Acoustic positioning method and system

Abstract

To provide an acoustic positioning method and a system that enable simultaneously position locations of a plurality of objects while eliminating cumbersome pre-processing as much as possible on the basis of an acoustic pulse a pinger transmits.SOLUTION: An acoustic positioning system 1 includes: a plurality of pingers 10 that transmits an acoustic pulse; a receiver 20 that positions a location of each pinger 10 on the basis of the acoustic pulse of the pinger. A cycle of a time slot transmitting the acoustic pulse is registered in a cycle setting part 101 of the pinger 10. The time slot cycle to be set to each pinger 10 is different from each other. Each pinger 10 is configured to transmit the acoustic pulse every time slot cycle. The receiver 20 mainly consists of a pulse reception unit 202, and a positioning unit 203, which are provided with at least three hydrophones 201. The positioning unit 203 is configured to calculate a direction and depth of each pinger 10 on the basis of the acoustic pulse each hydrophone 201 receives; and position the location of each pinger 10 on the basis of a calculation result.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an acoustic positioning method and system that determines the positions of multiple pingers or the position of a mobile object equipped with such pingers based on acoustic pulses transmitted by the pingers, and in particular to an acoustic positioning method and system that is suitable for simultaneously determining the positions of multiple underwater robots, drones, or divers equipped with pingers. [Background technology]

[0002] Non-Patent Document 1 discloses a "combined water-air drone" in which an aerial drone flies carrying an underwater drone, lands in the target water area, separates the underwater drone, and dives, and then retrieves and takes off after the operation is completed, as shown in Figure 5.

[0003] One of the features of the combined water-air drone is that it is equipped with "acoustic positioning" technology, which transmits acoustic pulses from a transmitter (pinger) attached to the underwater drone, receives them with an underwater microphone (hydrophone) on the aerial drone, and automatically analyzes them to calculate the underwater drone's position. Acoustic positioning technology is disclosed, for example, on pages 236-245 of Non-Patent Document 2.

[0004] The combined water-air drone uses the SSBL (Super Short Base Line) method for acoustic positioning, which first calculates the time difference between acoustic pulses received by three or more hydrophones and then calculates the position of the transmitter. There is also another acoustic positioning method called SBL (Short Base Line) (Non-Patent Document 2), which has higher positioning accuracy than SSBL. As disclosed in Patent Document 1, the combined water-air drone can also use the SBL method for acoustic positioning.

[0005] Non-Patent Document 3 discloses an example of an SSBL acoustic positioning system installed on a combined water-air drone. In the SSBL acoustic positioning system, a set of acoustic pulses is emitted within a certain period (for example, one second). One set of pulses consists of a certain number (for example, two pulses), and positioning is performed by receiving these pulses with a hydrophone and processing the signals.

[0006] As a method for simultaneously locating the positions of two pingers, Non-Patent Document 2, pp. 125 and 177, discloses a technique in which acoustic pulses are transmitted from one pinger as an up-chirp and from the other as a down-chirp, thereby separating the acoustic pulses when calculating cross-correlation even if the acoustic pulses collide. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent application No. 2022-145518 [Non-patent literature]

[0008] [Non-Patent Document 1] KDDI / KDDI Research / Prodrone, news release, "World's first combined water-air drone successfully captures remote underwater footage ~ Conducting safe and efficient inspections of offshore wind power generation facilities without launching a ship ~", December 14, 2021 https: / / news.kddi.com / kddi / corporate / newsrelease / 2021 / 12 / 14 / 5593.html [Non-patent document 2] "Fundamentals and Applications of Marine Acoustics", Society of Marine Acoustics, Seizando Shoten, pp. 236-245 [Non-patent document 3] Kawada, Nishitani, and Kojima: "Acoustic Positioning System for Combined Water-Air Drones," Proceedings of the Marine Acoustics Society Conference, No. 22-2, pp. 3-4 (2022) Summary of the Invention [Problem to be solved by the invention]

[0009] Let's consider the case where there is not just one target to be positioned, but multiple targets. The chirp signal pulse is a signal whose frequency changes continuously within the duration of the pulse (for example, from 40 kHz to 60 kHz, centered around 50 kHz). The change can be either up or down (up: start 40 kHz - end 60 kHz, down: start 60 kHz - end 40 kHz). Therefore, if there are two targets to be positioned, if each generates an up and down chirp signal, they can be separated during correlation calculations even if they are received simultaneously.

