CN1177410C - Frequency discrimination signal treating method and frequency discriminator adopting simplified maximum likelihood frequency difference - Google Patents

Abstract

The present invention relates to a simplified method for processing frequency discrimination signals with maximum likelihood frequency difference. On the basis of a maximum likelihood frequency difference estimation principle, a method for processing frequency difference estimation signals is simplified, and a frequency discriminator based on simplified maximum likelihood frequency difference is provided. Compared with a frequency discriminator with maximum likelihood frequency difference, the hardware of the frequency discriminator is greatly simplified on the basis of equivalently maintained properties. Compared with a traditional cross-product frequency discriminator, the properties are obviously improved under the condition that the complexity of the hardware is not highly increased. The characteristic of signal to noise ratio is improved when a phase-locked loop is utilized. The frequency discriminator has the advantages of simplified hardware, good property and favorable application prospect when applied in an automatic frequency control loop.

Description

The discrimination signal treating method and the frequency discriminator thereof of the maximum likelihood frequency difference of simplifying

The present invention relates to a kind of control technology of automatic frequency, exactly, relate to a kind of on the basis of maximum likelihood frequency difference estimation principle, under the prerequisite of certain signal to noise ratio, the frequency difference estimation equation is simplified and the discrimination signal treating method and the frequency discriminator thereof of the maximum likelihood frequency difference of a kind of simplification of proposing, and belonging in the digital communication system is the automatic frequency control technology field of modulation technique with MPSK (multiple phase shift keying).

In many wireless communication systems, because transmitting terminal and receiving terminal have adopted the clock source of different accuracy separately, cause like this existing certain frequency difference between the frequency of carrier signal that receives and the local synthetic carrier wave, and, along with the frequency converters at different levels of receiver are incorporated among the signal of actual demodulation, in the coherent demodulation process,, can make the signal generation error code of reception if do not eliminate this frequency difference.Usually the method for eliminating this frequency difference is to adopt automatic frequency control technology (AFC, Automatic Frequency Control).The automatic frequency control technology can be divided into control of open loop automatic frequency and the control of closed loop automatic frequency, and the control of open loop automatic frequency is the frequency difference of utilizing frequency discriminator direct estimation signal, and directly comes the frequency difference of correction signal with the frequency difference of estimating; The precision height that this open loop frequency difference control requires frequency discriminator to estimate.The control of closed loop automatic frequency is to utilize frequency discriminator that the frequency difference of estimated signal is fed back to voltage controlled oscillator, the frequency difference that the frequency difference of the output of adjusting voltage controlled oscillator is come corrected received signal and local signal; This is the process of a closed-loop adjustment, requires the frequency discrimination curve of frequency discriminator to have the odd symmetry characteristic.

Referring to shown in Figure 1 a kind of in spread spectrum communication the theory diagram of normally used automatic frequency control loop.The intermediate-freuqncy signal 1 that receives is owing to the clock source of transmitting terminal and receiving terminal employing different accuracy has frequency difference, intermediate-freuqncy signal 1 and local voltage controlled oscillator 107 (being generally local clock source) output signal are mixed quite, still had the two-way baseband signal 101,102 of the homophase and the quadrature of difference on the frequency.Then, this two paths of signals is sent into integration-remover 103,104 respectively, carry out the signal to noise ratio of digitlization and raising signal, obtain two-way digital baseband signal Ik and Qk, wherein Ik is a homophase item of digital baseband signal, and Qk is the orthogonal terms digital baseband signal.Again signal Ik, Qk are input to together the frequency discriminator 105 of frequency discrimination signal frequency difference, by certain signal processing method, output obtains forming with the signal frequency difference error correction voltage of certain proportion relation, this error correction voltage is by behind loop filter 106 filtering noises, send into voltage controlled oscillator 107, just can control the frequency of voltage controlled oscillator output signal, reach the purpose of proofreading and correct frequency difference.The correctness of the quality of frequency discriminator 105 performances decision frequency correction and the pull-in time of loop also are the key points that realizes the automatic frequency control technology in the above-mentioned feedback control procedure.

