Modem M64 Operating Principle


Auto Sync

After a few seconds the modems will be syncronized and ready to communicate


Data Communication

– Two-way communication
– 64 bit per second, both ways
– Typical latency ~500ms
– 200 meter range


Modem M64


Modem M64

1. Auto Sync

The modems (3) and (4) are set to the same channel and will auto-sync after a few seconds.

After sync is complete, each modem are given dedicated timeslots where they are allowed to transmit and when they shall listen.

2. Transmit / Receive

When a modem receives a payload of data from its host (in this case, an AUV) it will start transmitting this payload in a package structure where each package is 64 bits.

The other modem which is in sync, will receive the transmitted data packages in dedicated time slots.

3 & 4.  Modem M64

Each AUV carry a Modem M64 which is interfaced using a lightweight API.


The Modem-M64 has an advanced auto-sync feature which makes it extremely easy to use!

1. Syncing

Two modems configured on the same channel will auto-sync once they are within reach of each other. The auto-sync procedure only takes a few seconds!

Synced modems are ready to operate the two-way communication link.

2. Out of reach

If the two modems get out of reach of each other (>200 meter), they will automatically enter into search-mode. During search mode, they will not transmit payload packages.

3. Re-Syncing

When the modems get back into reach of each other, they will automatically sync up again and be ready to transmit payload packages!


In contrast to classic modems, the Modem-M64 is fully omnidirectional!

Omnidirectional means that the modems can be turned around all axes and still maintain its robust data link.

This is especially important for ROV/AUV applications where the modems are in constant motion.


When the first subsea acoustic modems came to the market (and actually still), the manufacturers designed their modems as simple “pingers” where the digital information was encoded as frequency A for “1” and frequency B for “0”. The receiving modem would pick up these frequencies and feed 0’s and 1’s to the receiving computer. This method is extremely vulnerable to packet loss and other interference and the result was that very often the information received was corrupt.

The Modem M64 takes a completely different approach. The M64 uses an advanced proprietary protocol where a significant portion of the gross available data rate in the wireless link is used to enclose the information with error correction features. The M64 customers can therefore put confidence in the data link. In many applications, it is a valuable feature that you can actually trust that the information received is correct.