BACKGROUND OF THE INVENTION Almost all of the existing types of the Underwater Apparatuses (UA) and systems for underwater visual inspections have the same essential deficiency that limits their using in the different applications. Such deficiency is an absence of the means and therefore opportunities of transmission the Real Time Video Imaging (RTVI) wirelessly, without any cable or wire links for communication. The only alternative for this wire/cable kind communication that could be used in the water environment is a hydro-acoustical channel with ultrasound communication link.

Numerous publications present detailed descriptions of the needs for a wireless underwater communications system for transmission of video, control, and data communications between underwater vehicles; or between an underwater vehicle and a surface platform; between underwater platforms; or the likes. These publications also review combinations of elements that the above average man of the art expects to be requisite for the enabling of such a system. Accordingly, the following publications are incorporated herein by reference: [1] Leo L. Beranek. "Acoustic Measurements". Office of Naval Research-Navy Department, Washington D. C. pp. 76,1949.

[2] Daniel B. Kilfoyle and Arthur B. Baggeroer. "The State of the Art in Underwater Acoustic Telemetry". IEEE Journal of Oceanic Engineering, Vol. 25, No. 1, pp. 1- 24, January 2000.

[3] Milica Stojanovic."Recent advances in High-Speed Underwater Acoustic Communications". IEEE Journal of Oceanic Engineering, Vol. 21, No. 2, pp. 125-136, April 1996.

[4] Xiaolong Yu, Ph. D. , LinkQuest Inc. , www. link-quest. com"Wireline Quality Underwater Wireless Communication Using High Speed Acoustic Modems". San Diego, California, 2000.

[5] J. Catipovic. "Performance Limitations in Underwater Acoustic Telemetry".

IEEE J. Ocean Eng. , Vol. OE-15, pp. 205-216, July, 1990.

Furthermore, there are a few relevant patents, which have taught specific novel combinations of elements requisite for partially enabling such a system; or more specifically, its functionally limited antecedents. Specifically, these patents are: US3688029. Cableless Acoustically Linked Underwater Television System. This patent suggests using acoustical link to transmit video images from a videocom tube. But the patent does not take into account multi-path reflections and other underwater phenomena in the real underwater environment.

US5301167. Apparatus for improved underwater acoustic telemetry utilizing phase coherent communications. This method could work only for low bandwidth data transmission - since it uses low frequency ultrasound link of up to 200 kHz.

US5701276. Underwater communication system by means of coded pulses. This patent is for short-range voice communications using insufficient kHz carrier frequencies. This method also ignores phase modulation techniques-making it very unstable in the real noise conditions of the underwater environment.

US6130859. Method and apparatus for carrying out high data rate and voice underwater communication. This patent used OFDM modulation technique that does not permit real time video communications-simply because its carrier frequencies are not high enough. Besides, when using OFDM for video communication we have to work with very wide bandwidth (a few MHz) that is not feasible when the carrier frequency is 1-2 MHz.

Simply stated, when one attempts to actualize high bandwidth underwater communications, even combining the prior art will not prove sufficient to overcome the harsh noise multi-path circumstances of the real underwater environment.

Furthermore, there is an outstanding unsolved problem in this field that relates to improved (real-time) transmission of volumes of data over distances of at least about 30-100 meters; and preferably up to at least 300 meters. According to the known prior art, this problem was solved before by using carrier frequencies generally in the up to 300-500 kHz range and occasionally in the up to almost MHz range.

In summary there have heretofore been two primary application paths for underwater communications-substantially non-real-time data communications and substantially real- time diver voice communications (or other low bandwidth applications). Accordingly, there is a longstanding need in the art to allow-100-200kHz bandwidth for real-time underwater communications (e. g. data or TV).

