On 2/18/06, John Becker <[EMAIL PROTECTED]> wrote:
PSK63 is a BPSK mode with twice the speed, and twice the bandwidth of PSK31. To cater for the 3 dB loss with respect to PSK31, PSK63 needs double the power to realise the same S/R ratio.
Like PSK31, PSK63 uses a varicode scheme with symbols of 3 bits (space) to 10 bits (the DEL character). In average, in normal english upper/lowercase text there is 6.5 bits per character, which is a lot better than ASCII (8N1, 10 bits), and even better than (upper case only) Baudot with 8 bits.
PSKmail puts protocol overhead on top of PSK63. Depending on block size, protocol overhead is 100% (8-character blocks with 8 extra bytes), down to 12% (64-character blocks with 8 extra bytes). By the way, the max. throughput of 6.3 cps was measured at 64-character blocks). As a frame normally contains 8 blocks, turnaround loss is much less important then the number of repeats.
PSK_arq cuts the text into blocks of 8 – 64 characters, depending on band conditions. Small blocks when there is a lot of QRM or QRN, large blocks when the signal is steady and the channel is clear.
The blocks are numbered and they all get a sequence number from 0 to 63. They also get a CRC16 number so the receiver can see if the block has been received ok.
The transmitter sends 8 blocks in a frame. The receiver checks every block against its CRC checksum and tells the transmitter with a short status block which text blocks were damaged. These will be prepended to the next frame, so the receiver gets another chance.
This goes on until the text has been received 100%. This is better than FEC. With FEC everything is send 2x, with PSK_arq only the parts that are damaged have to be repeated....
The protocol was proposed by Paul Schmidt, K9PS. It is documented in http://sharon.esrac.ele.tue.nl/pub/linux/ham/pskmail/ARQ2.pdf
Because of the adaptive frame lenght used (typically 8 blocks of 32 characters), PSK_arq seems uninteresting for keyboard-to-keyboard operation, but on-air tests show that PSK31 speed can be easily reached with reasonable channel quality. And of course at 0% error!!
Thanks Andy.
I'll give it a look.
Not a big fan of PSK but love the ARQ modes.
John, W0JAB
From their web site...
How does PSK-arq work in theory?
PSK63 is a BPSK mode with twice the speed, and twice the bandwidth of PSK31. To cater for the 3 dB loss with respect to PSK31, PSK63 needs double the power to realise the same S/R ratio.
Like PSK31, PSK63 uses a varicode scheme with symbols of 3 bits (space) to 10 bits (the DEL character). In average, in normal english upper/lowercase text there is 6.5 bits per character, which is a lot better than ASCII (8N1, 10 bits), and even better than (upper case only) Baudot with 8 bits.
PSKmail puts protocol overhead on top of PSK63. Depending on block size, protocol overhead is 100% (8-character blocks with 8 extra bytes), down to 12% (64-character blocks with 8 extra bytes). By the way, the max. throughput of 6.3 cps was measured at 64-character blocks). As a frame normally contains 8 blocks, turnaround loss is much less important then the number of repeats.
PSK_arq cuts the text into blocks of 8 – 64 characters, depending on band conditions. Small blocks when there is a lot of QRM or QRN, large blocks when the signal is steady and the channel is clear.
The blocks are numbered and they all get a sequence number from 0 to 63. They also get a CRC16 number so the receiver can see if the block has been received ok.
The transmitter sends 8 blocks in a frame. The receiver checks every block against its CRC checksum and tells the transmitter with a short status block which text blocks were damaged. These will be prepended to the next frame, so the receiver gets another chance.
This goes on until the text has been received 100%. This is better than FEC. With FEC everything is send 2x, with PSK_arq only the parts that are damaged have to be repeated....
The protocol was proposed by Paul Schmidt, K9PS. It is documented in http://sharon.esrac.ele.tue.nl/pub/linux/ham/pskmail/ARQ2.pdf
Because of the adaptive frame lenght used (typically 8 blocks of 32 characters), PSK_arq seems uninteresting for keyboard-to-keyboard operation, but on-air tests show that PSK31 speed can be easily reached with reasonable channel quality. And of course at 0% error!!
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