GB2457581A - An array of subsea radio modems is distributed on the seabed to provide a radio communications network - Google Patents

Abstract

An array of subsea radio modems 60-70 are deployed on the seabed throughout a shallow water area. The modems are organised through a communications protocol to communicate with each other to form a network. For example, the modems may form a mesh network. The network may form a communications link with a client communicating station such as a seabed deployed client 72, a submarine 73 or a surface vessel 74. Elements of the radio network 71 may be situated above the water to relay communications back to land.

Description

1 2457581 Shallow Water Radio Communications Network

Introduction

The present invention relates to an array of subsea radio modems distributed on the seabed throughout a shallow water area to provide a contiguous radio communications network.

Background

At present wired communications or acoustic modems are typically used for underwater communications. Shallow water areas close to the shore, particularly a harbour environment, are the most highly utilised sea areas and also represent the most challenging environments for conventional wired or acoustic subsea communications systems.

For acoustic modems, maximum range and quality of service are achieved vertically through deep water in contrast to the presently considered shallow operational environment. Acoustic modem communication systems are particularly affected by multi-path issues. Acoustic signals are reflected strongly at the water boundaries, at surface, seabed, and from stmctures and shipping. Because of their relatively low propagation speed compared to radio signals, strong reflections from short and medium range boundaries are significantly time delayed resulting in strong dispersed inter-symbol interference. Shallow water areas also experience the highest acoustic noise levels. Wave action, vessel movements and other operational activities result in broad band acoustic interference which also limits acoustic modem effective range.

Communication along the seabed is also amongst the most problematic application for acoustic modems. The vertical hydrostatic pressure gradient results in refraction of horizontal acoustic signals toward the surface. In practice, this limits horizontal range to several hundred metres. Acoustic communication requires direct line of sight between nodes and un-even seabed topology can impede communications.

Wired networks are difficult to deploy and are highly vulnerable to damage in the harbour environment. Anchors often damage submerged cables in harbour deployments and cables are especially vulnerable to damage where they emerge from the water onto land. A cabled system is inflexible in terms of access point positioning since connectors must be installed before deployment as retro-fitting at the sea bed is impractical. Wired communications networks are difficult to deploy so are only practically deployed as permanent installations.

Wired communication networks do not lend themselves to rapid deployment in response to dynamic operating conditions.

Conventional through air "terrestrial" radio communications techniques are sometimes employed by providing the communicating station with wired access to an antenna in air.

When using terrestrial radio communications, freely moving submerged vehicles need to surface to communicate and seabed deployed sensors require wired access to a moored buoy fitted with a surface antenna. Both these scenarios are undesirable since they create the risk of collision and damage with manoeuvring surface vessels.

As a result of the above considerations shallow water areas represent the most desirable application of wired and acoustic subsea communications systems but also their least effective environment. There is a need for an effective wireless subsea communications network system which can provide robust quality of service in a typical shallow water environment.

Summary of the Invention

According to one aspect of the present invention there is provided a multiplicity of subsea radio modems deployed on the seabed organised through a communications protocol to communicate with each other to form a network.

According to another aspect of the present invention there is provided a multiplicity of subsea radio modems deployed on the seabed organised through a communications protocol to communicate with each other to form a network and to form a communications link with at least one client communicating station.

According to another aspect of the present invention there is provided a system wherein the radio modems operate using a carrier frequency below 100 kHz.

According to another aspect of the present invention there is provided a system wherein the radio modem elements of the system are deployed to preferentially couple radio signal into the sea bed.

According to another aspect of the present invention there is provided a system wherein signal strength received from an identifiable network node at a client communicating station is utilised to determine the client station's position.

According to another aspect of the present invention there is provided an antenna diversity system wherein one of three mutually orthogonal antennas is selected for use as a transmitter or receiving antenna According to another aspect of the present invention there is provided an antenna diversity system wherein signals from/to three mutually orthogonal antennas are adjusted in relative phase to steer the composite maximum gain angle

Brief Description of Drawings

Various aspects of the invention will now be described by way of example only and with reference to the accompanying drawings, of which: Figure 1 shows a plan view of a harbour radio modem network; Figure 2 shows a communications transceiver suitable for use in the network shown in Figure 1; Figure 3 shows an example of a receiver for use with the transceiver of Figure 2; Figure 4 shows an example of a transmitter for use in the transceiver of Figure 2; Figure 5 illustrates alignment of a circular loop antenna; Figure 6 shows a half wave folded dipole antenna; Figure 7 shows a stacked loop antenna system; Figure 8 shows a planar arrayed antenna system; Figure 9 is a diagram of a multi-resonant antenna structure; Figure 10 shows the relative frequency responses firstly of the antenna system of Figure 9 and secondly of an isolated loop antenna system by way of comparison; Figure 11 shows a co-located transmit and receive antenna.

