This section describes shortly what are the possible parameters in the Linux DVB-API called "S2API" and now DVB API 5 in order to tune an ISDB-T/ISDB-Tsb demodulator:
This ISDB-T/ISDB-Tsb API extension should reflect all information needed to tune any ISDB-T/ISDB-Tsb hardware. Of course it is possible that some very sophisticated devices won't need certain parameters to tune.
The information given here should help application writers to know how to handle ISDB-T and ISDB-Tsb hardware using the Linux DVB-API.
The details given here about ISDB-T and ISDB-Tsb are just enough to basically show the dependencies between the needed parameter values, but surely some information is left out. For more detailed information see the following documents:
ARIB STD-B31 - "Transmission System for Digital Terrestrial Television Broadcasting" and
ARIB TR-B14 - "Operational Guidelines for Digital Terrestrial Television Broadcasting".
In order to read this document one has to have some knowledge the channel structure in ISDB-T and ISDB-Tsb. I.e. it has to be known to the reader that an ISDB-T channel consists of 13 segments, that it can have up to 3 layer sharing those segments, and things like that.
Parameters used by ISDB-T and ISDB-Tsb.
Central frequency of the channel.
For ISDB-T the channels are usally transmitted with an offset of 143kHz. E.g. a valid frequncy could be 474143 kHz. The stepping is bound to the bandwidth of the channel which is 6MHz.
As in ISDB-Tsb the channel consists of only one or three segments the frequency step is 429kHz, 3*429 respectively. As for ISDB-T the central frequency of the channel is expected.
Possible values:
For ISDB-T it should be always 6000000Hz (6MHz)
For ISDB-Tsb it can vary depending on the number of connected segments
Note: Hardware specific values might be given here, but standard applications should not bother to set a value to this field as standard demods are ignoring it anyway.
Bandwidth in ISDB-T is fixed (6MHz) or can be easily derived from other parameters (DTV_ISDBT_SB_SEGMENT_IDX, DTV_ISDBT_SB_SEGMENT_COUNT).
ISDB-T supports three carrier/symbol-size: 8K, 4K, 2K. It is called 'mode' in the standard: Mode 1 is 2K, mode 2 is 4K, mode 3 is 8K
Possible values: TRANSMISSION_MODE_2K, TRANSMISSION_MODE_8K,
TRANSMISSION_MODE_AUTO, TRANSMISSION_MODE_4K
If DTV_TRANSMISSION_MODE is set the TRANSMISSION_MODE_AUTO the
hardware will try to find the correct FFT-size (if capable) and will
use TMCC to fill in the missing parameters.
TRANSMISSION_MODE_4K is added at the same time as the other new parameters.
Possible values: GUARD_INTERVAL_1_32, GUARD_INTERVAL_1_16, GUARD_INTERVAL_1_8,
GUARD_INTERVAL_1_4, GUARD_INTERVAL_AUTO
If DTV_GUARD_INTERVAL is set the GUARD_INTERVAL_AUTO the hardware will
try to find the correct guard interval (if capable) and will use TMCC to fill
in the missing parameters.
If DTV_ISDBT_SOUND_BROADCASTING is '0' this bit-field represents whether
the channel is in partial reception mode or not.
If '1' DTV_ISDBT_LAYERA_* values are assigned to the center segment and
DTV_ISDBT_LAYERA_SEGMENT_COUNT has to be '1'.
If in addition DTV_ISDBT_SOUND_BROADCASTING is '1'
DTV_ISDBT_PARTIAL_RECEPTION represents whether this ISDB-Tsb channel
is consisting of one segment and layer or three segments and two layers.
Possible values: 0, 1, -1 (AUTO)
This field represents whether the other DTV_ISDBT_*-parameters are
referring to an ISDB-T and an ISDB-Tsb channel. (See also
DTV_ISDBT_PARTIAL_RECEPTION).
