CN115720117B - Packet direct sequence spread spectrum underwater sound modulation and demodulation method resistant to long multipath time delay - Google Patents

Abstract

The present invention discloses a grouped direct sequence spread spectrum underwater acoustic modulation and demodulation method that is resistant to long multipath delay, and belongs to the field of underwater acoustic communication. Specifically, the method is an underwater acoustic modulation and demodulation method based on direct sequence spread spectrum that adopts grouped PN codes to eliminate the influence of inter-group long multipath delay. First, the PN codes are grouped and designed to form PN code groups. Secondly, the source information is modulated based on the grouped PN code groups, and then the source information is demodulated based on the grouped PN code groups. The grouped direct sequence spread spectrum underwater acoustic modulation and demodulation method proposed by the present invention overcomes short multipath delays based on the orthogonality of the PN codes within the group, and overcomes underwater long multipath delays based on the orthogonality of the PN codes between groups, thereby effectively improving the effectiveness and reliability of the underwater acoustic spread spectrum communication system.

Description

A packet direct sequence spread spectrum underwater acoustic modulation and demodulation method resistant to long multipath delay

Technical Field

The invention belongs to the field of underwater acoustic communication, and in particular, relates to a grouped direct sequence spread spectrum underwater acoustic modulation and demodulation method capable of resisting long multipath time delay.

Background Art

Underwater acoustic communication technology uses sound waves as a carrier to achieve medium and long-distance data transmission underwater, and has broad prospects for military and civilian use. However, the underwater channel is a complex channel with time-space-frequency variation, which has obvious multipath effects and seriously affects the performance of the underwater acoustic communication system. At present, the main technologies for resisting multipath interference include spread spectrum technology, equalization technology, and diversity technology. Among them, spread spectrum technology modulates the information to be transmitted with a pseudo-random sequence at the transmitting end, expands its spectrum and then transmits it; the receiving end uses the same pseudo-random sequence for demodulation and correlation processing to restore the original data. Spread spectrum technology occupies a wide bandwidth, has strong anti-interference and multipath capabilities, low power spectrum density, and high concealment, and is increasingly widely used in underwater acoustic communications.

Although spread spectrum technology has a certain ability to resist multipath, when the multipath delay is greater than the length of a spread spectrum code, the multipath of the previous spread spectrum code in the multipath data received by the receiver will have a greater impact on the decision of the current spread spectrum code; and when the multipath delay is further increased, the multipath of the previous spread spectrum codes will affect the decision of the current spread spectrum code, resulting in misjudgment.

Referring to the basic flow diagram of direct sequence spread spectrum modulation and demodulation of existing underwater acoustic communication shown in Figure 1, the transmitting end directly uses the PN code to expand the spectrum of the information stream, modulates the carrier and sends it out through the transducer. The receiving end first synchronizes the received signal and removes the carrier, despreads it with the same PN code, and restores the widened spread spectrum signal to the original information stream.

In this way, when the multipath delay of the underwater acoustic channel is long enough, the multipaths of the previous spread spectrum codes will affect the judgment of the current spread spectrum code, resulting in misjudgment. As shown in Figure 2, the signal received by the receiving end is the superposition signal of the direct path, short multipath 1, long multipath 2, and long multipath 3. Therefore, when the direct path is correlated and despread, the first two PN codes of the direct path: PN1 and PN2 are not affected by the multipath and can be correctly despread to obtain the original information stream. However, when PN3 in the direct path is despread, it is affected by PN1 in short multipath 1; when PN4 in the direct path is despread, it is affected by PN1 and PN2 in short multipath 1. In this way, when there is a long multipath, refer to Figure 2 for the despreading of PN8 in the direct path. The result is affected by PN5 and PN6 in short multipath 1, PN3 and PN4 in long multipath 2, and PN1 and PN2 in long multipath 3, thereby reducing the despreading efficiency, resulting in demodulation failure, and affecting the underwater acoustic communication performance.

In order to overcome the influence of long multipath delay on underwater acoustic spread spectrum communication, the present invention proposes a packet direct sequence spread spectrum underwater acoustic modulation and demodulation method that is resistant to long multipath delay.

Summary of the invention

The purpose of the present invention is to overcome the shortcomings of the existing methods, and propose a group direct sequence spread spectrum underwater acoustic modulation and demodulation method that is resistant to long multipath delay, and adopts group PN code to eliminate the influence of long multipath delay between groups. First, the system time slots are divided into several groups, each group adopts a different PN code, and the PN codes between groups and within groups are mutually orthogonal. The transmitting end uses different group PN codes to modulate the source information, and the demodulation end uses the corresponding group PN code to demodulate to obtain the source information, thereby eliminating the influence of short multipath delay within the group and long multipath delay between groups on signal demodulation, and improving the effectiveness and reliability of the underwater acoustic spread spectrum communication system.

