• ADVANCE PRACTICAL CHANNEL SIMULATORS FOR LEO SATELLITE CHANNELS WITH SELECTIVE FADING AND DOPPLER SHIFTS

      Haghdad, Mehdi; Feher, Kamilo; University of California Davis (International Foundation for Telemetering, 2001-10)
      Dynamic hardware and software schemes for trajectory based simulation of LEO satellite channel are presented and evaluated. The simulation models are based on the practical LEO satellite channels and change dynamically with the trajectory using the latitude and longitude of the LEO satellite as input. The hardware simulator is consisted of a trajectory based selective fade generator, a trajectory based Doppler shifter, trajectory based time shadowing simulator and a standard channel for addition of noise, ACI and CCI. A FQPSK modulated signal is passed through a trajectory based dynamic fade generator and the spectrum is distorted. Then the resulting signal is exposed to a trajectory based dynamic Doppler Shifter, simulating the passage of the satellite overhead. Then the proper AWGN, ACI or CCI is added to the signal. At the final stage the signal is passed through a trajectory based time Shadowing simulator. The software simulator is a dynamic real time simulator written in MatLab and its structure is similar to the hardware simulator.
    • NON-FEEDBACK HIGH SPEED ADAPTIVE EQUALIZERS FOR FQPSK AND OTHER SPECTRAL EFFICIENCY SYSTEMS FOR LEO SATELLITE TELEMETRY SYSTEMS

      Haghdad, Mehdi; Feher, Kamilo; University of California Davis; Digcom, Inc. (International Foundation for Telemetering, 2001-10)
      A non-feedback adaptive equalizer based on Feher Equalizer (FE) is presented and its performance is evaluated. By artificially adding notch/notches to the corrupted spectrum resulted from selectively faded LEO environments, an artificial symmetry is created and as a result the BER/BLER is improved. The location and the depth of artificial additive notches are based on the shape of the spectrum of the corrupted signal. By measuring the power in narrow bands around certain frequencies the existence of notches around those frequencies are predicted. Based on this information notches with proper depths are added to the main spectrum which results in more symmetry in the spectrum. The selection process of artificial notch/notches are based on the shape of the signal spectrum, which means that this equalizer unlike most conventional equalizer does not need any feedback. The nonfeedback nature of this equalizer improves the adaptation time over that of alternative equalizers The results presented in this paper are based on both MatLab simulations and laboratory hardware measurements.
    • Test and Evaluation of Ultra High Spectral Efficient Feher Keying (FK)

      Lin, Jin-Song; Feher, Kamilo; University of California; DIGCOM, Inc. (International Foundation for Telemetering, 2001-10)
      Performances of a subclass of a new spectral efficient modulation scheme, designated as Feher Keying [1], or FK, is evaluated. The Power Spectral Density (PSD) and Bit Error Rate (BER) characteristics of FK are presented. FK has ultra high spectral efficiency and satisfies the frequency mask for WLAN defined in FCC part 15, and it has a simple structure for high bit rate implementation.