Underwater / surface communication system

Abstract

The invention relates to a communication system (20) comprising a plurality of surface communication partners (22, 24, 26, 28, 30), an underwater / surface communication partner (34) and a converter (32). The surface communication partners of the plurality of surface communication partners (22, 24, 26, 28, 30), the converter (32) and the underwater / surface communication partner (34) in the surface state are designed to each set up radio data connections (38) to one another. The converter (32) is designed to set up an underwater data connection (40') to the underwater / surface communication partner (34) and to transmit a data packet (40) arriving by means of the radio data connection (38) to the underwater communication partner (34) by means of the underwater data connection (40'). Furthermore, the converter (32) is designed to transmit the arriving surface data packet (40) to the underwater / surface communication partner (34) only if the converter (32) receives corresponding converter information.

Description

[0001] UNDERWATER-SURFACE COMMUNICATION SYSTEM

[0002] Description

[0003] The invention relates to a communication system, in particular an ad-hoc communication system, that can transmit data from the above-water area to the underwater area.

[0004] Establishing robust communication networks is of paramount importance for comprehensive maritime domain awareness (MDA) in remote marine areas, particularly in regions lacking conventional infrastructure. Disruption of these networks can have significant repercussions for social and economic stability. The emergence of mobile ad-hoc networks (MANETS) utilizing radio waves and the nascent underwater Internet of Things (UW-IoT), which uses acoustic signals, represent a significant advancement in underwater technology. These adaptive and scalable networks expand the capabilities of the Internet of Things (IoT) underwater, enabling enhanced data collection and real-time monitoring. The combination of these adaptive and scalable networks can also function in locations where traditional infrastructure has failed.

[0005] The growing reliance on maritime infrastructure for trade, energy, and environmental monitoring underscores the need for sophisticated communication solutions. Key technological developments include the deployment of mobile ad-hoc networks (MANETs) for terrestrial applications and the implementation of underwater MANETs for use in subaquatic environments. The integration of unmanned (underwater and surface) vehicles (USVs, UUVs, UAVs) and, optionally, communication buoys is of paramount importance, as these must be capable of seamlessly connecting terrestrial and underwater communication domains. The need for further innovation arises from the necessity of interconnecting these systems and developing new technologies to meet the challenges of technological advancement.

[0006] According to the European Commission, critical infrastructure is of paramount importance for maintaining societal functions and well-being. This includes ports, shipping lanes, submarine cables, and offshore platforms, all of which are exposed to a range of threats, including natural disasters and piracy. The development of robust communication networks is essential for real-time monitoring and rapid response to disruptions, ensuring the functionality and security of this infrastructure. Current protection strategies utilize technologies such as automatic identification systems (AIS) and satellite communications, which, while indispensable, have limitations such as range and high costs. Further development of communication technologies is necessary to enhance the robustness of maritime infrastructure protection.

[0007] The object of the present invention is therefore to create an improved concept for communication systems.

[0008] The problem is solved by the subject matter of the independent patent claims. Further advantageous embodiments are the subject matter of the dependent patent claims.

[0009] Exemplary embodiments show a communication system with multiple surface communication partners, an underwater-to-surface communication partner, and a repeater. The surface communication partners can be manned or unmanned aircraft (UAVs) or manned or unmanned surface vessels (USVs), unless they are equipped with a submersible transducer for underwater communication and a protocol converter (gateway) for converting radio communication to underwater communication (and optionally from underwater communication to radio communication). Alternatively, they can be an offshore platform or a land station located, for example, near the coast, or capable of establishing a radio link to a surface vessel or the repeater via an aircraft. Radio communication and underwater communication can be carried out using different modems in the repeater.

[0010] Underwater-surface communication partners can be manned or unmanned underwater vehicles (AUVs). These can communicate via radio using an antenna that penetrates the water's surface, for example, while traveling at periscope depth. Furthermore, underwater-surface communication partners can communicate both at the surface and while fully submerged, i.e., exchange data.

[0011] The transmitter is, for example, a sonar buoy or a manned or unmanned surface vessel. The transmitter preferably includes an antenna for radio communication and a transducer for underwater communication. Furthermore, the transmitter preferably includes a protocol converter that translates between radio and underwater communication. This means that the transmitter can send a data packet received via the radio data link to the underwater communication partner via the underwater data link. When a data packet is referenced, it can also be part of a data stream comprising a multitude of data packets, with the data packets within the multitude being processed in the same way as the individual data packets.

