Why do we need VSB modulation

In the case of SSB modulation, the bandpass filter may not work perfectly in practice when the sidebands pass through the filter, so some information may be lost. Therefore, in order to avoid this loss, a technique was chosen, which is a compromise between DSB-SC and SSB, called Vestigial Sideband (VSB) technique, or Vestigial Sideband. The word vestigial means "part", from which the name derives.

VSB is an amplitude modulation method (AM). It is based on double sideband modulation, and by designing a filter, the spectral component of one sideband of the signal is retained in principle, and only a small part of the spectral component of the other sideband is retained (residual ), such as the residual part of the upper sideband, refers to retaining most of the lower sideband and retaining a small part of the upper sideband. This modulation method not only overcomes the disadvantage of DSB signal occupying frequency bandwidth (saving spectrum compared with double sideband modulation) but also solves the difficult problem of SSB modulation (easier to demodulate than single sideband). VSB modulation is mainly used for television transmission.