DRM FAC

Reference Pilots

Typical 10 kHz mode B DRM spectrum centred on 12 kHz IF.

These three reference pilots (or carriers) are used by the DRM receiver software to help synchronise to the DRM signal. The three FAC reference carriers are transmitted at baseband 750 Hz, 2250 Hz, 3000 Hz (marked as F1, F2, F3).

Unlike all the other DRM carriers, they are dedicated reference carriers whereas all the other carriers constantly switch between either carrying data or used as a pilot (to enable channel estimation).

These FAC reference carriers have their amplitude boosted relative to carriers carrying data by a power gain of 2 so that the DRM software can recognize these FAC reference carriers.

FAC	IF frequency	actual frequency	mode A carrier	mode B carrier	mode C carrier	mode D carrier
F1	12750 Hz	750 Hz	18	16	11	7
F2	14250 Hz	2250 Hz	54	48	33	21
F3	15000 Hz	3000 Hz	72	64	44	28

Individual carriers designated for the three FAC carrier.

They are transmitted at the same frequency irrespective of the DRM mode being used. FAC reference carriers are used to calculate the initial coarse frequency offset of the received DRM signal compared to the receiver’s local oscillator. This is the first part of the COFDM synchronisation process required before the received DRM signal can be properly decoded.

FAC data

The FAC block contains 72 bits of information (64 bits of FAC data plus 8 bit CRC) to allow the DRM software to decode the multiplex. FAC parameters include: spectrum occupancy, interleaver, modulation mode, number of services, language, audio or data, programme type.

Whatever the spectrum occupancy or transmission mode the DRM decoder always needs this FAC information first to know how to decode the rest of the DRM signal. Consequently the FAC is always transmitted in the same place with a fixed code rate. Comparing DRM to AM then the FAC would occupy the equivalent location of AM upper sideband.

Each transmission frame contains an FAC block (400 mSec). When more than one service is carried in the multiplex, a number of FAC blocks are required to describe all the services.

base/ enhancement flag	1 bit	0 : base - decodable by all DRM receivers 1 : enhancement – only decodable by enhanced receivers
identity	2 bits	identifies current frame and validates SDC AFS index: 0 : first FAC of super frame and AFS index is valid 1 : second FAC of super frame 2 : third FAC of super frame 3 : first FAC of super frame, AFS index is invalid
spectrum occupancy	4 bits	00 : 4.5kHz 01 : 5.0kHz 02 : 9.0kHz 03 : 10kHz 04 : 18kHz 05 : 20kHz 06 : not defined :::::::: 15 : not defined
time interleaver depth flag	1 bit	0 : 2 Seconds (long interleaving) 1 : 400 milliSeconds (short interleaving)
MSC modulation mode	2 bits	0 : 64-QAM, no hierarchical 1 : 64-QAM, hierarchical on I 2 : 64-QAM, hierarchical on I&Q 3 : 16-QAM, no hierarchical
SDC mode	1 bit	0 : 16-QAM 1 : 4-QAM
number of audio and data services	4 bits	00 : 4 audio services 01 : 1 data service 02 : 2 data services 03 : 3 data services 04 : 1 audio service 05 : 1 audio service and 1 data service 06 : 1 audio service and 2 data services 07 : 1 audio service and 3 data services 08 : 2 audio services 09 : 2 audio services and 1 data service 10 : 2 audio services and 2 data services 11 : reserved 12 : 3 audio services 13 : 3 audio services and 1 data service 14 : reserved 15 : 4 data services
re- configuration index	3 bits	status and timing of a multiplex reconfiguration. Non-zero value indicates the number of transmission super frames before the new configuration will take effect.
rfu	2 bits	reserved for future use and set to zero until defined.
service identifier	24 bits	indicates the unique identifier for this service
short identifier	2 bits	assigned to this service and used as a reference in the SDC
conditional access flag	1 bit	0 : no CA system in use 1 : CA system in use (details provided by SDC data)
language of target audience	4 bits	00 : no language specified 01 : Arabic 02 : Bengali 03 : Mandarin 04 : Dutch 05 : English 06 : French 06 : German 08 : Hindi 09 : Japanese 10 : Javanese 11 : Korean 12 : Portuguese 13 : Russian 14 : Spanish 15 : Other language * further languages indicated by SDC data
audio/data flag	1 bit	0 : audio service 1 : data service
service descriptor	5 bits	if audio/data flag = 0 then the field indicates the programme type: 00 : no programme type 01 : news 02 : current Affairs 03 : information 04 : sport 05 : education 06 : drama 07 : culture 08 : science 09 : varied 10 : pop music 11 : rock music 12 : easy listening music 13 : light classical 14 : serious classical 15 : other music 16 : weather/meteorology 17 : finance/business 18 : children's programme 19 : social affairs 20 : religion 21 : phone in 22 : travel 23 : leisure 24 : jazz music 25 : country music 26 : national music 27 : oldies music 28 : folk music 29 : documentary 30 : not defined 31 : skip (test transmission) if audio/data flag = 1 (data) then the 5 bit field indicates the application identifier of a data service. A value of 0 indicates that the application details are provided by SDC. A value of 31 indicates that a DRM receiver should skip this broadcast and continue to scan, this allows test transmissions to be ignored by DRM receivers.
rfa	7 bits	reserved for future additions - set to zero until defined

FAC data 64 bits.