Detailed Description of the Drawings

Figure 1 shows a plan view for a harbour deployment of the present subsea communications network invention. Nodes 60, 61, 62, 63, 64, 65, 66, 67, 68, 69 and 70 represent seabed deployed radio modem network nodes. These nodes form a network communicating structure that also incorporates node 71 based on land. Seabed radio communications represent an effective means of linking a subsea network to conventional land based communications networks for relaying data to a command and control centre. In this example, node 71 acts as the network master unit. Node 72 represents a seabed deployed client station that is communicating over the network. Unmanned submarine 73 also communicates with the subsea network as a client as does surface vessel 74.

Figure 2 shows a communications transceiver 10 that has a transmitter 12, a receiver 14 and a processor 16 that can be connected to an analogue or digital data interface (not shown). Both the transmitter and receiver 12 and 14 respectively have a waterproof magnetic coupled antenna 18 and 20. Alternatively a single antenna can be shared between transmitter and receiver. This transceiver diagram represents further implementational details of the radio modems illustrated in network and client communicating stations illustrated in Figure 1 Figure 3 shows an example of a receiver 14 for use with the transceiver of Figure 2.

As with the transmitter, this has an electrically insulated magnetic antenna 20 adapted for underwater usage. This antenna is operable to receive magnetic field signals from the transmitter. Connected to the antenna 20 is a tuned filter 32 that is in turn connected to a receive amplifier 34. At the output of the amplifier 34 are a signal amplitude measurement module 36 that is coupled to a de-modulator 38 and a frequency synthesiser 40, which provides a local oscillator signal for down conversion of the modulated carrier. Connected to the de-modulator 38 are a processor 42 and a data interface 44, which is also connected to the processor 42. The data interface 44 is provided for transferring data from the receiver 14 to allow interface with other communicating means, for example a wired network.

Figure 4 shows an example of a transmitter 12 for use in transceiver 10 of Figure 2.

This has a data interface 22 that is connected to each of a processor 24 and a modulator 26 and serves as the interface with a secondary network where required. The modulator 26 is provided to encode data onto a carrier wave. At an output of the modulator 26 are a frequency synthesiser 28 for that provides a local oscillator signal for up-conversion of the modulated carrier and transmit amplifier 30, which is connected to the underwater, electrically insulated magnetic coupled antenna 18. In use, the transmitter processor 24 is operable to cause electromagnetic communication signals to be transmitted via the antenna at a selected carrier frequency.

Figure 5 illustrates a circular loop antenna in the x-y plane with the z-axis perpendicular to the loop plane.

The radio network described here allows rapid deployment in response to a dynamic operational environment and complete flexibility in the positioning of stations accessing the network.

Although subsea radio communications systems have several advantages over alternative systems as outlined above, the main limitation is the range which can be practically achieved by a single radio modem unit. Communications coverage can be provided over a wider area by an array of subsea radio modems distributed on the seabed throughout a region of shallow water. Each network node is able to communicate with neighbouring nodes distributed in space to provide contiguous coverage over a wider area. Once deployed, this radio modem network will provide communications capability over a volume of water for general client "communicating stations" also fitted with radio modem equipment which may be mobile or stationary deployed nodes.

A subsea radio network provides a means of communication to a central location, link to other communications networks or communications between client stations. One node in the network can be interfaced with an external communications network to act as a gateway between the two network protocols.

In this submission, a shallow water environment will be defined as one where depth does not exceed 100 m. Many harbour installations will be considerably shallower than this definition and in these cases the benefits of radio communications over acoustic methods will be even more pronounced.

Radio modems and client integrated radio modems typically may be powered from an integrated battery power supply.

Conventionally, electromagnetic transmission has not been considered an effective method when communication is partially or wholly underwater. Our pending patent application "Underwater Communications System" PCT/GB2006/002 123, the contents of which are incorporated herein by reference, describes how this may be accomplished over useful distances. One potential difficulty to be considered in communicating data underwater is the higher attenuation encountered by an electromagnetic signal when transmitted through this partially conductive medium compared to air.

