Hideho Tomita

New MLSE receiver free from sample timing and input level controls

A new maximum likelihood sequence estimator (MLSE) receiver which is tolerant of both aberrations in sample timing and variations in amplitude is presented. In the proposed receiver, input signals are represented in polar coordinates, and fractionally sampled signals are fed to the MLSE. These two features make it possible to greatly reduce control mechanisms without performance degradation. The performance of the receiver is evaluated both in computer simulations and in experiments in US time division multiple access (TDMA) cellular environments, and it is shown that under conditions of 65-dB amplitude variations it successfully achieves less than 3% bit error rate (BER) without controlling either input level or sample timing.

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 pi /4-shifted QPSK (quadrature phase-shift keying) demodulation is considered. An experimental receiver for pi /4-shifted QPSK has been built to evaluate its performance. The results show a bit error rate of 1*10/sup -2/ at 12-dB Eb/N/sub 0/ with postdetection diversity under fast fading environments. The results are quite satisfactory, showing good potential for future digital cellular communication applications.<<ETX>>