A multi-level overmodulation short packet communication method

Abstract

The present invention discloses a multi-level overmodulation short packet communication method, comprising: first information is modulated with a first overmodulation sequence to obtain second information; the second information is received as third information through a channel, the third information traverses all correlators to perform correlation operations, and the correlation value with the largest absolute value related to each correlator is taken as fourth information, and the first information to be transmitted is solved according to the correlator corresponding to the correlation value with the largest absolute value; the fourth information is multiplied with the corresponding element of the second overmodulation sequence and then summed, and the absolute value is taken to obtain the evaluation function value; when the evaluation function value is the largest, the corresponding second overmodulation sequence is the second overmodulation sequence used to modulate the first information. The present invention does not need to increase the demodulation complexity of the user, improves the information frame symbol synchronization performance, and adds additional information for without increasing the length of the data packet.

Description

Technical Field

[0001] The present invention relates to the technical field of signal modulation, and more specifically, to a multi-level overmodulation short packet communication method and device. Background Art

[0002] With the application and development of new scenarios of IoT and machine communication such as cloud connection, Internet of Vehicles, and unmanned driving, short data packet communication faces huge challenges in information capacity, latency, reliability, etc. One of the main challenges is to occasionally transmit control, command information and sensor data through small data packets in typical scenarios such as drones and robots, while meeting the communication requirements of high bandwidth utilization and fast information transmission rate. When facing multiple receiving targets, additional bit information is required to attach user features, which increases the length of short data packets to a certain extent, thereby affecting the transmission efficiency of short packet communication. In 2017, Kamil Senel used the approximate message passing (AMP) method to use the mutual difference of the leading sequence to realize user detection and a large number of device identification in cellular networks. In 2023, Zhang Gang's team proposed a multi-carrier correlated delay shift keying (TST-MUMC-CDSK) system based on time slot transformation. This scheme uses a permutation matrix to transform the reference signal to achieve the purpose of transmitting information, but the information-bearing signal is superimposed and sent simultaneously with the reference signal of the previous frame, introducing interference between users, thereby affecting the system's anti-noise performance. At the same time, in these traditional short data packet transmission schemes based on preamble training, the training overhead for channel estimation, information detection and synchronization, and identification accounts for a large proportion, resulting in a serious reduction in the transmission efficiency within the short data packet. The CCSK (Cyclic Code Shift Keying) modulation technology, with the help of the good autocorrelation and cross-correlation performance of the pseudo-random sequence, can realize the information detection and synchronization process without a preamble, and achieve high-speed transmission of short data packets. In 2022, Kassem SAIED proposed a quasi-cyclic short packet transmission scheme, which can realize pilot-free short data packet transmission under low signal-to-noise ratio based on CCSK modulation. This scheme can better realize the pilot-free detection and synchronization process, but it is necessary to add CCSK symbols in the information frame for identification. Summary of the invention

[0003] In response to at least one defect or improvement need in the prior art, the present invention provides a multi-level overmodulation short packet communication method, apparatus, device and storage medium, which does not increase the user's demodulation complexity, improves the information frame symbol synchronization performance, and adds additional information for use without increasing the data packet length.

[0004] To achieve the above object, according to a first aspect of the present invention, a multi-ary overmodulation short packet communication method is provided, comprising:

[0005] The first information is modulated with the first overmodulation sequence to obtain the second information; the first information is modulated with the initial CCSK sequence and the first information to be transmitted, and the first overmodulation sequence is a sequence selected from a plurality of overmodulation sequences according to the second information to be transmitted;

[0006] The second information is received through the channel as the third information, the third information traverses all the correlators to perform correlation operations, the correlation value with the largest absolute value associated with each correlator is taken as the fourth information, and the first information to be transmitted is solved according to the correlator corresponding to the correlation value with the largest absolute value; the correlators are obtained by cyclic shifting the initial CCSK sequence in sequence;

[0007] The fourth information is multiplied by the corresponding elements of the second overmodulation sequence and then summed, and the absolute value is taken to obtain the evaluation function value; when the evaluation function value is maximum, the corresponding second overmodulation sequence is the second overmodulation sequence used to modulate the first information, and then the second information to be transmitted is demodulated.

