CN116827381A

CN116827381A - Anti-interference frequency hopping synchronization method suitable for wireless ad hoc network and implementation device thereof

Info

Publication number: CN116827381A
Application number: CN202311029240.XA
Authority: CN
Inventors: 王霄峻; 张凯淇; 芮正翔; 蔡正新; 程科; 许杰瑞; 牛泽原; 张萌
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2023-08-16
Filing date: 2023-08-16
Publication date: 2023-09-29

Abstract

The invention discloses an anti-interference frequency hopping synchronization method and an implementation device thereof, which are suitable for a wireless ad hoc network, and belong to the technical field of communication. The method comprises the following 5 steps: and S1, evaluating all channels, and dividing the channels into available channels and unavailable channels. And S2, updating a default synchronous channel table according to TOD and an undisturbed channel, and generating a current synchronous channel table. And step S3, generating and applying a synchronous frequency hopping pattern according to the current synchronous channel table. Step S4: the receiver searches for synchronization hops and demodulates the frequency modulation synchronization information. If the missing detection or the false detection occurs, the process returns to the step S102, and if the detection is successful, the process proceeds to the step S5. Step S5: and (5) verifying the heel jump. If the missing detection or the false detection occurs, the step S1 is returned, and if the verification is successful, the frequency hopping synchronization flow is ended. The invention establishes a comprehensive mechanism combining the non-fixed synchronous frequency point, the perception interference frequency point and the avoidance interference frequency point, and can effectively improve the anti-interference capability of the receiver for executing the frequency hopping synchronous flow.

Description

Anti-interference frequency hopping synchronization method suitable for wireless ad hoc network and implementation device thereof

Technical Field

The invention belongs to the technical field of communication and electronic systems, and particularly relates to an anti-interference frequency hopping synchronization method and an implementation device thereof suitable for a wireless ad hoc network.

Background

The synchronous header method is a common frequency hopping synchronization technology in a frequency hopping system, has the advantages of strong anti-interference capability, no dependence on specific synchronous frequency points and the like, and is suitable for systems with high requirements on anti-interference performance and signal concealment. In the related technology, the self-synchronization method is also a frequency hopping synchronization technology with strong concealment and strong anti-interference performance, but a radio station is required to continuously send out a frequency hopping pattern with good self-synchronization performance, and the method is not suitable for a high-performance wireless ad hoc network scene. In order to reduce the delay of multi-hop routing, a node is generally not allowed to occupy a plurality of continuous time slots to send a specific frequency hopping pattern so as to prevent communication of multi-hop neighbors from being blocked, so that the self-synchronization method frequency hopping synchronization technology is not suitable for the wireless self-networking supporting frequency hopping anti-interference. Other typical frequency hopping synchronization techniques such as the common time base method (reference GPS) and the independent frequency point method have poorer anti-interference performance than the two methods.

In the related research, the performance of the synchronization header method is generally measured by two factors, namely, the initial frequency hopping synchronization probability and the frequency hopping initial synchronization time, which are generally contradictory. On the premise that the initial synchronization probability reaches a threshold value, the designer should reduce the frequency hopping initial synchronization time as much as possible. Or on the premise of fixed frequency hopping initial synchronization time, the designer should increase the frequency hopping initial synchronization probability as much as possible.

The bottleneck of the syncheader method is generally due to the following factors: (1) search strategy of synchronization header. (2) detecting the performance of the synchronization head. (3) searching the number of synchronous frequency points contained in the pattern in one round. (4) system time difference between the two transceivers. Many cases will control factor (1), factor (2), factor (3) as much as possible, while there is little discussion about the optimization of factor (4). On the premise of adopting the waiting search method, the factor (3) determines the maximum number of times of the frequency hopping synchronous information contained in a round of search pattern, and the factor (4) determines the actual number of times the information can be found.

Disclosure of Invention

The invention aims to provide an anti-interference frequency hopping synchronization method and an implementation device thereof suitable for wireless ad hoc networks, which are used for solving the technical problems of low efficiency of searching frequency hopping synchronization information, low initial synchronization probability and long initial synchronization time delay of a receiver in the prior art.

In order to solve the technical problems, the specific technical scheme of the invention is as follows:

the invention discloses an anti-interference frequency hopping synchronization method suitable for a wireless ad hoc network, which comprises the following steps:

step S1, firstly, a receiver evaluates frequency points to obtain the interfered state of each frequency hopping frequency point.

Step S2, the receiver searches frequency hopping synchronization information on the current synchronization frequency point table; the searching strategy adopts a waiting searching method; if the receiver does not search the frequency hopping synchronization information, the default synchronization frequency point is selected from the frequency hopping frequency point set again every appointed time, and the step S3 is carried out to generate a current synchronization frequency point table; if the receiver searches for the frequency hopping synchronization information, it proceeds to step S4.

And S3, the receiver replaces the interfered default synchronous frequency point with the undisturbed frequency hopping frequency point, and combines the interfered default synchronous frequency point (if any) to generate a current synchronous frequency point table. If the duration of the receiver executing the step S2 reaches the threshold, the step S1 is entered, otherwise, the step S2 is returned to.

Step S4: the receiver adjusts the local frequency hopping pattern according to the frequency hopping synchronization information, and the frequency hopping pattern of the transmitter can be predicted by matching and aligning the local frequency hopping pattern with the transmitter. Then the receiver consumes a certain time and processing capacity to verify that the frequency hopping pattern of the transmitter is predicted correctly, and the step S5 is performed; if the receiver cannot verify that the steps of the transmitter are correct, the step S2 is entered; the receiver may not verify the frequency hopping pattern of the transmitter and may take any verification method.

Step S5: and the frequency hopping synchronization flow is ended.

Further, the frequency point evaluation method comprises a blind evaluation method and a non-blind evaluation method; the blind evaluation method does not need a transmitter to send out a reference signal; the non-blind evaluation method requires reference to the signal of the transmitter; the frequency point evaluation method finally evaluates the frequency point as one of binary states, namely the frequency point is available or unavailable; the receiver adopts multiple frequency point evaluation methods to evaluate the same frequency point at the same time; when the results of the multiple methods evaluate the frequency point conflict, the results of the non-blind evaluation method are preferentially adopted to make decisions.

Further, the receiver adopts a synchronous frequency hopping pattern to search the frequency hopping synchronous information of the transmitter; the synchronous hopping pattern refers to a hopping pattern that hops on the current synchronous frequency bin table.

Further, the synchronous frequency hopping pattern is generated on the current synchronous frequency point table according to a waiting search method; cascading M single-round frequency hopping patterns into a complete synchronous frequency hopping pattern by a waiting search method; m hops are contained in the single-round frequency hopping pattern, and the frequency points are consistent; the parameter M is the element number of the current synchronous frequency point table; the frequency points of all M rounds of single-round frequency hopping patterns are selected from different elements of the current synchronous frequency point table, and the current synchronous frequency point table can be traversed.

