CN102970123A - Underwater acoustic communication apparatus with timesharing-implemented multichannel time reversal - Google Patents

Abstract

The utility model relates to an underwater acoustic communication device which realizes multi-channel time reversal by time sharing, and relates to an underwater acoustic communication. Provided is an underwater acoustic communicator capable of realizing multi-channel time reversal by time-division and repeated transmission, and suppressing channel multipath effects. A transmitting part and a receiving part are provided; the transmitting part is provided with an information symbol input interface, a spread spectrum modulation module, a convolution module, a probe signal generator, a frame synchronization signal generator, a signal framing module, a power amplifier and a transmitting Transducer; the receiving part is provided with a multi-element receiving array, a pre-processing module, a channel switcher, an A/D converter, a synchronization module, a time-reversal preprocessor, a serial/parallel multi-channel combiner and a data decoder ; Multipath focusing of underwater acoustic channels can be realized in real time on a digital processor chip, reducing the system complexity of implementing multi-channel time-reversal in underwater acoustic communicators, and suppressing time-selective fading caused by strong time-varying underwater acoustic channels.

Description

An Underwater Acoustic Communicator Realizing Multi-channel Time Reversal by Time Sharing

technical field

The invention relates to an underwater acoustic communication, in particular to an underwater acoustic communication device which realizes multi-channel time reversal by time sharing.

Background technique

With the increasing demand for marine information acquisition and transmission in the fields of marine resource development, marine environment three-dimensional monitoring, and marine national defense security, underwater acoustic communication technology has become an important frontier of marine high technology. However, the underwater acoustic channel has strong multipath interference, poor channel response stability, and typical non-stationary characteristics in the time-space-frequency domain, which brings great difficulties to the design of high-performance underwater acoustic communication systems.

Time reversal technology can effectively use time and space focusing to suppress multipath interference, and has become a research hotspot in the field of underwater acoustic communication and signal processing in recent years. According to different processing methods, time reversal technology can be divided into two types: active time reversal and passive time reversal: the receiver of the former needs a multi-element array in which the transmitting sound source and the receiving array are combined to receive the signal transmitted by the transmitter Retransmission after time reversal makes the sound field focus at the sound source position; the latter uses the received probe signal to obtain channel multipath information, and constructs a pre-processor to perform multipath focus on the received signal. Since the anti-technical signal only needs to be transmitted in one direction in passive mode, and there is no need to use a combined transceiver array, it is relatively simple in technology, so it has been extensively studied. Chen Dongsheng et al. (Chen Dongsheng, Tong Feng, Xu Xiaomei. Research on Time-Reverse Joint Channel Equalization Underwater Acoustic Communication System[J]. Acoustic Technology. 2011,30(3):195-197) Using Passive Time-Reverse Joint Equalization in Point-to-Point Communication System To resist interference and improve communication performance. Gong Gaiyun et al. (Gong Gaiyun, Yao Wenbin, Pan Xiang. Research on underwater acoustic communication combining passive time feedback and adaptive equalization [J]. Acoustic Technology. 2010,29(2):129-134) using passive time feedback Combined with adaptive equalization, the reliability and efficiency of the method is demonstrated in a phase-coherent underwater communication system. H.C.Song et al. (H.C.Song, W.S.Hodgkiss, W.A.Kuperman et al.Multiuser Communications Using Passive Time Reversal.IEEE JOURNAL OF OCEANICENGINEERING.2007,32(4):915-926) used decision feedback balance, lock Phase loop technology realizes multi-user underwater acoustic information transmission. G.F.Edelmann et al. (G.F.Edelmann, T.Akal, W.S.Hodgkiss et al., An initial demonstration of underwater acoustic communication using time reversal.IEEE J.Oceanic Eng.2002,27(3):602-609) in multipath channel Time inverse technology is used to effectively overcome intersymbol interference.