[0008] Furthermore, the multi-level overmodulation short packet communication method further includes:

[0009] The first information is modulated with the first overmodulation sequence to obtain the second information, specifically including:

[0010] The first overmodulation sequence is converted into a second overmodulation sequence; the second overmodulation sequence is sequentially multiplied with the first information to obtain second information;

[0011] The first overmodulation sequence is changed into the second overmodulation sequence, specifically, the elements in the first overmodulation sequence are changed from 0 and 1 to -1 and 1 respectively, so as to form the second overmodulation sequence.

[0012] Furthermore, the multi-level overmodulation short packet communication method further includes:

[0013] The information frame of the second information is represented as follows:

[0014] ,in:

[0015] The information frame of the first information is recorded as , the jth symbol of the first information is recorded as ,express Cyclic movement The sequence after the bit, represents the CCSK initial sequence;

[0016] The first overmodulation sequence is expressed as , where M represents the number of the first overmodulation sequence, N Indicates the number of symbols in each frame in the first information.

[0017] Furthermore, the multi-level overmodulation short packet communication method further includes:

[0018] The information frame of the second information is represented as follows:

[0019] ,in:

[0020] The information frame of the first information is recorded as , the jth symbol of the first information is recorded as ,express Cyclic movement The sequence after the bit, represents the CCSK initial sequence;

[0021] The first overmodulation sequence is expressed as , where M represents the number of overmodulation sequences, N Indicates the number of symbols in each frame in the first information.

[0022] Furthermore, the multi-level overmodulation short packet communication method further includes:

[0023] The correlator is initialized by the CCSK sequence Generated after shifting sequentially.

[0024] Furthermore, the multi-level overmodulation short packet communication method further includes:

[0025] The third information is correlated with the correlator to obtain fourth information, which specifically includes:

[0026] ;

[0027] ;

[0028] in, , indicating taking The largest value in , and the maximum value position is , Indicates the positive and negative signs. represents taking the real part;

[0029] Indicates the third information m The symbol is correlated with the n The correlation value of the correlation operation of the elements is the m The symbol is correlated with the n Multiply the numbers in the corresponding positions of the two sequences by elements, where , N represents the number of symbols in each frame in the third information, and q represents the length of the initial CCSK sequence.

[0030] Furthermore, the multi-level overmodulation short packet communication method further includes:

[0031] The evaluation function value is expressed as:

[0032] ;

[0033] The fourth information is , is the second overmodulation sequence at the receiving end.

[0034] According to a second aspect of the present invention, there is provided a multi-ary overmodulation short packet communication device, comprising:

[0035] Transmitter:

[0036] Modulating the first information with the first overmodulation sequence to obtain the second information; the first information is obtained by modulating the initial CCSK sequence with the information to be transmitted, and the first overmodulation sequence is a sequence selected from a plurality of overmodulation sequences according to the second information to be transmitted;

[0037] Receiver:

[0038] receiving the second information as the third information, traversing all the correlators for correlation operation, taking the correlation value with the largest absolute value associated with each correlator as the fourth information, and solving the first information to be transmitted according to the correlator corresponding to the correlation value with the largest absolute value; the correlators are obtained by cyclically shifting the initial CCSK sequence in sequence;

[0039] The fourth information is multiplied by the corresponding elements of the second overmodulation sequence and then summed, and the absolute value is taken to obtain the evaluation function value; when the evaluation function value is maximum, the corresponding second overmodulation sequence is the second overmodulation sequence used to modulate the first information, and then the second information to be transmitted is demodulated.

[0040] Furthermore, the multi-level overmodulation short packet communication device further comprises:

[0041] There is one transmitting end and multiple receiving ends, the first overmodulation sequence of the transmitting end includes identity information of all receiving ends, and the second overmodulation sequence of the receiving end includes identity information of the receiving end;

[0042] Or, there are multiple transmitting ends and one receiving end, the first overmodulation sequence of the transmitting end includes the identity information of the transmitting end, and the second overmodulation sequence of the receiving end includes the identity information of all transmitting ends.

[0043] According to a third aspect of the present invention, there is provided a multi-ary overmodulation short packet communication receiving terminal, comprising:

[0044] The second information is received as the third information, the third information traverses all the correlators to perform correlation operations, the correlation value with the largest absolute value related to each correlator is taken as the fourth information, and the first information to be transmitted is solved according to the correlator corresponding to the correlation value with the largest absolute value; the correlator is obtained by cyclic shifting the initial CCSK sequence in sequence; the second information is modulated by the first information and the first overmodulation sequence, and the first information is modulated by the initial CCSK sequence and the information to be transmitted;

[0045] The fourth information is multiplied by the corresponding elements of the second overmodulation sequence and then summed, and the absolute value is taken to obtain the evaluation function value; when the evaluation function value is maximum, the corresponding second overmodulation sequence is the second overmodulation sequence used to modulate the first information, and then the second information to be transmitted is demodulated.