Further, the default synchronous frequency point is updated by the receiver every time when the receiver reaches a preset time, the preset time is generated by the timing of a local clock of the receiver, and the preset time is generated every time when the preset time is fixed; the frequency hopping synchronization information of the transmitter includes the local clock time of the transmitter, and the receiver adjusts its own time in accordance with it at step S4.

Further, all the frequency hopping frequency points form a communication frequency point table, and elements in the table are arranged in sequence; in step S2, the default synchronization frequency point set is generated in the following manner, the receiver calculates an index from the local time, and takes out one frequency point in the communication frequency point table as the first default synchronization frequency point; the other elements of the default synchronous frequency point set are sequentially selected from the frequency points, if the index exceeds the range of the table, the table head is returned to be continuously selected until all the synchronous frequency point sets are selected; the initial value of the current synchronous frequency point table is equal to the default synchronous frequency point set; if the current synchronous frequency point table contains the interfered frequency points, the current synchronous frequency point table is sequentially replaced by the candidate frequency points in the step S3; the candidate frequency points are selected from the communication frequency point table, the candidate frequency points are arranged in sequence after the last default synchronous frequency point, and if the index of the candidate frequency points exceeds the range of the communication frequency point table, the candidate frequency points return to the table head to continue to be selected; the frequency hopping points are divided according to the difference of the center frequency, and the frequency band width occupied by each frequency hopping point is consistent.

Further, the frequency point estimation result obtained in the step S1 has a valid period; step S3 checks whether the duration of execution S2 reaches a threshold value calculated from the validity period.

Further, the verification means in step S4 is a heel-and-toe verification method; the follow-up verification method refers to that a receiver sequentially waits for the effective signal of a transmitter on a predicted transmitter frequency hopping pattern, detects the existence of the effective signal for a plurality of times, and detects at least once in each hop occupied by the transmitter; if the rule is met within the limit detection times, judging that the follow-up verification is successful, otherwise judging that the follow-up verification is failed; compliance rules mean that there are Y times in X times of detection that a valid signal of the transmitter is detected, wherein Y is less than X; the method for detecting the effective signal of the transmitter comprises the steps of demodulating the signal, detecting the frame synchronization information sent by the transmitter at a specific hop, or detecting the signal sent by the transmitter at any hop by means of filtering and the like.

Further, if the local clock of the transceiver has time difference, default synchronous frequency point sets of the two parties are different; even if the default synchronous frequency point sets of the transceivers are different, the current synchronous frequency point table still exists the same; if the time difference of the transceiver exceeds a threshold value, the default synchronous frequency point sets of the two parties are completely different, and no intersection exists; even if the default synchronous frequency point sets of the transceiver are completely different, the alternative synchronous frequency points with consistent selection exist, so that the current synchronous frequency point tables of the two parties have intersection, and the two parties can finish frequency hopping synchronization.

The invention also discloses an anti-interference frequency hopping synchronization realization device suitable for the wireless ad hoc network, which comprises:

the frequency point evaluation module: the signal to noise ratio or noise energy of the signal can be calculated according to a section of bit stream of the information receiving module and is recorded as a frequency point evaluation value; the frequency point evaluation module compares the externally set threshold value with the frequency point evaluation value, and marks the state of each frequency point with the result.

A frequency hopping pattern generator module: the hopping pattern of the system can be updated periodically according to the hopping sequence and the system time. The hopping pattern determines the current frequency of the radio frequency hopping signal. The frequency hopping pattern generator takes a value from the frequency hopping sequence according to time, maps the value to one frequency point on the communication frequency point set, and generates a final frequency hopping pattern. The frequency hopping pattern generator can accelerate the process of generating the frequency hopping sequence and the process of converting the system time into the frequency hopping pattern in a table look-up mode. The frequency hopping pattern of the information received by the system and the frequency hopping pattern of the information transmitted by the system can be consistent or inconsistent, and the effectiveness of the frequency hopping synchronization function is ensured under the transmission and searching strategies of the synchronization head.

And a synchronous frequency hopping sequence updating module: according to the input of the frequency point evaluation module, a frequency hopping sequence serving a frequency hopping synchronization function is generated, which has been stripped of the interfered frequency points as much as possible and replaced with the undisturbed frequency points.

An information sending module: the frequency hopping synchronization information is encoded into a bit stream. At the time of updating the frequency hopping pattern, the bit stream carried by the next hop is modulated into a radio frequency signal on a corresponding frequency point to be sent.

An information receiving module: frequency hopping synchronization information among the bit streams is extracted. At the time of updating the frequency hopping pattern, receiving the bit stream of the next hop at the frequency point indicated by the frequency hopping pattern after updating is started.

The anti-interference frequency hopping synchronization method and the implementation device thereof suitable for the wireless ad hoc network have the following advantages: the invention optimizes the set of the synchronous frequency points, so that the frequency hopping synchronous flow of the receiver is completed on the frequency hopping frequency points which are not interfered or are less interfered as much as possible, the defect that the synchronous frequency points are easy to attack is overcome, the anti-interference performance of the system is enhanced, the frequency hopping initial synchronous probability is improved, and the frequency hopping initial synchronous time delay is reduced. The method provided by the invention is general, is suitable for the wireless ad hoc network frequency hopping anti-interference system, and is also suitable for other communication systems needing frequency hopping synchronization.

In the occasion that the invention is applied to the wireless ad hoc network system, the frequency hopping synchronization technology can be flexibly combined with the TDMA ad hoc network system, and compared with the similar technology, the frequency spectrum resource cost and the hardware cost of the frequency hopping synchronization function can be reduced. If the invention is not applied to the wireless ad hoc network frequency hopping system, the anti-interference performance can be exerted as expected, but the effects of reducing the cost of spectrum resources and hardware cost cannot be ensured.

Drawings

Fig. 1 is a schematic implementation flow chart of an anti-interference frequency hopping synchronization method based on a synchronization head in embodiment 2 of the present invention.

Fig. 2 is a data structure diagram of the key parameter TOD in embodiment 3 of the present invention.

Fig. 3 is a frame structure diagram of a synchronous micro-frame in embodiment 3 of the present invention.

Fig. 4 is a flowchart of deriving an adaptive frequency bin set in embodiment 3 of the present invention.

Fig. 5 is a time-frequency distribution diagram of a round of initial synchronization head in embodiment 3 of the present invention.

Fig. 6 is a search pattern of an initial synchronization header by a receiver in embodiment 3 of the present invention.

Fig. 7 is a search pattern of service synchronization information by a receiver in embodiment 3 of the present invention.

Fig. 8 is a graph of the relationship between the synchronization micro-frame preamble detection rate and the signal to noise ratio under different thresholds in embodiment 3 of the present invention.

Fig. 9 is a graph showing the relationship between the synchronization micro-frame preamble detection and the signal to noise ratio under different thresholds in embodiment 3 of the present invention.