[0012] For example, the data packet is transmitted exclusively via the majority of surface communication partners, the underwater-to-surface communication partner, and the converter, with the majority of surface communication partners operating without a satellite. This means that a network is established without existing infrastructure, using only self-provided components.

[0013] The surface communication partners of the majority of surface communication partners, the repeater, and the underwater-to-surface communication partners in the surface state are each equipped to establish radio data links with each other. Data can be exchanged via broadcast, multicast, or unicast over the radio data link. The broadcast radio data link is suitable for establishing a routing table, while a multicast or unicast radio data link, using a routing table, can transmit the (payload) data. The entirety of the radio data links can also be referred to as a network. A network that is only established when data is to be sent, for example, because the network nodes are moving and not fixed in place, is called a reactive ad-hoc network. This means that the route for the data packet is only determined when the data packet is to be sent.In particular, the route is determined decentrally at each node. Reactive ad-hoc networks have the advantage over proactive ad-hoc networks of generating less data traffic. This is especially useful in the military sector.

[0014] The converter is configured to establish an underwater data link with the underwater-to-surface communication partner. However, the underwater data link is only established, or at least only used, if the converter receives the corresponding information to utilize underwater communication. In the absence of this information, the incoming surface data packet is sent to the underwater-to-surface communication partner via radio data link. This means the converter only sends the incoming surface data packet to the underwater-to-surface communication partner via the underwater data link if it receives the corresponding information (i.e., the presence of the information). This information could, for example, be a data bit contained in the message accompanying the data packet.One state of the data bit indicates the absence of the converter information, the other state the presence of the converter information. That is, the absence of the converter information indicates that the underwater-above-water communication partner is in the above-water state. The presence of the converter information indicates that the underwater-above-water communication partner is underwater or that the radio data link between the converter and the underwater-above-water communication partner cannot or should not be used for other reasons.

[0015] Using the converter information is advantageous because the converter typically does not know whether the underwater-surface communication partner is currently in its underwater or surface state. However, the sender does have this information. For example, the sender can obtain this information by constructing its routing table before sending the data packet. The routing table is constructed, for example, using route queries as described below.

[0016] The message may also include an access request. Based on the access request, the converter can initialize an underwater route to the receiver. Ideally, the converter can reach the receiver directly. Otherwise, underwater nodes establish a route to the receiver. Once the route is initialized—for example, once the underwater nodes have established their route table—the converter can send the cached data packet to the receiver. Specifically, the converter receives the data packet via a radio data protocol and translates it into an underwater communication protocol when it receives the appropriate conversion information.

[0017] Alternatively, the sending surface communication partner is configured to send an access request to the converter upon receiving the converter's response. This access request can include information indicating that the underwater-to-surface communication partner is underwater, allowing the converter to determine an underwater route to that partner. Knowing that the underwater route is initialized, the converter sends a route response back to the sending surface communication partner. Upon receiving the route response, the sending surface communication partner transmits the data packet to the receiver. This is advantageous because, in the event that the receiver cannot be reached by the converter, no unnecessary data traffic is generated.

[0018] The transmission of acoustic signals in underwater environments presents a number of significant technical challenges. Signals propagate at considerably lower speeds in aqueous media, resulting in substantial latency. Furthermore, attenuation is a critical factor in underwater communication, with signals weakening over distance due to absorption and scattering. Multipath propagation leads to signal distortion and data errors, as signals are reflected from the seabed and the water surface. Additionally, environmental factors such as variations in depth, temperature, and salinity negatively impact signal quality and speed. Therefore, the data packet is preferably sent directly from the transmitter to the receiver, i.e., the target underwater-to-surface communication partner.

[0019] It has now been shown that the simultaneous transmission of data underwater by multiple transducers leads to interference of the underwater sound signals. Due to this interference, the data encoded in underwater sound signals cannot be received at the underwater receivers, or only with a very long delay. The very narrow channel bandwidth underwater must be taken into account when considering this delay, as it already results in a significantly longer data transmission time underwater compared to radio communication.

