CN103001914A - Decimal carrier synchronization algorithm based on cyclic prefix - Google Patents

Abstract

The problem of the invention discloses a kind of Decimal carrier synchronization algorithm based on cyclic prefix, it is not high enough to solve Carrier Synchronization accuracy existing in the prior art, is not able to satisfy order of modulation growth requirement. The Decimal carrier synchronization algorithm based on cyclic prefix, the following steps are included: the signal received is divided into carrier wave frequency deviation part and remaining part, and carrier wave frequency deviation branch is divided into fractional part of frequency offset and integer frequency offset, and the single estimated value of fractional part of frequency offset is calculated According to the single estimated value of fractional part of frequency offset Obtain the estimated value of its i-th; Step (b) is repeated, the variance of gained fractional part of frequency offset is calculated, and calculates mean of variance; Thresholding V is set, if Vf amp; amp; gt; V then continues to execute step (a), and current fractional part of frequency offset estimated value is locked if Vf≤V, and carries out frequency deviation compensation always with the estimated value. Through the above scheme, it invention achieves reducing the residual error of decimal overtones band estimation, improving system stability, allows system to work purpose in smaller residual error environment, there is very high practical value and promotional value.

Description

Decimal times Carrier Synchronization Algorithm based on Cyclic Prefix

Technical field

The present invention relates to a kind of Carrier Synchronization Algorithm, specifically, relate to the decimal times Carrier Synchronization Algorithm based on Cyclic Prefix in a kind of high-order wire communication.

Background technology

In communication system, synchronized algorithm is the basis that communication control processor is realized, is research emphasis and the difficult point of any modulation-demodulation technique, and its performance is directly connected to the performance of whole communication system.Can say that synchronized algorithm is the prerequisite of realization information transmitting, only having accurately, synchronized algorithm just can carry out reliable transfer of data.

At present, ofdm system can be divided into synchronously frame synchronization, sign synchronization, carrier synchronization and sampling clock synchronous.Wherein, carrier synchronization is used for estimating the frequency shift (FS) of receiving end signal, and it is corrected, existing OFDM Carrier Synchronization can only control to residual error below 1% subcarrier spacing, thereby can only support 16 ~ 64AM order of modulation, yet HINOC has brought up to 16 ~ 1024QAM with order of modulation in order to improve data transfer rate, existing Carrier Synchronization obviously can not satisfy its demand, and we need to a kind ofly can be reduced to 1e with the frequency deviation residual error ^-3Even 1e ^-4Other synchronized algorithm of subcarrier spacing level.

Summary of the invention

The object of the present invention is to provide a kind of decimal times Carrier Synchronization Algorithm based on Cyclic Prefix, it is not high enough mainly to solve the Carrier Synchronization accuracy that exists in the prior art, can not satisfy the problem of order of modulation growth requirement.

To achieve these goals, the technical solution used in the present invention is as follows:

Decimal times Carrier Synchronization Algorithm based on Cyclic Prefix is characterized in that, may further comprise the steps:

(a) signal that receives is divided into carrier wave frequency deviation part and remaining part, and carrier wave frequency deviation branch is divided into fractional part of frequency offset and integer frequency offset, and calculate the single estimated value of fractional part of frequency offset

(b) according to the single estimated value of fractional part of frequency offset Obtain its estimated value of the i time, wherein, i is positive integer;

(c) repeated execution of steps (b) is calculated the variance of gained fractional part of frequency offset, and calculates mean of variance V _f

(d) thresholding V is set, if V _fV then continues execution in step (a), if V _f≤ V then locks current fractional part of frequency offset estimated value, and carries out compensate of frequency deviation with this estimated value all the time.

Specifically, in the described step (a), the single estimated value of decimal times carrier wave frequency deviation

Drawn by following steps:

(a1) k the time domain sampling point r (k) that establishes the OFDM symbol that receives behind the Complete Synchronization is:

r(k)=s(k)exp(j2πkf _F/N)+n(k)；

(a2) the related operation summation based on cyclic prefix CP draws

Wherein N is data segment, length 256, N _CPBe circulating prefix-length 16, The OFDM symbol original position that obtains for sign synchronization; And then draw the single estimated value of fractional part of frequency offset

Further, in the described step (b), the estimated value that fractional part of frequency offset is the i time is current estimated value and the mean value of estimated value before, that is:

Further, in the described step (c), the variance of fractional part of frequency offset is drawn by following formula: $D_f\left(i\right)={|{\hat{f}}_F\left(i\right)-E_f\left(i\right)|}^2={|{\hat{f}}_F\left(i\right)-\underset{j=0}{\overset{N_E-1}{\mathrm{\Σ}}}{\hat{f}}_F(i-j)|}^2,$ Its mean value is obtained by following formula: $V_f=\underset{j=0}{\overset{N_D}{\mathrm{\Σ}}}{D}_f(i-j);$

As preferably, in described step (a) and the step (b), be that 0.5 firstorder filter carries out mean value computation by parameter all.