Fig. 10 is a graph of the relationship between the synchronization micro-frame preamble detection miss rate and the signal to noise ratio under different thresholds in embodiment 3 of the present invention.

Fig. 11 is a diagram showing an example of the disturbed synchronization frequency point replacement method in embodiment 3 of the present invention.

Fig. 12 is a graph showing a comparison between the initial synchronization performance simulation and the conventional synchronization head method performance simulation of embodiment 3 of the present invention when α=0, η=0.5.

Fig. 13 is a graph showing a comparison between the initial synchronization performance simulation and the conventional synchronization head method performance simulation of embodiment 3 of the present invention when α=10, η=0.5.

Fig. 14 is a graph showing a comparison between the initial synchronization performance simulation and the conventional synchronization head method performance simulation of example 3 of the present invention when α=20, η=0.5.

Fig. 15 is a graph showing a comparison between the initial synchronization performance simulation and the conventional synchronization head method performance simulation of example 3 of the present invention when α=28, η=0.5.

Fig. 16 is a graph showing a comparison between the initial synchronization performance simulation and the conventional synchronization head method performance simulation of example 3 of the present invention when α=29, η=0.5.

Fig. 17 is a diagram showing a service synchronization deployment scenario capable of compressing the frequency hopping synchronization time according to embodiment 4 of the present invention.

Fig. 18 is a block diagram of an apparatus for implementing interference-free frequency hopping synchronization according to the present invention.

Fig. 19 is a flow chart of an anti-interference frequency hopping synchronization method applicable to wireless ad hoc networks.

Detailed Description

In order to better understand the purpose, structure and function of the present invention, the following describes in further detail an anti-interference frequency hopping synchronization method and its implementation device suitable for wireless ad hoc network with reference to the accompanying drawings.

Example 1:

an anti-interference frequency hopping synchronization method suitable for wireless ad hoc network comprises the following steps:

Step S5: and the frequency hopping synchronization flow is ended.

The frequency point evaluation method in the step S1 is a blind evaluation method, and a receiver can evaluate the state of each frequency point without a reference signal of a transmitter;

in the step S2, the default synchronous frequency point is selected by taking the system time as an index, and is updated progressively along with the system time;

the searching for the frequency hopping synchronization information in step S2 refers to detecting the frequency hopping pattern phase information of the transmitter.

In step S3, the frequency hopping frequency points not interfered are preferentially selected from default synchronization frequency points updated immediately in the future.

The method for verifying the frequency hopping pattern of the transmitter in the step S4 is a follow-up verification method, the receiver follows the hop for a plurality of times, whether each follow-up is successful or not is checked, and if the success ratio is greater than or equal to a threshold, the verification is considered as successful;

example 2:

as shown in fig. 1, the anti-interference frequency hopping synchronization method applicable to the wireless ad hoc network of the present invention includes the following steps considering the hardware implementation:

step S102: the set of hopping frequency points f1, f2...fn is traversed, the following is performed. Checking timeliness of the frequency point evaluation result, and re-evaluating the frequency hopping frequency point if the last evaluation of the frequency point is expired, and dividing the frequency hopping frequency point into an available frequency point and an unavailable frequency point; if the last evaluation of the frequency point is not expired, the frequency point is skipped, and the evaluation state is not changed.

Step S104: and updating a default synchronous frequency point table according to TOD, and updating the default synchronous frequency point table by using the undisturbed frequency points to generate a current synchronous frequency point table.

Step S106: and generating and applying a section of synchronous frequency hopping pattern according to the current synchronous frequency point table.

Step S108: searching synchronous hopping and demodulating frequency hopping synchronous information. If the synchronous hopping is searched and the frequency hopping synchronous information is successfully demodulated, executing a step S110; otherwise, executing step S102;

step S110: and verifying the correctness of the frequency hopping synchronous information by adopting a follow-up hopping verification method. If the verification is successful, the frequency hopping synchronization flow is ended; otherwise, executing step S102;

the minimum hardware required to implement the method includes: the system comprises a frequency hopping modulator, a frequency hopping demodulator, a high-precision system timing device, a low-power consumption timing device capable of working during system dormancy, and a central processing unit for executing software processes such as judgment, branching and the like.

The hopping pattern generator may be implemented by means of a logic device or an external memory. When the receiver acquires the frequency hopping synchronization information of the transmitter, it needs to be converted into a frequency hopping pattern phase, which may introduce a lot of operations. The logic device and the external energy storage accelerate the operation process in a table look-up mode. The frequency hopping pattern generator can also be implemented, maintained and updated by software through the central processing unit.

Example 3:

as shown in fig. 1, the anti-interference frequency hopping synchronization method applicable to the wireless ad hoc network of the present invention uses default synchronization frequency points equal to 2 and frequency hopping frequency points equal to 30 as examples to describe embodiment 2 in detail, and includes the following steps:

first, define the data format of TOD, this variable can control the implementation of all the processes of step S102, step S104, step S106, step S108, step S110, etc.

TOD is in units of hops with update interval equal to the hop rate of the communication hop pattern, and the local TOD count is incremented by one each time the communication hop pattern switches. In this embodiment, the hop rate of the communication hop pattern is 1200hop/s, which is also the speed of TOD update. TOD is also a representation of system time.

The time information added in the synchronization header has three items, including the lowest one bit of the TODH, and two items of TODM and TODL, and the three items are sequentially cascaded and called TOD_SEND. The high order bits of the TODH do not have to be transmitted in the synchronous micro-frames, thus ensuring the concealment of TOD. The complete TOD structure is shown in FIG. 2.

Taking the example of a hopping pattern length equal to 24 hours, the upper decimal count of TODL is zero if this value is exceeded, and the TODM is incremented by one. Similarly, TODL1 has an upper limit of TODH. Thus, the upper count limit for TOD is that TOD is zeroed beyond the upper limit. The period of TOD is 103680000 hops, which is exactly equal to the number of hops experienced by 24 hours of frequency hopping. Although the upper decade limit 863159999 of TOD is not equal to the number of hops 103680000 it contains in a cycle, TOD count and phase in a cycle are in one-to-one relationship and can be converted to each other as defined above and in the structure of fig. 2. When the TOD is used as an index to the hopping sequence, it is actually the phase of the hopping pattern generator that is fed into the hopping pattern generator, rather than the count.

The hop of the synchronization header transmitted by the frequency hopping transmitter is called a synchronization hop, and the time slot of transmitting other information is called a data hop. The hop speed of the sync hop may be greater than the hop speed of the data hop. In this embodiment, the data hop contains five equally long micro frames back to back, the micro frames being the minimum frame length units of the system. Service hops are data hops that contain at least one sync micro-frame. The initial sync hop contains only one micro-frame, called sync micro-frame. It is easy to know that the hop length of the initial synchronization hop is one fifth of the data hop. The hopping speed of the initial synchronous hopping pattern is five times that of the communication hopping pattern and is 6000hop/s. The frame structure of the sync micro-frame is shown in fig. 3.

