Robust-Packet (RPR, Robust Packet Radio) is a data transmission mode devised from Special Communications Systems GmbH & Co. KG.  It is optimized for the deployment in the short wave band. To accommodate the characteristics of this frequency range, for example fading and multipath propagation, a eight carrier OFDM was used.

Dependent on the speed level (r200 or r600) every carrier is DBPSK or DQPSK at a rate of 50 Bd modulated.  Just like in PACKET-RADIO the AX.25-protocol comes into operation.  The decoder module detects the speed level and the size of the transmitted packet automatically and shows the result. The payload of one packet can be up to 256 Byte.  The real length of one data packed depends on the amount of data to be send. There are 25 different packages. One for connect/disconnect and respectively 12 for the two speed levels with their variable packet length.

To make the transmission as robust as possible, there are several modifications applied onto the AX.25- data stream before the transmission. The call signs are compressed with a special algorithm, the data stream is scrambled, redundancy is added and it is interleaved over the full frame length.

The decoder output is divided in signaling information (call signs with SSIDs, package-identifier and AX.25 control word) and data. It is possible to represent the data as ITA5-US and HEX.

Further description to the signaling information can be found in the AX.25 Link Access Protocol for Amateur Packet Radio.

The package-identifier specifies the used layer 3 protocol.

In the following table, all possible package identifiers are given:

Package-Identifier PID