Compared with prior art, the present invention has following beneficial effect:

(1) times Carrier Synchronization Algorithm of the decimal among the present invention is accurately succinct, can effectively reduce the residual error that the decimal overtones band is estimated, reduce error code, thereby make system works in less residual error environment, can improve the error rate that Systems balanth also can further reduce data, conceive very ingeniously, efficiently solve the deficiency of existing synchronized algorithm, have outstanding substantive distinguishing features and marked improvement, be fit to large-scale promotion application.

(2) the present invention has also carried out average computing repeatedly on the basis that the carrier wave frequency deviation single is estimated, such computational methods have further improved computational accuracy, have strengthened serviceability.

(3) to adopt parameter be that 0.5 firstorder filter carries out mean value computation in the present invention, greatly improved technical efficiency and accuracy, the demand in the realistic application.

Description of drawings

Fig. 1 is schematic flow sheet of the present invention.

Fig. 2 is emulation schematic diagram one of the present invention.

Fig. 3 is emulation schematic diagram two of the present invention.

Embodiment

The invention will be further described below in conjunction with drawings and Examples, and embodiments of the present invention include but not limited to the following example.

Embodiment

Carrier wave frequency deviation is because the frequency of oscillation of transmitting terminal and receiving terminal is not mated to be produced, and it shows as a cumulative phase place in time domain, shows as the overall offset of subcarrier at frequency domain.Because ofdm system need to guarantee the orthogonality of its subcarrier, thereby very responsive to frequency shift (FS), and is higher to the requirement of carrier synchronization.In the present invention, we are divided into carrier wave frequency deviation part and remaining part with the signal that receives, and therefore, establish k the time domain sampling point that some OFDM of receiving behind the Complete Synchronization meet and are: r (k)=s (k) exp (j2 π Δ fkT _s)+n (k)=s (k) exp (j2 π Δ fkT/N)+n (k), doing some conversion can draw: r (k)=s (k) exp (j2 π k (f _I+ f _F)/N)+n (k) analyzed from numeric field, because k is integer, so f _IWithout impact, and then can draw r (k)=s (k) exp (j2 π kf to the signal time domain _F/ N)+n (k).

As can be seen from the above equation, obtain f _FThen need to eliminate time factor k, carry out the time delay related operation.Because the HINOC system does not have pilot tone, so the algorithm based on pilot tone can not use, and targeting sequencing is not two sections identical signals, thereby can not use based on the delay and correlation algorithm of sequence, therefore estimates that for the fractional part of frequency offset of HiNOC system we can only start with from cyclic prefix CP.

The algorithm of this part generally is based on is correlated with to do, and is applied to and carries out summation operation in the native system, and the specific algorithm step is:

Wherein N is data segment, length 256, N _CPBe circulating prefix-length 16,

The OFDM symbol original position that obtains for sign synchronization; And then draw the single estimated value of fractional part of frequency offset Here, accumulating operation is wanted to work as in phase place has been done on average.

According to emulation, when Eb/No=20dB, the fractional part of frequency offset evaluated error of existing algorithm in 0.01 times of subcarrier spacing, although for the low order system this error acceptable normally, following two reasons are arranged so that it is also inapplicable in the HINOC system.

First: the HINOC system is high order system, and its maximum modulation exponent number is 1024QAM, and 0.01 times fractional part of frequency offset can cause larger impact to systematic function, produces a large amount of error codes.

Second: in the frame structure of HINOC system, the OFDM symbolic component does not contain pilot tone, therefore can only carry out channel estimating one time at frame head, and can not carry out channel estimating to each symbol, carry out channel equalization repeatedly, thus impact that can not the correcting residual frequency deviation during channel equalization, so that the phase rotating that the residual frequency deviation accumulation brings constantly increases, until next frame head could correct, so this cumulative phase rotating can cause adverse effect to systematic function.

In order to address the above problem, we provide a kind of and not only can reduce residual error that the decimal overtones band estimates, have improved the stability of a system in the present invention, can also further reduce data error rate, allow the synchronized algorithm of system works in less residual error environment.

As shown in Figure 1, the method that we adopt the second order ring lock to judge is carried out the analysis of fractional part of frequency offset, mainly may further comprise the steps:

(1) according to the single estimated value of fractional part of frequency offset

Obtain its estimated value of the i time:

Be the average of current estimated value and estimated value before; Wherein i is positive integer, and its value can be 1,2,3......N.