As can be seen from the frame structure of the synchronous micro-frame, in embodiment 3, the OFDM modulation technique is adopted, so that the subcarrier interval of the OFDM symbol is 15khz, the available subcarriers are 1200 subcarriers (except the central direct current subcarrier) at the center of the frequency hopping point, the remaining subcarriers at two sides are used as the guard bandwidth, the sampling rate is 30.72Mhz, and the occupied communication bandwidth is about 20.48Mhz. Of 1200 available subcarriers, one fifth of the subcarriers are used for transmitting reference signals, the subcarrier modulation mode is unified to be QPSK, so that one OFDM symbol can accommodate 960 valid QPSK codes, and assuming that the source adopts (1920,1408) LDPC coding, the number of bits that can be accommodated by the synchronous micro-frame OFDM symbol is 1408. From previous analysis of TOD structure, the sync micro-frame is sufficient to accommodate TOD with an overhead of 27 bits. In order for the receiver to distinguish between the initial synchronization information and the service synchronization information, the synchronization micro-frame also needs to be added with 1 bit. In view of the fact that the hopping speed of the initial synchronization hopping pattern is 5 times higher than the updating speed of TOD, the synchronization micro-frames also need to be added with 3 bits to match with the TOD, and the phases of the initial synchronization micro-frames are marked together. Assuming that the network number and CRC check also require 30 bits, the overhead of the sync micro-frame for frequency hopping synchronization is 61 bits, which is much lower than the capacity of the sync micro-frame. In other words, in this embodiment, the radio station does not need to send a synchronization micro frame specifically, and can select to insert relevant synchronization information into a general data micro frame to realize the synchronization micro frame, so that redundant resources are fully utilized, and waste is reduced.

The cyclic prefix copies and transmits the later part of the OFDM symbol time domain in advance, and is a common multipath interference resistant technology. Leaving long guard intervals is a design requirement for ad hoc network systems. The synchronous preamble consists of two sections with the length of N _ZC The ZC sequence of=256 is repeatedly formed, and the occurrence formula of each ZC sequence is as follows:

wherein the method comprises the steps of

The final complete synchronization preamble sequence is: s (n) = [ x ] _q x _q ]。

Wherein x is _q Is a ZC sequence with length of 256, S (n) is a ZC sequence x which is formed by two identical segments _q And merging the formed synchronous preamble sequences.

In step S102, if the receiver is first powered on, the set of frequency hopping points f1, f2..

Each time the receiver evaluates a frequency bin, it will stay on the target frequency bin for at least one synchronization micro-frame, if a signal from the transmitter (whether the synchronization micro-frame or other micro-frames) is detected, then the non-blind evaluation (such as signal to noise ratio estimation) of the frequency bin is performed, and the signal to noise ratio estimation is compared with a threshold to divide the available state of the frequency bin. If no signal from the transmitter is detected, a frequency point blind evaluation (e.g., energy detection method) is performed, noise energy is compared with a threshold, and the available state of the frequency point is divided. In the actual signal processing flow, the two evaluation modes can be performed simultaneously, if the available result of the frequency point is obtained, the channel is marked as available, otherwise, the frequency point is marked as unavailable.

If the receiver is not powered on for the first time, the set of frequency hopping points f1, f2.. Whenever the local TOD is a multiple of 10 seconds, TODLmod12000 ₍₁₀₎ The TOD at the last update of the hop point is checked, and if it is earlier than 10 seconds, the point is re-evaluated. In this embodiment 3, the maximum time for the receiver search strategy to traverse all the frequency hopping points does not exceed 10 seconds, so the time interval threshold can ensure that all the frequency point evaluation results are utilized, and the waste phenomenon of repeatedly evaluating unused frequency points does not occur.

Finally, the receiver may use a bitmap to mark the available states of all the frequency hopping points, and the step S102 mentioned above realizes the establishment and update of the bitmap.

In step S104, the rule that the receiver selects the default synchronization frequency point according to the local TOD is as follows.

It is not just assumed that all the hopping frequency points sequentially form a communication frequency point set S _com The default synchronization frequency points form a sliding synchronization frequency point set S _sync The relationship between the two can be expressed as follows:

Sync_index＝TODH*(TODL1 _max +1)+TODL1

S _sync ＝{S _com ((Sync_index+1)mod N)，

S _com ((Sync_index+2)mod N)，

…,

S _com ((Sync_index+M)mod N)}

for S _com The index of (2) starts from 0. If the default synchronization frequency number M is additionally set, S can be filled according to the rule _sync Is not limited, and the rest of the elements of (a) are contained. In this embodiment, m=2 as described above. TODL1 _max ＝M＝2。S _sync The last element of (2) is S _com ((Sync_index+2) mod N), the index interval of its elements is 1.

The default set of synchronization frequency points is also referred to as a sliding synchronization frequency point set S _sync The above formula shows the law of "sliding" over the set of communication frequency points with local time TOD. The above formula also shows that as long as the Sync_index difference of the two transmitting and receiving parties is within a certain range, the default synchronous frequency point sets of the two parties have intersections. For this embodiment 3, the Sync_index difference tolerance is 2 (less than and not equal to 2), which also constrains the TOD difference range, which in this embodiment is equal to 120000 hops, 100 seconds.

The following describes how the current synchronization frequency point table is generated from the sliding synchronization frequency point set. The size of the current synchronous frequency point table is equal to the size M of the default synchronous frequency point set, and repeated elements can be accommodated.

And traversing the default synchronous frequency point set, counting beta interfered synchronous frequency points, executing the process shown in fig. 4 to select replacement frequency points, and replacing the corresponding interfered synchronous frequency points with the frequency points. The replacement frequency points constitute an adaptive set of frequency points (which may contain repeating elements).

It can be pointed out that if the adaptive frequency point set has a size of N _a Necessarily satisfy N _a And M is less than or equal to. Let the size of the sliding synchronous frequency point set be N _move At the moment, the element quantity is squeezed by the self-adaptive frequency point set, obeys N _move +N _a ＝M。

So far, the current synchronization frequency point table has been obtained, and step S104 is completed.

In step S106, the receiver generates a synchronization hopping pattern for searching for hopping synchronization information of the transmitter. In this embodiment, this function is equivalent to searching for the sync micro frame preamble of the transmitter and then demodulating the TOD information contained in the sync micro frame. In other words, the synchronous hopping pattern is just a search pattern, and the waiting search method is followed. As the search pattern, its function necessarily supports searching for both initial synchronization information and service synchronization information. The difference between them is that the initial synchronization information is contained in the initial synchronization micro-frame,

the service synchronization information is contained in a service synchronization micro-frame; the initial synchronization micro-frame will continuously transmit at least M ² And the service sync micro-frames may be sent discontinuously. The common point of the two is that the radio station sends out that the synchronous frequency point occupied by the next synchronous micro-frame is inconsistent with the synchronous frequency point occupied by the last synchronous micro-frame; a round of synchronous micro frames comprises M micro frames, and the current synchronous frequency point table with the size of M can be traversed.

