Stephen Michael Hladik

Performance of differentially detected pi /4-shifted DQPSK with diversity

The application of postdetection selection combining diversity in land mobile radio systems is addressed. Selection of an antenna-receiver pair is based on metrics that are functions of the signal-to-impairment power ratio at the outputs of differential detectors. That is, postdetection selection metrics are used. Because these schemes operate on the detector output, they can be used with hard-limited IF signals. The schemes are evaluated using the North American digital cellular channel structure and modulation. Simulation results are reported which show performance improvements in the presence of cochannel interference, multipath, and Doppler.<<ETX>>

On ACIPR of pi /4 shifted DQPSK for US digital land mobile radio systems

The adjacent channel interference characteristics of a system employing Nyquist-pulse, pi /4-shifted differential quadrature phase (DQPSK) modulation were investigated for a US digital land mobile radio application. The effects of transmit pulse-shape windowing, power amplifier characteristics, and the performance reference defining minimum receiver sensitivity on the achievable adjacent channel interference protection ratio (ACIPR) were examined via computer simulation. Estimates of in-band to adjacent-band power are presented, and ACIPR data obtained from simulations of the proposed system based on a modification of the selectivity measurement defined in EIA Standard RS204-C are given. These results indicate that the proposed system provides from 40 dB to 70 dB of ACIPR with a two-fold increase in capacity, depending on the transmitters power and required average probability of bit error.<<ETX>>

A tone-aided dual vestigial sideband system for digital communications on fading channels

A spectrally efficient tone-aided dual vestigial sideband (TA/DVSB) system for digital data communications on fading channels is presented and described analytically. This PSK (phase-shift-keying) system incorporates a feed-forward, tone-aided demodulation technique to compensate for Doppler frequency shift and channel- induced, multipath fading. In contrast to other tone-in-band-type systems, receiver synchronization is derived from the complete data VSBs. Simulation results for the Rician fading channel are presented. These results demonstrate the receivers ability to mitigate performance degradation due to fading and to obtain proper data carrier synchronization, suggesting that the proposed TA/DVSB system has promise for this application. Simulated BER (bit-error rate) data indicate that the TA/DVSB system effectively alleviates the channel distortions of the land mobile satellite application.<<ETX>>