CN101834632B - Method for capturing synchronization in frequency hopping communication - Google Patents

Abstract

The invention discloses a method for improving the capture of frequency-hopping synchronization based on a self-adaptive sliding filter and mainly aims to solve the problem of low correct judging rate of a synchronizing sequence under the condition of a low signal to noise ratio in the prior art. The method comprises the following steps of: 1) inserting a moving average filter into the front end of a correlator in a receiver; 2) filtering a received signal x(n) by using the moving average filter to obtain a filtered signal y(n); 3) performing a correlation operation on the filtered signal y(n) at the input end of the correlator to obtain a ratio of a main peak to a side peak in a correlation diagram; and 4) comparing the obtained ratio of the main peak to the side peak with a set threshold G, which is more than or equal to 3, of the main peak to the side peak, judging that frequency-hopping signal synchronization occurs if the ratio of the main peak to the side peak is more than or equal to G and judging the absence of a synchronization signal if the ratio of the main peak to the side peak is less than G. The method can be used for judging a transmitted synchronizing sequence with high accuracy under the condition of low signal to noise ratio, greatly improves synchronization performance and can be used in the fields of mobile communication, satellite communication, deep space communication and remote measuring.

Description

Catch synchronous method in the frequency hopping communications

Technical field

The invention belongs to communication technical field, relate to the stationary problem in the frequency hopping communications, specifically is to use self adaptation slip filtering method to improve to catch the synchronous correlator of frequency hopping, can be used for fields such as mobile communication, satellite communication, deep space communication and remote measurement.

Background technology

A major issue that runs in modern communications is anti-interference problem.Along with the development of telecommunications, the foundation of various types of communication net makes limited frequency spectrum resources more crowded, and interference each other is even more serious, how to prevent and reduces this interference each other, becomes a great problem.

At present the Anti-Jamming Technique that adopts in the communication mainly contains: 1. spread spectrum technique; 2. develop the millimeter wave frequency band of strong direction; 3. encryption technology; 4. burst communication technology; 5. antenna zero is to technology; 6. diversity technique.We focus on the frequency-hopping spread spectrum communication in the spread spectrum technique at this, claim FHSS (Frequency Hopping SpreadSystem) again.Realize that frequency hopping communications generally need solve three key technical problems: frequency synthesis, frequency hopping are synchronously and geocoding.One of key technology that guarantees the frequency-hopping communication system operate as normal is when data send, can be modulated on the higher frequency sending digital signal, like this, can reduce the influence that modulation signal may be subjected in the process of channel transmission, make the recipient can restore the data of transmission by down-conversion, and using it to the technology of judging that frequency hopping is synchronous, and the antijamming capability of the speed synchro system that frequency hopping is set up synchronously directly affects the performance of frequency-hopping system.Therefore, the synchronous realization of frequency hopping is one of emphasis of frequency hopping communications.

Present lot of documents has been done deep research synchronously to frequency hopping, as the independent channel method, needs special channel to transmit special synchronizing information, advantage is that the synchronizing information amount that transmits is big, the time weak point of setting up synchronously, and can constantly transmit synchronizing information, keep the synchronously long-time of system.But its acquisition frequency resource and signal power, its synchronizing information load mode is unhidden, is easy to be subjected to noise and enemy and disturbs.In order to make synchronizing information hidden, should adopt as far as possible short synchronous prefix, but what of the synchronizing information amount that the too short influence again of prefix synchronously transmits, need compromisely to consider.Adopt the frequency-hopping system of synchronous prefix method in order to keep the synchronously long-time of system, also need in communication process, to insert certain synchronizing information code word.Self-synchronizing method has advantage aspect saving frequency resource and the signal power, but because the synchronizing information that can imply in the digital information sequence that transmitting terminal sends is very limited, thus the synchronizing information that can extract at receiving terminal with regard to still less, easier other signals or the interference of noise of being subjected to.Therefore, utilizing above-mentioned several method to catch frequency hopping when synchronous, need the signal to noise ratio of input signal will satisfy certain requirement, when signal to noise ratio is big, noise is less to the influence of useful signal, and under such condition, noise influence in the process of calculating relevant peaks is less, the relevant peaks performance that obtains is fine, can judge the position of relevant peaks very easily, still, when signal to noise ratio reduces gradually, noise shared ratio in signal constantly increases, and can have influence on useful signal gradually.Under the low signal-to-noise ratio situation, because noise has uncertainty, when the signal based on noise signal is carried out correlation computations, the size of the relevant peaks that obtains is mixed and disorderly, the ratio that can cause main peak and other peak reduces, the mis-behave of relevant peaks is unfavorable for determining the position of relevant peaks being difficult to realize that frequency hopping is synchronous.

Summary of the invention

The objective of the invention is to overcome the deficiency of above-mentioned prior art, proposed to catch method for synchronous in a kind of frequency hopping communications, under the lower situation of signal to noise ratio, to improve the main peak of relevant peaks and the ratio at other peak, reduced performance loss, improve synchronous probability, judge the information of receiving in real time reliably.

