I/Q REVERSAL PHENOMENA IN 4-PHASE MODIFIED COSTAS LOOPS

摘要

There is a growing need to maximize data transmission flexibility in satellite-based scientific,military and commercial communication systems.Of specific interest in this paper is the utilization of unbalanced QPSK (UQPSK) to support the transmission of two independent data channels.Because considerable data rate flexibility is desired,significant care must be exercised in appropriately "matching" the transmitter modulator and receiver demodulator.Improper "matching" and/or improper operatione.g.,that arises from filtering and/or transients - may lead to anomalous demodulation behavior.One possibility is the reversal of the In-phase and quadrature channel outputs of the UQPSK demodulator,thereby leading to erroneous bit sychronization and data detection.This paper focusses on this I/Q reversal phenomenon under both acquisition and tracking conditions and establishes its physical basis.The important role that transmitter and receiver filtering plays is also explicitly demonstrated.