[linux-dvb] Re: 8psk format

[Holger Waechtler <holger@convergence.de>]

Jeremy Hall wrote:
> Hi,
> 
> Does anybody know what this 8psk format is?

8psk would be QAM8, QPSK would be QAM4 and BPSK would be called QAM2. 
The number describes the number of phase/amplitude transition states. 
Here some phase diagrams:

QPSK modulation:
(here each phase angle encodes a symbol out of 00, 01, 10, 11)

                |
     00 x       |        x 01
                |
                |
                |
                |
    --------------------------
                |
                |
                |
                |
     10 x       |        x 11
                |


QAM16:
The 'real' QAM modulations use both angle and amplitude of the 
transmitted signal to encode a symbol:

    0000  0001  |  0010  0011
        x    x  |  x     x
                |
                |
    0100  0101  |  0110  0011
        x    x  |  x     x
                |
    --------------------------
                |
                |
        x    x  |  x     x
    1000  1001  |  1010  1011
                |
                |
        x    x  |  x     x
    1100  0101  |  1110  1111
                |

So each of the 16 points in the phase/amplitude diagram above describes 
one binary symbol from 0...16. Since the mapping of points to symbols 
has to be defined somewhere the DVB standard defines a number of 
modulations, namely QPSK, QAM16, QAM32, QAM64, QAM128, QAM256.



> DO any supported cards have the ability to lock to an 8psk transponder?

Some Demodulators support BPSK and an alternative QAM128 mapping. I 
suppose you have to read the datasheets to find out if any of them 
supports 8psk.

Holger




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