Протокол любительской радиосвязи Olivia MFSK

Amateur telecommunications protocol

Olivia MFSK is an amateur radioteletype protocol, using multiple frequency shift keying (MFSK) and designed to work in difficult (low signal to noise ratio plus multipath propagation) conditions on shortwave bands. The signal can be accurately received even if the surrounding noise is 10 dB stronger. It is commonly used by amateur radio operators to reliably transmit ASCII characters over noisy channels using the high frequency (3–30 MHz) spectrum. The effective data rate of the Olivia MFSK protocol is 150 characters/minute. Olivia modes are commonly referred to as Olivia X / Y (or, alternatively, Olivia Y / X ), where X refers to the number of different audio tones transmitted and Y refers to the bandwidth in hertz over which these signals are spread. Examples of common Olivia modes are 16/500, 32/1000 and 8/250.

The protocol was developed at the end of 2003 by Pawel Jalocha. The first on the air tests were performed by two radio amateurs, Fred OH/DK4ZC and Les VK2DSG, on the Europe Australia path in the 20 meter amateur band. The tests proved that the protocol works well and can allow regular intercontinental radio contacts with as little as one watt RF power. Since 2005 Olivia has become a standard for digital data transfer under white noise, fading and multipath, flutter (polar path) and auroral conditions.

The modulation layer of the Olivia transmission system in the default mode sends one of 32 tones at a time. Each tone thus constitutes a symbol that carries 5 bits of information. For the FEC code, 64 symbols are taken to form a block. Within each block one bit out of every symbol is taken and it forms a 64 bit vector coded as a Walsh function. Every 64 bit vector represents a 7 bit ASCII character, thus each block represents 5 ASCII characters. This way, if one symbol (tone) becomes corrupted by the noise, only one bit of every 64 bit vector becomes corrupt, thus the transmission errors are spread uniformly across the characters within a block. The two layers (MFSK+Walsh function) of the FEC code can be treated as a two dimensional code: the first dimension is formed along the frequency axis by the MFSK itself while the second dimension is formed along the time axis by the Walsh functions. The two dimensional arrangement was made with the idea in mind to solve such arranged FEC code with an iterative algorithm, however, no such algorithm has yet been established. The scrambling and simple bit interleaving is applied to make the generated symbol patterns appear more random and with minimal self correlation. This avoids false locks at the receiver. Bit interleaving: The Walsh function for the first character in a block is constructed from the 1st bit of the 1st symbol, the 2nd bit of the 2nd symbol, and so on. The 2nd Walsh function is constructed from the 2nd bit of the 1st symbol, the 3rd bit of the 2nd symbol, and so on. Scrambling: The Walsh functions are scrambled with a pseudo random sequence 0xE257E6D0291574EC. The Walsh function for the 1st character in a block is scrambled with the scrambling sequence, the 2nd Walsh function is scrambled with the sequence rotated right by 13 bits, the 3rd with the sequence rotated by 26 bits, and so on.

The listed audio files both are encoded with the message: "Welcome to Wikipedia, the free encyclopedia that anyone can edit."

Contestia is a digital mode that is directly derived from Olivia, which is not as robust. It is more of a compromise between performance and speed. It sounds and looks almost identical to Olivia, and can be configured in as many ways, but has just over twice the speed. The mode was developed by Nick Fedoseev, UT2UZ, in 2005. The Contestia mode has 40 formats just like Olivia some of which are considered standard and they all have different characteristics. The formats have a variation in bandwidth (125, 250, 500, 1000, and 2000 Hz) and number of tones used (2, 4, 8, 16, 32, 64, 128, or 256). The standard Contestia formats (bandwidth/tones) are 125/4, 250/8, 500/16, 1000/32, and 2000/64. The most commonly used formats are 250/8, 500/16, and 1000/32.