R&S SMCVB-K156, Руководство пользователя, Страница: 15 / 79

About the T-DMB/DAB Option
R&S
®
SMCVB-K156
15 User Manual 1179.1029.02 ─ 02
The data, carried in the MSC, is divided at source into regular 24 ms bursts corre-
sponding to the sub-channel data capacity of each CIF. The CIF contains 55 296 bits,
divided at 864 capacity units, 64 bits each.
Fast Information Block (FIB) is a data burst of 256 bits. The sequence of FIBs is car-
ried by the Fast Information Channel FIC. The structure of the FIB is common to all
transmission modes.
The synchronization channel symbols comprise the null symbol and the phase refer-
ence symbol. The null symbols are also used to allow a limited number of OFDM carri-
ers to convey the Transmitter Identification Information (TII).
3.2.3.2 Transport Modes
Transmission mode is specific set of transmission parameters (e.g. number of carriers,
OFDM symbol duration). Four transmission modes (i.e. I, II, III and IV) are defined to
allow the system to be used for different network configurations and a range of operat-
ing frequencies. Depending on the transport mode, the transmission frame has differ-
ent organization and length, i.e. the transmission frame is specific to the four transmis-
sion modes.
The table below gives the transmission frame duration and the number of FIBs and
CIFs which are associated with each transmission frame for the four transport modes.
Table 3-1: Transmission Mode Characteristics
Transport
Mode Duration of
transmision
frame Number of
FIBs per trans-
mission frame Number of
CIFs per trans-
mission frame Number of car-
riers Carrier Spac-
ing
I 96 ms 12 4 1536 1 KHz
II 24 ms 3 1 384 4 KHz
III 24 ms 4 1 192 8 KHz
IV 48 ms 6 2 768 2 KHz
3.2.4 Pseudo Noise Scrambling
Prior to convolution encoding, the transmitted signal can be scrambled by a modulo-2
addition with a
PRBS .
The PRBS polynomial is of degree 9 and specified as P(X) =x
9
+x
5
+1.
The initialization word is applied in such a way that the first bit of the PRBS is obtained
when the outputs of all shift register stages are set to value "1".
3.2.5 Convolutional Coding
The process of convolution coding is applied at the output of each PN scrambler. The
channel encoding process is based on punctured convolutional coding, which allows
both equal and unequal error protection. Unequal error protection (UEP) is designed
About DAB/T-DMB