[0046] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art:

[0047] The present invention provides a multi-level overmodulation short packet communication method, which does not need to increase the demodulation complexity of users, improves the information frame symbol synchronization performance, adds additional information for use without increasing the data packet length, transmits the second information to be transmitted in each frame of information, and increases the communication throughput. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0049] Figure 1 A schematic flow chart of a multi-level overmodulation short packet communication method provided by an embodiment of the present invention;

[0050] Figure 2 A schematic diagram of constructing an evaluation function by cyclic shifting a search window and a CCSK sequence provided in an embodiment of the present invention;

[0051] Figure 3 A schematic diagram showing a comparison of symbol offsets when overmodulation and non-overmodulation information frame symbols are synchronized at -12dB provided in an embodiment of the present invention;

[0052] Figure 4 The error synchronization rate curve of the overmodulation and non-overmodulation information frame symbols provided by the embodiment of the present invention at [-16dB, -10dB];

[0053] Figure 5 The overmodulation and CCSK sequence information carrying bit error rate curve provided in the embodiment of the present invention. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0055] The terms "first", "second", "third", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish different objects, rather than to describe a specific order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices.

[0056] like Figure 1 As shown, as the first embodiment of the present invention, a multi-level overmodulation short packet communication method is provided. Figure 1 The upper middle part is a schematic diagram of modulation in this embodiment, and the lower middle part is a schematic diagram of demodulation in this embodiment.

[0057] The transmitter first performs CCSK modulation on the information to be transmitted (this step is not included in Figure 1 ), a series of CCSK sequences are generated, and the information to be transmitted after CCSK modulation is recorded as the first information. In this embodiment, the information frame of the first information is recorded as , the jth symbol of the first information is recorded as ,express Cyclic movement The sequence after the bit, Indicates the CCSK initial sequence.

[0058] The transmitting end also includes an overmodulation sequence generator, which generates M first overmodulation sequences, denoted as Different overmodulation sequences can carry different information. For example, in a multi-user communication scenario where a transmitter sends M receivers, the first overmodulation sequence can carry the identification information of the receiver and is used to send information only to a specific receiver. The receiver can confirm whether the receiver is the receiver that needs to receive the information by demodulating the first overmodulation sequence.

[0059] In this embodiment, the first overmodulation sequence is expressed as , where M represents the number of overmodulation sequences, N Indicates the number of symbols in each frame of the first information. The first overmodulation sequence is a sequence consisting of 0s and 1s, that is, each symbol therein is 0 or 1.

[0060] Select a first overmodulation sequence from the overmodulation sequences. For example, the selected first overmodulation sequence is , modulate the overmodulation sequence with the first information to obtain the second information. The modulation method first converts the first overmodulation sequence into the second overmodulation sequence, that is, the elements in the first overmodulation sequence are changed from 0 and 1 to -1 and 1 respectively, which can be 0→-1, 1→1 or 0→1, 1→-1. In this embodiment, The method is to change the elements of the overmodulation sequence from 0 to 1, 1 to -1. Another method is to use The conversion from 0 to -1 and from 1 to 1 is realized in this way. The overmodulation sequence after the conversion is the second overmodulation sequence.

[0061] The second step is to multiply in sequence, that is, to multiply the first symbol in each information frame by the first element in the second overmodulation sequence, and the second symbol in the information frame by the second element in the second overmodulation sequence, and so on, the information frame of the second information can be obtained as follows: .

[0062] After the second information is sent from the transmitting end to the receiving end through the channel, it is demodulated by the receiving end. The information received by the receiving end is recorded as the third information. Since the first information, the second information and the third information do not change the length of the information frame, the number of symbols in the information frame of the first information, the second information and the third information are all N In this embodiment, the receiving end first constructs a correlator, which is composed of the CCSK initial sequence After sequential shifting, there are a total of q elements, among which q is the number of chips contained in each symbol in the information frame of the first information and the second information. Since each symbol in the first information is a CCSK sequence, it is the CCSK initial sequence Move through the cycle The second information does not have an additional CCSK sequence. Therefore, in the information frames of the first information and the second information, the number of chips per symbol is the same, and the number of chips is the length of the CCSK sequence. The correlator is denoted as , where the elements Represents the initial sequence The sequence after shifting by i positions.