BRIEF SUMMARY OF THE INVENTION The aforesaid longstanding needs are significantly addressed by embodiments of the present invention, which generally relates to submerged wireless imaging system technologies, and more specifically relates to a wireless underwater communications system - preferably for transmission of video, control, and data communications between underwater vehicles; or between an underwater vehicle and a surface platform; between underwater platforms; or the likes. In this context, the instant method, apparatus, and protocol are especially useful in man-computer interactions wherein there exists a use for real time broadband communications to or with an autonomous (un-tethered) underwater vehicle or platform.

The instant invention relates to embodiments of an underwater communications system having (a) a high frequency ultrasound carrier for increasing quality of video signal transmission and incorporating (b) a communication protocol with channel sampling for compensation of environmental noise influences and signal attenuations because of multi- path reflections, Doppler effects, etc. The key factor enabling these embodiments is that the demodulation is based on the use of pseudo-noise sampling signal to determine multi-path replay delay and signal dispersion. Each transmission results in reflection (s) that has a different dispersion of the sampling signals. After measuring these dispersions the carrier frequency of the transmitter is shifted to minimize any interference in the receiver.

Specifically, the enabling of the instant for-underwater-use invention is based on correcting of carrier frequency, using Quadrature Phase Shift Key modulation (QPSK) and to overcome interference caused by multi-path reflection. The main purpose is overcoming the multi-path phenomena for the relatively high ultrasound carrier frequency and using the needed transmission bandwidth enough for real time video transmission. Another goal is to receive and transmit location data for the underwater platform or for an object that the platform is measuring, photographing, etc.

The present invention (see figure 6) relates to embodiments of A Wireless Underwater Communications System 600 including: a pair of at least half duplex submersible transceivers 610 620 having adaptive parametric tuning there-between, wherein the transceivers use at least one transmission frequency 630 640 of at least about 0.6 MHZ, and wherein the pair uses a QPSK modulation 650 for data-communications transmitted thereon. In general it works by preferably using pseudo-noise sampling, in each frame or block of frames. The sampling of the communications channel is to analyze and understand parameters for properly tuning the transceiver (s). For determination of platform's coordinates, we preferably use full duplex communications, and therewith also transmit control signals-used to manipulate the platforms navigation or/and TV-camera parameters.

According to one variation embodiment of the instant invention Wireless Underwater Communications System, the at least half duplex is full duplex.

According to another variation embodiment of the instant invention Wireless Underwater Communications System, the adaptive parametric tuning includes there-before an at least one sampling of signal and response.

According to a further variation embodiment of the instant invention Wireless Underwater Communications System contains PSK modulation (preferably quadrature (Q) or differential quadrature (DQ)). Other modulation methods (FSK or ASK) are not practical here because of poor reliability in the noisy underwater multi-path environment.

The present invention also relates to embodiments of (A) on-site transceiver with PSK modulator (especially useful in at least about 0.6 MHZ wireless underwater communications, and a generator of carrier frequency with respective parametric tuning based on respective responses from the second (on-surface) transceiver.

According to another variation embodiment of the instant invention transceivers uses the at least one test-sampling signal that is short compared to the length of a single video frame.

The preferred embodiment of the invention includes a first transceiver and a second transceiver (see figures 7 and 8). The first transceiver for transmission video and data from underwater object with PSK modulator especially useful in at least about 0.6 MHZ wireless underwater communications, and the transceiver includes: (A) generator of sampling signals with parametric tuning block working in accord with Pseudo-Noise signals responses from a second transducer and associated therewith (B) block for tuning of a carrier frequency of a PSK modulator-in accord with input sampling signals'parameters. The second transceiver for receiving of video and data from the a first transceiver with two PSK demodulators comprising a first means for video and data and a second means for Pseudo-Noise sampling signals, and wherein this transceiver has blocks for estimation of time dispersion of the sampling signals and transmit commands for tuning of carrier frequency of a first transceiver.