[0010] However, when there are three or more positioning targets, for example, if two of the same uplink chirp signals are received simultaneously, it becomes difficult to separate them, making positioning impossible. One solution to this problem is to appropriately shift the transmission timing of each pinger so that the reception timing at the hydrophone does not overlap. However, shifting the transmission timing of the pingers requires synchronization processing to synchronize the clocks of each pinger to a common clock, which makes pre-processing complicated.

[0011] Furthermore, even when chirp signals are used to separate colliding acoustic pulses, there is a technical problem in that if the levels of the colliding acoustic pulses differ significantly, accurate separation cannot be achieved when calculating cross-correlation.

[0012] The object of the present invention is to solve the above technical problems and provide an acoustic positioning method and system that can simultaneously determine the positions of multiple objects based on acoustic pulses transmitted by their pingers while minimizing the need for complicated pre-processing. [Means for solving the problem]

[0013] In order to achieve the above object, the present invention is an acoustic positioning method for locating the position of each pinger based on acoustic pulses transmitted from multiple pingers at a predetermined period, and is characterized by having the following configuration.

[0014] (1) Each pinger is assigned a time slot with a different period, and each pinger transmits an acoustic pulse in each time slot.

[0015] (2) The time slot period of each pinger is set to a different prime number multiple of the time slot length for each pinger.

[0016] (3) Multiple pingers were classified based on two types of encoding methods for their acoustic pulses corresponding to the code division multiplexing method, and the time slots of each pinger were time-division multiplexed for each group, with the time slot period set for each pinger being different for each group.

[0017] (4) Multiple pingers were classified based on two types of encoding methods for their acoustic pulses corresponding to the code division multiplexing method, and one pinger was selected from each group and combined into pairs, with the time slots of each pinger time-division multiplexed, and the time slot period set for each pinger was made different for each pair.

[0018] The present invention can be realized not only as an acoustic positioning method that includes such characteristic processing steps, but also as an acoustic positioning system that configures such steps with hardware. [Effects of the Invention]

[0019] (1) Each pinger is assigned a time slot with a different period, and each pinger transmits an acoustic pulse in each time slot. This not only reduces the chance of collisions between acoustic pulses transmitted by each pinger, but also prevents the collisions from becoming fixed. This reduces the probability of a pinger causing positioning failure.

[0020] (2) The time slot period of each pinger is set to a different prime number multiple of the time slot length for each pinger, so that the frequency of collisions between acoustic pulses transmitted by each pinger can be further reduced.

[0021] (3) By classifying multiple pingers based on two types of encoding schemes for their acoustic pulses corresponding to the code division multiplexing scheme, and time-division multiplexing the time slots of each pinger for each group, and setting different time slot cycles for each pinger for each group, the chances of collisions between acoustic pulses transmitted by each pinger can be reduced, and even if a collision does occur, the collision partner will not be fixed. Therefore, efficient simultaneous positioning can be achieved by combining the time division multiplexing scheme and the code division multiplexing scheme.

