Sadao Takenaka

A digital signal processing demodulator with a wide frequency acquisition range

A demodulator capable of variable baud rate (f/sub b/) operation satisfies the requirements for a forward error correcting decoder for satellite communication systems such as VSAT systems. A new method of frequency acquisition, called swept automatic frequency control has a wide f/sub b/-independent acquisition range and prevents false locking of the carrier recovery circuit. The authors have evaluated such a demodulator and confirm that it performs satisfactorily.<<ETX>>

Multilevel QAM Modulation Techniques for Digital Microwave Radios

A pilot carrier injection method is described together with feedback balance coding which reduces spectral power near the carrier. Robustness of carrier recovery using the pilot carrier injection method is theoretically estimated. The estimation suggests that recovered carrier SNR higher than 40 dB can be expected even under muitipath fading with notch depth of 45 dB located just at the carrier frequency. Signatures for multipath fading are estimated for a 64-QAM system with transversal equalizers as a countermeasure. Measured signatures agree reasonably well with the calculated ones. Dependences of signatures on modulation level, transversal equalizer tap number, and rolloff rate are also shown.

Burst DSP demodulator for low E/sub b//N/sub 0/ operation

The authors describe a receive filter modification that improves carrier and symbol timing recovery in a burst DSP (digital signal processing) QPSK (quadrature phase shift keying) demodulator for satellite communications. The experimental DSP demodulator has a low unique word miss probability (Pmiss) and cycle-skipping-rate at low E/sub b//N/sub 0/ (3 dB or less). The S/N (signal-to-noise ratio) of the carrier recovery is increased by about 1 dB and the S/N of the symbol timing recovery is increased by at least 3 dB. Pmiss is improved by a factor of 100 over that of a conventional DSP demodulator.<<ETX>>