[0020] If the recipient cannot be reached directly, an underwater communication network can be established. Ad-hoc underwater networks are increasingly used where conventional communication methods are ineffective. These networks utilize acoustic signals to overcome problems such as high latency and limited signal propagation. Innovations like Gossiping in Underwater Mobile Ad-Hoc Networks (GUWMANET) employ gossip-based algorithms to improve data propagation between underwater mobile nodes, thereby increasing the reliability and efficiency of the network. This approach provides a robust and flexible framework for network solutions for underwater activities, including scientific research and strategic monitoring. In this respect, underwater communication can also be established between multiple underwater-surface communication partners, for example, using the GUWMANET protocol.The converter can therefore be configured to send the data packet via the underwater data link using the GUWMANET (Gossiping in Underwater Mobile Ad-Hoc Networks) protocol.

[0021] The use of unmanned vehicles, including unmanned surface vehicles (USVs), unmanned underwater vehicles (UUVs), and unmanned aerial vehicles (UAVs), has the potential to significantly improve mobile ad-hoc networks (MANETs) in various operational areas. In maritime environments, unmanned surface and underwater vehicles (USVs and UUVs) enable robust communication via surface and underwater communication, respectively.

[0022] Underwater nodes, preferably utilizing technologies optimized for the respective medium, are being developed. Unmanned aerial vehicles (UAVs) in flying ad-hoc networks (FANETs) provide vital aerial connectivity in areas inaccessible to conventional networks. These technologies illustrate the potential of dynamic ad-hoc communication in vehicle-based (VANETs) and sensor-actuator networks (SANETs). These networks are crucial for real-time data exchange and operational efficiency in autonomous navigation and environmental monitoring.

[0023] Optimizing routing in multi-domain ad-hoc networks with wireless access networks requires an understanding of the associated technical challenges. The interaction of air and water in maritime environments creates obstacles that affect network stability and reliability. Integrating radio and acoustic communications presents a number of challenges, including latency, data volume management, and signal degradation. The dynamic behavior of nodes, particularly unmanned surface vessels (USVs), unmanned underwater vehicles (UUVs), and unmanned aerial vehicles (UAVs), adds further complexity. The dynamic maritime environment poses significant technical challenges to communication networks. Variable sea state, wave action, and weather conditions such as rain, fog, and wind can disrupt communication links and degrade signal quality.The movement of UPSs, UUVs, and UAVs leads to frequent topological changes, making the use of adaptive routing protocols such as AODV advantageous for ensuring stability. Physical obstacles, such as ships and offshore structures, can cause signal blockages and reflections. Furthermore, maintaining low latency and synchronization between dynamic nodes is a significant challenge.

[0024] For the integration of gateway nodes (converters) into ad-hoc networks with multiple domains, robust synchronization and efficient data routing between these media are advantageous. This is particularly beneficial given the mobility of UPS systems and the varying environmental conditions that can complicate the maintenance of stable connections. Suitable protocols such as GUWMANET (underwater) and AODV (abovewater) provide a solution to ensure stable data transmission.

[0025] The idea is now to utilize the significantly greater bandwidth of the radio data connection by transmitting data wirelessly as much as possible. The repeater only sends data via underwater communication when explicitly instructed to do so (i.e., when it receives the corresponding repeater information). This typically only occurs when it is known that the data destination is underwater.

[0026] In exemplary embodiments, a sending surface communication partner is configured to send a route request via radio before transmitting a data packet to a receiver if the route to the receiver is unknown. Using the AODV protocol, this can be the Route Request (RREQ). The remaining surface communication partners, the repeater, and the underwater-to-surface communication partner in the surface state are each configured to receive the route request and retransmit it with modified route information. The modification can consist of adding a corresponding entry to a cumulative list in the data packet, for example, one that is augmented with each node including the current node.Using the AODV protocol, the current node will store information from the route request indicating which node it received the request from and replace the stored node with the current node's name so that the subsequent node can also store the information about the originating node. In this way, each node builds its own routing table (RTABLE). The route request can be broadcast.

[0027] The receiver is configured, as soon as the route request is received, to send the route response (RREP) back to the sending surface communication partner, specifically via unicast, along the same route in the opposite direction, knowing the route information. This means that either the (fastest) route is included in the route request, so the route response already contains the entire route, or, for example, using the AODV protocol, the route response only contains the penultimate node, which, however, has stored where it received the route request from and sends the route response back to that node. Once the sending surface communication partner receives the route information, the route (from sender to receiver) is initialized.

