Class-IV PRS above the Nyquist rate

An improved efficiency technique for class-IV (modified duobinary) partial-response signalling (PRS) above the Nyquist rate transmission is described. Computer simulations and hardware measurements for a base-band seven-level class-IV PRS system using this technique are shown in good agreement. It is then demonstrated by computer simulations that, with the use of this technique for class-IV 225-QPRS (quadrature PRS), an increase of 4% or more above the Nyquist rate, i.e., a spectral efficiency of 6.24 b/s/Hz or higher, can be achieved by simple symbol-by-symbol detection with a small degradation. It is further shown that the advantages of combining this technique with class-IV PRS are that a small band-width around DC can be carved out for the use of a service channel and that an even higher increase in spectral efficiency can be obtained in an FDM SSB system.