At the same time, the theory and experiments show that when only a single receiving array element is used for passive time reversal processing, it is greatly affected by the multipath characteristics of the channel, and it is difficult to obtain ideal performance. In order to improve the performance of time reversal processing, it is generally necessary to adopt multi-array element reception for time reversal to achieve better multipath focusing and intersymbol interference suppression performance. Chinese patents 200910072531.0 and 200910071516.4 both use multiple receiving arrays to form multi-channel time reversal to realize underwater acoustic communication that suppresses multipath effects. However, since the multi-channel time-reversal processing requires multiple correlation calculations and processing of a large amount of data in each of the multiple receiving channels, for underwater nodes with extremely limited resources such as power supply and space in various underwater nodes, Acoustic communicator, it is difficult to realize real-time underwater acoustic communication based on multi-channel inversion processing to suppress multipath effect. Therefore, the multi-channel time-reversal underwater acoustic communication method in many literatures is still based on the theory and method research status of off-line and post-processing of multi-channel data, which limits the application of multi-channel time-reversal technology in the actual implementation of underwater acoustic communicators. application.

Chinese patent 2010105818403 proposes a passive underwater acoustic communication method suitable for mobile platforms, which uses the space diversity effect obtained by repeatedly transmitting the same information frame when at least one of the two parties is in motion to perform multi-channel time reversal processing, and performs multi-channel time reversal processing on signals received at different relative positions. Time inversion preprocessing and merging, so that the single-receiving hydrophone can be used to achieve the effect of multi-channel time inversion to suppress multipath interference, which can reduce the system complexity caused by multi-element reception. But the premise is that at least one of the transmitting and receiving parties is in motion, otherwise the expected focusing effect will not be obtained; Inhibition processing.

Contents of the invention

The object of the present invention is to provide an underwater acoustic communicator capable of realizing multi-channel time reversal by time-division and repeated transmission and suppressing channel multipath effect.

The present invention has a transmitting part and a receiving part;

The transmitting part is provided with an information symbol input interface, a spread spectrum modulation module, a convolution module, a probe signal generator, a frame synchronization signal generator, a signal framing module, a power amplifier and a transmitting transducer; the information code The element input interface is connected to the input end of the spread spectrum modulation module, the output end of the spread spectrum modulation module and the output end of the probe signal generator are connected to the input end of the convolution module, and the input ends of the signal framing module are respectively connected to the convolution module The output end of the probe signal generator is connected to the output end of the frame synchronization signal generator, and the input and output ends of the power amplifier are respectively connected to the output end of the signal framing module and the input end of the transmitting transducer.

The receiving part is equipped with a multi-element receiving array, a pre-processing module, a channel switcher, an A/D converter (ADC), a synchronization module, a time-reversal preprocessor, a serial/parallel multi-channel combiner and a data decoder; The multi-element receiving array is composed of at least 2 receiving array elements, the output end of the multi-element receiving array is connected with the input end of the pre-processing module, and the processed multi-channel signal output end of the pre-processing module is connected to A/A through the channel switcher. The input terminal of the D converter (ADC), the output terminal of the A/D converter (ADC) are respectively connected with the input terminal of the synchronization module and the input terminal of the time inversion preprocessor, and the frame synchronization signal output terminal of the synchronization module is connected with the time The frame synchronization signal input terminal of the inversion preprocessor is connected, and the passive time inverse processing signal output terminal of the time inversion preprocessor is connected to the data input terminal of each channel of the serial/parallel multi-channel combiner, and the serial/parallel multi-channel combiner The output terminal of the multi-channel time-inverted received signal is connected to the input terminal of the data decoder, and the data decoder performs data decoding to restore the original data.

Compared with the current multi-channel time-reversal method for underwater acoustic communication, the time-sharing multi-channel time-reversal underwater acoustic communication machine proposed by the present invention has two outstanding advantages:

First, due to the repeated transmission of the same information frame combined with multi-channel switching to achieve time-division and multi-channel time inversion, high-performance underwater acoustic channel multi-path focusing can be realized in real time on a digital processor chip, greatly reducing underwater acoustics. The system complexity of realizing multi-channel time inversion in the communication machine can significantly improve the performance of the underwater acoustic communication machine;

Second, due to the repeated transmission of the same information frame, the effect of time diversity can be obtained at the same time, and the time-selective fading caused by the strong time-varying underwater acoustic channel can be suppressed. Acoustic communicators have good suppression performance on multipath and time-varying underwater acoustic channels.