[0022] (4) Multiple pingers are classified based on two types of encoding schemes for their acoustic pulses that correspond to the code division multiplexing scheme, and one pinger is selected from each group and paired together. The time slots of each pinger are time-division multiplexed for each pair, and the time slot cycles set for each pinger are made different for each pair. This reduces the chance of collisions between acoustic pulses transmitted by each pinger, and even if a collision does occur, they can be separated. Therefore, efficient simultaneous positioning can be achieved by combining the time division multiplexing scheme and the code division multiplexing scheme. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a functional block diagram showing the configuration of an acoustic positioning system to which the present invention is applied. [Figure 2] 1A and 1B are diagrams illustrating a method for transmitting an acoustic pulse according to a first embodiment of the present invention. [Figure 3] 10A and 10B are diagrams illustrating a method for transmitting acoustic pulses according to a second embodiment of the present invention. [Figure 4] 10A and 10B are diagrams illustrating a method for transmitting acoustic pulses according to a third embodiment of the present invention. [Figure 5] FIG. 10 is a diagram showing an example of a combined water-air drone. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Fig. 1 is a functional block diagram showing the configuration of an acoustic positioning system 1 to which the present invention is applied, and the system mainly comprises a plurality of pingers 10 that transmit acoustic pulses and a receiver 20 that determines the position of each pinger 10 based on the acoustic pulses. When the present invention is applied to a combined air-water drone, the receiver 20 is mounted on the air drone, and at least one of the pingers 10 is mounted on the underwater drone.

[0025] Each pinger 10 mainly comprises a period setting unit 101, a pressure sensor 102, a depth measurement unit 103, a pulse generation unit 104, and a pulse transmission unit 105, and the time frame (time slot) for transmitting acoustic pulses and its period are registered in the period setting unit 101. The time slot periods preset for each pinger 10 are different from each other, and each pinger 10 transmits an acoustic pulse at each unique time slot period set in its own period setting unit 101.

[0026] The receiver 20 mainly comprises a pulse receiving unit 202 equipped with at least three hydrophones 201, and a positioning unit 203. The positioning unit 203 includes a direction calculation unit 203a and a depth calculation unit 203b, and calculates the direction and depth of each pinger 10 based on the acoustic pulses received by each hydrophone 201, and determines the position of each pinger 10 based on the calculation results.

[0027] Such a receiver 20 can be configured by installing an application (program) that realizes each function described in detail below on a general-purpose computer or server equipped with a CPU, ROM, RAM, bus, interface, etc. Alternatively, it can be configured as a dedicated machine or a single-function machine in which part of the application is implemented as hardware or software.

[0028] FIG. 2 is a diagram showing a method for transmitting acoustic pulses according to a first embodiment of the present invention, characterized in that a plurality of pingers 10 repeatedly transmit acoustic signals (pulses) AP at mutually different time slot periods.

[0029] In this embodiment, each pinger 10 transmits a positioning pulse AP1 and a depth pulse AP2 as acoustic pulses AP in this order for each time slot. The positioning pulse AP1 is transmitted to allow the receiver 20 to calculate the direction of the pinger 10 based on the difference in reception time at the three hydrophones 201. The depth pulse AP2 is transmitted to allow the receiver 20 to calculate the depth of the pinger 10 based on the time difference from the positioning pulse AP1.

[0030] The duration of each of the positioning pulse AP1 and depth pulse AP2 is set to 1.6 ms. In this embodiment, the transmission interval and time slot length of each pulse AP1 and AP2 are set based on the maximum acoustic pulse arrival time of 50 / 1500=0.033 [s]=33 ms, assuming that the maximum distance from the pinger 10 to the receiver 20 is 50 m and the speed of sound is 1500 [m / s].

[0031] In each pinger 10, a time that is a prime multiple of the time slot length (150 ms) is pre-registered as the time slot period in the period setting unit 101. In this embodiment, a time that is the time slot period multiplied by a prime number that differs for each pinger 10 is pre-registered as the time slot period so that the time slot period of each pinger 10 is set to a prime multiple of the time slot length that differs for each pinger.

[0032] The pulse generating unit 104 generates a positioning pulse AP1 with a duration of 1.6 ms for each time slot. The pulse generating unit 104 further generates a depth pulse AP2 at a time that is 50 ms after the transmission of the positioning pulse AP1, with the depth being set to 0 m, plus a time interval proportional to the depth measured by the depth measuring unit 103 based on the output of the pressure sensor 102.