Seawater is partially conductive and in this medium, radio signal attenuation increases rapidly with frequency. This has driven sub-sea radio communications systems toward operation at very low frequencies to maximize operational range. Long range sub-sea radio communications systems typically operate below 100 kHz and in some cases the operating frequency can beneficially be lowered down to 1 Hz. The subsea radio modem array described here will operate at a centre frequency below 100 kHz. This frequency range strikes a balance between useful data transfer rates and desirable operational range between relay nodes.

A digital modulation scheme will be employed to carry communications data between the radio modem nodes and to communicating stations. Means may be provided for compressing the data that has to be transmitted. Through water electromagnetic attenuation increases rapidly with frequency. Compressing the data prior to transmission causes the occupied transmission bandwidth to be reduced. This allows use of a lower carrier frequency, which leads to lower attenuation and in turn allows communication over greater transmission distances. This significantly alleviates the difficulty of communication through water.

The functionality described for a multi-element network system could be achieved through many alternative protocol implementations. By way of illustration, one method of operation is outlined as follows. Network radio modem elements can be flexibly deployed within an operational volume of water and must organise to form a mesh network. Each network node has a unique identifying address. Network nodes must periodically exchange control and configuration information and must be aware of the overall network topology particularly neighbouring nodes within direct communicating range. A time domain multiplexing scheme could be envisaged for network configuration and maintenance. A network node designated as master initiates mesh network formation by transmitting an initiating signal. Any slave nodes receiving this signal respond after a unique time delay, defined by their node address, engineered to avoid signal collisions. The master registers the responding slave's presence within communicating range and adds this to the network map shared by all nodes that are currently part of the network. The master can then request that each discovered node broadcasts an initiating signal in turn to further propagate network discovery and formation to nodes adjacent to networked slaves. In this way a mesh network can be formed.

A client communicating station initiates contact with the deployed network by transmitting a signal. All network receivers are active and received signal strength is measured for each.

Active communications is achieved through the network unit with the largest received signal and only this unit responds with a transmit signal. All receivers continue to operate and, if the client station moves within the network volume, the active client to network communications link can hand over to the strongest available link for each communications packet.

Client to client communications can be achieved over the network by routing the communications data according to a network configuration map known by each network node which includes the current network location of each client station.

The deployed radio modem network can provide communications with client stations for a wide variety of purposes. Client stations can be interfaced to a range of equipment to provide beneficial functionality. By way of illustration and not for the purposes of limitation we list here some of the systems the present underwater radio network could support:- * Unmanned vehicles Remotely Operated via the radio network * Unmanned submerged vehicle relay of measured data or images * Diver communications -speech or text * Diver telemetry * Seabed condition monitoring telemetry * Dredging monitors * Turbidity sensors * Salinity sensors * Oxygen sensors * Depth sensors * Intrusion sensor systems as described in detail in our co-pending application "A System for Detection of Underwater Objects" GB2007000 1743. The seabed network can provide a means of communicating alarm status and target characteristics.

Each of these systems will be integrated with a radio modem and antenna to provision radio communications as a client to the radio network.

In some network systems the radio modems may be integrated with data generating and/or utilising systems to form both network provisioning nodes and network clients. For example a radio modem may be directly integrated with a pressure sensor for deployment on the seabed to monitor wave action. In this configuration the radio modem will act to convey data traffic from other nodes through the network and also to communicate the data generated from its own integrated sensors. Similarly control information may be communicated to the sensors to adjust their operating parameters.

A magnetic loop carrying an alternating current produces three distinct field components. In addition to conductive attenuation, each term has a different geometric loss as we move distance r from the launching loop. An inductive term varies with a coefficient which 3. . includes a hr term, a quasi-static term by hr and a propagating wave by hr. All these terms can be employed in a radio communications link and it is the object of this invention to utilise all three elements of the electromagnetic field described above to implement a communications link.

Loop antennas, whose advantages are disclosed in patent application PCT/GB2006/002 123, may be adopted in the underwater applications envisioned.

