary representation of the PN sequence of given length 192 is as follows, wherein bit 1 representative+1, bit 0 representative-1.Make that two-value full-pass sequence is the anti-discrete Fourier transform (DFT) of this PN sequence.

011000000001000011111101011001111011100000110101001110001111000100100110010100100000011100101111001000110110001010001000101110101010110101111111001110111110000101011100110111101000001011011011101100100101010000100111110110100011101001101001011000011001100

Emulation and analyze the time domain obtain PN sequence and two-value full-pass sequence, frequency domain, auto-correlation, frequency domain channel evaluation characteristic as shown in Figure 2.Compare with the PN sequence, two-value full-pass sequence has the frequency domain constant amplitude, and autocorrelation performance is good, and frequency domain channel estimates that complexity is low, characteristics such as frequency domain channel estimated accuracy height.Similar with the PN sequence, two-value full-pass sequence also can be assisted and be carried out timing recovery, carrier wave recovery, frame synchronization (data block is synchronous) and Noise Estimation etc.The shortcoming of two-value full-pass sequence is that the peak-to-average force ratio value is higher, and time domain is relevant complicated.

Description of drawings

Fig. 1 explanation is used for the protection interval fill method of piece transmission, comprises PN and BAP sequence fill method:

Fig. 1 .a explanation inter-block-interference (Inter Block Interference, IBI);

Fig. 1 .b explanation protection interval (Guard Interval, GI);

Fig. 1 .c explanation protection can be eliminated inter-block-interference at interval;

Fig. 1 .d explanation is based on the protection interval fill method of PN training sequence;

Fig. 1 .e explanation is based on the protection interval fill method of BAP training sequence.

Fig. 2 contrasts the BAP sequence (sequence length N=192) of PN sequence and the present invention's proposition:

Fig. 2 .a contrast time domain (discrete domain) characteristic;

Fig. 2 .a.1 is a PN sequence time domain amplitude characteristic;

Fig. 2 .a.2 is a BAP sequence time domain amplitude characteristic (peak-to-average force ratio=3.475dB);

Fig. 2 .b contrast frequency domain (discrete Fourier transform domain) characteristic;

Fig. 2 .b.1 is a PN sequence frequency domain amplitude characteristic;

Fig. 2 .b.2 is a PN sequence frequency domain amplitude characteristic;

Fig. 2 .c contrasts autocorrelation performance;

Fig. 2 .c.1 is PN sequence auto-correlation result;

Fig. 2 .c.2 is BAP sequence auto-correlation result;

Fig. 2 .d contrast frequency domain channel estimated result (free of data is disturbed for h (n)=δ (n-32)+δ (n-96), SNR=12dB);

Fig. 2 .d.1 is based on the frequency domain channel estimated result of PN;

Fig. 2 .d.2 is based on the frequency domain channel estimated result of BAP sequence.

Fig. 3 illustrates the single carrier multicarrier modulation system of compatible PN sequence and BAP sequence.

Fig. 4 explanation is based on the FB(flow block) of the frequency domain channel estimation method of two-value full-pass sequence protection interval filling.

Embodiment

The objective of the invention is to propose a kind of new protection interval fill method based on training sequence, can be used for single carrier and multicarrier system, embodiment is as follows in digital integrated circuit or computer:

The present invention of BAP sequence definition proposes a kind of new training sequence, and two-value full-pass sequence (Binary All Pass, BAP).(Discrete Fourier Transform DFT) has only two values ,+1 or-1 to the discrete Fourier transform (DFT) of definition BAP sequence.For example, (Inverse Discrete Fourier Transform DFT) is exactly the BAP sequence to the anti-discrete Fourier transform (DFT) of PN sequence.

BAP sequence search peak-to-average force ratio is a key property of multicarrier and single carrier wireless system.The peak-to-average force ratio difference of considering different B AP sequence is very big, and the present invention proposes the BAP sequence that a kind of method is simplified search peak-to-average force ratio minimum.If BAP sequence { x (n) }=[x (0) x (1) ... x (N-1)], N is a training sequence length.{X(k)}＝[X(0)X(1)…X(N-1)]＝DFT({x(n)})。According to the BAP sequence definition,

X (k)=+ 1 or-1, k=0,1 ..., N-1.

With N=192 is example, has 2 ¹⁹²Individual sequence satisfies the BAP sequence definition.Can utilize Monte Carlo method from 2 ¹⁹²Sequence space select sequence at random, the sequence of search peak-to-average force ratio minimum.In the experiment, searching times is up to 5000000 times, the binary representation of the BAP sequence of search is as follows: { X (k) }=11,001,000,001,011,111,101,001,101,101,111,111,000,001,000,110,010,101,101 11,001,101,001,011,111,100,111,110,110,010,001,001,100,001,101,011,000,000 01,001,011,010,011,110,001,110,100,001,010,110,111,000,101,010,101,010,011 110000100001000011101001, wherein bit 1 representative+1, bit 0 representative-1, its peak-to-average force ratio is 3.879dB.

