Complete Communications Engineering

The ATSC Terrestrial TV standard is based on an 8-VSB modulation with pilot insertion. The sequence of 8 level symbols with levels ±1, ±3, ±5 and ±7 is the input to the 8-VSB modulator. The symbol rate is 10.762 Msb/s. The modulator has to modulate these symbols using VSB modulation and form the VSB spectrum that fits within a terrestrial 6 MHz channel.

8-VSB Signal Spectrum
Fig.1 8-VSB signal spectrum


To form this spectrum, the 8-VSB modulator has to process symbols by real and imaginary VSB filters and create a complex 8-VSB spectrum. The real VSB filter is a bypass filter that is just a delay block. The pilot insertion happens by adding a constant value to the input filter. For ATSC the standard pilot value is 1.25. The rolloff of the spectrum and respectively of the imaginary filter has to be 0.115.

8-VSB Modulator
Fig.2 8-VSB Modulator


After modulation to the intermediate frequency fIF the signal is then shifted to radio frequency (RF).

8-VSB Real and Imaginary filter frequency responses
Fig.3 8-VSB Real and Imaginary filter frequency responses

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