Preferably: the carrier frequency is tuning as the results of the replays on the sampling signal request; the sampling signals are Pseudo-Noise signals; the PSK modulator- demodulator transform simultaneously video, data and command signals in every transmitted frame; the sampling signal is a single test sampling signal that is sent before every single video frame; the sampling signal is a single test sampling signal that is sent before a group of video frames; and/or before transmission of a frame, containing the video and/or data information the parameters of time delay and dissipation of the communication ultrasound channel are estimated.

Advantages, Objects And Benefits Of The Invention-Technical Issues: The instant invention facilitates real time data acquisition system for obtaining real time data from underwater TV camera, using high frequency ultrasound communication link. This real time data acquisition system permits simultaneous transmission of command control signals and information from a sensor array aboard an apparatus; to define the speed and coordinates of the apparatus by means of using pilot signals for definition of the parameters of the ultrasound communication channel. Most critically, the instant invention facilitates a real time underwater data acquisition system using frequency diversity during channel sampling for excluding phenomenon of the signals'interference because of multi-path reflections.

Advantages, Objects And Benefits Of The Invention-Economic Issues: The instant invention facilitates a truly affordable system for high frequency wireless underwater ultrasound communications-thereby making many professional and hobbyist inspections tasks feasible using an autonomous vehicle.

NOTICES: The reader should also appreciate that a reference to an existing commercial product, which circumstantially derives from granted or pending patents, should be considered as a reference to the present best enabling mode of the technology disclosed in those patents. Furthermore, the present invention is herein described with a certain degree of particularity, however those versed in the art will readily appreciate that various modifications and alterations may be carried out without departing from either the spirit or scope, as hereinafter claimed. Accordingly, in describing the present invention, explanations are presented in light of currently accepted scientific, mathematical or technological- theories and models. Such theories and models are subject to changes, both adiabatic and radical. Often these changes occur because representations for fundamental component elements are innovated, because new transformations between these elements are conceived, or because new interpretations arise for these elements or for their transformations.

Therefore, it is important to note that the present invention relates to specific technological actualization in embodiments. Thus, theory or model dependent explanations herein, related to these embodiments, are presented for the purpose of teaching, the current man of the art or the current team of the art, how these embodiments may be substantially realized in practice.

Alternative or equivalent explanations for these embodiments may neither deny nor alter their realization.

This application claims priority to provisional U. S. Application Ser. No. 60/429,013, filed November 26,2002.

Furthermore, a portion of the disclosure of this patent document contains material, which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

BRIEF DESCRIPTION OF THE DRAWINGS In order to understand the invention and to see how it may be carried out in practice, embodiments including the preferred embodiment will now be described, by way of non- limiting example only, with reference to the accompanying drawings. Furthermore, a more complete understanding of the present invention and the advantages thereof may be acquired by referring to the following description in consideration of the accompanying drawings, in which like reference numbers indicate like features and wherein: Figure 1 illustrates a schematic block diagram of a first transceiver; Figure 2 illustrates a schematic block diagram of a second transceiver; Figure 3 illustrates an abstracted view of process calculation of a time dispersion channel and time propagation signal; Figure 4 illustrates a typical structuring of frames for the first transceiver ; Figure 5 illustrates a typical structuring of frames for the second transceiver ; Figure 6 illustrates a schematic view of a Wireless Underwater Communications System; Figure 7 illustrates a block-schema of a first, on-site transceiver ; and Figure 8 illustrates a block-schema of a second"on-surface"transceiver.

DETAILED DESCRIPTION OF THE INVENTION Almost all of the existing types of the Underwater Apparatuses (UA) and systems for underwater visual inspections have the same essential deficiency that limits their using in the different applications. Such deficiency is an absence of the means and therefore opportunities of transmission the Real Time Video Imaging (RTVI) wirelessly, without any cable or wire links for communication. The only alternative for this wire/cable kind of communication that could be used in the underwater environment is a hydro-acoustical channel with ultrasound communication link.