(2) repeated execution of steps (b) is calculated the variance of gained fractional part of frequency offset, and calculates mean of variance; In the present invention, the variance of fractional part of frequency offset is drawn by following formula: $D_f\left(i\right)={|{\hat{f}}_F\left(i\right)-E_f\left(i\right)|}^2={|{\hat{f}}_F\left(i\right)-\underset{j=0}{\overset{N_E-1}{\mathrm{\Σ}}}{\hat{f}}_F(i-j)|}^2,$ Its mean value is obtained by following formula: $V_f=\underset{j=0}{\overset{N_D}{\mathrm{\Σ}}}{D}_f(i-j);$

(3) thresholding V is set, if V _fThe V single of then proceeding fractional part of frequency offset estimates, if V _f≤ V then locks current fractional part of frequency offset estimated value, and carries out compensate of frequency deviation with this estimated value all the time.

Can find out, the present invention is on the basis that the carrier wave frequency deviation single is estimated, carried out average computing repeatedly, improve estimated accuracy with this, the method of averaging namely parameter is 0.5 firstorder filter, when the average of variance during less than a thresholding, illustrates that the carrier wave frequency deviation that estimates tends to be steady, at this moment lock, just can obtain a comparatively accurate fractional part of frequency offset and estimate.

Such as Fig. 2, shown in Figure 3, we have carried out emulation to the algorithm among the present invention.Simulation parameter is Eb/No=10 ~ 25dB; Fractional part of frequency offset is 0.1, i.e. 6250Hz; Thresholding V=0.0005, multipath channel, ideal communication channel is estimated.As seen from the figure, with raising frequency deviation shortening locking time of signal to noise ratio, frequency deviation locking precision is totally improving, but a fluctuation range is arranged.This is because emulation carries out is the locking of single, does not carry out a large amount of emulation and averages, so have certain randomness.As can also be seen from Figure, when signal to noise ratio when 17dB is above, residual frequency deviation is locked in the 1Hz basically, and locking time is in 0.04 second.For the communication of this wired non sudden, such as cable TV, 0.04 second delay be complete acceptable, even under more high-precision requirement, can reduce thresholding V, so that residual frequency deviation is locked in lower interval, its service behaviour is very good again.

According to above-described embodiment, just can realize well the present invention.

Claims (5)

1. based on the decimal times Carrier Synchronization Algorithm of Cyclic Prefix, it is characterized in that, may further comprise the steps:

(a) signal that receives is divided into carrier wave frequency deviation part and remaining part, and carrier wave frequency deviation branch is divided into fractional part of frequency offset and integer frequency offset, and calculate the single estimated value of fractional part of frequency offset

(b) according to the single estimated value of fractional part of frequency offset

Obtain its estimated value of the i time, wherein, i is positive integer;

(c) repeated execution of steps (b) is calculated the variance of gained fractional part of frequency offset, and calculates mean of variance V _f

(d) thresholding V is set, if current V _fV then continues execution in step (a), if V _f≤ V then locks current fractional part of frequency offset estimated value, and carries out compensate of frequency deviation with this estimated value all the time.

2. the decimal times Carrier Synchronization Algorithm based on Cyclic Prefix according to claim 1 is characterized in that, in the described step (a), and the single estimated value of decimal times carrier wave frequency deviation Drawn by following steps:

(a1) k the time domain sampling point r (k) that establishes the OFDM symbol that receives behind the Complete Synchronization is: r (k)=s (k) exp (j2 π kf _F/ N)+n (k);

(a2) the related operation summation based on cyclic prefix CP draws

Wherein N is data segment, length 256, N _CPBe circulating prefix-length 16,

The OFDM symbol original position that obtains for sign synchronization; And then draw the single estimated value of fractional part of frequency offset

3. the decimal times Carrier Synchronization Algorithm based on Cyclic Prefix according to claim 2 is characterized in that, in the described step (b), the estimated value that fractional part of frequency offset is the i time is current estimated value and the mean value of estimated value before, that is: ${\hat{f}}_F\left(i\right)=({\hat{f}}_F(i-1)+{\hat{f}}_F)/2.$

4. the decimal times Carrier Synchronization Algorithm based on Cyclic Prefix according to claim 3 is characterized in that in the described step (c), the variance of fractional part of frequency offset is drawn by following formula: $D_f\left(i\right)={|{\hat{f}}_F\left(i\right)-E_f\left(i\right)|}^2={|{\hat{f}}_F\left(i\right)-\underset{j=0}{\overset{N_E-1}{\mathrm{\Σ}}}{\hat{f}}_F(i-j)|}^2,$ Its mean value is obtained by following formula: $V_f=\underset{j=0}{\overset{N_D}{\mathrm{\Σ}}}{D}_f(i-j).$

5. the decimal times Carrier Synchronization Algorithm based on Cyclic Prefix according to claim 4 is characterized in that, in described step (a) and the step (b), is that 0.5 firstorder filter carries out mean value computation by parameter all.

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