[0063] The third information is correlated with the correlator to obtain N The absolute maximum correlation value In this embodiment, if , , then the related function .

[0064] like Figure 2 As shown, Indicates the third information m Symbol and Correlator The n The correlation value of the correlation operation of the elements, where The maximum absolute value of the correlation between each symbol and the CCSK sequence is taken. The positive or negative value of this value depends on whether the symbols are aligned during overmodulation and demodulation. The process is shown in formulas (1) and (2).

[0065] (1)

[0066] (2)

[0067] in, , indicating taking The largest value in , and the maximum value position is , Indicates the positive and negative signs. Indicates taking the real part. Thus, the fourth information can be obtained. The fourth information is the correlation value with the largest absolute value associated with each correlator as the fourth information, that is, the fourth information is The set composed of At the same time, the correlator corresponding to the correlation value with the largest absolute value can be recorded, that is, the corresponding initial CCSK sequence Only the CCSK sequence that is the same as the transmitting end will obtain the maximum value. Therefore, the correlator corresponding to the correlation value with the largest absolute value is the CCSK sequence order of the transmitting end, that is, the first information.

[0068] Finally, the N correlation values ​​of the fourth information are traversed and multiplied by the corresponding elements in the second overmodulation sequence of the receiving end, and the absolute value is taken after summing to obtain several evaluation function values. For example, if the receiving end stores the same M second overmodulation sequences as the transmitting end, the evaluation function value can be expressed as , where the evaluation function value of the second overmodulation sequence at the receiving end is expressed as ,in is the second overmodulation sequence at the receiving end.

[0069] For the above evaluation function value, only the second overmodulation sequence that is the same as the second overmodulation sequence selected by the transmitting end will obtain the maximum evaluation function value. Therefore, according to the second overmodulation sequence corresponding to the maximum evaluation function value, the information carried by the second overmodulation sequence can be demodulated. Then, according to the conversion relationship between the second overmodulation sequence and the first overmodulation sequence and the relationship between the first overmodulation sequence and the information it carries, the information carried by the overmodulation sequence can be decoded at the receiving end.

[0070] The multi-level overmodulation short packet communication method adopted in this embodiment can be applied to short packet communication between a transmitter and multiple user terminals. For example, if the transmitter needs to send information to 16 user terminals, the user terminals can be recorded as 0~15 respectively, and then encoded into 16 overmodulation sequences in sequence. The second overmodulation sequences stored in different user terminals only contain the overmodulation sequences corresponding to the user numbers. In this way, when the transmitter decides to send information to a specific user terminal, it selects the overmodulation sequence corresponding to the user terminal to modulate the CCSK sequence. Even if the modulated second information is sent to all user terminals, it can be set to demodulate the CCSK sequence only at the user terminal with the largest evaluation function value, so as to realize directional transmission of multiple user terminals.

[0071] Similarly, the multi-level overmodulation short packet communication method adopted in this embodiment can also be applied to short packet communication between multiple transmitters and one user terminal. In this case, different first overmodulation sequences are stored in different transmitters, and all second overmodulation sequences are stored in the user terminal. The first overmodulation sequence of the transmitter is used to store the identity information of the transmitter.

[0072] The following is an explanation of the principle of overmodulation during symbol synchronization. In actual applications, due to the small signal-to-noise ratio, the correlation value between noise and CCSK sequence will also appear large. If overmodulation is not used, The values ​​of are all positive numbers, and the arrival time of the information frame is often offset during symbol synchronization. The offset between the search window and the arrival time of the signal frame is assumed to be an integer multiple of , and this offset can be reduced well by overmodulation. These cases are explained below. .

[0073] a. When Δ = 0, the search window is completely aligned with the information frame, and the maximum value of the evaluation function can be obtained when noise is not considered.

[0074] When the signal-to-noise ratio is within a certain range, the evaluation function

[0075] (3)

[0076] Z represents the noise signal within the search window.

[0077] b. When hour, Considered here , Similarly, the offset is An integer multiple of , a smaller evaluation function value will be obtained through overmodulation.

[0078] (4)

[0079] Represents a sequence Middle to elements.