The time-frequency distribution of the initial synchronization head of a round is shown in fig. 5, and as described above, the initial synchronization head comprises M continuous synchronization micro-frames, and M elements of the current synchronization frequency point table are traversed. The frequency hopping pattern for searching using the waiting search method equal to the initial synchronization header is shown in fig. 6, and the transmitter repeatedly transmits the initial synchronization header as shown in fig. 5 until the receiver completes searching on all the synchronization frequency points.

As shown in fig. 6, as long as the step length of the receiver for switching the frequency points is greater than the length of the initial synchronization head, when the receiver resides in the M frequency points of the current synchronization frequency point table for searching, at least one opportunity exists on each frequency point, so that the frequency points of the synchronization micro-frame are consistent with the frequency points of the receiver, and therefore the receiver can detect the TOD information of the transmitter, and the subsequent frequency hopping synchronization process is completed, which is the principle of waiting for the searching method. As can be seen from the previous discussion, if there is no difference in TOD of the transceiver, the receiver can detect synchronization information on M frequency points. Fig. 6 shows only the limit of detecting synchronization information at one frequency point, where the difference in TOD of the transceiver is close to the tolerance, and meets the most basic requirement of frequency hopping synchronization.

The frequency hopping pattern of the receiver searching for the service synchronization information is shown in fig. 7. And ellipses exist between the service synchronization micro frames, which means that the synchronization micro frames are not continuously transmitted and are not immediately and repeatedly transmitted.

As can be seen from fig. 7, in the searching process for service synchronization, the residence time of the receiver at a certain frequency point is required to be long enough to cover a service synchronization micro-frame, so that the fast-transmitting and slow-receiving method can be applied. If the transmitter is able to perform service hopping in turns at M different frequency points, at least one frequency point may coincide with the receiver. And after the M frequency points reside for a preset time length, the receiver completes the service synchronous micro-frame search on all the synchronous frequency points.

Such a search pattern obviously also allows for searching for initial synchronization, and the search pattern for initial synchronization and service synchronization is uniform for the receiver, as shown in fig. 6 and 7. As long as the residence time of the receiver at a certain frequency point is long enough, continuous M initial synchronization micro frames can be covered, and searching of the initial synchronization head is considered.

Suppose that the shortest interval for sending out service synchronous micro-frames by the radio station is T _{sync_hop} . Then the search pattern has a length T _search ＝M ² *T _{sync_hop} This is also the shortest time for the initial synchronization of frequency hopping. It should be noted that, the requirement for completing the search of the frequency hopping synchronization information in step S106 is that the transmitter will not miss some frames when sending out the service synchronization micro-frame or the initial synchronization micro-frame, and will not introduce missed detection artificially.

Thus far, the manner in which the receiver synchronizes to the hopping pattern (i.e., the search pattern) has been illustrated. Meanwhile, a constraint is also made on the way that the transmitter sends out the synchronous micro-frames to ensure the validity of the waiting search method. It is worth noting that the synchronous hopping pattern of the transmitter and the receiver is not uniform. The transmitter sends out an initial synchronization header and a service synchronization micro-frame, and the receiver searches for it in a search pattern. When the flow of the transmitter generating the current synchronous channel table is consistent with the receiver. In embodiment 4, another search pattern that can be used with the present invention is shown and discussed.

In step S106, the initial synchronization hop where the initial synchronization micro frame is located and the service hop where the service synchronization micro frame is located are both synchronization hops, but the hop length and the hop speed are different. The receiver can demodulate the frequency hopping synchronization information no matter which kind of synchronization hops is searched.

In step S108, the receiver searches for a synchronization hop, and demodulates the frequency hopping synchronization information therein. The principle of searching for the synchronization hops follows the waiting search method, which has been explained in the implementation method of step S106. In this embodiment, TOD_SEND is used to communicate the frequency hopping synchronization information, while in other embodiments, system time, current frequency hopping pattern phase, frequency hopping sequence generation register status, etc. information may be used to communicate the frequency hopping synchronization information, as long as the information can help the receiver predict the frequency hopping pattern of the transmitter (including communication frequency hopping pattern and synchronization frequency hopping pattern).

In this embodiment 3, the receiver detects the presence of the preamble of the sync micro-frame to decide whether to continue demodulating the OFDM signal and extract tod_send. In the related art, there are various methods of designing a preamble and detecting its existence. The present embodiment will select one of the examples operating at AWGN frequency, which does not affect the advantages and functional effectiveness of the present invention when it is used with other related technologies.

Let the receiving end receive the signal asWhere v (n) is an AWGN signal, then the metric M (n) can be set as follows.

Where l=512 and p=256, just corresponds to the preamble. Wherein f _c Is a carrier frequency and can be an intermediate frequency of each frequency hopping point. Comparing the metric M (n) with a given threshold eta, if M (n)>η is regarded as detected (synchronized), whereas η is regarded as undetected. If s (n) =0 is substituted into the above process, a corresponding false alarm result and false alarm probability are obtained. For this methodThe software simulation results of (2) are shown in fig. 9.

It should be noted that the plot of the false alarm rate shown in fig. 9 lacks two curves, which are not incomplete but are zero. The ZC preamble detection method referred to in this embodiment is insensitive to the signal-to-noise ratio, but is sensitive to the detection threshold η, so the curve of fig. 9 hardly changes with the signal-to-noise ratio.

As can be seen from fig. 8, 9 and 10, the smaller η is, the larger the false alarm rate is, the smaller the omission factor is, and the optimization of both are in contradictory relation. Therefore, when the system parameters are designed, the threshold eta and the ZC sequence repetition number can be adjusted, and the preamble detection probability and the false alarm rate are balanced to meet the design constraint.

In the similar research, during the follow-up verification, only the synchronous preamble on the follow-up frequency hopping point is needed to be repeatedly detected, and the synchronous micro-frame is not needed to be demodulated. Although this embodiment requires first acquiring the TOD_SEND once and has to demodulate the sync micro-frame, it may choose to check only the presence of the sync preamble during the skip following verification so that the receiver can perform the skip following verification on the data skip. Therefore, step S108 can also refer to the conventional approach, and approximately considers that the probability of demodulating the synchronous micro frame to obtain the tod_send depends only on the preamble detection probability, and the demodulation tod_send probability is irrelevant. In summary, the probability of demodulating the frequency hopping synchronization information focused in step S108 may be replaced by the probability of demodulating the synchronization micro-frame to obtain the tod_send. This probabilistic modeling helps to measure the performance of the present invention without affecting the fair comparison of the present invention to the prior art of the same class, and is therefore emphasized in this example 3.

