Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

Interaction Channel for DVB-T: DVB-RCT 295Table 5-54Number of useful data bytes per burstParameters QPSK 16-QAM 64-QAMFEC encoding rate R = 1/2 R = 3/4 R = 1/2 R = 3/4 R = 1/2 R = 3/4Number of data bytes in144 symbols18 27 36 54 54 81Table 5-55Overall encoding ratesOuter RS encoding rate Inner CC encoding rate Overal code rateR outer R inner R total = R outer R inner3/4 2/3 1/29/10 5/6 3/4Table 5-56Coding parameters for combinations of coding rate and modulationModulation RS input CC input Number of CCcode rateoutput bitsQPSK 1/2 144 bits = 24 RS symbols 32 RS symbols = 192 bits 288QPSK 3/4 216 bits = 36 RS symbols 40 RS symbols = 240 bits 28816-QAM 1/2 288 bits = 48 RS symbols 2 × 32 RS symols = 384 bits 57616-QAM 3/4 432 bits = 72 RS symbols 2 × 40 RS symbols = 480 bits 57664-QAM 1/2 432 bits = 72 RS symbols 3 × 32 RS symbols = 576 bits 86464-QAM 3/4 648 bits = 108 RS symbols 3 × 40 RS symbols = 720 bits 864The outer Reed Solomon encoding process uses a shortened systematic RS(63, 55,t = 4) encoder over a Galois field GF(64); i.e. each RS symbol consists of 6 bits. Databits issued from the Reed Solomon encoder are fed to the convolutional encoder ofconstraint length 9. To produce the two total coding rates expected (1/2 and 3/4) the RSand convolutional encoder have implemented the coding rates defined in Table 5-55.The terminal station uses the modulation scheme determined by the base station throughMAC messages. The encoding parameters defined in Table 5-56 are used to produce thedesired coding rate in relation with the modulation schemes. It should be noted that thenumber of symbols per burst in all combinations remains constant, i.e. 144 modulatedsymbols per burst.Pilot sub-carriers are inserted into each data burst in order to constitute the burststructure and are modulated according to their sub-carrier location. Two power levels areused for these pilots, corresponding to +2.5 dB or 0 dB relative to the mean useful symbolpower. The selected power depends on the position of the pilot inside the burst structure.