Practical and robust equalization techniques for FQPSK systems in multipath fading environment

Practical and low complexity adaptive equalization techniques to effectively combat multipath interference for Feher's patented Quadrature Phase Shift Keying (FQPSK), a power and spectrally efficient modulation, in recently standardized U.S. and international telemetry applications are demonstrated by analysis, and by hardware development as well as by computer simulation. The presented adaptive equalization techniques can be classified into two categories:; 1. Practical and low complexity equalization techniques. Low complexity, efficient and fast dynamic equalization techniques, designated as Feher Equalizers (FE), employ a non-redundant error detection (NRED) named pseudo error on-line detection approach for parameter adjustments of the equalizer. The NRED avoids the need of any training sequences from the transmitter to adjust the equalizer parameters. Unlike conventional compensation, the amplitude response of the low complexity equalizer mirrors the amplitude response of multipath fading channel from the carrier frequency with an opposite slope in order to reduce the fade notch depth. The hardware measurement results demonstrate that the adaptive low complexity FE statistically reduces the Block Error Rate (BLER) by more than 60% in a delay spreading range from 20–200 ns without the need of a training sequence and without the increase of carrier recovery and demodulation time.; 2. Joint adaptive equalization and carrier phase tracking techniques for offset quadrature signals. Joint blind adaptive equalization and carrier phase tracking algorithms for non-linearly amplified (NLA) FQPSK through multipath frequency selective fading channels are originally developed, analyzed, and demonstrated in mathematical equations and computer simulations. It has been verified that a T_S/2-spaced equalizer based on a constant modulus algorithm (CMA) and decision-directed (DD) carrier phase tracking loop can converge to the MSSE criterion by using the proposed method, named an offset sampling method, to estimate phase errors.