Realize the technical scheme of the object of the invention, comprise the steps:

(1) the correlator front end in receiver inserts moving average filter;

(2) utilize moving average filter to received signal x (n) carry out filtering, obtain filtered signal y (n);

(3) at the correlator input, utilize filtered signal y (n) and local sequence to carry out related operation, obtain the main other p-ratio of correlation diagram;

The main other p-ratio that (4) will obtain and the main other peak thresholding G of setting compare, and G＞=3 are if main other p-ratio then is judged to Frequency Hopping Signal and occurs synchronously, otherwise then be not synchronizing signal more than or equal to G.

Described moving average filter is window by the length setting intercepting original signal that slides, and replaces in the sliding window sometime input signal values with the mean value of the input signal of the whole moment point in the sliding window.

Described utilize moving average filter to received signal x (n) carry out filtering, undertaken by following formula:

$y\left(n\right)=\frac{1}{m+k+1}\underset{i=n-m}{\overset{n+k}{\mathrm{\Σ}}}x\left(i\right)$

In the formula, m represents first input time point of sliding window, and k represents last input time point of sliding window, and n represents the current input time point of sliding window.

The present invention is owing to insert sliding filter in receiver, therefore can be under lower signal to noise ratio condition, judge the synchronizing sequence of transmission with higher accuracy, bigger improvement synchronization performance; Because the principle of sliding filter is simple, computation complexity is low, elapsed time is few, so utilize moving average filter x (n) filtering to received signal, can satisfies the requirement of real-time communication, and can save transmitting power simultaneously.

Description of drawings

The flow chart that Fig. 1 the present invention realizes

Fig. 2 length of window is the amplitude-frequency characteristic of 9 moving average filter

Fig. 3 does not use moving average filter, the emulation correlation diagram that signal to noise ratio obtains during for 0dB

Fig. 4 does not use moving average filter, the emulation correlation diagram that signal to noise ratio obtains during for-10dB

Fig. 5 is after adopting moving average filter, the emulation correlation diagram that signal to noise ratio obtains during for 0dB

Fig. 6 is after adopting moving average filter, the emulation correlation diagram that signal to noise ratio obtains during for-10dB

Embodiment

Describe performing step of the present invention in detail below in conjunction with accompanying drawing, it is 8BB9A4D75AC2FCC6 that present embodiment is got synchronizing sequence, but is not limited to this sequence.

Step 1, insertion moving average filter x (n) to received signal carries out filtering.

Front end at receiver inserts moving average filter, moving average filter has low-pass characteristic, for example length of window is 9 filter, the amplitude-frequency characteristic of its unit impact response can characterize with the fft conversion of its 2048 bit, as shown in Figure 2, the amplitude-frequency characteristic of this low pass filter relatively meets the amplitude-frequency characteristic of signal, can be good at the noise in the filtered signal like this, the moving average filter that the present invention adopts, be exactly window by the length setting intercepting original signal that slides, replace in the sliding window sometime input signal values with the mean value of the input signal of the whole moment point in the sliding window.

Step 2 is selected the moving average filter length of window.

The length of moving average filter window is to determine that by adaptively selected mode concrete steps are as follows:

2a) length of window is preset as 9, carries out that filtering is relevant to obtain a main other p-ratio;

2b) add 1 in the length of window that presets, relevant to follow-up signal filtering again, obtain new main other p-ratio;

2c) twice main other p-ratio compared, if new main other p-ratio is greater than 2a) in main other p-ratio, then length of window continues to add 1, otherwise, length of window is subtracted 1;

2d) in continuous filtering correlated process, if new main other p-ratio is bigger than old main other p-ratio, just length of window is carried out operating the same processing with last time, if new main other p-ratio is littler than old main other p-ratio, then carry out opposite processing;

If 2e) length of window is reduced to 1,2d set by step again) handle, make length of window change into 0, if this occurs, then getting length of window is 1;

By step 2a)～2e), obtain table 1, from table 1, can be clearly seen that sef-adapting filter under different signal to noise ratios, length of window is 9 o'clock, main other p-ratio is best, so this project employing length of window is fixed as 9 moving average filter;

The main other p-ratio of the correlation diagram under table 1 different windows length and the signal to noise ratio

Step 3, receiver utilize moving average filter that input signal x (n) is carried out filtering.

3.1) acquisition of input signal x (n):

The x of this example (n) adopts the MSK modulation by transmitting terminal to synchronizing sequence, each code element is got 8 samplings and is obtained modulation signal s (n), s (n) is local sequence, s (n) arrives the signal x (n) of receiver again through channel then, have 512 centrifugal pumps, it comprises component and quadrature component in the same way;

3.2) utilize moving average filter to signal to noise ratio for 0db and-the input signal x (n) that obtains during 10db carries out filtering and obtains signal y (n):

$y\left(n\right)=\frac{1}{m+k+1}\underset{i=n-m}{\overset{n+k}{\mathrm{\Σ}}}x\left(i\right)$

In the formula, m represents first input time point of sliding window, and k represents last input time point of sliding window, and n represents the current input time point of sliding window; M+k+1 is preset window length, and its value is 9 m=3 wherein, k=5;

3.3) utilize the matlab software programming, specifically calculate.

