Method and device for generating a constant envelope navigation signal with four independent codes

A device for generating a modulated navigation signal which is intended to be used to position a downlink receiver, comprising multiple pseudorandom navigation codes of chip rhythms greater than 0.5 MHz, modulated onto a carrier of frequency fp greater than 500 MHz, this device comprising:

• a circuit to generate pseudorandom navigation codes,
• a phase-shifting modulator circuit which supplies the modulated navigation signal on the carrier,
• an emitter circuit, comprising at least one power amplification stage, and suitable for emitting a radio frequency signal corresponding to the modulated navigation signal,
• wherein the modulator circuit is suitable for modulating, on the carrier, four pseudorandom navigation codes C1, C2, C1′, C2′ of which the frequencies are an integer multiple of one of them fc, according to an 8-PSK modulation of constant amplitude with a modulation frequency fM such that:
• 8fc≦fM
• where fc=Max(fci), and fci designates the chip rhythms fc1, fc1′, fc2, fc2′ of the navigation codes C1, C2, C1′, C2′, each fci value being such that fM=Ni.fci, Ni being an integer greater than or equal to 8, two navigation codes C1, C1′ being quadrature modulated at frequency f1=fp−fM/8, and two other navigation codes C2, C2′ being quadrature modulated at frequency f2=fp+fM/8, and the modulated navigation signal presenting a constant envelope.