To further illustrate the optimization effect of the present invention (to increase the actual number of times the receiver finds the frequency hopping synchronization information in a round of search patterns), fig. 11 illustrates the receiver search pattern and search results after the substitution of the interfered synchronization frequency points.

As can be seen from fig. 11, the receiving and transmitting parties have time difference, and the unique intersection set (frequency point No. 4) of the default synchronization frequency point set is interfered, so the receiver cannot find the synchronization information in the current search pattern according to the conventional synchronization header method, and only can wait for the synchronization frequency point sets of the two parties to update to a state of no interference along with time. After the process of replacing the interfered synchronous frequency points is adopted, the interfered No. 4 synchronous frequency points are replaced by the No. 9 frequency points which are not interfered, and the receiver can find the synchronous signal of the transmitter in the current searching pattern to complete frequency hopping synchronization. It should be noted that default synchronization frequency points, such as frequency points 5, 6, 7 and 8, which will be adopted by both parties later are already interfered, which means that the frequency hopping synchronization functions of both parties are completely destroyed within a period of time, and the present invention can continuously avoid this situation.

In step S110, the receiver adjusts the local tod_send to be consistent with the transmitter on the premise of obtaining the transmitter tod_send. As described above, if the time difference between the transmitting and receiving sides is within a certain range (equal to 100 seconds in the present embodiment), the TODs of both sides can be matched. At this time, the receiver should be able to predict the frequency hopping pattern of the transmitter for follow-up verification.

The following hop verification process is as follows, the receiver waits for the effective signal of the transmitter on the predicted transmitter frequency hopping pattern in turn, detects the existence of the effective signal for a plurality of times, and detects at least once in each hop occupied by the transmitter; if the rule is met within the limit detection times, judging that the follow-up verification is successful, otherwise judging that the follow-up verification is failed; compliance rules mean that there are Y times in X times of detection that a valid signal of the transmitter is detected, where Y is less than X. In this example 3, Y is 5 and X is 3.

In embodiment 3, other micro frames inserted between service micro frames also include ZC synchronization preambles, which can be used for follow-up verification, so that the receiver can choose to use data hops and synchronization hops simultaneously to perform follow-up verification, so as to speed up the verification, instead of being constrained to perform follow-up verification on synchronization hops. The receiver is likely to encounter this situation given that the search pattern is compatible with searching for initial synchronization header and service synchronization micro-frames.

In order to further embody the optimization effect of the invention on the anti-interference performance of frequency hopping synchronization, the initial synchronization probability simulation result of the embodiment is shown as follows. The simulation conditions are described in table 1.

Table 1 simulation parameters of initial synchronization probability of anti-interference frequency hopping synchronization method

It can be found that the interference is in the form of partial band blocking interference, so that α frequency points (after channel estimation) of the transceiver are not used, which is the interference level constraint. The interfered frequency points of the transmitting and receiving parties can be identical or different, the situation of complete identical is called a symmetric frequency table, and the other situation is called an asymmetric frequency table. The simulation is carried out in a Monte Carlo simulation mode, and each simulation randomly interferes with alpha frequency points of the transceiver.

It should be noted that one round of the search pattern contains a synchronization micro-frame number of 240, representing that the receiver experiences 120 synchronization micro-frames at the dwell frequency point, which is equal to 60 rounds of initial synchronization header. In practice, the receiver does not need to go through as many rounds of synchronization information to complete the initial frequency hopping synchronization, which is wasteful of the search pattern in order to be compatible with searching for service synchronization information. One round of searching patterns can only reside in M=2 frequency points, and M is searched at most ² =4 service sync subframes. This phenomenon shows that any service synchronous micro frame of the transmitter is not missed by the receiver, so that the necessity of the two transceivers working on the available synchronous frequency point is further reflected, and the advantage of the invention for strengthening the anti-interference performance of the synchronous head method is reflected.

The data output by simulation is P _{fsc_sym} 、P _{fsc_asym} 、P _{fsc_bfh} 。

P _{fsc_sym} Is the average initial synchronization probability P obtained by Monte Carlo simulation in the case of the symmetrical frequency table in this embodiment 3 _fsc 。

P _{fsc_asym} Is the average initial synchronization probability P obtained by Monte Carlo simulation in the case of the asymmetric frequency table in this embodiment 3 _fsc 。

P _{fsc_bfh} Is the average initial synchronization probability P obtained by Monte Carlo simulation under the condition of an asymmetric frequency table by the traditional synchronization head method _fsc . The traditional synchronization header method refers to a synchronization header method without finding and replacing the disturbed synchronization frequency point flow. In this embodiment, it is equivalent to directly replacing the current with the default synchronization frequency point setThe synchronization channel table generates a synchronization hopping pattern scenario.

Note that P _{fsc_sym} And P _{fsc_bfh} The comparison of (1) does not conform to the analysis principle of the control univariate. Thus simulation result shows P _{fsc_sym} /P _{fsc_bfh} There is no practical significance whether greater than 1 or less than 1. However, by comparing P _{fsc_sym} /P _{fsc_bfh} And P _{fsc_asym} /P _{fsc_bfh} The positional relationship of the two curves can verify that the performance of the present embodiment in the case of the asymmetric frequency table is inferior to that in the case of the symmetric frequency table as long as the latter is below the former. This indirect comparison eliminates P _{fsc_bfh} Is a function of (a) and (b).

When α=0, η=0.5, the initial synchronization probability P _fsc The simulation results are shown in fig. 12.

As can be seen from fig. 12, when there is no interference, the performance of the present embodiment is identical to that of the conventional synchronous head method, which is equivalent to the case shown in fig. 12.

When α=10, η=0.5, the initial synchronization probability P _fsc The simulation results are shown in fig. 13.

As can be seen from fig. 13, when one third of the frequency points are interfered, the performance of the present embodiment is superior to that of the conventional synchronization head method. The performance of the present embodiment is better in the case of the symmetric frequency table than in the case of the asymmetric frequency table.

When α=20, η=0.5, the initial synchronization probability P _fsc The simulation results are shown in fig. 14.

When α=20, η=0.5, and there are two-thirds of the frequency points that are disturbed, the conclusion is similar to the case of α=10, η=0.5. The initial synchronization probability of this embodiment is improved by an order of magnitude compared to the conventional method.

When α=28, η=0.5, and when α=29, η=0.5, the initial synchronization probability P _fsc The simulation results are shown in fig. 15 and 16.

As can be seen from fig. 15 and 16, when almost all the frequency points are interfered, the performance of the embodiment is better than that of the conventional method, and the initial synchronization probability can be improved by two orders of magnitude. When α=n=29, all frequency points are disturbed, and the above performance comparison is not significant.