[0033] For example, if the measurement depth is 10 m, the depth pulse AP2 is generated when 50 + 10 = 60 ms has elapsed since the transmission time of the positioning pulse AP1. If the measurement depth is the maximum depth of 50 m, the depth pulse AP2 is generated when 50 + 50 = 100 ms has elapsed. The pulse transmitting unit 105 transmits the positioning pulse AP1 and depth pulse AP2 at their generation times.

[0034] In this embodiment, the time slot length is set to 150 ms, so that even if the position of the pinger 10 is at the maximum distance and maximum depth from the receiver 20, the transmission time from transmission to reception of each pulse signal AP1, AP2 can be kept within the time slot.

[0035] In the receiver 20, the three hydrophones 201 receive the acoustic pulses AP transmitted from each pinger 10. In this embodiment, before positioning begins, the transmission timing of the acoustic pulse is learned (recorded) for each pinger 10, for example, when the pinger 10 and the receiver 20 are in contact with each other and the distance between them is zero. This allows the receiver 20 to predict the time slots in which it is likely to receive the acoustic pulses AP from each pinger 10, making it possible to receive and process the acoustic pulses from each pinger 10 separately. Note that this kind of pre-processing is simpler than the process of synchronizing the clocks of all pingers 10 and the receiver 20, and can be completed in a short time.

[0036] In the positioning unit 203, the direction calculation unit 203a calculates the direction of the pinger 10 based on the difference in the time when each hydrophone 201 receives the positioning pulse AP1. The depth calculation unit 203b calculates the depth of the pinger 10 based on the difference in the reception time between the positioning pulse AP1 and the depth pulse Ap2. The positioning unit 203 locates the position of the pinger 10 based on the calculation results of the direction and depth.

[0037] In this embodiment, the time slot period of each pinger 10 is set to a length obtained by multiplying the time slot length by a different prime number. In the example of Fig. 2, the time slot period of one pinger 10a is set to a time (750 ms) obtained by multiplying the time slot length (150 ms) by the prime number 5, while the time slot period of the other pinger 10b is set to a time (1050 ms) obtained by multiplying the time slot length by the prime number 7.

[0038] If the time slot period of each pinger 10 is set as described above, for example, if the time slots of pingers 10a and 10b initially overlap, the next time they overlap will be after a time equal to 15, the least common multiple of the prime numbers 3 and 5, multiplied by the time slot length of 150 ms (15 × 150 ms = 5250 ms). In other words, the acoustic pulse transmitted by pinger 10a will collide with another acoustic pulse only once in seven times, and the acoustic pulse transmitted by pinger 10b will collide with another acoustic pulse only once in five times. Therefore, if only the period when the collision occurs is considered missing, the positions of each pinger 10 can be accurately and simultaneously determined without any problems.

[0039] If there are three pingers 10 (10a, 10b, 10c), the time slot period of pinger 10c can be set to the time obtained by multiplying the time slot length by a different prime number 11 (150×11=1650 ms).

[0040] In this case, the frequency of collisions between acoustic pulses transmitted by pingers 10b and 10c is every 55, the least common multiple of the prime numbers 5 and 11, multiplied by the time slot length of 150 ms (55 × 150 ms = 8250 ms), and the frequency of collisions between acoustic pulses transmitted by pingers 10a and 10c is every 33, the least common multiple of the prime numbers 3 and 11, multiplied by the time slot length of 150 ms (33 × 150 ms = 4950 ms), both of which are essentially negligible.

[0041] In the above example, the time slot length is set to 150 ms to transmit two acoustic pulses (positioning pulse AP1 and depth pulse AP2) in each time slot, but it is also possible to omit the depth pulse AP2 and transmit only the positioning pulse AP1. In that case, the time slot length can be shortened to about 50 ms (assuming a maximum distance of about 50 meters), so if the time slot period is set to about 1 second, the time slot period can be set as follows even when simultaneously positioning the positions of five pingers 10:

[0042] 1st: 50ms×13=650ms 2nd: 50ms×17=850ms 3rd: 50ms×19=950ms 4th: 50 ms×23=1150ms 5th: 50 ms×29=1450ms

[0043] In this way, according to this embodiment, time slots with different cycles are assigned to each pinger 10, and each pinger 10 transmits an acoustic pulse in each time slot, which not only reduces the chance of collisions between acoustic pulses transmitted by each pinger 10, but also prevents the collision partner from becoming fixed, thereby reducing the probability of a pinger causing positioning failure.