In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

A grouped direct sequence spread spectrum underwater acoustic modulation and demodulation method resistant to long multipath delay comprises the following steps: S1: grouping PN codes to form PN code groups; S2: modulating source information based on the grouped PN code groups; S3: demodulating the source information based on the grouped PN code groups; wherein, in the PN code groups obtained in step S1, each group uses a different PN code, and the PN codes between groups and the PN codes within a group are mutually orthogonal.

In some embodiments, the grouping and designing of PN codes to form PN code groups in step S1 includes the following steps: using an m sequence as a spread spectrum code, defining the length of the long multipath delay of the underwater acoustic channel as , the period of the selected m sequence is , select m sequences are used as PN code groups, and the formed PN code groups are as follows:

,

Among them, there are groups, each with indivual Code, each The period of the code is ,and , is a power of 2.

In some embodiments, indivual The codes are mutually orthogonal.

In some embodiments, the specific steps of modulating the source information based on the grouped PN code group in step S2 include: S2-1: grouping the secondary source information; S2-2: modulating the grouped PN code group.

In some embodiments, the secondary source information is grouped in step S2-1 as follows:

Define the source information to be modulated after source coding as in The value is 0 or 1. Carry a bit of information, The first level grouping is based on each group containing bits, The following groups are obtained:

;

Next, the second level grouping will Each group contains indivual After grouping, we get the following groups:

,

Each of The groups cycle;

The modulation method of the grouped PN code group in step S2-2 is as follows:

S2-2-1: Modulate the PN code group after the first level grouping. , the first bit of each group is the phase information bit, Indicates negative phase, Indicates positive phase, the rear of each group bits for Code number selection bit, where The decimal numbers corresponding to the bits are , that is, every bits correspond to a sequence number Code; bit corresponds to a phase information Code, that is, each Corresponding to one ;

S2-2-2: Modulate the PN code group after the second level grouping. ,Every indivual Constitute a Code groups, each using different Code group modulation; that is, for the first group , using the first group Code Group Modulation is performed; for the second group , using the second group Code Group Modulate; and so on, each Group into a cycle, that is, for the Group , again using the first group Code Group Modulation is performed; the modulated signal is multiplied by the carrier and a synchronization header is added to it, and then sent as the transmitting signal of the transmitter.

In some embodiments, the specific steps of demodulating the source information based on the grouped PN code group in step S3 include: S3-1: constructing the same PN code group as the transmitting end at the receiving end; S3-2: demodulating the grouped PN code group.

In some embodiments, the code group is constructed in step S3-1 as follows:

,

The demodulation method of the grouped PN code group in step S3-2 is as follows:

S3-2-1: Demodulate the PN code group after the second level grouping, first detect the synchronization head of the received signal, and obtain the received modulated signal after removing the carrier; then use the PN code in the PN code group to demodulate the received modulated signal in sequence; the process of demodulating the received modulated signal in sequence is as follows:

First, use the first group Code Group Correlate and demodulate the received modulated signal to obtain ; Then use the second group Code Group Correlate and demodulate the received modulated signal to obtain ; and so on, Group a cycle, that is, use the Group Code Group Demodulate and correlate the received modulated signal to obtain ;

S3-2-2: Demodulate the PN code group after the first level grouping, and demodulate the second level grouping The data obtained by code demodulation , detect in sequence The phase and correspondence Code number; when the phase is negative, the bit information is 0; when the phase is positive, the bit information is 1; the corresponding The code number is converted into a binary number. bits of information; each The demodulated bit data are arranged in order to obtain the source data restored by the receiving end.

Compared with the existing methods, the present invention, based on direct sequence spread spectrum, adopts grouped PN codes to implement an underwater acoustic modulation and demodulation method that eliminates the influence of long multipath delay between groups. The orthogonality of the PN codes within the group overcomes the short multipath delay, and the orthogonality of the PN codes between groups overcomes the underwater long multipath delay, thereby effectively improving the effectiveness and reliability of the underwater acoustic spread spectrum communication system.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG1 is a schematic diagram of the basic flow of direct sequence spread spectrum modulation and demodulation in existing underwater acoustic communication;

FIG2 is a schematic diagram showing the effect of existing long multipath delay on direct sequence spread spectrum;

3 is a schematic flow chart of a packet direct sequence spread spectrum underwater acoustic modulation and demodulation method resistant to long multipath delay according to the present invention;

FIG. 4 is a diagram of the present invention. Schematic diagram of time-group direct sequence spread spectrum modulation;

FIG. 5 is a diagram of the present invention. Schematic diagram of time-packet direct sequence spread spectrum demodulation;

FIG. 6 is a diagram of the present invention. Schematic diagram of time-resistance to long multipath delay.