It should be noted that these illustrated ratio curves are not flat. One of the reasons for this is that the present invention makes the number of difference elements N of the two-node synchronous frequency point set _e Reduction, which is represented by P in the low signal-to-noise ratio interval _fsc Raised several times. The second reason for this is that as the number of rounds of Monte Carlo simulation increases, it averages P _fsc The distribution of (2) necessarily favors N _e Distribution at the time of decrease. This is why the ratio curves of these simulation results show a decrease, but eventually converge to the lower limit of the performance optimization. This lower limit is greater than the performance of the conventional synchronization head method, and marks the performance optimization effect of the embodiment in the high signal-to-noise ratio range.

The data hop length shown in this embodiment 3 is equal to 5 micro frames, so that the highest hop speed that can be supported by the system is 5 data hop speeds, namely 6000hop/s, without breaking the micro frames. In the simulation condition, the initial synchronous frequency hopping pattern hopping speed sent by the sender is five times of the communication frequency hopping pattern and is 6000hop/s. This increases the hardware overhead and power consumption overhead of the sender, and as can be seen from the previous analysis, the redundant initial synchronization micro-frames constitute a waste. Thus, the sender may compress the hop-speed when sending the initial synchronization header, which may even be lower than the data hop-speed 1200hop/s. The specific implementation method can be that a protection interval is prolonged at the tail part of the synchronous micro-frame, M rounds of initial synchronous heads are sent in the time length of the searching pattern, and each round of initial synchronous heads comprise M initial synchronous micro-frames on different synchronous frequency points.

The above discussion about the hop rate indicates the flexibility and adjustability of the hop mechanism of the sender, and the characteristics of the invention that the performance of the hop synchronization anti-interference is optimized will not be affected regardless of the hop rate setting.

So far, the optimization effect exhibited by the present invention in this embodiment has been fully explained. Compared with the traditional synchronous head frequency hopping synchronous method, the method can improve the actual times of the receiver for finding the frequency hopping synchronous information in a round of searching patterns, improve the frequency hopping initial synchronous probability, and reduce the optimization effects of follow-up frequency hopping verification delay and the like.

Example 4:

the service synchronization micro-frame distribution shown in embodiment 3 allows the transmitter to insert other data information in the service hops instead of transmitting one service synchronization micro-frame immediately after the next synchronization micro-frame is transmitted, which increases the shortest interval T of the service hops _{sync_hop} The searching pattern is prolonged, and the time delay of compression frequency hopping synchronization is not facilitated. The service synchronization micro-frame shown in embodiment 3 is suitable for high performance wireless ad hoc networks employing TDMA-MAC, and can flexibly combine synchronization hops and TDMA-MAC, which is a compromise design, and cannot be seen to limit the advantages of the present invention.

To further illustrate this, embodiment 4, referring to embodiment 3, modifies the ad hoc network MAC based on embodiment 3, combines unequal interval hopping with the ad hoc network TDMA-MAC, and shows an application case where the search pattern is shorter than that of embodiment 3, and the initial synchronization probability is identical to that of embodiment 3. The initial synchronization header structure is the same as that described in example 3, but the service micro-frame deployment is as shown in fig. 17.

The scheme shown in fig. 17 is characterized in that the sender continuously sends M service synchronization micro frames, traverses the current synchronization channel table, repeats the process at intervals, and totally sends/searches a pattern M times, and is completely one round. During the continuous transmission of the service synchronization micro-frames by the sender, the jump speed is multiplied. Comparing fig. 7, it can be found that the scheme shown in fig. 17 compresses the time between service synchronization micro frames, and allows the transceiver to agree on a search pattern with a shorter duration, so as to achieve the compression of the frequency hopping synchronization time.

Example 4 the protocol described in example 4 enables compression of T _{sync_hop} Its search pattern length still obeys T _search ＝M ² *T _{sync_hop} . Thus, embodiment 4 has a shorter frequency hopping synchronization time than embodiment 3, with other conditions and results unchanged. As can be seen from fig. 17, the time between service sync micro frames can also continue to be compressed, and the gain effect is within the expected effect of the present invention.

In embodiment 3, it has been pointed out that the sender inserts gaps between service synchronization micro frames in order to reserve redundant time slots, avoid collision with multi-hop neighbors and avoid mutual interference, which is a necessary consideration for TDMA ad hoc networks. The scheme shown in embodiment 4 may be implemented by modifying the TDMA ad hoc network MAC. For example, a plurality of empty time slots are inserted at regular intervals at the switching moment of the wireless frame, so that the node can increase the speed of the jump, send M service synchronization micro frames, and then resume the speed of the jump. This modification will undoubtedly bring many compatibility problems to TDMA ad hoc MAC and frequency hopping techniques, and also increases power consumption, hardware cost, and time slot resource overhead, which need to be studied and discussed in depth, but is not a practical case of the present invention.

Although the TDMA ad hoc network system shown in embodiment 3 is a typical application scenario in which the advantages of the present invention can be exerted. However, it should be noted that the effect of the present invention on the interference performance of the frequency hopping synchronization method is not limited to the TDMA ad hoc network system described in embodiment 3. For example, the service synchronization deployment scheme of embodiment 4 can be applied to non-TDMA ad hoc network systems, such as CSMA/CA or RTS/CTS based ad hoc networks, thereby avoiding the cost of TDMA-compatible ad hoc networks described above. The service synchronous deployment scheme shown in embodiment 4 can also be applied to non-ad hoc network systems, such as conventional FSK frequency hopping stations. In fact, many conventional FSK frequency hopping station designs have adopted a service synchronization information deployment approach similar to that of FIG. 17.

Example 5:

an anti-interference frequency hopping synchronization implementation device suitable for wireless ad hoc networks, as shown in fig. 18, comprises:

The application combines the frequency hopping pattern generation flow and the mechanism avoiding the interfered frequency points by optimizing the synchronous frequency hopping sequence updating module, so that the frequency hopping synchronous flow of the receiver is completed on the frequency hopping frequency points which are not interfered or are interfered less as much as possible, the defect that the synchronous frequency points are easy to attack is overcome, the anti-interference performance of the system is enhanced, the frequency hopping initial synchronization probability is improved, and the frequency hopping initial synchronization time delay is reduced. The method provided by the application is general, is suitable for the wireless ad hoc network frequency hopping anti-interference system, and is also suitable for other communication systems needing frequency hopping synchronization.

It will be understood that the application has been described in terms of several embodiments, and that various changes and equivalents may be made to these features and embodiments by those skilled in the art without departing from the spirit and scope of the application. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the application without departing from the essential scope thereof. Therefore, it is intended that the application not be limited to the particular embodiment disclosed, but that the application will include all embodiments falling within the scope of the appended claims.