Description of drawings

FIG. 1 is a schematic diagram of the composition of the transmitting part of the embodiment of the present invention.

Fig. 2 is a schematic diagram of the composition of the receiving part of the embodiment of the present invention.

FIG. 3 is a design diagram of a transmit signal frame according to an embodiment of the present invention.

Fig. 4 is a circuit schematic diagram of the pre-module of the receiving part according to the embodiment of the present invention.

Fig. 5 is a schematic diagram of the interface circuit of the channel selector, the analog-to-digital converter and the DSP in the receiving part of the embodiment of the present invention.

FIG. 6 is a schematic diagram of the time-division switching of each channel by the DSP control channel selector according to the embodiment of the present invention.

Detailed ways

In order to make the technical content, features and advantages of the present invention more comprehensible, the following embodiments will further illustrate the present invention in conjunction with the accompanying drawings.

Referring to Figures 1 and 2, the embodiment of the present invention is provided with a transmitting part and a receiving part;

The transmitting part is provided with an information symbol input interface 11, a spread spectrum modulation module 12, a convolution module 13, a probe signal generator 14, a frame synchronization signal generator 15, a signal framing module 16, a power amplifier 17 and a transmitting converter. energy device 18; the information symbol input interface 11 is connected to the input end of the spread spectrum modulation module 12, and the output end of the spread spectrum modulation module 12 and the output end of the probe signal generator 14 are connected to the input end of the convolution module 13 , the input end of the signal framing module 16 is respectively connected with the output end of the convolution module 13, the output end of the probe signal generator 14 and the output end of the frame synchronization signal generator 15, and the input end and the output end of the power amplifier 17 are connected with the output end of the power amplifier 17 respectively. The output of the signal framing module 16 is connected to the input of the transmitting transducer 18 .

The receiving part is provided with a multi-element receiving array 21, a pre-processing module 22, a channel switcher 23, an A/D converter (ADC) 24, a synchronization module 25, a time-reversal preprocessor 26, and serial/parallel multi-channel combination device 27 and data decoder 28; the multi-element receiving array 21 is made up of at least 2 receiving array elements, the output end of the multi-element receiving array 21 is connected with the input end of the pre-processing module 22, and the processed pre-processing module 22 The output terminal of the multi-channel signal is connected to the input terminal of the A/D converter (ADC) 24 through the channel switcher 23, and the output terminal of the A/D converter (ADC) 24 is respectively connected with the input terminal of the synchronization module 25 and the time inversion preprocessing The input terminal of device 26 is connected, the frame synchronization signal output terminal of synchronization module 25 is connected with the frame synchronization signal input terminal of time reversal preprocessor 26, and the reverse processing signal output terminal of time reversal preprocessor 26 is connected in series / and each channel data input end of the multi-channel combiner 27, the input end of the received signal output after the multi-channel time inversion of the serial/parallel multi-channel combiner 27 is connected to the input end of the data decoder 28, and the data decoding is carried out by the data decoder 28 , restore the original data. The pre-processing module is provided with a pre-amplifier 221 and a filter 222 .

The working principle of the present invention is given below:

1. Launch part:

The transmitted signal adopts direct sequence spread spectrum differential phase modulation (DS-DBPSK), the sampling rate is 96kHz, the carrier frequency is 15kHz, the bandwidth is 13-18kHz, and the m-sequence spread spectrum is adopted. The length of the m-sequence is 63 bits, and each symbol The width is 15.75ms; the probe signal is a probe sequence with a length of 23.8ms obtained through 63-bit m-sequence spread spectrum; the frame synchronization signal is a chirp signal with a low-end frequency of 13kHz, a high-end frequency of 18kHz, and a length of 30ms. In the signal frame format parameters: the guard interval is 30ms, and the information frame is composed of 200bit symbols after spread spectrum modulation, that is, the length of each information frame is 3.15s. This embodiment adopts the method of repeating N=4 times in time Time-division repeated transmission. In this embodiment, both the probe signal and the frame synchronization signal are generated by a digital signal processor in a software programming manner.