DETAILED DESCRIPTION

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; the technical features designed in different implementation modes of the present invention described below can be combined with each other as long as they do not conflict with each other; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

In the description of the present invention, it should be understood that the terms "center", "lateral", "up", "down", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more. In addition, the term "including" and any variation thereof all mean "at least including".

Please refer to FIG3, which is a flow chart of a packet direct sequence spread spectrum underwater acoustic modulation and demodulation method resistant to long multipath delay of the present invention. In order to solve the influence of long multipath delay on spread spectrum communication, the present invention provides a packet direct sequence spread spectrum underwater acoustic communication modulation and demodulation method. As shown in the figure, the packet direct sequence spread spectrum underwater acoustic communication modulation and demodulation method includes the following steps:

S1: Grouping and designing PN codes to form PN code groups;

S2: modulate the source information based on the grouped PN code group;

S3: Demodulate the source information based on the grouped PN code group;

Among the PN code groups obtained in step S1, each group uses a different PN code, and the PN codes between groups and the PN codes within a group are orthogonal to each other.

The step S1 of grouping PN codes to form a PN code group includes the following steps: using an m sequence as a spread spectrum code, defining the length of the long multipath delay of the underwater acoustic channel as , the period of the selected m sequence is , select m sequences are used as PN code groups, and the formed PN code groups are as follows:

,

Among them, there are groups, each with indivual Code, each The period of the code is ,and , is a power of 2, indivual The codes are mutually orthogonal.

The specific steps of modulating the source information based on the grouped PN code group in step S2 include:

S2-1: Grouping secondary source information;

S2-2: Modulate the grouped PN code groups.

The method of grouping the secondary source information in step S2-1 is as follows:

Define the source information to be modulated after source coding as in The value is 0 or 1. Carry a bit of information, The first level grouping is based on each group containing bits, The following groups are obtained:

;

Next, the second level grouping will Each group contains indivual After grouping, we get the following groups:

,

Each of The groups cycle;

The modulation method of the grouped PN code group in step S2-2 is as follows:

S2-2-1: Modulate the PN code group after the first level grouping. , the first bit of each group is the phase information bit, Indicates negative phase, Indicates positive phase, the rear of each group bits for Code number selection bit, where The decimal numbers corresponding to the bits are , that is, every bits correspond to a sequence number Code; bit corresponds to a phase information Code, that is, each Corresponding to one ;

S2-2-2: Modulate the PN code group after the second level grouping. ,Every indivual Constitute a Code groups, each using different Code group modulation; that is, for the first group , using the first group Code Group Modulation is performed; for the second group , using the second group Code Group Modulate; and so on, each Group into a cycle, that is, for the Group , again using the first group Code Group Modulation is performed; the modulated signal is multiplied by the carrier and a synchronization header is added to it, and then sent as the transmitting signal of the transmitter.

The specific steps of demodulating the source information based on the grouped PN code groups in step S3 include:

S3-1: construct the same PN code group as the transmitting end at the receiving end;

S3-2: Demodulate the grouped PN code groups.

The code group constructed in step S3-1 is as follows:

,

The demodulation method of the grouped PN code group in step S3-2 is as follows:

S3-2-1: Demodulate the PN code group after the second level grouping, first detect the synchronization head of the received signal, and obtain the received modulated signal after removing the carrier; then use the PN code in the PN code group to demodulate the received modulated signal in sequence; the process of demodulating the received modulated signal in sequence is as follows:

First, use the first group Code Group Correlate and demodulate the received modulated signal to obtain ; Then use the second group Code Group Correlate and demodulate the received modulated signal to obtain ; and so on, Group a cycle, that is, use the Group Code Group Demodulate and correlate the received modulated signal to obtain ;

S3-2-2: Demodulate the PN code group after the first level grouping, and demodulate the second level grouping The data obtained by code demodulation , detect in sequence The phase and correspondence Code number; when the phase is negative, the bit information is 0; when the phase is positive, the bit information is 1; the corresponding The code number is converted into a binary number. bits of information; each The demodulated bit data are arranged in order to obtain the source data restored by the receiving end.