At present the frequency discriminator that uses has two classes usually: a class is to adopt the cross product frequency discriminator of cross product principle, its basic theory diagram as shown in Figure 2, wherein Ik, Qk are respectively homophase item and orthogonal terms digital baseband signal, the formula equation of its corresponding signal process is:

vd(k)＝I _k-1Q _k-I _kQ _k-1

The frequency discrimination scope of this cross product frequency discriminator is: $\mathrm{\Δf}=\frac{1}{2T},$ Wherein T represents receiver unit's sampling time.The characteristics of this frequency discriminator are that the frequency discrimination scope is big, and still, the ability that suppresses noise is general.Need obtain higher noise ability by the bandwidth that reduces loop filter, the corresponding lengthening of the pull-in time of loop makes the contradiction between noiseproof feature and the pull-in time be difficult to overcome like this.

The another kind of frequency discriminator that is based on the maximal possibility estimation principle, the equation of its corresponding signal process method is:

${\widehat{\mathrm{\ω}}}_d=\arg \max {\left|\underset{k=0}{\overset{N-1}{\mathrm{\Σ}}}{r}_k{e}^{-\mathrm{jk}{\mathrm{\ω}}_{d}T}\right|}^2$

Wherein,

The frequency difference that expression identifies, arg[.] represent to get the argument operation, max represents to get maximum, | | represent to take absolute value operation, N represents that receiving symbol participates in the number of signal processing, r _kThe complex representation form of representing k received signal, T represents the sampling period of received signal, ∑ is represented accumulating operation. ${\mathrm{\ω}}_d=\frac{2\mathrm{\π}}{N}$ Be fundamental frequency.The formula equation of this frequency discriminator signal processing method is actually by sequence r to received signal _kCarry out the discrete Fourier transform (DFT) computing, find the frequency of maximum periodic peaks correspondence to obtain estimating frequency difference, the precision of its estimation can reach a carat Metro lower bound (CRLB), and the frequency difference that estimates is the frequency difference of correction signal directly.But the computing workload of this frequency discriminator signal processing equation is quite big.Though, can reduce the computing workload and the operation time of discrete Fourier transform (DFT) by fast fourier transform, yet the complexity of this computing is handled for real-time operation, and is particularly just very unsuitable as real-time frequency discriminator in automatic frequency control loop.Simultaneously, if can not utilize loop to improve the characteristic of signal to noise ratio, the assurance of its estimated accuracy is must be under certain signal to noise ratio condition.That is to say that the raising of this frequency discriminator precision is a cost to improve complexity.

From last surface analysis as can be known, currently used two kinds of frequency discrimination methods are difficult to overcome the contradiction between precision and pull-in time, precision and the complexity.Though cross product frequency discriminator structure and computing are all fairly simple,, it improves precision is cost to increase pull-in time.The maximum likelihood frequency difference estimation then needs to carry out complex calculations, and the signal to noise ratio snr that the frequency difference estimation of open loop needs is higher.

The discrimination signal treating method that the purpose of this invention is to provide a kind of maximum likelihood frequency difference of new simplification, it is to propose on the basis that present maximum likelihood estimator module is further simplified, reducing under the few prerequisite of original estimated accuracy, reduce the complexity of its realization greatly, improved the contradiction between precision and the complexity; Utilize its lower complexity simultaneously and, be applied in the automatic frequency control loop, reaching under the same tracking accuracy, can dwindle the pull-in time of loop greatly with respect to the degree of precision of cross product frequency discriminator.Simultaneously, utilize the characteristic frequency discriminator of loop can be operated in the lower signal to noise ratio environment, strengthened its practicality.

Another object of the present invention provides a kind of frequency discriminator of discrimination signal treating method of the maximum likelihood frequency difference that adopts simplification.

A further object of the present invention provides a kind of discrimination signal treating method of maximum likelihood frequency difference of application simplification, the frequency discriminator of using in automatic frequency control loop, for automatic frequency control loop provides a kind of practical hardware circuit of simplifying.