The present invention proposes the search that a kind of method is simplified the BAP sequence of peak-to-average force ratio minimum, and its search routine as shown in Figure 4.Search step is as follows:

Step 1: according to given sequence length N, 2 ^P-1≤ N＜2 ^p, set PN sequence length Np to be searched, Np=2 ^p-1.Prepare PN sequence generator polynomial and initial phase according to sequence length.And the minimum peak-to-average force ratio of initialization is maximum, i.e. positive infinity.The peak-to-average force ratio that defines certain sequence is: the ratio of the peak power of this sequence and average power.With N=192 is example, searches for from length is the PN sequence of Np=255, and total Ng=16 generator polynomial and Np=255 initial phase can generate the PN sequence of length 255, and it is individual that PN sequence to be searched has Np*Ng=255*16=4080.

Step 2:, generate a PN sequence to each PN sequence generator polynomial and each initial phase.

Step 3: the top n sample to the PN sequence that generates, calculate its anti-discrete Fourier transform (DFT) and obtain the BAP sequence.

Step 4: calculate the peak-to-average force ratio of BAP sequence,, then write down this BAP sequence, comprise PN generator polynomial and initial phase if less than the equal ratio of the smallest peaks that has write down

Step 5: finish search after the PN sequence search of all initial phases, all generator polynomials is finished, obtain the BAP sequence of peak-to-average force ratio minimum.

The BAP sequence binary representation that finally searches the peak-to-average force ratio minimum is as follows: X (k)=01,100,000,000,100,001,111,110,101,100,111,101,110,000,011,010,100,111,000 11,110,001,001,001,100,101,001,000,000,111,001,011,110,010,001,101,100,010 10,001,000,101,110,101,010,110,101,111,111,001,110,111,110,000,101,011,100 11,011,110,100,000,101,101,101,110,110,010,010,101,000,010,011,111,011,010 0011101001101001011000011001100, wherein bit 1 representative+1, bit 0 representative-1, its peak-to-average force ratio is 3.475dB.The result who obtains with Monte Car1o method compares, and can think that what search from the PN sequence is peak-to-average force ratio near minimum BAP sequence.Fig. 2 .a/b/c compares time domain specification, frequency domain amplitude characteristic and the sequence autocorrelation performance of BAP sequence and PN sequence.

Fill method is similar at interval for filling of BAP sequence and CP, ZP and PN protection, can obtain with BAP training sequence protection interval fill method.This new fill method is applicable to single carrier and the multiple carrier wireless transmission system based on data block, shown in Fig. 1 .e.

Can be used for the estimation of multipath channel based on the frequency domain channel estimation method BAP sequence of BAP sequence filling.If the output result behind BAP sequence x (n) the process multipath channel h (n) is r (n), suppose that h (n) is finite impulse response, impingement length is not more than N, r (n)=x (n) * h (n)+u (n) then, 0≤n＜2*N, wherein * represents the linear convolution computing, and u (n) is that the noise and the data of linear convolution system are disturbed.The present invention proposes the frequency domain channel estimation method based on the BAP sequence, and its step is as follows:

Step 1: the circular convolution that obtains BAP sequence x (n) and multipath channel h (n) is y (n) as a result

If $y\left(n\right)=x\left(n\right)\&CircleTimes;h\left(n\right)+v\left(n\right),0\&le;n<N$

Wherein

The computing of expression circular convolution, v (n) is circular convolution noise superimposed and data interference as a result, y (n) is shown below and is calculated by the linear convolution result

y(n)＝r(n)+r(n+N)，0≤n<N

Step 2: the circular convolution of calculating BAP sequence x (n) and superimposed noise is the discrete Fourier transform (DFT) of y (n) as a result

Y(k)＝DFT(y(n))

X(k)＝DFT(x(n))

Wherein according to the BAP sequence character, X (k) be+1, the binary sequence of-1}

Step 3: by division obtain estimated value H_est (k) H_est (k)=Y (k)/X (k) of the discrete Fourier transform (DFT) H (k) of multipath channel impulse response h (n)=+ Y (k) or-Y (k)

Obviously and since X (k) be+1, the binary sequence of-1}, the division arithmetic of channel estimating is very simple.

Step 4: calculate the anti-discrete Fourier transform (DFT) of H_est (k), obtain the estimated value of multipath channel impulse response h (n).

h_est(n)＝IDFT(H_est(k))

The method that the present invention proposes utilizes the circular convolution result to carry out the frequency domain channel estimation, utilizes the BAP sequence characteristic to simplify the division arithmetic that frequency domain channel is estimated.If channel estimating is h_est (n), the channel estimation error noise is w (n), and the DFT of h (n) and v (n) is H (k) and V (k), then

Y(k)＝X(k)H(k)+V(k)

h_est(n)＝IDFT(Y(k)/X(k))＝IDFT(H(k)+V(k)/X(k))＝h(n)+w(n)，

W (n)=IDFT (V (k)/X (k)) wherein,

As seen, because X (k) value is+1 or-1, therefore can not amplify white noise when the DFT transform domain carries out division arithmetic, promptly noise w (n) is identical with the energy of noise v (n), so channel estimated accuracy is guaranteed.