Embodiments of the instant invention's system permits RTVI acquisition for practically any type of UA module construction of the equipment for underwater inspection has also been designed, that is an underwater carrier, that could use Submerged Wireless Imaging System Technologies (SWIST). By using said modules this carrier could be simply transformed from the underwater viewing camera to the ROV or tethered system or some other type of the apparatus without some umbilical or with it, but all the information data flow from the apparatus or to it is realized using said ultrasound channel.

SWIST (the instant invention in its preferred embodiments) uses high frequency ultrasound waves (1-2MHz) and bandwidth preferably of about 100-200 KHZ (but less preferably about 400 KHz) for data transmission somewhat as a function of the compression coefficients (1: 100 or more). Special algorithms are developed for compensation of multi- path reflection effects, Doppler effect and noise.

The following description contains the fundamental principle and construction of the acoustical communication channel-which is useful for construction of an underwater device for wireless video inspection. Clear to all skilled in the art that said communication channel could be used for transmission any data, not only video information, but the signals from any kind of underwater sensors, still cameras, control and state parameters of other on board equipment etc. There is an essential relation between communications and application, as on the one hand the dynamics and exploitation parameters of the underwater apparatus defines the limitation and demands to the communication channel and on the other hand the features of the communication channels form the specific demands to the environmental conditions where the underwater devices could be used successfully. This also includes the limitation to the mutual movement of the marine objects to support a reliable communication, demands to the transceiver antennas, carrier frequency and bandwidth of the communication link and some other parameters.

Such novel approach permits the design of the universal equipment for underwater video inspection and communication channel for the short-range data transmission in the water environment.

Turning to Underwater Apparatuses and Acoustical Communications, there are some publications demonstrating the theoretical ability of using high frequency ultrasound for the short-range data transmission. In practice, the main UW apparatus that explore such techniques are Autonomous Underwater Vehicles (AUV). But most AUVs use an acoustical channel with the medium frequency diapason (hundreds KHz), mainly for transmitting instrumental data during environmental monitoring. Such channel may also be used for feedback during real time control of the AUVs from the surface ships. In this case the main task of the designers was to build a communication channel for transmission of a limited volume of information at a small rate, but over the maximum possible distance.

Another large class of the underwater apparatuses-Remotely Operated Vehicle (ROV), where the main task is transmission of large information flows (such as Real Time Video)- has in general cable communication link, while its length defines the communication range. Such underwater cables are rather expensive and cut down the ROV's maneuverability to a large degree. Alternatively, using the novel technique, it is possible to replace the communication cable with a simple cheap umbilical (that will serve only as mechanical failsafe connection), but for transmission of information the acoustical one must be used.

There is one more large class of the UW apparatuses, Tethered Systems, that does not have its own thrusters, but includes different inspection devices and TV cameras. This class also needs data transmission to the support vessel, but for the above reasons they don't use acoustical communication.

So, at present, the main"clients"of the underwater acoustical communication technology are divers, but usually they use low frequency (tens KHz) acoustics, that excludes RTV transmission. That means, after being lowered to a subsurface position, a remotely located technician or pilot must utilize a ROV's principles and communication systems.

Clearly, ROVs can be used to perform relatively complex tasks, including construction support, platform cleaning, inspection, subsurface pipeline completion, etc. Although they are quite flexible in that they can be adapted to perform a wide variety of tasks, ROVs are also fairly expensive to operate, as they require a complicated cable system among other reasons, with surface support platforms. This results in ROVs, or other subsurface vehicles that are connected to a surface or to another submerged vessel by a physical linkage, incurring heave- induced damage. Heave is the up and down motion of an object produced by waves on the surface. Underwater vehicles physically attached to a floating surface platform therefore move in accordance with the platform. Therefore, when an underwater vehicle is located near a fixed object on the seabed, heave-induced movement of the platform can damage both the vehicle and the fixed object. To alleviate this problem, devices such as heave-induced motion compensators and tether management systems (both rather expensive) have been employed to reduce the transfer of heave to underwater vehicles. But clearly, in the case short-range communication linkage the most"cost effective"decision could be replacing said cable altogether.