Radio modem antennas in this system make use of the seabed as a radio signal path between nodes. A horizontal loop can be defined as one where plane x-y in Figure 5 is oriented parallel to the seabed and this orientation can be described as a vertical magnetic dipole (VMD). An alternative vertical loop has the z-axis parallel to the ground and this orientation can be described as a horizontal magnetic dipole (HMD). While a HMD loop deployment at transmit and receive can offer the most effective signal coupling between two radio modems at the seabed it has a directional field property which requires co-planar alignment of the two antennas for optimal performance. In a HMD loop deployment, the position of neighbouring radio modems may result in loops which are aligned with perpendicular major axes. This alignment represents a null in the coupled energy transferred between loops and is highly undesirable. The most efficient coupling is achieved by aligning loop or solenoid antennas so their axis is parallel to magnetic field lines. To achieve this in a two dimensional seabed network deployment the system may be implemented with multiple antennas arranged with varying alignment to allow selection of the most appropriate antenna orientation for the incident magnetic field. In one example implementation a loop antenna forms a VMD as shown in figure 5 while solenoid antennas may be oriented on the X and Y axes. This construction forms a three antenna system with mutually perpendicular axes. The radio modem may select the antenna which receives the largest signal for the prevailing incident magnetic field or the signals from all three antennas may be combined to form a composite antenna response that is optimally aligned with the incident magnetic field. A transmit antenna system may be arranged in a similar way. In this case the antenna system will be utilised to launch a magnetic field that is parallel to the seabed in the direction of the intended receiver.

Electrical conductivity is the main mechanism for attenuation of electromagnetic signals in water. While sea water has a typical conductivity of 4 S/rn, conductivity falls away rapidly with depth below the sea bed. Loops deployed horizontally on the sea bed lie at the interface between conductive sea water and the material of the sea bed which always offers a lower conductivity path for electromagnetic signalling. Half of the field generated by a horizontal loop will penetrate into the seabed. Communication between another network node or client communicating station also positioned on the seabed will benefit from extended range compared to purely through water communications.

While access to terrestrial radio networks requires deployment of equipment at the surface as described above, the subject of this invention provides a radio network based on the seabed.

Sensors or submerged vehicles can communicate while deployed close to or at the seabed safely below the draft of ship's hulls and this represents a further desirable feature of the present invention.

Some systems of antennas and associated transceivers used for the purpose of underwater communication via a seabed path are discussed in our co-pending patent application, Transmission of underwater electromagnetic radiation through the seabed" GB 0810980.3, the contents of which are incorporated herein by reference.

Magnetic loops generate an alternating magnetic field whose strength is commonly defined by the well understood term magnetic moment. For signal detection at greatest distance, the largest achievable magnetic moment is desirable. The magnetic moment is directly proportional to each of the three parameters: ioop area, loop current, and number of loop turns. Equivalently, it may stated that the magnetic moment is proportional to both the ampere-turn product of the loop and to the area of the loop.

Beneficial antenna implementations are discussed in our co-pending patent applications which are listed below and their contents incorporated here by reference.

"Antenna formed of multiple loops", GB 0817176.1, the contents of which are hereby incorporated by reference, describes a method of antenna construction formed of multiple separate conducting loops so that larger magnetic moments may be achieved without requiring greater drive voltage. A multi-turn loop is desirable to achieve a large magnetic moment but presents the difficulty of driving a large current through a high inductance. In this implementation a multi-turn loop is split into several loops of equal diameter, in the same plane and arranged around a common central axis. All sub-loops share the flux generated by the others but the total inductance is divided among the sub-loops. Each sub-loop has a separate drive amplifier that only has to develop a driving voltage required to produce the desired current through a fraction of the total inductance. This type of antenna system will be referred to as "stacked" multiple loops.

Figure 7 shows an example of a "stacked" composite antenna loop comprised of several sub-loops. In this example, there are ten sub-loops, of which only five sub-loops 711, 712, 713... 719, 720 are shown for simplicity. Although shown spatially separated somewhat for clarity, it is advantageous if the ten sub-loops 711 to 720 are situated in close proximity and with similar axes. In a loop antenna increased magnetic moment produces increase in range.

Each sub-loop has its own corresponding driver, of which only five drivers 721, 722, 723 729, 730 are shown for simplicity. Each sub-loop has one tenth the impedance of an equivalent single loop formed by connecting all ten loops in series. The current driven in each sub-loop will be ten times greater than that required from a single driver connected across a series combined loop. The ten drivers 721 to 730 must be designed with ability to generate (source) this higher current. For optimum performance the ten drivers 721 to 730 should provide signal currents in their corresponding sub-loops that are substantially in phase with each other. This is easily achieved if the drivers are nominally identical and all supplied from the same common signal source 731.