[0028] The sending above-water communication partner can now send the data packet, in particular a data stream, to the receiver via the known route.

[0029] Whether the underwater-above-water communication partner is currently above or below water is usually unknown. Therefore, it's possible that the route response to the route request will remain unanswered. If the route response to the route request is not received within a specified time period and the route to the repeater is unknown, the sender can transmit a relay request. The route to the repeater can also be unknown if a known route has become invalid, for example, after a specified time period. The relay request can be an extension of the AODV protocol, implemented analogously to the route request. However, instead of the receiver, as with the route request, the relay request determines the route to the repeater.The remaining surface communication partners of the majority of surface communication partners can receive the converter request and resend it with modified route information.

[0030] Once the relay request is received, the relay can send a relay reply, containing the route information, back to the sending surface communication partner along the same route in the opposite direction. The explanations regarding route requests apply accordingly to relay requests.

[0031] The sending surface communication partner can now send an access request to the repeater. Besides the desired receiver, the access request contains repeater information, such as a flag indicating that the repeater should switch to underwater communication. On the surface, i.e., from the sender to the repeater, the access request is equivalent to a direct connection from the receiver to the repeater. That is, the access request is sent to the repeater via unicast. When the access request reaches the repeater, the repeater uses the included information indicating that it should switch to underwater communication to determine the route to the receiver underwater.

[0032] Determining the underwater route to the receiver can be done analogously to determining the route to the receiver above water. This means a broadcast message, for example, an underwater route request, can be sent. When the broadcast message reaches the underwater receiver, it sends an underwater route response to the repeater. The repeater then forwards the route response to the sender. The sender can now send the data to be transmitted, particularly based on the respective decentralized routing tables, to the underwater receiver. Alternatively, the data can be sent directly to the repeater along with the access request. The repeater can temporarily store the data until the underwater route response arrives. However, this carries the risk of unnecessary data transfer (traffic) if the underwater receiver is unreachable.Unnecessary data transfer is particularly undesirable in the military sector.

[0033] Regarding the protocol used, for example, the GUWMANET protocol, optimized for underwater communication, can be used instead of the AODV protocol, which is optimized for surface communication. Other suitable protocols can also be used.

[0034] Examples show that the majority of surface communication partners, the underwater-to-surface communication partner, and the repeater for exchanging data packets via the radio data link use the AODV (advanced ad hoc on-demand distance vector) protocol with additional network message types to establish underwater communication. Using a modified AODV protocol is advantageous because no generally accepted protocol for integrating gateway nodes into ad-hoc networks is currently known. The additional network message types can include the repeater request and the repeater response. Furthermore, the additional network message types can include an access request.

[0035] The Ad-hoc On-Demand Distance Vector (AODV) protocol is a decentralized routing protocol for communication systems, particularly within mobile ad-hoc networks (MANETs). It is designed to establish routes between nodes only when needed, thereby reducing overall network overhead and latency. This makes it a suitable choice for use in dynamic environments, such as those found in mobile or remote operations with frequent topology changes.

[0036] AODV is capable of rapidly adapting to changes in network topology, thereby ensuring reliable communication between mobile nodes. The protocol uses route request (RREQ) and route response (RREP) messages, along with a routing table (RTABLE) and a message cache, to effectively manage routes. An adaptation called A-AODV, which incorporates the Automatic Identification System (AIS), was developed for maritime environments to improve communication across water.

[0037] The Ad-hoc On-Demand Distance Vector (AODV) protocol plays a central role in managing data packets and determining their routes. When a node needs to find a route to a destination, it sends a Route Request (RREQ) message. Incoming messages first undergo a verification process where their content is compared to the contents of the message cache. This ensures that the messages are not duplicates. If the message is new and has been added to the cache, it is checked whether the current node is the intended destination. If the node is the destination, the message has been successfully delivered, a Route Reply (RREP) is sent back to the source, and the message is processed. If the node is not the intended destination, the node forwards the message to the next hop, as specified in the routing table entries.This method ensures the efficient and reliable delivery of messages within the network. The AODV protocol operates at the network layer of the ISO-OSI model.

[0038] Mobile ad-hoc networks (MANETs) are self-configuring networks consisting of wirelessly connected mobile devices that form the communication system. Each node (surface communication partner, underwater-to-surface communication partner, repeater) in a MANET is capable of acting as a router, thereby facilitating the forwarding of data to other nodes that are not within direct transmission range.