[0044] Furthermore, if the time slot period of each pinger 10 is set to a different prime number multiple of the time slot length for each pinger, the frequency of collisions between acoustic pulses transmitted by each pinger 10 can be further reduced.

[0045] FIG. 3 is a diagram showing an acoustic positioning method according to a second embodiment of the present invention, focusing on the timing at which ten pingers 10 transmit acoustic pulses. Simultaneous positioning of multiple pingers is achieved by combining time division multiplexing and code division multiplexing.

[0046] In this embodiment, a chirp signal is used as the code division multiplexing method, and multiple pingers 10 are divided into two groups: one group modulates the acoustic pulses using an up-chirp method in which the pulse frequency gradually increases, and the other group modulates the acoustic pulses using a down-chirp method in which the pulse frequency gradually decreases. This embodiment is characterized by the fact that the time slots of each pinger are time-division multiplexed for each group, and the time slot period set for each pinger is different for each group.

[0047] Figure 1(a) shows an example of time slots set for channels in group A that transmit acoustic pulses as upstream chirps, where the transmission frame (1000 ms) is divided equally into five time slots, each assigned to one of five pingers (0, 1, 2, 3, 4). The period of each time slot in the channel is set to a prime multiple of the time slot length (200 ms) (here, 1000 ms, which is five times the length).

[0048] Figure 1(b) shows an example of time slots set for Group B channels that transmit acoustic pulses as downlink chirps, where the transmission frame (1000 ms) is divided equally into five time slots, each assigned to one of five pingers (5, 6, 7, 8, 9). The period of each time slot in this channel is set to a prime multiple of the time slot length (200 ms) different from that of Group A (here, 1400 ms, which is 7 times the time slot length).

[0049] In this way, according to this embodiment, the period of each time slot in group A and the period of each time slot in group B are set to a time obtained by multiplying the time slot length by different prime numbers, so that the combination of colliding time slots can be made different for each period.

[0050] For example, the time slots of Pinger 5 and Pinger 6 collide with the time slots of Pinger 0 and Pinger 1, respectively, in the first cycle, but collide with the time slots of Pinger 2 and Pinger 3, respectively, in the next cycle.

[0051] Therefore, even if the level of the acoustic pulses transmitted by Pinger 0 and Pinger 1 is particularly low and not the same as the level of the acoustic pulses transmitted by Pinger 5 and Pinger 6, making separation difficult using correlation signal processing, positioning is possible in the next period because neither of the time slots for Pingers 0 and 1 collide with any other time slots.

[0052] Furthermore, since the time slots of pingers 5 and 6 collide with the time slots of pingers 2 and 3, if the levels of the acoustic pulses transmitted by pingers 2 and 3 are equivalent to those of pingers 5 and 6, positioning is possible by separating them using correlation signal processing.

[0053] As described above, according to this embodiment, the acoustic pulses of the multiple pingers 10 are classified based on two types of encoding methods corresponding to the code division multiplexing method, the time slots of each pinger 10 are time-division multiplexed for each group, and the time slot period set for each pinger is different for each group. This reduces the chance of collision between acoustic pulses transmitted by each pinger, and even if a collision does occur, the collision partner is not fixed. Therefore, efficient simultaneous positioning can be achieved by combining the time division multiplexing method and the code division multiplexing method.

[0054] FIG. 4 is a diagram illustrating an acoustic positioning method according to a third embodiment of the present invention, focusing on the timing at which ten pingers 10 transmit acoustic pulses. Simultaneous positioning of multiple pingers is achieved by combining time division multiplexing and code division multiplexing.