Step 4 at the correlator input, utilizes filtered signal y (n) and local sequence to carry out related operation.

4.1) carry out related operation by following formula:

$r\left(j\right)=\frac{1}{D}\underset{i=0}{\overset{D-1}{\mathrm{\Σ}}}{s}_i^{*}{y}_{i+j}$

D is local sequence length in the formula, s _i ^*The complex conjugate of representing local sequence, y _I+jExpression and y _iBe separated by j the point output signal value;

4.2) with matlab software correlation is drawn, obtain correlation diagram;

4.3) according to correlation diagram, the ratio of the top of calculating correlation and the absolute value of ebb obtains main other p-ratio.

Step 5, the main other peak thresholding G with setting compares with the main other p-ratio that obtains, and G＞=3 are if main side p-ratio then is judged to Frequency Hopping Signal and occurs synchronously, otherwise then be not synchronizing signal more than or equal to G.

Effect of the present invention can further specify by following emulation:

1. the content of emulation:

To not using moving average filter, the correlation diagram when signal to noise ratio is 0dB carries out emulation, result such as Fig. 3;

To not using moving average filter, the correlation diagram of signal to noise ratio during for-10dB carries out emulation, result such as Fig. 4;

After using moving average filter, the correlation diagram when signal to noise ratio is 0dB carries out emulation, result such as Fig. 5;

After using moving average filter, the correlation diagram of signal to noise ratio during for-10dB carries out emulation, result such as Fig. 6.

2. simulation result is relatively:

By Fig. 3 and Fig. 4 as can be seen, existing related algorithm is under the signal to noise ratio conditions of higher, and its correlated performance is better, reaches about 3.97 as the ratio at relevant peaks main peak and other peak among Fig. 3, and among Fig. 4 along with the decline of signal to noise ratio, the ratio at relevant peaks main peak and other peak drops to about 1.12; As seen along with the decline of signal to noise ratio, the ratio at relevant peaks main peak and other peak surpasses the thresholding of setting, and so just can not correctly adjudicate, and it is more than 3-5 times of other peak-to-peak value that thresholding is commonly defined as main peak.

As can be seen from Figure 5, after having adopted average sliding filter, when signal to noise ratio was 0dB, the ratio at relevant peaks main peak and other peak was more than 6.5, the relevant peaks main peak that obtains much larger than Fig. 3 and the ratio 3.97 at other peak;

As can be seen from Figure 6 after having adopted average sliding filter, in signal to noise ratio be-during 10dB, the ratio at relevant peaks main peak and other peak is about 3.9 the relevant peaks main peak that obtains much larger than Fig. 4 and the ratio 1.12 at other peak;

As seen after having adopted average sliding filter along with the decline of signal to noise ratio, even under than the low signal-to-noise ratio condition, the ratio at relevant peaks main peak and other peak still can surpass the thresholding that sets, can obtain a correlated performance preferably, this provides strong help synchronously to judging, can satisfy the requirement that communication system is handled in real time fully.

Claims (2)

1. catch synchronous method in a frequency hopping communications, comprise the steps:

(1) the correlator front end in receiver inserts moving average filter, this moving average filter, it is the window slip intercepting original signal by a length setting, replace in the sliding window sometime input signal values with the mean value of the input signal of the whole moment point in the sliding window, the length setting of window wherein, be carry out as follows adaptively selected:

1a) length of window is preset as 9, carries out that filtering is relevant to obtain a main other p-ratio;

1b) at 1a) length of window set adds 1, and is relevant to follow-up signal filtering again, obtains new main by p-ratio;

1c) twice main other p-ratio compared, if new main other p-ratio is greater than 1a) in main other p-ratio, then length of window continues to add 1, otherwise, length of window is subtracted 1;

1d) in continuous filtering correlated process, if new main other p-ratio is bigger than old main other p-ratio, just length of window is added 1, if the other p-ratio of new master is littler than old main other p-ratio, then length of window is subtracted 1;

If 1e) length of window is reduced to 1,1d set by step again) handle, make length of window change into 0, if this occurs, then getting length of window is 1.

(2) utilize moving average filter to received signal x (n) carry out filtering, obtain filtered signal y (n);

(3) at the correlator input, utilize filtered signal y (n) and local sequence to carry out related operation, obtain the main other p-ratio of correlation diagram;

The main other p-ratio that (4) will obtain and the main other peak thresholding G of setting compare, and G＞=3 are if main other p-ratio then is judged to Frequency Hopping Signal and occurs synchronously, otherwise then be not synchronizing signal more than or equal to G.

2. according to claim 1ly catch synchronous method, wherein step (2) described utilize moving average filter to received signal x (n) carry out filtering, undertaken by following formula:

$y\left(n\right)=\frac{1}{m+k+1}\underset{i=n-m}{\overset{n+k}{\mathrm{\Σ}}}x\left(i\right)$

In the formula, m represents first input time point of sliding window, and k represents last input time point of sliding window, and n represents the current input time point of sliding window.

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