An alternative method of antenna construction formed of multiple separate conducting loops so that larger magnetic moments may be achieved without requiring greater drive voltage, is described in "Antenna formed of multiple planar arrayed loops", GB0823218.3, the contents of which are hereby incorporated by reference. In this arrangement the area available for antenna deployment is occupied by a number of smaller loops deployed side by side in a common plane. The magnetic moment of these sub-loops has a combined effect that is equivalent to a single large loop with an area equal to the combined sub-loops. Again, the drive amplifier requirement for each sub-loop is more manageable compared to a single amplifier designed to drive a larger single loop. This type of antenna system will be referred to as "planar" arrayed loops.

Figure 8 illustrates a composite loop, divided into 9 smaller loops deployed in a single plane.

The arrows illustrate the flow of current at any instant of time. Let us consider, for sake of simplicity, each sub-loop driven by a constant current source. Loop E illustrates an embedded sub-loop with no component at the periphery. The arrows indicate instantaneous flow of equal currents and it can be seen that each element of loop E has a neighbouring current element which is equal in amplitude but of opposite direction. In this arrangement, each element of loop E generates electromagnetic fields that are exactly cancelled by those from adjacent current elements. The remaining S sub-loops all have partial field cancellation in a similar manner. For example, loop F has cancelling currents along 3 of its 4 sides. It can readily be seen that the combined effect of the 9 sub-loops is exactly equivalent to a single loop, of the same dimensions as the array periphery, driven with the same current. The main practical advantage of the array arrangement is in the reduced voltage required to drive the required current though each of the sub-loops compared to a single large ioop of area equal to the total combine loop area.

"Antenna formed of multiple resonant loops", GB0823203.5, the Contents of which are hereby incorporated by reference, describes electromagnetic and/or magneto-inductive antennas formed of multiple separate conducting loops which are resonantly tuned and loosely coupled together for increased antenna bandwidth. This type of antenna system will be referred to as "multiple resonant loops".

As depicted in Figure 9, each of two receive loops 921, 922 which have partial mutual coupling by virtue of their physical spacing 923 may be brought to resonance by connecting across them respective parallel capacitors 925, 927. To control the Q value of each, respective parallel resistors 924, 926 may be included, where lower values of each resistor will decrease Q due to its parallel connection. Thus, two partially coupled parallel tuned circuits are created, and the voltage across each represents a contribution to the combined signal received by the antenna. The voltages are fed to the input of a summing device, which may be a summing amplifier 928. After summation, the aggregate signal can be further conveyed to whatever receive signal processing device 929 may be arranged to handle the signal.

A typical signal response and bandwidth of this arrangement is depicted in one of the graphs of Figure 10. The shape of the alternating current response 1031 is plotted on the graph with respect to frequency. It can be seen that the bandwidth likely to be useable about the centre frequency is limited to a relatively narrow range 1033. By changing the Q value it is possible to change the bandwidth somewhat. However, while a decreased Q will provide a wider bandwidth, this effect is at the expense of lesser signal gain. This trade-off between bandwidth and gain is undesirable, and it is one objective of this invention to provide an improved compromise.

A co-located antenna system that is simultaneously optimised for transmit and receive performance is described in "Co-located Transmit-Receive antenna system" GB08232 14.2, the contents of which are hereby incorporated by reference. A large open cored loop is used for transmit with a high permeability, low conductivity cored solenoid used for receive. The solenoid is at least three times longer than its diameter and is arranged along the diameter of the large transmit loop. This type of antenna system will be referred to as "co-located transmit-receive antenna".

Figure 11 shows a block diagram representation of a three antenna diversity scheme.

Antennas 50, 54 and 57 are arranged with their radial gain maximums in mutually orthogonal axes. Switches 51, 55 and 58 may be used to isolate any of the three antennas. Phase shifters 52, 56 and 59 allow variable adjustment of the relative phase of the three antenna signals before they are summed in transceiver 53. In transmit mode a similar description applies. The transceiver acts as a common signal source and phase shifters 52, 56 and 59 adjust the relative phases of the transmit signals applied to the three antennas. This system allows control of antenna gain direction in a simple fashion through selection of the antenna that is best aligned with the incident signal or a more complex scheme wherein the relative phase of multiple antennas is adjusted to steer the combined antenna gain or a combination of both techniques.