The transmitting transducer in the embodiment of the present invention can be composed of a cylindrical piezoelectric ceramic underwater acoustic transducer with a center frequency of 13-18kHz produced by the State-run 612 Factory, and a power amplifier circuit known in the art is used for signal transmission.

2. Receiving part:

First select the default channel (set to 1 channel in the embodiment) and use the copy correlation operation to perform frame synchronization capture on the input signal, judge whether the frame synchronization is reached by judging whether the copy correlation result exceeds the set threshold, and determine the frame synchronization time starting point.

After the frame synchronization is established, for the time-division multi-channel time-reversal implementation scheme adopted by the underwater acoustic communicator of the present invention, according to the frame time sequence of the transmitted signal, the channel selector is sequentially controlled to select the i-th channel in the receiving array (i=1, 2, 3, …N) corresponding probe signals are input to the digital processor to obtain the probe needle numbers p _ir (t) transmitted by each receiving channel of the array, and after time-reversing it, the time-inverse preprocessor coefficient p of each channel is obtained _ir (-t).

After the probe signal acquisition of each channel is completed, the channel selector is sequentially controlled to select the corresponding information frame signal of the i-th channel (i=1, 2, 3, ... N) in the receiving array to input to the digital processor. Assuming that the impulse response of the i-th channel in the receiving array is h _i (t), which satisfies randomness, Indicates the convolution operation, then the i-th channel receives the information symbol s _ir (t) as

${\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; ir</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; is</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In formula (1), n _is (t) is the interference noise superimposed on the information signal, and the received information frame s _ir (t) of each channel passes through the time inverse preprocessor p _ir (-t) of the corresponding channel, That is, the convolution operation with p _ir (-t) can be obtained:

${{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; ir</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; ir</span>}}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

为时反聚焦后的各通道信道响应，近似δ(t)。In formula (2), n _1i (t) is the noise interference item,

The time is the channel response of each channel after defocusing, approximately δ(t).

In order to eliminate p _i (-t) in the result, convolve r _i '(t) with the probe signal p _i (t), we have

${\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&ap;</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CircleTimes;</span>\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CircleTimes;</span>\mathrm{<span\; class="notranslate">\; \&delta;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

The convolution operation in this step is performed by the convolution module set at the transmitting end in the technical solution proposed by the present invention, so as to reduce the real-time calculation amount required for demodulation at the receiving end. In formula (3), n _i (t) is the noise interference term of the i-th channel:

${\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Then, after channel switching, the received signal of each channel in the receiving array passes through the time-inversion preprocessor of each corresponding channel successively to obtain the time-inversion signal r _i (t) corresponding to each channel, where the noise interference term is n _i (t).

The serial/parallel multi-channel combiner performs serial-to-parallel conversion on the time-inverted information frame signals of each channel input serially in accordance with the transmission frame timing, and merges the time-inverted signals and noise interference items of each multi-channel after conversion. The processing expression is:

${\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; no</span>}}^{<span\; class="notranslate">\; \&prime;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

It can be seen from formulas (1) to (6) that under the time-division multi-channel time inverse processing scheme adopted in the present invention, since the same information frame is repeatedly transmitted, the receiving end can realize the same multi-channel input channel by switching the channel selector. Inverts the effect of the channel. That is, the inverse channel of the original transmitted signal s(t) is actually the convolution of the autocorrelation of the channel impulse response and the autocorrelation of the probe signal. When the multipath of the acoustic channel is complex and the autocorrelation peak of the probe signal is sharp , the channel can be approximated as a time defocusing channel, and s'(t) can be approximated as the signal s(t) at the time of transmission. The multi-channel signals are combined after their respective time inverters, which not only focuses on the signals to eliminate multipath, restores the original signals, but also improves the signal gain in space and time. In this processing process, the background noise item is effectively suppressed after being combined due to the irrelevance of the noise of each channel.

The information frame has completed multipath focusing after time-division and multi-channel time inverse processing, which greatly suppresses the interference caused by the multi-path effect. After the information frame after multi-channel time inverse processing is sent to the data decoder, it is In the DSP chip, despread and demodulate the DS-DBPSK signal to obtain information symbols.

