Principles of Modern Radar - Volume 2 1891121537

17.5 2D-CCF Sidelobe Control 787TABLE 17-7Main Parameters of 2k and 8k Modes DVB-T SignalsParameter 2k mode 8k modeNumber of subcarriers 1705 6817Useful symbol duration T U 224 μs 896 μsT U /32 7 μs 28 μsGuard interval T GT U /16 14 μs 56 μsT U /8 28μs 112 μsT U /4 56μs 224 μsBandwidth 7.61 MHz 7.61 MHzthe above parameters are scaled so that the subcarriers span the 7.61 MHz bandwidthallocated to the DVB-T channel. The DVB-T signal structure is organized in frames witheach frame consisting of 68 OFDM symbols, as shown in Figure 17-23. In addition to thedata carriers, the DVB-T signal contains pilot carriers and transport parameter signalling(TPS) carriers, which are used for receiver synchronisation, channel estimation, and systemparameters transmission. To this aim, the pilots carriers are transmitted at boosted powerlevel E P = 16/9 while the power level of data carriers and TPS pilots is normalizedto 1. The pilot and TPS carriers are scattered at given frequencies, and according to aknown rule [53]. In particular, the pilots carriers include continual pilots having a fixedfrequency position from symbol to symbol and scattered pilots, whose frequency positionsare changed from symbol to symbol over four symbols period (i.e. a super-symbol).For example, Figure 17-24 reports the AF for a simulated DVB-T signal of duration20 ms in 2k mode for T G = T U /32 and shows the number of side peaks due to theguard interval and the pilot carriers. Specifically, in 2k mode, the peak generated by guardinterval occurs at τ = 224 μs, whereas the peaks due to pilot subcarriers can be dividedinto intrasymbol peaks (0 ≤ τ ≤ T S ), and intersymbol peaks (τ >T S ).As for the WiMAX signal, the position of the undesired peaks in the range-Dopplerplane can be identified based on the parameters adopted by the standard. Similarly, the expectedvalue of the AF can be evaluated. Thus, the linear filter for range sidelobes reductioncan be modified according to (17.34) by using the actual expression for the signal ACF. Theresults obtained for the signal considered in Figure 17-24 are reported in Figure 17-25.ScatteredPilotsContinualPilotsFIGURE 17-23DVB-T signal framestructure.s 66s 67s 0s 1s 2Time(symbol)c 0 c 1 c 2 c 3 c 4 c maxFrequencyTPS Pilots(carrier)