The discrimination signal treating method of the maximum likelihood frequency difference that the present invention simplifies is achieved in that establishing input signal is r _k=I (k)+jQ (k), the complex representation form of expression received signal, wherein I (k) is its real part, Q (k) is its imaginary part; The physical significance of this input signal is respectively homophase item and the orthogonal terms two-way baseband digital signal behind the multiple phase shift keying mpsk signal intermediate frequency demodulation, has remaining frequency difference; Include following performing step: (1) sends the signal that receives into conjugate operation units (301), and its concrete method of operation is: real part I (k) signal remains unchanged, and with imaginary signals Q (k) negate;

(2) will through the received signal after the conjugate operation units (301) send into thereafter a plurality of delay units (302) that are linked in sequence, (303) ... (304), the progression of these a plurality of delay units is by the decision of maximal correlation length M, and delay time T is the sampling time of received signal;

(3) signal of delay units at different levels output is carried out respectively plural number add up operation (305), (306) ... (307), (308);

(4) signal that enters of signal after will adding up and current time successively carries out complex multiplication and gets the imaginary part operation; This complex multiplication and get imaginary part operation and realize it by two real multipliers (309), (310) and a real add musical instruments used in a Buddhist or Taoist mass (311);

(5) result with complex multiplication smoothly adds up, operating process is that the top n number is moved displacement backward, when the N number was moved out of sliding filter, first number of vacating was then replenished it with the value of new input, and at this moment N value being added up be averaged obtains current filtering result;

(6) with the complex result value that obtains, handle accordingly, obtain required frequency difference value.

The formula of this signal processing method is:

${\hat{f}}_d==\frac{1}{\mathrm{\πT}(M+1)}\arg \left\{\underset{k=1}{\overset{M}{\mathrm{\Σ}}}\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{r}_i{r}_{i-k}^{*}\right\}$

Wherein, T represents the sampling period of received signal, and N represents that receiving symbol participates in the number of signal processing, r _kThe complex representation form of representing k received signal, M represents the maximal correlation length between the received signal.Arg[.] the argument operation is got in expression.

Above-mentioned (6) step can be that numerical value according to the real part of resulting complex result value and imaginary part is as the address, obtain its corresponding argument value by tabling look-up in a memory form that stores corresponding argument value in advance, this argument value is exactly the frequency difference value that will detect.

The present invention adopts the frequency discriminator of discrimination signal treating method of the maximum likelihood frequency difference of simplification to be achieved in that and includes following hardware device: receive respectively via the homophase item I (k) of intermediate frequency demodulation and the conjugate operation device of orthogonal terms Q (k) two-way base band tributary signal, with the conjugate operation that wherein imaginary signals Q (k) is carried out negate; The two-way output signal of this conjugate operation device then links to each other with thereafter delayer respectively, and multistage delayer has been linked in sequence after this delayer; Be provided with many group accumulators and a complex multiplier, so that the two-way output signal of every grade of delayer is carried out the plural number operation that adds up with the output signal of the delayer of one-level thereafter respectively, and this sampled signal values that adds up sum and current time is sent into complex multiplier carry out the complex multiplication operation operation; Also being provided with a N length sliding filter and one stores and calculates argument module and corresponding frequency difference read-only memory thereof, smoothly add up with result above-mentioned complex multiplication, obtain current filtering result that N value added up and be averaged, again with resulting complex result value, and according to the numerical value of this real and imaginary part as the address, obtain its corresponding argument value by tabling look-up in a memory form that stores corresponding argument value in advance, this argument value is exactly the frequency difference value that will detect.

The progression of the multistage delayer that said sequence connects is to be determined by the maximal correlation length M between the received signal.

Above-mentioned complex multiplier includes four real multipliers and two real add musical instruments used in a Buddhist or Taoist mass.

The present invention uses the discrimination signal treating method of the maximum likelihood frequency difference of simplification, the frequency discriminator used in automatic frequency control loop is achieved in that and includes following hardware device: receive respectively via the homophase item I (k) of intermediate frequency demodulation and the conjugate operation device of orthogonal terms Q (k) two-way baseband signal, with the conjugate operation that wherein imaginary signals Q (k) is carried out negate; The two-way output signal of this conjugate operation device then links to each other with thereafter delayer respectively, and multistage delayer has been linked in sequence after this delayer; Be provided with many group accumulators and a complex multiplier, so that the two-way output signal of every grade of delayer is carried out the plural number operation that adds up with the output signal of the delayer of one-level thereafter respectively, and this sampled signal values that adds up sum and current time is sent into complex multiplier carry out complex multiplication operation and get the imaginary part operation; Also be provided with a N length sliding filter, smoothly add up with the imaginary part result that above-mentioned complex multiplication is obtained, N value added up is averaged the error voltage value that obtains sending into loop filter.