In terms of the hardware implementation of the underwater acoustic communication machine, the receiving underwater acoustic transducer array in the embodiment of the present invention is composed of 4 broadband receiving hydrophones that are vertically arranged and produced by the state-owned 612 factory, that is, the number of receiving arrays is N=4, and in the array The distance between two adjacent hydrophones is 1.5m. The pre-processing module in each component module is composed of the AD620 low-noise pre-amplifier chip of the American AD company, the TL084 operational amplifier chip, and the MAX274 switched capacitor filter chip of the Maxium company. bandpass filter. The specific circuit is shown in Figure 4. After pre-amplification and band-pass filtering, the output signal is divided into A, B, C, D 4 channels and sent to the subsequent channel selector.

The channel selector and analog-to-digital conversion chip are composed of 4052 chip, AD9851DDS chip and MAX153 analog-to-digital conversion chip. The wave signal is used to control the analog-to-digital conversion chip to perform analog-to-digital conversion on the input signal. The connection circuit diagram between 4052, AD9851DDS chip, MAX153 analog-to-digital conversion chip and TMS320C6713 processor is shown in Figure 5. In the initialization stage, the TMS320C6713 processor sets the pins of the AD9851DDS chip through the IO ports GP0, GP1, GP2, and GP3, and sets the type and frequency of the output waveform of the output pins of the AD9851 chip. In this embodiment, the output type is square wave, and the output The oscillation frequency of the square wave is set to f _s =96kHz.

After the frame synchronization is established, the TMS320C6713 processor controls the input channel of the channel selection terminal of the channel selector chip 4052 through the IO ports GP8 and GP9, that is, the DSP chip controls the A, B, C, D4 channel signals of the multi-element receiving array through the 4052 chip The probe and information frame signals are input into the follow-up analog-to-digital conversion chip and DSP for processing. The principle of channel time-sharing switching is shown in Figure 5. After the frame synchronization is established, the probe signals and information of each channel A, B, C, and D are sequentially selected according to the time sequence of the repeated transmission of the probe signal and the information frame signal in the transmission frame. The frame signal, after passing through the channel selector, the multi-channel received signal is converted into a channel and each channel is arranged in sequence corresponding to the probe and information frame signal. The probe and information needle signals represented by the gray boxes in Figure 6 are the input channels selected by the channel selector at each moment. From Figure 6, it can be seen that the probe signals and information needle signals of each channel are output successively after channel selection . After the data of each channel is time-divided and sequentially output through the channel selector, the calculation amount of the real-time processing of the time-reversal operation is greatly reduced, and it is convenient for the real-time realization of the subsequent time-reversal convolution preprocessing operation on a DSP chip.

After the input channel is selected by the channel selector, the signal enters the analog-to-digital conversion chip and the DSP interface circuit. As shown in Figure 5, the connection mode between the AD9851DDS chip, the MAX153 analog-to-digital conversion chip and the TMS320C6713 processor in the receiving part of the underwater acoustic communicator of the embodiment is described as follows: after the input signal is sent into the input V _in pin of the MAX153 chip, it is input by the AD9851 The square wave signal with a chip output frequency of 96kHz is connected to the WR/RDY and RD terminals of the MAX153 chip to start the analog-to-digital conversion. When the analog-to-digital conversion is completed, the INT signal of the MAX153 chip sends a low level. The EXINT7 pins are connected to trigger the external interrupt service program of the DSP chip, and the data lines ED0-ED7 of the DSP are connected to the data lines D0-D7 of the MAX153 chip U1 to input the analog-to-digital conversion result. After the external interrupt service program obtains the conversion data of the analog-to-digital conversion chip, the data input to the DSP chip is processed in a double-buffered manner.

In the underwater acoustic communication machine of the embodiment, steps such as probe signal generation, frame synchronization signal generation, spread spectrum modulation, convolution, signal framing, synchronization establishment, time inverse preprocessing, merging, and data decoding are all performed in the TMS320C6713 digital signal processor (DSP) chip software programming.