In contrast to ROVs, while underwater AUVs are not subject to heave-induced damage because they are not usually physically connected to a support platform. Common AUVs are essentially unmanned submarines that contain on-board power and a pre-programmed control system. But AUVs have practical limitations rendering them unsuitable for certain underwater operations when real time control is needed. AUVs conventionally employ an acoustical modem for communicating with a remote operator. However, such acoustic communications do not convey data as rapidly or accurately as a cable link, so that the transfer of data, encoding RTV signals or real time command instructions from a remote operator, is not efficient given current technology. As a result, it could be worthwhile to equip this class of the UW vehicles with a high frequency acoustical modem to carry out unanticipated tasks or jobs requiring a great deal of operator input.

Other underwater apparatuses also suffer drawbacks such as subjection to heave or poor communications. Therefore, the need exists for a device to help overcome these limitations.

Thus, the present application is directed both to UW vehicles for performing subsurface tasks and to complement manned underwater inspection.

The communication link that we suggest be used between the UW apparatus and its operator is an ultrasonic channel, that permits duplex linkage between said"clients"to transmit command control from an operator, receiving RTV information from an apparatus.

In its simplest version such apparatus could be an UW TV camera (tethered or fixed on- site) with an acoustical modem for RTV transmission to the operator/supervisor. The divers, to transmit information to the surface and/or to one another, could use such a camera. Clearly, that apparatus could be fully autonomous, or could have a physical safety tether with its operator/supervisor.

Turning to Feasibility of the short-range acoustical modem for RTV, existing acoustical modems for UW speech communication or data transmission use ultrasonic waves with the frequency diapason of about 40-100 KHz, that permits long range (some kilometers) communication but with essential limitation of data rate flow, not permitting RTV transmission. As tested by the authors, in order to realize such a task, it is necessary to use a frequency bandwidth of no less than 100 KHz. The carrier frequency must be of aboutl-2 MHz. -no less because of the minimum information flow rate and no more because of the ultrasonic waves attenuation. Such attenuation of the sound in the water environment on the frequency 1-2Mhz is rather high-about 0.25dB/m, so that at a range of some 100m it will be about 25dB.

But the sensitivity of the modern transceivers and the electronics for the data transmission permits reliable data communications link in the said conditions of the attenuation of the sound signals. It was also known that the carrier frequency of 1 MHz, permits data transmission at a rate of about 500kb per sec. Recent publications also show an opportunity of short range UW RTV transmission in the case of efficient data compression of the video images together with sophisticated modulation and encoding/decoding of transmitting signals.

Finally, there is a problem in the phenomenon of the acoustical channel transmission technique, that should be considered in the design of the telemetry system for video imaging, is the real water environment with inherent ambient noise, transmission losses, multi-path refraction, etc.

Therefore, a reliable high data rate communication for RTV transmission is achievable only if changes in the underwater acoustic channel will be detected, accounted for and compensated against.

In communication systems (usually it is now digital communication) having transceivers on both sides of the channel, it is customary to input intelligent information to be conveyed onto a carrier frequency for transmission with one of different modulation procedures. There are three main types of modulation technique-frequency, phase and amplitude. The best one for underwater acoustical signal transmission is the Phase Shift Key modulation that in its turn includes Binary PSK or Quadrature PSK. When information is modulated onto a carrier by either BPSK or QPSK, a signal is transmitted from the transmitter. But the problem is that the phase space of the received signal generally differs from that of the transmitted one due to several reasons, such as frequency differences between the oscillators at the transceivers on both sides, the effect of variance time delays, frequency and phase shifts in the propagation path, etc.

