1. A circuit system for deciding a symbol upon reception of received symbols coupled with a quadrature signal, whereby phase noise and Gaussian noise are superimposed on at least one of the received symbols, the circuit system comprising: an apparatus for determining or estimating the phase noise and the Gaussian noise of the at least one of the received symbols; a regulating system for regulating reception parameters for decisions concerning subsequently received symbols, wherein the apparatus for determining or estimating the phase noise and the Gaussian noise performs the determination or estimation of the phase noise and the Gaussian noise in a manner which differentiates between the phase noise and the Gaussian noise, and is connected to the regulating system for applying a result of the differentiated determination or estimation to the regulating system for regulating the reception parameters, and wherein the apparatus for determining or estimating the phase noise and the Gaussian noise comprises: a rotator for phase-correcting rotation of the at least one of the received symbols, using a previously estimated phase rotation angle, a first decider, downstream from the rotator, which decides on a Cartesian basis and determines a first phase error and/or a first radius error, and a second decider, downstream from the rotator and parallel to the first decider, which decides at least on a polar basis and determines a second phase error and/or a second radius error.