[0039] In a preferred embodiment, an improved ad-hoc on-demand distance vector (AODV) protocol for multi-domain ad-hoc networks is disclosed, integrating communication domains above and below water. This integration utilizes unmanned surface vessels (USVs) or sonar buoys as gateways between surface and underwater communication in conjunction with unmanned underwater vehicles (UUVs) (surface-underwater communication partners) and unmanned aerial vehicles (UAVs), thus ensuring robust communication in challenging maritime environments.

[0040] Similarly, a method for communication between a plurality of above-water communication partners, an underwater-to-above-water communication partner, and a converter is disclosed, comprising the following steps: a) transmitting a data packet by radio from an above-water communication partner; b) receiving the data packet by the converter; c) checking whether the received data packet should be transmitted by underwater communication or by radio if the converter is not the destination of the data packet; d) sending the received data packet by underwater communication to the underwater-to-above-water communication partner if the check shows that the data packet should be sent by underwater communication. The check in step c) is performed, for example, using the converter information.

[0041] Preferred embodiments of the present invention are explained below with reference to the accompanying drawings. These show:

[0042] Fig. 1: a schematic representation of a communication system for communicating with an underwater-above-water communication partner located above water; and

[0043] Fig. 2: a schematic representation of the communication system from Fig. 1 for communication with the underwater-above-water communication partner who is located underwater, where Fig. 2a, Fig. 2b and Fig. 2c show chronologically different times of the route setup.

[0044] Before exemplary embodiments of the present invention are explained in detail below with reference to the drawings, it should be noted that identical, functionally equivalent or equivalent elements, objects and / or structures in the different figures are provided with the same reference numerals, so that the description of these elements shown in different exemplary embodiments is interchangeable or can be applied to one another.

[0045] Fig. 1 shows a schematic diagram of a communication system 20. The communication system comprises a plurality of above-water communication partners 22, 24, 26, 28, 30, a converter 32, and an underwater-to-above-water communication partner 34. The aforementioned participants 22, 24, 26, 28, 30, 32, 34 of the communication system 20 can also be referred to as nodes. The underwater-to-above-water communication partner 34 can be located above water (as shown) or below water (see Fig. 2), as indicated by arrow 36. The number of nodes is purely exemplary and can be any number.

[0046] The nodes located above water can now establish radio data links 38', 38" to each other, thus forming a communication network 38. In the illustrated embodiment, a node 22, which can be, for example, an unmanned aerial vehicle (UAV), initiates a route request (RREQ) with the aim of reaching the target node 34, which is an unmanned underwater vehicle (AUV), i.e., an example of an underwater-surface communication partner. The route request can be initially broadcast by node 22 and forwarded by the nodes receiving the route request until it reaches the destination. The route request is transmitted through the network 38 according to a defined methodology, for example, specified in the AODV protocol.Route request 38' is represented by dashed arrows and, as an example, starts at node 22 and first reaches nodes 24 and 26. Node 24 then sends route request 38' again, this time reaching nodes 26 and 28. It should be noted that, for example, node 26 cannot reach node 34, perhaps due to distance or other reasons.

[0047] Transmission channel characteristics. This process repeats for each node that receives the route request. After reaching the destination node, in this case node 34 at the current position, a route response (RREP) 38 is sent back. The route response is represented by a solid line. Each node independently updates its routing table, which contains the next hop.

[0048] The source node (sender 22) then uses the optimal route determined by the route request to transmit data to node 34. This is the route with the solid lines, but in the opposite direction compared to the route response. As an example, a route was selected as the best, and in particular the fastest.

[0049] Figure 2 reveals a scenario in which node 34 is located underwater. However, the sending node 22 does not know whether receiver 34 is above or below water. Figure 2a reveals that, even in this case, the route request 38' is initially sent. However, a predetermined time interval is exceeded without a route response 38" being received by sender 22.

[0050] In this case, shown in Fig. 2b, the transmitter initiates a converter request 38'", which is structured analogously to the route request 38', but has converter 32 as its destination. Accordingly, the converter sends a converter response 38"" back to transmitter 22, analogous to the route response. The route to converter 32 is initialized by means of the converter response.