[0055] In this embodiment, multiple pingers are classified into Group A, which modulates and transmits acoustic pulses using the upstream chirp method, and Group B, which modulates and transmits acoustic pulses using the downstream chirp method. This embodiment is characterized in that the time slots of each pinger are time-division multiplexed for each pair, combining the time slot of one pinger selected from Group A with the time slot of one pinger selected from Group B, and the time slot period set for each pinger is made different for each pair.

[0056] In the first channel of Figure 1(a), the transmission frame (100 ms) is divided equally into two time slots, with the time slot of Pinger 0 selected from Group A being assigned to the leading time slot, and the time slot of Pinger 5 selected from Group B being assigned to the trailing time slot.

[0057] Similarly, in the second channel of the same figure (b), the leading time slot is assigned to the time slot of pinger 1 selected from group A, and the trailing time slot is assigned to the time slot of pinger 6 selected from group B.

[0058] Similarly, in the third channel, the leading time slot is assigned to the time slot of pinger 2 selected from group A, and the trailing time slot is assigned to the time slot of pinger 7 selected from group B. In the fourth channel, the leading time slot is assigned to the time slot of pinger 3 selected from group A, and the trailing time slot is assigned to the time slot of pinger 8 selected from group B.

[0059] In the fifth channel of the same figure (c), the leading time slot is assigned to the time slot of pinger 4 selected from group A, and the trailing time slot is assigned to the time slot of pinger 9 selected from group B.

[0060] Here, the time slot period for the first channel is set to a time length (650 mm) obtained by multiplying the time slot length (50 mm) by the prime number 13. For the second channel, it is set to a time length (850 ms) obtained by multiplying the time slot length by the prime number 17. Similarly, for the third channel, it is set to a time length (950 ms) obtained by multiplying the time slot length by a multiple of the prime number 19, for the fourth channel, it is set to a time length (1150 ms) obtained by multiplying the time slot length by the prime number 23, and for the fifth channel, it is set to a time length (1450 ms) obtained by multiplying the time slot length by the prime number 29.

[0061] According to this embodiment, the time slot period is set to a time obtained by multiplying the time slot length by a prime number that is different for each channel, so that the frequency of time slot collisions can be reduced.

[0062] In addition, since the transmission frame of each channel is composed of a pair of uplink chirp time slots and downlink chirp time slots, even if time slots collide, positioning is possible by separating the uplink chirp time slot and the downlink chirp time slot using correlation signal processing.

[0063] Furthermore, according to each of the above embodiments, the positions of a large number of moving objects can be simultaneously determined without the need for cumbersome pre-processing, making it possible to contribute to Goal 9 "Build resilient infrastructure and promote inclusive and sustainable industrialization" and Goal 11 "Make cities inclusive, safe, resilient and sustainable" of the Sustainable Development Goals (SDGs) led by the United Nations. [Explanation of symbols]

[0064] 10... Pinger, 20... Receiver, 101... Period setting unit, 102... Pressure sensor, 103... Depth measurement unit, 104... Pulse generation unit, 105... Pulse transmission unit, 201... Hydrophone, 202... Pulse reception unit, 203... Positioning unit, 203a... Direction calculation unit, 203b... Depth calculation unit

Claims

1. 1. An acoustic positioning method in which a computer determines the position of each pinger based on acoustic pulses transmitted from a plurality of pingers at a predetermined cycle, comprising: Each pinger is assigned a time slot with a different period, each pinger transmitting an acoustic pulse in each of said time slots; An acoustic positioning method, characterized in that the time slot period of each pinger is set to a different prime number multiple of the time slot length for each pinger.

2. An acoustic positioning method in which a computer determines the position of each pinger based on acoustic pulses transmitted from multiple pingers at a predetermined cycle, classifying the plurality of pingers into a first group whose acoustic pulses are modulated by a first coding scheme corresponding to a code division multiplexing scheme and a second group whose acoustic pulses are modulated by a second coding scheme; The clocks of each pinger are synchronized for each group. time division multiplexing the time slots of each pinger for each group based on the time of the clock; The time slot period set for each pinger is different for each group, An acoustic positioning method, characterized in that each pinger transmits an acoustic pulse for each of said time slots.

