Digital intermediate frequency demodulation technique for cellular communication systems

A novel modulation scheme suitable for digital cellular communication systems is proposed. This scheme first converts the IF (intermediate frequency) signal to a logic level; phase detection is then performed entirely by digital operations. Since analog components such as an I/Q detector and A/D (analog/digital) converters are eliminated with this scheme, a low power consuming and adjustment free receiver can be realized. An application to π/4-shifted QPSK (quadrature phase-shift keying) demodulation is considered. An experimental receiver for π/4-shifted QPSK has been built to evaluate its performance. The results show a bit error rate of 1×10^-2 at 12-dB Eb/N₀ with postdetection diversity under fast fading environments. The results are quite satisfactory, showing good potential for future digital cellular communication applications