To sum up, the time-division realization of multi-channel time-reversal underwater acoustic communicator disclosed in the present invention utilizes the transmitting end to repeatedly transmit information frame signals and the receiving end channel switching to realize the successive input of multi-channel received signals, thus greatly reducing the multi-channel time The real-time calculation amount of inversion makes it possible to realize an underwater acoustic communication machine that uses multi-channel time inversion to improve communication performance based on a single DSP processor chip.

The starting position of the transmission frame format of the present invention is a frame synchronization signal, which is used to establish the starting point of data demodulation time at the receiving end; after the frame synchronization signal is a probe signal, which is used to obtain channel multipath information through channel transmission; after the probe signal is an information frame, and each original information symbol obtained from the information symbol input interface is spread-spectrum modulated and then convolved with the probe signal to form an information frame. The signal framing module arranges the frame synchronization signal, the probe signal and the information frame in the time domain according to the frame format with the set timing and guard interval, so as to form a complete signal frame. In order to perform time-division multi-channel time-reversal in the present invention, for an N-element receiving array, the probe signal and the information frame in the transmitting signal frame are repeated N times in time for repeated transmission. At the same time, in order to avoid intersymbol interference caused by frame synchronization, probes and information frames, a guard interval is inserted in the frame synchronization header, probes and information frames. Taking the 3-element receiving array with N=3 as an example, the signal frame format of repeated transmission of the same probe and information frame signals is shown in Figure 3.

The information symbol input interface obtains information symbols from an information source (upper computer or user input).

The frame synchronization signal generator is used to generate the frame synchronization signal.

The probe signal generator is used to generate probe signals.

The spread spectrum modulation module performs spread spectrum modulation on the information symbols.

The convolution module uses the probe signal to perform convolution operation processing on the information symbols after spread spectrum modulation to form an information frame.

Receive part:

The preamplifier and the filter are connected to the receiving signal end of the receiving array element at the receiving end to pre-process the multi-channel receiving signal.

The channel selector is connected to the pre-processed multi-channel signal, and is used to switch the signal channel input to the subsequent analog-to-digital conversion chip, time reversal processing and data decoding.

The synchronization module uses the copy correlation operation to capture the frame synchronization signal, which is used to establish the time starting point for reverse processing and decoding when receiving data.

The time inversion preprocessor receives the multi-channel signals serially output from the channel selector, captures the probe signal corresponding to each channel, and then reverses the time of each channel probe signal to the corresponding channel information frame that arrives subsequently Carry out the convolution operation, after completing the reverse processing at the passive time, send it to the serial-parallel multi-channel combiner one by one.

The serial/parallel multi-channel combiner receives the data of each channel serially input after passive time inversion processing, performs serial/parallel conversion according to the timing of each channel, and then merges to realize multi-channel time inversion.

The data decoder performs data decoding on the multi-channel time-inverted received signal according to its modulation mode, and restores the original data.

The basic implementation idea of the present invention is that the transmitting end repeatedly transmits information frames, and the receiving end of the underwater acoustic communication machine collects data from different receiving array elements sequentially through channel switching after establishing frame synchronization, and performs time-reverse processing of each array element receiving data successively, and finally Merging is performed, so that the multi-channel multi-path focusing effect can be obtained with low real-time computing overhead. Considering that the amount of communication data is not large and the data rate is low in most underwater acoustic communicators, the present invention pays for obtaining multi-channel time-reversal performance with relatively low computing hardware (such as a single-chip digital signal processor chip). The cost of repeated transmission of information frames is affordable.

Among the functional modules of the underwater acoustic communicator, pre-processing, channel switching, ADC, and power amplifier are composed of hardware circuits such as pre-amplification, filter, analog-to-digital conversion chip, channel selector chip, and power amplifier; multi-channel Time inverse preprocessing, serial/parallel multi-channel combination, data decoding, frame synchronization establishment, spread spectrum modulation, convolution, signal framing, frame synchronization generator, probe signal generator and other modules are digital signal processing links, and are controlled by DSP Chip software programming.