[0080] If there is no overmodulation, it is equivalent to the overmodulation sequence B The value of is 1, then

[0081] (5)

[0082] If there is overmodulation, and the overmodulation sequence B is strictly cyclically uncorrelated, then

[0083] (6)

[0084] (7)

[0085] c. When When the first symbol of the search window has only a part of the signal,

[0086] (8)

[0087] Starting from the second symbol of the search frame, each consists of two parts of CCSK sequence.

[0088] (9)

[0089] (10)

[0090] in . Z i Indicates the first i symbols of noise signal.

[0091] Under a certain signal-to-noise ratio, when If we want to maximize the correlation values, The values ​​of the first term of formula (8) and the second terms of formulas (9) and (10) are , the CCSK sequence strictly meets the cyclic uncorrelated condition, and the first term of equations (9) and (10) is approximately 0. At this time, the evaluation function is:

[0092] (11)

[0093] when If we want to maximize the correlation values, , the values ​​of the first term of formula (8) and the first terms of formulas (9) and (10) are , whose sign depends on the overmodulation sequence. The CCSK sequence strictly meets the cyclic irrelevant condition, and the second term of equations (9) and (10) is approximately 0. At this time, the evaluation function

[0094] (12)

[0095] If there is no overmodulation, it is equivalent to the overmodulation sequence B The elements of are all 1, the evaluation function

[0096] (13)

[0097] If there is overmodulation, and the overmodulation sequence B strictly complies with the cyclic irrelevance

[0098] (14)

[0099] (15)

[0100] Under a certain signal-to-noise ratio, the larger the value of the evaluation function, the higher the probability of determining synchronization within this offset range. When , a smaller evaluation function is obtained, and the main factor of misjudgment at this time is noise power. Therefore, overmodulation can more accurately assist the symbol synchronization process. When the search window and the signal frame deviate from a certain symbol length, overmodulation can reduce the value of the evaluation function and enhance the symbol synchronization performance of the signal frame.

[0101] As another embodiment of the present invention, the overmodulation short packet communication method of the above embodiment is provided to analyze the synchronization performance of the CCSK frame without overmodulation in the AWGN channel, and simulate the M The binary overmodulation carries information about the bit error rate of demodulation at a certain frame length and symbol length.

[0102] First select M Unrelated cycles gold The sequence is used as an overmodulation sequence, and the sequence length is N , a cycle is not related m The sequence is CCSK sequence. N =60, symbol length q =64 frames, M Select 1, 2, 4, 8, and 16 respectively. When the signal-to-noise ratio is [-16dB, -10dB], perform 10 4A Monte Carlo experiment was conducted to compare the symbol synchronization performance under M-ary overmodulation and no overmodulation. The symbol synchronization is considered successful when the frame header and information frame arrival time offset corresponding to the maximum evaluation function of the search window are within 1 / 2 symbol length. Let the probability of missynchronization be The overmodulation sequence corresponding to the maximum evaluation function is consistent with the initially selected overmodulation sequence, and the information carried by the overmodulation sequence is considered to be decoded correctly. Let the bit error rate of the M-ary overmodulation information be The bit error rate of CCSK information is , this value is affected by the synchronization performance The total bit error rate of the information received by a user is The simulation results are as follows: Figure 3-4 As shown. Figure 3 This is a schematic diagram of symbol offset when synchronizing at -12dB. Figure 4 This is the error synchronization rate curve under [-16dB, -10dB].

[0103] Without overmodulation, the symbol offset is large and the symbol synchronization performance is poor. Under the condition of -12dB signal-to-noise ratio, the missynchronization rate is as high as 67.62%. When M=1, that is, adding overmodulation but not carrying information, the symbol missynchronization rate is significantly reduced to 0.91%. When M=2, 4, 8, 16, adding overmodulation and carrying information (carrying 1 respectively) bit , 2 bit , 3 bit , 4 bit Information), the symbol synchronization performance is still greatly improved compared with no overmodulation. Figure 4 It can be seen that under the condition of signal-to-noise ratio [-16dB, -10dB], as the overmodulation order increases, the missynchronization rate increases slightly, but it is far better than the synchronization performance without overmodulation.

[0104] In the M-ary overmodulation and CCSK sequence information demodulation experiments, as the overmodulation order increases, the bit error rate gradually increases, but it is significantly better than the case without overmodulation. The reason for the decline in symbol synchronization performance and decoding performance is that the overmodulation sequences cannot be completely uncorrelated, and this correlation causes a slight decline in demodulation performance. Figure 5 It can be seen that the bit error rate curves of M-ary overmodulation and CCSK sequence carrying information are very close, and the bit error performance difference between the two curves is less than 0.1dB. This shows that for the receiving end, the addition of M-ary overmodulation has almost no impact on the transmission performance of short data packets, and at the same time provides a reliable transmission solution for communication.