The progression of the multistage delayer that said sequence connects is to be determined by the maximal correlation length M between the received signal.

Above-mentioned complex multiplier includes two real multipliers and a real add musical instruments used in a Buddhist or Taoist mass, gets the operation of imaginary part to finish complex multiplication.

Main feature of the present invention is: compare with the formula of the signal processing method of maximal possibility estimation principle frequency discriminator, simplified the complexity of computing greatly.Here can estimate the operand of discrimination signal treating method of the present invention: total operand of this signal processing method is 4N real multiplications, 2N (M-1)+2 (N-1) real number addition and a ROM read operation.The precision of frequency discriminator of the present invention can be near the lower bound that reaches carat Metro circle, and its frequency discrimination scope is:

$\left|{\hat{f}}_d\right|<{\left[(M+1)T\right]}^{-1}$

Wherein: M is the maximal correlation length of frequency discriminator.

Compare with the cross product frequency discriminator, though frequency discrimination scope of the present invention makes the frequency discrimination scope reduce to some extent along with the increase of M,, can satisfy different frequency discrimination requirements by suitable adjusting M value.

In a word, compare with two kinds of present frequency discriminators, a kind of new simplification maximum Likelihood that the present invention proposes has solved the contradiction that improves between frequency discrimination performance and the reduction complexity preferably.In the application process of automatic frequency control AFC loop, though the cross product frequency discriminator is relatively simple for structure, realization easily is during the noiseproof feature that will realize, the necessary long enough of the pull-in time of loop, the automatic frequency that can't be applied in quick tracking is controlled the field.And some simplification maximum Likelihood of maximum likelihood frequency difference estimation and application at present, because its complexity is difficult to realize that with hardware majority is used in the frequency difference estimation field of reprocessing and open loop; Though the automatic frequency of open loop control can improve frequency difference correction time, the frequency difference estimation of this open loop need just can have preferable performance under very high signal to noise ratio condition.Estimated performance of the present invention is near CRLB (carat Metro) lower bound, and simplified implementation procedure greatly, can be used on the open loop frequency difference estimation in real time; And the frequency discriminator performing step more simplified has been proposed at automatic frequency control loop, can also make the hardware designs simple and flexible according to performance requirement.Realizing that its pull-in time doubles than cross product frequency discriminator, can be used in the quick frequency difference tracking field under the identical performance condition.

Below in conjunction with drawings and Examples, introduce processing method of the present invention, hardware composition structure, signal processing step and effect in detail:

Fig. 1 is the theory diagram of now general automatic frequency control loop.

Fig. 2 is the frequency discriminator structural principle block diagram of the cross product automatic frequency control of use now.

Fig. 3 is the hardware configuration theory diagram of frequency discriminator of the discrimination signal treating method of the present invention's maximum likelihood frequency difference of using simplification.

Fig. 4 is that the present invention uses the discrimination signal treating method of the maximum likelihood frequency difference of simplification, the hardware configuration theory diagram of the frequency discriminator in automatic frequency control loop.

The present invention is a kind of discrimination signal treating method of maximum likelihood frequency difference of simplification, it is to propose on the basis that present maximum likelihood frequency difference estimation device is done further to simplify, reducing under the few prerequisite of original estimated accuracy, reduce the complexity of its realization greatly, improved the contradiction between precision and the complexity; Utilize its lower complexity simultaneously and, be applied in the automatic frequency control loop, reaching under the same tracking accuracy, can dwindle the pull-in time of loop greatly with respect to the degree of precision of cross product frequency discriminator.Simultaneously, utilize the characteristic frequency discriminator of loop, can be operated in the lower signal to noise ratio environment, strengthened its practicality.

