Quadrature Vestigial Sideband (QVSB) Data Transmission

The combined use of quadrature modulation and vestigial sideband filtering is investigated as a means of obtaining a spectrally efficient modulation scheme. The name quadrature vestigial sideband (QVSB) aptly describes the new system, whereby two independent data streams are each VSB modulated into the same passband, but on quadrature related carriers. The inherent interference between the quadrature related channels is shown to be of a controlled form, similar to the intersymbol interference (ISI) in partial response (PR) systems. Techniques suitable for "unwinding" the ISI in PR systems are shown to be also applicable to QVSB. Precoding with bit-by-bit, decoding, nonoptimum and optimum probablistic decoding are investigated. The latter method results in only a 1.2 dBE_{b}/N_{0}degradation, atP_{b} = 10^{-5}, compared to coherent binary phase shift keying (BPSK), although up to a fourfold increase in spectral efficiency can be obtained.