In the embodiment of the present invention, the information symbol input interface of the transmitting part obtains the information symbol from the information source (upper computer or user input), and the obtained information symbol is sent to the spread spectrum adjustment module. The spread spectrum modulation module acquires information symbols from the information symbol input interface and performs spread spectrum modulation, and then sends the spread spectrum modulated information symbols to the convolution module. The probe signal generator is used to generate probe signals, and the generated probe signals are respectively sent to the convolution module and the signal framing module. The convolution module uses the probe signal to perform convolution operation processing on the information symbols after spread spectrum modulation to form an information frame and send it to the signal framing module. The frame synchronization signal generator is used to generate the frame synchronization signal, and the generated frame synchronization signal is sent to the signal framing module. The signal framing module arranges the frame synchronization signal output by the frame synchronization signal generator, the probe signal output by the probe signal generator and the information frame signal output by the convolution module in the time domain according to the timing and guard interval set by the signal frame format Then form a complete signal frame. And send the complete signal frame to the power amplifier. The power amplifier amplifies the power of the complete signal frame output by the framing module and sends it to the transmitting transducer for underwater acoustic emission.

The pre-amplification and filter of the receiving part are connected to the receiving signal end of the receiving array element at the receiving end for pre-processing the multi-channel receiving signal; the channel selector is connected to the pre-processed multi-channel signal for switching input subsequent Analog-to-digital conversion chip, signal channel for time-reversal processing and data decoding; the synchronization module uses copy correlation operations to capture frame synchronization signals, which are used to establish the time starting point for inverse processing and decoding when receiving data; time-inversion preprocessor receives the slave channel The multi-channel signal serially output by the selector captures the probe signal corresponding to each channel, and then reverses the time of each channel probe signal and performs convolution operation with the corresponding channel information frame that arrives subsequently to complete the passive time After inverse processing, it is sent to the serial-parallel multi-channel combiner one by one; the serial/parallel multi-channel combiner receives the data of each channel serially input after passive inverse processing, performs serial/parallel conversion according to the timing of each channel, and then merges them. Realize multi-channel time inversion; the data decoder performs data decoding on the received signal after multi-channel time inversion according to its modulation mode, and restores the original data.

The problem to be solved by the present invention is to use limited processor hardware resources in the underwater acoustic communication machine to provide a time-reversal method in which the same information frame is repeatedly transmitted by the transmitting end, and the receiving end performs time-sharing on the multi-channel signal by channel switching. preprocessing, merging.

Claims (1)

1. A time-sharing underwater acoustic communicator that realizes multi-channel time reversal is characterized in that a transmitting part and a receiving part are provided; The transmitting part is provided with an information symbol input interface, a spread spectrum modulation module, a convolution module, a probe signal generator, a frame synchronization signal generator, a signal framing module, a power amplifier and a transmitting transducer; the information code The element input interface is connected to the input end of the spread spectrum modulation module, the output end of the spread spectrum modulation module and the output end of the probe signal generator are connected to the input end of the convolution module, and the input ends of the signal framing module are respectively connected to the convolution module The output end of the probe signal generator is connected to the output end of the frame synchronization signal generator, and the input and output ends of the power amplifier are respectively connected to the output end of the signal framing module and the input end of the transmitting transducer; The receiving part is provided with a multiple receiving array, a pre-processing module, a channel switcher, an A/D converter, a synchronization module, a time reversal preprocessor, a serial/parallel multi-channel combiner and a data decoder; the multiple The receiving array is composed of at least 2 receiving array elements, the output end of the multi-element receiving array is connected to the input end of the pre-processing module, and the processed multi-channel signal output end of the pre-processing module is connected to the A/D converter through the channel switcher The input terminal of the A/D converter is connected with the input terminal of the synchronization module and the input terminal of the time reversal preprocessor respectively, and the frame synchronization signal output terminal of the synchronization module is connected with the frame synchronization signal of the time reversal preprocessor Input terminal connection, time inversion preprocessor completed passive time inverse processing signal output terminal connected to each channel data input terminal of serial/parallel multi-channel combiner, received signal after multi-channel time inversion of serial/parallel multi-channel combiner The output terminal is connected to the input terminal of the data decoder, and the data decoder performs data decoding to restore the original data.

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