DAB TII

Decoding the DAB Transmitter Identification Information Signal.

The Transmitter Identification Information signal (TII)

TII

The Transmitter Identification Information signal (TII) uniquely identifies each transmitter in a DAB network. The TII is optional. It's slipped in every other NULL "Sync" symbol within the 96 ms frame. That's an update of around 5 times a second.

DAB uses a signal frequency network (SFN). Every transmitter in that network sends identical OFDM carriers - the "Multicarrier Modulation" of 1536 frequencies.

The TII is unique for each transmitter, so breaks that "identical" rule.

TII Main and Sub-identifier Codes

During the NULL symbol each transmitter switches on some of the 1536 available OFDM carriers in a unique pattern. This pattern is duplicated 4 times to improve signal to noise. So that's 384 carriers. We're looking for pairs of carriers, so that's 192 pairs. Sub-identifier codes are repeated 8 times - we getting to 192/8 = 24. Sub-identifier codes range between [0..23].

The Main code is encoded by the sub-identifier code repetition. There's another rule: the Sub-identifier code can only use 4 out of the 8 pairs. There are 70 combinations of 4 objects from a set of eight. So that give the range of main codes [0..69].

See the DAB standard, section 14.8.  

TII - Screenshot

screen shot

What are we looking at? (Other than a screen shot of some code in development.) The pink trace (Manhattan plot) shows signal strength for each carrier pair. The dark grey and light grey bands show the MainID 4 of 8 blocks.

Transmitter IDs are taken from Ofcom data.

Swaffham Sub ID is 14 [Dark Green]. That's the 14th carrier pair in the 24 carrier pair block. The carrier pair appears in blocks 0,2,3,7. that's 10110001 or 0xB1. Code 0xB1 is the 51st 4 of 8 code, so the Main ID is 51.
Wisbeach Sub ID is 13 [Pink]. That's the 13th carrier pair in the 24 carrier pair block. The carrier pair appears in block 1,3,4,5. that's 01101100 or 0x6C. Code 0x6C is the 30th 4 of 8 code, so the Main ID is 30.

The count of 579 shows decoding over 579 * 96 ms = 55.5 seconds. (Cogitation time?) Some codes were not in the Ofcom table. (Note the DX from Chesterfield.)

Coldham, 12 beam headings

12B BBC National DAB multiplex as seen at Coldham.The Screen Shots were taken as the beam was cranked around 30°.

Links

QIRX is the open source project used by this demo. Their DABTII dll source is closed, but their C# interface wasn't. I put something together.

The DAB standard (ETSI EN 300 401)
Read section 14.8 Transmitter Identification Information signal and Figure 64.

Design and Implementation of the DAB/DMB Transmitter Identification Information Decoder

Receiver synchronization for Digital Audio Broadcasting Ofcom - Technical parameters for broadcast radio transmitters

Yagi Wiki (I like the animation!)

Anritsu S114C Site Master Cable and Antenna Analyzer

Open DAB TX

MonkeyBoard DAB Radio Development

5 Element Astrabream(sic) VHF/DAB Aerials. Born again JBeam! A bream is a fish.
Can you really have a yagi covering 174–240 MHz?

Page last edited 3rd April 2019. [email protected]



DAB TII