The equation of the discrimination signal treating method of the maximum likelihood frequency difference that the present invention simplifies or processing formula is:

${\hat{f}}_d=\frac{1}{\mathrm{\&pi;T}(M+1)}\arg \left\{\underset{k=1}{\overset{M}{\mathrm{\&Sigma;}}}\frac{1}{N-1}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{r}_i{r}_{i-k}^{*}\right\}=\frac{1}{\mathrm{\&pi;T}(M+1)}\arg \left\{\underset{k=1}{\overset{M}{\mathrm{\&Sigma;}}}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{r}_i{r}_{i-k}^{*}\right\}$

Wherein, T represents the sampling period of received signal, and N represents that receiving symbol participates in the number of signal processing, r _kThe complex representation form of representing k received signal, M represents the maximal correlation length between the received signal.Arg[.] the argument operation is got in expression.Adopt above-mentioned signal processing method, its estimated accuracy can be near carat Metro circle, and therefore this frequency discriminator can be applied in the control of open loop automatic frequency.At this signal processing method, the present invention gives its hard-wired structural principle block diagram, as shown in Figure 3.It includes following hardware device: receive respectively via the homophase item I (k) of intermediate frequency demodulation and the conjugate operation device 301 of orthogonal terms Q (k) two-way base band tributary signal, with the conjugate operation that wherein imaginary signals Q (k) is carried out negate; The two-way output signal of this conjugate operation device then links to each other with thereafter delayer 302 respectively, be linked in sequence after this delayer 302 multistage delayer 303 ... 304, this multistage delayer 303 that is linked in sequence ... 304 progression is to be determined by the maximal correlation length M between the received signal.Be provided with 305,306,307,308,313,314 and complex multipliers 315 of many group accumulators, so that the two-way output signal of every grade of delayer is carried out the plural number operation that adds up with the output signal of the delayer of one-level thereafter respectively, and this sampled signal values that adds up sum and current time is sent into complex multiplier 315 carry out the complex multiplication operation operation, this complex multiplication operation operation is finished by 309,310,311,312 and two real add musical instruments used in a Buddhist or Taoist mass 313,314 of four multipliers.Also being provided with a N length sliding filter 316 and one stores and calculates argument module and corresponding frequency difference read-only memory 317 thereof, smoothly add up with result above-mentioned complex multiplication, obtain current filtering result that N value added up and be averaged, again with resulting complex result value, and according to the numerical value of this real and imaginary part as the address, obtain its corresponding argument value in the memory form that stores corresponding argument value in advance by tabling look-up.

The signal processing step of frequency discriminator shown in Figure 3 is as follows: establishing input signal is r _k=I (k)+jQ (k), the complex representation form of expression received signal, wherein I (k) is its real part, Q (k) is its imaginary part; The physical significance of this input signal is respectively homophase and the quadrature two-way baseband digital signal behind the multiple phase shift keying mpsk signal intermediate frequency demodulation, has remaining frequency difference.

(1) signal that receives is sent into conjugate operation units 301, its concrete method of operation is: real part I (k) signal remains unchanged, and with imaginary signals Q (k) negate;

(2) will through the received signal after the conjugate operation units 301 send into thereafter a plurality of delayers unit 302,303 that is linked in sequence ... 304, the progression of these a plurality of delay units is by the decision of maximal correlation length M, and delay time T is the sampling time of received signal;

(3) signal of delay units at different levels output is carried out respectively plural number add up operation 305,306 ... 307,308;

(4) signal that enters of signal after will adding up and current time successively carries out the complex multiplication operation, and this complex multiplication operation is by 309,310,311,312 and real add musical instruments used in a Buddhist or Taoist mass 313,314 realizations of four real multipliers;

(5) result with complex multiplication smoothly adds up, operating process is that the top n number is moved displacement backward, when the N number was moved out of sliding filter, first number of vacating was then replenished it with the value of new input, and at this moment N value being added up be averaged obtains current filtering result;

(6) with the complex result value that obtains, according to the numerical value of this real and imaginary part as the address, obtain its corresponding argument value by tabling look-up in a memory form that stores corresponding argument value in advance, this argument value is exactly the frequency difference value that will detect, thereby improves arithmetic speed greatly.