[0051] Figure 2c shows that, based on the converter response 38", the transmitter now sends an access request 38"'' to the converter 32. The access request 38"'' contains the converter information that a route to node 34 should be established underwater. The converter 32 thus initiates an underwater route request 39, specifically as a broadcast. In the simple example shown, node 34 can be reached directly by the converter, so the underwater route request 39 is already completed at the first received node. In principle, however, it is also possible, analogous to radio communication, for the route request to have to pass through several underwater nodes to reach the receiver. The receiver 34 then sends its underwater route response 39' back to the converter 32. The converter 32 then initiates the route response 38' and sends it to the transmitter 22.

[0052] The route to the underwater receiver 34 is then initialized. The transmitter 22 can send the data 40 (shown as a dashed line) to the repeater 32. The repeater 32 establishes an underwater data link 40' to the underwater-to-surface communication partner 34 and transmits the data 40 received via the radio data link to the underwater communication partner 34 using the underwater data link 40'.

[0053] The converter 32 therefore includes a radio module 42 and an underwater sound transducer 44. A data processing unit (not shown) can convert data received by radio into an (acoustic) underwater communication message, and vice versa.

[0054] The disclosed (underwater) sound transducers are designed for use underwater, particularly in the sea. The transducers can convert underwater sound into an electrical signal (e.g., voltage or current) corresponding to the sound pressure, the (received) underwater sound signal. Furthermore, it is possible for the transducers to convert an applied electrical voltage into underwater sound. The electrical voltage can follow a predefined pattern and then be referred to as the (transmitted) sonar signal, while the underwater sound resulting from the sonar signal to be transmitted is referred to as the (transmitted) sonar signal. Examples of sonar signals are a chirp (frequency-modulated signal) or, as a special case of the chirp, a sweep (linearly frequency-modulated signal). The transducers can therefore be used as underwater sound receivers and / or underwater sound transmitters.The transducers can utilize a piezoelectric material, such as a piezoceramic, as the sensor material. Multiple underwater transducers, or one or more underwater transducers combined with a signal processing unit, can be referred to as a sonar system. The transducers can be used for (active and / or passive) sonar (sound navigation and ranging, dl: sound navigation and distance determination), as well as for underwater communication. The transducers are preferably not suitable for, or are not used in, medical applications. Likewise, the transducers are preferably not used for, or are not suitable for, the ultrasonic testing of materials.

[0055] Although some aspects have been described in connection with a device, it is understood that these aspects also constitute a description of the corresponding process, so that a block or component of a device can also be understood as a corresponding process step or as a feature of a process step. Similarly, aspects described in connection with or as a process step also constitute a description of a corresponding block, detail, or feature of a corresponding device.

[0056] The embodiments described above merely illustrate the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be obvious to other people skilled in the art. Therefore, it is intended that the invention be limited only by the scope of protection set forth in the following claims and not by the specific details presented herein by way of description and explanation of the embodiments.

[0057] Reference symbol list:

[0058] 20 Communication system

[0059] 22 above-water communication partners

[0060] 24 above-water communication partners

[0061] 26 above-water communication partners

[0062] 28 above-water communication partners

[0063] 30 above-water communication partners

[0064] 32 converters

[0065] 34 underwater-above-water communication partners

[0066] 36 Arrow

[0067] 38 Communication network

[0068] 38' Route request

[0069] 38" Route response

[0070] 38'“ Converter request

[0071] 38"" Converter response

[0072] 38""' Access request

[0073] 39 Underwater route request

[0074] 39' Underwater route answer

[0075] 40 data

[0076] 40' Underwater communication

[0077] 42 radio module

[0078] 44 underwater transducers

Claims

Patent claims 1. Communication system (20) with the following features: - a majority of above-water communication partners (22, 24, 26, 28, 30), - an underwater-above-water communication partner (34), - a converter (32); - wherein the surface communication partners of the majority of surface communication partners (22, 24, 26, 28, 30), the converter (32) and the underwater surface communication partner (34) are configured in the surface state to establish radio data links (38) to each other; - wherein the converter (32) is configured to establish an underwater data link (40') to the underwater-surface communication partner (34); and - wherein the converter (32) is configured to send a data packet (40) received via the radio data link (38) to the underwater communication partner (34) via the underwater data link (40'); - wherein the converter (32) is configured to send the incoming surface data packet to the underwater-surface communication partner via radio data link in the absence of converter information and, a) to establish the underwater data link to the underwater-surface communication partner only when the converter (32) receives the corresponding converter information; or b) to send the incoming surface data packet (40) to the underwater-surface communication partner (34) via the underwater data link only when the converter (32) receives the corresponding converter information.