In order to facilitate understanding of the entire process of the packet direct sequence spread spectrum underwater acoustic modulation and demodulation method with long multipath delay resistance described in the present invention, the following will take N=4, M=4 as an example for illustration (this example is not intended to limit the present invention), please understand in conjunction with Figures 4 to 6, and the example is as follows:

Referring to Figure 4, , will soon indivual Code is divided into Group, each group indivual Each of which The code can carry 3 bits of information, including 1 bit of phase information, 2 bits of As shown in FIG4 , the information stream to be modulated is: 100010101111101000111010…100110101111100110101111…. According to the specific steps of the present invention, firstly design m sequence as Code group:

,

Each PN code period is ,and , the PN codes are mutually orthogonal and have good autocorrelation and cross-correlation characteristics.

because Available Therefore, the first-level grouping can be divided into groups containing 3 bits each, namely '100''010''101''111''101''000''111''010'…'100''110''101''111''100''110''101''111'…. Further, the second-level grouping can be divided into groups containing 3 bits each, namely '100''010''101''111''101''111'…. 3 bits, can be divided into "'100''010''101''111'""'101''000''111''010'" ... "'100''110''101''111'""'100''110''101''111'"...; each The groups cycle;

Then the grouped PN code is used to spread spectrum modulate the grouped information stream. For the first-level grouped information stream, '100''010''101''111''101''000''111''010'…'100''110''101''111''101''110''101''111'…, the first bit of each group is the phase information bit. Indicates negative phase: -; Indicates positive phase: +; after each group bits are Code number selection bit, '00' represents PN1, '01' represents PN2, '10' represents PN3, '11' represents PN4. Therefore, the information after spread spectrum can be expressed as: "+PN1 -PN3 +PN2 +PN4""+PN2 -PN1 +PN4 -PN3" ... "+PN1 +PN3 +PN2 +PN4""+PN1 +PN3 +PN2 +PN4" ...

Conventional spread spectrum communication directly transmits the spread signal after multiplying it by a carrier wave. The method proposed in the present invention needs to further modulate the spread signal. For +PN1 -PN3 +PN2 +PN4 +PN2 -PN1 +PN4 -PN3 ...+PN1 +PN3 +PN2 +PN4 +PN1 +PN3 +PN2 +PN4 ..., Each group uses different Code group modulation; that is, for the first group + PN1 - PN3 + PN2 + PN4, the first group Code Group Modulate to get +PN11 -PN13 +PN12 +PN14; for the second group +PN2 -PN1 +PN4 -PN3, use the second group Code Group Modulate and get +PN2 +PN22 -PN21 +PN24 -PN23; and so on, The modulated signal is multiplied by the carrier and then a synchronization header is added to it, which is then sent as the transmitting signal at the transmitting end;

The demodulation process is the reverse process of modulation. First, the synchronization head of the received signal is detected, and after removing the carrier, the received modulated signal +PN11 -PN13 +PN12 +PN14 +PN22 -PN21 +PN24 -PN23 ... +PN41 +PN43 +PN42 +PN44 +PN11 +PN13 +PN12 +PN14 ... is obtained. As shown in reference 4, use Grouping in code group The received modulated signal is demodulated in sequence. First, the first group Code Group Correlation demodulation is performed on the first group of modulation signals corresponding to the received modulation signal to obtain "'100''010''101''111'"; then the second group Code Group The second group of modulation signals corresponding to the received modulation signal is demodulated to obtain "'101''000''111''010'"; and so on. After a cycle is formed, the original information stream is finally demodulated to obtain "'100''010''101''111'""'101''000''111''010'"…"'100''110''101''111'""'100''110''101''111'"…

The principle of anti-long multipath proposed by the present invention is shown in FIG6 . The signal received by the receiving end is the superposition signal of the direct path, short multipath 1, long multipath 2, and long multipath 3. For the first four PN codes in the direct path: +PN11 -PN13 +PN12 +PN14, the first group Code Group The first two PN codes: +PN11 and -PN13 are not affected by multipath and can be correctly despread to get the original information stream; the third PN code +PN12 will be affected by +PN11 in short multipath 1; the fourth PN code +PN14 will be affected by +PN11 and -PN13 in short multipath 1. However, due to the effect of group PN code spreading, the 5th to 8th PN codes in the direct path: +PN22 -PN21 +PN24 -PN23 are obtained by the second group Code Group Spread spectrum is obtained by the first group The multipath of +PN11-PN13 +PN12 +PN14 obtained by code group spread spectrum will not affect the second group The despreading of +PN22 -PN21 +PN24 -PN23 obtained by code group spread spectrum, that is, the 5th PN code +PN22 in the direct path is not affected by -PN13 and +PN12 in short multipath 1, and +PN11 in long multipath 2. Similarly, for the 13th PN code +PN11 in the direct path, it will not be affected by the 10th PN code +PN43 and the 11th PN code +PN42 in short multipath 1, the 9th PN code +PN41 in long multipath 2, and the 7th PN code +PN24 and the 8th PN code -PN23 in long multipath 3. This overcomes the underwater long multipath delay and effectively improves the effectiveness and reliability of the underwater acoustic spread spectrum communication system.