Other training sequence, non-constant in the amplitude of DFT transform domain as the PN sequence, through after the above-mentioned channel estimating computing, noise may be exaggerated, and has reduced channel estimated accuracy.Fig. 2 .d compares the frequency domain channel evaluation characteristic of BAP sequence and PN sequence.As can be seen, more accurate based on the frequency domain channel estimation of BAP sequence.

The single carrier multicarrier system protection of BAP sequence and PN sequence coexistence fill method at interval is irrelevant with the system modulation mode, therefore the system that can be used for single carrier and multicarrier and deposit based on the protection interval fill method of training sequence.Because the anti-discrete Fourier transform (DFT) of PN sequence is the BAP sequence, so the present invention proposes a kind of PN sequence and BAP sequence and single carrier of depositing and multi-carrier wireless communications system (transmitting terminal), as shown in Figure 3.By switch 2, can between filling of PN sequence and the filling of BAP sequence, switch.By switch 1, can between single carrier and multicarrier system, switch.

Claims (3)

1, the frequency domain channel estimation method of filling based on two-value full-pass sequence protection interval is characterized in that, this method realizes in digital integrated circuit or computer successively as follows:

At transmitting terminal

Step (1) is according to given training sequence length N, 2 ^P-1≤ N＜2 ^p, a PN sequence length Np to be searched is proposed, Np=2 ^p-1, wherein p is a positive integer, Ng generator polynomial and Np initial phase are correspondingly arranged, Ng is a positive integer, the number of PN sequence to be searched is Ng*Np, the minimum peak-to-average force ratio PARmin of initialization is a maximum, i.e. positive infinity, and the peak-to-average force ratio of defined nucleotide sequence is: the ratio of the peak power of sequence and average power;

Step (2), each PN sequence generator polynomial and each initial phase to obtaining in the step (1) generate a PN sequence;

Step (3) is got the anti-discrete Fourier transform (DFT) of top n sample calculation of PN sequence, obtain the two-value full-pass that length is N (Binary All Pass, BAP) sequence, the discrete Fourier transform (DFT) value of two-value full-pass sequence are+1 or-1;

Step (4), if the peak-to-average force ratio by definition calculating two-value full-pass sequence less than minimum peak-to-average force ratio PARmin, then upgrades PARmin, and writes down this two-value full-pass sequence and corresponding PN sequence, comprises PN generator polynomial and initial phase;

Step (5) finishes search after the PN sequence search for the treatment of all initial phases, all generator polynomials is finished, and obtains the two-value full-pass sequence of peak-to-average force ratio minimum;

Step (6) to single carrier and the multicarrier system based on data block, is filled protection at interval with two-value full-pass sequence;

Step (7), two-value full-pass sequence and data to be transmitted piece obtain base band output successively after framing and back-end processing; At receiving terminal

Step (1 ') obtains the circular convolution y (n) of two-value full-pass sequence x (n) and multipath channel impulse response h (n):

$y\left(n\right)=x\left(n\right)\&CircleTimes;h\left(n\right)+v\left(n\right),$

Wherein, symbol

The computing of expression circular convolution, v (n) is circular convolution noise superimposed and data interference as a result, n is an integer, expression time-domain sampling point sequence number;

Step (2 '): calculate two-value full-pass sequence x (n) and the circular convolution discrete Fourier transform (DFT) of y (n) as a result

Y(k)＝DFT(y(n))

X(k)＝DFT(x(n))

Wherein according to two-value full-pass sequence character, X (k) is that {+1, the binary sequence of-1}, k are integer, expression frequency domain sample point sequence number;

Step (3 '): be calculated as follows estimated value H_est (k)=Y (k)/X (k) of the discrete Fourier transform (DFT) H (k) of multipath channel impulse response h (n)=+ Y (k) or-Y (k)

Obviously and since X (k) be+1, the binary sequence of-1}, the division arithmetic of channel estimating is very simple;

Step (4 '): the anti-discrete Fourier transform (DFT) of the H_est that calculation procedure (3 ') obtains (k), so that obtain the estimated value of multipath channel impulse response h (n)

h_est(n)＝IDFT(H_est(k))。

2, frequency domain channel estimation method of filling according to claim 1 based on two-value full-pass sequence protection interval; it is characterized in that; at transmitting terminal, the two-value full-pass sequence that PN sequence and this PN sequence obtain through anti-discrete Fourier transform (DFT) enters the framing step after through a gating switch.

3, frequency domain channel estimation method of filling based on two-value full-pass sequence protection interval according to claim 1 is characterized in that, at transmitting terminal, multi-carrier signal and single-carrier signal enter the framing step after through a gating switch.

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