[linux-dvb] DVB-S2 and other (new) modulation standards

Felix Domke tmbinc at elitedvb.net
Tue Nov 22 22:53:22 CET 2005


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Hi,

in the tuxbox irc channel we were discussing how to tune to DVB-S2
transponders, of course using all that not-yet-existing (at least not in
numbers) hardware which we all wait for.

The problem is that the current dvb_qpsk_parameters cannot really be
extended without breaking backward compatibility, and still, -S2 isn't
strictly QPSK but QAM too, but on the other hand has nothing to do with
DVB-C and the already defined dvb_qam_parameters.

Basically we had two ideas:

The first one was:

#define FE_SET_FRONTEND_EX    _IOW('o', xx, struct
dvb_frontend_parameters_ex)

#define FE_STANDARD_DVB_S 0
#define FE_STANDARD_DVB_C 1
#define FE_STANDARD_DVB_T 2
#define FE_STANDARD_DVB_S2 3

struct dvb_frontend_parameters_ex {
  int standard; /* this is new! */

  __u32 frequency;
  fe_spectral_inversion_t inversion;
  union {
    struct dvb_qpsk_parameters qpsk;
    struct dvb_qpsk2_parameters qpsk2; // qpsk + -S2 specific stuff
    struct dvb_qam_parameters  qam;
    struct dvb_ofdm_parameters ofdm;
    struct dvb_vsb_parameters vsb;
  } u;
};


The other method, which i prefer, is:

#define FE_SET_STANDARD     _IOW('o', xx, int)

#define FE_STANDARD_DVB_S 0
#define FE_STANDARD_DVB_C 1
#define FE_STANDARD_DVB_T 2
#define FE_STANDARD_DVB_S2 3

FE_CAN_DVBS = xxx,
FE_CAN_DVBC = xxx,
FE_CAN_DVBT = xxx,
FE_CAN_ATSC = xxx,
FE_CAN_DVBS2 = xxx,

The current dvb_frontend_parameters could be extended for the new
standard. Each standard would define to use exactly one
"dvb_xxx_parameters" in that union.

This method would also catch the DVB-S/DVB-T-combi frontends which
lately appeared here. One could set the STANDARD, and the frontend would
change it's complete personality (probably including other FE_CAN_-caps,
changing the frequency_min/max/..-limits etc.). A frontend could decide
to stop supporting SEC commands when switched to DVB-T mode etc.


A final question was how to support DVB-H. Is DVB-H totally backward
compatible to DVB-T? (ignoring the 4k mode, of course, but that could be
added backward-compatible to DVB-T) Do we want to support that power
management features, if yes, how? A new dvb_dvbh_parameters, based on
the _ofdm-one, with some added fields? I never did anything DVB-H
related, so please excuse my ignorance.

Comments?


Felix
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