In addition, those skilled in the art should understand that, although there are many problems in the prior art, each embodiment or technical solution of the present invention can be improved in only one or several aspects, without having to solve all the technical problems listed in the prior art or background technology at the same time. Those skilled in the art should understand that the content not mentioned in a claim should not be used as a limitation on the claim.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims (4)

1. A packet direct sequence spread spectrum underwater acoustic modulation and demodulation method resistant to long multipath delay, characterized in that it comprises the following steps: S1: Grouping and designing PN codes to form PN code groups; S2: modulate the source information based on the grouped PN code group; S3: Demodulate the source information based on the grouped PN code group; Among them, in the PN code groups obtained in step S1, each group uses a different PN code, and the PN codes between groups and the PN codes within the group are orthogonal to each other; The step S1 of grouping PN codes to form a PN code group includes the following steps: using an m sequence as a spread spectrum code, defining the length of the long multipath delay of the underwater acoustic channel as , the period of the selected m sequence is , select m sequences are used as PN code groups, and the formed PN code groups are as follows: , Among them, there are groups, each with indivual Code, each The period of the code is ,and , is a power of 2; The specific steps of modulating the source information based on the grouped PN code group in step S2 include: S2-1: Grouping secondary source information; S2-2: modulate the grouped PN code groups; The method of grouping the secondary source information in step S2-1 is as follows: Define the source information to be modulated after source coding as in The value is 0 or 1. Carry a bit of information, The first level grouping is based on each group containing bits, The following groups are obtained: ; Next, the second level grouping will Each group contains indivual After grouping, we get the following groups: , Each of The groups cycle; The modulation method of the grouped PN code group in step S2-2 is as follows: S2-2-1: Modulate the PN code group after the first level grouping. , the first bit of each group is the phase information bit, Indicates negative phase, Indicates positive phase, the rear of each group bits for Code number selection bit, where The decimal numbers corresponding to the bits are , that is, every bits correspond to a sequence number Code; bit corresponds to a phase information Code, that is, each Corresponding to one ; S2-2-2: Modulate the PN code group after the second level grouping. ,Every indivual Constitute a Code groups, each using different Code group modulation; that is, for the first group , using the first group Code Group Modulation is performed; for the second group , using the second group Code Group Modulate; and so on, each Group into a cycle, that is, for the Group , again using the first group Code Group Modulation is performed; the modulated signal is multiplied by the carrier and a synchronization header is added to it, and then sent as the transmitting signal of the transmitter. 2. The method for grouped direct sequence spread spectrum underwater acoustic modulation and demodulation with resistance to long multipath delay according to claim 1 is characterized in that: indivual The codes are mutually orthogonal. 3. The method for grouped direct sequence spread spectrum underwater acoustic modulation and demodulation with resistance to long multipath delay according to claim 1 is characterized in that the specific step of demodulating the source information based on the grouped PN code group in step S3 comprises: S3-1: construct the same PN code group as the transmitting end at the receiving end; S3-2: Demodulate the grouped PN code groups. 4. The method for grouped direct sequence spread spectrum underwater acoustic modulation and demodulation with resistance to long multipath delay according to claim 3 is characterized in that: The code group constructed in step S3-1 is as follows: , The demodulation method of the grouped PN code group in step S3-2 is as follows: S3-2-1: Demodulate the PN code group after the second level grouping, first detect the synchronization head of the received signal, and obtain the received modulated signal after removing the carrier; then use the PN code in the PN code group to demodulate the received modulated signal in sequence; the process of demodulating the received modulated signal in sequence is as follows: First, use the first group Code Group Correlate and demodulate the received modulated signal to obtain ; Then use the second group Code Group Correlate and demodulate the received modulated signal to obtain ; and so on, Group a cycle, that is, use the Group Code Group Demodulate and correlate the received modulated signal to obtain ; S3-2-2: Demodulate the PN code group after the first level grouping, and demodulate the second level grouping The data obtained by code demodulation , detect in sequence The phase and correspondence Code number; when the phase is negative, the bit information is 0; when the phase is positive, the bit information is 1; the corresponding The code number is converted into a binary number. bits of information; each The demodulated bit data are arranged in order to obtain the source data restored by the receiving end.