Capacity calculation for the FIC payload
The Fast Information Channel (FIC) consists of three “modulation cycles” or three “time slots,” sometimes also referred to as symbols within the transmission frame.
These symbols are spread across the 1,536 carriers used in DAB Mode I.
This results in:
3 × 2 bits × 1,536 = 9,216 bits per transmission frame of 96 ms.
Converted to a bitrate:
9,216 bits / 0.096 s ≈ 96,000 bits per second (96 kbps).
This is the raw capacity available for the FIC.
However, the transmitter applies forward error correction (FEC) using a 1/3-rate convolutional code. As a result, the effective user data rate becomes 32 kbps.
From the Perspective of the ETI-LI Frame
Within the ETI-LI frame, 96 bytes are allocated for the FIC payload in DAB Mode I (source: ETSI ETS 300 799).
The reasoning is as follows:
- 96 bytes = 768 bits
- 768 bits / 24 ms = 3072 bits per 96 ms = 32,000 bits/s (32 kbps)
This calculation shows that the ETI-LI interface indeed transports 32 kbps of actual FIC information from the multiplexer to the transmitter.
At the transmitter side, FEC 1/3 is applied, expanding the data so that the final transmission frame contains the full 96 kbps FIC channel capacity over the air.
This approach uses strong FEC but omits time interleaving, ensuring the receiver obtains FIC information as quickly as possible.
Another way to view this is through the FICL (FIC Length) parameter in the ETI-LI frame.
Conclusion:
For DAB Modes I, II, and IV, FICL = 24 words (bytes).
In the FIC field, the structure defines FICL (bytes) × 4 = 96 bytes, consistent with the statements in other documents.
Caution: Do not confuse the 24 words with the net FIC data capacity for ETI-LI. There is a factor-of-4 difference, as clearly stated in the description of the ETI-LI frame in the ETSI documents.