2. Communication system (20) according to claim 1 , - wherein a sending surface communication partner (22) is trained of the majority of surface communication partners (22, 24, 26, 28, 30) to send a route request (38') by radio before sending a data packet to a receiver (34) if the route to the receiver (34) is unknown, - wherein the remaining surface communication partners (24, 26, 28, 30) of the majority of surface communication partners (22, 24, 26, 28, 30), the converter (32) and the underwater surface communication partner (34) are each configured in the surface state to receive the route request (38') and retransmit it with modified route information; - wherein the receiver (34) is trained, as soon as the route request (38') has been received, to send a route response (38") in the reverse direction to the sending above-water communication partner (22) with knowledge of the route information about the same route (38").

3. Communication system (20) according to claim 2, wherein the sending above-water communication partner (22) is configured to send the data packet to the receiver (34) via the known route (38").

4. Communication system (20) according to one of claims 2 or 3, - wherein the transmitting above-water communication partner (22) is trained to send a repeater request by radio if the route response (38") to the route request is not received within a specified time period and the route to the repeater (32) is unknown; - wherein the remaining surface communication partners (24, 26, 28, 30) of the majority of surface communication partners (22, 24, 26, 28, 30) are trained to receive the converter request and resend it with modified route information; - wherein the converter (32) is trained, as soon as the converter request is received, to send a converter response, with knowledge of the route information, over the same route in the reverse direction to the sending overwater communication partner.

5. Communication system (20) according to claim 4, - wherein the sending surface communication partner is trained to send the surface data packet (40) and the converter information to the converter (32) in order to send the data (40) to the underwater surface communication partner (34).

6. Communication system (20) according to claim 5, - wherein the sending above-water communication partner (22) is trained to send the converter information as a flag in a message containing the data packet (40).

7. Communication system (20) according to claim 4, - wherein the sending above-water communication partner (22) is trained to send an access request to the converter, knowing the converter's response, - wherein the access request contains the converter information that the underwater-above-water communication partner is underwater, so that the converter determines an underwater route to the underwater-above-water communication partner, - wherein the converter is trained, knowing that the underwater route is initialized, to send the route response (38") back to the sending above-water communication partner (22); - wherein the sending above-water communication partner is trained to send the data packet to the receiver upon receipt of the route response (38").

8. Communication system (20) according to one of the preceding claims, wherein the plurality of above-water communication partners (22, 24, 26, 28, 30), the underwater-to-above-water communication partner (34) and the converter (32) for exchanging data packets via the radio data link use the AODV protocol (advanced ad hoc on-demand distance vector) with additional network messages to establish underwater communication.

9. Communication system (20) according to one of the preceding claims, wherein the converter (32) is configured to receive a data packet by means of a radio data protocol and to convert it into an underwater communication protocol (40') when the converter (32) receives the corresponding converter information.

10. Communication system (20) according to one of the preceding claims, wherein the converter (32) is configured to send the data packet (40) via the underwater data link using the GUWMANET (Gossiping in Underwater Mobile Ad-Hoc Networks) protocol.

11. Communication system (20) according to one of the preceding claims, wherein the sending underwater-above water communication partner (22) is configured to determine the route for the data packet only when the data packet is to be sent.

12. Communication system (20) according to one of the preceding claims, wherein the data packet is transmitted exclusively by means of the plurality of surface communication partners, the underwater-surface communication partner and the converter, wherein the plurality of surface communication partners (22, 24, 26, 28, 30) are in the absence of a satellite.

13. Communication system (20) according to one of the preceding claims, wherein the communication system (20) is an ad-hoc communication system.

14. Method for communication between a plurality of surface communication partners (22, 24, 26, 28, 30), an underwater-surface communication partner (34) and a converter (32) comprising the following steps: - Sending a data packet (40) by radio from a surface communication partner (22) to the underwater-surface communication partner (34); - Receiving the data packet (40) by the converter (32); - Check whether the received data packet (40) is to be sent to the underwater-surface communication partner (34) by means of underwater communication or by means of radio; - Send the received data packet to the underwater-surface communication partner (34) only via underwater communication (40') if the check shows that the data packet should be sent via underwater communication.

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