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

Interaction Channel for DVB-T: DVB-RCT 293TimeTransmission frame type 1FrequencyRangingsymbolsNull symbolFigure 5-55Data symbols carryingBurst structure 1 or 2 (not simultaneously)Ranging symbolsOrganization of the TF1 frameData symbolswhich means one pilot carrier is inserted for approximately every five data sub-carriers.Furthermore, they result in various combinations of time and frequency diversity, therebyproviding various degrees of robustness, burst duration, and a wide range of bit rates tothe system.Each burst structure makes use of a set of sub-carriers called a sub-channel. One orseveral sub-channels can be used simultaneously by a given terminal station dependingon the allocation performed by the MAC process.Figure 5-55 depicts the organization of a TF1 frame in the time domain. It should benoticed that the burst structures are symbolized regarding their duration and not regardingtheir occupancy in the frequency domain. The corresponding sub-carrier(s) of burststructures 1 and 2 are spread over the whole RCT channel.Null symbol and ranging symbols always use the rectangular shaping. The user symbolsof TF1 can use either rectangular shaping or Nyquist shaping. If the user part employsrectangular shaping, the guard interval value will be identical for any OFDM symbolembedded in the whole TF1 frame. If the user part performs Nyquist shaping, the guardinterval value to apply on to the null symbol and ranging symbols will be T s /4. The userpart of the TF1 frame is suitable to carry one burst structure 1 or four burst structure 2.Both burst structures should not be mixed in a given DVB-RCT channel.The time duration of a transmission frame depends on the number of consecutive OFDMsymbols and on the time duration of the OFDM symbol. The time duration of an OFDMsymbol depends on– the reference downlink DVB-T system clock;– the sub-carrier spacing; and– the rectangular filtering of the guard interval (1/4, 1/8, 1/16, 1/32 times T s ).In Table 5-53, the values of the frame durations in seconds for TF1 using burst structure1 are given.Figure 5-56 depicts the organization of the TF2 frame in the time domain. The correspondingsub-carrier(s) of burst structures 2 and 3 are spread on the whole RCT channel.TF2 is used only in the rectangular pulse shaping case. The guard interval applied onany OFDM symbols embedded in the whole TF2 is the same (i.e. either 1/4, 1/8, 1/16 or