To coherently demodulate the PSK modulated signals it is necessary for the receiver to form an estimate of the transmitter's phase so that the tumbling received signals may be transformed back into the original phase space of the transmitter. This process is known as "phase tracking". The phase difference between the incoming phase and the estimated phase is influenced by the true differences between the phase systems of the transmitter and receiver, by phase and thermal noise present in receiver, by the symbol's data content which changes the angle by a multiple of. pi/2. for QPSK or. pi. for BPSK.

In the past said coherent PSK modulation systems have been used in the UW acoustical modems to transmit data, in particular in a vertical direction and in deep water application while the phenomenon multi-path or channel parameters fluctuation are neglected.

In the present short range and low depth application, the direction of the transmitted signals will not necessarily be vertical and therefore many unique channel characteristics such as fading, extended multi-path, refractive properties etc. could preclude direct application of classical approaches. Therefore many approaches (among them FSK modulation that failed to provide bandwidth efficiency for high data rate that is even less than that needed for RTV) have failed in real harsh aquatic environments. The reason is the occurrence of phenomena such as acoustical signal degradation, caused by reverberation in the form of multi-path inter-symbol interference or other factors such as Doppler spread, medium non homogeneities etc.

Short ranges have relatively mild phase fluctuations, and such channels encompass a plurality of vertical and horizontal paths. Therefore, sampling"pilot"signals in this type of channel should be done at regular short intervals.

According to the instant invention, solving these problems is by appreciating characteristics of reflections from the different objects or environmental boundaries at shallow water, transmission loss, channel transfer functions-by way of accurate prediction, using modulation techniques and constant sampling of the real environment.

According to the instant invention's preferred embodiment of the acoustical communication link, an ultrasound communication link consists of minimum two transceivers, placed at the ROV's hull or on any other underwater constructions (ships, platforms or else). These transceivers forms ultrasound frequencies, modulated using special PSK modulation technique.

Demodulation of PSK frequencies is realized by the receiver's electronics, also containing an intelligent electronics, whereby, on the one side of the link there is an underwater TV camera and on the other side there is a TV display and control unit. So, that such communication link permits control by the object, where TV camera is set, or control by the TV camera itself, and on the other side the operator of the link could view the TV display and realize his inspection mission.

According to another aspect of the instant invention, the environmental parameters are such that the carrier phase fluctuation in the acoustical channel are low and time dissipations of the channel are no more than tens milliseconds.

Acoustical modem forms pulses on the input of the PSK modulator with the rate of about 600 kbit/sec, that permits transmitting video images with the VGA format (650x480pixels) at the standard rate 25image/sec, using their compression by up to relation 1: 100, as permits MPEG-4 technology. (In general it should be mentioned that there are some reserves in the rate of transmission. The first is an opportunity to decrease the needed rate itself up to 16image per second without essential loss of image qualities, and another reserve is the more modern compression algorithms, permitting now 1: 200 and even 1: 400 relations.

Such reserve permits to transmit larger image formats, if necessary, or to improve the image quality.

It was already mentioned above on the essential relation between ROV's dynamics and acoustical link. In particular, we consider that because of low movement of the ROV (ROV speed should not be more than 0.5 knot in case video inspection) the phase channel fluctuation are rather low and the carrier Doppler shift is no more 0.015%. Therefore as the modulation technique we can use a coherent. pi/4. QPSK and as a phase tracking method we use a second order Phase Locked Loop (PLL) transformation, that defines the carrier phase in the receiver.

As a more simple modulation method for identification of carrier phase fluctuations could be used the method of. pi/4. DQPSK. This method has better amplitude and spectral efficiency, but it is more sensitive to the noise-about 3dB in compare with QPSK. But because of 1 MHz carrier frequency and a short-range communication, the channel attenuation will be about 25dB per 100m, so said 3dB of noise losses are not large and could be compensated by a small increasing in the transmitting power.