Another beneficial antenna may be based on a half wave folded dipole ioop. Figure 6 shows the basic construction of this class of antenna. Insulated wire ioop 1200 is supplied with a balanced ac voltage across terminals 1201 and 1202. In situations where the operational wavelength results in practical A/2 dimensions this type of antenna may be beneficial. This situation will occur for higher frequency operation for high bandwidth systems where wavelength is shorter or for deployments on large submerged or airborne structures. This type of antenna has a higher radiation resistance than an electrically small ioop.

The magnitude of the signal exchanged between a magnetic coupled loop antenna mounted on a mobile client and an array of stationary magnetic coupled loop antennas is used as a means of determining the position of the client. All the stationary network node antennas may be constructed to an identical design and comparison of received signal strength provides positional information for the mobile client. Each node in the network and each communicating station must be associated with a unique address to identify the origin of the signal. To operate this navigation function, the position of each node must be known and this can be recorded during deployment of the network.

Further implementation details of an underwater navigation system based on electromagnetic signal magnitude are disclosed in our co-pending application "Underwater Navigation System" PCT/GB2006/002 111, and the details of this are hereby incorporated by reference.

Those familiar with communications and sensing techniques will understand that the foregoing is but one possible example of the principle according to this invention. In particular, to achieve some or most of the advantages of this invention, practical implementations may not necessarily be exactly as exemplified and can include variations within the scope of the invention. For example, a similar system description could apply to client stations integrated with equipment other than that specified in the foregoing examples.

Also, whilst the systems and methods described are generally applicable to seawater, fresh water and any brackish composition in between, because relatively pure fresh water environments exhibit different electromagnetic propagation properties from saline, seawater, different operating conditions may be needed in different environments. Any optimisation required for specific saline constitutions will be obvious to any practitioner skilled in this area. Accordingly the above description of the specific embodiment is made by way of example only and not for the purposes of limitation. It will be clear to the skilled person that minor modifications may be made without significant changes to the operation described.

Claims (20)

1. Claims 1. A submerged communications system comprising a multiplicity of subsea radio modems deployed on the seabed organised through a communications protocol to communicate with each other to form a network.
2. 2. A system according to claim I adapted to form a communications link with at least one client communicating station.
3. 3. A system according to claim 1 wherein the subsea radio modems provision the radio network and act as client nodes
4. 4. A submerged client communicating station provisioned with a radio modem which implements a communications link with the deployed radio network of claim 1.
5. 5. A system according to any of the preceding claims wherein the radio modems operate using loop antennas; stacked ioop antennas; arrayed loop antennas; multiple resonant loop antennas or co-located transmit-receive antennas.
6. 6. A system according to any of the preceding claims wherein the radio modems are integrated with data generating andlor utilising systems to form both network provisioning nodes and network clients.
7. 7. A system according to any of the preceding claims wherein the radio modems operate using a carrier frequency below 100 kHz
8. 8. A system according to any of the preceding claims wherein the radio modem elements of the system are deployed to preferentially couple radio signal into the sea bed
9. 9. A system according to any of the preceding claims wherein some nodes of the radio modern network are situated on land
10. 10. A system according to any of the preceding claims wherein some nodes of the radio modem network are situated above the surface of the water
11. II. A system according to any of the preceding claims wherein signal strength received from an identifiable network node at a client communicating station is utilised to determine the client station's position.
12. 12. A system according to any of the preceding claims wherein data from a client system is compressed prior to through water radio transmission.
13. 13. An antenna diversity system adapted for use in a system according to any of the preceding claims.
14. 14. An antenna diversity system according to claim 12 wherein one of three mutually orthogonal antennas is selected for use as a transmitter or receiving antenna
15. 15. An antenna diversity system according to claim 12 wherein signals fromlto three mutually orthogonal antennas are adjusted in relative phase to steer the composite maximum gain angle
16. 16. A communications protocol adapted for forming an underwater radio mesh network.
17. 17. A communications protocol adapted for provisioning a service for a mobile client node in through an underwater radio network
18. 18. A communications protocol adapted for provisioning a service for mobile client to mobile client communications through an underwater radio network
19. 19. A client system according to claim 2 that is integrated with a diver's communications equipment to provision relay of speech or text
20. 20. A client system according to claim 2 that is integrated with a turbidity sensor; salinity sensor; unmanned submarine vehicle; diver telemetiy system or seabed condition monitoring sensor