[0105] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0106] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A multi-level overmodulation short packet communication method, comprising: The transmitting end changes the first overmodulation sequence into a second overmodulation sequence, and sequentially multiplies the second overmodulation sequence with the first information to obtain second information; The first information is obtained by modulating an initial CCSK sequence and the first information to be transmitted, and the first overmodulation sequence is a sequence selected from a plurality of overmodulation sequences according to the second information to be transmitted; After the second information is sent from the transmitting end to the receiving end through the channel, it is demodulated by the receiving end, and the information received by the receiving end is used as the third information. The number of symbols of the information frames of the first information, the second information, and the third information is N. The third information traverses all correlators to perform correlation operations, and the correlation value with the largest absolute value is obtained by performing correlation operations on each symbol of the third information and each element of each correlator. The set of N correlation values ​​with the largest absolute values ​​is used as the fourth information. The correlators corresponding to the N correlation values ​​with the largest absolute values ​​constitute the first information. The first information is demodulated by the initial CCSK sequence to decode the first information to be transmitted; the correlators are obtained by cyclic shifting the initial CCSK sequence in sequence; The N correlation values ​​with the largest absolute values ​​in the fourth information are traversed and multiplied by the corresponding elements of several second overmodulation sequences at the receiving end, and then summed up, and several evaluation function values ​​are obtained after taking the absolute values. The number of second overmodulation sequences stored at the receiving end is the same as the number of second overmodulation sequences stored at the transmitting end; when the evaluation function value is the largest, the corresponding second overmodulation sequence at the receiving end is the second overmodulation sequence selected by the transmitting end, and the information carried by the second overmodulation sequence at the receiving end corresponding to the maximum evaluation function value is demodulated, and then the second information to be transmitted is demodulated according to the conversion relationship between the second overmodulation sequence and the first overmodulation sequence and the relationship between the first overmodulation sequence and the information it carries.

2. The multi-level overmodulation short packet communication method according to claim 1, characterized in that: The first overmodulation sequence is changed into the second overmodulation sequence, specifically, the elements in the first overmodulation sequence are changed from 0 and 1 to -1 and 1 respectively, so as to form the second overmodulation sequence.

3. The multi-level overmodulation short packet communication method according to claim 2, characterized in that: The information frame of the second information is represented as follows: in: The information frame of the first information is recorded as The jth symbol of the first information is denoted by P ckj , indicating that P0 cyclically moves ck j The sequence after the bit, P0 represents the initial CCSK sequence; The first overmodulation sequence is denoted as B i =[b i,1 ,b i,2 ,...,b i,N ], i = 1, 2, ..., M, where M represents the total number of overmodulation sequences.

4. The multi-level overmodulation short packet communication method according to claim 2, characterized in that: The information frame of the second information is represented as follows: in: The information frame of the first information is recorded as The jth symbol of the first information is denoted by P ckj , indicating that P0 cyclically moves ck j The sequence after the bit, P0 represents the initial CCSK sequence; The first overmodulation sequence is denoted as B i =[b i,1 ,b i,2 ,...,b i,N ], i = 1, 2, ..., M, where M represents the total number of overmodulation sequences.

5. The multi-level overmodulation short packet communication method according to claim 1, characterized in that: The third information is correlated with the correlator to obtain fourth information, which specifically includes: [R' m,max ,I0]=max{|R m,0 |,|R m,1 |,...,|R m,q-1 |}; Among them, [R' m,max ,I0]=max{|R m,0 |,|R m,1 |,...,|R m,q-1 |}, indicating taking |R m,0 |~|R m,q-1 The largest value in | is R' m,max , and the maximum value is I0, sign() means taking the positive and negative signs, and Re() means taking the real part; R m,n The correlation value representing the correlation operation between the m-th symbol in the third information and the n-th element in the correlator is the product of the numbers at corresponding positions in the two sequences of the m-th symbol in the third information and the n-th element in the correlator, where 1≤m≤N, 0≤n≤q-1, and q represents the length of the initial CCSK sequence.