Taking into account the above mentioned time dissipation (about 10msec), the bandwidth of coherency of the acoustical channel is: Af = 1/Tm = 1/0.01 = 100 (Hz), that is sufficiently less than the signal bandwidth efficiency of the channel, because said bandwidth efficiency. pi/4. DPSK has 1,6 bits/sec/Hz character so the bandwidth on the output of the modulator in the data-link channel will be in 1.6 time less (from 100 to 400kHz) in comparison BPSK.

That shows, that the bandwidth of the signal is much more than the bandwidth of coherency of channel, that is about fc =100Hz. Such phenomenon, when W>> A fc realizes in multi-path signal dissipation. To compensate such effect, it is suggested a specific measuring procedure for identification of the time dissipation parameter, using pseudo-noise sampling "pilot"signal in the bandwidth of chennel (100-400kHz) So, depending on the resolution, compression and frame rate, the bandwidth could be from 100 to 400 kHz.

The real time data acquisition system include, in case ROV or AUV applications, as the main part the"Transceiver 1"which processes the data flow not only from the TV camera, but from all sensors 101-110, installed on board an underwater vehicle. As shown in Fig. 1, the signals from the TV image sensor and from other sensors pass to the compressor/multiplexor 111 (where the video images are transformed by the said MPEG program) and then pass to the encoder 112 for data coding (using for example latticed encoder) and for data modulation in modulator 113 (using above mentioned QPSK or. pi/4.

DQPSK). The modulated signals should be after that amplified by the Power Amplifier 114 and after that the output signals are emitted by the Transducer 115 into the environment in the form of acoustical pulses, which contain encoded information data frames.

According to the above-mentioned reasons, before transmission, for every information frame, the parameters of the acoustical channel should be estimated. They are time delay and dissipation. In case these parameters do not change fast such procedure could be done not every frame, but from time to time, when it is needed. During such pilot sampling of the communication channel the Block of Control and Processing 116 stops the work of the Encoder 112 and starts the work of the Generator of Pseudo-Noise signal 117. This signal modulates the mentioned carrier frequency fl=lMHz (using the same PSK modulator 113 in the same (from 100 to 400kHz) bandwidth and such pilot signals are emitted by the same transducer.

Passing through the acoustical channel these Pseudo-Noise signals enter the transducer 221 of Transceiver 2 (see Fig. 2) and after that are processed successively by the BP filter 222, low noise amplifier 223, A/D converter 224, equalizer 225 and then followed to the Demodulator 226 of the Pseudo-Noise signals (that is also PSK demodulator). The carrier frequency fl is recovered in the recover of the carrier frequency 241 using second order PLL procedures to compensate the Doppler shift of the frequency.

Under condition W>> A fc, the output of the Demodulator 226 of Pseudo-Noise signals contains the replays on the multi-path acoustical signals, that enter the receiver from different directions (see time diagram of Fig. 4). These replays pass to the Time Dispersion Calculator 227, which forms a control signal on receiving the first replay. This control signal starts the Control Block 228 that in its turn restart the Generator of Pseudo-Noise signals 229. It begins to form modulation pulses by the PSK Modulator 230 of the Transceiver 2, but on the carrier frequency f2=lMHz, formed by the generator 231. The output signals, modulated with the Pseudo-Noise signal pulses are emitted by the Transducer 233 of the Transceiver 2 to the Transducer 121 of the Transceiverl, where they pass through the"f2 channel in the analog way-BP filter 122, low noise amplifier 123, A/D converter 124, Demodulator Pseudo-Noise 125 (also PSK, could be QPSK or. pi/4. DQPSK) and recover of the Carrier Frequency f2 126, where second order PLL is also used. On the output of the Pseudo-Noise Demodulator 125 will be formed the signals, entering into the receiver from the different directions (see Fig. 4).

The first reply through the Block of Control and Processing 116 permits working of the Generator of Pseudo-Noise signals 117, that sends to the channel the same Pseudo-Noise signal again (Fig. 4).

