In this paper, a new phase precoding technique is developed to combat the intersymbol interference (ISI) resulting from a frequency-selective slowly fading channel in a personal communication system using quadrature phase-shift keying (QPSK). Based on a new dimension partitioning technique, the precoder predistorts only the phase of the transmitted signal to keep a constant transmitted signal amplitude and, therefore, to ensure the stability of the precoder even in equalizing a nonminimum-phase channel. Under the constraint of the constant amplitude, the dimension partitioning method is developed to guarantee the possibility of correct detection for all transmitted information symbols and to further improve the transmission accuracy by increasing the size of decision regions. Analytical and simulation results demonstrate that over frequency-selective Rayleigh and Rician fading channels, the system using the proposed channel precoder can achieve a bit error rate (BER) comparable with that using a conventional decision feedback equalizer (DFE). The precoder can outperform DFE in an indoor environment where there is a strong direct propagation path. The main advantage of using the precoder is that the impairment of ISI due to multipath propagation on the transmission performance can be mitigated without increasing the complexity of the portable unit receiver. The proposed technique is especially useful for personal communications, where ISI due to multipath fading channels can severely deteriorate the BER transmission performance and where the simplicity of portable units is a vital characteristic of the system.
Characterization of fiber channels has always been of interest to many researchers as we approach higher frequencies in the millimeter wave spectrum. In this paper, we propose a stochastic impulse model of an optical double sideband signal (ODSB) signal traveling in the optical fiber channel taking into account the attenuation and chromatic dispersion effect. The radio-over-fiber (ROF) fiber link is setup at the 38GHz millimeter wave spectrum. Statistical and experimental methods are employed to derive the parameters of the system. Index Terms -Impulse response, radio over fiber (ROF), optical double sideband signal (ODSB).
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