Possible values: 0, 1, -1 (AUTO)
This field only applies if DTV_ISDBT_SOUND_BROADCASTING is '1'.
(Note of the author: This might not be the correct description of the
SUBCHANNEL-ID in all details, but it is my understanding of the technical
background needed to program a device)
An ISDB-Tsb channel (1 or 3 segments) can be broadcasted alone or in a set of connected ISDB-Tsb channels. In this set of channels every channel can be received independently. The number of connected ISDB-Tsb segment can vary, e.g. depending on the frequency spectrum bandwidth available.
Example: Assume 8 ISDB-Tsb connected segments are broadcasted. The broadcaster has several possibilities to put those channels in the air: Assuming a normal 13-segment ISDB-T spectrum he can align the 8 segments from position 1-8 to 5-13 or anything in between.
The underlying layer of segments are subchannels: each segment is consisting of several subchannels with a predefined IDs. A sub-channel is used to help the demodulator to synchronize on the channel.
An ISDB-T channel is always centered over all sub-channels. As for the example above, in ISDB-Tsb it is no longer as simple as that.
The DTV_ISDBT_SB_SUBCHANNEL_ID parameter is used to give the
sub-channel ID of the segment to be demodulated.
Possible values: 0 .. 41, -1 (AUTO)
This field only applies if DTV_ISDBT_SOUND_BROADCASTING is '1'.
DTV_ISDBT_SB_SEGMENT_IDX gives the index of the segment to be
demodulated for an ISDB-Tsb channel where several of them are
transmitted in the connected manner.
Possible values: 0 .. DTV_ISDBT_SB_SEGMENT_COUNT - 1
Note: This value cannot be determined by an automatic channel search.
This field only applies if DTV_ISDBT_SOUND_BROADCASTING is '1'.
DTV_ISDBT_SB_SEGMENT_COUNT gives the total count of connected ISDB-Tsb
channels.
Possible values: 1 .. 13
Note: This value cannot be determined by an automatic channel search.
ISDB-T channels can be coded hierarchically. As opposed to DVB-T in ISDB-T hierarchical layers can be decoded simultaneously. For that reason a ISDB-T demodulator has 3 viterbi and 3 reed-solomon-decoders.
ISDB-T has 3 hierarchical layers which each can use a part of the available segments. The total number of segments over all layers has to 13 in ISDB-T.
Hierarchical reception in ISDB-T is achieved by enabling or disabling
layers in the decoding process. Setting all bits of
DTV_ISDBT_LAYER_ENABLED to '1' forces all layers (if applicable) to be
demodulated. This is the default.
If the channel is in the partial reception mode
(DTV_ISDBT_PARTIAL_RECEPTION = 1) the central segment can be decoded
independently of the other 12 segments. In that mode layer A has to
have a SEGMENT_COUNT of 1.
In ISDB-Tsb only layer A is used, it can be 1 or 3 in ISDB-Tsb
according to DTV_ISDBT_PARTIAL_RECEPTION. SEGMENT_COUNT must be filled
accordingly.
Possible values: 0x1, 0x2, 0x4 (|-able)
DTV_ISDBT_LAYER_ENABLED[0:0] - layer A
DTV_ISDBT_LAYER_ENABLED[1:1] - layer B
DTV_ISDBT_LAYER_ENABLED[2:2] - layer C
DTV_ISDBT_LAYER_ENABLED[31:3] unused
Possible values: QAM_AUTO, QPSK, QAM_16, QAM_64, DQPSK
Note: If layer C is DQPSK layer B has to be DQPSK. If layer B is DQPSK
and DTV_ISDBT_PARTIAL_RECEPTION=0 layer has to be DQPSK.
Possible values: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, -1 (AUTO)
Note: Truth table for DTV_ISDBT_SOUND_BROADCASTING and
DTV_ISDBT_PARTIAL_RECEPTION and LAYER*_SEGMENT_COUNT