Transducer 2, in accord with the described way, can register the replays from the multi- path signals (Fig. 4). Such procedure can be repeated some times for reliable compensation of the multi-path Phenomenon.

Time Dispersion Calculator 227 estimates the times tl/tn of the signal spreading along different paths between the transceivers 1,2 and calculates the time of signal spreading Ts=Tp+T4 from the Transceiverl to the Transceiver2, and the times of signal dispersion t2, t3, t8, t9.

After estimation of an average time dispersion Tm Tm= (SUMti)/n, i=2,3, 8,9 the Time Dispersion Calculator of the Transceiver 2 sends this value to the Block of Control 228, that in its turn forms the command to the PSK Modulator 230 to change the carrier frequency in the Synthesizer 118 of the Transceiver 1 on the value A fc= 1/Tm, that is the bandwidth of coherency of the acoustical channel.

Such procedure realizes receiving of the signals with frequency diversity, that permits to remove the interference inside the acoustical channel. The command to change the carrier frequency is also formed by the coded Pseudo-Noise signals.

The described method of measuring the time Tm is based on the assumption, that the time variations of the channel are much slower than the time of information replays between the transceivers.

Equalizer 225 that should process the carrier frequency fl could be of the Decision Feedback type, which helps to decrease the inter-symbol interference signals..

While measuring Tm, the output replays from the Demodulator of the Pseudo-Noise signals 226 of the Transceiver-2 sends signals to the Tact Synchronizer 240 for tuning the tact synchronization in accord with the first replay, received from the Demodulator 226.

After the time Tm is measured the data frame (see Fig. 3 and Fig. 5) from the Transceiver-1 could be sent to the Transceiver-2 (see Fig. 4) and the feedback control command frame could be sent from the Transceiver-2 to the Transceiver-1. These two data flows are demodulated in the appropriate Demodulator-234 a Transceiver2 and 125 a Transceiverl using PSK method. In the Transceiver2 the data from the Demodulator is decoded in the decoder 242 and then decompressed (by, for example, MPEG-4 for video data flow) in the Decompressor/Demultiplexer 235. After that two information flow from the Transceiver-1 (the first flow is the video information and the second flow is the information from the sensors) are divided and processed independently, as two parallel information channels.

Processing of the information from the sensors 101-110, that could be installed at the ROV, is realized as a low data rate sub-frame stream inside the main frame (block 238). It concerns, for example, such parameters of ROV's movement as depth, speed, position of the ROV or some environmental parameters-temperature, pressure or else. All such information could be represented on the operator's monitor 236 together with RTV from the underwater TV camera.

The command control could be sent from the operator's control console 237. As it was already mentioned, the Control Block 228 of the Transceiver-2 forms such commands and sends their codes to the PSK Modulator 230 for the following transmission on the carrier frequency f2 in the form of Pseudo-Noise signal sequence.

The time parameter ts, after its estimation, could be used for the measurement of the distance Ds to the ROV from the surface ship and also for the estimation of ROV relative speed regarding the ship.

By the scanning of the ships receiver antenna it could be defined the direction to the ROV ; that, together with information about its depth and distance from the ship, permits to estimate the position of the ROV regarding said ship (block 239).

Transceiver 1 has special electronics to form signals for ROV maneuvering using thrusters, as described in followed. Such Blocks are 128 and 129, besides there are also blocks 119-120 to control antenna's axe in the needed direction.

Fig. 5 shows the structure of the data frames from thee Transceiver 2. As it was mentioned, this transceiver is used both for measuring of the time dispersions and for sending control commands to the ROV during"supervising"its work. In the same way could be controlled the work of the TV camera, for example if it is needed to switch on its lighting, to change its sensitivity or to realize some other under control regimes.

While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention as set forth in the appended claims. For example, the present invention could be used to implement a larger system of underwater receivers and repeaters (retransmission stations) thus overcoming any distance lamentation inherent in a single pair of units.