3. 3. The acoustic positioning method according to claim 2, wherein the time slot period set for each of said pingers is set to a prime number multiple of the time slot length that differs for each of said groups.

4. An acoustic positioning method in which a computer determines the position of each pinger based on acoustic pulses transmitted from multiple pingers at a predetermined cycle, classifying the plurality of pingers into a first group whose acoustic pulses are modulated by a first coding scheme corresponding to a code division multiplexing scheme and a second group whose acoustic pulses are modulated by a second coding scheme; One pinger is selected from each group and the clock is set for each pair. time-division multiplexing the time slots of each pinger for each pair based on the time of said clock; The time slot period set for each pinger is different for each pair, An acoustic positioning method, characterized in that each pinger transmits an acoustic pulse for each of said time slots.

5. 5. The acoustic positioning method according to claim 4, wherein the time slot period set for each of said pingers is set to a prime number multiple of the time slot length that differs for each of said pairs.

6. 6. The acoustic positioning method according to claim 2, wherein the first and second encoding methods are an up-chirp and a down-chirp, respectively.

7. each pinger having a pressure sensor for determining depth; Transmitting a positioning pulse and a depth pulse in that order for each time slot; 6. The acoustic positioning method according to claim 1, wherein the interval between the positioning pulse and the depth pulse is variable depending on the depth positioning result.

8. In an acoustic positioning system in which a receiver receives acoustic pulses transmitted from a plurality of pingers at a predetermined cycle and determines the position of each pinger, Each pinger means for setting time slots having different periods; means for transmitting an acoustic pulse for each of said time slots; An acoustic positioning system, wherein the means for setting the time slots sets the time slot period of each of the pingers to a prime number multiple of the time slot length that differs for each of the pingers.

9. In an acoustic positioning system in which a receiver receives acoustic pulses transmitted from multiple pingers at a predetermined cycle and determines the position of each pinger, classifying the plurality of pingers into a first group whose acoustic pulses are modulated by a first coding scheme corresponding to a code division multiplexing scheme and a second group whose acoustic pulses are modulated by a second coding scheme; Each pinger is means for synchronizing the clocks of each pinger for each group; means for time-division multiplexing the time slots of each pinger for each group based on the time of said clock; means for transmitting an acoustic pulse for each of said time slots; An acoustic positioning system characterized in that the time slot period set for each pinger group is different for each group.

10. 10. The acoustic positioning system according to claim 9, wherein the time slot period set for each of the pingers is set to a prime number multiple of the time slot length that differs for each of the groups.

11. In an acoustic positioning system in which a receiver receives acoustic pulses transmitted from a plurality of pingers at a predetermined cycle and determines the position of each pinger, classifying the plurality of pingers into a first group whose acoustic pulses are modulated by a first coding scheme corresponding to a code division multiplexing scheme and a second group whose acoustic pulses are modulated by a second coding scheme; Each pinger is a means for selecting one pinger from each group and combining them to set the clock for each pair; means for time-division multiplexing the time slots of each pinger for each pair based on the time of said clock; means for transmitting an acoustic pulse for each of said time slots; An acoustic positioning system, characterized in that the time slot period set for each pinger pair is different for each of the pairs.

12. 12. The acoustic positioning system according to claim 11, wherein the time slot period set for each of the pingers is set to a different prime number multiple of the time slot length for each of the pairs.

13. 13. The acoustic positioning system according to claim 9, wherein the first and second encoding methods are an upward chirp and a downward chirp, respectively.

14. each pinger having a pressure sensor for determining depth; the transmitting means transmits a positioning pulse and a depth pulse in that order for each time slot; 13. The acoustic positioning system according to claim 8, wherein the interval between the positioning pulse and the depth pulse is variable depending on the depth positioning result.

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