Transmission method and radio system

DETAILED DESCRIPTION OF THE INVENTION The solution of the invention is particularly applicable for use in a radio system of the GSM type without, however, restricting to it.
Let us first study the inventive method and receiver by means of FIG.
1.
The receiver, either a base station or a terminal, receives a signal by an antenna 100.
The radio-frequency signal propagates from the antenna to radio frequency means 102 which multiply the signal received by a signal of a local oscillator and low-pass filter the multiplication result.
The intermediate or baseband signal so formed is converted into a digital signal in an A/D converter 104.
The digital signal is demodulated in the demodulator 106.
The demodulator 106 operates in such a way that it comprises a specific demodulator for each of the N modulation alternatives.
After the demodulator 106, an impulse response estimate is formed for the demodulated signal in means 108.
The impulse response estimates propagate to means 110 which preferably infer, on the basis of maximum likelihood, the modulation by which the received signal was modulated upon transmission.
The principle of maximum likelihood can be based on the energy of the impulse response, a signal-to-noise ratio or a signal-to-interference ratio.
High impulse response energy, a good signal-to-noise ratio or a good signal-to-interference ratio indicate the most probable modulation method.
The means 110 control a selection means 112, preferably a multiplexer, to select a signal to a detector 114 from the demodulator which, on the basis of the maximum likelihood, corresponds best to the modulation of the signal.
The means 110 also control the detector 114 to operate in a correct mode with respect to the modulation of the signal.
The detected signal further propagates to prior art processes which are irrelevant to the inventive solution.
FIG.
2 shows another receiver solution which is applicable when differently modulated signals can be demodulated by a single demodulation method.
Such modulation methods include Gaussian minimum shift keying (GMSK) and differentially coded binary continuous phase modulation (DBCPM) methods, for example