Because in the automatic frequency control loop The Application of Technology, frequency discriminator mainly satisfies odd symmetric condition, frequency difference that just can correction signal, therefore, the present invention has done further modification again to above-mentioned operating procedure shown in Figure 3 and has simplified, can obtain simplification maximum likelihood frequency discriminator practical more in automatic frequency control loop, the theory diagram that its hardware configuration is formed is referring to shown in Figure 4.It includes following hardware device: receive respectively via the homophase item I (k) of intermediate frequency demodulation and the conjugate operation device 301 of orthogonal terms Q (k) two-way baseband signal, with the conjugate operation that wherein imaginary signals Q (k) is carried out negate; The two-way output signal of this conjugate operation device 301 then links to each other with thereafter delayer 302 respectively, be linked in sequence after this delayer 302 multistage delayer 303 ... 304, the progression of the multistage delayer that this is linked in sequence is to be determined by the maximal correlation length M between the received signal.Be provided with 305,306,307,308 and complex multipliers 318 of many group accumulators, so that the two-way output signal of every grade of delayer is carried out the plural number operation that adds up with the output signal of the delayer of one-level thereafter respectively, and this sampled signal values that adds up sum and current time is sent into complex multiplier 318 carry out complex multiplication operation and get imaginary part operation, this complex multiplication and the arithmetic operation of getting imaginary part are finished by 309,310 and real add musical instruments used in a Buddhist or Taoist mass 313 of two real multipliers; Also be provided with a N length sliding filter 319, smoothly add up with the imaginary part result that above-mentioned complex multiplication is obtained, N value added up is averaged the error voltage value that obtains sending into loop filter.

The signal processing step of frequency discriminator shown in Figure 4 and frequency discriminator signal processing step shown in Figure 3 are basic identical, also are that to establish input signal be r _k=I (k)+jQ (k), the complex representation form of expression received signal, wherein I (k) is its real part, Q (k) is its imaginary part; The physical significance of this input signal is respectively homophase and the quadrature two-way baseband digital signal behind the multiple phase shift keying mpsk signal intermediate frequency demodulation, has remaining frequency difference.

(1) signal that receives is sent into conjugate operation units 301, its concrete method of operation is: real part I (k) signal remains unchanged, and with imaginary signals Q (k) negate;

(2) will through the received signal after the conjugate operation units 301 send into thereafter a plurality of delay units that are linked in sequence 302,303 ... 304, the progression of these a plurality of delay units is by the decision of maximal correlation length M, and delay time T is the sampling time of received signal;

(3) signal of delay units at different levels output is carried out respectively plural number add up operation 305,306 ... 307,308;

(4) signal that enters of signal after will adding up and current time successively carries out complex multiplication and gets the imaginary part operation;

This complex multiplication and get imaginary part operation by 309,310 and real add musical instruments used in a Buddhist or Taoist mass 311 realizations of two real multipliers;

(5) the imaginary part result who obtains is smoothly added up, operating process is that the top n number is moved displacement backward, when the N number is moved out of sliding filter, first number of vacating is then replenished it with the value of new input, at this moment N value is added up and is averaged the error voltage value that obtains sending into loop filter.

Comparison diagram 3 and Fig. 4, the present invention is on the basis of maximum likelihood frequency difference estimation, propose a kind of discrimination signal treating method, and provided the hardware configuration realization theory diagram of signal processing and the new realization theory diagram of more simplifying that is applicable to the frequency discriminator hardware configuration of using on the automatic frequency control loop according to this method for simplifying.

The present invention carries out l-G simulation test under the COSSAP of Synopsys company simulated environment, and has carried out test and implement in the band spread receiver of applicant's development, and on the open loop frequency difference estimation, its performance is near CRLB (carat Metro) lower bound.The formula of CRLB (carat Metro) lower bound is as follows:

${\mathrm{\&sigma;}}_{\mathrm{\&Delta;f}}^2=\frac{3}{2{\mathrm{\&pi;}}^{2}T}\&CenterDot;\frac{1}{\mathrm{SNR}\&CenterDot;(N^2-1)}$

σ wherein _{Δ f}Be the frequency difference estimation variance, T represents the sampling time of received signal, and N represents the number of signal processing, and SNR is the signal to noise ratio of signal.Work as N=10,20,30, SNR=7dB, T=1/16, during 000s, CRLB (carat Metro) lower bound that can calculate estimated accuracy is: σ _{Δ f}=85Hz, 31Hz, 16Hz.

