Recommended sampling rate and bitrate combinationsedit
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 protocol was developed at the end of by Pawel Jalocha. The tests proved that the protocol works well and can allow regular intercontinental radio contacts with as little as recommended sampling rate and bitrate combinationsedit watt RF power.
Since Olivia has become a standard for digital data transfer under white noise, fading and multipathflutter polar path and auroral conditions. As a result, amateur radio operators have voluntarily decided upon channelization for this mode. This channelization allows even imperceptibly weak signals to be properly tuned for reception and decoding.
The following table lists the common center frequencies used in the amateur radio bands. The possible number of tones that can be chosen are 2, 4, 8, 16, 32, 64,and with higher numbers of tones giving more data redundancy but slower throughput and lower numbers of tones giving faster throughput at the cost of less redundancy. Recommended sampling rate and bitrate combinationsedit characters are sent in blocks of 5. Each block takes 2 seconds to transmit, thus the effective data rate is 2.
To accommodate for different conditions and for the purpose of experimentation the bandwidth and the baud rate can be recommended sampling rate and bitrate combinationsedit. The Olivia transmission system is constructed of two layers: Both layers are of similar nature: For the first layer the orthogonal functions are co sine functions, with 32 different frequencies tones. At a given time only one of those 32 tones is being sent.
The demodulator measures the amplitudes of all the 32 possible tones using a Fourier transform and knowing that only one of those 32 could have been sent picks up the tone with the highest amplitude.
For the second FEC layer: The receiver again measures the amplitudes for all 64 vectors here comes the Hadamard Transform and chooses the greatest. For optimal performance the actual demodulators work with soft decisions and the final hard decision to decode recommended sampling rate and bitrate combinationsedit character is taken only at the second layer.
Thus recommended sampling rate and bitrate combinationsedit first layer demodulator actually produces soft decisions for each of the 5 bits associated to an MFSK tone instead of simply picking up the highest tone to produce hard decisions for those 5 bits. In order to avoid simple transmitted patterns like a constant tone and to minimize the chance for a false lock at the synchronizer the characters encoded into the Walsh function pass through a scrambler and interleaver.
This stage simply shifts and XORs bits with predefined scrambling vectors and so it does not improve the performance where the white uncorrelated noise is concerned, but the resulting pattern gains certain recommended sampling rate and bitrate combinationsedit characteristics which are of great help to the synchronizer.
The receiver synchronizes automatically by searching through possible time and frequency offsets for a matching pattern. The tones are shaped to minimize the amount of recommended sampling rate and bitrate combinationsedit sent outside the nominal bandwidth. The coefficients represent the symbol shape in the frequency domain and were calculated by a minimization procedure which sought to make the smallest crosstalk and the smallest frequency spillover.
The tones are sent at The phase is not preserved from one tone to the next: Because the symbols are smoothly shaped there is no need to keep the phase constant, which normally is the case when no e.
The modulator uses the Gray code to encode 5-bit symbols into the tone numbers. The tones are spaced by samples in time and the window that shapes them is samples long. The demodulator is based on the FFT with the size of points. To adapt the system to different propagation conditions, the number of tones and the bandwidth can be changed and the time and frequency parameters are proportionally scaled. The number of tones can be 2, 4, 8, 16, 32, 64, or 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 bit vector coded as a Walsh function. This way, if one symbol tone becomes corrupted by the noise, only one bit of every bit vector becomes corrupt, thus the transmission errors are spread uniformly across the characters within a block. 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 recommended sampling rate and bitrate combinationsedit 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. 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. 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: 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 twice the speed. The Contestia mode has 40 formats just like Olivia - some of which are considered standard and they all have different characteristics.
This reduced character set does not print out in both upper and lower case such as RTTY. Some traffic nets may not like to use this mode as it does not support upper and lower case characters and extended characters found in many documents and messages.
This does not pose a problem for normal digital chats within ham communications. From Wikipedia, the free encyclopedia. Archived from the original on December 22, Archived from the original on September 27, Contestia Digital Mode Information. Retrieved 1 May Amateur radio digital modes. MT63 based on PSK. Retrieved from " https: Quantized radio modulation modes Amateur radio.
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