Claims

1. An anti-interference frequency hopping synchronization method suitable for wireless ad hoc networks is characterized by comprising the following steps:

step S1, firstly, a receiver evaluates frequency points to obtain the interfered state of each frequency hopping frequency point;

step S2, the receiver searches frequency hopping synchronization information on the current synchronization frequency point table; the searching strategy adopts a waiting searching method; if the receiver does not search the frequency hopping synchronization information, the default synchronization frequency point is selected from the frequency hopping frequency point set again every appointed time, and the step S3 is carried out to generate a current synchronization frequency point table; if the receiver searches the frequency hopping synchronous information, the step S4 is entered;

s3, the receiver replaces the interfered default synchronous frequency point with the undisturbed frequency hopping frequency point, and combines the interfered default synchronous frequency point with the undisturbed default synchronous frequency point to generate a current synchronous frequency point table; if the time for the receiver to execute the step S2 reaches the threshold value, the step S1 is entered, otherwise, the step S2 is returned to;

step S4: the receiver adjusts the local frequency hopping pattern according to the frequency hopping synchronous information, is consistent with the transmitter and aligns the phase, and can predict the frequency hopping pattern of the transmitter; then the receiver consumes a certain time and processing capacity to verify that the frequency hopping pattern of the transmitter is predicted correctly, and the step S5 is performed; if the receiver cannot verify that the steps of the transmitter are correct, the step S2 is entered;

Step S5: and the frequency hopping synchronization flow is ended.

2. The anti-interference frequency hopping synchronization method applicable to the wireless ad hoc network according to claim 1, wherein the frequency point evaluation method comprises a blind evaluation method and a non-blind evaluation method; the blind evaluation method does not need a transmitter to send out a reference signal; the non-blind evaluation method requires reference to the signal of the transmitter; the frequency point evaluation method finally evaluates the frequency point as one of binary states, namely the frequency point is available or unavailable; the receiver adopts multiple frequency point evaluation methods to evaluate the same frequency point at the same time; when the results of the multiple methods evaluate the frequency point conflict, the results of the non-blind evaluation method are preferentially adopted to make decisions.

3. The anti-interference frequency hopping synchronization method for wireless ad hoc network according to claim 1, wherein the receiver adopts a synchronization frequency hopping pattern to search for frequency hopping synchronization information of the transmitter; the synchronous hopping pattern refers to a hopping pattern that hops on the current synchronous frequency bin table.

4. The anti-interference frequency hopping synchronization method for wireless ad hoc network according to claim 3, wherein the synchronous frequency hopping pattern is generated on the current synchronous frequency point table according to the waiting search method; cascading M single-round frequency hopping patterns into a complete synchronous frequency hopping pattern by a waiting search method; m hops are contained in the single-round frequency hopping pattern, and the frequency points are consistent; the parameter M is the element number of the current synchronous frequency point table; the frequency points of all M rounds of single-round frequency hopping patterns are selected from different elements of the current synchronous frequency point table, and the current synchronous frequency point table can be traversed.

5. The method of claim 1, wherein the default synchronization frequency point is updated every time the receiver reaches a predetermined time, the predetermined time being generated by the timing of a local clock of the receiver, the predetermined time being generated every fixed time interval; the frequency hopping synchronization information of the transmitter includes the local clock time of the transmitter, and the receiver adjusts its own time in accordance with it at step S4.

6. The method for synchronizing anti-interference frequency hopping applicable to wireless ad hoc network according to claim 5, wherein all frequency hopping frequency points form a communication frequency point table, and elements in the table are arranged in sequence; in step S2, the default synchronization frequency point set is generated in the following manner, the receiver calculates an index from the local time, and takes out one frequency point in the communication frequency point table as the first default synchronization frequency point; the other elements of the default synchronous frequency point set are sequentially selected from the frequency points, if the index exceeds the range of the table, the table head is returned to be continuously selected until all the synchronous frequency point sets are selected; the initial value of the current synchronous frequency point table is equal to the default synchronous frequency point set; if the current synchronous frequency point table contains the interfered frequency points, the current synchronous frequency point table is sequentially replaced by the candidate frequency points in the step S3; the candidate frequency points are selected from the communication frequency point table, the candidate frequency points are arranged in sequence after the last default synchronous frequency point, and if the index of the candidate frequency points exceeds the range of the communication frequency point table, the candidate frequency points return to the table head to continue to be selected; the frequency hopping points are divided according to the difference of the center frequency, and the frequency band width occupied by each frequency hopping point is consistent.

7. The anti-interference frequency hopping synchronization method applicable to the wireless ad hoc network according to claim 1, wherein the frequency point evaluation result obtained in the step S1 has a valid period; step S3 checks whether the duration of execution S2 reaches a threshold value calculated from the validity period.

8. The method for anti-interference frequency hopping synchronization for wireless ad hoc networks according to claim 1, wherein the verification means in step S4 is a follow-up-hop verification method; the follow-up verification method refers to that a receiver sequentially waits for the effective signal of a transmitter on a predicted transmitter frequency hopping pattern, detects the existence of the effective signal for a plurality of times, and detects at least once in each hop occupied by the transmitter; if the rule is met within the limit detection times, judging that the follow-up verification is successful, otherwise judging that the follow-up verification is failed; compliance rules mean that there are Y times in X times of detection that a valid signal of the transmitter is detected, wherein Y is less than X; the method for detecting the effective signal of the transmitter comprises the steps of demodulating the signal, detecting the frame synchronization information sent by the transmitter at a specific hop, or detecting the signal sent by the transmitter at any hop by means of filtering and the like.

9. The method of anti-interference frequency hopping synchronization for wireless ad hoc networks according to claim 6, wherein if there is a time difference between local clocks of the transceivers, default synchronization frequency point sets of both parties are different; even if the default synchronous frequency point sets of the transceivers are different, the current synchronous frequency point table still exists the same; if the time difference of the transceiver exceeds a threshold value, the default synchronous frequency point sets of the two parties are completely different, and no intersection exists; even if the default synchronous frequency point sets of the transceiver are completely different, the alternative synchronous frequency points with consistent selection exist, so that the current synchronous frequency point tables of the two parties have intersection, and the two parties can finish frequency hopping synchronization.

10. An anti-interference frequency hopping synchronization device suitable for wireless ad hoc networks, which is characterized by comprising:

the frequency point evaluation module: the signal to noise ratio or noise energy of the signal can be calculated according to a section of bit stream of the information receiving module and is recorded as a frequency point evaluation value; the frequency point evaluation module compares the externally set threshold value with the frequency point evaluation value, and marks the state of each frequency point by using the result;

a frequency hopping pattern generator module: the frequency hopping pattern of the system can be updated periodically according to the frequency hopping sequence and the system time; the frequency hopping pattern determines the current frequency of the radio frequency hopping signal;

and a synchronous frequency hopping sequence updating module: generating a frequency hopping sequence serving a frequency hopping synchronization function according to the input of the frequency point evaluation module;

an information sending module: encoding the frequency hopping synchronization information into a bit stream; at the time of updating the frequency hopping pattern, the bit stream carried by the next hop is modulated into a radio frequency signal on a corresponding frequency point to be sent;

an information receiving module: extracting frequency hopping synchronization information in the bit stream; at the time of updating the frequency hopping pattern, receiving the bit stream of the next hop at the frequency point indicated by the frequency hopping pattern after updating is started.