For whether the precision of the maximum likelihood frequency difference estimation of verifying simplification can reach a carat Metro lower bound, at N=10,20,30, SNR=7dB, T=1/16,000s, f _dDone emulation under the additive Gaussian channel of=500Hz, its result is respectively shown in table 5.1, table 5.2, table 5.3:

Estimated accuracy when table 5.1 N=10, different M

M

	1	2	3	4	5	6
							Estimated accuracy σ Δf(HZ)	100	68	55	51	45	40

Estimated accuracy when table 5.2 N=20, different M

M

	1	2	3	5	6	8	10	12	14
										Estimated accuracy σ Δf(Hz)	65	40	33	22	21	19	18	17	17

Estimated accuracy when table 5.3 N=30, different M

M

	1	2	4	6	8	10	12	14	15	16	18
												Estimated accuracy σ Δf(Hz)	42	26	18	15	14	13	12	12	12	11

From three top tables, can see that the selection of M and estimated accuracy are that certain relation is arranged.When M＞N/2, method of estimation of the present invention is little to the effect of improving amount of calculation, and this has illustrated that the present invention simplifies the feasibility of maximal possibility estimation, can select M=N/2.In addition, from above-mentioned each table as can be seen: when the different N, the precision of estimation has all surpassed CR (carat Metro) boundary.This be because accumulator added up expanded range, in fact be equivalent to increase the N value, estimated accuracy is improved, and when M=1, in fact has been reduced to the cross product automatic frequency and has controlled.

Because simplify estimator after selecting suitable M, N parameter, good performance can be arranged, but need higher signal to noise ratio, and on automatic frequency control loop, use, just in time can eliminate this influence, make like this when the present invention is applied to automatic frequency control loop under identical signal to noise ratio, than the pull-in time shortening of cross product automatic frequency control.Through emulation, when M=N/2, the pull-in time that the present invention simplifies estimator doubles than the control of cross product automatic frequency.So, utilize phase-locked loop can improve the characteristic of signal to noise ratio, frequency discriminator of the present invention is in automatic frequency control loop is used, and its premium properties can access better embodiment, and therefore frequency discriminator of the present invention has application promise in clinical practice in automatic frequency control loop.

Claims (9)

1. the discrimination signal treating method of the maximum likelihood frequency difference of a simplification, it is characterized in that: establishing input signal is rk=I (k)+jQ (k), and wherein I (k) is its real part, and Q (k) is its imaginary part; The physical significance of this input signal is respectively homophase item and the orthogonal terms two-way baseband digital signal after the demodulation of multiple phase shift keying signal intermediate frequency, has remaining frequency difference; It includes following performing step:

(1) described input signal is sent into conjugate operation units (301), its concrete method of operation is: real part I (k) signal remains unchanged, and with imaginary signals Q (k) negate;

(2) will through the described input signal after the conjugate operation units (301) send into thereafter a plurality of delay units (302) that are linked in sequence, (303) ... (304), the progression of these a plurality of delay units is by the decision of maximal correlation length M, and delay time T is the sampling time of received signal;

(3) signal of delay units at different levels output is carried out the plural number operation that adds up respectively;

(4) signal that enters of signal after will adding up and current time successively carries out complex multiplication and gets the imaginary part operation; This complex multiplication and get imaginary part operation and realize by two real multipliers (309), (310) and a real add musical instruments used in a Buddhist or Taoist mass (311);

(5) result with complex multiplication smoothly adds up, operating process is that the top n number is moved displacement backward, when the N number was moved out of sliding filter, first number of vacating was then replenished with the value of new input, and at this moment N value being added up be averaged obtains current filtering result;

(6) with the complex result value that obtains, handle accordingly, obtain required frequency difference value.