6. The multi-level overmodulation short packet communication method according to claim 1, characterized in that: The evaluation function value is expressed as: S ∑j =|R 1,max *B j,1 +...+R N,max *B j,N |; The fourth information is R=[R 1,max ,...,R N,max ], R m,max Indicates the correlation value with the largest absolute value, 1≤m≤N, B j =[B j,1 ,B j,2 ...B j,N ] is the second overmodulation sequence at the receiving end, j=1,2,...,M, and M represents the total number of overmodulation sequences stored at the transmitting end.

7. A multi-level overmodulation short packet communication device, comprising: Transmitter: Convert the first overmodulation sequence into a second overmodulation sequence, and sequentially multiply the second overmodulation sequence by the first information to obtain second information; The first information is obtained by modulating an initial CCSK sequence and the first information to be transmitted, and the first overmodulation sequence is a sequence selected from a plurality of overmodulation sequences according to the second information to be transmitted; Receiver: receiving the second information as the third information, the number of symbols of the information frames of the first information, the second information and the third information is N, the third information traverses all the correlators to perform correlation operations, taking the correlation value with the largest absolute value obtained by performing correlation operations on each symbol of the third information and each element of each correlator, taking the set of N correlation values ​​with the largest absolute values ​​as the fourth information, the correlators corresponding to the N correlation values ​​with the largest absolute values ​​constitute the first information, demodulating the first information through the initial CCSK sequence, and decoding the first information to be transmitted; the correlators are obtained by cyclically shifting the initial CCSK sequence in sequence; The N correlation values ​​with the largest absolute values ​​in the fourth information are respectively multiplied by the corresponding elements of several second overmodulation sequences of the receiving end, and then summed up, and several evaluation function values ​​are obtained after taking the absolute values. The number of second overmodulation sequences stored at the receiving end is the same as the number of second overmodulation sequences stored at the transmitting end; when the evaluation function value is the largest, the corresponding second overmodulation sequence of the receiving end is the second overmodulation sequence selected by the transmitting end, and the information carried by the second overmodulation sequence of the receiving end corresponding to the maximum evaluation function value is demodulated, and then the second information to be transmitted is demodulated according to the conversion relationship between the second overmodulation sequence and the first overmodulation sequence and the relationship between the first overmodulation sequence and the information it carries.

8. The multi-level overmodulation short packet communication device according to claim 7, characterized in that: There is one transmitting end and multiple receiving ends, the first overmodulation sequence of the transmitting end includes identity information of all receiving ends, and the second overmodulation sequence of the receiving end includes identity information of the receiving end; Or, there are multiple transmitting ends and one receiving end, the first overmodulation sequence of the transmitting end includes the identity information of the transmitting end, and the second overmodulation sequence of the receiving end includes the identity information of all transmitting ends.

9. A multi-level overmodulation short packet communication receiving terminal, comprising: Receive the second information as the third information, the number of symbols in the information frames of the first information, the second information and the third information is N, the third information traverses all the correlators to perform correlation operations, take each symbol of the third information and each element of each correlator to perform correlation operations to obtain the correlation value with the largest absolute value, take the set of N correlation values ​​with the largest absolute values ​​as the fourth information, the correlators corresponding to the N correlation values ​​with the largest absolute values ​​constitute the first information, demodulate the first information through the initial CCSK sequence to decode the first information to be transmitted; the correlator is obtained by cyclic shifting the initial CCSK sequence in sequence; the second information is obtained by multiplying the first information and the second overmodulation sequence in sequence at the transmitting end, the first information is modulated by the initial CCSK sequence and the first information to be transmitted at the transmitting end, the first overmodulation sequence is a sequence selected from multiple overmodulation sequences at the transmitting end according to the second information to be transmitted, and the second overmodulation sequence is converted from the first overmodulation sequence at the transmitting end; The N correlation values ​​with the largest absolute values ​​in the fourth information are traversed and multiplied by the corresponding elements of several second overmodulation sequences at the receiving end, and then summed up, and several evaluation function values ​​are obtained after taking the absolute values. The number of second overmodulation sequences stored at the receiving end is the same as the number of second overmodulation sequences stored at the transmitting end; when the evaluation function value is the largest, the corresponding second overmodulation sequence at the receiving end is the second overmodulation sequence selected by the transmitting end, and the information carried by the second overmodulation sequence at the receiving end corresponding to the maximum evaluation function value is demodulated, and then the second information to be transmitted is demodulated according to the conversion relationship between the second overmodulation sequence and the first overmodulation sequence and the relationship between the first overmodulation sequence and the information it carries.

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