2. the discrimination signal treating method of the maximum likelihood frequency difference of simplification as claimed in claim 1, it is characterized in that: this method for processing signals is carried out according to following formula:

${\hat{f}}_d=\frac{1}{\mathrm{\&pi;T}(M+1)}\arg \left\{\underset{k=1}{\overset{M}{\mathrm{\&Sigma;}}}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{r}_i{r}_{i-k}^{*}\right\}$

Wherein, T represents the sampling period of received signal, and N represents that receiving symbol participates in the number of signal processing, r _iThe complex representation form of representing i received signal, M represents the maximal correlation length between the received signal, arg[.] expression gets the argument operation.

3. the discrimination signal treating method of the maximum likelihood frequency difference of simplification as claimed in claim 1, it is characterized in that: above-mentioned (6) step is that numerical value according to the real part of resulting complex result value and imaginary part is as the address, obtain its corresponding argument value by tabling look-up in a memory form that stores corresponding argument value in advance, this argument value is exactly the frequency difference value that will detect.

4. the frequency discriminator of the discrimination signal treating method of a maximum likelihood frequency difference of using simplification, it is characterized in that: include following hardware device: receive respectively via the homophase item I (k) of intermediate frequency demodulation and the conjugate operation device of orthogonal terms Q (k) two-way base band tributary signal, with the conjugate operation that Q (k) is carried out negate; The two-way output signal of this conjugate operation device then links to each other with thereafter delayer respectively, and multistage delayer has been linked in sequence after this delayer; Be provided with many group accumulators and a complex multiplier, so that the two-way output signal of every grade of delayer is carried out the plural number operation that adds up with the output signal of the delayer of one-level thereafter respectively, and this sampled signal values that adds up sum and current time sent into complex multiplier, to carry out the complex multiplication operation operation; Also be provided with a N length sliding filter and a read-only memory that stores calculating argument module and corresponding frequency difference thereof, smoothly add up with result above-mentioned complex multiplication, obtain current filtering result that N value added up and be averaged, again with resulting complex result value, according to the numerical value of this real and imaginary part as the address, obtain its corresponding argument value by tabling look-up in a memory form that stores corresponding argument value in advance, this argument value is exactly the frequency difference value that will detect.

5. the frequency discriminator of the discrimination signal treating method of the maximum likelihood frequency difference that application as claimed in claim 4 is simplified is characterized in that: the progression of the multistage delayer that said sequence connects is to be determined by the maximal correlation length M between the received signal.

6. the frequency discriminator of the discrimination signal treating method of the maximum likelihood frequency difference that application as claimed in claim 4 is simplified, it is characterized in that: above-mentioned complex multiplier includes four real multipliers and two real add musical instruments used in a Buddhist or Taoist mass.

7. use the discrimination signal treating method of the maximum likelihood frequency difference of simplification, the frequency discriminator of in automatic frequency control loop, using for one kind, it is characterized in that: include following hardware device: receive respectively via the homophase item I (k) of intermediate frequency demodulation and the conjugate operation device of orthogonal terms Q (k) two-way baseband signal, with the conjugate operation that Q (k) is carried out negate; The two-way output signal of this conjugate operation device then links to each other with thereafter delayer respectively, and multistage delayer has been linked in sequence after this delayer; Be provided with many group accumulators and a complex multiplier, so that the two-way output signal of every grade of delayer is carried out the plural number operation that adds up with the output signal of the delayer of one-level thereafter respectively, and this sampled signal values that adds up sum and current time is sent into complex multiplier carry out complex multiplication operation and get the imaginary part operation; Also be provided with a N length sliding filter, smoothly add up with the imaginary part result that above-mentioned complex multiplication is obtained, N value added up is averaged the error voltage value that obtains sending into loop filter.

8. the discrimination signal treating method of the maximum likelihood frequency difference that application as claimed in claim 7 is simplified, the frequency discriminator of using in automatic frequency control loop is characterized in that: the progression of the multistage delayer that said sequence connects is to be determined by the maximal correlation length M between the received signal.

9. the discrimination signal treating method of the maximum likelihood frequency difference that application as claimed in claim 7 is simplified, the frequency discriminator of in automatic frequency control loop, using, it is characterized in that: above-mentioned complex multiplier includes two real multipliers and a real add musical instruments used in a Buddhist or Taoist mass, gets the operation of imaginary part to finish complex multiplication.

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